draft-ietf-httpbis-semantics-12.txt   draft-ietf-httpbis-semantics-13.txt 
HTTP Working Group R. Fielding, Ed. HTTP Working Group R. Fielding, Ed.
Internet-Draft Adobe Internet-Draft Adobe
Obsoletes: 2818, 7230, 7231, 7232, 7233, 7235, M. Nottingham, Ed. Obsoletes: 2818, 7230, 7231, 7232, 7233, 7235, M. Nottingham, Ed.
7538, 7615, 7694 (if approved) Fastly 7538, 7615, 7694 (if approved) Fastly
Intended status: Standards Track J. Reschke, Ed. Updates: 3864 (if approved) J. Reschke, Ed.
Expires: April 5, 2021 greenbytes Intended status: Standards Track greenbytes
October 2, 2020 Expires: June 17, 2021 December 14, 2020
HTTP Semantics HTTP Semantics
draft-ietf-httpbis-semantics-12 draft-ietf-httpbis-semantics-13
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is a stateless application- The Hypertext Transfer Protocol (HTTP) is a stateless application-
level protocol for distributed, collaborative, hypertext information level protocol for distributed, collaborative, hypertext information
systems. This document defines the semantics of HTTP: its systems. This document defines the semantics shared by all versions
architecture, terminology, the "http" and "https" Uniform Resource of HTTP, including its architecture, terminology, core protocol
Identifier (URI) schemes, core request methods, request header elements, and extensibility mechanisms, along with the "http" and
fields, response status codes, response header fields, and content "https" Uniform Resource Identifier (URI) schemes.
negotiation.
This document obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC This document obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC
7235, RFC 7538, RFC 7615, RFC 7694, and portions of RFC 7230. 7235, RFC 7538, RFC 7615, RFC 7694, and portions of RFC 7230.
Editorial Note Editorial Note
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>. <https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at <https://httpwg.org/>; Working Group information can be found at <https://httpwg.org/>;
source code and issues list for this draft can be found at source code and issues list for this draft can be found at
<https://github.com/httpwg/http-core>. <https://github.com/httpwg/http-core>.
The changes in this draft are summarized in Appendix C.13. The changes in this draft are summarized in Appendix C.14.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2021. This Internet-Draft will expire on June 17, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 42 skipping to change at page 2, line 42
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 9
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2. Evolution . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2. History and Evolution . . . . . . . . . . . . . . . . . . 9
1.3. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3. Core Semantics . . . . . . . . . . . . . . . . . . . . . 10
1.4. Obsoletes . . . . . . . . . . . . . . . . . . . . . . . . 11 1.4. Specifications Obsoleted by this Document . . . . . . . . 11
2. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 12 2. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 12 2.1. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 11
2.2. Requirements Notation . . . . . . . . . . . . . . . . . . 12 2.2. Requirements Notation . . . . . . . . . . . . . . . . . . 12
2.3. Length Requirements . . . . . . . . . . . . . . . . . . . 13 2.3. Length Requirements . . . . . . . . . . . . . . . . . . . 13
2.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 14 2.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 13
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5. Protocol Version . . . . . . . . . . . . . . . . . . . . 14
3.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 14 3. Terminology and Core Concepts . . . . . . . . . . . . . . . . 15
3.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2. Connections . . . . . . . . . . . . . . . . . . . . . . . 15 3.2. Connections . . . . . . . . . . . . . . . . . . . . . . . 15
3.3. Messages . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3. Messages . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4. User Agent . . . . . . . . . . . . . . . . . . . . . . . 15 3.4. User Agent . . . . . . . . . . . . . . . . . . . . . . . 16
3.5. Origin Server . . . . . . . . . . . . . . . . . . . . . . 16 3.5. Origin Server . . . . . . . . . . . . . . . . . . . . . . 17
3.6. Example Request and Response . . . . . . . . . . . . . . 16 3.6. Intermediaries . . . . . . . . . . . . . . . . . . . . . 17
3.7. Intermediaries . . . . . . . . . . . . . . . . . . . . . 17 3.7. Caches . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.8. Caches . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.8. Example Message Exchange . . . . . . . . . . . . . . . . 20
4. Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . 20 4. Identifiers in HTTP . . . . . . . . . . . . . . . . . . . . . 21
4.1. URI References . . . . . . . . . . . . . . . . . . . . . 20 4.1. URI References . . . . . . . . . . . . . . . . . . . . . 21
4.2. URI Schemes . . . . . . . . . . . . . . . . . . . . . . . 21 4.2. HTTP-Related URI Schemes . . . . . . . . . . . . . . . . 22
4.2.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 22 4.2.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 22
4.2.2. https URI Scheme . . . . . . . . . . . . . . . . . . 22 4.2.2. https URI Scheme . . . . . . . . . . . . . . . . . . 23
4.2.3. http(s) Normalization and Comparison . . . . . . . . 23 4.2.3. http(s) Normalization and Comparison . . . . . . . . 24
4.2.4. http(s) Deprecated userinfo . . . . . . . . . . . . . 24 4.2.4. Deprecation of userinfo in http(s) URIs . . . . . . . 24
4.2.5. http(s) References with Fragment Identifiers . . . . 24 4.2.5. http(s) References with Fragment Identifiers . . . . 25
4.3. Authoritative Access . . . . . . . . . . . . . . . . . . 24 4.3. Authoritative Access . . . . . . . . . . . . . . . . . . 25
4.3.1. URI Origin . . . . . . . . . . . . . . . . . . . . . 24 4.3.1. URI Origin . . . . . . . . . . . . . . . . . . . . . 25
4.3.2. http origins . . . . . . . . . . . . . . . . . . . . 25 4.3.2. http origins . . . . . . . . . . . . . . . . . . . . 26
4.3.3. https origins . . . . . . . . . . . . . . . . . . . . 26 4.3.3. https origins . . . . . . . . . . . . . . . . . . . . 27
4.3.4. https certificate verification . . . . . . . . . . . 27 4.3.4. https certificate verification . . . . . . . . . . . 28
5. Message Abstraction . . . . . . . . . . . . . . . . . . . . . 28 5. Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1. Protocol Version . . . . . . . . . . . . . . . . . . . . 28 5.1. Field Names . . . . . . . . . . . . . . . . . . . . . . . 29
5.2. Framing . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.2. Field Lines and Combined Field Value . . . . . . . . . . 30
5.3. Control Data . . . . . . . . . . . . . . . . . . . . . . 30 5.3. Field Order . . . . . . . . . . . . . . . . . . . . . . . 30
5.3.1. Request . . . . . . . . . . . . . . . . . . . . . . . 30 5.4. Field Limits . . . . . . . . . . . . . . . . . . . . . . 31
5.3.2. Response . . . . . . . . . . . . . . . . . . . . . . 30 5.5. Field Values . . . . . . . . . . . . . . . . . . . . . . 32
5.4. Header Fields . . . . . . . . . . . . . . . . . . . . . . 30 5.6. Common Rules for Defining Field Values . . . . . . . . . 34
5.4.1. Field Ordering and Combination . . . . . . . . . . . 32 5.6.1. Lists (#rule ABNF Extension) . . . . . . . . . . . . 34
5.4.2. Field Limits . . . . . . . . . . . . . . . . . . . . 33 5.6.2. Tokens . . . . . . . . . . . . . . . . . . . . . . . 35
5.4.3. Field Names . . . . . . . . . . . . . . . . . . . . . 33 5.6.3. Whitespace . . . . . . . . . . . . . . . . . . . . . 35
5.4.4. Field Values . . . . . . . . . . . . . . . . . . . . 33 5.6.4. Quoted Strings . . . . . . . . . . . . . . . . . . . 36
5.5. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.6.5. Comments . . . . . . . . . . . . . . . . . . . . . . 37
5.5.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 35 5.6.6. Parameters . . . . . . . . . . . . . . . . . . . . . 37
5.5.2. Identification . . . . . . . . . . . . . . . . . . . 36 5.6.7. Date/Time Formats . . . . . . . . . . . . . . . . . . 37
5.5.3. Payload Metadata . . . . . . . . . . . . . . . . . . 37 6. Message Abstraction . . . . . . . . . . . . . . . . . . . . . 39
5.5.4. Payload Body . . . . . . . . . . . . . . . . . . . . 37 6.1. Framing and Completeness . . . . . . . . . . . . . . . . 40
5.6. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 37 6.2. Control Data . . . . . . . . . . . . . . . . . . . . . . 41
5.6.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 38 6.3. Header Fields . . . . . . . . . . . . . . . . . . . . . . 42
5.6.2. Limitations . . . . . . . . . . . . . . . . . . . . . 38 6.4. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.6.3. Processing . . . . . . . . . . . . . . . . . . . . . 39 6.4.1. Payload Semantics . . . . . . . . . . . . . . . . . . 43
5.7. Common Rules for Defining Field Values . . . . . . . . . 39 6.4.2. Identifying Payloads . . . . . . . . . . . . . . . . 44
5.7.1. Lists (#rule ABNF Extension) . . . . . . . . . . . . 39 6.5. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 45
5.7.2. Tokens . . . . . . . . . . . . . . . . . . . . . . . 41 6.5.1. Limitations on use of Trailers . . . . . . . . . . . 45
5.7.3. Whitespace . . . . . . . . . . . . . . . . . . . . . 41 6.5.2. Processing Trailer Fields . . . . . . . . . . . . . . 46
5.7.4. Quoted Strings . . . . . . . . . . . . . . . . . . . 42 7. Routing HTTP Messages . . . . . . . . . . . . . . . . . . . . 47
5.7.5. Comments . . . . . . . . . . . . . . . . . . . . . . 42 7.1. Determining the Target Resource . . . . . . . . . . . . . 47
5.7.6. Parameters . . . . . . . . . . . . . . . . . . . . . 43 7.2. Host and :authority . . . . . . . . . . . . . . . . . . . 48
5.7.7. Date/Time Formats . . . . . . . . . . . . . . . . . . 43 7.3. Routing Inbound Requests . . . . . . . . . . . . . . . . 48
6. Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 7.3.1. To a Cache . . . . . . . . . . . . . . . . . . . . . 48
6.1. Target Resource . . . . . . . . . . . . . . . . . . . . . 45 7.3.2. To a Proxy . . . . . . . . . . . . . . . . . . . . . 49
6.1.1. Request Target . . . . . . . . . . . . . . . . . . . 45 7.3.3. To the Origin . . . . . . . . . . . . . . . . . . . . 49
6.1.2. Host . . . . . . . . . . . . . . . . . . . . . . . . 46 7.4. Rejecting Misdirected Requests . . . . . . . . . . . . . 49
6.1.3. Reconstructing the Target URI . . . . . . . . . . . . 47 7.5. Response Correlation . . . . . . . . . . . . . . . . . . 49
6.2. Routing Inbound . . . . . . . . . . . . . . . . . . . . . 47 7.6. Message Forwarding . . . . . . . . . . . . . . . . . . . 50
6.2.1. To a Cache . . . . . . . . . . . . . . . . . . . . . 47 7.6.1. Connection . . . . . . . . . . . . . . . . . . . . . 50
6.2.2. To a Proxy . . . . . . . . . . . . . . . . . . . . . 48 7.6.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 52
6.2.3. To the Origin . . . . . . . . . . . . . . . . . . . . 48 7.6.3. Via . . . . . . . . . . . . . . . . . . . . . . . . . 52
6.3. Response Correlation . . . . . . . . . . . . . . . . . . 48 7.7. Message Transformations . . . . . . . . . . . . . . . . . 54
6.4. Message Forwarding . . . . . . . . . . . . . . . . . . . 48 7.8. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.4.1. Connection . . . . . . . . . . . . . . . . . . . . . 49 8. Representations . . . . . . . . . . . . . . . . . . . . . . . 57
6.4.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 50 8.1. Selected Representations . . . . . . . . . . . . . . . . 58
6.4.3. Via . . . . . . . . . . . . . . . . . . . . . . . . . 51 8.2. Representation Data . . . . . . . . . . . . . . . . . . . 58
6.5. Transformations . . . . . . . . . . . . . . . . . . . . . 53 8.3. Representation Metadata . . . . . . . . . . . . . . . . . 58
6.6. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 54 8.4. Content-Type . . . . . . . . . . . . . . . . . . . . . . 59
7. Representations . . . . . . . . . . . . . . . . . . . . . . . 56 8.4.1. Media Type . . . . . . . . . . . . . . . . . . . . . 60
7.1. Selected Representation . . . . . . . . . . . . . . . . . 57 8.4.2. Charset . . . . . . . . . . . . . . . . . . . . . . . 60
7.2. Data . . . . . . . . . . . . . . . . . . . . . . . . . . 57 8.4.3. Canonicalization and Text Defaults . . . . . . . . . 61
7.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 57 8.4.4. Multipart Types . . . . . . . . . . . . . . . . . . . 61
7.4. Content-Type . . . . . . . . . . . . . . . . . . . . . . 58 8.5. Content-Encoding . . . . . . . . . . . . . . . . . . . . 62
7.4.1. Media Type . . . . . . . . . . . . . . . . . . . . . 59 8.5.1. Content Codings . . . . . . . . . . . . . . . . . . . 63
7.4.2. Charset . . . . . . . . . . . . . . . . . . . . . . . 59 8.6. Content-Language . . . . . . . . . . . . . . . . . . . . 64
7.4.3. Canonicalization and Text Defaults . . . . . . . . . 60 8.6.1. Language Tags . . . . . . . . . . . . . . . . . . . . 65
7.4.4. Multipart Types . . . . . . . . . . . . . . . . . . . 61 8.7. Content-Length . . . . . . . . . . . . . . . . . . . . . 65
7.5. Content-Encoding . . . . . . . . . . . . . . . . . . . . 61 8.8. Content-Location . . . . . . . . . . . . . . . . . . . . 67
7.5.1. Content Codings . . . . . . . . . . . . . . . . . . . 62 8.9. Validator Fields . . . . . . . . . . . . . . . . . . . . 68
7.6. Content-Language . . . . . . . . . . . . . . . . . . . . 63 8.9.1. Weak versus Strong . . . . . . . . . . . . . . . . . 69
7.6.1. Language Tags . . . . . . . . . . . . . . . . . . . . 64 8.9.2. Last-Modified . . . . . . . . . . . . . . . . . . . . 71
7.7. Content-Length . . . . . . . . . . . . . . . . . . . . . 65 8.9.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 73
7.8. Content-Location . . . . . . . . . . . . . . . . . . . . 66 8.9.4. When to Use Entity-Tags and Last-Modified Dates . . . 76
7.9. Validators . . . . . . . . . . . . . . . . . . . . . . . 68 9. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.9.1. Weak versus Strong . . . . . . . . . . . . . . . . . 69 9.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 77
7.9.2. Last-Modified . . . . . . . . . . . . . . . . . . . . 71 9.2. Common Method Properties . . . . . . . . . . . . . . . . 78
7.9.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 73 9.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 79
7.9.4. When to Use Entity-Tags and Last-Modified Dates . . . 76 9.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 80
8. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 9.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 81
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 77 9.3. Method Definitions . . . . . . . . . . . . . . . . . . . 81
8.2. Common Method Properties . . . . . . . . . . . . . . . . 78 9.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 81
8.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 79 9.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 82
8.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 80 9.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 83
8.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 81 9.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 84
8.3. Method Definitions . . . . . . . . . . . . . . . . . . . 81 9.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 87
8.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 81 9.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 88
8.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 82 9.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 90
8.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 83 9.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 91
8.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 84 10. Message Context . . . . . . . . . . . . . . . . . . . . . . . 91
8.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 87 10.1. Request Context Fields . . . . . . . . . . . . . . . . . 91
8.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 88 10.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 91
8.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 89 10.1.2. From . . . . . . . . . . . . . . . . . . . . . . . . 94
8.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 90 10.1.3. Referer . . . . . . . . . . . . . . . . . . . . . . 94
9. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 10.1.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.1. Request Context . . . . . . . . . . . . . . . . . . . . . 91 10.1.5. Trailer . . . . . . . . . . . . . . . . . . . . . . 96
9.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 92 10.1.6. User-Agent . . . . . . . . . . . . . . . . . . . . . 96
9.1.2. From . . . . . . . . . . . . . . . . . . . . . . . . 94 10.2. Response Context Fields . . . . . . . . . . . . . . . . 97
9.1.3. Referer . . . . . . . . . . . . . . . . . . . . . . . 95 10.2.1. Allow . . . . . . . . . . . . . . . . . . . . . . . 98
9.1.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . 96 10.2.2. Date . . . . . . . . . . . . . . . . . . . . . . . . 98
9.1.5. Trailer . . . . . . . . . . . . . . . . . . . . . . . 96 10.2.3. Location . . . . . . . . . . . . . . . . . . . . . . 99
9.1.6. User-Agent . . . . . . . . . . . . . . . . . . . . . 97 10.2.4. Retry-After . . . . . . . . . . . . . . . . . . . . 101
9.2. Response Context . . . . . . . . . . . . . . . . . . . . 98 10.2.5. Server . . . . . . . . . . . . . . . . . . . . . . . 101
9.2.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . 98 11. HTTP Authentication . . . . . . . . . . . . . . . . . . . . . 102
9.2.2. Date . . . . . . . . . . . . . . . . . . . . . . . . 99 11.1. Authentication Scheme . . . . . . . . . . . . . . . . . 102
9.2.3. Location . . . . . . . . . . . . . . . . . . . . . . 100 11.2. Authentication Parameters . . . . . . . . . . . . . . . 102
9.2.4. Retry-After . . . . . . . . . . . . . . . . . . . . . 101 11.3. Challenge and Response . . . . . . . . . . . . . . . . . 103
9.2.5. Server . . . . . . . . . . . . . . . . . . . . . . . 102 11.4. Credentials . . . . . . . . . . . . . . . . . . . . . . 104
10. Authentication . . . . . . . . . . . . . . . . . . . . . . . 102 11.5. Establishing a Protection Space (Realm) . . . . . . . . 104
10.1. Authentication Scheme . . . . . . . . . . . . . . . . . 102 11.6. Authenticating Users to Origin Servers . . . . . . . . . 105
10.2. Authentication Parameters . . . . . . . . . . . . . . . 103 11.6.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 105
10.3. Challenge and Response . . . . . . . . . . . . . . . . . 103 11.6.2. Authorization . . . . . . . . . . . . . . . . . . . 106
10.4. Credentials . . . . . . . . . . . . . . . . . . . . . . 104 11.6.3. Authentication-Info . . . . . . . . . . . . . . . . 107
10.5. Protection Space (Realm) . . . . . . . . . . . . . . . . 105 11.7. Authenticating Clients to Proxies . . . . . . . . . . . 107
10.6. Authenticating User to Origin Server . . . . . . . . . . 106 11.7.1. Proxy-Authenticate . . . . . . . . . . . . . . . . . 107
10.6.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 106 11.7.2. Proxy-Authorization . . . . . . . . . . . . . . . . 108
10.6.2. Authorization . . . . . . . . . . . . . . . . . . . 107 11.7.3. Proxy-Authentication-Info . . . . . . . . . . . . . 108
10.6.3. Authentication-Info . . . . . . . . . . . . . . . . 107 12. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 109
10.7. Authenticating Client to Proxy . . . . . . . . . . . . . 108 12.1. Proactive Negotiation . . . . . . . . . . . . . . . . . 110
10.7.1. Proxy-Authenticate . . . . . . . . . . . . . . . . . 108 12.2. Reactive Negotiation . . . . . . . . . . . . . . . . . . 111
10.7.2. Proxy-Authorization . . . . . . . . . . . . . . . . 108 12.3. Request Payload Negotiation . . . . . . . . . . . . . . 112
10.7.3. Proxy-Authentication-Info . . . . . . . . . . . . . 109 12.4. Content Negotiation Field Features . . . . . . . . . . . 112
11. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 109 12.4.1. Absence . . . . . . . . . . . . . . . . . . . . . . 112
11.1. Proactive Negotiation . . . . . . . . . . . . . . . . . 110 12.4.2. Quality Values . . . . . . . . . . . . . . . . . . . 113
11.1.1. Shared Negotiation Features . . . . . . . . . . . . 111 12.4.3. Wildcard Values . . . . . . . . . . . . . . . . . . 113
11.1.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 113 12.5. Content Negotiation Fields . . . . . . . . . . . . . . . 113
11.1.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 115 12.5.1. Accept . . . . . . . . . . . . . . . . . . . . . . . 114
11.1.4. Accept-Encoding . . . . . . . . . . . . . . . . . . 116 12.5.2. Accept-Charset . . . . . . . . . . . . . . . . . . . 116
11.1.5. Accept-Language . . . . . . . . . . . . . . . . . . 117 12.5.3. Accept-Encoding . . . . . . . . . . . . . . . . . . 116
11.2. Reactive Negotiation . . . . . . . . . . . . . . . . . . 119 12.5.4. Accept-Language . . . . . . . . . . . . . . . . . . 118
11.2.1. Vary . . . . . . . . . . . . . . . . . . . . . . . . 120 12.5.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . 119
11.3. Request Payload Negotiation . . . . . . . . . . . . . . 121 13. Conditional Requests . . . . . . . . . . . . . . . . . . . . 121
12. Conditional Requests . . . . . . . . . . . . . . . . . . . . 121 13.1. Preconditions . . . . . . . . . . . . . . . . . . . . . 121
12.1. Preconditions . . . . . . . . . . . . . . . . . . . . . 122 13.1.1. If-Match . . . . . . . . . . . . . . . . . . . . . . 121
12.1.1. If-Match . . . . . . . . . . . . . . . . . . . . . . 122 13.1.2. If-None-Match . . . . . . . . . . . . . . . . . . . 123
12.1.2. If-None-Match . . . . . . . . . . . . . . . . . . . 124 13.1.3. If-Modified-Since . . . . . . . . . . . . . . . . . 124
12.1.3. If-Modified-Since . . . . . . . . . . . . . . . . . 125 13.1.4. If-Unmodified-Since . . . . . . . . . . . . . . . . 126
12.1.4. If-Unmodified-Since . . . . . . . . . . . . . . . . 127 13.1.5. If-Range . . . . . . . . . . . . . . . . . . . . . . 127
12.1.5. If-Range . . . . . . . . . . . . . . . . . . . . . . 128 13.2. Evaluation of Preconditions . . . . . . . . . . . . . . 129
12.2. Evaluation . . . . . . . . . . . . . . . . . . . . . . . 129 13.3. Precedence of Preconditions . . . . . . . . . . . . . . 130
12.3. Precedence . . . . . . . . . . . . . . . . . . . . . . . 130 14. Range Requests . . . . . . . . . . . . . . . . . . . . . . . 131
13. Range Requests . . . . . . . . . . . . . . . . . . . . . . . 131 14.1. Range Units . . . . . . . . . . . . . . . . . . . . . . 131
13.1. Range Units . . . . . . . . . . . . . . . . . . . . . . 132 14.1.1. Range Specifiers . . . . . . . . . . . . . . . . . . 132
13.1.1. Range Specifiers . . . . . . . . . . . . . . . . . . 133 14.1.2. Byte Ranges . . . . . . . . . . . . . . . . . . . . 133
13.1.2. Byte Ranges . . . . . . . . . . . . . . . . . . . . 134 14.2. Range . . . . . . . . . . . . . . . . . . . . . . . . . 135
13.2. Range . . . . . . . . . . . . . . . . . . . . . . . . . 135 14.3. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . 136
13.3. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . 137 14.4. Content-Range . . . . . . . . . . . . . . . . . . . . . 137
13.4. Content-Range . . . . . . . . . . . . . . . . . . . . . 137 14.5. Media Type multipart/byteranges . . . . . . . . . . . . 139
13.5. Media Type multipart/byteranges . . . . . . . . . . . . 139 15. Status Codes . . . . . . . . . . . . . . . . . . . . . . . . 140
14. Status Codes . . . . . . . . . . . . . . . . . . . . . . . . 141 15.1. Overview of Status Codes . . . . . . . . . . . . . . . . 141
14.1. Overview of Status Codes . . . . . . . . . . . . . . . . 142 15.2. Informational 1xx . . . . . . . . . . . . . . . . . . . 142
14.2. Informational 1xx . . . . . . . . . . . . . . . . . . . 142 15.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 142
14.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 142 15.2.2. 101 Switching Protocols . . . . . . . . . . . . . . 143
14.2.2. 101 Switching Protocols . . . . . . . . . . . . . . 143 15.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 143
14.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 143 15.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 143
14.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 143 15.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . 144
14.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . 144 15.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 144
14.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 144 15.3.4. 203 Non-Authoritative Information . . . . . . . . . 145
14.3.4. 203 Non-Authoritative Information . . . . . . . . . 145 15.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 145
14.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 145 15.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . 146
14.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . 146 15.3.7. 206 Partial Content . . . . . . . . . . . . . . . . 146
14.3.7. 206 Partial Content . . . . . . . . . . . . . . . . 146 15.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 149
14.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 149 15.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 152
14.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 152 15.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . 153
14.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . 153 15.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 153
14.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 153 15.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . 154
14.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . 154 15.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 154
14.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 154 15.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 155
14.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 155 15.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 155
14.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 155 15.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 155
14.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 155 15.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 156
14.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 156 15.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 156
14.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 156 15.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 156
14.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 156 15.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 156
14.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 156 15.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 157
14.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 157 15.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 157
14.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 157 15.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 157
14.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 157 15.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 158
14.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 158 15.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 158
14.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 158 15.5.8. 407 Proxy Authentication Required . . . . . . . . . 158
14.5.8. 407 Proxy Authentication Required . . . . . . . . . 158 15.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . 158
14.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . 158 15.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 159
14.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 159 15.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 159
14.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 159 15.5.12. 411 Length Required . . . . . . . . . . . . . . . . 159
14.5.12. 411 Length Required . . . . . . . . . . . . . . . . 159 15.5.13. 412 Precondition Failed . . . . . . . . . . . . . . 160
14.5.13. 412 Precondition Failed . . . . . . . . . . . . . . 160 15.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . 160
14.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . 160 15.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 160
14.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 160 15.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 160
14.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 160 15.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . 161
14.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . 161 15.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 161
14.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 161 15.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 162
14.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 162 15.5.20. 422 Unprocessable Payload . . . . . . . . . . . . . 162
14.5.20. 422 Unprocessable Payload . . . . . . . . . . . . . 162 15.5.21. 426 Upgrade Required . . . . . . . . . . . . . . . . 162
14.5.21. 426 Upgrade Required . . . . . . . . . . . . . . . . 162 15.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 163
14.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 163 15.6.1. 500 Internal Server Error . . . . . . . . . . . . . 163
14.6.1. 500 Internal Server Error . . . . . . . . . . . . . 163 15.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . 163
14.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . 163 15.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 163
14.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 163 15.6.4. 503 Service Unavailable . . . . . . . . . . . . . . 163
14.6.4. 503 Service Unavailable . . . . . . . . . . . . . . 163 15.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 164
14.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 164 15.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 164
14.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 164 16. Extending HTTP . . . . . . . . . . . . . . . . . . . . . . . 164
15. Extending HTTP . . . . . . . . . . . . . . . . . . . . . . . 164 16.1. Method Extensibility . . . . . . . . . . . . . . . . . . 165
15.1. Method Extensibility . . . . . . . . . . . . . . . . . . 165 16.1.1. Method Registry . . . . . . . . . . . . . . . . . . 165
15.1.1. Method Registry . . . . . . . . . . . . . . . . . . 165 16.1.2. Considerations for New Methods . . . . . . . . . . . 165
15.1.2. Considerations for New Methods . . . . . . . . . . . 165 16.2. Status Code Extensibility . . . . . . . . . . . . . . . 166
15.2. Status Code Extensibility . . . . . . . . . . . . . . . 166 16.2.1. Status Code Registry . . . . . . . . . . . . . . . . 166
15.2.1. Status Code Registry . . . . . . . . . . . . . . . . 166 16.2.2. Considerations for New Status Codes . . . . . . . . 166
15.2.2. Considerations for New Status Codes . . . . . . . . 166 16.3. Field Extensibility . . . . . . . . . . . . . . . . . . 167
15.3. Field Name Extensibility . . . . . . . . . . . . . . . . 167 16.3.1. Field Name Registry . . . . . . . . . . . . . . . . 168
15.3.1. Field Name Registry . . . . . . . . . . . . . . . . 167 16.3.2. Considerations for New Field Names . . . . . . . . . 169
15.3.2. Considerations for New Field Names . . . . . . . . . 168 16.3.3. Considerations for New Field Values . . . . . . . . 169
15.3.3. Considerations for New Field Values . . . . . . . . 169 16.4. Authentication Scheme Extensibility . . . . . . . . . . 171
15.4. Authentication Scheme Extensibility . . . . . . . . . . 171 16.4.1. Authentication Scheme Registry . . . . . . . . . . . 171
15.4.1. Authentication Scheme Registry . . . . . . . . . . . 171 16.4.2. Considerations for New Authentication Schemes . . . 171
15.4.2. Considerations for New Authentication Schemes . . . 171 16.5. Range Unit Extensibility . . . . . . . . . . . . . . . . 172
15.5. Range Unit Extensibility . . . . . . . . . . . . . . . . 172 16.5.1. Range Unit Registry . . . . . . . . . . . . . . . . 173
15.5.1. Range Unit Registry . . . . . . . . . . . . . . . . 172 16.5.2. Considerations for New Range Units . . . . . . . . . 173
15.5.2. Considerations for New Range Units . . . . . . . . . 173 16.6. Content Coding Extensibility . . . . . . . . . . . . . . 173
15.6. Content Coding Extensibility . . . . . . . . . . . . . . 173 16.6.1. Content Coding Registry . . . . . . . . . . . . . . 173
15.6.1. Content Coding Registry . . . . . . . . . . . . . . 173 16.6.2. Considerations for New Content Codings . . . . . . . 174
15.6.2. Considerations for New Content Codings . . . . . . . 173 16.7. Upgrade Token Registry . . . . . . . . . . . . . . . . . 174
15.7. Upgrade Token Registry . . . . . . . . . . . . . . . . . 174 17. Security Considerations . . . . . . . . . . . . . . . . . . . 175
16. Security Considerations . . . . . . . . . . . . . . . . . . . 174 17.1. Establishing Authority . . . . . . . . . . . . . . . . . 175
16.1. Establishing Authority . . . . . . . . . . . . . . . . . 175 17.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 176
16.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 176 17.3. Attacks Based on File and Path Names . . . . . . . . . . 177
16.3. Attacks Based on File and Path Names . . . . . . . . . . 176 17.4. Attacks Based on Command, Code, or Query Injection . . . 177
16.4. Attacks Based on Command, Code, or Query Injection . . . 177 17.5. Attacks via Protocol Element Length . . . . . . . . . . 178
16.5. Attacks via Protocol Element Length . . . . . . . . . . 177 17.6. Attacks using Shared-dictionary Compression . . . . . . 178
16.6. Attacks using Shared-dictionary Compression . . . . . . 178 17.7. Disclosure of Personal Information . . . . . . . . . . . 179
16.7. Disclosure of Personal Information . . . . . . . . . . . 178 17.8. Privacy of Server Log Information . . . . . . . . . . . 179
16.8. Privacy of Server Log Information . . . . . . . . . . . 179 17.9. Disclosure of Sensitive Information in URIs . . . . . . 180
16.9. Disclosure of Sensitive Information in URIs . . . . . . 179 17.10. Disclosure of Fragment after Redirects . . . . . . . . . 180
16.10. Disclosure of Fragment after Redirects . . . . . . . . . 180 17.11. Disclosure of Product Information . . . . . . . . . . . 181
16.11. Disclosure of Product Information . . . . . . . . . . . 180 17.12. Browser Fingerprinting . . . . . . . . . . . . . . . . . 181
16.12. Browser Fingerprinting . . . . . . . . . . . . . . . . . 181 17.13. Validator Retention . . . . . . . . . . . . . . . . . . 182
16.13. Validator Retention . . . . . . . . . . . . . . . . . . 182 17.14. Denial-of-Service Attacks Using Range . . . . . . . . . 182
16.14. Denial-of-Service Attacks Using Range . . . . . . . . . 182 17.15. Authentication Considerations . . . . . . . . . . . . . 183
16.15. Authentication Considerations . . . . . . . . . . . . . 183 17.15.1. Confidentiality of Credentials . . . . . . . . . . 183
16.15.1. Confidentiality of Credentials . . . . . . . . . . 183 17.15.2. Credentials and Idle Clients . . . . . . . . . . . 183
16.15.2. Credentials and Idle Clients . . . . . . . . . . . 183 17.15.3. Protection Spaces . . . . . . . . . . . . . . . . . 184
16.15.3. Protection Spaces . . . . . . . . . . . . . . . . . 184 17.15.4. Additional Response Fields . . . . . . . . . . . . 184
16.15.4. Additional Response Fields . . . . . . . . . . . . 184 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 184
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 184 18.1. URI Scheme Registration . . . . . . . . . . . . . . . . 185
17.1. URI Scheme Registration . . . . . . . . . . . . . . . . 185 18.2. Method Registration . . . . . . . . . . . . . . . . . . 185
17.2. Method Registration . . . . . . . . . . . . . . . . . . 185 18.3. Status Code Registration . . . . . . . . . . . . . . . . 185
17.3. Status Code Registration . . . . . . . . . . . . . . . . 185 18.4. Field Name Registration . . . . . . . . . . . . . . . . 187
17.4. HTTP Field Name Registration . . . . . . . . . . . . . . 187 18.5. Authentication Scheme Registration . . . . . . . . . . . 189
17.5. Authentication Scheme Registration . . . . . . . . . . . 189 18.6. Content Coding Registration . . . . . . . . . . . . . . 189
17.6. Content Coding Registration . . . . . . . . . . . . . . 189 18.7. Range Unit Registration . . . . . . . . . . . . . . . . 189
17.7. Range Unit Registration . . . . . . . . . . . . . . . . 189 18.8. Media Type Registration . . . . . . . . . . . . . . . . 190
17.8. Media Type Registration . . . . . . . . . . . . . . . . 189 18.9. Port Registration . . . . . . . . . . . . . . . . . . . 190
17.9. Port Registration . . . . . . . . . . . . . . . . . . . 189 18.10. Upgrade Token Registration . . . . . . . . . . . . . . . 190
17.10. Upgrade Token Registration . . . . . . . . . . . . . . . 190 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 190
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 190 19.1. Normative References . . . . . . . . . . . . . . . . . . 190
18.1. Normative References . . . . . . . . . . . . . . . . . . 190 19.2. Informative References . . . . . . . . . . . . . . . . . 192
18.2. Informative References . . . . . . . . . . . . . . . . . 192 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 199
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 198
Appendix B. Changes from previous RFCs . . . . . . . . . . . . . 203 Appendix B. Changes from previous RFCs . . . . . . . . . . . . . 203
B.1. Changes from RFC 2818 . . . . . . . . . . . . . . . . . . 203 B.1. Changes from RFC 2818 . . . . . . . . . . . . . . . . . . 203
B.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 203 B.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 204
B.3. Changes from RFC 7231 . . . . . . . . . . . . . . . . . . 204 B.3. Changes from RFC 7231 . . . . . . . . . . . . . . . . . . 205
B.4. Changes from RFC 7232 . . . . . . . . . . . . . . . . . . 205 B.4. Changes from RFC 7232 . . . . . . . . . . . . . . . . . . 206
B.5. Changes from RFC 7233 . . . . . . . . . . . . . . . . . . 205 B.5. Changes from RFC 7233 . . . . . . . . . . . . . . . . . . 206
B.6. Changes from RFC 7235 . . . . . . . . . . . . . . . . . . 205 B.6. Changes from RFC 7235 . . . . . . . . . . . . . . . . . . 206
B.7. Changes from RFC 7538 . . . . . . . . . . . . . . . . . . 205 B.7. Changes from RFC 7538 . . . . . . . . . . . . . . . . . . 207
B.8. Changes from RFC 7615 . . . . . . . . . . . . . . . . . . 205 B.8. Changes from RFC 7615 . . . . . . . . . . . . . . . . . . 207
B.9. Changes from RFC 7694 . . . . . . . . . . . . . . . . . . 206 B.9. Changes from RFC 7694 . . . . . . . . . . . . . . . . . . 207
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 206 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 207
C.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 206 C.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 207
C.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 206 C.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 207
C.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 207 C.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 208
C.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 208 C.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 209
C.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 209 C.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 210
C.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 210 C.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 211
C.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 210 C.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 211
C.8. Since draft-ietf-httpbis-semantics-06 . . . . . . . . . . 212 C.8. Since draft-ietf-httpbis-semantics-06 . . . . . . . . . . 213
C.9. Since draft-ietf-httpbis-semantics-07 . . . . . . . . . . 213 C.9. Since draft-ietf-httpbis-semantics-07 . . . . . . . . . . 214
C.10. Since draft-ietf-httpbis-semantics-08 . . . . . . . . . . 214 C.10. Since draft-ietf-httpbis-semantics-08 . . . . . . . . . . 215
C.11. Since draft-ietf-httpbis-semantics-09 . . . . . . . . . . 216 C.11. Since draft-ietf-httpbis-semantics-09 . . . . . . . . . . 217
C.12. Since draft-ietf-httpbis-semantics-10 . . . . . . . . . . 216 C.12. Since draft-ietf-httpbis-semantics-10 . . . . . . . . . . 217
C.13. Since draft-ietf-httpbis-semantics-11 . . . . . . . . . . 217 C.13. Since draft-ietf-httpbis-semantics-11 . . . . . . . . . . 219
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 218 C.14. Since draft-ietf-httpbis-semantics-12 . . . . . . . . . . 219
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 218 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 221
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 222
1. Introduction 1. Introduction
1.1. Purpose 1.1. Purpose
The Hypertext Transfer Protocol (HTTP) is a family of stateless, The Hypertext Transfer Protocol (HTTP) is a family of stateless,
application-level, request/response protocols that share a generic application-level, request/response protocols that share a generic
interface, extensible semantics, and self-descriptive messages to interface, extensible semantics, and self-descriptive messages to
enable flexible interaction with network-based hypertext information enable flexible interaction with network-based hypertext information
systems. systems.
skipping to change at page 9, line 39 skipping to change at page 9, line 39
One consequence of this flexibility is that the protocol cannot be One consequence of this flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions the communication is considered in isolation, then successful actions
ought to be reflected in corresponding changes to the observable ought to be reflected in corresponding changes to the observable
interface provided by servers. However, since multiple clients might interface provided by servers. However, since multiple clients might
act in parallel and perhaps at cross-purposes, we cannot require that act in parallel and perhaps at cross-purposes, we cannot require that
such changes be observable beyond the scope of a single response. such changes be observable beyond the scope of a single response.
1.2. Evolution 1.2. History and Evolution
HTTP has been the primary information transfer protocol for the World HTTP has been the primary information transfer protocol for the World
Wide Web since its introduction in 1990. It began as a trivial Wide Web since its introduction in 1990. It began as a trivial
mechanism for low-latency requests, with a single method (GET) to mechanism for low-latency requests, with a single method (GET) to
request transfer of a presumed hypertext document identified by a request transfer of a presumed hypertext document identified by a
given pathname. This original protocol is now referred to as given pathname. This original protocol is now referred to as
HTTP/0.9. HTTP/0.9 (see [HTTP/0.9]).
HTTP's version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version")
indicates the messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version within that major
version to which the sender is conformant (able to understand for
future communication).
As the Web grew, HTTP was extended to enclose requests and responses As the Web grew, HTTP was extended to enclose requests and responses
within messages, transfer arbitrary data formats using MIME-like within messages, transfer arbitrary data formats using MIME-like
media types, and route requests through intermediaries, eventually media types, and route requests through intermediaries, eventually
being defined as HTTP/1.0 [RFC1945]. being defined as HTTP/1.0 [RFC1945].
HTTP/1.1 was designed to refine the protocol's features while HTTP/1.1 was designed to refine the protocol's features while
retaining compatibility with the existing text-based messaging retaining compatibility with the existing text-based messaging
syntax, improving its interoperability, scalability, and robustness syntax, improving its interoperability, scalability, and robustness
across the Internet. This included length-based payload delimiters across the Internet. This included length-based payload delimiters
for both fixed and dynamic (chunked) content, a consistent framework for both fixed and dynamic (chunked) content, a consistent framework
for content negotiation, opaque validators for conditional requests, for content negotiation, opaque validators for conditional requests,
cache controls for better cache consistency, range requests for cache controls for better cache consistency, range requests for
partial updates, and default persistent connections. HTTP/1.1 was partial updates, and default persistent connections. HTTP/1.1 was
introduced in 1995 and published on the standards track in 1997 introduced in 1995 and published on the standards track in 1997
[RFC2068], 1999 [RFC2616], and 2014 ([RFC7230] - [RFC7235]). [RFC2068], 1999 [RFC2616], and 2014 ([RFC7230] - [RFC7235]).
HTTP/2 ([RFC7540]) introduced a multiplexed session layer on top of HTTP/2 ([RFC7540]) introduced a multiplexed session layer on top of
the existing TLS and TCP protocols for exchanging concurrent HTTP the existing TLS and TCP protocols for exchanging concurrent HTTP
messages with efficient header field compression and server push. messages with efficient field compression and server push. HTTP/3
HTTP/3 ([HTTP3]) provides greater independence for concurrent ([HTTP3]) provides greater independence for concurrent messages by
messages by using QUIC as a secure multiplexed transport over UDP using QUIC as a secure multiplexed transport over UDP instead of TCP.
instead of TCP.
All three major versions of HTTP rely on the semantics defined by All three major versions of HTTP rely on the semantics defined by
this document. They have not obsoleted each other because each one this document. They have not obsoleted each other because each one
has specific benefits and limitations depending on the context of has specific benefits and limitations depending on the context of
use. Implementations are expected to choose the most appropriate use. Implementations are expected to choose the most appropriate
transport and messaging syntax for their particular context. transport and messaging syntax for their particular context.
This revision of HTTP separates the definition of semantics (this This revision of HTTP separates the definition of semantics (this
document) and caching ([Caching]) from the current HTTP/1.1 messaging document) and caching ([Caching]) from the current HTTP/1.1 messaging
syntax ([Messaging]) to allow each major protocol version to progress syntax ([Messaging]) to allow each major protocol version to progress
independently while referring to the same core semantics. independently while referring to the same core semantics.
1.3. Semantics 1.3. Core Semantics
HTTP provides a uniform interface for interacting with a resource HTTP provides a uniform interface for interacting with a resource
(Section 3.1), regardless of its type, nature, or implementation, by (Section 3.1), regardless of its type, nature, or implementation, by
sending messages that manipulate or transfer representations sending messages that manipulate or transfer representations
(Section 7). (Section 8).
Each message is either a request or a response. A client constructs Each message is either a request or a response. A client constructs
request messages that communicate its intentions and routes those request messages that communicate its intentions and routes those
messages toward an identified origin server. A server listens for messages toward an identified origin server. A server listens for
requests, parses each message received, interprets the message requests, parses each message received, interprets the message
semantics in relation to the identified target resource, and responds semantics in relation to the identified target resource, and responds
to that request with one or more response messages. The client to that request with one or more response messages. The client
examines received responses to see if its intentions were carried examines received responses to see if its intentions were carried
out, determining what to do next based on the received status and out, determining what to do next based on the received status and
payloads. payloads.
HTTP semantics include the intentions defined by each request method HTTP semantics include the intentions defined by each request method
(Section 8), extensions to those semantics that might be described in (Section 9), extensions to those semantics that might be described in
request header fields, status codes that describe the response request header fields, status codes that describe the response
(Section 14), and other control data and resource metadata that might (Section 15), and other control data and resource metadata that might
be given in response fields. be given in response fields.
Semantics also include representation metadata that describe how a Semantics also include representation metadata that describe how a
payload is intended to be interpreted by a recipient, request header payload is intended to be interpreted by a recipient, request header
fields that might influence content selection, and the various fields that might influence content selection, and the various
selection algorithms that are collectively referred to as "content selection algorithms that are collectively referred to as "_content
negotiation" (Section 11). negotiation_" (Section 12).
1.4. Obsoletes 1.4. Specifications Obsoleted by this Document
This document obsoletes the following specifications: This document obsoletes the following specifications:
-------------------------------------------- ----------- --------- -------------------------------------------- ----------- ---------
Title Reference Changes Title Reference Changes
-------------------------------------------- ----------- --------- -------------------------------------------- ----------- ---------
HTTP Over TLS [RFC2818] B.1 HTTP Over TLS [RFC2818] B.1
HTTP/1.1 Message Syntax and Routing [*] [RFC7230] B.2 HTTP/1.1 Message Syntax and Routing [*] [RFC7230] B.2
HTTP/1.1 Semantics and Content [RFC7231] B.3 HTTP/1.1 Semantics and Content [RFC7231] B.3
HTTP/1.1 Conditional Requests [RFC7232] B.4 HTTP/1.1 Conditional Requests [RFC7232] B.4
skipping to change at page 11, line 50 skipping to change at page 11, line 40
HTTP Status Code 308 (Permanent Redirect) [RFC7538] B.7 HTTP Status Code 308 (Permanent Redirect) [RFC7538] B.7
HTTP Authentication-Info and Proxy- [RFC7615] B.8 HTTP Authentication-Info and Proxy- [RFC7615] B.8
Authentication-Info Response Header Fields Authentication-Info Response Header Fields
HTTP Client-Initiated Content-Encoding [RFC7694] B.9 HTTP Client-Initiated Content-Encoding [RFC7694] B.9
-------------------------------------------- ----------- --------- -------------------------------------------- ----------- ---------
Table 1 Table 1
[*] This document only obsoletes the portions of RFC 7230 that are [*] This document only obsoletes the portions of RFC 7230 that are
independent of the HTTP/1.1 messaging syntax and connection independent of the HTTP/1.1 messaging syntax and connection
management; the remaining bits of RFC 7230 are obsoleted by "HTTP/1.1 management; the remaining bits of RFC 7230 are obsoleted by
Messaging" [Messaging]. "HTTP/1.1" [Messaging].
2. Conformance 2. Conformance
2.1. Syntax Notation 2.1. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234], extended with the notation for case- notation of [RFC5234], extended with the notation for case-
sensitivity in strings defined in [RFC7405]. sensitivity in strings defined in [RFC7405].
It also uses a list extension, defined in Section 5.7.1, that allows It also uses a list extension, defined in Section 5.6.1, that allows
for compact definition of comma-separated lists using a '#' operator for compact definition of comma-separated lists using a '#' operator
(similar to how the '*' operator indicates repetition). Appendix A (similar to how the '*' operator indicates repetition). Appendix A
shows the collected grammar with all list operators expanded to shows the collected grammar with all list operators expanded to
standard ABNF notation. standard ABNF notation.
As a convention, ABNF rule names prefixed with "obs-" denote As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons. "obsolete" grammar rules that appear for historical reasons.
The following core rules are included by reference, as defined in The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return), Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
(line feed), OCTET (any 8-bit sequence of data), SP (space), and (line feed), OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character). VCHAR (any visible US-ASCII character).
Section 5.7 defines some generic syntactic components for field Section 5.6 defines some generic syntactic components for field
values. values.
The rule below is defined in [Messaging];
transfer-coding = <transfer-coding, see [Messaging], Section 7>
This specification uses the terms "character", "character encoding This specification uses the terms "character", "character encoding
scheme", "charset", and "protocol element" as they are defined in scheme", "charset", and "protocol element" as they are defined in
[RFC6365]. [RFC6365].
2.2. Requirements Notation 2.2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
skipping to change at page 14, line 28 skipping to change at page 14, line 16
protocol element from an invalid construct. HTTP does not define protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct specific error handling mechanisms except when they have a direct
impact on security, since different applications of the protocol impact on security, since different applications of the protocol
require different error handling strategies. For example, a Web require different error handling strategies. For example, a Web
browser might wish to transparently recover from a response where the browser might wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF, whereas a Location header field doesn't parse according to the ABNF, whereas a
systems control client might consider any form of error recovery to systems control client might consider any form of error recovery to
be dangerous. be dangerous.
Some requests can be automatically retried by a client in the event Some requests can be automatically retried by a client in the event
of an underlying connection failure, as described in Section 8.2.2. of an underlying connection failure, as described in Section 9.2.2.
3. Terminology 2.5. Protocol Version
HTTP's version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version")
indicates the messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version within that major
version to which the sender is conformant (able to understand for
future communication).
While HTTP's core semantics don't change between protocol versions,
the expression of them "on the wire" can change, and so the HTTP
version number changes when incompatible changes are made to the wire
format. Additionally, HTTP allows incremental, backwards-compatible
changes to be made to the protocol without changing its version
through the use of defined extension points (Section 16).
The protocol version as a whole indicates the sender's conformance
with the set of requirements laid out in that version's corresponding
specification of HTTP. For example, the version "HTTP/1.1" is
defined by the combined specifications of this document, "HTTP
Caching" [Caching], and "HTTP/1.1" [Messaging].
HTTP's major version number is incremented when an incompatible
message syntax is introduced. The minor number is incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender.
The minor version advertises the sender's communication capabilities
even when the sender is only using a backwards-compatible subset of
the protocol, thereby letting the recipient know that more advanced
features can be used in response (by servers) or in future requests
(by clients).
When a major version of HTTP does not define any minor versions, the
minor version "0" is implied and is used when referring to that
protocol within a protocol element that requires sending a minor
version.
3. Terminology and Core Concepts
HTTP was created for the World Wide Web (WWW) architecture and has HTTP was created for the World Wide Web (WWW) architecture and has
evolved over time to support the scalability needs of a worldwide evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the hypertext system. Much of that architecture is reflected in the
terminology and syntax productions used to define HTTP. terminology and syntax productions used to define HTTP.
3.1. Resources 3.1. Resources
The target of an HTTP request is called a "resource". HTTP does not The target of an HTTP request is called a "_resource_". HTTP does
limit the nature of a resource; it merely defines an interface that not limit the nature of a resource; it merely defines an interface
might be used to interact with resources. Most resources are that might be used to interact with resources. Most resources are
identified by a Uniform Resource Identifier (URI), as described in identified by a Uniform Resource Identifier (URI), as described in
Section 4. Section 4.
One design goal of HTTP is to separate resource identification from One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request request semantics, which is made possible by vesting the request
semantics in the request method (Section 8) and a few request- semantics in the request method (Section 9) and a few request-
modifying header fields. If there is a conflict between the method modifying header fields. If there is a conflict between the method
semantics and any semantic implied by the URI itself, as described in semantics and any semantic implied by the URI itself, as described in
Section 8.2.1, the method semantics take precedence. Section 9.2.1, the method semantics take precedence.
HTTP relies upon the Uniform Resource Identifier (URI) standard HTTP relies upon the Uniform Resource Identifier (URI) standard
[RFC3986] to indicate the target resource (Section 6.1) and [RFC3986] to indicate the target resource (Section 7.1) and
relationships between resources. relationships between resources.
3.2. Connections 3.2. Connections
HTTP is a client/server protocol that operates over a reliable HTTP is a client/server protocol that operates over a reliable
transport- or session-layer "connection". transport- or session-layer "_connection_".
An HTTP "client" is a program that establishes a connection to a An HTTP "_client_" is a program that establishes a connection to a
server for the purpose of sending one or more HTTP requests. An HTTP server for the purpose of sending one or more HTTP requests. An HTTP
"server" is a program that accepts connections in order to service "_server_" is a program that accepts connections in order to service
HTTP requests by sending HTTP responses. HTTP requests by sending HTTP responses.
The terms "client" and "server" refer only to the roles that these The terms "client" and "server" refer only to the roles that these
programs perform for a particular connection. The same program might programs perform for a particular connection. The same program might
act as a client on some connections and a server on others. act as a client on some connections and a server on others.
3.3. Messages 3.3. Messages
HTTP is a stateless request/response protocol for exchanging HTTP is a stateless request/response protocol for exchanging
"messages" across a connection. The terms "sender" and "recipient" "_messages_" across a connection. The terms "_sender_" and
refer to any implementation that sends or receives a given message, "_recipient_" refer to any implementation that sends or receives a
respectively. given message, respectively.
A client sends requests to a server in the form of a request message A client sends requests to a server in the form of a _request_
with a method (Section 8) and request target (Section 6.1.1). The message with a method (Section 9) and request target (Section 7.1).
request might also contain header fields (Section 5.4) for request The request might also contain header fields (Section 6.3) for
modifiers, client information, and representation metadata, a payload request modifiers, client information, and representation metadata, a
body (Section 5.5.4) to be processed in accordance with the method, payload (Section 6.4) to be processed in accordance with the method,
and trailer fields (Section 5.6) for metadata collected while sending and trailer fields (Section 6.5) for metadata collected while sending
the payload. the payload.
A server responds to a client's request by sending one or more A server responds to a client's request by sending one or more
response messages, each including a status code (Section 14). The _response_ messages, each including a status code (Section 15). The
response might also contain header fields for server information, response might also contain header fields for server information,
resource metadata, and representation metadata, a payload body to be resource metadata, and representation metadata, payload data to be
interpreted in accordance with the status code, and trailer fields interpreted in accordance with the status code, and trailer fields
for metadata collected while sending the payload. for metadata collected while sending the payload.
3.4. User Agent 3.4. User Agent
The term "user agent" refers to any of the various client programs The term "_user agent_" refers to any of the various client programs
that initiate a request. that initiate a request.
The most familiar form of user agent is the general-purpose Web The most familiar form of user agent is the general-purpose Web
browser, but that's only a small percentage of implementations. browser, but that's only a small percentage of implementations.
Other common user agents include spiders (web-traversing robots), Other common user agents include spiders (web-traversing robots),
command-line tools, billboard screens, household appliances, scales, command-line tools, billboard screens, household appliances, scales,
light bulbs, firmware update scripts, mobile apps, and communication light bulbs, firmware update scripts, mobile apps, and communication
devices in a multitude of shapes and sizes. devices in a multitude of shapes and sizes.
Being a user agent does not imply that there is a human user directly Being a user agent does not imply that there is a human user directly
skipping to change at page 16, line 30 skipping to change at page 17, line 12
reporting of errors to the user, it is acceptable for such reporting reporting of errors to the user, it is acceptable for such reporting
to only be observable in an error console or log file. Likewise, to only be observable in an error console or log file. Likewise,
requirements that an automated action be confirmed by the user before requirements that an automated action be confirmed by the user before
proceeding might be met via advance configuration choices, run-time proceeding might be met via advance configuration choices, run-time
options, or simple avoidance of the unsafe action; confirmation does options, or simple avoidance of the unsafe action; confirmation does
not imply any specific user interface or interruption of normal not imply any specific user interface or interruption of normal
processing if the user has already made that choice. processing if the user has already made that choice.
3.5. Origin Server 3.5. Origin Server
The term "origin server" refers to a program that can originate The term "_origin server_" refers to a program that can originate
authoritative responses for a given target resource. authoritative responses for a given target resource.
The most familiar form of origin server are large public websites. The most familiar form of origin server are large public websites.
However, like user agents being equated with browsers, it is easy to However, like user agents being equated with browsers, it is easy to
be misled into thinking that all origin servers are alike. Common be misled into thinking that all origin servers are alike. Common
origin servers also include home automation units, configurable origin servers also include home automation units, configurable
networking components, office machines, autonomous robots, news networking components, office machines, autonomous robots, news
feeds, traffic cameras, real-time ad selectors, and video-on-demand feeds, traffic cameras, real-time ad selectors, and video-on-demand
platforms. platforms.
3.6. Example Request and Response
Most HTTP communication consists of a retrieval request (GET) for a Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. In the simplest representation of some resource identified by a URI. In the simplest
case, this might be accomplished via a single bidirectional case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server connection (===) between the user agent (UA) and the origin server
(O). (O).
request > request >
UA ======================================= O UA ======================================= O
< response < response
Figure 1 Figure 1
The following example illustrates a typical message exchange for a 3.6. Intermediaries
GET request (Section 8.3.1) on the URI "http://www.example.com/
hello.txt":
Client request:
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
Server response:
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain
Hello World! My payload includes a trailing CRLF.
3.7. Intermediaries
HTTP enables the use of intermediaries to satisfy requests through a HTTP enables the use of intermediaries to satisfy requests through a
chain of connections. There are three common forms of HTTP chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases, a single _intermediary_: proxy, gateway, and tunnel. In some cases, a single
intermediary might act as an origin server, proxy, gateway, or intermediary might act as an origin server, proxy, gateway, or
tunnel, switching behavior based on the nature of each request. tunnel, switching behavior based on the nature of each request.
> > > > > > > >
UA =========== A =========== B =========== C =========== O UA =========== A =========== B =========== C =========== O
< < < < < < < <
Figure 2 Figure 2
The figure above shows three intermediaries (A, B, and C) between the The figure above shows three intermediaries (A, B, and C) between the
skipping to change at page 18, line 12 skipping to change at page 18, line 16
with the nearest, non-tunnel neighbor, only to the endpoints of the with the nearest, non-tunnel neighbor, only to the endpoints of the
chain, or to all connections along the chain. Although the diagram chain, or to all connections along the chain. Although the diagram
is linear, each participant might be engaged in multiple, is linear, each participant might be engaged in multiple,
simultaneous communications. For example, B might be receiving simultaneous communications. For example, B might be receiving
requests from many clients other than A, and/or forwarding requests requests from many clients other than A, and/or forwarding requests
to servers other than C, at the same time that it is handling A's to servers other than C, at the same time that it is handling A's
request. Likewise, later requests might be sent through a different request. Likewise, later requests might be sent through a different
path of connections, often based on dynamic configuration for load path of connections, often based on dynamic configuration for load
balancing. balancing.
The terms "upstream" and "downstream" are used to describe The terms "_upstream_" and "_downstream_" are used to describe
directional requirements in relation to the message flow: all directional requirements in relation to the message flow: all
messages flow from upstream to downstream. The terms "inbound" and messages flow from upstream to downstream. The terms "inbound" and
"outbound" are used to describe directional requirements in relation "outbound" are used to describe directional requirements in relation
to the request route: "inbound" means toward the origin server and to the request route: "_inbound_" means toward the origin server and
"outbound" means toward the user agent. "_outbound_" means toward the user agent.
A "proxy" is a message-forwarding agent that is chosen by the client, A "_proxy_" is a message-forwarding agent that is chosen by the
usually via local configuration rules, to receive requests for some client, usually via local configuration rules, to receive requests
type(s) of absolute URI and attempt to satisfy those requests via for some type(s) of absolute URI and attempt to satisfy those
translation through the HTTP interface. Some translations are requests via translation through the HTTP interface. Some
minimal, such as for proxy requests for "http" URIs, whereas other translations are minimal, such as for proxy requests for "http" URIs,
requests might require translation to and from entirely different whereas other requests might require translation to and from entirely
application-level protocols. Proxies are often used to group an different application-level protocols. Proxies are often used to
organization's HTTP requests through a common intermediary for the group an organization's HTTP requests through a common intermediary
sake of security, annotation services, or shared caching. Some for the sake of security, annotation services, or shared caching.
proxies are designed to apply transformations to selected messages or Some proxies are designed to apply transformations to selected
payloads while they are being forwarded, as described in Section 6.5. messages or payloads while they are being forwarded, as described in
Section 7.7.
A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as A "_gateway_" (a.k.a. "_reverse proxy_") is an intermediary that acts
an origin server for the outbound connection but translates received as an origin server for the outbound connection but translates
requests and forwards them inbound to another server or servers. received requests and forwards them inbound to another server or
Gateways are often used to encapsulate legacy or untrusted servers. Gateways are often used to encapsulate legacy or untrusted
information services, to improve server performance through information services, to improve server performance through
"accelerator" caching, and to enable partitioning or load balancing "_accelerator_" caching, and to enable partitioning or load balancing
of HTTP services across multiple machines. of HTTP services across multiple machines.
All HTTP requirements applicable to an origin server also apply to All HTTP requirements applicable to an origin server also apply to
the outbound communication of a gateway. A gateway communicates with the outbound communication of a gateway. A gateway communicates with
inbound servers using any protocol that it desires, including private inbound servers using any protocol that it desires, including private
extensions to HTTP that are outside the scope of this specification. extensions to HTTP that are outside the scope of this specification.
However, an HTTP-to-HTTP gateway that wishes to interoperate with However, an HTTP-to-HTTP gateway that wishes to interoperate with
third-party HTTP servers ought to conform to user agent requirements third-party HTTP servers ought to conform to user agent requirements
on the gateway's inbound connection. on the gateway's inbound connection.
A "tunnel" acts as a blind relay between two connections without A "_tunnel_" acts as a blind relay between two connections without
changing the messages. Once active, a tunnel is not considered a changing the messages. Once active, a tunnel is not considered a
party to the HTTP communication, though the tunnel might have been party to the HTTP communication, though the tunnel might have been
initiated by an HTTP request. A tunnel ceases to exist when both initiated by an HTTP request. A tunnel ceases to exist when both
ends of the relayed connection are closed. Tunnels are used to ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when extend a virtual connection through an intermediary, such as when
Transport Layer Security (TLS, [RFC8446]) is used to establish Transport Layer Security (TLS, [RFC8446]) is used to establish
confidential communication through a shared firewall proxy. confidential communication through a shared firewall proxy.
The above categories for intermediary only consider those acting as The above categories for intermediary only consider those acting as
participants in the HTTP communication. There are also participants in the HTTP communication. There are also
intermediaries that can act on lower layers of the network protocol intermediaries that can act on lower layers of the network protocol
stack, filtering or redirecting HTTP traffic without the knowledge or stack, filtering or redirecting HTTP traffic without the knowledge or
permission of message senders. Network intermediaries are permission of message senders. Network intermediaries are
indistinguishable (at a protocol level) from an on-path attacker, indistinguishable (at a protocol level) from an on-path attacker,
often introducing security flaws or interoperability problems due to often introducing security flaws or interoperability problems due to
mistakenly violating HTTP semantics. mistakenly violating HTTP semantics.
For example, an "interception proxy" [RFC3040] (also commonly known For example, an "_interception proxy_" [RFC3040] (also commonly known
as a "transparent proxy" [RFC1919] or "captive portal") differs from as a "_transparent proxy_" [RFC1919] or "_captive portal_") differs
an HTTP proxy because it is not chosen by the client. Instead, an from an HTTP proxy because it is not chosen by the client. Instead,
interception proxy filters or redirects outgoing TCP port 80 packets an interception proxy filters or redirects outgoing TCP port 80
(and occasionally other common port traffic). Interception proxies packets (and occasionally other common port traffic). Interception
are commonly found on public network access points, as a means of proxies are commonly found on public network access points, as a
enforcing account subscription prior to allowing use of non-local means of enforcing account subscription prior to allowing use of non-
Internet services, and within corporate firewalls to enforce network local Internet services, and within corporate firewalls to enforce
usage policies. network usage policies.
HTTP is defined as a stateless protocol, meaning that each request HTTP is defined as a stateless protocol, meaning that each request
message can be understood in isolation. Many implementations depend message can be understood in isolation. Many implementations depend
on HTTP's stateless design in order to reuse proxied connections or on HTTP's stateless design in order to reuse proxied connections or
dynamically load balance requests across multiple servers. Hence, a dynamically load balance requests across multiple servers. Hence, a
server MUST NOT assume that two requests on the same connection are server MUST NOT assume that two requests on the same connection are
from the same user agent unless the connection is secured and from the same user agent unless the connection is secured and
specific to that agent. Some non-standard HTTP extensions (e.g., specific to that agent. Some non-standard HTTP extensions (e.g.,
[RFC4559]) have been known to violate this requirement, resulting in [RFC4559]) have been known to violate this requirement, resulting in
security and interoperability problems. security and interoperability problems.
3.8. Caches 3.7. Caches
A "cache" is a local store of previous response messages and the A "_cache_" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion. subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel. cannot be used by a server while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C) chain if B has a cached copy of an earlier response from O (via C)
for a request that has not been cached by UA or A. for a request that has not been cached by UA or A.
> > > >
UA =========== A =========== B - - - - - - C - - - - - - O UA =========== A =========== B - - - - - - C - - - - - - O
< < < <
Figure 3 Figure 3
A response is "cacheable" if a cache is allowed to store a copy of A response is "_cacheable_" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests. Even the response message for use in answering subsequent requests. Even
when a response is cacheable, there might be additional constraints when a response is cacheable, there might be additional constraints
placed by the client or by the origin server on when that cached placed by the client or by the origin server on when that cached
response can be used for a particular request. HTTP requirements for response can be used for a particular request. HTTP requirements for
cache behavior and cacheable responses are defined in Section 2 of cache behavior and cacheable responses are defined in Section 2 of
[Caching]. [Caching].
There is a wide variety of architectures and configurations of caches There is a wide variety of architectures and configurations of caches
deployed across the World Wide Web and inside large organizations. deployed across the World Wide Web and inside large organizations.
These include national hierarchies of proxy caches to save These include national hierarchies of proxy caches to save
transoceanic bandwidth, collaborative systems that broadcast or transoceanic bandwidth, collaborative systems that broadcast or
multicast cache entries, archives of pre-fetched cache entries for multicast cache entries, archives of pre-fetched cache entries for
use in off-line or high-latency environments, and so on. use in off-line or high-latency environments, and so on.
4. Identifiers 3.8. Example Message Exchange
The following example illustrates a typical HTTP/1.1 message exchange
for a GET request (Section 9.3.1) on the URI "http://www.example.com/
hello.txt":
Client request:
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
Server response:
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain
Hello World! My payload includes a trailing CRLF.
4. Identifiers in HTTP
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources (Section 3.1). HTTP as the means for identifying resources (Section 3.1).
4.1. URI References 4.1. URI References
URI references are used to target requests, indicate redirects, and URI references are used to target requests, indicate redirects, and
define relationships. define relationships.
The definitions of "URI-reference", "absolute-URI", "relative-part", The definitions of "URI-reference", "absolute-URI", "relative-part",
skipping to change at page 21, line 23 skipping to change at page 22, line 6
query = <query, see [RFC3986], Section 3.4> query = <query, see [RFC3986], Section 3.4>
absolute-path = 1*( "/" segment ) absolute-path = 1*( "/" segment )
partial-URI = relative-part [ "?" query ] partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows any form indicate in its ABNF production whether the element allows any form
of reference (URI-reference), only a URI in absolute form (absolute- of reference (URI-reference), only a URI in absolute form (absolute-
URI), only the path and optional query components, or some URI), only the path and optional query components, or some
combination of the above. Unless otherwise indicated, URI references combination of the above. Unless otherwise indicated, URI references
are parsed relative to the target URI (Section 6.1). are parsed relative to the target URI (Section 7.1).
It is RECOMMENDED that all senders and recipients support, at a It is RECOMMENDED that all senders and recipients support, at a
minimum, URIs with lengths of 8000 octets in protocol elements. Note minimum, URIs with lengths of 8000 octets in protocol elements. Note
that this implies some structures and on-wire representations (for that this implies some structures and on-wire representations (for
example, the request line in HTTP/1.1) will necessarily be larger in example, the request line in HTTP/1.1) will necessarily be larger in
some cases. some cases.
4.2. URI Schemes 4.2. HTTP-Related URI Schemes
IANA maintains the registry of URI Schemes [BCP35] at IANA maintains the registry of URI Schemes [BCP35] at
<https://www.iana.org/assignments/uri-schemes/>. Although requests <https://www.iana.org/assignments/uri-schemes/>. Although requests
might target any URI scheme, the following schemes are inherent to might target any URI scheme, the following schemes are inherent to
HTTP servers: HTTP servers:
------------ ------------------------------------ ------- ------------ ------------------------------------ -------
URI Scheme Description Ref. URI Scheme Description Ref.
------------ ------------------------------------ ------- ------------ ------------------------------------ -------
http Hypertext Transfer Protocol 4.2.1 http Hypertext Transfer Protocol 4.2.1
skipping to change at page 22, line 42 skipping to change at page 23, line 26
The hierarchical path component and optional query component identify The hierarchical path component and optional query component identify
the target resource within that origin server's name space. the target resource within that origin server's name space.
4.2.2. https URI Scheme 4.2.2. https URI Scheme
The "https" URI scheme is hereby defined for minting identifiers The "https" URI scheme is hereby defined for minting identifiers
within the hierarchical namespace governed by a potential origin within the hierarchical namespace governed by a potential origin
server listening for TCP connections on a given port and capable of server listening for TCP connections on a given port and capable of
establishing a TLS ([RFC8446]) connection that has been secured for establishing a TLS ([RFC8446]) connection that has been secured for
HTTP communication. In this context, "secured" specifically means HTTP communication. In this context, "_secured_" specifically means
that the server has been authenticated as acting on behalf of the that the server has been authenticated as acting on behalf of the
identified authority and all HTTP communication with that server has identified authority and all HTTP communication with that server has
been protected for confidentiality and integrity through the use of been protected for confidentiality and integrity through the use of
strong encryption. strong encryption.
https-URI = "https" "://" authority path-abempty [ "?" query ] https-URI = "https" "://" authority path-abempty [ "?" query ]
The origin server for an "https" URI is identified by the authority The origin server for an "https" URI is identified by the authority
component, which includes a host identifier and optional port number component, which includes a host identifier and optional port number
([RFC3986], Section 3.2.2). If the port subcomponent is empty or not ([RFC3986], Section 3.2.2). If the port subcomponent is empty or not
skipping to change at page 24, line 5 skipping to change at page 24, line 37
"reserved" set are equivalent to their percent-encoded octets: the "reserved" set are equivalent to their percent-encoded octets: the
normal form is to not encode them (see Sections 2.1 and 2.2 of normal form is to not encode them (see Sections 2.1 and 2.2 of
[RFC3986]). [RFC3986]).
For example, the following three URIs are equivalent: For example, the following three URIs are equivalent:
http://example.com:80/~smith/home.html http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html http://EXAMPLE.com:/%7esmith/home.html
4.2.4. http(s) Deprecated userinfo 4.2.4. Deprecation of userinfo in http(s) URIs
The URI generic syntax for authority also includes a userinfo The URI generic syntax for authority also includes a userinfo
subcomponent ([RFC3986], Section 3.2.1) for including user subcomponent ([RFC3986], Section 3.2.1) for including user
authentication information in the URI. In that subcomponent, the use authentication information in the URI. In that subcomponent, the use
of the format "user:password" is deprecated. of the format "user:password" is deprecated.
Some implementations make use of the userinfo component for internal Some implementations make use of the userinfo component for internal
configuration of authentication information, such as within command configuration of authentication information, such as within command
invocation options, configuration files, or bookmark lists, even invocation options, configuration files, or bookmark lists, even
though such usage might expose a user identifier or password. though such usage might expose a user identifier or password.
skipping to change at page 24, line 33 skipping to change at page 25, line 17
its presence as an error; it is likely being used to obscure the its presence as an error; it is likely being used to obscure the
authority for the sake of phishing attacks. authority for the sake of phishing attacks.
4.2.5. http(s) References with Fragment Identifiers 4.2.5. http(s) References with Fragment Identifiers
Fragment identifiers allow for indirect identification of a secondary Fragment identifiers allow for indirect identification of a secondary
resource, independent of the URI scheme, as defined in Section 3.5 of resource, independent of the URI scheme, as defined in Section 3.5 of
[RFC3986]. Some protocol elements that refer to a URI allow [RFC3986]. Some protocol elements that refer to a URI allow
inclusion of a fragment, while others do not. They are distinguished inclusion of a fragment, while others do not. They are distinguished
by use of the ABNF rule for elements where fragment is allowed; by use of the ABNF rule for elements where fragment is allowed;
otherwise, a specific rule that excludes fragments is used (see otherwise, a specific rule that excludes fragments is used.
Section 6.1).
| *Note:* the fragment identifier component is not part of the | *Note:* The fragment identifier component is not part of the
| actual scheme definition for a URI scheme (see Section 4.3 of | scheme definition for a URI scheme (see Section 4.3 of
| [RFC3986]), thus does not appear in the ABNF definitions for | [RFC3986]), thus does not appear in the ABNF definitions for
| the "http" and "https" URI schemes above. | the "http" and "https" URI schemes above.
4.3. Authoritative Access 4.3. Authoritative Access
See Section 16.1 for security considerations related to establishing Authoritative access refers to dereferencing a given identifier, for
the sake of access to the identified resource, in a way that the
client believes is authoritative (controlled by the resource owner).
The process for determining that access is defined by the URI scheme
and often uses data within the URI components, such as the authority
component when the generic syntax is used. However, authoritative
access is not limited to the identified mechanism.
Section 4.3.1 defines the concept of an origin as an aid to such
uses, and the subsequent subsections explain how to establish a
peer's association with an authority to represent an origin.
See Section 17.1 for security considerations related to establishing
authority. authority.
4.3.1. URI Origin 4.3.1. URI Origin
The "origin" for a given URI is the triple of scheme, host, and port The "_origin_" for a given URI is the triple of scheme, host, and
after normalizing the scheme and host to lowercase and normalizing port after normalizing the scheme and host to lowercase and
the port to remove any leading zeros. If port is elided from the normalizing the port to remove any leading zeros. If port is elided
URI, the default port for that scheme is used. For example, the URI from the URI, the default port for that scheme is used. For example,
the URI
https://Example.Com/happy.js https://Example.Com/happy.js
would have the origin would have the origin
{ "https", "example.com", "443" } { "https", "example.com", "443" }
which can also be described as the normalized URI prefix with port which can also be described as the normalized URI prefix with port
always present: always present:
https://example.com:443 https://example.com:443
Each origin defines its own namespace and controls how identifiers Each origin defines its own namespace and controls how identifiers
within that namespace are mapped to resources. In turn, how the within that namespace are mapped to resources. In turn, how the
origin responds to valid requests, consistently over time, determines origin responds to valid requests, consistently over time, determines
skipping to change at page 26, line 12 skipping to change at page 27, line 6
indirect identifier for use with a name resolution service, such as indirect identifier for use with a name resolution service, such as
DNS, to find an address for an appropriate origin server. DNS, to find an address for an appropriate origin server.
When an "http" URI is used within a context that calls for access to When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the the indicated resource, a client MAY attempt access by resolving the
host identifier to an IP address, establishing a TCP connection to host identifier to an IP address, establishing a TCP connection to
that address on the indicated port, and sending an HTTP request that address on the indicated port, and sending an HTTP request
message to the server containing the URI's identifying data. message to the server containing the URI's identifying data.
If the server responds to such a request with a non-interim HTTP If the server responds to such a request with a non-interim HTTP
response message, as described in Section 14, then that response is response message, as described in Section 15, then that response is
considered an authoritative answer to the client's request. considered an authoritative answer to the client's request.
Note, however, that the above is not the only means for obtaining an Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]). For example, the Alt- response is always necessary (see [Caching]). For example, the Alt-
Svc header field [RFC7838] allows an origin server to identify other Svc header field [RFC7838] allows an origin server to identify other
services that are also authoritative for that origin. Access to services that are also authoritative for that origin. Access to
"http" identified resources might also be provided by protocols "http" identified resources might also be provided by protocols
outside the scope of this document. outside the scope of this document.
skipping to change at page 26, line 50 skipping to change at page 27, line 44
secured connection if the URI origin's host matches any of the hosts secured connection if the URI origin's host matches any of the hosts
present in the server's certificate and the client believes that it present in the server's certificate and the client believes that it
could open a connection to that host for that URI. In practice, a could open a connection to that host for that URI. In practice, a
client will make a DNS query to check that the origin's host contains client will make a DNS query to check that the origin's host contains
the same server IP address as the established connection. This the same server IP address as the established connection. This
restriction can be removed by the origin server sending an equivalent restriction can be removed by the origin server sending an equivalent
ORIGIN frame [RFC8336]. ORIGIN frame [RFC8336].
The request target's host and port value are passed within each HTTP The request target's host and port value are passed within each HTTP
request, identifying the origin and distinguishing it from other request, identifying the origin and distinguishing it from other
namespaces that might be controlled by the same server. It is the namespaces that might be controlled by the same server (Section 7.2).
origin's responsibility to ensure that any services provided with It is the origin's responsibility to ensure that any services
control over its certificate's private key are equally responsible provided with control over its certificate's private key are equally
for managing the corresponding "https" namespaces, or at least responsible for managing the corresponding "https" namespaces, or at
prepared to reject requests that appear to have been misdirected. A least prepared to reject requests that appear to have been
server might be unwilling to serve as the origin for some hosts even misdirected. A server might be unwilling to serve as the origin for
when they have the authority to do so. some hosts even when they have the authority to do so.
For example, if a network attacker causes connections for port N to For example, if a network attacker causes connections for port N to
be received at port Q, checking the target URI is necessary to ensure be received at port Q, checking the target URI is necessary to ensure
that the attacker can't cause "https://example.com:N/foo" to be that the attacker can't cause "https://example.com:N/foo" to be
replaced by "https://example.com:Q/foo" without consent. replaced by "https://example.com:Q/foo" without consent.
Note that the "https" scheme does not rely on TCP and the connected Note that the "https" scheme does not rely on TCP and the connected
port number for associating authority, since both are outside the port number for associating authority, since both are outside the
secured communication and thus cannot be trusted as definitive. secured communication and thus cannot be trusted as definitive.
Hence, the HTTP communication might take place over any channel that Hence, the HTTP communication might take place over any channel that
skipping to change at page 27, line 30 skipping to change at page 28, line 26
When an "https" URI is used within a context that calls for access to When an "https" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the the indicated resource, a client MAY attempt access by resolving the
host identifier to an IP address, establishing a TCP connection to host identifier to an IP address, establishing a TCP connection to
that address on the indicated port, securing the connection end-to- that address on the indicated port, securing the connection end-to-
end by successfully initiating TLS over TCP with confidentiality and end by successfully initiating TLS over TCP with confidentiality and
integrity protection, and sending an HTTP request message over that integrity protection, and sending an HTTP request message over that
connection containing the URI's identifying data. connection containing the URI's identifying data.
If the server responds to such a request with a non-interim HTTP If the server responds to such a request with a non-interim HTTP
response message, as described in Section 14, then that response is response message, as described in Section 15, then that response is
considered an authoritative answer to the client's request. considered an authoritative answer to the client's request.
Note, however, that the above is not the only means for obtaining an Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]). response is always necessary (see [Caching]).
4.3.4. https certificate verification 4.3.4. https certificate verification
To establish a secured connection to dereference a URI, a client MUST To establish a secured connection to dereference a URI, a client MUST
verify that the service's identity is an acceptable match for the verify that the service's identity is an acceptable match for the
skipping to change at page 28, line 21 skipping to change at page 29, line 18
If the certificate is not valid for the URI's origin server, a user If the certificate is not valid for the URI's origin server, a user
agent MUST either notify the user (user agents MAY give the user an agent MUST either notify the user (user agents MAY give the user an
option to continue with the connection in any case) or terminate the option to continue with the connection in any case) or terminate the
connection with a bad certificate error. Automated clients MUST log connection with a bad certificate error. Automated clients MUST log
the error to an appropriate audit log (if available) and SHOULD the error to an appropriate audit log (if available) and SHOULD
terminate the connection (with a bad certificate error). Automated terminate the connection (with a bad certificate error). Automated
clients MAY provide a configuration setting that disables this check, clients MAY provide a configuration setting that disables this check,
but MUST provide a setting which enables it. but MUST provide a setting which enables it.
5. Message Abstraction 5. Fields
Each major version of HTTP defines its own syntax for the
communication of messages. However, they share a common data
abstraction.
A message consists of control data to describe and route the message,
optional header fields that modify or extend the message semantics,
describe the sender, the payload, or provide additional context, a
potentially unbounded stream of payload data, and optional trailer
fields for metadata collected while sending the payload.
Messages are intended to be self-descriptive. This means that
everything a recipient needs to know about the message can be
determined by looking at the message itself, after decoding or
reconstituting parts that have been compressed or elided in transit,
without requiring an understanding of the sender's current
application state (established via prior messages).
5.1. Protocol Version
While HTTP's core semantics don't change between protocol versions,
the expression of them "on the wire" can change, and so the HTTP
version number changes when incompatible changes are made to the wire
format. Additionally, HTTP allows incremental, backwards-compatible
changes to be made to the protocol without changing its version
through the use of defined extension points (Section 15).
The protocol version as a whole indicates the sender's conformance
with the set of requirements laid out in that version's corresponding
specification of HTTP. For example, the version "HTTP/1.1" is
defined by the combined specifications of this document, "HTTP
Caching" [Caching], and "HTTP/1.1 Messaging" [Messaging].
HTTP's major version number is incremented when an incompatible
message syntax is introduced. The minor number is incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender.
The minor version advertises the sender's communication capabilities
even when the sender is only using a backwards-compatible subset of
the protocol, thereby letting the recipient know that more advanced
features can be used in response (by servers) or in future requests
(by clients).
A client SHOULD send a request version equal to the highest version
to which the client is conformant and whose major version is no
higher than the highest version supported by the server, if this is
known. A client MUST NOT send a version to which it is not
conformant.
A client MAY send a lower request version if it is known that the
server incorrectly implements the HTTP specification, but only after
the client has attempted at least one normal request and determined
from the response status code or header fields (e.g., Server) that
the server improperly handles higher request versions.
A server SHOULD send a response version equal to the highest version
to which the server is conformant that has a major version less than
or equal to the one received in the request. A server MUST NOT send
a version to which it is not conformant. A server can send a 505
(HTTP Version Not Supported) response if it wishes, for any reason,
to refuse service of the client's major protocol version.
When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the
recipient implements, the recipient SHOULD process the message as if
it were in the highest minor version within that major version to
which the recipient is conformant. A recipient can assume that a
message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any
implementation of the same major version.
When a major version of HTTP does not define any minor versions, the
minor version "0" is implied and is used when referring to that
protocol within a protocol element that requires sending a minor
version.
5.2. Framing
// Message framing defines how each message begins and ends, such
// that the message can be distinguished from other message (or
// noise) on the same connection. Framing is specific to each major
// version of HTTP.
One of the functions of message framing is to assure that messages HTTP uses "_fields_" to provide data in the form of extensible key/
are complete. A message is considered complete when all of the value pairs with a registered key namespace. Fields are sent and
octets indicated by its framing are available. Note that, when no received within the header and trailer sections of messages
explicit framing is used, a response message that is ended by the (Section 6).
transport connection's close is considered complete even though it
might be indistinguishable from an incomplete response, unless a
transport-level error indicates that it is not complete.
5.3. Control Data 5.1. Field Names
5.3.1. Request A field name labels the corresponding field value as having the
semantics defined by that name. For example, the Date header field
is defined in Section 10.2.2 as containing the origination timestamp
for the message in which it appears.
HTTP communication is initiated by a user agent for some purpose. field-name = token
The purpose is a combination of request semantics and a target
resource upon which to apply those semantics.
5.3.2. Response Field names are case-insensitive and ought to be registered within
the "Hypertext Transfer Protocol (HTTP) Field Name Registry"; see
Section 16.3.1.
5.4. Header Fields The interpretation of a field does not change between minor versions
of the same major HTTP version, though the default behavior of a
recipient in the absence of such a field can change. Unless
specified otherwise, fields are defined for all versions of HTTP. In
particular, the Host and Connection fields ought to be recognized by
all HTTP implementations whether or not they advertise conformance
with HTTP/1.1.
HTTP messages use key/value pairs to convey data about the message, New fields can be introduced without changing the protocol version if
its payload, the target resource, or the connection. They are called their defined semantics allow them to be safely ignored by recipients
"HTTP fields" or just "fields". that do not recognize them; see Section 16.3.
Fields that are sent/received before the message body are referred to A proxy MUST forward unrecognized header fields unless the field name
as "header fields" (or just "headers", colloquially) and are located is listed in the Connection header field (Section 7.6.1) or the proxy
within the "header section" of a message. We refer to some named is specifically configured to block, or otherwise transform, such
fields specifically as a "header field" when they are only allowed to fields. Other recipients SHOULD ignore unrecognized header and
be sent in the header section. trailer fields. Adhering to these requirements allows HTTP's
functionality to be extended without updating or removing deployed
intermediaries.
Fields that are sent/received after the header section has ended 5.2. Field Lines and Combined Field Value
(usually after the message body begins to stream) are referred to as
"trailer fields" (or just "trailers", colloquially) and located
within a "trailer section". One or more trailer sections are only
possible when supported by the version of HTTP in use and enabled by
an extensible mechanism for framing message sections.
Both sections are composed of any number of "field lines", each with Field sections are composed of any number of "_field lines_", each
a "field name" (see Section 5.4.3) identifying the field, and a with a "_field name_" (see Section 5.1) identifying the field, and a
"field line value" that conveys data for the field. "_field line value_" that conveys data for that instance of the
field.
Each field name present in a section has a corresponding "field When a field name is only present once in a section, the combined
value" for that section, composed from all field line values with "_field value_" for that field consists of the corresponding field
that given field name in that section, concatenated together and line value. When a field name is repeated within a section, its
separated with commas. See Section 5.4.1 for further discussion of combined field value consists of the list of corresponding field line
the semantics of field ordering and combination in messages, and values within that section, concatenated in order, with each non-
Section 5.4.4 for more discussion of field values. empty field line value separated by a comma.
For example, this section: For example, this section:
Example-Field: Foo, Bar Example-Field: Foo, Bar
Example-Field: Baz Example-Field: Baz
contains two field lines, both with the field name "Example-Field". contains two field lines, both with the field name "Example-Field".
The first field line has a field line value of "Foo, Bar", while the The first field line has a field line value of "Foo, Bar", while the
second field line value is "Baz". The field value for "Example- second field line value is "Baz". The field value for "Example-
Field" is a list with three members: "Foo", "Bar", and "Baz". Field" is a list with three members: "Foo", "Bar", and "Baz".
The interpretation of a field does not change between minor versions 5.3. Field Order
of the same major HTTP version, though the default behavior of a
recipient in the absence of such a field can change. Unless
specified otherwise, fields are defined for all versions of HTTP. In
particular, the Host and Connection fields ought to be implemented by
all HTTP/1.x implementations whether or not they advertise
conformance with HTTP/1.1.
New fields can be introduced without changing the protocol version if
their defined semantics allow them to be safely ignored by recipients
that do not recognize them; see Section 15.3.
A proxy MUST forward unrecognized header fields unless the field name
is listed in the Connection header field (Section 6.4.1) or the proxy
is specifically configured to block, or otherwise transform, such
fields. Other recipients SHOULD ignore unrecognized header and
trailer fields. These requirements allow HTTP's functionality to be
enhanced without requiring prior update of deployed intermediaries.
5.4.1. Field Ordering and Combination
The order in which field lines with differing names are received in a
message is not significant. However, it is good practice to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST NOT
apply a request to the target resource until the entire request
header section is received, since later header field lines might
include conditionals, authentication credentials, or deliberately
misleading duplicate header fields that would impact request
processing.
A recipient MAY combine multiple field lines with the same field name A recipient MAY combine multiple field lines within a field section
into one field line, without changing the semantics of the message, that have the same field name into one field line, without changing
by appending each subsequent field line value to the initial field the semantics of the message, by appending each subsequent field line
line value in order, separated by a comma and OWS (optional value to the initial field line value in order, separated by a comma
whitespace). For consistency, use comma SP. and OWS (optional whitespace). For consistency, use comma SP.
The order in which field lines with the same name are received is The order in which field lines with the same name are received is
therefore significant to the interpretation of the field value; a therefore significant to the interpretation of the field value; a
proxy MUST NOT change the order of these field line values when proxy MUST NOT change the order of these field line values when
forwarding a message. forwarding a message.
This means that, aside from the well-known exception noted below, a This means that, aside from the well-known exception noted below, a
sender MUST NOT generate multiple field lines with the same name in a sender MUST NOT generate multiple field lines with the same name in a
message (whether in the headers or trailers), or append a field line message (whether in the headers or trailers), or append a field line
when a field line of the same name already exists in the message, when a field line of the same name already exists in the message,
unless that field's definition allows multiple field line values to unless that field's definition allows multiple field line values to
be recombined as a comma-separated list [i.e., at least one be recombined as a comma-separated list [i.e., at least one
alternative of the field's definition allows a comma-separated list, alternative of the field's definition allows a comma-separated list,
such as an ABNF rule of #(values) defined in Section 5.7.1]. such as an ABNF rule of #(values) defined in Section 5.6.1].
| *Note:* In practice, the "Set-Cookie" header field ([RFC6265]) | *Note:* In practice, the "Set-Cookie" header field ([RFC6265])
| often appears in a response message across multiple field lines | often appears in a response message across multiple field lines
| and does not use the list syntax, violating the above | and does not use the list syntax, violating the above
| requirements on multiple field lines with the same field name. | requirements on multiple field lines with the same field name.
| Since it cannot be combined into a single field value, | Since it cannot be combined into a single field value,
| recipients ought to handle "Set-Cookie" as a special case while | recipients ought to handle "Set-Cookie" as a special case while
| processing fields. (See Appendix A.2.3 of [Kri2001] for | processing fields. (See Appendix A.2.3 of [Kri2001] for
| details.) | details.)
5.4.2. Field Limits The order in which field lines with differing field names are
received in a section is not significant. However, it is good
practice to send header fields that contain additional control data
first, such as Host on requests and Date on responses, so that
implementations can decide when not to handle a message as early as
possible.
A server MUST NOT apply a request to the target resource until the
entire request header section is received, since later header field
lines might include conditionals, authentication credentials, or
deliberately misleading duplicate header fields that would impact
request processing.
5.4. Field Limits
HTTP does not place a predefined limit on the length of each field HTTP does not place a predefined limit on the length of each field
line, field value, or on the length of a header or trailer section as line, field value, or on the length of a header or trailer section as
a whole, as described in Section 2. Various ad hoc limitations on a whole, as described in Section 2. Various ad hoc limitations on
individual lengths are found in practice, often depending on the individual lengths are found in practice, often depending on the
specific field's semantics. specific field's semantics.
A server that receives a request header field line, field value, or A server that receives a request header field line, field value, or
set of fields larger than it wishes to process MUST respond with an set of fields larger than it wishes to process MUST respond with an
appropriate 4xx (Client Error) status code. Ignoring such header appropriate 4xx (Client Error) status code. Ignoring such header
fields would increase the server's vulnerability to request smuggling fields would increase the server's vulnerability to request smuggling
attacks (Section 11.2 of [Messaging]). attacks (Section 11.2 of [Messaging]).
A client MAY discard or truncate received field lines that are larger A client MAY discard or truncate received field lines that are larger
than the client wishes to process if the field semantics are such than the client wishes to process if the field semantics are such
that the dropped value(s) can be safely ignored without changing the that the dropped value(s) can be safely ignored without changing the
message framing or response semantics. message framing or response semantics.
5.4.3. Field Names 5.5. Field Values
The field-name token labels the corresponding field value as having
the semantics defined by that field. For example, the Date header
field is defined in Section 9.2.2 as containing the origination
timestamp for the message in which it appears.
field-name = token
Field names are case-insensitive and ought to be registered within
the "Hypertext Transfer Protocol (HTTP) Field Name Registry"; see
Section 15.3.1.
5.4.4. Field Values
HTTP field values typically have their syntax defined using ABNF HTTP field values typically have their syntax defined using ABNF
([RFC5234]), using the extension defined in Section 5.7.1 as ([RFC5234]), using the extension defined in Section 5.6.1 as
necessary, and are usually constrained to the range of US-ASCII necessary, and are usually constrained to the range of US-ASCII
characters. Fields needing a greater range of characters can use an characters. Fields needing a greater range of characters can use an
encoding such as the one defined in [RFC8187]. encoding such as the one defined in [RFC8187].
field-value = *field-content field-value = *field-content
field-content = field-vchar field-content = field-vchar
[ 1*( SP / HTAB / field-vchar ) field-vchar ] [ 1*( SP / HTAB / field-vchar ) field-vchar ]
field-vchar = VCHAR / obs-text field-vchar = VCHAR / obs-text
Historically, HTTP allowed field content with text in the ISO-8859-1 Historically, HTTP allowed field content with text in the ISO-8859-1
skipping to change at page 34, line 16 skipping to change at page 32, line 38
treat other octets in field content (obs-text) as opaque data. treat other octets in field content (obs-text) as opaque data.
Field values containing control (CTL) characters such as CR or LF are Field values containing control (CTL) characters such as CR or LF are
invalid; recipients MUST either reject a field value containing invalid; recipients MUST either reject a field value containing
control characters, or convert them to SP before processing or control characters, or convert them to SP before processing or
forwarding the message. forwarding the message.
Leading and trailing whitespace in raw field values is removed upon Leading and trailing whitespace in raw field values is removed upon
field parsing (e.g., Section 5.1 of [Messaging]). Field definitions field parsing (e.g., Section 5.1 of [Messaging]). Field definitions
where leading or trailing whitespace in values is significant will where leading or trailing whitespace in values is significant will
have to use a container syntax such as quoted-string (Section 5.7.4). have to use a container syntax such as quoted-string (Section 5.6.4).
Commas (",") often are used to separate members in field values. Commas (",") often are used to separate members in field values.
Fields that allow multiple members are referred to as list-based Fields that allow multiple members are referred to as _list-based
fields. Fields that only anticipate a single member are referred to fields_. Fields that only anticipate a single member are referred to
as singleton fields. as _singleton fields_.
Because commas are used as a generic delimiter between members, they Because commas are used as a generic delimiter between members, they
need to be treated with care if they are allowed as data within a need to be treated with care if they are allowed as data within a
member. This is true for both list-based and singleton fields, since member. This is true for both list-based and singleton fields, since
a singleton field might be sent with multiple members erroneously; a singleton field might be sent with multiple members erroneously;
being able to detect this condition improves interoperability. being able to detect this condition improves interoperability.
Fields that expect to contain a comma within a member, such as an Fields that expect to contain a comma within a member, such as an
HTTP-date or URI-reference element, ought to be defined with HTTP-date or URI-reference element, ought to be defined with
delimiters around that element to distinguish any comma within that delimiters around that element to distinguish any comma within that
data from potential list separators. data from potential list separators.
skipping to change at page 34, line 45 skipping to change at page 33, line 27
these: these:
Example-URI-Field: "http://example.com/a.html,foo", Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/" "http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005" Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double- quoted-string production; using a different syntax inside double-
quotes will likely cause unnecessary confusion. quotes will likely cause unnecessary confusion.
Many fields (such as Content-Type, defined in Section 7.4) use a Many fields (such as Content-Type, defined in Section 8.4) use a
common syntax for parameters that allows both unquoted (token) and common syntax for parameters that allows both unquoted (token) and
quoted (quoted-string) syntax for a parameter value (Section 5.7.6). quoted (quoted-string) syntax for a parameter value (Section 5.6.6).
Use of common syntax allows recipients to reuse existing parser Use of common syntax allows recipients to reuse existing parser
components. When allowing both forms, the meaning of a parameter components. When allowing both forms, the meaning of a parameter
value ought to be the same whether it was received as a token or a value ought to be the same whether it was received as a token or a
quoted string. quoted string.
Historically, HTTP field values could be extended over multiple lines Historically, HTTP field values could be extended over multiple lines
by preceding each extra line with at least one space or horizontal by preceding each extra line with at least one space or horizontal
tab (obs-fold). This document assumes that any such obsolete line tab (obs-fold). This document assumes that any such obsolete line
folding has been replaced with one or more SP octets prior to folding has been replaced with one or more SP octets prior to
interpreting the field value, as described in Section 5.2 of interpreting the field value, as described in Section 5.2 of
[Messaging]. [Messaging].
| *Note:* This specification does not use ABNF rules to define | *Note:* This specification does not use ABNF rules to define
| each "Field Name: Field Value" pair, as was done in earlier | each "Field Name: Field Value" pair, as was done in earlier
| editions (published before [RFC7230]). Instead, ABNF rules are | editions (published before [RFC7230]). Instead, ABNF rules are
| named according to each registered field name, wherein the rule | named according to each registered field name, wherein the rule
| defines the valid grammar for that field's corresponding field | defines the valid grammar for that field's corresponding field
| values (i.e., after the field value has been extracted by a | values (i.e., after the field value has been extracted by a
| generic field parser). | generic field parser).
5.5. Payload 5.6. Common Rules for Defining Field Values
Some HTTP messages transfer a complete or partial representation as
the message "payload". In some cases, a payload might contain only
the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code).
5.5.1. Purpose
The purpose of a payload in a request is defined by the method
semantics. For example, a representation in the payload of a PUT
request (Section 8.3.4) represents the desired state of the target
resource if the request is successfully applied, whereas a
representation in the payload of a POST request (Section 8.3.3)
represents information to be processed by the target resource.
In a response, the payload's purpose is defined by both the request
method and the response status code. For example, the payload of a
200 (OK) response to GET (Section 8.3.1) represents the current state
of the target resource, as observed at the time of the message
origination date (Section 9.2.2), whereas the payload of the same
status code in a response to POST might represent either the
processing result or the new state of the target resource after
applying the processing. Response messages with an error status code
usually contain a payload that represents the error condition, such
that it describes the error state and what next steps are suggested
for resolving it.
5.5.2. Identification
When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to
that representation.
For a request message:
o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the
resource identified by the Content-Location field value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by this specification). The information
might still be useful for revision history links.
o Otherwise, the payload is unidentified.
For a response message, the following rules are applied in order
until a match is found:
1. If the request method is GET or HEAD and the response status code
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload is a representation of the resource
identified by the target URI (Section 6.1).
2. If the request method is GET or HEAD and the response status code
is 203 (Non-Authoritative Information), the payload is a
potentially modified or enhanced representation of the target
resource as provided by an intermediary.
3. If the response has a Content-Location header field and its field
value is a reference to the same URI as the target URI, the
payload is a representation of the target resource.
4. If the response has a Content-Location header field and its field
value is a reference to a URI different from the target URI, then
the sender asserts that the payload is a representation of the
resource identified by the Content-Location field value.
However, such an assertion cannot be trusted unless it can be
verified by other means (not defined by this specification).
5. Otherwise, the payload is unidentified.
5.5.3. Payload Metadata
Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing.
5.5.4. Payload Body
The payload body contains the data of a request or response. This is
distinct from the message body (e.g., Section 6 of [Messaging]),
which is how the payload body is transferred "on the wire", and might
be encoded, depending on the HTTP version in use.
It is also distinct from a request or response's representation data
(Section 7.2), which can be inferred from protocol operation, rather
than necessarily appearing "on the wire."
The presence of a payload body in a request depends on whether the
request method used defines semantics for it.
The presence of a payload body in a response depends on both the
request method to which it is responding and the response status code
(Section 14).
Responses to the HEAD request method (Section 8.3.2) never include a
payload body because the associated response header fields indicate
only what their values would have been if the request method had been
GET (Section 8.3.1).
2xx (Successful) responses to a CONNECT request method
(Section 8.3.6) switch the connection to tunnel mode instead of
having a payload body.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
responses do not include a payload body.
All other responses do include a payload body, although that body
might be of zero length.
5.6. Trailer Fields
5.6.1. Purpose
In some HTTP versions, additional metadata can be sent after the
initial header section has been completed (during or after
transmission of the payload body), such as a message integrity check,
digital signature, or post-processing status. For example, the
chunked coding in HTTP/1.1 allows a trailer section after the payload
body (Section 7.1.2 of [Messaging]) which can contain trailer fields:
field names and values that share the same syntax and namespace as
header fields but that are received after the header section.
Trailer fields ought to be processed and stored separately from the
fields in the header section to avoid contradicting message semantics
known at the time the header section was complete. The presence or
absence of certain header fields might impact choices made for the
routing or processing of the message as a whole before the trailers
are received; those choices cannot be unmade by the later discovery
of trailer fields.
5.6.2. Limitations
Many fields cannot be processed outside the header section because
their evaluation is necessary prior to receiving the message body,
such as those that describe message framing, routing, authentication,
request modifiers, response controls, or payload format. A sender
MUST NOT generate a trailer field unless the sender knows the
corresponding header field name's definition permits the field to be
sent in trailers.
Trailer fields can be difficult to process by intermediaries that
forward messages from one protocol version to another. If the entire
message can be buffered in transit, some intermediaries could merge
trailer fields into the header section (as appropriate) before it is
forwarded. However, in most cases, the trailers are simply
discarded. A recipient MUST NOT merge a trailer field into a header
section unless the recipient understands the corresponding header
field definition and that definition explicitly permits and defines
how trailer field values can be safely merged.
The presence of the keyword "trailers" in the TE header field
(Section 9.1.4) indicates that the client is willing to accept
trailer fields, on behalf of itself and any downstream clients. For
requests from an intermediary, this implies that all downstream
clients are willing to accept trailer fields in the forwarded
response. Note that the presence of "trailers" does not mean that
the client(s) will process any particular trailer field in the
response; only that the trailer section(s) will not be dropped by any
of the clients.
Because of the potential for trailer fields to be discarded in
transit, a server SHOULD NOT generate trailer fields that it believes
are necessary for the user agent to receive.
5.6.3. Processing
Like header fields, trailer fields with the same name are processed
in the order received; multiple trailer field lines with the same
name have the equivalent semantics as appending the multiple values
as a list of members, even when the field lines are received in
separate trailer sections. Trailer fields that might be generated
more than once during a message MUST be defined as a list value even
if each member value is only processed once per field line received.
Trailer fields are expected (but not required) to be processed one
trailer section at a time. That is, for each trailer section
received, a recipient that is looking for trailer fields will parse
the received section into fields, invoke any associated processing
for those fields at that point in the message processing, and then
append those fields to the set of trailer fields received for the
overall message.
This behavior allows for iterative processing of trailer fields that
contain incremental signatures or mid-stream status information, and
fields that might refer to each other's values within the same
section. However, there is no guarantee that trailer sections won't
shift in relation to the message body stream, or won't be recombined
(or dropped) in transit, so trailer fields that refer to data outside
the present trailer section need to use self-descriptive references
(i.e., refer to the data by name, ordinal position, or an octet
range) rather than assume it is the data most recently received.
Likewise, at the end of a message, a recipient MAY treat the entire
set of received trailer fields as one data structure to be considered
as the message concludes. Additional processing expectations, if
any, can be defined within the field specification for a field
intended for use in trailers.
5.7. Common Rules for Defining Field Values
5.7.1. Lists (#rule ABNF Extension) 5.6.1. Lists (#rule ABNF Extension)
A #rule extension to the ABNF rules of [RFC5234] is used to improve A #rule extension to the ABNF rules of [RFC5234] is used to improve
readability in the definitions of some list-based field values. readability in the definitions of some list-based field values.
A construct "#" is defined, similar to "*", for defining comma- A construct "#" is defined, similar to "*", for defining comma-
delimited lists of elements. The full form is "<n>#<m>element" delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS). single comma (",") and optional whitespace (OWS).
5.7.1.1. Sender Requirements 5.6.1.1. Sender Requirements
In any production that uses the list construct, a sender MUST NOT In any production that uses the list construct, a sender MUST NOT
generate empty list elements. In other words, a sender MUST generate generate empty list elements. In other words, a sender MUST generate
lists that satisfy the following syntax: lists that satisfy the following syntax:
1#element => element *( OWS "," OWS element ) 1#element => element *( OWS "," OWS element )
and: and:
#element => [ 1#element ] #element => [ 1#element ]
and for n >= 1 and m > 1: and for n >= 1 and m > 1:
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element ) <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
Appendix A shows the collected ABNF for senders after the list Appendix A shows the collected ABNF for senders after the list
constructs have been expanded. constructs have been expanded.
5.7.1.2. Recipient Requirements 5.6.1.2. Recipient Requirements
Empty elements do not contribute to the count of elements present. A Empty elements do not contribute to the count of elements present. A
recipient MUST parse and ignore a reasonable number of empty list recipient MUST parse and ignore a reasonable number of empty list
elements: enough to handle common mistakes by senders that merge elements: enough to handle common mistakes by senders that merge
values, but not so much that they could be used as a denial-of- values, but not so much that they could be used as a denial-of-
service mechanism. In other words, a recipient MUST accept lists service mechanism. In other words, a recipient MUST accept lists
that satisfy the following syntax: that satisfy the following syntax:
#element => [ element ] *( OWS "," OWS [ element ] ) #element => [ element ] *( OWS "," OWS [ element ] )
Note that because of the potential presence of empty list elements, Note that because of the potential presence of empty list elements,
the RFC 5234 ABNF cannot enforce the cardinality of list elements, the RFC 5234 ABNF cannot enforce the cardinality of list elements,
and consequently all cases are mapped as if there was no cardinality and consequently all cases are mapped as if there was no cardinality
specified. specified.
For example, given these ABNF productions: For example, given these ABNF productions:
example-list = 1#example-list-elmt example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 5.7.2 example-list-elmt = token ; see Section 5.6.2
Then the following are valid values for example-list (not including Then the following are valid values for example-list (not including
the double quotes, which are present for delimitation only): the double quotes, which are present for delimitation only):
"foo,bar" "foo,bar"
"foo ,bar," "foo ,bar,"
"foo , ,bar,charlie" "foo , ,bar,charlie"
In contrast, the following values would be invalid, since at least In contrast, the following values would be invalid, since at least
one non-empty element is required by the example-list production: one non-empty element is required by the example-list production:
"" ""
"," ","
", ," ", ,"
5.7.2. Tokens 5.6.2. Tokens
Many HTTP field values are defined using common syntax components, Many HTTP field values are defined using common syntax components,
separated by whitespace or specific delimiting characters. separated by whitespace or specific delimiting characters.
Delimiters are chosen from the set of US-ASCII visual characters not Delimiters are chosen from the set of US-ASCII visual characters not
allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}"). allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}").
Tokens are short textual identifiers that do not include whitespace Tokens are short textual identifiers that do not include whitespace
or delimiters. or delimiters.
token = 1*tchar token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA / DIGIT / ALPHA
; any VCHAR, except delimiters ; any VCHAR, except delimiters
5.7.3. Whitespace 5.6.3. Whitespace
This specification uses three rules to denote the use of linear This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace). BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace octets The OWS rule is used where zero or more linear whitespace octets
might appear. For protocol elements where optional whitespace is might appear. For protocol elements where optional whitespace is
preferred to improve readability, a sender SHOULD generate the preferred to improve readability, a sender SHOULD generate the
optional whitespace as a single SP; otherwise, a sender SHOULD NOT optional whitespace as a single SP; otherwise, a sender SHOULD NOT
generate optional whitespace except as needed to white out invalid or generate optional whitespace except as needed to white out invalid or
skipping to change at page 42, line 20 skipping to change at page 36, line 28
BWS has no semantics. Any content known to be defined as BWS MAY be BWS has no semantics. Any content known to be defined as BWS MAY be
removed before interpreting it or forwarding the message downstream. removed before interpreting it or forwarding the message downstream.
OWS = *( SP / HTAB ) OWS = *( SP / HTAB )
; optional whitespace ; optional whitespace
RWS = 1*( SP / HTAB ) RWS = 1*( SP / HTAB )
; required whitespace ; required whitespace
BWS = OWS BWS = OWS
; "bad" whitespace ; "bad" whitespace
5.7.4. Quoted Strings 5.6.4. Quoted Strings
A string of text is parsed as a single value if it is quoted using A string of text is parsed as a single value if it is quoted using
double-quote marks. double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF obs-text = %x80-FF
The backslash octet ("\") can be used as a single-octet quoting The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string and comment constructs. Recipients mechanism within quoted-string and comment constructs. Recipients
skipping to change at page 42, line 42 skipping to change at page 37, line 5
as if it were replaced by the octet following the backslash. as if it were replaced by the octet following the backslash.
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text ) quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
A sender SHOULD NOT generate a quoted-pair in a quoted-string except A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within where necessary to quote DQUOTE and backslash octets occurring within
that string. A sender SHOULD NOT generate a quoted-pair in a comment that string. A sender SHOULD NOT generate a quoted-pair in a comment
except where necessary to quote parentheses ["(" and ")"] and except where necessary to quote parentheses ["(" and ")"] and
backslash octets occurring within that comment. backslash octets occurring within that comment.
5.7.5. Comments 5.6.5. Comments
Comments can be included in some HTTP fields by surrounding the Comments can be included in some HTTP fields by surrounding the
comment text with parentheses. Comments are only allowed in fields comment text with parentheses. Comments are only allowed in fields
containing "comment" as part of their field value definition. containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-pair / comment ) ")" comment = "(" *( ctext / quoted-pair / comment ) ")"
ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text
5.7.6. Parameters 5.6.6. Parameters
Parameters are zero or more instances of a name=value pair; they are Parameters are instances of name=value pairs; they are often used in
often used in field values as a common syntax for appending auxiliary field values as a common syntax for appending auxiliary information
information to an item. Each parameter is usually delimited by an to an item. Each parameter is usually delimited by an immediately
immediately preceding semicolon. preceding semicolon.
parameters = *( OWS ";" OWS [ parameter ] ) parameters = *( OWS ";" OWS [ parameter ] )
parameter = parameter-name "=" parameter-value parameter = parameter-name "=" parameter-value
parameter-name = token parameter-name = token
parameter-value = ( token / quoted-string ) parameter-value = ( token / quoted-string )
Parameter names are case-insensitive. Parameter values might or Parameter names are case-insensitive. Parameter values might or
might not be case-sensitive, depending on the semantics of the might not be case-sensitive, depending on the semantics of the
parameter name. Examples of parameters and some equivalent forms can parameter name. Examples of parameters and some equivalent forms can
be seen in media types (Section 7.4.1) and the Accept header field be seen in media types (Section 8.4.1) and the Accept header field
(Section 11.1.2). (Section 12.5.1).
A parameter value that matches the token production can be A parameter value that matches the token production can be
transmitted either as a token or within a quoted-string. The quoted transmitted either as a token or within a quoted-string. The quoted
and unquoted values are equivalent. and unquoted values are equivalent.
| *Note:* Parameters do not allow whitespace (not even "bad" | *Note:* Parameters do not allow whitespace (not even "bad"
| whitespace) around the "=" character. | whitespace) around the "=" character.
5.7.7. Date/Time Formats 5.6.7. Date/Time Formats
Prior to 1995, there were three different formats commonly used by Prior to 1995, there were three different formats commonly used by
servers to communicate timestamps. For compatibility with old servers to communicate timestamps. For compatibility with old
implementations, all three are defined here. The preferred format is implementations, all three are defined here. The preferred format is
a fixed-length and single-zone subset of the date and time a fixed-length and single-zone subset of the date and time
specification used by the Internet Message Format [RFC5322]. specification used by the Internet Message Format [RFC5322].
HTTP-date = IMF-fixdate / obs-date HTTP-date = IMF-fixdate / obs-date
An example of the preferred format is An example of the preferred format is
skipping to change at page 45, line 9 skipping to change at page 39, line 16
; e.g., 02-Jun-82 ; e.g., 02-Jun-82
day-name-l = %s"Monday" / %s"Tuesday" / %s"Wednesday" day-name-l = %s"Monday" / %s"Tuesday" / %s"Wednesday"
/ %s"Thursday" / %s"Friday" / %s"Saturday" / %s"Thursday" / %s"Friday" / %s"Saturday"
/ %s"Sunday" / %s"Sunday"
asctime-date = day-name SP date3 SP time-of-day SP year asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT )) date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; e.g., Jun 2 ; e.g., Jun 2
HTTP-date is case sensitive. A sender MUST NOT generate additional HTTP-date is case sensitive. Note that Section 4.2 of [Caching]
whitespace in an HTTP-date beyond that specifically included as SP in relaxes this for cache recipients.
the grammar. The semantics of day-name, day, month, year, and
time-of-day are the same as those defined for the Internet Message A sender MUST NOT generate additional whitespace in an HTTP-date
Format constructs with the corresponding name ([RFC5322], beyond that specifically included as SP in the grammar. The
Section 3.3). semantics of day-name, day, month, year, and time-of-day are the same
as those defined for the Internet Message Format constructs with the
corresponding name ([RFC5322], Section 3.3).
Recipients of a timestamp value in rfc850-date format, which uses a Recipients of a timestamp value in rfc850-date format, which uses a
two-digit year, MUST interpret a timestamp that appears to be more two-digit year, MUST interpret a timestamp that appears to be more
than 50 years in the future as representing the most recent year in than 50 years in the future as representing the most recent year in
the past that had the same last two digits. the past that had the same last two digits.
Recipients of timestamp values are encouraged to be robust in parsing Recipients of timestamp values are encouraged to be robust in parsing
timestamps unless otherwise restricted by the field definition. For timestamps unless otherwise restricted by the field definition. For
example, messages are occasionally forwarded over HTTP from a non- example, messages are occasionally forwarded over HTTP from a non-
HTTP source that might generate any of the date and time HTTP source that might generate any of the date and time
specifications defined by the Internet Message Format. specifications defined by the Internet Message Format.
| *Note:* HTTP requirements for the date/time stamp format apply | *Note:* HTTP requirements for the date/time stamp format apply
| only to their usage within the protocol stream. | only to their usage within the protocol stream.
| Implementations are not required to use these formats for user | Implementations are not required to use these formats for user
| presentation, request logging, etc. | presentation, request logging, etc.
6. Routing 6. Message Abstraction
HTTP is used in a wide variety of applications, ranging from general- Each major version of HTTP defines its own syntax for communicating
purpose computers to home appliances. In some cases, communication messages. This section defines an abstract data type for HTTP
options are hard-coded in a client's configuration. However, most messages based on a generalization of those message characteristics,
HTTP clients rely on the same resource identification mechanism and common structure, and capacity for conveying semantics. This
configuration techniques as general-purpose Web browsers. abstraction is used to define requirements on senders and recipients
that are independent of the HTTP version, such that a message in one
version can be relayed through other versions without changing its
meaning.
A _message_ consists of control data to describe and route the
message, a headers lookup table of key/value pairs for extending that
control data and conveying additional information about the sender,
message, payload, or context, a potentially unbounded stream of
payload data, and a trailers lookup table of key/value pairs for
communicating information obtained while sending the payload.
Framing and control data is sent first, followed by a header section
containing fields for the headers table. When a message includes a
payload, the payload data is sent after the header section and
potentially interleaved with zero or more trailer sections containing
fields for the trailers table.
Messages are expected to be processed as a stream, wherein the
purpose of that stream and its continued processing is revealed while
being read. Hence, control data describes what the recipient needs
to know immediately, header fields describe what needs to be known
before receiving a payload, the payload (when present) presumably
contains what the recipient wants or needs to fulfill the message
semantics, and trailer fields provide additional metadata that can be
dropped (safely ignored) when not desired.
Messages are intended to be _self-descriptive_: everything a
recipient needs to know about the message can be determined by
looking at the message itself, after decoding or reconstituting parts
that have been compressed or elided in transit, without requiring an
understanding of the sender's current application state (established
via prior messages).
Note that this message abstraction is a generalization across many
versions of HTTP, including features that might not be found in some
versions. For example, trailers were introduced within the HTTP/1.1
chunked transfer coding as a single trailer section at the end of the
payload data. An equivalent feature is present in HTTP/2 and HTTP/3
within the header block that terminates each stream. However,
multiple trailer sections interleaved with payload data have only
been deployed as frame extensions.
6.1. Framing and Completeness
Message framing indicates how each message begins and ends, such that
each message can be distinguished from other messages or noise on the
same connection. Each major version of HTTP defines its own framing
mechanism.
HTTP/0.9 and early deployments of HTTP/1.0 used closure of the
underlying connection to end a response. For backwards
compatibility, this implicit framing is also allowed in HTTP/1.1.
However, implicit framing can fail to distinguish an incomplete
response if the connection closes early. For that reason, almost all
modern implementations use explicit framing in the form of length-
delimited sequences of message data.
A message is considered _complete_ when all of the octets indicated
by its framing are available. Note that, when no explicit framing is
used, a response message that is ended by the underlying connection's
close is considered complete even though it might be
indistinguishable from an incomplete response, unless a transport-
level error indicates that it is not complete.
6.2. Control Data
Messages start with control data that describe its primary purpose.
Request message control data includes a request method (Section 9),
request target (Section 7.1), and protocol version (Section 2.5).
Response message control data includes a status code (Section 15),
optional reason phrase, and protocol version.
In HTTP/1.1 [Messaging] and earlier, control data is sent as the
first line of a message. In HTTP/2 ([RFC7540]) and HTTP/3 ([HTTP3]),
control data is sent as pseudo-header fields with a reserved name
prefix (e.g., ":authority").
Every HTTP message has a protocol version. Depending on the version
in use, it might be identified within the message explicitly or
inferred by the connection over which the message is received.
Recipients use that version information to determine limitations or
potential for later communication with that sender.
When a message is forwarded by an intermediary, the protocol version
is updated to reflect the version used by that intermediary. The Via
header field (Section 7.6.3) is used to communicate upstream protocol
information within a forwarded message.
A client SHOULD send a request version equal to the highest version
to which the client is conformant and whose major version is no
higher than the highest version supported by the server, if this is
known. A client MUST NOT send a version to which it is not
conformant.
A client MAY send a lower request version if it is known that the
server incorrectly implements the HTTP specification, but only after
the client has attempted at least one normal request and determined
from the response status code or header fields (e.g., Server) that
the server improperly handles higher request versions.
A server SHOULD send a response version equal to the highest version
to which the server is conformant that has a major version less than
or equal to the one received in the request. A server MUST NOT send
a version to which it is not conformant. A server can send a 505
(HTTP Version Not Supported) response if it wishes, for any reason,
to refuse service of the client's major protocol version.
When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the
recipient implements, the recipient SHOULD process the message as if
it were in the highest minor version within that major version to
which the recipient is conformant. A recipient can assume that a
message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any
implementation of the same major version.
6.3. Header Fields
Fields (Section 5) that are sent/received before the payload are
referred to as "header fields" (or just "headers", colloquially).
The "_header section_" of a message consists of a sequence of of
header field lines. Each header field might modify or extend message
semantics, describe the sender, define the payload, or provide
additional context.
| *Note:* We refer to named fields specifically as a "header
| field" when they are only allowed to be sent in the header
| section.
6.4. Payload
HTTP messages often transfer a complete or partial representation as
the message "_payload_", including both representation metadata
transferred as fields and representation data transferred as _payload
data_: a stream of octets sent after the header section, as
delineated by the message framing.
This abstract definition of a payload reflects the data after it has
been extracted from the message framing. For example, an HTTP/1.1
message body (Section 6 of [Messaging]) might consist of a stream of
data encoded with the chunked transfer coding-a sequence of data
chunks, one zero-length chunk, and a trailer section-whereas the
payload data of that same message includes only the data stream after
the transfer coding has been decoded; it does not include the chunk
lengths, chunked framing syntax, nor the trailer fields
(Section 6.5).
6.4.1. Payload Semantics
The purpose of a payload in a request is defined by the method
semantics (Section 9).
For example, a representation in the payload of a PUT request
(Section 9.3.4) represents the desired state of the target resource
after the request is successfully applied, whereas a representation
in the payload of a POST request (Section 9.3.3) represents
information to be processed by the target resource.
In a response, the payload's purpose is defined by both the request
method and the response status code (Section 15). For example, the
payload of a 200 (OK) response to GET (Section 9.3.1) represents the
current state of the target resource, as observed at the time of the
message origination date (Section 10.2.2), whereas the payload of the
same status code in a response to POST might represent either the
processing result or the new state of the target resource after
applying the processing.
The payload of a 206 (Partial Content) response to GET contains
either a single part of the selected representation or a multipart
message body containing multiple parts of that representation, as
described in Section 15.3.7.
Response messages with an error status code usually contain a payload
that represents the error condition, such that the payload data
describes the error state and what steps are suggested for resolving
it.
Responses to the HEAD request method (Section 9.3.2) never include a
payload because the associated response header fields indicate only
what their values would have been if the request method had been GET
(Section 9.3.1).
2xx (Successful) responses to a CONNECT request method
(Section 9.3.6) switch the connection to tunnel mode instead of
having a payload.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
responses do not include a payload.
All other responses do include a payload, although that payload data
might be of zero length.
6.4.2. Identifying Payloads
When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to
that representation.
For a request message:
o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the
resource identified by the Content-Location field value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by this specification). The information
might still be useful for revision history links.
o Otherwise, the payload is unidentified.
For a response message, the following rules are applied in order
until a match is found:
1. If the request method is GET or HEAD and the response status code
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload is a representation of the resource
identified by the target URI (Section 7.1).
2. If the request method is GET or HEAD and the response status code
is 203 (Non-Authoritative Information), the payload is a
potentially modified or enhanced representation of the target
resource as provided by an intermediary.
3. If the response has a Content-Location header field and its field
value is a reference to the same URI as the target URI, the
payload is a representation of the target resource.
4. If the response has a Content-Location header field and its field
value is a reference to a URI different from the target URI, then
the sender asserts that the payload is a representation of the
resource identified by the Content-Location field value.
However, such an assertion cannot be trusted unless it can be
verified by other means (not defined by this specification).
5. Otherwise, the payload is unidentified.
6.5. Trailer Fields
Fields (Section 5) that are sent/received after the header section
has ended (usually after the payload data begins to stream) are
referred to as "trailer fields" (or just "trailers", colloquially)
and located within a "_trailer section_". Trailer fields can be
useful for supplying message integrity checks, digital signatures,
delivery metrics, or post-processing status information.
Trailer fields ought to be processed and stored separately from the
fields in the header section to avoid contradicting message semantics
known at the time the header section was complete. The presence or
absence of certain header fields might impact choices made for the
routing or processing of the message as a whole before the trailers
are received; those choices cannot be unmade by the later discovery
of trailer fields.
6.5.1. Limitations on use of Trailers
Trailer sections are only possible when supported by the version of
HTTP in use and enabled by an explicit framing mechanism. For
example, the chunked coding in HTTP/1.1 allows a trailer section to
be sent after the payload data (Section 7.1.2 of [Messaging]).
Many fields cannot be processed outside the header section because
their evaluation is necessary prior to receiving the payload data,
such as those that describe message framing, routing, authentication,
request modifiers, response controls, or payload data format. A
sender MUST NOT generate a trailer field unless the sender knows the
corresponding header field name's definition permits the field to be
sent in trailers.
Trailer fields can be difficult to process by intermediaries that
forward messages from one protocol version to another. If the entire
message can be buffered in transit, some intermediaries could merge
trailer fields into the header section (as appropriate) before it is
forwarded. However, in most cases, the trailers are simply
discarded. A recipient MUST NOT merge a trailer field into a header
section unless the recipient understands the corresponding header
field definition and that definition explicitly permits and defines
how trailer field values can be safely merged.
The presence of the keyword "trailers" in the TE header field
(Section 10.1.4) indicates that the client is willing to accept
trailer fields, on behalf of itself and any downstream clients. For
requests from an intermediary, this implies that all downstream
clients are willing to accept trailer fields in the forwarded
response. Note that the presence of "trailers" does not mean that
the client(s) will process any particular trailer field in the
response; only that the trailer section(s) will not be dropped by any
of the clients.
Because of the potential for trailer fields to be discarded in
transit, a server SHOULD NOT generate trailer fields that it believes
are necessary for the user agent to receive.
6.5.2. Processing Trailer Fields
Like header fields, trailer fields with the same name are processed
in the order received; multiple trailer field lines with the same
name have the equivalent semantics as appending the multiple values
as a list of members, even when the field lines are received in
separate trailer sections. Trailer fields that might be generated
more than once during a message MUST be defined as a list-based field
even if each member value is only processed once per field line
received.
Trailer fields are expected (but not required) to be processed one
trailer section at a time. That is, for each trailer section
received, a recipient that is looking for trailer fields will parse
the received section into fields, invoke any associated processing
for those fields at that point in the message processing, and then
append those fields to the set of trailer fields received for the
overall message.
This behavior allows for iterative processing of trailer fields that
contain incremental signatures or mid-stream status information, and
fields that might refer to each other's values within the same
section. However, there is no guarantee that trailer sections won't
shift in relation to the payload data stream, or won't be recombined
(or dropped) in transit. Trailer fields that refer to data outside
the present trailer section need to use self-descriptive references
(i.e., refer to the data by name, ordinal position, or an octet
range) rather than assume it is the data most recently received.
Likewise, at the end of a message, a recipient MAY treat the entire
set of received trailer fields as one data structure to be considered
as the message concludes. Additional processing expectations, if
any, can be defined within the field specification for a field
intended for use in trailers.
7. Routing HTTP Messages
HTTP request message routing is determined by each client based on HTTP request message routing is determined by each client based on
the target resource, the client's proxy configuration, and the target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the response routing follows the same connection chain back to the
client. client.
6.1. Target Resource 7.1. Determining the Target Resource
6.1.1. Request Target
The "request target" is the protocol element that identifies the Although HTTP is used in a wide variety of applications, most clients
"target resource". rely on the same resource identification mechanism and configuration
techniques as general-purpose Web browsers. Even when communication
options are hard-coded in a client's configuration, we can think of
their combined effect as a URI reference (Section 4.1).
Typically, the request target is a URI reference (Section 4) which a A URI reference is resolved to its absolute form in order to obtain
user agent would resolve to its absolute form in order to obtain the the "_target URI_". The target URI excludes the reference's fragment
"target URI". The target URI excludes the reference's fragment
component, if any, since fragment identifiers are reserved for component, if any, since fragment identifiers are reserved for
client-side processing ([RFC3986], Section 3.5). client-side processing ([RFC3986], Section 3.5).
However, there are two special, method-specific forms allowed for the To perform an action on a "_target resource_", the client sends a
request target in specific circumstances: request message containing enough components of its parsed target URI
to enable recipients to identify that same resource. For historical
reasons, the parsed target URI components, collectively referred to
as the "_request target_", are sent within the message control data
and the Host header field (Section 7.2).
o For CONNECT (Section 8.3.6), the request target is the host name There are two unusual cases for which the request target components
are in a method-specific form:
o For CONNECT (Section 9.3.6), the request target is the host name
and port number of the tunnel destination, separated by a colon. and port number of the tunnel destination, separated by a colon.
o For OPTIONS (Section 8.3.7), the request target can be a single o For OPTIONS (Section 9.3.7), the request target can be a single
asterisk ("*"). asterisk ("*").
See the respective method definitions for details. These forms MUST See the respective method definitions for details. These forms MUST
NOT be used with other methods. NOT be used with other methods.
6.1.2. Host Upon receipt of a client's request, a server reconstructs the target
URI from the received components in accordance with their local
configuration and incoming connection context. This reconstruction
is specific to each major protocol version. For example, Appendix of
[Messaging] defines how a server determines the target URI of an
HTTP/1.1 request.
| *Note:* Previous specifications defined the recomposed target
| URI as a distinct concept, the _effective request URI_.
7.2. Host and :authority
The "Host" header field in a request provides the host and port The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple distinguish among resources while servicing requests for multiple
host names on a single IP address. host names.
In HTTP/2 [RFC7540] and HTTP/3 [HTTP3], the Host header field is, in
some cases, supplanted by the ":authority" pseudo-header field of a
request's control data.
Host = uri-host [ ":" port ] ; Section 4 Host = uri-host [ ":" port ] ; Section 4
Since the Host field value is critical information for handling a The target URI's authority information is critical for handling a
request, a user agent SHOULD generate Host as the first field in the request. A user agent SHOULD generate Host as the first field in the
header section. header section of a request unless it has already generated that
information as an ":authority" pseudo-header field.
For example, a GET request to the origin server for For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with: <http://www.example.org/pub/WWW/> would begin with:
GET /pub/WWW/ HTTP/1.1 GET /pub/WWW/ HTTP/1.1
Host: www.example.org Host: www.example.org
Since the Host header field acts as an application-level routing Since the host and port information acts as an application-level
mechanism, it is a frequent target for malware seeking to poison a routing mechanism, it is a frequent target for malware seeking to
shared cache or redirect a request to an unintended server. An poison a shared cache or redirect a request to an unintended server.
interception proxy is particularly vulnerable if it relies on the An interception proxy is particularly vulnerable if it relies on the
Host field value for redirecting requests to internal servers, or for host and port information for redirecting requests to internal
use as a cache key in a shared cache, without first verifying that servers, or for use as a cache key in a shared cache, without first
the intercepted connection is targeting a valid IP address for that verifying that the intercepted connection is targeting a valid IP
host. address for that host.
6.1.3. Reconstructing the Target URI
Once an inbound connection is obtained, the client sends an HTTP
request message.
Depending on the nature of the request, the client's target URI might
be split into components and transmitted (or implied) within various
parts of a request message. These parts are recombined by each
recipient, in accordance with their local configuration and incoming
connection context, to determine the target URI. Appendix of
[Messaging] defines how a server determines the target URI for an
HTTP/1.1 request.
Once the target URI has been reconstructed, an origin server needs to
decide whether or not to provide service for that URI via the
connection in which the request was received. For example, the
request might have been misdirected, deliberately or accidentally,
such that the information within a received Host header field differs
from the host or port upon which the connection has been made. If
the connection is from a trusted gateway, that inconsistency might be
expected; otherwise, it might indicate an attempt to bypass security
filters, trick the server into delivering non-public content, or
poison a cache. See Section 16 for security considerations regarding
message routing.
| *Note:* previous specifications defined the recomposed target
| URI as a distinct concept, the effective request URI.
6.2. Routing Inbound 7.3. Routing Inbound Requests
Once the target URI and its origin are determined, a client decides Once the target URI and its origin are determined, a client decides
whether a network request is necessary to accomplish the desired whether a network request is necessary to accomplish the desired
semantics and, if so, where that request is to be directed. semantics and, if so, where that request is to be directed.
6.2.1. To a Cache 7.3.1. To a Cache
If the client has a cache [Caching] and the request can be satisfied If the client has a cache [Caching] and the request can be satisfied
by it, then the request is usually directed there first. by it, then the request is usually directed there first.
6.2.2. To a Proxy 7.3.2. To a Proxy
If the request is not satisfied by a cache, then a typical client If the request is not satisfied by a cache, then a typical client
will check its configuration to determine whether a proxy is to be will check its configuration to determine whether a proxy is to be
used to satisfy the request. Proxy configuration is implementation- used to satisfy the request. Proxy configuration is implementation-
dependent, but is often based on URI prefix matching, selective dependent, but is often based on URI prefix matching, selective
authority matching, or both, and the proxy itself is usually authority matching, or both, and the proxy itself is usually
identified by an "http" or "https" URI. If a proxy is applicable, identified by an "http" or "https" URI. If a proxy is applicable,
the client connects inbound by establishing (or reusing) a connection the client connects inbound by establishing (or reusing) a connection
to that proxy. to that proxy.
6.2.3. To the Origin 7.3.3. To the Origin
If no proxy is applicable, a typical client will invoke a handler If no proxy is applicable, a typical client will invoke a handler
routine, usually specific to the target URI's scheme, to connect routine, usually specific to the target URI's scheme, to connect
directly to an origin for the target resource. How that is directly to an origin for the target resource. How that is
accomplished is dependent on the target URI scheme and defined by its accomplished is dependent on the target URI scheme and defined by its
associated specification. associated specification.
6.3. Response Correlation 7.4. Rejecting Misdirected Requests
Before performing a request, a server decides whether or not to
provide service for the target URI via the connection in which the
request is received. For example, a request might have been
misdirected, deliberately or accidentally, such that the information
within a received Host header field differs from the connection's
host or port.
If the connection is from a trusted gateway, such inconsistency might
be expected; otherwise, it might indicate an attempt to bypass
security filters, trick the server into delivering non-public
content, or poison a cache. See Section 17 for security
considerations regarding message routing.
7.5. Response Correlation
A connection might be used for multiple request/response exchanges. A connection might be used for multiple request/response exchanges.
The mechanism used to correlate between request and response messages The mechanism used to correlate between request and response messages
is version dependent; some versions of HTTP use implicit ordering of is version dependent; some versions of HTTP use implicit ordering of
messages, while others use an explicit identifier. messages, while others use an explicit identifier.
Responses (both final and interim) can be sent at any time after a Responses (both final and interim) can be sent at any time after a
request is received, even if it is not yet complete. However, request is received, even if it is not yet complete. However,
clients (including intermediaries) might abandon a request if the clients (including intermediaries) might abandon a request if the
response is not forthcoming within a reasonable period of time. response is not forthcoming within a reasonable period of time.
6.4. Message Forwarding 7.6. Message Forwarding
As described in Section 3.7, intermediaries can serve a variety of As described in Section 3.6, intermediaries can serve a variety of
roles in the processing of HTTP requests and responses. Some roles in the processing of HTTP requests and responses. Some
intermediaries are used to improve performance or availability. intermediaries are used to improve performance or availability.
Others are used for access control or to filter content. Since an Others are used for access control or to filter content. Since an
HTTP stream has characteristics similar to a pipe-and-filter HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an architecture, there are no inherent limits to the extent an
intermediary can enhance (or interfere) with either direction of the intermediary can enhance (or interfere) with either direction of the
stream. stream.
An intermediary not acting as a tunnel MUST implement the Connection An intermediary not acting as a tunnel MUST implement the Connection
header field, as specified in Section 6.4.1, and exclude fields from header field, as specified in Section 7.6.1, and exclude fields from
being forwarded that are only intended for the incoming connection. being forwarded that are only intended for the incoming connection.
An intermediary MUST NOT forward a message to itself unless it is An intermediary MUST NOT forward a message to itself unless it is
protected from an infinite request loop. In general, an intermediary protected from an infinite request loop. In general, an intermediary
ought to recognize its own server names, including any aliases, local ought to recognize its own server names, including any aliases, local
variations, or literal IP addresses, and respond to such requests variations, or literal IP addresses, and respond to such requests
directly. directly.
An HTTP message can be parsed as a stream for incremental processing An HTTP message can be parsed as a stream for incremental processing
or forwarding downstream. However, recipients cannot rely on or forwarding downstream. However, recipients cannot rely on
incremental delivery of partial messages, since some implementations incremental delivery of partial messages, since some implementations
will buffer or delay message forwarding for the sake of network will buffer or delay message forwarding for the sake of network
efficiency, security checks, or payload transformations. efficiency, security checks, or payload transformations.
6.4.1. Connection 7.6.1. Connection
The "Connection" header field allows the sender to list desired The "Connection" header field allows the sender to list desired
control options for the current connection. control options for the current connection.
When a field aside from Connection is used to supply control When a field aside from Connection is used to supply control
information for or about the current connection, the sender MUST list information for or about the current connection, the sender MUST list
the corresponding field name within the Connection header field. the corresponding field name within the Connection header field.
Note that some versions of HTTP prohibit the use of fields for such Note that some versions of HTTP prohibit the use of fields for such
information, and therefore do not allow the Connection field. information, and therefore do not allow the Connection field.
skipping to change at page 49, line 48 skipping to change at page 51, line 14
recipients on the chain ("end-to-end"), enabling the message to be recipients on the chain ("end-to-end"), enabling the message to be
self-descriptive and allowing future connection-specific extensions self-descriptive and allowing future connection-specific extensions
to be deployed without fear that they will be blindly forwarded by to be deployed without fear that they will be blindly forwarded by
older intermediaries. older intermediaries.
Furthermore, intermediaries SHOULD remove or replace field(s) whose Furthermore, intermediaries SHOULD remove or replace field(s) whose
semantics are known to require removal before forwarding, whether or semantics are known to require removal before forwarding, whether or
not they appear as a Connection option, after applying those fields' not they appear as a Connection option, after applying those fields'
semantics. This includes but is not limited to: semantics. This includes but is not limited to:
o Proxy-Connection (Appendix C.1.2 of [Messaging]) o Proxy-Connection (Appendix C.2.2 of [Messaging])
o Keep-Alive (Section 19.7.1 of [RFC2068]) o Keep-Alive (Section 19.7.1 of [RFC2068])
o TE (Section 9.1.4) o TE (Section 10.1.4)
o Trailer (Section 9.1.5)
o Trailer (Section 10.1.5)
o Transfer-Encoding (Section 6.1 of [Messaging]) o Transfer-Encoding (Section 6.1 of [Messaging])
o Upgrade (Section 6.6) o Upgrade (Section 7.8)
The Connection header field's value has the following grammar: The Connection header field's value has the following grammar:
Connection = #connection-option Connection = #connection-option
connection-option = token connection-option = token
Connection options are case-insensitive. Connection options are case-insensitive.
A sender MUST NOT send a connection option corresponding to a field A sender MUST NOT send a connection option corresponding to a field
that is intended for all recipients of the payload. For example, that is intended for all recipients of the payload. For example,
skipping to change at page 50, line 33 skipping to change at page 51, line 49
the message, since a connection-specific field might not be needed if the message, since a connection-specific field might not be needed if
there are no parameters associated with a connection option. In there are no parameters associated with a connection option. In
contrast, a connection-specific field that is received without a contrast, a connection-specific field that is received without a
corresponding connection option usually indicates that the field has corresponding connection option usually indicates that the field has
been improperly forwarded by an intermediary and ought to be ignored been improperly forwarded by an intermediary and ought to be ignored
by the recipient. by the recipient.
When defining new connection options, specification authors ought to When defining new connection options, specification authors ought to
document it as reserved field name and register that definition in document it as reserved field name and register that definition in
the Hypertext Transfer Protocol (HTTP) Field Name Registry the Hypertext Transfer Protocol (HTTP) Field Name Registry
(Section 15.3.1), to avoid collisions. (Section 16.3.1), to avoid collisions.
6.4.2. Max-Forwards 7.6.2. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 8.3.8) and OPTIONS (Section 8.3.7) request methods to limit (Section 9.3.8) and OPTIONS (Section 9.3.7) request methods to limit
the number of times that the request is forwarded by proxies. This the number of times that the request is forwarded by proxies. This
can be useful when the client is attempting to trace a request that can be useful when the client is attempting to trace a request that
appears to be failing or looping mid-chain. appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded. number of times this request message can be forwarded.
Each intermediary that receives a TRACE or OPTIONS request containing Each intermediary that receives a TRACE or OPTIONS request containing
skipping to change at page 51, line 13 skipping to change at page 52, line 31
intermediary MUST NOT forward the request; instead, the intermediary intermediary MUST NOT forward the request; instead, the intermediary
MUST respond as the final recipient. If the received Max-Forwards MUST respond as the final recipient. If the received Max-Forwards
value is greater than zero, the intermediary MUST generate an updated value is greater than zero, the intermediary MUST generate an updated
Max-Forwards field in the forwarded message with a field value that Max-Forwards field in the forwarded message with a field value that
is the lesser of a) the received value decremented by one (1) or b) is the lesser of a) the received value decremented by one (1) or b)
the recipient's maximum supported value for Max-Forwards. the recipient's maximum supported value for Max-Forwards.
A recipient MAY ignore a Max-Forwards header field received with any A recipient MAY ignore a Max-Forwards header field received with any
other request methods. other request methods.
6.4.3. Via 7.6.3. Via
The "Via" header field indicates the presence of intermediate The "Via" header field indicates the presence of intermediate
protocols and recipients between the user agent and the server (on protocols and recipients between the user agent and the server (on
requests) or between the origin server and the client (on responses), requests) or between the origin server and the client (on responses),
similar to the "Received" header field in email (Section 3.6.7 of similar to the "Received" header field in email (Section 3.6.7 of
[RFC5322]). Via can be used for tracking message forwards, avoiding [RFC5322]). Via can be used for tracking message forwards, avoiding
request loops, and identifying the protocol capabilities of senders request loops, and identifying the protocol capabilities of senders
along the request/response chain. along the request/response chain.
Via = #( received-protocol RWS received-by [ RWS comment ] ) Via = #( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version received-protocol = [ protocol-name "/" ] protocol-version
; see Section 6.6 ; see Section 7.8
received-by = pseudonym [ ":" port ] received-by = pseudonym [ ":" port ]
pseudonym = token pseudonym = token
Each member of the Via field value represents a proxy or gateway that Each member of the Via field value represents a proxy or gateway that
has forwarded the message. Each intermediary appends its own has forwarded the message. Each intermediary appends its own
information about how the message was received, such that the end information about how the message was received, such that the end
result is ordered according to the sequence of forwarding recipients. result is ordered according to the sequence of forwarding recipients.
A proxy MUST send an appropriate Via header field, as described A proxy MUST send an appropriate Via header field, as described
below, in each message that it forwards. An HTTP-to-HTTP gateway below, in each message that it forwards. An HTTP-to-HTTP gateway
MUST send an appropriate Via header field in each inbound request MUST send an appropriate Via header field in each inbound request
message and MAY send a Via header field in forwarded response message and MAY send a Via header field in forwarded response
messages. messages.
For each intermediary, the received-protocol indicates the protocol For each intermediary, the received-protocol indicates the protocol
and protocol version used by the upstream sender of the message. and protocol version used by the upstream sender of the message.
Hence, the Via field value records the advertised protocol Hence, the Via field value records the advertised protocol
capabilities of the request/response chain such that they remain capabilities of the request/response chain such that they remain
visible to downstream recipients; this can be useful for determining visible to downstream recipients; this can be useful for determining
what backwards-incompatible features might be safe to use in what backwards-incompatible features might be safe to use in
response, or within a later request, as described in Section 5.1. response, or within a later request, as described in Section 2.5.
For brevity, the protocol-name is omitted when the received protocol For brevity, the protocol-name is omitted when the received protocol
is HTTP. is HTTP.
The received-by portion is normally the host and optional port number The received-by portion is normally the host and optional port number
of a recipient server or client that subsequently forwarded the of a recipient server or client that subsequently forwarded the
message. However, if the real host is considered to be sensitive message. However, if the real host is considered to be sensitive
information, a sender MAY replace it with a pseudonym. If a port is information, a sender MAY replace it with a pseudonym. If a port is
not provided, a recipient MAY interpret that as meaning it was not provided, a recipient MAY interpret that as meaning it was
received on the default TCP port, if any, for the received-protocol. received on the default TCP port, if any, for the received-protocol.
skipping to change at page 53, line 5 skipping to change at page 54, line 14
could be collapsed to could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
A sender SHOULD NOT combine multiple list members unless they are all A sender SHOULD NOT combine multiple list members unless they are all
under the same organizational control and the hosts have already been under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine members that have replaced by pseudonyms. A sender MUST NOT combine members that have
different received-protocol values. different received-protocol values.
6.5. Transformations 7.7. Message Transformations
Some intermediaries include features for transforming messages and Some intermediaries include features for transforming messages and
their payloads. A proxy might, for example, convert between image their payloads. A proxy might, for example, convert between image
formats in order to save cache space or to reduce the amount of formats in order to save cache space or to reduce the amount of
traffic on a slow link. However, operational problems might occur traffic on a slow link. However, operational problems might occur
when these transformations are applied to payloads intended for when these transformations are applied to payloads intended for
critical applications, such as medical imaging or scientific data critical applications, such as medical imaging or scientific data
analysis, particularly when integrity checks or digital signatures analysis, particularly when integrity checks or digital signatures
are used to ensure that the payload received is identical to the are used to ensure that the payload received is identical to the
original. original.
An HTTP-to-HTTP proxy is called a "transforming proxy" if it is An HTTP-to-HTTP proxy is called a "_transforming proxy_" if it is
designed or configured to modify messages in a semantically designed or configured to modify messages in a semantically
meaningful way (i.e., modifications, beyond those required by normal meaningful way (i.e., modifications, beyond those required by normal
HTTP processing, that change the message in a way that would be HTTP processing, that change the message in a way that would be
significant to the original sender or potentially significant to significant to the original sender or potentially significant to
downstream recipients). For example, a transforming proxy might be downstream recipients). For example, a transforming proxy might be
acting as a shared annotation server (modifying responses to include acting as a shared annotation server (modifying responses to include
references to a local annotation database), a malware filter, a references to a local annotation database), a malware filter, a
format transcoder, or a privacy filter. Such transformations are format transcoder, or a privacy filter. Such transformations are
presumed to be desired by whichever client (or client organization) presumed to be desired by whichever client (or client organization)
chose the proxy. chose the proxy.
If a proxy receives a target URI with a host name that is not a fully If a proxy receives a target URI with a host name that is not a fully
qualified domain name, it MAY add its own domain to the host name it qualified domain name, it MAY add its own domain to the host name it
received when forwarding the request. A proxy MUST NOT change the received when forwarding the request. A proxy MUST NOT change the
host name if the target URI contains a fully qualified domain name. host name if the target URI contains a fully qualified domain name.
A proxy MUST NOT modify the "absolute-path" and "query" parts of the A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received target URI when forwarding it to the next inbound server, received target URI when forwarding it to the next inbound server,
except as noted above to replace an empty path with "/" or "*". except as noted above to replace an empty path with "/" or "*".
A proxy MUST NOT transform the payload (Section 5.5) of a message A proxy MUST NOT transform the payload (Section 6.4) of a message
that contains a no-transform cache-control response directive that contains a no-transform cache-control response directive
(Section 5.2 of [Caching]). Note that this does not include changes (Section 5.2 of [Caching]). Note that this does not include changes
to the message body that do not affect the payload, such as transfer to the message body that do not affect the payload, such as transfer
codings (Section 7 of [Messaging]). codings (Section 7 of [Messaging]).
A proxy MAY transform the payload of a message that does not contain A proxy MAY transform the payload of a message that does not contain
a no-transform cache-control directive. A proxy that transforms the a no-transform cache-control directive. A proxy that transforms the
payload of a 200 (OK) response can inform downstream recipients that payload of a 200 (OK) response can inform downstream recipients that
a transformation has been applied by changing the response status a transformation has been applied by changing the response status
code to 203 (Non-Authoritative Information) (Section 14.3.4). code to 203 (Non-Authoritative Information) (Section 15.3.4).
A proxy SHOULD NOT modify header fields that provide information A proxy SHOULD NOT modify header fields that provide information
about the endpoints of the communication chain, the resource state, about the endpoints of the communication chain, the resource state,
or the selected representation (other than the payload) unless the or the selected representation (other than the payload) unless the
field's definition specifically allows such modification or the field's definition specifically allows such modification or the
modification is deemed necessary for privacy or security. modification is deemed necessary for privacy or security.
6.6. Upgrade 7.8. Upgrade
The "Upgrade" header field is intended to provide a simple mechanism The "Upgrade" header field is intended to provide a simple mechanism
for transitioning from HTTP/1.1 to some other protocol on the same for transitioning from HTTP/1.1 to some other protocol on the same
connection. connection.
A client MAY send a list of protocol names in the Upgrade header A client MAY send a list of protocol names in the Upgrade header
field of a request to invite the server to switch to one or more of field of a request to invite the server to switch to one or more of
the named protocols, in order of descending preference, before the named protocols, in order of descending preference, before
sending the final response. A server MAY ignore a received Upgrade sending the final response. A server MAY ignore a received Upgrade
header field if it wishes to continue using the current protocol on header field if it wishes to continue using the current protocol on
skipping to change at page 55, line 43 skipping to change at page 57, line 6
request: request:
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: upgrade Connection: upgrade
Upgrade: websocket Upgrade: websocket
[... data stream switches to websocket with an appropriate response [... data stream switches to websocket with an appropriate response
(as defined by new protocol) to the "GET /hello" request ...] (as defined by new protocol) to the "GET /hello" request ...]
When Upgrade is sent, the sender MUST also send a Connection header When Upgrade is sent, the sender MUST also send a Connection header
field (Section 6.4.1) that contains an "upgrade" connection option, field (Section 7.6.1) that contains an "upgrade" connection option,
in order to prevent Upgrade from being accidentally forwarded by in order to prevent Upgrade from being accidentally forwarded by
intermediaries that might not implement the listed protocols. A intermediaries that might not implement the listed protocols. A
server MUST ignore an Upgrade header field that is received in an server MUST ignore an Upgrade header field that is received in an
HTTP/1.0 request. HTTP/1.0 request.
A client cannot begin using an upgraded protocol on the connection A client cannot begin using an upgraded protocol on the connection
until it has completely sent the request message (i.e., the client until it has completely sent the request message (i.e., the client
can't change the protocol it is sending in the middle of a message). can't change the protocol it is sending in the middle of a message).
If a server receives both an Upgrade and an Expect header field with If a server receives both an Upgrade and an Expect header field with
the "100-continue" expectation (Section 9.1.1), the server MUST send the "100-continue" expectation (Section 10.1.1), the server MUST send
a 100 (Continue) response before sending a 101 (Switching Protocols) a 100 (Continue) response before sending a 101 (Switching Protocols)
response. response.
The Upgrade header field only applies to switching protocols on top The Upgrade header field only applies to switching protocols on top
of the existing connection; it cannot be used to switch the of the existing connection; it cannot be used to switch the
underlying connection (transport) protocol, nor to switch the underlying connection (transport) protocol, nor to switch the
existing communication to a different connection. For those existing communication to a different connection. For those
purposes, it is more appropriate to use a 3xx (Redirection) response purposes, it is more appropriate to use a 3xx (Redirection) response
(Section 14.4). (Section 15.4).
This specification only defines the protocol name "HTTP" for use by This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of Section 5.1 and future updates to this version rules of Section 2.5 and future updates to this
specification. Additional protocol names ought to be registered specification. Additional protocol names ought to be registered
using the registration procedure defined in Section 15.7. using the registration procedure defined in Section 16.7.
7. Representations 8. Representations
A "representation" is information that is intended to reflect a past, A "_representation_" is information that is intended to reflect a
current, or desired state of a given resource, in a format that can past, current, or desired state of a given resource, in a format that
be readily communicated via the protocol. A representation consists can be readily communicated via the protocol. A representation
of a set of representation metadata and a potentially unbounded consists of a set of representation metadata and a potentially
stream of representation data. unbounded stream of representation data.
HTTP allows "information hiding" behind its uniform interface by HTTP allows "information hiding" behind its uniform interface by
phrasing communication with respect to a transferable representation phrasing communication with respect to a transferable representation
of the resource state, rather than transferring the resource itself. of the resource state, rather than transferring the resource itself.
This allows the resource identified by a URI to be anything, This allows the resource identified by a URI to be anything,
including temporal functions like "the current weather in Laguna including temporal functions like "the current weather in Laguna
Beach", while potentially providing information that represents that Beach", while potentially providing information that represents that
resource at the time a message is generated [REST]. resource at the time a message is generated [REST].
The uniform interface is similar to a window through which one can The uniform interface is similar to a window through which one can
observe and act upon a thing only through the communication of observe and act upon a thing only through the communication of
messages to an independent actor on the other side. A shared messages to an independent actor on the other side. A shared
abstraction is needed to represent ("take the place of") the current abstraction is needed to represent ("take the place of") the current
or desired state of that thing in our communications. When a or desired state of that thing in our communications. When a
representation is hypertext, it can provide both a representation of representation is hypertext, it can provide both a representation of
the resource state and processing instructions that help guide the the resource state and processing instructions that help guide the
recipient's future interactions. recipient's future interactions.
7.1. Selected Representation 8.1. Selected Representations
An origin server might be provided with, or be capable of generating, An origin server might be provided with, or be capable of generating,
multiple representations that are each intended to reflect the multiple representations that are each intended to reflect the
current state of a target resource. In such cases, some algorithm is current state of a target resource. In such cases, some algorithm is
used by the origin server to select one of those representations as used by the origin server to select one of those representations as
most applicable to a given request, usually based on content most applicable to a given request, usually based on content
negotiation. This "selected representation" is used to provide the negotiation. This "_selected representation_" is used to provide the
data and metadata for evaluating conditional requests (Section 12.1) data and metadata for evaluating conditional requests (Section 13.1)
and constructing the payload for 200 (OK), 206 (Partial Content), and and constructing the payload for 200 (OK), 206 (Partial Content), and
304 (Not Modified) responses to GET (Section 8.3.1). 304 (Not Modified) responses to GET (Section 9.3.1).
7.2. Data 8.2. Representation Data
The representation data associated with an HTTP message is either The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the provided as the payload data of the message or referred to by the
message semantics and the target URI. The representation data is in message semantics and the target URI. The representation data is in
a format and encoding defined by the representation metadata header a format and encoding defined by the representation metadata header
fields. fields.
The data type of the representation data is determined via the header The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer, fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model: ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) ) representation-data := Content-Encoding( Content-Type( bits ) )
7.3. Metadata 8.3. Representation Metadata
Representation header fields provide metadata about the Representation header fields provide metadata about the
representation. When a message includes a payload body, the representation. When a message includes payload data, the
representation header fields describe how to interpret the representation header fields describe how to interpret that data. In
representation data enclosed in the payload body. In a response to a a response to a HEAD request, the representation header fields
HEAD request, the representation header fields describe the describe the representation data that would have been enclosed in the
representation data that would have been enclosed in the payload body payload if the same request had been a GET.
if the same request had been a GET.
The following header fields convey representation metadata:
------------------ ------
Field Name Ref.
------------------ ------
Content-Type 7.4
Content-Encoding 7.5
Content-Language 7.6
Content-Length 7.7
Content-Location 7.8
------------------ ------
Table 3
7.4. Content-Type 8.4. Content-Type
The "Content-Type" header field indicates the media type of the The "Content-Type" header field indicates the media type of the
associated representation: either the representation enclosed in the associated representation: either the representation enclosed in the
message payload or the selected representation, as determined by the message payload or the selected representation, as determined by the
message semantics. The indicated media type defines both the data message semantics. The indicated media type defines both the data
format and how that data is intended to be processed by a recipient, format and how that data is intended to be processed by a recipient,
within the scope of the received message semantics, after any content within the scope of the received message semantics, after any content
codings indicated by Content-Encoding are decoded. codings indicated by Content-Encoding are decoded.
Content-Type = media-type Content-Type = media-type
Media types are defined in Section 7.4.1. An example of the field is Media types are defined in Section 8.4.1. An example of the field is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
A sender that generates a message containing a payload body SHOULD A sender that generates a message containing payload data SHOULD
generate a Content-Type header field in that message unless the generate a Content-Type header field in that message unless the
intended media type of the enclosed representation is unknown to the intended media type of the enclosed representation is unknown to the
sender. If a Content-Type header field is not present, the recipient sender. If a Content-Type header field is not present, the recipient
MAY either assume a media type of "application/octet-stream" MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the data to determine its type. ([RFC2046], Section 4.5.1) or examine the data to determine its type.
In practice, resource owners do not always properly configure their In practice, resource owners do not always properly configure their
origin server to provide the correct Content-Type for a given origin server to provide the correct Content-Type for a given
representation. Some user agents examine a payload's content and, in representation. Some user agents examine a payload's content and, in
certain cases, override the received type (for example, see certain cases, override the received type (for example, see
skipping to change at page 59, line 13 skipping to change at page 60, line 5
encouraged to provide a means to disable such sniffing. encouraged to provide a means to disable such sniffing.
Furthermore, although Content-Type is defined as a singleton field, Furthermore, although Content-Type is defined as a singleton field,
it is sometimes incorrectly generated multiple times, resulting in a it is sometimes incorrectly generated multiple times, resulting in a
combined field value that appears to be a list. Recipients often combined field value that appears to be a list. Recipients often
attempt to handle this error by using the last syntactically valid attempt to handle this error by using the last syntactically valid
member of the list, but note that some implementations might have member of the list, but note that some implementations might have
different error handling behaviors, leading to interoperability and/ different error handling behaviors, leading to interoperability and/
or security issues. or security issues.
7.4.1. Media Type 8.4.1. Media Type
HTTP uses media types [RFC2046] in the Content-Type (Section 7.4) and HTTP uses media types [RFC2046] in the Content-Type (Section 8.4) and
Accept (Section 11.1.2) header fields in order to provide open and Accept (Section 12.5.1) header fields in order to provide open and
extensible data typing and type negotiation. Media types define both extensible data typing and type negotiation. Media types define both
a data format and various processing models: how to process that data a data format and various processing models: how to process that data
in accordance with each context in which it is received. in accordance with each context in which it is received.
media-type = type "/" subtype parameters media-type = type "/" subtype parameters
type = token type = token
subtype = token subtype = token
The type and subtype tokens are case-insensitive. The type and subtype tokens are case-insensitive.
The type/subtype MAY be followed by semicolon-delimited parameters The type/subtype MAY be followed by semicolon-delimited parameters
(Section 5.7.6) in the form of name=value pairs. The presence or (Section 5.6.6) in the form of name=value pairs. The presence or
absence of a parameter might be significant to the processing of a absence of a parameter might be significant to the processing of a
media type, depending on its definition within the media type media type, depending on its definition within the media type
registry. Parameter values might or might not be case-sensitive, registry. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. depending on the semantics of the parameter name.
For example, the following media types are equivalent in describing For example, the following media types are equivalent in describing
HTML text data encoded in the UTF-8 character encoding scheme, but HTML text data encoded in the UTF-8 character encoding scheme, but
the first is preferred for consistency (the "charset" parameter value the first is preferred for consistency (the "charset" parameter value
is defined as being case-insensitive in [RFC2046], Section 4.1.2): is defined as being case-insensitive in [RFC2046], Section 4.1.2):
text/html;charset=utf-8 text/html;charset=utf-8
Text/HTML;Charset="utf-8" Text/HTML;Charset="utf-8"
text/html; charset="utf-8" text/html; charset="utf-8"
text/html;charset=UTF-8 text/html;charset=UTF-8
Media types ought to be registered with IANA according to the Media types ought to be registered with IANA according to the
procedures defined in [BCP13]. procedures defined in [BCP13].
7.4.2. Charset 8.4.2. Charset
HTTP uses charset names to indicate or negotiate the character HTTP uses _charset_ names to indicate or negotiate the character
encoding scheme of a textual representation [RFC6365]. A charset is encoding scheme of a textual representation [RFC6365]. A charset is
identified by a case-insensitive token. identified by a case-insensitive token.
charset = token charset = token
Charset names ought to be registered in the IANA "Character Sets" Charset names ought to be registered in the IANA "Character Sets"
registry (<https://www.iana.org/assignments/character-sets>) registry (<https://www.iana.org/assignments/character-sets>)
according to the procedures defined in Section 2 of [RFC2978]. according to the procedures defined in Section 2 of [RFC2978].
| *Note:* In theory, charset names are defined by the "mime- | *Note:* In theory, charset names are defined by the "mime-
| charset" ABNF rule defined in Section 2.3 of [RFC2978] (as | charset" ABNF rule defined in Section 2.3 of [RFC2978] (as
| corrected in [Err1912]). That rule allows two characters that | corrected in [Err1912]). That rule allows two characters that
| are not included in "token" ("{" and "}"), but no charset name | are not included in "token" ("{" and "}"), but no charset name
| registered at the time of this writing includes braces (see | registered at the time of this writing includes braces (see
| [Err5433]). | [Err5433]).
7.4.3. Canonicalization and Text Defaults 8.4.3. Canonicalization and Text Defaults
Media types are registered with a canonical form in order to be Media types are registered with a canonical form in order to be
interoperable among systems with varying native encoding formats. interoperable among systems with varying native encoding formats.
Representations selected or transferred via HTTP ought to be in Representations selected or transferred via HTTP ought to be in
canonical form, for many of the same reasons described by the canonical form, for many of the same reasons described by the
Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the
performance characteristics of email deployments (i.e., store and performance characteristics of email deployments (i.e., store and
forward messages to peers) are significantly different from those forward messages to peers) are significantly different from those
common to HTTP and the Web (server-based information services). common to HTTP and the Web (server-based information services).
Furthermore, MIME's constraints for the sake of compatibility with Furthermore, MIME's constraints for the sake of compatibility with
skipping to change at page 60, line 42 skipping to change at page 61, line 36
MIME's canonical form requires that media subtypes of the "text" type MIME's canonical form requires that media subtypes of the "text" type
use CRLF as the text line break. HTTP allows the transfer of text use CRLF as the text line break. HTTP allows the transfer of text
media with plain CR or LF alone representing a line break, when such media with plain CR or LF alone representing a line break, when such
line breaks are consistent for an entire representation. An HTTP line breaks are consistent for an entire representation. An HTTP
sender MAY generate, and a recipient MUST be able to parse, line sender MAY generate, and a recipient MUST be able to parse, line
breaks in text media that consist of CRLF, bare CR, or bare LF. In breaks in text media that consist of CRLF, bare CR, or bare LF. In
addition, text media in HTTP is not limited to charsets that use addition, text media in HTTP is not limited to charsets that use
octets 13 and 10 for CR and LF, respectively. This flexibility octets 13 and 10 for CR and LF, respectively. This flexibility
regarding line breaks applies only to text within a representation regarding line breaks applies only to text within a representation
that has been assigned a "text" media type; it does not apply to that has been assigned a "text" media type; it does not apply to
"multipart" types or HTTP elements outside the payload body (e.g., "multipart" types or HTTP elements outside the payload data (e.g.,
header fields). header fields).
If a representation is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data ought to be in a form defined above prior to being encoded. data ought to be in a form defined above prior to being encoded.
7.4.4. Multipart Types 8.4.4. Multipart Types
MIME provides for a number of "multipart" types - encapsulations of MIME provides for a number of "multipart" types - encapsulations of
one or more representations within a single message body. All one or more representations within a single message body. All
multipart types share a common syntax, as defined in Section 5.1.1 of multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and include a boundary parameter as part of the media type [RFC2046], and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body parts. generate only CRLF to represent line breaks between body parts.
HTTP message framing does not use the multipart boundary as an HTTP message framing does not use the multipart boundary as an
indicator of message body length, though it might be used by indicator of message body length, though it might be used by
implementations that generate or process the payload. For example, implementations that generate or process the payload. For example,
the "multipart/form-data" type is often used for carrying form data the "multipart/form-data" type is often used for carrying form data
in a request, as described in [RFC7578], and the "multipart/ in a request, as described in [RFC7578], and the "multipart/
byteranges" type is defined by this specification for use in some 206 byteranges" type is defined by this specification for use in some 206
(Partial Content) responses (see Section 14.3.7). (Partial Content) responses (see Section 15.3.7).
7.5. Content-Encoding 8.5. Content-Encoding
The "Content-Encoding" header field indicates what content codings The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the have been applied to the representation, beyond those inherent in the
media type, and thus what decoding mechanisms have to be applied in media type, and thus what decoding mechanisms have to be applied in
order to obtain data in the media type referenced by the Content-Type order to obtain data in the media type referenced by the Content-Type
header field. Content-Encoding is primarily used to allow a header field. Content-Encoding is primarily used to allow a
representation's data to be compressed without losing the identity of representation's data to be compressed without losing the identity of
its underlying media type. its underlying media type.
Content-Encoding = #content-coding Content-Encoding = #content-coding
skipping to change at page 62, line 29 skipping to change at page 63, line 14
choose to publish the same data as multiple representations that choose to publish the same data as multiple representations that
differ only in whether the coding is defined as part of Content-Type differ only in whether the coding is defined as part of Content-Type
or Content-Encoding, since some user agents will behave differently or Content-Encoding, since some user agents will behave differently
in their handling of each response (e.g., open a "Save as ..." dialog in their handling of each response (e.g., open a "Save as ..." dialog
instead of automatic decompression and rendering of content). instead of automatic decompression and rendering of content).
An origin server MAY respond with a status code of 415 (Unsupported An origin server MAY respond with a status code of 415 (Unsupported
Media Type) if a representation in the request message has a content Media Type) if a representation in the request message has a content
coding that is not acceptable. coding that is not acceptable.
7.5.1. Content Codings 8.5.1. Content Codings
Content coding values indicate an encoding transformation that has Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently, underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and the representation is stored in coded form, transmitted directly, and
only decoded by the final recipient. only decoded by the final recipient.
content-coding = token content-coding = token
All content codings are case-insensitive and ought to be registered All content codings are case-insensitive and ought to be registered
within the "HTTP Content Coding Registry", as described in within the "HTTP Content Coding Registry", as described in
Section 15.6 Section 16.6
Content-coding values are used in the Accept-Encoding Content-coding values are used in the Accept-Encoding
(Section 11.1.4) and Content-Encoding (Section 7.5) header fields. (Section 12.5.3) and Content-Encoding (Section 8.5) header fields.
The following content-coding values are defined by this
specification:
------------ ------------------------------------------- ---------
Name Description Ref.
------------ ------------------------------------------- ---------
compress UNIX "compress" data format [Welch] 7.5.1.1
deflate "deflate" compressed data ([RFC1951]) 7.5.1.2
inside the "zlib" data format ([RFC1950])
gzip GZIP file format [RFC1952] 7.5.1.3
identity Reserved 11.1.4
x-compress Deprecated (alias for compress) 7.5.1.1
x-gzip Deprecated (alias for gzip) 7.5.1.3
------------ ------------------------------------------- ---------
Table 4
7.5.1.1. Compress Coding 8.5.1.1. Compress Coding
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
[Welch] that is commonly produced by the UNIX file compression [Welch] that is commonly produced by the UNIX file compression
program "compress". A recipient SHOULD consider "x-compress" to be program "compress". A recipient SHOULD consider "x-compress" to be
equivalent to "compress". equivalent to "compress".
7.5.1.2. Deflate Coding 8.5.1.2. Deflate Coding
The "deflate" coding is a "zlib" data format [RFC1950] containing a The "deflate" coding is a "zlib" data format [RFC1950] containing a
"deflate" compressed data stream [RFC1951] that uses a combination of "deflate" compressed data stream [RFC1951] that uses a combination of
the Lempel-Ziv (LZ77) compression algorithm and Huffman coding. the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
| *Note:* Some non-conformant implementations send the "deflate" | *Note:* Some non-conformant implementations send the "deflate"
| compressed data without the zlib wrapper. | compressed data without the zlib wrapper.
7.5.1.3. Gzip Coding 8.5.1.3. Gzip Coding
The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy
Check (CRC) that is commonly produced by the gzip file compression Check (CRC) that is commonly produced by the gzip file compression
program [RFC1952]. A recipient SHOULD consider "x-gzip" to be program [RFC1952]. A recipient SHOULD consider "x-gzip" to be
equivalent to "gzip". equivalent to "gzip".
7.6. Content-Language 8.6. Content-Language
The "Content-Language" header field describes the natural language(s) The "Content-Language" header field describes the natural language(s)
of the intended audience for the representation. Note that this of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the might not be equivalent to all the languages used within the
representation. representation.
Content-Language = #language-tag Content-Language = #language-tag
Language tags are defined in Section 7.6.1. The primary purpose of Language tags are defined in Section 8.6.1. The primary purpose of
Content-Language is to allow a user to identify and differentiate Content-Language is to allow a user to identify and differentiate
representations according to the users' own preferred language. representations according to the users' own preferred language.
Thus, if the content is intended only for a Danish-literate audience, Thus, if the content is intended only for a Danish-literate audience,
the appropriate field is the appropriate field is
Content-Language: da Content-Language: da
If no Content-Language is specified, the default is that the content If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language, sender does not consider it to be specific to any natural language,
skipping to change at page 64, line 35 skipping to change at page 65, line 5
However, just because multiple languages are present within a However, just because multiple languages are present within a
representation does not mean that it is intended for multiple representation does not mean that it is intended for multiple
linguistic audiences. An example would be a beginner's language linguistic audiences. An example would be a beginner's language
primer, such as "A First Lesson in Latin", which is clearly intended primer, such as "A First Lesson in Latin", which is clearly intended
to be used by an English-literate audience. In this case, the to be used by an English-literate audience. In this case, the
Content-Language would properly only include "en". Content-Language would properly only include "en".
Content-Language MAY be applied to any media type - it is not limited Content-Language MAY be applied to any media type - it is not limited
to textual documents. to textual documents.
7.6.1. Language Tags 8.6.1. Language Tags
A language tag, as defined in [RFC5646], identifies a natural A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer communication of information to other human beings. Computer
languages are explicitly excluded. languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and HTTP uses language tags within the Accept-Language and
Content-Language header fields. Accept-Language uses the broader Content-Language header fields. Accept-Language uses the broader
language-range production defined in Section 11.1.5, whereas language-range production defined in Section 12.5.4, whereas
Content-Language uses the language-tag production defined below. Content-Language uses the language-tag production defined below.
language-tag = <Language-Tag, see [RFC5646], Section 2.1> language-tag = <Language-Tag, see [RFC5646], Section 2.1>
A language tag is a sequence of one or more case-insensitive subtags, A language tag is a sequence of one or more case-insensitive subtags,
each separated by a hyphen character ("-", %x2D). In most cases, a each separated by a hyphen character ("-", %x2D). In most cases, a
language tag consists of a primary language subtag that identifies a language tag consists of a primary language subtag that identifies a
broad family of related languages (e.g., "en" = English), which is broad family of related languages (e.g., "en" = English), which is
optionally followed by a series of subtags that refine or narrow that optionally followed by a series of subtags that refine or narrow that
language's range (e.g., "en-CA" = the variety of English as language's range (e.g., "en-CA" = the variety of English as
communicated in Canada). Whitespace is not allowed within a language communicated in Canada). Whitespace is not allowed within a language
tag. Example tags include: tag. Example tags include:
fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information. See [RFC5646] for further information.
7.7. Content-Length 8.7. Content-Length
The "Content-Length" header field indicates the associated The "Content-Length" header field indicates the associated
representation's data length as a decimal non-negative integer number representation's data length as a decimal non-negative integer number
of octets. When transferring a representation in a message, Content- of octets. When transferring a representation as a payload, Content-
Length refers specifically to the amount of data enclosed so that it Length refers specifically to the amount of data enclosed so that it
can be used to delimit framing of the message body (e.g., Section 6.2 can be used to delimit framing (e.g., Section 6.2 of [Messaging]).
of [Messaging]). In other cases, Content-Length indicates the In other cases, Content-Length indicates the selected
selected representation's current length, which can be used by representation's current length, which can be used by recipients to
recipients to estimate transfer time or compare to previously stored estimate transfer time or compare to previously stored
representations. representations.
Content-Length = 1*DIGIT Content-Length = 1*DIGIT
An example is An example is
Content-Length: 3495 Content-Length: 3495
A sender MUST NOT send a Content-Length header field in any message A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field. that contains a Transfer-Encoding header field.
A user agent SHOULD send a Content-Length in a request message when A user agent SHOULD send a Content-Length in a request message when
no Transfer-Encoding is sent and the request method defines a meaning no Transfer-Encoding is sent and the request method defines a meaning
for an enclosed payload body. For example, a Content-Length header for an enclosed payload. For example, a Content-Length header field
field is normally sent in a POST request even when the value is 0 is normally sent in a POST request even when the value is 0
(indicating an empty payload body). A user agent SHOULD NOT send a (indicating an empty payload data). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain Content-Length header field when the request message does not contain
a payload body and the method semantics do not anticipate such a a payload data and the method semantics do not anticipate such data.
body.
A server MAY send a Content-Length header field in a response to a A server MAY send a Content-Length header field in a response to a
HEAD request (Section 8.3.2); a server MUST NOT send Content-Length HEAD request (Section 9.3.2); a server MUST NOT send Content-Length
in such a response unless its field value equals the decimal number in such a response unless its field value equals the decimal number
of octets that would have been sent in the payload body of a response of octets that would have been sent in the payload of a response if
if the same request had used the GET method. the same request had used the GET method.
A server MAY send a Content-Length header field in a 304 (Not A server MAY send a Content-Length header field in a 304 (Not
Modified) response to a conditional GET request (Section 14.4.5); a Modified) response to a conditional GET request (Section 15.4.5); a
server MUST NOT send Content-Length in such a response unless its server MUST NOT send Content-Length in such a response unless its
field value equals the decimal number of octets that would have been field value equals the decimal number of octets that would have been
sent in the payload body of a 200 (OK) response to the same request. sent in the payload data of a 200 (OK) response to the same request.
A server MUST NOT send a Content-Length header field in any response A server MUST NOT send a Content-Length header field in any response
with a status code of 1xx (Informational) or 204 (No Content). A with a status code of 1xx (Informational) or 204 (No Content). A
server MUST NOT send a Content-Length header field in any 2xx server MUST NOT send a Content-Length header field in any 2xx
(Successful) response to a CONNECT request (Section 8.3.6). (Successful) response to a CONNECT request (Section 9.3.6).
Aside from the cases defined above, in the absence of Transfer- Aside from the cases defined above, in the absence of Transfer-
Encoding, an origin server SHOULD send a Content-Length header field Encoding, an origin server SHOULD send a Content-Length header field
when the payload body size is known prior to sending the complete when the payload data size is known prior to sending the complete
header section. This will allow downstream recipients to measure header section. This will allow downstream recipients to measure
transfer progress, know when a received message is complete, and transfer progress, know when a received message is complete, and
potentially reuse the connection for additional requests. potentially reuse the connection for additional requests.
Any Content-Length field value greater than or equal to zero is Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of a valid. Since there is no predefined limit to the length of a
payload, a recipient MUST anticipate potentially large decimal payload, a recipient MUST anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion numerals and prevent parsing errors due to integer conversion
overflows (Section 16.5). overflows (Section 17.5).
If a message is received that has a Content-Length header field value If a message is received that has a Content-Length header field value
consisting of the same decimal value as a comma-separated list consisting of the same decimal value as a comma-separated list
(Section 5.7.1) - for example, "Content-Length: 42, 42" - indicating (Section 5.6.1) - for example, "Content-Length: 42, 42" - indicating
that duplicate Content-Length header fields have been generated or that duplicate Content-Length header fields have been generated or
combined by an upstream message processor, then the recipient MUST combined by an upstream message processor, then the recipient MUST
either reject the message as invalid or replace the duplicated field either reject the message as invalid or replace the duplicated field
values with a single valid Content-Length field containing that values with a single valid Content-Length field containing that
decimal value prior to determining the message body length or decimal value.
forwarding the message.
7.8. Content-Location 8.8. Content-Location
The "Content-Location" header field references a URI that can be used The "Content-Location" header field references a URI that can be used
as an identifier for a specific resource corresponding to the as an identifier for a specific resource corresponding to the
representation in this message's payload. In other words, if one representation in this message's payload. In other words, if one
were to perform a GET request on this URI at the time of this were to perform a GET request on this URI at the time of this
message's generation, then a 200 (OK) response would contain the same message's generation, then a 200 (OK) response would contain the same
representation that is enclosed as payload in this message. representation that is enclosed as payload in this message.
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
The field value is either an absolute-URI or a partial-URI. In the The field value is either an absolute-URI or a partial-URI. In the
latter case (Section 4), the referenced URI is relative to the target latter case (Section 4), the referenced URI is relative to the target
URI ([RFC3986], Section 5). URI ([RFC3986], Section 5).
The Content-Location value is not a replacement for the target URI The Content-Location value is not a replacement for the target URI
(Section 6.1). It is representation metadata. It has the same (Section 7.1). It is representation metadata. It has the same
syntax and semantics as the header field of the same name defined for syntax and semantics as the header field of the same name defined for
MIME body parts in Section 4 of [RFC2557]. However, its appearance MIME body parts in Section 4 of [RFC2557]. However, its appearance
in an HTTP message has some special implications for HTTP recipients. in an HTTP message has some special implications for HTTP recipients.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its value refers (after conversion to absolute form) to a message and its value refers (after conversion to absolute form) to a
URI that is the same as the target URI, then the recipient MAY URI that is the same as the target URI, then the recipient MAY
consider the payload to be a current representation of that resource consider the payload to be a current representation of that resource
at the time indicated by the message origination date. For a GET at the time indicated by the message origination date. For a GET
(Section 8.3.1) or HEAD (Section 8.3.2) request, this is the same as (Section 9.3.1) or HEAD (Section 9.3.2) request, this is the same as
the default semantics when no Content-Location is provided by the the default semantics when no Content-Location is provided by the
server. For a state-changing request like PUT (Section 8.3.4) or server. For a state-changing request like PUT (Section 9.3.4) or
POST (Section 8.3.3), it implies that the server's response contains POST (Section 9.3.3), it implies that the server's response contains
the new representation of that resource, thereby distinguishing it the new representation of that resource, thereby distinguishing it
from representations that might only report about the action (e.g., from representations that might only report about the action (e.g.,
"It worked!"). This allows authoring applications to update their "It worked!"). This allows authoring applications to update their
local copies without the need for a subsequent GET request. local copies without the need for a subsequent GET request.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its field value refers to a URI that differs from the message and its field value refers to a URI that differs from the
target URI, then the origin server claims that the URI is an target URI, then the origin server claims that the URI is an
identifier for a different resource corresponding to the enclosed identifier for a different resource corresponding to the enclosed
representation. Such a claim can only be trusted if both identifiers representation. Such a claim can only be trusted if both identifiers
skipping to change at page 68, line 29 skipping to change at page 68, line 43
For example, if a client makes a PUT request on a negotiated resource For example, if a client makes a PUT request on a negotiated resource
and the origin server accepts that PUT (without redirection), then and the origin server accepts that PUT (without redirection), then
the new state of that resource is expected to be consistent with the the new state of that resource is expected to be consistent with the
one representation supplied in that PUT; the Content-Location cannot one representation supplied in that PUT; the Content-Location cannot
be used as a form of reverse content selection identifier to update be used as a form of reverse content selection identifier to update
only one of the negotiated representations. If the user agent had only one of the negotiated representations. If the user agent had
wanted the latter semantics, it would have applied the PUT directly wanted the latter semantics, it would have applied the PUT directly
to the Content-Location URI. to the Content-Location URI.
7.9. Validators 8.9. Validator Fields
Validator header fields convey metadata about the selected Validator fields convey metadata about the selected representation
representation (Section 7). In responses to safe requests, validator (Section 8). In responses to safe requests, validator fields
fields describe the selected representation chosen by the origin describe the selected representation chosen by the origin server
server while handling the response. Note that, depending on the while handling the response. Note that, depending on the status code
status code semantics, the selected representation for a given semantics, the selected representation for a given response is not
response is not necessarily the same as the representation enclosed necessarily the same as the representation enclosed as response
as response payload. payload.
In a successful response to a state-changing request, validator In a successful response to a state-changing request, validator
fields describe the new representation that has replaced the prior fields describe the new representation that has replaced the prior
selected representation as a result of processing the request. selected representation as a result of processing the request.
For example, an ETag field in a 201 (Created) response communicates For example, an ETag field in a 201 (Created) response communicates
the entity-tag of the newly created resource's representation, so the entity-tag of the newly created resource's representation, so
that it can be used in later conditional requests to prevent the that it can be used in later conditional requests to prevent the
"lost update" problem Section 12.1. "lost update" problem Section 13.1.
--------------- -------
Field Name Ref.
--------------- -------
ETag 7.9.3
Last-Modified 7.9.2
--------------- -------
Table 5
This specification defines two forms of metadata that are commonly This specification defines two forms of metadata that are commonly
used to observe resource state and test for preconditions: used to observe resource state and test for preconditions:
modification dates (Section 7.9.2) and opaque entity tags modification dates (Section 8.9.2) and opaque entity tags
(Section 7.9.3). Additional metadata that reflects resource state (Section 8.9.3). Additional metadata that reflects resource state
has been defined by various extensions of HTTP, such as Web has been defined by various extensions of HTTP, such as Web
Distributed Authoring and Versioning (WebDAV, [RFC4918]), that are Distributed Authoring and Versioning (WebDAV, [RFC4918]), that are
beyond the scope of this specification. A resource metadata value is beyond the scope of this specification. A resource metadata value is
referred to as a "validator" when it is used within a precondition. referred to as a "_validator_" when it is used within a precondition.
7.9.1. Weak versus Strong 8.9.1. Weak versus Strong
Validators come in two flavors: strong or weak. Weak validators are Validators come in two flavors: strong or weak. Weak validators are
easy to generate but are far less useful for comparisons. Strong easy to generate but are far less useful for comparisons. Strong
validators are ideal for comparisons but can be very difficult (and validators are ideal for comparisons but can be very difficult (and
occasionally impossible) to generate efficiently. Rather than impose occasionally impossible) to generate efficiently. Rather than impose
that all forms of resource adhere to the same strength of validator, that all forms of resource adhere to the same strength of validator,
HTTP exposes the type of validator in use and imposes restrictions on HTTP exposes the type of validator in use and imposes restrictions on
when weak validators can be used as preconditions. when weak validators can be used as preconditions.
A "strong validator" is representation metadata that changes value A "_strong validator_" is representation metadata that changes value
whenever a change occurs to the representation data that would be whenever a change occurs to the representation data that would be
observable in the payload body of a 200 (OK) response to GET. observable in the payload data of a 200 (OK) response to GET.
A strong validator might change for reasons other than a change to A strong validator might change for reasons other than a change to
the representation data, such as when a semantically significant part the representation data, such as when a semantically significant part
of the representation metadata is changed (e.g., Content-Type), but of the representation metadata is changed (e.g., Content-Type), but
it is in the best interests of the origin server to only change the it is in the best interests of the origin server to only change the
value when it is necessary to invalidate the stored responses held by value when it is necessary to invalidate the stored responses held by
remote caches and authoring tools. remote caches and authoring tools.
Cache entries might persist for arbitrarily long periods, regardless Cache entries might persist for arbitrarily long periods, regardless
of expiration times. Thus, a cache might attempt to validate an of expiration times. Thus, a cache might attempt to validate an
skipping to change at page 70, line 19 skipping to change at page 70, line 19
accessible to GET. A collision-resistant hash function applied to accessible to GET. A collision-resistant hash function applied to
the representation data is also sufficient if the data is available the representation data is also sufficient if the data is available
prior to the response header fields being sent and the digest does prior to the response header fields being sent and the digest does
not need to be recalculated every time a validation request is not need to be recalculated every time a validation request is
received. However, if a resource has distinct representations that received. However, if a resource has distinct representations that
differ only in their metadata, such as might occur with content differ only in their metadata, such as might occur with content
negotiation over media types that happen to share the same data negotiation over media types that happen to share the same data
format, then the origin server needs to incorporate additional format, then the origin server needs to incorporate additional
information in the validator to distinguish those representations. information in the validator to distinguish those representations.
In contrast, a "weak validator" is representation metadata that might In contrast, a "_weak validator_" is representation metadata that
not change for every change to the representation data. This might not change for every change to the representation data. This
weakness might be due to limitations in how the value is calculated, weakness might be due to limitations in how the value is calculated,
such as clock resolution, an inability to ensure uniqueness for all such as clock resolution, an inability to ensure uniqueness for all
possible representations of the resource, or a desire of the resource possible representations of the resource, or a desire of the resource
owner to group representations by some self-determined set of owner to group representations by some self-determined set of
equivalency rather than unique sequences of data. An origin server equivalency rather than unique sequences of data. An origin server
SHOULD change a weak entity-tag whenever it considers prior SHOULD change a weak entity-tag whenever it considers prior
representations to be unacceptable as a substitute for the current representations to be unacceptable as a substitute for the current
representation. In other words, a weak entity-tag ought to change representation. In other words, a weak entity-tag ought to change
whenever the origin server wants caches to invalidate old responses. whenever the origin server wants caches to invalidate old responses.
skipping to change at page 71, line 12 skipping to change at page 71, line 12
they differ only in the representation metadata, such as when two they differ only in the representation metadata, such as when two
different media types are available for the same representation data. different media types are available for the same representation data.
Strong validators are usable for all conditional requests, including Strong validators are usable for all conditional requests, including
cache validation, partial content ranges, and "lost update" cache validation, partial content ranges, and "lost update"
avoidance. Weak validators are only usable when the client does not avoidance. Weak validators are only usable when the client does not
require exact equality with previously obtained representation data, require exact equality with previously obtained representation data,
such as when validating a cache entry or limiting a web traversal to such as when validating a cache entry or limiting a web traversal to
recent changes. recent changes.
7.9.2. Last-Modified 8.9.2. Last-Modified
The "Last-Modified" header field in a response provides a timestamp The "Last-Modified" header field in a response provides a timestamp
indicating the date and time at which the origin server believes the indicating the date and time at which the origin server believes the
selected representation was last modified, as determined at the selected representation was last modified, as determined at the
conclusion of handling the request. conclusion of handling the request.
Last-Modified = HTTP-date Last-Modified = HTTP-date
An example of its use is An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
7.9.2.1. Generation 8.9.2.1. Generation
An origin server SHOULD send Last-Modified for any selected An origin server SHOULD send Last-Modified for any selected
representation for which a last modification date can be reasonably representation for which a last modification date can be reasonably
and consistently determined, since its use in conditional requests and consistently determined, since its use in conditional requests
and evaluating cache freshness ([Caching]) results in a substantial and evaluating cache freshness ([Caching]) results in a substantial
reduction of HTTP traffic on the Internet and can be a significant reduction of HTTP traffic on the Internet and can be a significant
factor in improving service scalability and reliability. factor in improving service scalability and reliability.
A representation is typically the sum of many parts behind the A representation is typically the sum of many parts behind the
resource interface. The last-modified time would usually be the most resource interface. The last-modified time would usually be the most
skipping to change at page 72, line 13 skipping to change at page 72, line 13
the last modification time is derived from implementation-specific the last modification time is derived from implementation-specific
metadata that evaluates to some time in the future, according to the metadata that evaluates to some time in the future, according to the
origin server's clock, then the origin server MUST replace that value origin server's clock, then the origin server MUST replace that value
with the message origination date. This prevents a future with the message origination date. This prevents a future
modification date from having an adverse impact on cache validation. modification date from having an adverse impact on cache validation.
An origin server without a clock MUST NOT assign Last-Modified values An origin server without a clock MUST NOT assign Last-Modified values
to a response unless these values were associated with the resource to a response unless these values were associated with the resource
by some other system or user with a reliable clock. by some other system or user with a reliable clock.
7.9.2.2. Comparison 8.9.2.2. Comparison
A Last-Modified time, when used as a validator in a request, is A Last-Modified time, when used as a validator in a request, is
implicitly weak unless it is possible to deduce that it is strong, implicitly weak unless it is possible to deduce that it is strong,
using the following rules: using the following rules:
o The validator is being compared by an origin server to the actual o The validator is being compared by an origin server to the actual
current validator for the representation and, current validator for the representation and,
o That origin server reliably knows that the associated o That origin server reliably knows that the associated
representation did not change twice during the second covered by representation did not change twice during the second covered by
the presented validator. the presented validator;
or or
o The validator is about to be used by a client in an o The validator is about to be used by a client in an
If-Modified-Since, If-Unmodified-Since, or If-Range header field, If-Modified-Since, If-Unmodified-Since, or If-Range header field,
because the client has a cache entry for the associated because the client has a cache entry for the associated
representation, and representation, and
o That cache entry includes a Date value, which gives the time when o That cache entry includes a Date value which is at least one
the origin server sent the original response, and second after the Last-Modified value and the client has reason to
believe that they were generated by the same clock or that there
o The presented Last-Modified time is at least 60 seconds before the is enough difference between the Last-Modified and Date values to
Date value. make clock synchronization issues unlikely;
or or
o The validator is being compared by an intermediate cache to the o The validator is being compared by an intermediate cache to the
validator stored in its cache entry for the representation, and validator stored in its cache entry for the representation, and
o That cache entry includes a Date value, which gives the time when o That cache entry includes a Date value which is at least one
the origin server sent the original response, and second after the Last-Modified value and the cache has reason to
believe that they were generated by the same clock or that there
o The presented Last-Modified time is at least 60 seconds before the is enough difference between the Last-Modified and Date values to
Date value. make clock synchronization issues unlikely.
This method relies on the fact that if two different responses were This method relies on the fact that if two different responses were
sent by the origin server during the same second, but both had the sent by the origin server during the same second, but both had the
same Last-Modified time, then at least one of those responses would same Last-Modified time, then at least one of those responses would
have a Date value equal to its Last-Modified time. The arbitrary have a Date value equal to its Last-Modified time.
60-second limit guards against the possibility that the Date and
Last-Modified values are generated from different clocks or at
somewhat different times during the preparation of the response. An
implementation MAY use a value larger than 60 seconds, if it is
believed that 60 seconds is too short.
7.9.3. ETag 8.9.3. ETag
The "ETag" field in a response provides the current entity-tag for The "ETag" field in a response provides the current entity-tag for
the selected representation, as determined at the conclusion of the selected representation, as determined at the conclusion of
handling the request. An entity-tag is an opaque validator for handling the request. An entity-tag is an opaque validator for
differentiating between multiple representations of the same differentiating between multiple representations of the same
resource, regardless of whether those multiple representations are resource, regardless of whether those multiple representations are
due to resource state changes over time, content negotiation due to resource state changes over time, content negotiation
resulting in multiple representations being valid at the same time, resulting in multiple representations being valid at the same time,
or both. An entity-tag consists of an opaque quoted string, possibly or both. An entity-tag consists of an opaque quoted string, possibly
prefixed by a weakness indicator. prefixed by a weakness indicator.
skipping to change at page 74, line 8 skipping to change at page 73, line 50
Examples: Examples:
ETag: "xyzzy" ETag: "xyzzy"
ETag: W/"xyzzy" ETag: W/"xyzzy"
ETag: "" ETag: ""
An entity-tag can be either a weak or strong validator, with strong An entity-tag can be either a weak or strong validator, with strong
being the default. If an origin server provides an entity-tag for a being the default. If an origin server provides an entity-tag for a
representation and the generation of that entity-tag does not satisfy representation and the generation of that entity-tag does not satisfy
all of the characteristics of a strong validator (Section 7.9.1), all of the characteristics of a strong validator (Section 8.9.1),
then the origin server MUST mark the entity-tag as weak by prefixing then the origin server MUST mark the entity-tag as weak by prefixing
its opaque value with "W/" (case-sensitive). its opaque value with "W/" (case-sensitive).
A sender MAY send the Etag field in a trailer section (see A sender MAY send the Etag field in a trailer section (see
Section 5.6). However, since trailers are often ignored, it is Section 6.5). However, since trailers are often ignored, it is
preferable to send Etag as a header field unless the entity-tag is preferable to send Etag as a header field unless the entity-tag is
generated while sending the message body. generated while sending the payload data.
7.9.3.1. Generation 8.9.3.1. Generation
The principle behind entity-tags is that only the service author The principle behind entity-tags is that only the service author
knows the implementation of a resource well enough to select the most knows the implementation of a resource well enough to select the most
accurate and efficient validation mechanism for that resource, and accurate and efficient validation mechanism for that resource, and
that any such mechanism can be mapped to a simple sequence of octets that any such mechanism can be mapped to a simple sequence of octets
for easy comparison. Since the value is opaque, there is no need for for easy comparison. Since the value is opaque, there is no need for
the client to be aware of how each entity-tag is constructed. the client to be aware of how each entity-tag is constructed.
For example, a resource that has implementation-specific versioning For example, a resource that has implementation-specific versioning
applied to all changes might use an internal revision number, perhaps applied to all changes might use an internal revision number, perhaps
skipping to change at page 74, line 41 skipping to change at page 74, line 34
representation content, a combination of various file attributes, or representation content, a combination of various file attributes, or
a modification timestamp that has sub-second resolution. a modification timestamp that has sub-second resolution.
An origin server SHOULD send an ETag for any selected representation An origin server SHOULD send an ETag for any selected representation
for which detection of changes can be reasonably and consistently for which detection of changes can be reasonably and consistently
determined, since the entity-tag's use in conditional requests and determined, since the entity-tag's use in conditional requests and
evaluating cache freshness ([Caching]) can result in a substantial evaluating cache freshness ([Caching]) can result in a substantial
reduction of HTTP network traffic and can be a significant factor in reduction of HTTP network traffic and can be a significant factor in
improving service scalability and reliability. improving service scalability and reliability.
7.9.3.2. Comparison 8.9.3.2. Comparison
There are two entity-tag comparison functions, depending on whether There are two entity-tag comparison functions, depending on whether
or not the comparison context allows the use of weak validators: or not the comparison context allows the use of weak validators:
o Strong comparison: two entity-tags are equivalent if both are not _Strong comparison_: two entity-tags are equivalent if both are not
weak and their opaque-tags match character-by-character. weak and their opaque-tags match character-by-character.
o Weak comparison: two entity-tags are equivalent if their opaque- _Weak comparison_: two entity-tags are equivalent if their opaque-
tags match character-by-character, regardless of either or both tags match character-by-character, regardless of either or both
being tagged as "weak". being tagged as "weak".
The example below shows the results for a set of entity-tag pairs and The example below shows the results for a set of entity-tag pairs and
both the weak and strong comparison function results: both the weak and strong comparison function results:
-------- -------- ------------------- ----------------- -------- -------- ------------------- -----------------
ETag 1 ETag 2 Strong Comparison Weak Comparison ETag 1 ETag 2 Strong Comparison Weak Comparison
-------- -------- ------------------- ----------------- -------- -------- ------------------- -----------------
W/"1" W/"1" no match match W/"1" W/"1" no match match
W/"1" W/"2" no match no match W/"1" W/"2" no match no match
W/"1" "1" no match match W/"1" "1" no match match
"1" "1" match match "1" "1" match match
-------- -------- ------------------- ----------------- -------- -------- ------------------- -----------------
Table 6 Table 3
7.9.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources 8.9.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources
Consider a resource that is subject to content negotiation Consider a resource that is subject to content negotiation
(Section 11), and where the representations sent in response to a GET (Section 12), and where the representations sent in response to a GET
request vary based on the Accept-Encoding request header field request vary based on the Accept-Encoding request header field
(Section 11.1.4): (Section 12.5.3):
>> Request: >> Request:
GET /index HTTP/1.1 GET /index HTTP/1.1
Host: www.example.com Host: www.example.com
Accept-Encoding: gzip Accept-Encoding: gzip
In this case, the response might or might not use the gzip content In this case, the response might or might not use the gzip content
coding. If it does not, the response might look like: coding. If it does not, the response might look like:
skipping to change at page 76, line 25 skipping to change at page 76, line 23
...binary data... ...binary data...
| *Note:* Content codings are a property of the representation | *Note:* Content codings are a property of the representation
| data, so a strong entity-tag for a content-encoded | data, so a strong entity-tag for a content-encoded
| representation has to be distinct from the entity tag of an | representation has to be distinct from the entity tag of an
| unencoded representation to prevent potential conflicts during | unencoded representation to prevent potential conflicts during
| cache updates and range requests. In contrast, transfer | cache updates and range requests. In contrast, transfer
| codings (Section 7 of [Messaging]) apply only during message | codings (Section 7 of [Messaging]) apply only during message
| transfer and do not result in distinct entity-tags. | transfer and do not result in distinct entity-tags.
7.9.4. When to Use Entity-Tags and Last-Modified Dates 8.9.4. When to Use Entity-Tags and Last-Modified Dates
In 200 (OK) responses to GET or HEAD, an origin server: In 200 (OK) responses to GET or HEAD, an origin server:
o SHOULD send an entity-tag validator unless it is not feasible to o SHOULD send an entity-tag validator unless it is not feasible to
generate one. generate one.
o MAY send a weak entity-tag instead of a strong entity-tag, if o MAY send a weak entity-tag instead of a strong entity-tag, if
performance considerations support the use of weak entity-tags, or performance considerations support the use of weak entity-tags, or
if it is unfeasible to send a strong entity-tag. if it is unfeasible to send a strong entity-tag.
skipping to change at page 77, line 15 skipping to change at page 77, line 15
o MAY send the Last-Modified value in subrange cache validation o MAY send the Last-Modified value in subrange cache validation
requests (using If-Unmodified-Since) if only a Last-Modified value requests (using If-Unmodified-Since) if only a Last-Modified value
has been provided by an HTTP/1.0 origin server. The user agent has been provided by an HTTP/1.0 origin server. The user agent
SHOULD provide a way to disable this, in case of difficulty. SHOULD provide a way to disable this, in case of difficulty.
o SHOULD send both validators in cache validation requests if both o SHOULD send both validators in cache validation requests if both
an entity-tag and a Last-Modified value have been provided by the an entity-tag and a Last-Modified value have been provided by the
origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to
respond appropriately. respond appropriately.
8. Methods 9. Methods
8.1. Overview 9.1. Overview
The request method token is the primary source of request semantics; The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. and what is expected by the client as a successful result.
The request method's semantics might be further specialized by the The request method's semantics might be further specialized by the
semantics of some header fields when present in a request if those semantics of some header fields when present in a request if those
additional semantics do not conflict with the method. For example, a additional semantics do not conflict with the method. For example, a
client can send conditional request header fields (Section 12.1) to client can send conditional request header fields (Section 13.1) to
make the requested action conditional on the current state of the make the requested action conditional on the current state of the
target resource. target resource.
method = token
HTTP was originally designed to be usable as an interface to HTTP was originally designed to be usable as an interface to
distributed object systems. The request method was envisioned as distributed object systems. The request method was envisioned as
applying semantics to a target resource in much the same way as applying semantics to a target resource in much the same way as
invoking a defined method on an identified object would apply invoking a defined method on an identified object would apply
semantics. semantics.
method = token
The method token is case-sensitive because it might be used as a The method token is case-sensitive because it might be used as a
gateway to object-based systems with case-sensitive method names. By gateway to object-based systems with case-sensitive method names. By
convention, standardized methods are defined in all-uppercase US- convention, standardized methods are defined in all-uppercase US-
ASCII letters. ASCII letters.
Unlike distributed objects, the standardized request methods in HTTP Unlike distributed objects, the standardized request methods in HTTP
are not resource-specific, since uniform interfaces provide for are not resource-specific, since uniform interfaces provide for
better visibility and reuse in network-based systems [REST]. Once better visibility and reuse in network-based systems [REST]. Once
defined, a standardized method ought to have the same semantics when defined, a standardized method ought to have the same semantics when
applied to any resource, though each resource determines for itself applied to any resource, though each resource determines for itself
whether those semantics are implemented or allowed. whether those semantics are implemented or allowed.
This specification defines a number of standardized methods that are This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. commonly used in HTTP, as outlined by the following table.
--------- -------------------------------------------- ------- --------- -------------------------------------------- -------
Method Description Ref. Method Description Ref.
--------- -------------------------------------------- ------- --------- -------------------------------------------- -------
GET Transfer a current representation of the 8.3.1 GET Transfer a current representation of the 9.3.1
target resource. target resource.
HEAD Same as GET, but do not transfer the 8.3.2 HEAD Same as GET, but do not transfer the 9.3.2
response body. response payload.
POST Perform resource-specific processing on 8.3.3 POST Perform resource-specific processing on 9.3.3
the request payload. the request payload.
PUT Replace all current representations of the 8.3.4 PUT Replace all current representations of the 9.3.4
target resource with the request payload. target resource with the request payload.
DELETE Remove all current representations of the 8.3.5 DELETE Remove all current representations of the 9.3.5
target resource. target resource.
CONNECT Establish a tunnel to the server 8.3.6 CONNECT Establish a tunnel to the server 9.3.6
identified by the target resource. identified by the target resource.
OPTIONS Describe the communication options for the 8.3.7 OPTIONS Describe the communication options for the 9.3.7
target resource. target resource.
TRACE Perform a message loop-back test along the 8.3.8 TRACE Perform a message loop-back test along the 9.3.8
path to the target resource. path to the target resource.
--------- -------------------------------------------- ------- --------- -------------------------------------------- -------
Table 7 Table 4
All general-purpose servers MUST support the methods GET and HEAD. All general-purpose servers MUST support the methods GET and HEAD.
All other methods are OPTIONAL. All other methods are OPTIONAL.
The set of methods allowed by a target resource can be listed in an The set of methods allowed by a target resource can be listed in an
Allow header field (Section 9.2.1). However, the set of allowed Allow header field (Section 10.2.1). However, the set of allowed
methods can change dynamically. When a request method is received methods can change dynamically. When a request method is received
that is unrecognized or not implemented by an origin server, the that is unrecognized or not implemented by an origin server, the
origin server SHOULD respond with the 501 (Not Implemented) status origin server SHOULD respond with the 501 (Not Implemented) status
code. When a request method is received that is known by an origin code. When a request method is received that is known by an origin
server but not allowed for the target resource, the origin server server but not allowed for the target resource, the origin server
SHOULD respond with the 405 (Method Not Allowed) status code. SHOULD respond with the 405 (Method Not Allowed) status code.
Additional methods, outside the scope of this specification, have Additional methods, outside the scope of this specification, have
been specified for use in HTTP. All such methods ought to be been specified for use in HTTP. All such methods ought to be
registered within the "Hypertext Transfer Protocol (HTTP) Method registered within the "Hypertext Transfer Protocol (HTTP) Method
Registry", as described in Section 15.1. Registry", as described in Section 16.1.
8.2. Common Method Properties 9.2. Common Method Properties
8.2.1. Safe Methods 9.2.1. Safe Methods
Request methods are considered "safe" if their defined semantics are Request methods are considered "_safe_" if their defined semantics
essentially read-only; i.e., the client does not request, and does are essentially read-only; i.e., the client does not request, and
not expect, any state change on the origin server as a result of does not expect, any state change on the origin server as a result of
applying a safe method to a target resource. Likewise, reasonable applying a safe method to a target resource. Likewise, reasonable
use of a safe method is not expected to cause any harm, loss of use of a safe method is not expected to cause any harm, loss of
property, or unusual burden on the origin server. property, or unusual burden on the origin server.
This definition of safe methods does not prevent an implementation This definition of safe methods does not prevent an implementation
from including behavior that is potentially harmful, that is not from including behavior that is potentially harmful, that is not
entirely read-only, or that causes side effects while invoking a safe entirely read-only, or that causes side effects while invoking a safe
method. What is important, however, is that the client did not method. What is important, however, is that the client did not
request that additional behavior and cannot be held accountable for request that additional behavior and cannot be held accountable for
it. For example, most servers append request information to access it. For example, most servers append request information to access
skipping to change at page 80, line 5 skipping to change at page 80, line 5
the request method semantics. For example, it is common for Web- the request method semantics. For example, it is common for Web-
based content editing software to use actions within query based content editing software to use actions within query
parameters, such as "page?do=delete". If the purpose of such a parameters, such as "page?do=delete". If the purpose of such a
resource is to perform an unsafe action, then the resource owner MUST resource is to perform an unsafe action, then the resource owner MUST
disable or disallow that action when it is accessed using a safe disable or disallow that action when it is accessed using a safe
request method. Failure to do so will result in unfortunate side request method. Failure to do so will result in unfortunate side
effects when automated processes perform a GET on every URI reference effects when automated processes perform a GET on every URI reference
for the sake of link maintenance, pre-fetching, building a search for the sake of link maintenance, pre-fetching, building a search
index, etc. index, etc.
8.2.2. Idempotent Methods 9.2.2. Idempotent Methods
A request method is considered "idempotent" if the intended effect on A request method is considered "_idempotent_" if the intended effect
the server of multiple identical requests with that method is the on the server of multiple identical requests with that method is the
same as the effect for a single such request. Of the request methods same as the effect for a single such request. Of the request methods
defined by this specification, PUT, DELETE, and safe request methods defined by this specification, PUT, DELETE, and safe request methods
are idempotent. are idempotent.
Like the definition of safe, the idempotent property only applies to Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each what has been requested by the user; a server is free to log each
request separately, retain a revision control history, or implement request separately, retain a revision control history, or implement
other non-idempotent side effects for each idempotent request. other non-idempotent side effects for each idempotent request.
Idempotent methods are distinguished because the request can be Idempotent methods are distinguished because the request can be
skipping to change at page 81, line 5 skipping to change at page 81, line 5
retrying the requests that failed. retrying the requests that failed.
Some clients use weaker signals to initiate automatic retries. For Some clients use weaker signals to initiate automatic retries. For
example, when a POST request is sent, but the underlying transport example, when a POST request is sent, but the underlying transport
connection is closed before any part of the response is received. connection is closed before any part of the response is received.
Although this is commonly implemented, it is not recommended. Although this is commonly implemented, it is not recommended.
A proxy MUST NOT automatically retry non-idempotent requests. A A proxy MUST NOT automatically retry non-idempotent requests. A
client SHOULD NOT automatically retry a failed automatic retry. client SHOULD NOT automatically retry a failed automatic retry.
8.2.3. Methods and Caching 9.2.3. Methods and Caching
For a cache to store and use a response, the associated method needs For a cache to store and use a response, the associated method needs
to explicitly allow caching, and detail under what conditions a to explicitly allow caching, and detail under what conditions a
response can be used to satisfy subsequent requests; a method response can be used to satisfy subsequent requests; a method
definition which does not do so cannot be cached. For additional definition which does not do so cannot be cached. For additional
requirements see [Caching]. requirements see [Caching].
This specification defines caching semantics for GET, HEAD, and POST, This specification defines caching semantics for GET, HEAD, and POST,
although the overwhelming majority of cache implementations only although the overwhelming majority of cache implementations only
support GET and HEAD. support GET and HEAD.
8.3. Method Definitions 9.3. Method Definitions
8.3.1. GET 9.3.1. GET
The GET method requests transfer of a current selected representation The GET method requests transfer of a current selected representation
for the target resource. for the target resource.
GET is the primary mechanism of information retrieval and the focus GET is the primary mechanism of information retrieval and the focus
of almost all performance optimizations. Hence, when people speak of of almost all performance optimizations. Hence, when people speak of
retrieving some identifiable information via HTTP, they are generally retrieving some identifiable information via HTTP, they are generally
referring to making a GET request. A successful response reflects referring to making a GET request. A successful response reflects
the quality of "sameness" identified by the target URI. In turn, the quality of "sameness" identified by the target URI. In turn,
constructing applications such that they produce a URI for each constructing applications such that they produce a URI for each
important resource results in more resources being available for important resource results in more resources being available for
other applications, producing a network effect that promotes further other applications, producing a network effect that promotes further
expansion of the Web. expansion of the Web.
It is tempting to think of resource identifiers as remote file system It is tempting to think of resource identifiers as remote file system
pathnames and of representations as being a copy of the contents of pathnames and of representations as being a copy of the contents of
such files. In fact, that is how many resources are implemented (see such files. In fact, that is how many resources are implemented (see
Section 16.3 for related security considerations). However, there Section 17.3 for related security considerations). However, there
are no such limitations in practice. are no such limitations in practice.
The HTTP interface for a resource is just as likely to be implemented The HTTP interface for a resource is just as likely to be implemented
as a tree of content objects, a programmatic view on various database as a tree of content objects, a programmatic view on various database
records, or a gateway to other information systems. Even when the records, or a gateway to other information systems. Even when the
URI mapping mechanism is tied to a file system, an origin server URI mapping mechanism is tied to a file system, an origin server
might be configured to execute the files with the request as input might be configured to execute the files with the request as input
and send the output as the representation rather than transfer the and send the output as the representation rather than transfer the
files directly. Regardless, only the origin server needs to know how files directly. Regardless, only the origin server needs to know how
each of its resource identifiers corresponds to an implementation and each of its resource identifiers corresponds to an implementation and
how each implementation manages to select and send a current how each implementation manages to select and send a current
representation of the target resource in a response to GET. representation of the target resource in a response to GET.
A client can alter the semantics of GET to be a "range request", A client can alter the semantics of GET to be a "range request",
requesting transfer of only some part(s) of the selected requesting transfer of only some part(s) of the selected
representation, by sending a Range header field in the request representation, by sending a Range header field in the request
(Section 13.2). (Section 14.2).
A client SHOULD NOT generate a body in a GET request. A payload A client SHOULD NOT generate payload data in a GET request. A
received in a GET request has no defined semantics, cannot alter the payload received in a GET request has no defined semantics, cannot
meaning or target of the request, and might lead some implementations alter the meaning or target of the request, and might lead some
to reject the request and close the connection because of its implementations to reject the request and close the connection
potential as a request smuggling attack (Section 11.2 of because of its potential as a request smuggling attack (Section 11.2
[Messaging]). of [Messaging]).
The response to a GET request is cacheable; a cache MAY use it to The response to a GET request is cacheable; a cache MAY use it to
satisfy subsequent GET and HEAD requests unless otherwise indicated satisfy subsequent GET and HEAD requests unless otherwise indicated
by the Cache-Control header field (Section 5.2 of [Caching]). A by the Cache-Control header field (Section 5.2 of [Caching]). A
cache that receives a payload in a GET request is likely to ignore cache that receives a payload in a GET request is likely to ignore
that payload and cache regardless of the payload contents. that payload and cache regardless of the payload contents.
When information retrieval is performed with a mechanism that When information retrieval is performed with a mechanism that
constructs a target URI from user-provided information, such as the constructs a target URI from user-provided information, such as the
query fields of a form using GET, potentially sensitive data might be query fields of a form using GET, potentially sensitive data might be
provided that would not be appropriate for disclosure within a URI provided that would not be appropriate for disclosure within a URI
(see Section 16.9). In some cases, the data can be filtered or (see Section 17.9). In some cases, the data can be filtered or
transformed such that it would not reveal such information. In transformed such that it would not reveal such information. In
others, particularly when there is no benefit from caching a others, particularly when there is no benefit from caching a
response, using the POST method (Section 8.3.3) instead of GET will response, using the POST method (Section 9.3.3) instead of GET can
usually transmit such information in the request body rather than transmit such information in the request payload rather than within
construct a new URI. the target URI.
8.3.2. HEAD 9.3.2. HEAD
The HEAD method is identical to GET except that the server MUST NOT The HEAD method is identical to GET except that the server MUST NOT
send a message body in the response (i.e., the response terminates at send payload data in the response and the response always terminates
the end of the header section). The server SHOULD send the same at the end of the header section. HEAD is used to obtain metadata
header fields in response to a HEAD request as it would have sent if about the selected representation without transferring its
the request had been a GET, except that the payload header fields representation data, often for the sake of testing hypertext links or
(Section 5.5) MAY be omitted. This method can be used for obtaining finding recent modifications.
metadata about the selected representation without transferring the
representation data and is often used for testing hypertext links for The server SHOULD send the same header fields in response to a HEAD
validity, accessibility, and recent modification. request as it would have sent if the request method had been GET.
However, a server MAY omit header fields for which a value is
determined only while generating the payload data. For example, some
servers buffer a dynamic response to GET until a minimum amount of
data is generated so that they can more efficiently delimit small
responses or make late decisions with regard to content selection.
Such a response to GET might contain Content-Length and Vary fields,
for example, that are not generated within a HEAD response. These
minor inconsistencies are considered preferable to generating and
discarding the payload data for a HEAD request, since HEAD is usually
requested for the sake of efficiency.
A payload within a HEAD request message has no defined semantics; A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing sending payload data in a HEAD request might cause some existing
implementations to reject the request. implementations to reject the request.
The response to a HEAD request is cacheable; a cache MAY use it to The response to a HEAD request is cacheable; a cache MAY use it to
satisfy subsequent HEAD requests unless otherwise indicated by the satisfy subsequent HEAD requests unless otherwise indicated by the
Cache-Control header field (Section 5.2 of [Caching]). A HEAD Cache-Control header field (Section 5.2 of [Caching]). A HEAD
response might also have an effect on previously cached responses to response might also affect previously cached responses to GET; see
GET; see Section 4.3.5 of [Caching]. Section 4.3.5 of [Caching].
8.3.3. POST 9.3.3. POST
The POST method requests that the target resource process the The POST method requests that the target resource process the
representation enclosed in the request according to the resource's representation enclosed in the request according to the resource's
own specific semantics. For example, POST is used for the following own specific semantics. For example, POST is used for the following
functions (among others): functions (among others):
o Providing a block of data, such as the fields entered into an HTML o Providing a block of data, such as the fields entered into an HTML
form, to a data-handling process; form, to a data-handling process;
o Posting a message to a bulletin board, newsgroup, mailing list, o Posting a message to a bulletin board, newsgroup, mailing list,
skipping to change at page 83, line 40 skipping to change at page 84, line 9
appropriate status code depending on the result of processing the appropriate status code depending on the result of processing the
POST request; almost all of the status codes defined by this POST request; almost all of the status codes defined by this
specification could be received in a response to POST (the exceptions specification could be received in a response to POST (the exceptions
being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not
Satisfiable)). Satisfiable)).
If one or more resources has been created on the origin server as a If one or more resources has been created on the origin server as a
result of successfully processing a POST request, the origin server result of successfully processing a POST request, the origin server
SHOULD send a 201 (Created) response containing a Location header SHOULD send a 201 (Created) response containing a Location header
field that provides an identifier for the primary resource created field that provides an identifier for the primary resource created
(Section 9.2.3) and a representation that describes the status of the (Section 10.2.3) and a representation that describes the status of
request while referring to the new resource(s). the request while referring to the new resource(s).
Responses to POST requests are only cacheable when they include Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.2.1 of [Caching]) and a explicit freshness information (see Section 4.2.1 of [Caching]) and a
Content-Location header field that has the same value as the POST's Content-Location header field that has the same value as the POST's
target URI (Section 7.8). A cached POST response can be reused to target URI (Section 8.8). A cached POST response can be reused to
satisfy a later GET or HEAD request, but not a POST request, since satisfy a later GET or HEAD request, but not a POST request, since
POST is required to be written through to the origin server, because POST is required to be written through to the origin server, because
it is unsafe; see Section 4 of [Caching]. it is unsafe; see Section 4 of [Caching].
If the result of processing a POST would be equivalent to a If the result of processing a POST would be equivalent to a
representation of an existing resource, an origin server MAY redirect representation of an existing resource, an origin server MAY redirect
the user agent to that resource by sending a 303 (See Other) response the user agent to that resource by sending a 303 (See Other) response
with the existing resource's identifier in the Location field. This with the existing resource's identifier in the Location field. This
has the benefits of providing the user agent a resource identifier has the benefits of providing the user agent a resource identifier
and transferring the representation via a method more amenable to and transferring the representation via a method more amenable to
shared caching, though at the cost of an extra request if the user shared caching, though at the cost of an extra request if the user
agent does not already have the representation cached. agent does not already have the representation cached.
8.3.4. PUT 9.3.4. PUT
The PUT method requests that the state of the target resource be The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given enclosed in the request message payload. A successful PUT of a given
representation would suggest that a subsequent GET on that same representation would suggest that a subsequent GET on that same
target resource will result in an equivalent representation being target resource will result in an equivalent representation being
sent in a 200 (OK) response. However, there is no guarantee that sent in a 200 (OK) response. However, there is no guarantee that
such a state change will be observable, since the target resource such a state change will be observable, since the target resource
might be acted upon by other user agents in parallel, or might be might be acted upon by other user agents in parallel, or might be
subject to dynamic processing by the origin server, before any subject to dynamic processing by the origin server, before any
skipping to change at page 84, line 38 skipping to change at page 85, line 5
If the target resource does not have a current representation and the If the target resource does not have a current representation and the
PUT successfully creates one, then the origin server MUST inform the PUT successfully creates one, then the origin server MUST inform the
user agent by sending a 201 (Created) response. If the target user agent by sending a 201 (Created) response. If the target
resource does have a current representation and that representation resource does have a current representation and that representation
is successfully modified in accordance with the state of the enclosed is successfully modified in accordance with the state of the enclosed
representation, then the origin server MUST send either a 200 (OK) or representation, then the origin server MUST send either a 200 (OK) or
a 204 (No Content) response to indicate successful completion of the a 204 (No Content) response to indicate successful completion of the
request. request.
An origin server SHOULD ignore unrecognized header and trailer fields
received in a PUT request (i.e., do not save them as part of the
resource state).
An origin server SHOULD verify that the PUT representation is An origin server SHOULD verify that the PUT representation is
consistent with any constraints the server has for the target consistent with any constraints the server has for the target
resource that cannot or will not be changed by the PUT. This is resource that cannot or will not be changed by the PUT. This is
particularly important when the origin server uses internal particularly important when the origin server uses internal
configuration information related to the URI in order to set the configuration information related to the URI in order to set the
values for representation metadata on GET responses. When a PUT values for representation metadata on GET responses. When a PUT
representation is inconsistent with the target resource, the origin representation is inconsistent with the target resource, the origin
server SHOULD either make them consistent, by transforming the server SHOULD either make them consistent, by transforming the
representation or changing the resource configuration, or respond representation or changing the resource configuration, or respond
with an appropriate error message containing sufficient information with an appropriate error message containing sufficient information
skipping to change at page 85, line 44 skipping to change at page 85, line 44
origin server beyond what can be expressed by the intent of the user origin server beyond what can be expressed by the intent of the user
agent request and the semantics of the origin server response. It agent request and the semantics of the origin server response. It
does not define what a resource might be, in any sense of that word, does not define what a resource might be, in any sense of that word,
beyond the interface provided via HTTP. It does not define how beyond the interface provided via HTTP. It does not define how
resource state is "stored", nor how such storage might change as a resource state is "stored", nor how such storage might change as a
result of a change in resource state, nor how the origin server result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking, translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are all implementation details behind the resource interface are
intentionally hidden by the server. intentionally hidden by the server.
An origin server MUST NOT send a validator header field This extends to how header and trailer fields are stored; while
(Section 7.9), such as an ETag or Last-Modified field, in a common header fields like Content-Type will typically be stored and
successful response to PUT unless the request's representation data returned upon subsequent GET requests, header and trailer field
was saved without any transformation applied to the body (i.e., the handling is specific to the resource that received the request. As a
resource's new representation data is identical to the representation result, an origin server SHOULD ignore unrecognized header and
data received in the PUT request) and the validator field value trailer fields received in a PUT request (i.e., do not save them as
reflects the new representation. This requirement allows a user part of the resource state).
agent to know when the representation body it has in memory remains
current as a result of the PUT, thus not in need of being retrieved An origin server MUST NOT send a validator field (Section 8.9), such
again from the origin server, and that the new validator(s) received as an ETag or Last-Modified field, in a successful response to PUT
in the response can be used for future conditional requests in order unless the request's representation data was saved without any
to prevent accidental overwrites (Section 12.1). transformation applied to the payload data (i.e., the resource's new
representation data is identical to the payload data received in the
PUT request) and the validator field value reflects the new
representation. This requirement allows a user agent to know when
the representation it has in memory remains current as a result of
the PUT, thus not in need of being retrieved again from the origin
server, and that the new validator(s) received in the response can be
used for future conditional requests in order to prevent accidental
overwrites (Section 13.1).
The fundamental difference between the POST and PUT methods is The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the enclosed representation. highlighted by the different intent for the enclosed representation.
The target resource in a POST request is intended to handle the The target resource in a POST request is intended to handle the
enclosed representation according to the resource's own semantics, enclosed representation according to the resource's own semantics,
whereas the enclosed representation in a PUT request is defined as whereas the enclosed representation in a PUT request is defined as
replacing the state of the target resource. Hence, the intent of PUT replacing the state of the target resource. Hence, the intent of PUT
is idempotent and visible to intermediaries, even though the exact is idempotent and visible to intermediaries, even though the exact
effect is only known by the origin server. effect is only known by the origin server.
skipping to change at page 86, line 40 skipping to change at page 86, line 50
identifying "the current version" (a resource) that is separate from identifying "the current version" (a resource) that is separate from
the URIs identifying each particular version (different resources the URIs identifying each particular version (different resources
that at one point shared the same state as the current version that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be the state of the target resource, and might also cause links to be
added between the related resources. added between the related resources.
An origin server that allows PUT on a given target resource MUST send An origin server that allows PUT on a given target resource MUST send
a 400 (Bad Request) response to a PUT request that contains a a 400 (Bad Request) response to a PUT request that contains a
Content-Range header field (Section 13.4), since the payload is Content-Range header field (Section 14.4), since the payload is
likely to be partial content that has been mistakenly PUT as a full likely to be partial content that has been mistakenly PUT as a full
representation. Partial content updates are possible by targeting a representation. Partial content updates are possible by targeting a
separately identified resource with state that overlaps a portion of separately identified resource with state that overlaps a portion of
the larger resource, or by using a different method that has been the larger resource, or by using a different method that has been
specifically defined for partial updates (for example, the PATCH specifically defined for partial updates (for example, the PATCH
method defined in [RFC5789]). method defined in [RFC5789]).
Responses to the PUT method are not cacheable. If a successful PUT Responses to the PUT method are not cacheable. If a successful PUT
request passes through a cache that has one or more stored responses request passes through a cache that has one or more stored responses
for the target URI, those stored responses will be invalidated (see for the target URI, those stored responses will be invalidated (see
Section 4.4 of [Caching]). Section 4.4 of [Caching]).
8.3.5. DELETE 9.3.5. DELETE
The DELETE method requests that the origin server remove the The DELETE method requests that the origin server remove the
association between the target resource and its current association between the target resource and its current
functionality. In effect, this method is similar to the rm command functionality. In effect, this method is similar to the "rm" command
in UNIX: it expresses a deletion operation on the URI mapping of the in UNIX: it expresses a deletion operation on the URI mapping of the
origin server rather than an expectation that the previously origin server rather than an expectation that the previously
associated information be deleted. associated information be deleted.
If the target resource has one or more current representations, they If the target resource has one or more current representations, they
might or might not be destroyed by the origin server, and the might or might not be destroyed by the origin server, and the
associated storage might or might not be reclaimed, depending associated storage might or might not be reclaimed, depending
entirely on the nature of the resource and its implementation by the entirely on the nature of the resource and its implementation by the
origin server (which are beyond the scope of this specification). origin server (which are beyond the scope of this specification).
Likewise, other implementation aspects of a resource might need to be Likewise, other implementation aspects of a resource might need to be
skipping to change at page 87, line 48 skipping to change at page 88, line 11
o a 202 (Accepted) status code if the action will likely succeed but o a 202 (Accepted) status code if the action will likely succeed but
has not yet been enacted, has not yet been enacted,
o a 204 (No Content) status code if the action has been enacted and o a 204 (No Content) status code if the action has been enacted and
no further information is to be supplied, or no further information is to be supplied, or
o a 200 (OK) status code if the action has been enacted and the o a 200 (OK) status code if the action has been enacted and the
response message includes a representation describing the status. response message includes a representation describing the status.
A client SHOULD NOT generate a body in a DELETE request. A payload A client SHOULD NOT generate a payload in a DELETE request. A
received in a DELETE request has no defined semantics, cannot alter payload received in a DELETE request has no defined semantics, cannot
the meaning or target of the request, and might lead some alter the meaning or target of the request, and might lead some
implementations to reject the request. implementations to reject the request.
Responses to the DELETE method are not cacheable. If a successful Responses to the DELETE method are not cacheable. If a successful
DELETE request passes through a cache that has one or more stored DELETE request passes through a cache that has one or more stored
responses for the target URI, those stored responses will be responses for the target URI, those stored responses will be
invalidated (see Section 4.4 of [Caching]). invalidated (see Section 4.4 of [Caching]).
8.3.6. CONNECT 9.3.6. CONNECT
The CONNECT method requests that the recipient establish a tunnel to The CONNECT method requests that the recipient establish a tunnel to
the destination origin server identified by the request target and, the destination origin server identified by the request target and,
if successful, thereafter restrict its behavior to blind forwarding if successful, thereafter restrict its behavior to blind forwarding
of data, in both directions, until the tunnel is closed. Tunnels are of data, in both directions, until the tunnel is closed. Tunnels are
commonly used to create an end-to-end virtual connection, through one commonly used to create an end-to-end virtual connection, through one
or more proxies, which can then be secured using TLS (Transport Layer or more proxies, which can then be secured using TLS (Transport Layer
Security, [RFC8446]). Security, [RFC8446]).
Because CONNECT changes the request/response nature of an HTTP Because CONNECT changes the request/response nature of an HTTP
skipping to change at page 89, line 33 skipping to change at page 89, line 39
proxy into relaying spam email. Proxies that support CONNECT SHOULD proxy into relaying spam email. Proxies that support CONNECT SHOULD
restrict its use to a limited set of known ports or a configurable restrict its use to a limited set of known ports or a configurable
whitelist of safe request targets. whitelist of safe request targets.
A server MUST NOT send any Transfer-Encoding or Content-Length header A server MUST NOT send any Transfer-Encoding or Content-Length header
fields in a 2xx (Successful) response to CONNECT. A client MUST fields in a 2xx (Successful) response to CONNECT. A client MUST
ignore any Content-Length or Transfer-Encoding header fields received ignore any Content-Length or Transfer-Encoding header fields received
in a successful response to CONNECT. in a successful response to CONNECT.
A payload within a CONNECT request message has no defined semantics; A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing sending payload data in a CONNECT request might cause some existing
implementations to reject the request. implementations to reject the request.
Responses to the CONNECT method are not cacheable. Responses to the CONNECT method are not cacheable.
8.3.7. OPTIONS 9.3.7. OPTIONS
The OPTIONS method requests information about the communication The OPTIONS method requests information about the communication
options available for the target resource, at either the origin options available for the target resource, at either the origin
server or an intervening intermediary. This method allows a client server or an intervening intermediary. This method allows a client
to determine the options and/or requirements associated with a to determine the options and/or requirements associated with a
resource, or the capabilities of a server, without implying a resource, or the capabilities of a server, without implying a
resource action. resource action.
An OPTIONS request with an asterisk ("*") as the request target An OPTIONS request with an asterisk ("*") as the request target
(Section 6.1) applies to the server in general rather than to a (Section 7.1) applies to the server in general rather than to a
specific resource. Since a server's communication options typically specific resource. Since a server's communication options typically
depend on the resource, the "*" request is only useful as a "ping" or depend on the resource, the "*" request is only useful as a "ping" or
"no-op" type of method; it does nothing beyond allowing the client to "no-op" type of method; it does nothing beyond allowing the client to
test the capabilities of the server. For example, this can be used test the capabilities of the server. For example, this can be used
to test a proxy for HTTP/1.1 conformance (or lack thereof). to test a proxy for HTTP/1.1 conformance (or lack thereof).
If the request target is not an asterisk, the OPTIONS request applies If the request target is not an asterisk, the OPTIONS request applies
to the options that are available when communicating with the target to the options that are available when communicating with the target
resource. resource.
skipping to change at page 90, line 28 skipping to change at page 90, line 37
header that might indicate optional features implemented by the header that might indicate optional features implemented by the
server and applicable to the target resource (e.g., Allow), including server and applicable to the target resource (e.g., Allow), including
potential extensions not defined by this specification. The response potential extensions not defined by this specification. The response
payload, if any, might also describe the communication options in a payload, if any, might also describe the communication options in a
machine or human-readable representation. A standard format for such machine or human-readable representation. A standard format for such
a representation is not defined by this specification, but might be a representation is not defined by this specification, but might be
defined by future extensions to HTTP. defined by future extensions to HTTP.
A client MAY send a Max-Forwards header field in an OPTIONS request A client MAY send a Max-Forwards header field in an OPTIONS request
to target a specific recipient in the request chain (see to target a specific recipient in the request chain (see
Section 6.4.2). A proxy MUST NOT generate a Max-Forwards header Section 7.6.2). A proxy MUST NOT generate a Max-Forwards header
field while forwarding a request unless that request was received field while forwarding a request unless that request was received
with a Max-Forwards field. with a Max-Forwards field.
A client that generates an OPTIONS request containing a payload body A client that generates an OPTIONS request containing payload data
MUST send a valid Content-Type header field describing the MUST send a valid Content-Type header field describing the
representation media type. Note that this specification does not representation media type. Note that this specification does not
define any use for such a payload. define any use for such a payload.
Responses to the OPTIONS method are not cacheable. Responses to the OPTIONS method are not cacheable.
8.3.8. TRACE 9.3.8. TRACE
The TRACE method requests a remote, application-level loop-back of The TRACE method requests a remote, application-level loop-back of
the request message. The final recipient of the request SHOULD the request message. The final recipient of the request SHOULD
reflect the message received, excluding some fields described below, reflect the message received, excluding some fields described below,
back to the client as the message body of a 200 (OK) response with a back to the client as the payload data of a 200 (OK) response with a
Content-Type of "message/http" (Section 10.1 of [Messaging]). The Content-Type of "message/http" (Section 10.1 of [Messaging]). The
final recipient is either the origin server or the first server to final recipient is either the origin server or the first server to
receive a Max-Forwards value of zero (0) in the request receive a Max-Forwards value of zero (0) in the request
(Section 6.4.2). (Section 7.6.2).
A client MUST NOT generate fields in a TRACE request containing A client MUST NOT generate fields in a TRACE request containing
sensitive data that might be disclosed by the response. For example, sensitive data that might be disclosed by the response. For example,
it would be foolish for a user agent to send stored user credentials it would be foolish for a user agent to send stored user credentials
Section 10 or cookies [RFC6265] in a TRACE request. The final (Section 11) or cookies [RFC6265] in a TRACE request. The final
recipient of the request SHOULD exclude any request fields that are recipient of the request SHOULD exclude any request fields that are
likely to contain sensitive data when that recipient generates the likely to contain sensitive data when that recipient generates the
response body. response payload.
TRACE allows the client to see what is being received at the other TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 6.4.3) is of information. The value of the Via header field (Section 7.6.3) is of
particular interest, since it acts as a trace of the request chain. particular interest, since it acts as a trace of the request chain.
Use of the Max-Forwards header field allows the client to limit the Use of the Max-Forwards header field allows the client to limit the
length of the request chain, which is useful for testing a chain of length of the request chain, which is useful for testing a chain of
proxies forwarding messages in an infinite loop. proxies forwarding messages in an infinite loop.
A client MUST NOT send a message body in a TRACE request. A client MUST NOT send payload data in a TRACE request.
Responses to the TRACE method are not cacheable. Responses to the TRACE method are not cacheable.
9. Context 10. Message Context
9.1. Request Context
A client sends request header fields to provide more information 10.1. Request Context Fields
about the request context, make the request conditional based on the
target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation.
The following request header fields provide additional information The request header fields below provide additional information about
about the request context, including information about the user, user the request context, including information about the user, user
agent, and resource behind the request. agent, and resource behind the request.
------------ ------- 10.1.1. Expect
Field Name Ref.
------------ -------
Expect 9.1.1
From 9.1.2
Referer 9.1.3
TE 9.1.4
Trailer 9.1.5
User-Agent 9.1.6
------------ -------
Table 8
9.1.1. Expect
The "Expect" header field in a request indicates a certain set of The "Expect" header field in a request indicates a certain set of
behaviors (expectations) that need to be supported by the server in behaviors (expectations) that need to be supported by the server in
order to properly handle this request. order to properly handle this request.
Expect = #expectation Expect = #expectation
expectation = token [ "=" ( token / quoted-string ) parameters ] expectation = token [ "=" ( token / quoted-string ) parameters ]
The Expect field value is case-insensitive. The Expect field value is case-insensitive.
The only expectation defined by this specification is "100-continue" The only expectation defined by this specification is "100-continue"
(with no defined parameters). (with no defined parameters).
A server that receives an Expect field value containing a member A server that receives an Expect field value containing a member
other than 100-continue MAY respond with a 417 (Expectation Failed) other than 100-continue MAY respond with a 417 (Expectation Failed)
status code to indicate that the unexpected expectation cannot be status code to indicate that the unexpected expectation cannot be
met. met.
A 100-continue expectation informs recipients that the client is A _100-continue_ expectation informs recipients that the client is
about to send a (presumably large) message body in this request and about to send a (presumably large) payload in this request and wishes
wishes to receive a 100 (Continue) interim response if the method, to receive a 100 (Continue) interim response if the method, target
target URI, and header fields are not sufficient to cause an URI, and header fields are not sufficient to cause an immediate
immediate success, redirect, or error response. This allows the success, redirect, or error response. This allows the client to wait
client to wait for an indication that it is worthwhile to send the for an indication that it is worthwhile to send the payload data
message body before actually doing so, which can improve efficiency before actually doing so, which can improve efficiency when the data
when the message body is huge or when the client anticipates that an is huge or when the client anticipates that an error is likely (e.g.,
error is likely (e.g., when sending a state-changing method, for the when sending a state-changing method, for the first time, without
first time, without previously verified authentication credentials). previously verified authentication credentials).
For example, a request that begins with For example, a request that begins with
PUT /somewhere/fun HTTP/1.1 PUT /somewhere/fun HTTP/1.1
Host: origin.example.com Host: origin.example.com
Content-Type: video/h264 Content-Type: video/h264
Content-Length: 1234567890987 Content-Length: 1234567890987
Expect: 100-continue Expect: 100-continue
allows the origin server to immediately respond with an error allows the origin server to immediately respond with an error
message, such as 401 (Unauthorized) or 405 (Method Not Allowed), message, such as 401 (Unauthorized) or 405 (Method Not Allowed),
before the client starts filling the pipes with an unnecessary data before the client starts filling the pipes with an unnecessary data
transfer. transfer.
Requirements for clients: Requirements for clients:
o A client MUST NOT generate a 100-continue expectation in a request o A client MUST NOT generate a 100-continue expectation in a request
that does not include a message body. that does not include payload data.
o A client that will wait for a 100 (Continue) response before o A client that will wait for a 100 (Continue) response before
sending the request message body MUST send an Expect header field sending the request payload data MUST send an Expect header field
containing a 100-continue expectation. containing a 100-continue expectation.
o A client that sends a 100-continue expectation is not required to o A client that sends a 100-continue expectation is not required to
wait for any specific length of time; such a client MAY proceed to wait for any specific length of time; such a client MAY proceed to
send the message body even if it has not yet received a response. send the payload even if it has not yet received a response.
Furthermore, since 100 (Continue) responses cannot be sent through Furthermore, since 100 (Continue) responses cannot be sent through
an HTTP/1.0 intermediary, such a client SHOULD NOT wait for an an HTTP/1.0 intermediary, such a client SHOULD NOT wait for an
indefinite period before sending the message body. indefinite period before sending the payload.
o A client that receives a 417 (Expectation Failed) status code in o A client that receives a 417 (Expectation Failed) status code in
response to a request containing a 100-continue expectation SHOULD response to a request containing a 100-continue expectation SHOULD
repeat that request without a 100-continue expectation, since the repeat that request without a 100-continue expectation, since the
417 response merely indicates that the response chain does not 417 response merely indicates that the response chain does not
support expectations (e.g., it passes through an HTTP/1.0 server). support expectations (e.g., it passes through an HTTP/1.0 server).
Requirements for servers: Requirements for servers:
o A server that receives a 100-continue expectation in an HTTP/1.0 o A server that receives a 100-continue expectation in an HTTP/1.0
request MUST ignore that expectation. request MUST ignore that expectation.
o A server MAY omit sending a 100 (Continue) response if it has o A server MAY omit sending a 100 (Continue) response if it has
already received some or all of the message body for the already received some or all of the payload for the corresponding
corresponding request, or if the framing indicates that there is request, or if the framing indicates that there is no payload.
no message body.
o A server that sends a 100 (Continue) response MUST ultimately send o A server that sends a 100 (Continue) response MUST ultimately send
a final status code, once the message body is received and a final status code, once the payload is received and processed,
processed, unless the connection is closed prematurely. unless the connection is closed prematurely.
o A server that responds with a final status code before reading the o A server that responds with a final status code before reading the
entire request payload body SHOULD indicate whether it intends to entire request payload SHOULD indicate whether it intends to close
close the connection (e.g., see Section 9.6 of [Messaging]) or the connection (e.g., see Section 9.6 of [Messaging]) or continue
continue reading the payload body. reading the request payload.
An origin server MUST, upon receiving an HTTP/1.1 (or later) request An origin server MUST, upon receiving an HTTP/1.1 (or later) request
that has a method, target URI, and complete header section that that has a method, target URI, and complete header section that
contains a 100-continue expectation and indicates a request message contains a 100-continue expectation and indicates a request payload
body will follow, either send an immediate response with a final will follow, either send an immediate response with a final status
status code, if that status can be determined by examining just the code, if that status can be determined by examining just the method,
method, target URI, and header fields, or send an immediate 100 target URI, and header fields, or send an immediate 100 (Continue)
(Continue) response to encourage the client to send the request's response to encourage the client to send the request payload. The
message body. The origin server MUST NOT wait for the message body origin server MUST NOT wait for the payload before sending the 100
before sending the 100 (Continue) response. (Continue) response.
A proxy MUST, upon receiving an HTTP/1.1 (or later) request that has A proxy MUST, upon receiving an HTTP/1.1 (or later) request that has
a method, target URI, and complete header section that contains a a method, target URI, and complete header section that contains a
100-continue expectation and indicates a request message body will 100-continue expectation and indicates a request payload will follow,
follow, either send an immediate response with a final status code, either send an immediate response with a final status code, if that
if that status can be determined by examining just the method, target status can be determined by examining just the method, target URI,
URI, and header fields, or begin forwarding the request toward the and header fields, or begin forwarding the request toward the origin
origin server by sending a corresponding request-line and header server by sending a corresponding request-line and header section to
section to the next inbound server. If the proxy believes (from the next inbound server. If the proxy believes (from configuration
configuration or past interaction) that the next inbound server only or past interaction) that the next inbound server only supports
supports HTTP/1.0, the proxy MAY generate an immediate 100 (Continue) HTTP/1.0, the proxy MAY generate an immediate 100 (Continue) response
response to encourage the client to begin sending the message body. to encourage the client to begin sending the payload.
| *Note:* The Expect header field was added after the original
| publication of HTTP/1.1 [RFC2068] as both the means to request
| an interim 100 (Continue) response and the general mechanism
| for indicating must-understand extensions. However, the
| extension mechanism has not been used by clients and the must-
| understand requirements have not been implemented by many
| servers, rendering the extension mechanism useless. This
| specification has removed the extension mechanism in order to
| simplify the definition and processing of 100-continue.
9.1.2. From 10.1.2. From
The "From" header field contains an Internet email address for a The "From" header field contains an Internet email address for a
human user who controls the requesting user agent. The address ought human user who controls the requesting user agent. The address ought
to be machine-usable, as defined by "mailbox" in Section 3.4 of to be machine-usable, as defined by "mailbox" in Section 3.4 of
[RFC5322]: [RFC5322]:
From = mailbox From = mailbox
mailbox = <mailbox, see [RFC5322], Section 3.4> mailbox = <mailbox, see [RFC5322], Section 3.4>
skipping to change at page 95, line 9 skipping to change at page 94, line 38
A robotic user agent SHOULD send a valid From header field so that A robotic user agent SHOULD send a valid From header field so that
the person responsible for running the robot can be contacted if the person responsible for running the robot can be contacted if
problems occur on servers, such as if the robot is sending excessive, problems occur on servers, such as if the robot is sending excessive,
unwanted, or invalid requests. unwanted, or invalid requests.
A server SHOULD NOT use the From header field for access control or A server SHOULD NOT use the From header field for access control or
authentication, since most recipients will assume that the field authentication, since most recipients will assume that the field
value is public information. value is public information.
9.1.3. Referer 10.1.3. Referer
The "Referer" [sic] header field allows the user agent to specify a The "Referer" [sic] header field allows the user agent to specify a
URI reference for the resource from which the target URI was obtained URI reference for the resource from which the target URI was obtained
(i.e., the "referrer", though the field name is misspelled). A user (i.e., the "referrer", though the field name is misspelled). A user
agent MUST NOT include the fragment and userinfo components of the agent MUST NOT include the fragment and userinfo components of the
URI reference [RFC3986], if any, when generating the Referer field URI reference [RFC3986], if any, when generating the Referer field
value. value.
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
skipping to change at page 95, line 39 skipping to change at page 95, line 20
restricting cross-site request forgery (CSRF), but not all requests restricting cross-site request forgery (CSRF), but not all requests
contain it. contain it.
Example: Example:
Referer: http://www.example.org/hypertext/Overview.html Referer: http://www.example.org/hypertext/Overview.html
If the target URI was obtained from a source that does not have its If the target URI was obtained from a source that does not have its
own URI (e.g., input from the user keyboard, or an entry within the own URI (e.g., input from the user keyboard, or an entry within the
user's bookmarks/favorites), the user agent MUST either exclude the user's bookmarks/favorites), the user agent MUST either exclude the
Referer field or send it with a value of "about:blank". Referer header field or send it with a value of "about:blank".
The Referer field has the potential to reveal information about the The Referer header field has the potential to reveal information
request context or browsing history of the user, which is a privacy about the request context or browsing history of the user, which is a
concern if the referring resource's identifier reveals personal privacy concern if the referring resource's identifier reveals
information (such as an account name) or a resource that is supposed personal information (such as an account name) or a resource that is
to be confidential (such as behind a firewall or internal to a supposed to be confidential (such as behind a firewall or internal to
secured service). Most general-purpose user agents do not send the a secured service). Most general-purpose user agents do not send the
Referer header field when the referring resource is a local "file" or Referer header field when the referring resource is a local "file" or
"data" URI. A user agent MUST NOT send a Referer header field in an "data" URI. A user agent MUST NOT send a Referer header field in an
unsecured HTTP request if the referring page was received with a unsecured HTTP request if the referring page was received with a
secure protocol. See Section 16.9 for additional security secure protocol. See Section 17.9 for additional security
considerations. considerations.
Some intermediaries have been known to indiscriminately remove Some intermediaries have been known to indiscriminately remove
Referer header fields from outgoing requests. This has the Referer header fields from outgoing requests. This has the
unfortunate side effect of interfering with protection against CSRF unfortunate side effect of interfering with protection against CSRF
attacks, which can be far more harmful to their users. attacks, which can be far more harmful to their users.
Intermediaries and user agent extensions that wish to limit Intermediaries and user agent extensions that wish to limit
information disclosure in Referer ought to restrict their changes to information disclosure in Referer ought to restrict their changes to
specific edits, such as replacing internal domain names with specific edits, such as replacing internal domain names with
pseudonyms or truncating the query and/or path components. An pseudonyms or truncating the query and/or path components. An
intermediary SHOULD NOT modify or delete the Referer header field intermediary SHOULD NOT modify or delete the Referer header field
when the field value shares the same scheme and host as the target when the field value shares the same scheme and host as the target
URI. URI.
9.1.4. TE 10.1.4. TE
The "TE" header field in a request can be used to indicate that the The "TE" header field in a request can be used to indicate that the
sender will not discard trailer fields when it contains a "trailers" sender will not discard trailer fields when it contains a "trailers"
member, as described in Section 5.6. member, as described in Section 6.5.
Additionally, specific HTTP versions can use it to indicate the Additionally, specific HTTP versions can use it to indicate the
transfer codings the client is willing to accept in the response. transfer codings the client is willing to accept in the response.
The TE field-value consists of a list of tokens, each allowing for The TE field value consists of a list of tokens, each allowing for
optional parameters (as described in Section 5.7.6). optional parameters (except for the special case "trailers").
TE = #t-codings TE = #t-codings
t-codings = "trailers" / ( transfer-coding [ t-ranking ] ) t-codings = "trailers" / ( transfer-coding [ weight ] )
t-ranking = OWS ";" OWS "q=" rank transfer-coding = token *( OWS ";" OWS transfer-parameter )
rank = ( "0" [ "." 0*3DIGIT ] ) transfer-parameter = token BWS "=" BWS ( token / quoted-string )
/ ( "1" [ "." 0*3("0") ] )
9.1.5. Trailer 10.1.5. Trailer
The "Trailer" header field provides a list of field names that the The "Trailer" header field provides a list of field names that the
sender anticipates sending as trailer fields within that message. sender anticipates sending as trailer fields within that message.
This allows a recipient to prepare for receipt of the indicated This allows a recipient to prepare for receipt of the indicated
metadata before it starts processing the body. metadata before it starts processing the payload.
Trailer = #field-name Trailer = #field-name
For example, a sender might indicate that a message integrity check For example, a sender might indicate that a message integrity check
will be computed as the payload is being streamed and provide the will be computed as the payload is being streamed and provide the
final signature as a trailer field. This allows a recipient to final signature as a trailer field. This allows a recipient to
perform the same check on the fly as the payload data is received. perform the same check on the fly as the payload data is received.
A sender that intends to generate one or more trailer fields in a A sender that intends to generate one or more trailer fields in a
message SHOULD generate a Trailer header field in the header section message SHOULD generate a Trailer header field in the header section
of that message to indicate which fields might be present in the of that message to indicate which fields might be present in the
trailers. trailers.
9.1.6. User-Agent 10.1.6. User-Agent
The "User-Agent" header field contains information about the user The "User-Agent" header field contains information about the user
agent originating the request, which is often used by servers to help agent originating the request, which is often used by servers to help
identify the scope of reported interoperability problems, to work identify the scope of reported interoperability problems, to work
around or tailor responses to avoid particular user agent around or tailor responses to avoid particular user agent
limitations, and for analytics regarding browser or operating system limitations, and for analytics regarding browser or operating system
use. A user agent SHOULD send a User-Agent field in each request use. A user agent SHOULD send a User-Agent header field in each
unless specifically configured not to do so. request unless specifically configured not to do so.
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
The User-Agent field value consists of one or more product The User-Agent field value consists of one or more product
identifiers, each followed by zero or more comments (Section 5.7.5), identifiers, each followed by zero or more comments (Section 5.6.5),
which together identify the user agent software and its significant which together identify the user agent software and its significant
subproducts. By convention, the product identifiers are listed in subproducts. By convention, the product identifiers are listed in
decreasing order of their significance for identifying the user agent decreasing order of their significance for identifying the user agent
software. Each product identifier consists of a name and optional software. Each product identifier consists of a name and optional
version. version.
product = token ["/" product-version] product = token ["/" product-version]
product-version = token product-version = token
A sender SHOULD limit generated product identifiers to what is A sender SHOULD limit generated product identifiers to what is
skipping to change at page 97, line 40 skipping to change at page 97, line 28
advertising or other nonessential information within the product advertising or other nonessential information within the product
identifier. A sender SHOULD NOT generate information in identifier. A sender SHOULD NOT generate information in
product-version that is not a version identifier (i.e., successive product-version that is not a version identifier (i.e., successive
versions of the same product name ought to differ only in the versions of the same product name ought to differ only in the
product-version portion of the product identifier). product-version portion of the product identifier).
Example: Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
A user agent SHOULD NOT generate a User-Agent field containing A user agent SHOULD NOT generate a User-Agent header field containing
needlessly fine-grained detail and SHOULD limit the addition of needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed User-Agent subproducts by third parties. Overly long and detailed User-Agent
field values increase request latency and the risk of a user being field values increase request latency and the risk of a user being
identified against their wishes ("fingerprinting"). identified against their wishes ("fingerprinting").
Likewise, implementations are encouraged not to use the product Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. If a user with them, as this circumvents the purpose of the field. If a user
agent masquerades as a different user agent, recipients can assume agent masquerades as a different user agent, recipients can assume
that the user intentionally desires to see responses tailored for that the user intentionally desires to see responses tailored for
that identified user agent, even if they might not work as well for that identified user agent, even if they might not work as well for
the actual user agent being used. the actual user agent being used.
9.2. Response Context 10.2. Response Context Fields
Response header fields can supply control data that supplements the Response header fields can supply control data that supplements the
status code, directs caching, or instructs the client where to go status code, directs caching, or instructs the client where to go
next. next.
The response header fields allow the server to pass additional The response header fields allow the server to pass additional
information about the response beyond the status code. These header information about the response beyond the status code. These header
fields give information about the server, about further access to the fields give information about the server, about further access to the
target resource, or about related resources. target resource, or about related resources.
Although each response header field has a defined meaning, in Although each response header field has a defined meaning, in
general, the precise semantics might be further refined by the general, the precise semantics might be further refined by the
semantics of the request method and/or response status code. semantics of the request method and/or response status code.
The remaining response header fields provide more information about The remaining response header fields provide more information about
the target resource for potential use in later requests. the target resource for potential use in later requests.
------------- ------- 10.2.1. Allow
Field Name Ref.
------------- -------
Allow 9.2.1
Date 9.2.2
Location 9.2.3
Retry-After 9.2.4
Server 9.2.5
------------- -------
Table 9
9.2.1. Allow
The "Allow" header field lists the set of methods advertised as The "Allow" header field lists the set of methods advertised as
supported by the target resource. The purpose of this field is supported by the target resource. The purpose of this field is
strictly to inform the recipient of valid request methods associated strictly to inform the recipient of valid request methods associated
with the resource. with the resource.
Allow = #method Allow = #method
Example of use: Example of use:
Allow: GET, HEAD, PUT Allow: GET, HEAD, PUT
The actual set of allowed methods is defined by the origin server at The actual set of allowed methods is defined by the origin server at
the time of each request. An origin server MUST generate an Allow the time of each request. An origin server MUST generate an Allow
field in a 405 (Method Not Allowed) response and MAY do so in any header field in a 405 (Method Not Allowed) response and MAY do so in
other response. An empty Allow field value indicates that the any other response. An empty Allow field value indicates that the
resource allows no methods, which might occur in a 405 response if resource allows no methods, which might occur in a 405 response if
the resource has been temporarily disabled by configuration. the resource has been temporarily disabled by configuration.
A proxy MUST NOT modify the Allow header field - it does not need to A proxy MUST NOT modify the Allow header field - it does not need to
understand all of the indicated methods in order to handle them understand all of the indicated methods in order to handle them
according to the generic message handling rules. according to the generic message handling rules.
9.2.2. Date 10.2.2. Date
The "Date" header field represents the date and time at which the The "Date" header field represents the date and time at which the
message was originated, having the same semantics as the Origination message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The
field value is an HTTP-date, as defined in Section 5.7.7. field value is an HTTP-date, as defined in Section 5.6.7.
Date = HTTP-date Date = HTTP-date
An example is An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT Date: Tue, 15 Nov 1994 08:12:31 GMT
When a Date header field is generated, the sender SHOULD generate its When a Date header field is generated, the sender SHOULD generate its
field value as the best available approximation of the date and time field value as the best available approximation of the date and time
of message generation. In theory, the date ought to represent the of message generation. In theory, the date ought to represent the
skipping to change at page 100, line 5 skipping to change at page 99, line 30
corresponding Date header field to the message's header section if it corresponding Date header field to the message's header section if it
is cached or forwarded downstream. is cached or forwarded downstream.
A user agent MAY send a Date header field in a request, though A user agent MAY send a Date header field in a request, though
generally will not do so unless it is believed to convey useful generally will not do so unless it is believed to convey useful
information to the server. For example, custom applications of HTTP information to the server. For example, custom applications of HTTP
might convey a Date if the server is expected to adjust its might convey a Date if the server is expected to adjust its
interpretation of the user's request based on differences between the interpretation of the user's request based on differences between the
user agent and server clocks. user agent and server clocks.
9.2.3. Location 10.2.3. Location
The "Location" header field is used in some responses to refer to a The "Location" header field is used in some responses to refer to a
specific resource in relation to the response. The type of specific resource in relation to the response. The type of
relationship is defined by the combination of request method and relationship is defined by the combination of request method and
status code semantics. status code semantics.
Location = URI-reference Location = URI-reference
The field value consists of a single URI-reference. When it has the The field value consists of a single URI-reference. When it has the
form of a relative reference ([RFC3986], Section 4.2), the final form of a relative reference ([RFC3986], Section 4.2), the final
skipping to change at page 101, line 5 skipping to change at page 100, line 35
which suggests that the user agent redirect to which suggests that the user agent redirect to
"http://www.example.net/index.html#larry", preserving the original "http://www.example.net/index.html#larry", preserving the original
fragment identifier. fragment identifier.
There are circumstances in which a fragment identifier in a Location There are circumstances in which a fragment identifier in a Location
value would not be appropriate. For example, the Location header value would not be appropriate. For example, the Location header
field in a 201 (Created) response is supposed to provide a URI that field in a 201 (Created) response is supposed to provide a URI that
is specific to the created resource. is specific to the created resource.
| *Note:* Some recipients attempt to recover from Location fields | *Note:* Some recipients attempt to recover from Location header
| that are not valid URI references. This specification does not | fields that are not valid URI references. This specification
| mandate or define such processing, but does allow it for the | does not mandate or define such processing, but does allow it
| sake of robustness. A Location field value cannot allow a list | for the sake of robustness. A Location field value cannot
| of members because the comma list separator is a valid data | allow a list of members because the comma list separator is a
| character within a URI-reference. If an invalid message is | valid data character within a URI-reference. If an invalid
| sent with multiple Location field instances, a recipient along | message is sent with multiple Location field lines, a recipient
| the path might combine the field instances into one value. | along the path might combine those field lines into one value.
| Recovery of a valid Location field value from that situation is | Recovery of a valid Location field value from that situation is
| difficult and not interoperable across implementations. | difficult and not interoperable across implementations.
| *Note:* The Content-Location header field (Section 7.8) differs | *Note:* The Content-Location header field (Section 8.8) differs
| from Location in that the Content-Location refers to the most | from Location in that the Content-Location refers to the most
| specific resource corresponding to the enclosed representation. | specific resource corresponding to the enclosed representation.
| It is therefore possible for a response to contain both the | It is therefore possible for a response to contain both the
| Location and Content-Location header fields. | Location and Content-Location header fields.
9.2.4. Retry-After 10.2.4. Retry-After
Servers send the "Retry-After" header field to indicate how long the Servers send the "Retry-After" header field to indicate how long the
user agent ought to wait before making a follow-up request. When user agent ought to wait before making a follow-up request. When
sent with a 503 (Service Unavailable) response, Retry-After indicates sent with a 503 (Service Unavailable) response, Retry-After indicates
how long the service is expected to be unavailable to the client. how long the service is expected to be unavailable to the client.
When sent with any 3xx (Redirection) response, Retry-After indicates When sent with any 3xx (Redirection) response, Retry-After indicates
the minimum time that the user agent is asked to wait before issuing the minimum time that the user agent is asked to wait before issuing
the redirected request. the redirected request.
The value of this field can be either an HTTP-date or a number of The Retry-After field value can be either an HTTP-date or a number of
seconds to delay after the response is received. seconds to delay after the response is received.
Retry-After = HTTP-date / delay-seconds Retry-After = HTTP-date / delay-seconds
A delay-seconds value is a non-negative decimal integer, representing A delay-seconds value is a non-negative decimal integer, representing
time in seconds. time in seconds.
delay-seconds = 1*DIGIT delay-seconds = 1*DIGIT
Two examples of its use are Two examples of its use are
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120 Retry-After: 120
In the latter example, the delay is 2 minutes. In the latter example, the delay is 2 minutes.
9.2.5. Server 10.2.5. Server
The "Server" header field contains information about the software The "Server" header field contains information about the software
used by the origin server to handle the request, which is often used used by the origin server to handle the request, which is often used
by clients to help identify the scope of reported interoperability by clients to help identify the scope of reported interoperability
problems, to work around or tailor requests to avoid particular problems, to work around or tailor requests to avoid particular
server limitations, and for analytics regarding server or operating server limitations, and for analytics regarding server or operating
system use. An origin server MAY generate a Server field in its system use. An origin server MAY generate a Server header field in
responses. its responses.
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
The Server field value consists of one or more product identifiers, The Server header field value consists of one or more product
each followed by zero or more comments (Section 5.7.5), which identifiers, each followed by zero or more comments (Section 5.6.5),
together identify the origin server software and its significant which together identify the origin server software and its
subproducts. By convention, the product identifiers are listed in significant subproducts. By convention, the product identifiers are
decreasing order of their significance for identifying the origin listed in decreasing order of their significance for identifying the
server software. Each product identifier consists of a name and origin server software. Each product identifier consists of a name
optional version, as defined in Section 9.1.6. and optional version, as defined in Section 10.1.6.
Example: Example:
Server: CERN/3.0 libwww/2.17 Server: CERN/3.0 libwww/2.17
An origin server SHOULD NOT generate a Server field containing An origin server SHOULD NOT generate a Server header field containing
needlessly fine-grained detail and SHOULD limit the addition of needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed Server field subproducts by third parties. Overly long and detailed Server field
values increase response latency and potentially reveal internal values increase response latency and potentially reveal internal
implementation details that might make it (slightly) easier for implementation details that might make it (slightly) easier for
attackers to find and exploit known security holes. attackers to find and exploit known security holes.
10. Authentication 11. HTTP Authentication
10.1. Authentication Scheme 11.1. Authentication Scheme
HTTP provides a general framework for access control and HTTP provides a general framework for access control and
authentication, via an extensible set of challenge-response authentication, via an extensible set of challenge-response
authentication schemes, which can be used by a server to challenge a authentication schemes, which can be used by a server to challenge a
client request and by a client to provide authentication information. client request and by a client to provide authentication information.
It uses a case-insensitive token to identify the authentication It uses a case-insensitive token to identify the authentication
scheme scheme
auth-scheme = token auth-scheme = token
Aside from the general framework, this document does not specify any Aside from the general framework, this document does not specify any
authentication schemes. New and existing authentication schemes are authentication schemes. New and existing authentication schemes are
specified independently and ought to be registered within the specified independently and ought to be registered within the
"Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry". "Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry".
For example, the "basic" and "digest" authentication schemes are For example, the "basic" and "digest" authentication schemes are
defined by RFC 7617 and RFC 7616, respectively. defined by RFC 7617 and RFC 7616, respectively.
10.2. Authentication Parameters 11.2. Authentication Parameters
The authentication scheme is followed by additional information The authentication scheme is followed by additional information
necessary for achieving authentication via that scheme as either a necessary for achieving authentication via that scheme as either a
comma-separated list of parameters or a single sequence of characters comma-separated list of parameters or a single sequence of characters
capable of holding base64-encoded information. capable of holding base64-encoded information.
token68 = 1*( ALPHA / DIGIT / token68 = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"=" "-" / "." / "_" / "~" / "+" / "/" ) *"="
The token68 syntax allows the 66 unreserved URI characters The token68 syntax allows the 66 unreserved URI characters
skipping to change at page 103, line 35 skipping to change at page 103, line 8
encoding, with or without padding, but excluding whitespace encoding, with or without padding, but excluding whitespace
([RFC4648]). ([RFC4648]).
Authentication parameters are name=value pairs, where the name token Authentication parameters are name=value pairs, where the name token
is matched case-insensitively and each parameter name MUST only occur is matched case-insensitively and each parameter name MUST only occur
once per challenge. once per challenge.
auth-param = token BWS "=" BWS ( token / quoted-string ) auth-param = token BWS "=" BWS ( token / quoted-string )
Parameter values can be expressed either as "token" or as "quoted- Parameter values can be expressed either as "token" or as "quoted-
string" (Section 5.7). Authentication scheme definitions need to string" (Section 5.6). Authentication scheme definitions need to
accept both notations, both for senders and recipients, to allow accept both notations, both for senders and recipients, to allow
recipients to use generic parsing components regardless of the recipients to use generic parsing components regardless of the
authentication scheme. authentication scheme.
For backwards compatibility, authentication scheme definitions can For backwards compatibility, authentication scheme definitions can
restrict the format for senders to one of the two variants. This can restrict the format for senders to one of the two variants. This can
be important when it is known that deployed implementations will fail be important when it is known that deployed implementations will fail
when encountering one of the two formats. when encountering one of the two formats.
10.3. Challenge and Response 11.3. Challenge and Response
A 401 (Unauthorized) response message is used by an origin server to A 401 (Unauthorized) response message is used by an origin server to
challenge the authorization of a user agent, including a challenge the authorization of a user agent, including a
WWW-Authenticate header field containing at least one challenge WWW-Authenticate header field containing at least one challenge
applicable to the requested resource. applicable to the requested resource.
A 407 (Proxy Authentication Required) response message is used by a A 407 (Proxy Authentication Required) response message is used by a
proxy to challenge the authorization of a client, including a proxy to challenge the authorization of a client, including a
Proxy-Authenticate header field containing at least one challenge Proxy-Authenticate header field containing at least one challenge
applicable to the proxy for the requested resource. applicable to the proxy for the requested resource.
skipping to change at page 104, line 26 skipping to change at page 104, line 5
A user agent that wishes to authenticate itself with an origin server A user agent that wishes to authenticate itself with an origin server
- usually, but not necessarily, after receiving a 401 (Unauthorized) - usually, but not necessarily, after receiving a 401 (Unauthorized)
- can do so by including an Authorization header field with the - can do so by including an Authorization header field with the
request. request.
A client that wishes to authenticate itself with a proxy - usually, A client that wishes to authenticate itself with a proxy - usually,
but not necessarily, after receiving a 407 (Proxy Authentication but not necessarily, after receiving a 407 (Proxy Authentication
Required) - can do so by including a Proxy-Authorization header field Required) - can do so by including a Proxy-Authorization header field
with the request. with the request.
10.4. Credentials 11.4. Credentials
Both the Authorization field value and the Proxy-Authorization field Both the Authorization field value and the Proxy-Authorization field
value contain the client's credentials for the realm of the resource value contain the client's credentials for the realm of the resource
being requested, based upon a challenge received in a response being requested, based upon a challenge received in a response
(possibly at some point in the past). When creating their values, (possibly at some point in the past). When creating their values,
the user agent ought to do so by selecting the challenge with what it the user agent ought to do so by selecting the challenge with what it
considers to be the most secure auth-scheme that it understands, considers to be the most secure auth-scheme that it understands,
obtaining credentials from the user as appropriate. Transmission of obtaining credentials from the user as appropriate. Transmission of
credentials within header field values implies significant security credentials within header field values implies significant security
considerations regarding the confidentiality of the underlying considerations regarding the confidentiality of the underlying
connection, as described in Section 16.15.1. connection, as described in Section 17.15.1.
credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ] credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Upon receipt of a request for a protected resource that omits Upon receipt of a request for a protected resource that omits
credentials, contains invalid credentials (e.g., a bad password) or credentials, contains invalid credentials (e.g., a bad password) or
partial credentials (e.g., when the authentication scheme requires partial credentials (e.g., when the authentication scheme requires
more than one round trip), an origin server SHOULD send a 401 more than one round trip), an origin server SHOULD send a 401
(Unauthorized) response that contains a WWW-Authenticate header field (Unauthorized) response that contains a WWW-Authenticate header field
with at least one (possibly new) challenge applicable to the with at least one (possibly new) challenge applicable to the
requested resource. requested resource.
Likewise, upon receipt of a request that omits proxy credentials or Likewise, upon receipt of a request that omits proxy credentials or
contains invalid or partial proxy credentials, a proxy that requires contains invalid or partial proxy credentials, a proxy that requires
authentication SHOULD generate a 407 (Proxy Authentication Required) authentication SHOULD generate a 407 (Proxy Authentication Required)
response that contains a Proxy-Authenticate header field with at response that contains a Proxy-Authenticate header field with at
least one (possibly new) challenge applicable to the proxy. least one (possibly new) challenge applicable to the proxy.
A server that receives valid credentials that are not adequate to A server that receives valid credentials that are not adequate to
gain access ought to respond with the 403 (Forbidden) status code gain access ought to respond with the 403 (Forbidden) status code
(Section 14.5.4). (Section 15.5.4).
HTTP does not restrict applications to this simple challenge-response HTTP does not restrict applications to this simple challenge-response
framework for access authentication. Additional mechanisms can be framework for access authentication. Additional mechanisms can be
used, such as authentication at the transport level or via message used, such as authentication at the transport level or via message
encapsulation, and with additional header fields specifying encapsulation, and with additional header fields specifying
authentication information. However, such additional mechanisms are authentication information. However, such additional mechanisms are
not defined by this specification. not defined by this specification.
Note that various custom mechanisms for user authentication use the Note that various custom mechanisms for user authentication use the
Set-Cookie and Cookie header fields, defined in [RFC6265], for Set-Cookie and Cookie header fields, defined in [RFC6265], for
passing tokens related to authentication. passing tokens related to authentication.
10.5. Protection Space (Realm) 11.5. Establishing a Protection Space (Realm)
The "realm" authentication parameter is reserved for use by The "_realm_" authentication parameter is reserved for use by
authentication schemes that wish to indicate a scope of protection. authentication schemes that wish to indicate a scope of protection.
A protection space is defined by the canonical root URI (the scheme A _protection space_ is defined by the origin (see Section 4.3.1) of
and authority components of the target URI; see Section 6.1) of the the server being accessed, in combination with the realm value if
server being accessed, in combination with the realm value if
present. These realms allow the protected resources on a server to present. These realms allow the protected resources on a server to
be partitioned into a set of protection spaces, each with its own be partitioned into a set of protection spaces, each with its own
authentication scheme and/or authorization database. The realm value authentication scheme and/or authorization database. The realm value
is a string, generally assigned by the origin server, that can have is a string, generally assigned by the origin server, that can have
additional semantics specific to the authentication scheme. Note additional semantics specific to the authentication scheme. Note
that a response can have multiple challenges with the same auth- that a response can have multiple challenges with the same auth-
scheme but with different realms. scheme but with different realms.
The protection space determines the domain over which credentials can The protection space determines the domain over which credentials can
be automatically applied. If a prior request has been authorized, be automatically applied. If a prior request has been authorized,
skipping to change at page 106, line 10 skipping to change at page 105, line 29
authentication scheme, parameters, and/or user preferences (such as a authentication scheme, parameters, and/or user preferences (such as a
configurable inactivity timeout). Unless specifically allowed by the configurable inactivity timeout). Unless specifically allowed by the
authentication scheme, a single protection space cannot extend authentication scheme, a single protection space cannot extend
outside the scope of its server. outside the scope of its server.
For historical reasons, a sender MUST only generate the quoted-string For historical reasons, a sender MUST only generate the quoted-string
syntax. Recipients might have to support both token and quoted- syntax. Recipients might have to support both token and quoted-
string syntax for maximum interoperability with existing clients that string syntax for maximum interoperability with existing clients that
have been accepting both notations for a long time. have been accepting both notations for a long time.
10.6. Authenticating User to Origin Server 11.6. Authenticating Users to Origin Servers
10.6.1. WWW-Authenticate 11.6.1. WWW-Authenticate
The "WWW-Authenticate" header field indicates the authentication The "WWW-Authenticate" header field indicates the authentication
scheme(s) and parameters applicable to the target resource. scheme(s) and parameters applicable to the target resource.
WWW-Authenticate = #challenge