draft-ietf-httpbis-http2-04.txt   draft-ietf-httpbis-http2-05.txt 
HTTPbis Working Group M. Belshe HTTPbis Working Group M. Belshe
Internet-Draft Twist Internet-Draft Twist
Intended status: Standards Track R. Peon Intended status: Standards Track R. Peon
Expires: January 9, 2014 Google, Inc Expires: February 14, 2014 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Microsoft Microsoft
A. Melnikov, Ed. A. Melnikov, Ed.
Isode Ltd Isode Ltd
July 8, 2013 August 13, 2013
Hypertext Transfer Protocol version 2.0 Hypertext Transfer Protocol version 2.0
draft-ietf-httpbis-http2-04 draft-ietf-httpbis-http2-05
Abstract Abstract
This specification describes an optimized expression of the syntax of This specification describes an optimized expression of the syntax of
the Hypertext Transfer Protocol (HTTP). The HTTP/2.0 encapsulation the Hypertext Transfer Protocol (HTTP). The HTTP/2.0 encapsulation
enables more efficient use of network resources and reduced enables more efficient use of network resources and reduced
perception of latency by allowing header field compression and perception of latency by allowing header field compression and
multiple concurrent messages on the same connection. It also multiple concurrent messages on the same connection. It also
introduces unsolicited push of representations from servers to introduces unsolicited push of representations from servers to
clients. clients.
This document is an alternative to, but does not obsolete the This document is an alternative to, but does not obsolete the
HTTP/1.1 message format or protocol. HTTP's existing semantics HTTP/1.1 message format or protocol. HTTP's existing semantics
remain unchanged. remain unchanged.
This version of the draft has been marked for implementation.
Interoperability testing will occur in the HTTP/2.0 interim in
Hamburg, DE, starting 2013-08-05.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information and related documents can be found at Working Group information and related documents can be found at
<http://tools.ietf.org/wg/httpbis/> (Wiki) and <http://tools.ietf.org/wg/httpbis/> (Wiki) and
<https://github.com/http2/http2-spec> (source code and issues <https://github.com/http2/http2-spec> (source code and issues
tracker). tracker).
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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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 January 9, 2014. This Internet-Draft will expire on February 14, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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 Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.2. HTTP Multiplexing . . . . . . . . . . . . . . . . . . . . 7 2.2. HTTP Multiplexing . . . . . . . . . . . . . . . . . . . . 7
2.3. HTTP Semantics . . . . . . . . . . . . . . . . . . . . . . 7 2.3. HTTP Semantics . . . . . . . . . . . . . . . . . . . . . . 7
3. Starting HTTP/2.0 . . . . . . . . . . . . . . . . . . . . . . 7 3. Starting HTTP/2.0 . . . . . . . . . . . . . . . . . . . . . . 7
3.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 8 3.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 8
3.2. Starting HTTP/2.0 for "http" URIs . . . . . . . . . . . . 8 3.2. Starting HTTP/2.0 for "http" URIs . . . . . . . . . . . . 8
3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10 3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10
3.3. Starting HTTP/2.0 for "https" URIs . . . . . . . . . . . . 10 3.3. Starting HTTP/2.0 for "https" URIs . . . . . . . . . . . . 10
3.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10 3.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10
3.5. Connection Header . . . . . . . . . . . . . . . . . . . . 11 3.5. Connection Header . . . . . . . . . . . . . . . . . . . . 11
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Frame Header . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Header Compression and Decompression . . . . . . . . . . . 13 4.3. Header Compression and Decompression . . . . . . . . . . . 13
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 14 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 18 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 18
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 18 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 19
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 18 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 19
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 19 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 19
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 20 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 21
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 20 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 21
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 21 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 22
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 21 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 22
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 22 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 22
5.4.3. Connection Termination . . . . . . . . . . . . . . . . 22 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 23
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 22 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 23
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 25 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 26 6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 27
6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 27 6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 28
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 27 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 28
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 31 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 33
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 32 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 34
6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 33 6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 35
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 34 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 36
6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 34 6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 36
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 35 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 36
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 36 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 36 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 38
8.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 37 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 39
8.1.2. Request Header Fields . . . . . . . . . . . . . . . . 38 8.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 39
8.1.3. Response Header Fields . . . . . . . . . . . . . . . . 39 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . . 41
8.1.4. GZip Content-Encoding . . . . . . . . . . . . . . . . 40 8.1.3. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 43
8.1.5. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 40 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 43
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 41 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 44
9. Additional HTTP Requirements/Considerations . . . . . . . . . 43 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . . 45
9.1. Frame Size Limits for HTTP . . . . . . . . . . . . . . . . 43 9. Additional HTTP Requirements/Considerations . . . . . . . . . 46
9.2. Connection Management . . . . . . . . . . . . . . . . . . 43 9.1. Connection Management . . . . . . . . . . . . . . . . . . 46
10. Security Considerations . . . . . . . . . . . . . . . . . . . 43 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 46
10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 43 9.3. Frame Size Limits for HTTP . . . . . . . . . . . . . . . . 47
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 44 9.4. GZip Content-Encoding . . . . . . . . . . . . . . . . . . 47
10.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 44 10. Security Considerations . . . . . . . . . . . . . . . . . . . 47
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 45 10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 47
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 47
12.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 45 10.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 48
12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 46 11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 48
12.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 47 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
12.4. HTTP2-Settings Header Field Registration . . . . . . . . . 47 12.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 49
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 48 12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 49
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48 12.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 50
14.1. Normative References . . . . . . . . . . . . . . . . . . . 48 12.4. HTTP2-Settings Header Field Registration . . . . . . . . . 51
14.2. Informative References . . . . . . . . . . . . . . . . . . 50 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 51
14.1. Normative References . . . . . . . . . . . . . . . . . . . 51
14.2. Informative References . . . . . . . . . . . . . . . . . . 53
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 50 publication) . . . . . . . . . . . . . . . . . . . . 53
A.1. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 50 A.1. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 53
A.2. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 50 A.2. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 54
A.3. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 50 A.3. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 54
A.4. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 51 A.4. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 54
A.5. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 51 A.5. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 55
A.6. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 55
1. Introduction 1. Introduction
The Hypertext Transfer Protocol (HTTP) is a wildly successful The Hypertext Transfer Protocol (HTTP) is a wildly successful
protocol. However, the HTTP/1.1 message format ([HTTP-p1], Section protocol. However, the HTTP/1.1 message format ([HTTP-p1], Section
3) is optimized for implementation simplicity and accessibility, not 3) is optimized for implementation simplicity and accessibility, not
application performance. As such it has several characteristics that application performance. As such it has several characteristics that
have a negative overall effect on application performance. have a negative overall effect on application performance.
In particular, HTTP/1.0 only allows one request to be delivered at a In particular, HTTP/1.0 only allows one request to be delivered at a
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single new TCP connection. single new TCP connection.
This document addresses these issues by defining an optimized mapping This document addresses these issues by defining an optimized mapping
of HTTP's semantics to an underlying connection. Specifically, it of HTTP's semantics to an underlying connection. Specifically, it
allows interleaving of request and response messages on the same allows interleaving of request and response messages on the same
connection and uses an efficient coding for HTTP header fields. It connection and uses an efficient coding for HTTP header fields. It
also allows prioritization of requests, letting more important also allows prioritization of requests, letting more important
requests complete more quickly, further improving perceived requests complete more quickly, further improving perceived
performance. performance.
The resulting protocol is designed to have be more friendly to the The resulting protocol is designed to be more friendly to the
network, because fewer TCP connections can be used, in comparison to network, because fewer TCP connections can be used, in comparison to
HTTP/1.x. This means less competition with other flows, and longer- HTTP/1.x. This means less competition with other flows, and longer-
lived connections, which in turn leads to better utilization of lived connections, which in turn leads to better utilization of
available network capacity. available network capacity.
Finally, this encapsulation also enables more scalable processing of Finally, this encapsulation also enables more scalable processing of
messages through use of binary message framing. messages through use of binary message framing.
1.1. Document Organization 1.1. Document Organization
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HTTP/2.0 provides the ability to multiplex multiple HTTP requests and HTTP/2.0 provides the ability to multiplex multiple HTTP requests and
responses onto a single connection. Multiple requests or responses responses onto a single connection. Multiple requests or responses
can be sent concurrently on a connection using streams (Section 5). can be sent concurrently on a connection using streams (Section 5).
In order to maintain independent streams, flow control and In order to maintain independent streams, flow control and
prioritization are necessary. prioritization are necessary.
2.3. HTTP Semantics 2.3. HTTP Semantics
HTTP/2.0 defines how HTTP requests and responses are mapped to HTTP/2.0 defines how HTTP requests and responses are mapped to
streams (see Section 8) and introduces a new interaction model, streams (see Section 8.1) and introduces a new interaction model,
server push (Section 8.2). server push (Section 8.2).
3. Starting HTTP/2.0 3. Starting HTTP/2.0
HTTP/2.0 uses the same "http" and "https" URI schemes used by HTTP/2.0 uses the same "http" and "https" URI schemes used by
HTTP/1.1. HTTP/2.0 shares the same default port numbers: 80 for HTTP/1.1. HTTP/2.0 shares the same default port numbers: 80 for
"http" URIs and 443 for "https" URIs. As a result, implementations "http" URIs and 443 for "https" URIs. As a result, implementations
processing requests for target resource URIs like processing requests for target resource URIs like
"http://example.org/foo" or "https://example.com/bar" are required to "http://example.org/foo" or "https://example.com/bar" are required to
first discover whether the upstream server (the immediate peer to first discover whether the upstream server (the immediate peer to
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The protocol defined in this document is identified using the string The protocol defined in this document is identified using the string
"HTTP/2.0". This identification is used in the HTTP/1.1 Upgrade "HTTP/2.0". This identification is used in the HTTP/1.1 Upgrade
header field, in the TLS application layer protocol negotiation header field, in the TLS application layer protocol negotiation
extension [TLSALPN] field, and other places where protocol extension [TLSALPN] field, and other places where protocol
identification is required. identification is required.
Negotiating "HTTP/2.0" implies the use of the transport, security, Negotiating "HTTP/2.0" implies the use of the transport, security,
framing and message semantics described in this document. framing and message semantics described in this document.
[[anchor6: Editor's Note: please remove the following text prior to [[anchor6: Editor's Note: please remove the remainder of this section
the publication of a final version of this document.]] prior to the publication of a final version of this document.]]
Only implementations of the final, published RFC can identify Only implementations of the final, published RFC can identify
themselves as "HTTP/2.0". Until such an RFC exists, implementations themselves as "HTTP/2.0". Until such an RFC exists, implementations
MUST NOT identify themselves using "HTTP/2.0". MUST NOT identify themselves using "HTTP/2.0".
Examples and text throughout the rest of this document use "HTTP/2.0" Examples and text throughout the rest of this document use "HTTP/2.0"
as a matter of editorial convenience only. Implementations of draft as a matter of editorial convenience only. Implementations of draft
versions MUST NOT identify using this string. versions MUST NOT identify using this string. The exception to this
rule is the string included in the connection header sent by clients
immediately after establishing an HTTP/2.0 connection (see
Section 3.5); this fixed length sequence of octets does not change.
Implementations of draft versions of the protocol MUST add the string Implementations of draft versions of the protocol MUST add the string
"-draft-" and the corresponding draft number to the identifier before "-draft-" and the corresponding draft number to the identifier before
the separator ('/'). For example, draft-ietf-httpbis-http2-03 is the separator ('/'). For example, draft-ietf-httpbis-http2-03 is
identified using the string "HTTP-draft-03/2.0". identified using the string "HTTP-draft-03/2.0".
Non-compatible experiments that are based on these draft versions Non-compatible experiments that are based on these draft versions
MUST instead replace the string "draft" with a different identifier. MUST instead replace the string "draft" with a different identifier.
For example, an experimental implementation of packet mood-based For example, an experimental implementation of packet mood-based
encoding based on draft-ietf-httpbis-http2-07 might identify itself encoding based on draft-ietf-httpbis-http2-07 might identify itself
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"token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters "token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters
are encouraged to coordinate their experiments on the are encouraged to coordinate their experiments on the
ietf-http-wg@w3.org mailing list. ietf-http-wg@w3.org mailing list.
3.2. Starting HTTP/2.0 for "http" URIs 3.2. Starting HTTP/2.0 for "http" URIs
A client that makes a request to an "http" URI without prior A client that makes a request to an "http" URI without prior
knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism
(Section 6.7 of [HTTP-p1]). The client makes an HTTP/1.1 request (Section 6.7 of [HTTP-p1]). The client makes an HTTP/1.1 request
that includes an Upgrade header field identifying HTTP/2.0. The that includes an Upgrade header field identifying HTTP/2.0. The
HTTP/1.1 request MUST include an HTTP2-Settings (Section 3.2.1) HTTP/1.1 request MUST include exactly one HTTP2-Settings
header field. (Section 3.2.1) header field.
For example: For example:
GET /default.htm HTTP/1.1 GET /default.htm HTTP/1.1
Host: server.example.com Host: server.example.com
Connection: Upgrade, HTTP2-Settings Connection: Upgrade, HTTP2-Settings
Upgrade: HTTP/2.0 Upgrade: HTTP/2.0
HTTP2-Settings: <base64url encoding of HTTP/2.0 SETTINGS payload> HTTP2-Settings: <base64url encoding of HTTP/2.0 SETTINGS payload>
Requests that contain a request entity body MUST be sent in their Requests that contain a request entity body MUST be sent in their
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connection header (Section 3.5), which includes a SETTINGS frame. connection header (Section 3.5), which includes a SETTINGS frame.
The HTTP/1.1 request that is sent prior to upgrade is associated with The HTTP/1.1 request that is sent prior to upgrade is associated with
stream 1 and is assigned the highest possible priority. Stream 1 is stream 1 and is assigned the highest possible priority. Stream 1 is
implicitly half closed from the client toward the server, since the implicitly half closed from the client toward the server, since the
request is completed as an HTTP/1.1 request. After commencing the request is completed as an HTTP/1.1 request. After commencing the
HTTP/2.0 connection, stream 1 is used for the response. HTTP/2.0 connection, stream 1 is used for the response.
3.2.1. HTTP2-Settings Header Field 3.2.1. HTTP2-Settings Header Field
A client that upgrades from HTTP/1.1 to HTTP/2.0 MUST include an A client that upgrades from HTTP/1.1 to HTTP/2.0 MUST include exactly
"HTTP2-Settings" header field. The "HTTP2-Settings" header field is one "HTTP2-Settings" header field. The "HTTP2-Settings" header field
a hop-by-hop header field that includes settings that govern the is a hop-by-hop header field that includes settings that govern the
HTTP/2.0 connection, provided in anticipation of the server accepting HTTP/2.0 connection, provided in anticipation of the server accepting
the request to upgrade. A server MUST reject an attempt to upgrade the request to upgrade. A server MUST reject an attempt to upgrade
if this header is not present. if this header is not present.
HTTP2-Settings = token68 HTTP2-Settings = token68
The content of the "HTTP2-Settings" header field is the payload of a The content of the "HTTP2-Settings" header field is the payload of a
SETTINGS frame (Section 6.5), encoded as a base64url string (that is, SETTINGS frame (Section 6.5), encoded as a base64url string (that is,
the URL- and filename-safe Base64 encoding described in Section 5 of the URL- and filename-safe Base64 encoding described in Section 5 of
[RFC4648], with any trailing '=' characters omitted). The ABNF [RFC4648], with any trailing '=' characters omitted). The ABNF
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A server decodes and interprets these values as it would any other A server decodes and interprets these values as it would any other
SETTINGS frame. Providing these values in the Upgrade request SETTINGS frame. Providing these values in the Upgrade request
ensures that the protocol does not require default values for the ensures that the protocol does not require default values for the
above settings, and gives a client an opportunity to provide other above settings, and gives a client an opportunity to provide other
settings prior to receiving any frames from the server. settings prior to receiving any frames from the server.
3.3. Starting HTTP/2.0 for "https" URIs 3.3. Starting HTTP/2.0 for "https" URIs
A client that makes a request to an "https" URI without prior A client that makes a request to an "https" URI without prior
knowledge about support for HTTP/2.0 uses TLS [RFC5246] with the knowledge about support for HTTP/2.0 uses TLS [TLS12] with the
application layer protocol negotiation extension [TLSALPN]. application layer protocol negotiation extension [TLSALPN].
Once TLS negotiation is complete, both the client and the server send Once TLS negotiation is complete, both the client and the server send
a connection header (Section 3.5). a connection header (Section 3.5).
3.4. Starting HTTP/2.0 with Prior Knowledge 3.4. Starting HTTP/2.0 with Prior Knowledge
A client can learn that a particular server supports HTTP/2.0 by A client can learn that a particular server supports HTTP/2.0 by
other means. A client MAY immediately send HTTP/2.0 frames to a other means. A client MAY immediately send HTTP/2.0 frames to a
server that is known to support HTTP/2.0, after the connection header server that is known to support HTTP/2.0, after the connection header
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initial settings for the HTTP/2.0 connection. initial settings for the HTTP/2.0 connection.
The client connection header is a sequence of 24 octets, which in hex The client connection header is a sequence of 24 octets, which in hex
notation are: notation are:
505249202a20485454502f322e300d0a0d0a534d0d0a0d0a 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n") followed by a (the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n") followed by a
SETTINGS frame (Section 6.5). The client sends the client connection SETTINGS frame (Section 6.5). The client sends the client connection
header immediately upon receipt of a 101 Switching Protocols response header immediately upon receipt of a 101 Switching Protocols response
(indicating a successful upgrade), or after receiving a TLS Finished (indicating a successful upgrade), or as the first application data
message from the server. If starting an HTTP/2.0 connection with octets of a TLS connection. If starting an HTTP/2.0 connection with
prior knowledge of server support for the protocol, the client prior knowledge of server support for the protocol, the client
connection header is sent upon connection establishment. connection header is sent upon connection establishment.
The client connection header is selected so that a large The client connection header is selected so that a large
proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do
not attempt to process further frames. Note that this does not not attempt to process further frames. Note that this does not
address the concerns raised in [TALKING]. address the concerns raised in [TALKING].
The server connection header consists of just a SETTINGS frame The server connection header consists of just a SETTINGS frame
(Section 6.5) that MUST be the first frame the server sends in the (Section 6.5) that MUST be the first frame the server sends in the
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Clients and servers MUST terminate the TCP connection if either peer Clients and servers MUST terminate the TCP connection if either peer
does not begin with a valid connection header. A GOAWAY frame does not begin with a valid connection header. A GOAWAY frame
(Section 6.8) MAY be omitted if it is clear that the peer is not (Section 6.8) MAY be omitted if it is clear that the peer is not
using HTTP/2.0. using HTTP/2.0.
4. HTTP Frames 4. HTTP Frames
Once the HTTP/2.0 connection is established, endpoints can begin Once the HTTP/2.0 connection is established, endpoints can begin
exchanging frames. exchanging frames.
4.1. Frame Header 4.1. Frame Format
All frames begin with an 8-octet header followed by a payload of All frames begin with an 8-octet header followed by a payload of
between 0 and 65,535 octets. between 0 and 65,535 octets.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (16) | Type (8) | Flags (8) | | Length (16) | Type (8) | Flags (8) |
+-+-------------+---------------+-------------------------------+ +-+-------------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
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Frame Header Frame Header
The fields of the frame header are defined as: The fields of the frame header are defined as:
Length: The length of the frame payload expressed as an unsigned 16- Length: The length of the frame payload expressed as an unsigned 16-
bit integer. The 8 octets of the frame header are not included in bit integer. The 8 octets of the frame header are not included in
this value. this value.
Type: The 8-bit type of the frame. The frame type determines how Type: The 8-bit type of the frame. The frame type determines how
the remainder of the frame header and payload are interpreted. the remainder of the frame header and payload are interpreted.
Implementations MUST ignore unsupported and unrecognized frame Implementations MUST ignore frames of unsupported or unrecognized
types. types.
Flags: An 8-bit field reserved for frame-type specific boolean Flags: An 8-bit field reserved for frame-type specific boolean
flags. flags.
Flags are assigned semantics specific to the indicated frame type. Flags are assigned semantics specific to the indicated frame type.
Flags that have no defined semantics for a particular frame type Flags that have no defined semantics for a particular frame type
MUST be ignored, and MUST be left unset (0) when sending. MUST be ignored, and MUST be left unset (0) when sending.
R: A reserved 1-bit field. The semantics of this bit are undefined R: A reserved 1-bit field. The semantics of this bit are undefined
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A header in HTTP/2.0 is a name-value pair with one or more associated A header in HTTP/2.0 is a name-value pair with one or more associated
values. They are used within HTTP request and response messages as values. They are used within HTTP request and response messages as
well as server push operations (see Section 8.2). well as server push operations (see Section 8.2).
Header sets are logical collections of zero or more header fields Header sets are logical collections of zero or more header fields
arranged at the application layer. When transmitted over a arranged at the application layer. When transmitted over a
connection, the header set is serialized into a header block using connection, the header set is serialized into a header block using
HTTP Header Compression [COMPRESSION]. The serialized header block HTTP Header Compression [COMPRESSION]. The serialized header block
is then divided into one or more octet sequences, called header block is then divided into one or more octet sequences, called header block
fragments, and transmitted within the payload of HEADERS fragments, and transmitted within the payload of HEADERS
(Section 6.2) or PUSH_PROMISE (Section 6.6) frames. The receiving (Section 6.2), PUSH_PROMISE (Section 6.6) or CONTINUATION
endpoint reassembles the header block by concatenating the individual (Section 6.10) frames. The receiving endpoint reassembles the header
fragments, then decompresses the block to reconstruct the header set. block by concatenating the individual fragments, then decompresses
the block to reconstruct the header set.
Header block fragments can only be sent as the payload of HEADERS or Header block fragments can only be sent as the payload of HEADERS,
PUSH_PROMISE frames. PUSH_PROMISE or CONTINUATION frames.
A compressed and encoded header block is transmitted in one or more A compressed and encoded header block is transmitted in a HEADERS or
HEADERS or PUSH_PROMISE frames. If the number of octets in the block PUSH_PROMISE frame, followed by zero or more CONTINUATION frames. If
is greater than the space remaining in the frame, the block is the number of octets in the block is greater than the space remaining
divided into multiple fragments, which are then transmitted in in the frame, the block is divided into multiple fragments, which are
multiple frames. then transmitted in multiple frames.
Header blocks MUST be transmitted as a contiguous sequence of frames, Header blocks MUST be transmitted as a contiguous sequence of frames,
with no interleaved frames of any other type, or from any other with no interleaved frames of any other type, or from any other
stream. The last frame in a sequence of HEADERS frames MUST have the stream. The last frame in a sequence of HEADERS/CONTINUATION frames
END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE MUST have the END_HEADERS flag set. The last frame in a sequence of
frames MUST have the END_PUSH_PROMISE flag set. PUSH_PROMISE/CONTINUATION frames MUST have the END_PUSH_PROMISE/
END_HEADERS flag set (respectively).
HEADERS and PUSH_PROMISE frames carry data that can modify the HEADERS, PUSH_PROMISE and CONTINUATION frames carry data that can
compression context maintained by a receiver. An endpoint receiving modify the compression context maintained by a receiver. An endpoint
HEADERS or PUSH_PROMISE frames MUST reassemble header blocks and receiving HEADERS, PUSH_PROMISE or CONTINUATION frames MUST
perform decompression even if the frames are to be discarded, which reassemble header blocks and perform decompression even if the frames
is likely to occur after a stream is reset. A receiver MUST are to be discarded, which is likely to occur after a stream is
terminate the connection with a connection error (Section 5.4.1) of reset. A receiver MUST terminate the connection with a connection
type COMPRESSION_ERROR, if it does not decompress a header block. error (Section 5.4.1) of type COMPRESSION_ERROR, if it does not
decompress a header block.
5. Streams and Multiplexing 5. Streams and Multiplexing
A "stream" is an independent, bi-directional sequence of HEADER and A "stream" is an independent, bi-directional sequence of HEADERS and
DATA frames exchanged between the client and server within an DATA frames exchanged between the client and server within an
HTTP/2.0 connection. Streams have several important characteristics: HTTP/2.0 connection. Streams have several important characteristics:
o A single HTTP/2.0 connection can contain multiple concurrently o A single HTTP/2.0 connection can contain multiple concurrently
active streams, with either endpoint interleaving frames from active streams, with either endpoint interleaving frames from
multiple streams. multiple streams.
o Streams can be established and used unilaterally or shared by o Streams can be established and used unilaterally or shared by
either the client or server. either the client or server.
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promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame
reserves an idle stream by associating the stream with an open reserves an idle stream by associating the stream with an open
stream that was initiated by the remote peer (see Section 8.2). stream that was initiated by the remote peer (see Section 8.2).
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* The endpoint can send a HEADERS frame. This causes the stream * The endpoint can send a HEADERS frame. This causes the stream
to open in a "half closed (remote)" state. to open in a "half closed (remote)" state.
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This also releases the stream reservation.
An endpoint MUST NOT send any other type of frame in this state. An endpoint MUST NOT send any other type of frame in this state.
Receiving any frame other than RST_STREAM or PRIORITY MUST be
treated as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
reserved (remote): reserved (remote):
A stream in the "reserved (remote)" state has been reserved by a A stream in the "reserved (remote)" state has been reserved by a
remote peer. remote peer.
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* Receiving a HEADERS frame causes the stream to transition to * Receiving a HEADERS frame causes the stream to transition to
"half closed (local)". "half closed (local)".
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This also releases the stream reservation.
Receiving any other type of frame MUST be treated as a stream Receiving any other type of frame MUST be treated as a stream
error (Section 5.4.2) of type PROTOCOL_ERROR. error (Section 5.4.2) of type PROTOCOL_ERROR. An endpoint MAY
send RST_STREAM or PRIORITY frames in this state to cancel or
reprioritize the reserved stream.
open: open:
The "open" state is where both peers can send frames. In this The "open" state is where both peers can send frames of any type.
state, sending peers observe advertised stream level flow control In this state, sending peers observe advertised stream level flow
limits (Section 5.2). control limits (Section 5.2).
From this state either endpoint can send a frame with a END_STREAM From this state either endpoint can send a frame with a END_STREAM
flag set, which causes the stream to transition into one of the flag set, which causes the stream to transition into one of the
"half closed" states: an endpoint sending a END_STREAM flag causes "half closed" states: an endpoint sending a END_STREAM flag causes
the stream state to become "half closed (local)"; an endpoint the stream state to become "half closed (local)"; an endpoint
receiving a END_STREAM flag causes the stream state to become receiving a END_STREAM flag causes the stream state to become
"half closed (remote)". "half closed (remote)".
Either endpoint can send a RST_STREAM frame from this state, Either endpoint can send a RST_STREAM frame from this state,
causing it to transition immediately to "closed". causing it to transition immediately to "closed".
half closed (local): half closed (local):
A stream that is "half closed (local)" cannot be used for sending A stream that is "half closed (local)" cannot be used for sending
frames. frames.
A stream transitions from this state to "closed" when a frame that A stream transitions from this state to "closed" when a frame that
contains a END_STREAM flag is received, or when either peer sends contains a END_STREAM flag is received, or when either peer sends
a RST_STREAM frame. a RST_STREAM frame.
A receiver can ignore WINDOW_UPDATE or PRIORITY frames in this
state. These frame types might arrive for a short period after a
frame bearing the END_STREAM flag is sent.
half closed (remote): half closed (remote):
A stream that is "half closed (remote)" is no longer being used by A stream that is "half closed (remote)" is no longer being used by
the peer to send frames. In this state, an endpoint is no longer the peer to send frames. In this state, an endpoint is no longer
obligated to maintain a receiver flow control window if it obligated to maintain a receiver flow control window if it
performs flow control. performs flow control.
If an endpoint receives additional frames for a stream that is in If an endpoint receives additional frames for a stream that is in
this state it MUST respond with a stream error (Section 5.4.2) of this state it MUST respond with a stream error (Section 5.4.2) of
type STREAM_CLOSED. type STREAM_CLOSED.
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RST_STREAM frame. RST_STREAM frame.
closed: closed:
The "closed" state is the terminal state. The "closed" state is the terminal state.
An endpoint MUST NOT send frames on a closed stream. An endpoint An endpoint MUST NOT send frames on a closed stream. An endpoint
that receives a frame after receiving a RST_STREAM or a frame that receives a frame after receiving a RST_STREAM or a frame
containing a END_STREAM flag on that stream MUST treat that as a containing a END_STREAM flag on that stream MUST treat that as a
stream error (Section 5.4.2) of type STREAM_CLOSED. stream error (Section 5.4.2) of type STREAM_CLOSED.
WINDOW_UPDATE or PRIORITY frames can be received in this state for
a short period after a a frame containing an END_STREAM flag is
sent. Until the remote peer receives and processes the frame
bearing the END_STREAM flag, it might send either frame type.
Endpoints MUST ignore WINDOW_UPDATE frames received in this state,
though endpoints MAY choose to treat WINDOW_UPDATE frames that
arrive a significant time after sending END_STREAM as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
If this state is reached as a result of sending a RST_STREAM If this state is reached as a result of sending a RST_STREAM
frame, the peer that receives the RST_STREAM might have already frame, the peer that receives the RST_STREAM might have already
sent - or enqueued for sending - frames on the stream that cannot sent - or enqueued for sending - frames on the stream that cannot
be withdrawn. An endpoint that sends a RST_STREAM frame MUST be withdrawn. An endpoint MUST ignore frames that it receives on
ignore frames that it receives on closed streams after it has sent closed streams after it has sent a RST_STREAM frame. An endpoint
a RST_STREAM frame. An endpoint MAY choose to limit the period MAY choose to limit the period over which it ignores frames and
over which it ignores frames and treat frames that arrive after treat frames that arrive after this time as being in error.
this time as being in error.
An endpoint might receive a PUSH_PROMISE frame after it sends Flow controlled frames (i.e., DATA) received after sending
RST_STREAM. PUSH_PROMISE causes a stream to become "reserved". RST_STREAM are counted toward the connection flow control window.
If promised streams are not desired, a RST_STREAM can be used to Even though these frames might be ignored, because they are sent
close any of those streams. before the sender receives the RST_STREAM, the sender will
consider the frames to count against the flow control window.
An endpoint might receive a PUSH_PROMISE or a CONTINUATION frame
after it sends RST_STREAM. PUSH_PROMISE causes a stream to become
"reserved". If promised streams are not desired, a RST_STREAM can
be used to close any of those streams.
In the absence of more specific guidance elsewhere in this document,
implementations SHOULD treat the receipt of a message that is not
expressly permitted in the description of a state as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
5.1.1. Stream Identifiers 5.1.1. Stream Identifiers
Streams are identified with an unsigned 31-bit integer. Streams Streams are identified with an unsigned 31-bit integer. Streams
initiated by a client MUST use odd-numbered stream identifiers; those initiated by a client MUST use odd-numbered stream identifiers; those
initiated by the server MUST use even-numbered stream identifiers. A initiated by the server MUST use even-numbered stream identifiers. A
stream identifier of zero (0x0) is used for connection control stream identifier of zero (0x0) is used for connection control
message; the stream identifier zero MUST NOT be used to establish a message; the stream identifier zero MUST NOT be used to establish a
new stream. new stream. A stream identifier of one (0x1) is used to respond to
the HTTP/1.1 request which was specified during Upgrade (see
Section 3.2); the stream identifier one MUST NOT be used to establish
a new stream.
The identifier of a newly established stream MUST be numerically The identifier of a newly established stream MUST be numerically
greater than all streams that the initiating endpoint has opened or greater than all streams that the initiating endpoint has opened or
reserved. This governs streams that are opened using a HEADERS frame reserved. This governs streams that are opened using a HEADERS frame
and streams that are reserved using PUSH_PROMISE. An endpoint that and streams that are reserved using PUSH_PROMISE. An endpoint that
receives an unexpected stream identifier MUST respond with a receives an unexpected stream identifier MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The first use of a new stream identifier implicitly closes all idle
streams that might have been initiated by that peer with a lower-
valued stream identifier.
Stream identifiers cannot be reused. Long-lived connections can Stream identifiers cannot be reused. Long-lived connections can
result in endpoint exhausting the available range of stream result in endpoint exhausting the available range of stream
identifiers. A client that is unable to establish a new stream identifiers. A client that is unable to establish a new stream
identifier can establish a new connection for new streams. identifier can establish a new connection for new streams.
5.1.2. Stream Concurrency 5.1.2. Stream Concurrency
A peer can limit the number of concurrently active streams using the A peer can limit the number of concurrently active streams using the
SETTINGS_MAX_CONCURRENT_STREAMS parameters within a SETTINGS frame. SETTINGS_MAX_CONCURRENT_STREAMS parameters within a SETTINGS frame.
The maximum concurrent streams setting is specific to each endpoint The maximum concurrent streams setting is specific to each endpoint
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5.2. Flow Control 5.2. Flow Control
Using streams for multiplexing introduces contention over use of the Using streams for multiplexing introduces contention over use of the
TCP connection, resulting in blocked streams. A flow control scheme TCP connection, resulting in blocked streams. A flow control scheme
ensures that streams on the same connection do not destructively ensures that streams on the same connection do not destructively
interfere with each other. Flow control is used for both individual interfere with each other. Flow control is used for both individual
streams and for the connection as a whole. streams and for the connection as a whole.
HTTP/2.0 provides for flow control through use of the WINDOW_UPDATE HTTP/2.0 provides for flow control through use of the WINDOW_UPDATE
(Section 6.9) frame type. frame type.
5.2.1. Flow Control Principles 5.2.1. Flow Control Principles
Experience with TCP congestion control has shown that algorithms can Experience with TCP congestion control has shown that algorithms can
evolve over time to become more sophisticated without requiring evolve over time to become more sophisticated without requiring
protocol changes. TCP congestion control and its evolution is protocol changes. TCP congestion control and its evolution is
clearly different from HTTP/2.0 flow control, though the evolution of clearly different from HTTP/2.0 flow control, though the evolution of
TCP congestion control algorithms shows that a similar approach could TCP congestion control algorithms shows that a similar approach could
be feasible for HTTP/2.0 flow control. be feasible for HTTP/2.0 flow control.
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and for the entire connection. This is a credit-based scheme. and for the entire connection. This is a credit-based scheme.
3. Flow control is directional with overall control provided by the 3. Flow control is directional with overall control provided by the
receiver. A receiver MAY choose to set any window size that it receiver. A receiver MAY choose to set any window size that it
desires for each stream and for the entire connection. A sender desires for each stream and for the entire connection. A sender
MUST respect flow control limits imposed by a receiver. Clients, MUST respect flow control limits imposed by a receiver. Clients,
servers and intermediaries all independently advertise their flow servers and intermediaries all independently advertise their flow
control preferences as a receiver and abide by the flow control control preferences as a receiver and abide by the flow control
limits set by their peer when sending. limits set by their peer when sending.
4. The initial value for the flow control window is 65536 bytes for 4. The initial value for the flow control window is 65535 bytes for
both new streams and the overall connection. both new streams and the overall connection.
5. The frame type determines whether flow control applies to a 5. The frame type determines whether flow control applies to a
frame. Of the frames specified in this document, only DATA frame. Of the frames specified in this document, only DATA
frames are subject to flow control; all other frame types do not frames are subject to flow control; all other frame types do not
consume space in the advertised flow control window. This consume space in the advertised flow control window. This
ensures that important control frames are not blocked by flow ensures that important control frames are not blocked by flow
control. control.
6. Flow control can be disabled by a receiver. A receiver can 6. Flow control can be disabled by a receiver. A receiver can
choose to either disable flow control for a stream or connection choose to disable both forms of flow control by sending the
by sending a window update frame with a specific flag. See SETTINGS_FLOW_CONTROL_OPTIONS setting. See Ending Flow Control
Ending Flow Control (Section 6.9.4) for more details. (Section 6.9.4) for more details.
7. HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame 7. HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame
(Section 6.9). This does not stipulate how a receiver decides (Section 6.9). This does not stipulate how a receiver decides
when to send this frame or the value that it sends. Nor does it when to send this frame or the value that it sends. Nor does it
specify how a sender chooses to send packets. Implementations specify how a sender chooses to send packets. Implementations
are able to select any algorithm that suits their needs. are able to select any algorithm that suits their needs.
Implementations are also responsible for managing how requests and Implementations are also responsible for managing how requests and
responses are sent based on priority; choosing how to avoid head of responses are sent based on priority; choosing how to avoid head of
line blocking for requests; and managing the creation of new streams. line blocking for requests; and managing the creation of new streams.
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cannot be disabled for sending. Sending data is always subject to cannot be disabled for sending. Sending data is always subject to
the flow control window advertised by the receiver. the flow control window advertised by the receiver.
Deployments with constrained resources (for example, memory) MAY Deployments with constrained resources (for example, memory) MAY
employ flow control to limit the amount of memory a peer can consume. employ flow control to limit the amount of memory a peer can consume.
Note, however, that this can lead to suboptimal use of available Note, however, that this can lead to suboptimal use of available
network resources if flow control is enabled without knowledge of the network resources if flow control is enabled without knowledge of the
bandwidth-delay product (see [RFC1323]). bandwidth-delay product (see [RFC1323]).
Even with full awareness of the current bandwidth-delay product, Even with full awareness of the current bandwidth-delay product,
implementation of flow control is difficult. However, it can ensure implementation of flow control can be difficult. When using flow
that constrained resources are protected without any reduction in control, the receive MUST read from the TCP receive buffer in a
connection utilization. timely fashion. Failure to do so could lead to a deadlock when
critical frames, such as WINDOW_UPDATE, are not available to
HTTP/2.0. However, flow control can ensure that constrained
resources are protected without any reduction in connection
utilization.
5.3. Stream priority 5.3. Stream priority
The endpoint establishing a new stream can assign a priority for the The endpoint establishing a new stream can assign a priority for the
stream. Priority is represented as an unsigned 31-bit integer. 0 stream. Priority is represented as an unsigned 31-bit integer. 0
represents the highest priority and 2^31-1 represents the lowest represents the highest priority and 2^31-1 represents the lowest
priority. priority.
The purpose of this value is to allow the initiating endpoint to The purpose of this value is to allow an endpoint to express the
request that frames for the stream be processed with a specified relative priority of a stream. An endpoint can use this information
priority relative to other concurrently active streams. That is, if to preferentially allocate resources to a stream. Within HTTP/2.0,
an endpoint receives interleaved frames for multiple streams, the priority can be used to select streams for transmitting frames when
endpoint ought to make a best-effort attempt at processing frames for there is limited capacity for sending. For instance, an endpoint
higher priority streams before processing those for lower priority might enqueue frames for all concurrently active streams. As
streams. transmission capacity becomes available, frames from higher priority
streams might be sent before lower priority streams.
Explicitly setting the priority for a stream does not guarantee any Explicitly setting the priority for a stream does not guarantee any
particular processing order for the stream relative to any other particular processing or transmision order for the stream relative to
stream. Nor is there any mechanism provided by which the initiator any other stream. Nor is there any mechanism provided by which the
of a stream can force or require a receiving endpoint to process initiator of a stream can force or require a receiving endpoint to
frames from one stream before processing frames from another. process concurrent streams in a particular order.
Unless explicitly specified in the HEADERS frame (Section 6.2) during Unless explicitly specified in the HEADERS frame (Section 6.2) during
stream creation, the default stream priority is 2^30. Pushed streams stream creation, the default stream priority is 2^30.
(Section 8.2) are assumed to inherit the priority of the associated
stream plus one (or 2^31-1 if the the associated stream priority is Pushed streams (Section 8.2) have a lower priority than their
2^31-1), i.e. they have priority one lower than the associated associated stream. The promised stream inherits the priority value
stream. of the associated stream plus one, up to a maximum of 2^31-1.
5.4. Error Handling 5.4. Error Handling
HTTP/2.0 framing permits two classes of error: HTTP/2.0 framing permits two classes of error:
o An error condition that renders the entire connection unusable is o An error condition that renders the entire connection unusable is
a connection error. a connection error.
o An error in an individual stream is a stream error. o An error in an individual stream is a stream error.
A list of error codes is included in Section 7. A list of error codes is included in Section 7.
5.4.1. Connection Error Handling 5.4.1. Connection Error Handling
A connection error is any error which prevents further processing of A connection error is any error which prevents further processing of
the framing layer or which corrupts any connection state. the framing layer or which corrupts any connection state.
An endpoint that encounters a connection error SHOULD first send a An endpoint that encounters a connection error SHOULD first send a
GOAWAY (Section 6.8) frame with the stream identifier of the last GOAWAY frame (Section 6.8) with the stream identifier of the last
stream that it successfully received from its peer. The GOAWAY frame stream that it successfully received from its peer. The GOAWAY frame
includes an error code that indicates why the connection is includes an error code that indicates why the connection is
terminating. After sending the GOAWAY frame, the endpoint MUST close terminating. After sending the GOAWAY frame, the endpoint MUST close
the TCP connection. the TCP connection.
It is possible that the GOAWAY will not be reliably received by the It is possible that the GOAWAY will not be reliably received by the
receiving endpoint. In the event of a connection error, GOAWAY only receiving endpoint. In the event of a connection error, GOAWAY only
provides a best-effort attempt to communicate with the peer about why provides a best-effort attempt to communicate with the peer about why
the connection is being terminated. the connection is being terminated.
An endpoint can end a connection at any time. In particular, an An endpoint can end a connection at any time. In particular, an
endpoint MAY choose to treat a stream error as a connection error if endpoint MAY choose to treat a stream error as a connection error.
the error is recurrent. Endpoints SHOULD send a GOAWAY frame when Endpoints SHOULD send a GOAWAY frame when ending a connection, as
ending a connection, as long as circumstances permit it. long as circumstances permit it.
5.4.2. Stream Error Handling 5.4.2. Stream Error Handling
A stream error is an error related to a specific stream identifier A stream error is an error related to a specific stream identifier
that does not affect processing of other streams. that does not affect processing of other streams.
An endpoint that detects a stream error sends a RST_STREAM An endpoint that detects a stream error sends a RST_STREAM frame
(Section 6.4) frame that contains the stream identifier of the stream (Section 6.4) that contains the stream identifier of the stream where
where the error occurred. The RST_STREAM frame includes an error the error occurred. The RST_STREAM frame includes an error code that
code that indicates the type of error. indicates the type of error.
A RST_STREAM is the last frame that an endpoint can send on a stream. A RST_STREAM is the last frame that an endpoint can send on a stream.
The peer that sends the RST_STREAM frame MUST be prepared to receive The peer that sends the RST_STREAM frame MUST be prepared to receive
any frames that were sent or enqueued for sending by the remote peer. any frames that were sent or enqueued for sending by the remote peer.
These frames can be ignored, except where they modify connection These frames can be ignored, except where they modify connection
state (such as the state maintained for header compression state (such as the state maintained for header compression
(Section 4.3)). (Section 4.3)).
Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame
for any stream. However, an endpoint MAY send additional RST_STREAM for any stream. However, an endpoint MAY send additional RST_STREAM
skipping to change at page 23, line 16 skipping to change at page 24, line 9
6.1. DATA 6.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of DATA frames (type=0x0) convey arbitrary, variable-length sequences of
octets associated with a stream. One or more DATA frames are used, octets associated with a stream. One or more DATA frames are used,
for instance, to carry HTTP request or response payloads. for instance, to carry HTTP request or response payloads.
The DATA frame defines the following flags: The DATA frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that this frame is the END_STREAM (0x1): Bit 1 being set indicates that this frame is the
last that the endpoint will send for the identified stream. last that the endpoint will send for the identified stream.
Setting this flag causes the stream to enter a "half closed" state Setting this flag causes the stream to enter a "half closed" or
(Section 5.1). "closed" state (Section 5.1).
RESERVED (0x2): Bit 2 is reserved for future use. RESERVED (0x2): Bit 2 is reserved for future use.
DATA frames MUST be associated with a stream. If a DATA frame is DATA frames MUST be associated with a stream. If a DATA frame is
received whose stream identifier field is 0x0, the recipient MUST received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
DATA frames are subject to flow control and can only be sent when a
stream is in the "open" or "half closed (remote)" states.
6.2. HEADERS 6.2. HEADERS
The HEADERS frame (type=0x1) carries name-value pairs. The HEADERS The HEADERS frame (type=0x1) carries name-value pairs. It is used to
is used to open a stream (Section 5.1). Any number of HEADERS frames open a stream (Section 5.1). HEADERS frames can be sent on a stream
can be sent on an existing stream at any time. in the "open" or "half closed (remote)" states.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Priority (31) | |X| Priority (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
HEADERS Frame Payload HEADERS Frame Payload
skipping to change at page 24, line 12 skipping to change at page 24, line 52
Setting this flag causes the stream to enter a "half closed" state Setting this flag causes the stream to enter a "half closed" state
(Section 5.1). (Section 5.1).
RESERVED (0x2): Bit 2 is reserved for future use. RESERVED (0x2): Bit 2 is reserved for future use.
END_HEADERS (0x4): The END_HEADERS bit indicates that this frame END_HEADERS (0x4): The END_HEADERS bit indicates that this frame
ends the sequence of header block fragments necessary to provide a ends the sequence of header block fragments necessary to provide a
complete set of headers. complete set of headers.
The payload for a complete header block is provided by a sequence The payload for a complete header block is provided by a sequence
of HEADERS frames, terminated by a HEADERS frame with the of that starts with a HEADERS frame, followed by zero or more
END_HEADERS flag set. Once the sequence terminates, the payload CONTINUATION frames. The sequence is terminated by a frame with
of all HEADERS frames are concatenated and interpreted as a single the END_HEADERS flag set. Once the sequence terminates, the
block. payload of all HEADERS and CONTINUATION frames are concatenated
and interpreted as a single block.
A HEADERS frame without the END_HEADERS flag set MUST be followed A HEADERS frame without the END_HEADERS flag set MUST be followed
by a HEADERS frame for the same stream. A receiver MUST treat the by a CONTINUATION frame for the same stream. A receiver MUST
receipt of any other type of frame or a frame on a different treat the receipt of any other type of frame or a frame on a
stream as a connection error (Section 5.4.1) of type different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
PRIORITY (0x8): Bit 4 being set indicates that the first four octets PRIORITY (0x8): Bit 4 being set indicates that the first four octets
of this frame contain a single reserved bit and a 31-bit priority; of this frame contain a single reserved bit and a 31-bit priority;
see Section 5.3. If this bit is not set, the four bytes do not see Section 5.3. If this bit is not set, the four bytes do not
appear and the frame only contains a header block fragment. appear and the frame only contains a header block fragment.
The payload of a HEADERS frame contains a header block fragment The payload of a HEADERS frame contains a header block fragment
(Section 4.3). (Section 4.3). A header block that does not fit within a HEADERS
frame is continued in a CONTINUATION frame (Section 6.10).
HEADERS frames MUST be associated with a stream. If a HEADERS frame HEADERS frames MUST be associated with a stream. If a HEADERS frame
is received whose stream identifier field is 0x0, the recipient MUST is received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
The HEADERS frame changes the connection state as defined in The HEADERS frame changes the connection state as described in
Section 4.3. Section 4.3.
6.3. PRIORITY 6.3. PRIORITY
The PRIORITY frame (type=0x2) specifies the sender-advised priority The PRIORITY frame (type=0x2) specifies the sender-advised priority
of a stream. It can be sent at any time for an existing stream. of a stream. It can be sent at any time for an existing stream.
This enables reprioritisation of existing streams. This enables reprioritisation of existing streams.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 25, line 15 skipping to change at page 26, line 8
The payload of a PRIORITY frame contains a single reserved bit and a The payload of a PRIORITY frame contains a single reserved bit and a
31-bit priority. 31-bit priority.
The PRIORITY frame does not define any flags. The PRIORITY frame does not define any flags.
The PRIORITY frame is associated with an existing stream. If a The PRIORITY frame is associated with an existing stream. If a
PRIORITY frame is received with a stream identifier of 0x0, the PRIORITY frame is received with a stream identifier of 0x0, the
recipient MUST respond with a connection error (Section 5.4.1) of recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
The PRIORITY frame can be sent on a stream in any of the "reserved
(remote)", "open", "half-closed (local)", or "half closed (remote)"
states, though it cannot be sent between consecutive frames that
comprise a single header block (Section 4.3). Note that this frame
could arrive after processing or frame sending has completed, which
would cause it to have no effect. For a stream that is in the "half
closed (remote)" state, this frame can only affect processing of the
stream and not frame transmission.
6.4. RST_STREAM 6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for abnormal termination of a The RST_STREAM frame (type=0x3) allows for abnormal termination of a
stream. When sent by the initiator of a stream, it indicates that stream. When sent by the initiator of a stream, it indicates that
they wish to cancel the stream or that an error condition has they wish to cancel the stream or that an error condition has
occurred. When sent by the receiver of a stream, it indicates that occurred. When sent by the receiver of a stream, it indicates that
either the receiver is rejecting the stream, requesting that the either the receiver is rejecting the stream, requesting that the
stream be cancelled or that an error condition has occurred. stream be cancelled or that an error condition has occurred.
0 1 2 3 0 1 2 3
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The RST_STREAM frame fully terminates the referenced stream and The RST_STREAM frame fully terminates the referenced stream and
causes it to enter the closed state. After receiving a RST_STREAM on causes it to enter the closed state. After receiving a RST_STREAM on
a stream, the receiver MUST NOT send additional frames for that a stream, the receiver MUST NOT send additional frames for that
stream. However, after sending the RST_STREAM, the sending endpoint stream. However, after sending the RST_STREAM, the sending endpoint
MUST be prepared to receive and process additional frames sent on the MUST be prepared to receive and process additional frames sent on the
stream that might have been sent by the peer prior to the arrival of stream that might have been sent by the peer prior to the arrival of
the RST_STREAM. the RST_STREAM.
RST_STREAM frames MUST be associated with a stream. If a RST_STREAM RST_STREAM frames MUST be associated with a stream. If a RST_STREAM
frame is received whose stream identifier field is 0x0 the recipient frame is received with a stream identifier of 0x0, the recipient MUST
MUST respond with a connection error (Section 5.4.1) of type treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
RST_STREAM frames MUST NOT be sent for a stream in the "idle" state.
If a RST_STREAM frame identifying an idle stream is received, the
recipient MUST treat this as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR.
6.5. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that The SETTINGS frame (type=0x4) conveys configuration parameters that
affect how endpoints communicate. The parameters are either affect how endpoints communicate. The parameters are either
constraints on peer behavior or preferences. constraints on peer behavior or preferences.
SETTINGS frames MUST be sent at the start of a connection, and MAY be SETTINGS frames MUST be sent at the start of a connection, and MAY be
sent at any other time by either endpoint over the lifetime of the sent at any other time by either endpoint over the lifetime of the
connection. connection.
Implementations MUST support all of the settings defined by this Implementations MUST support all of the settings defined by this
specification and MAY support additional settings defined by specification and MAY support additional settings defined by
extensions. Unsupported or unrecognized settings MUST be ignored. extensions. Unsupported or unrecognized settings MUST be ignored.
New settings MUST NOT be defined or implemented in a way that New settings MUST NOT be defined or implemented in a way that
requires endpoints to understand them in order to communicate requires endpoints to understand them in order to communicate
successfully. successfully.
A SETTINGS frame is not required to include every defined setting; Each setting in a SETTINGS frame replaces the existing value for that
senders can include only those parameters for which it has accurate setting. Settings are processed in the order in which they appear,
values and a need to convey. When multiple parameters are sent, they and a receiver of a SETTINGS frame does not need to maintain any
SHOULD be sent in order of numerically lowest ID to highest ID. A state other than the current value of settings. Therefore, the value
single SETTINGS frame MUST NOT contain multiple values for the same of a setting is the last value that is seen by a receiver. This
ID. If the receiver of a SETTINGS frame discovers multiple values permits the inclusion of the same settings multiple times in the same
for the same ID, it MUST ignore all values for that ID except the SETTINGS frame, though doing so does nothing other than waste
first one. connection capacity.
Over the lifetime of a connection, an endpoint MAY send multiple
SETTINGS frames containing previously unspecified parameters or new
values for parameters whose values have already been established.
Only the most recent provided setting value applies.
The SETTINGS frame does not define any flags. The SETTINGS frame does not define any flags.
SETTINGS frames always apply to a connection, never a single stream. SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a settings frame MUST be zero. If an The stream identifier for a settings frame MUST be zero. If an
endpoint receives a SETTINGS frame whose stream identifier field is endpoint receives a SETTINGS frame whose stream identifier field is
anything other than 0x0, the endpoint MUST respond with a connection anything other than 0x0, the endpoint MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
The SETTINGS frame affects connection state. A badly formed or The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error incomplete SETTINGS frame MUST be treated as a connection error
(Section 5.4.1). (Section 5.4.1) of type PROTOCOL_ERROR.
6.5.1. Setting Format 6.5.1. Setting Format
The payload of a SETTINGS frame consists of zero or more settings. The payload of a SETTINGS frame consists of zero or more settings.
Each setting consists of an 8-bit reserved field, an unsigned 24-bit Each setting consists of an 8-bit reserved field, an unsigned 24-bit
setting identifier, and an unsigned 32-bit value. setting identifier, and an unsigned 32-bit value.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 27, line 32 skipping to change at page 28, line 32
permits the receiver to create. By default there is no limit. It permits the receiver to create. By default there is no limit. It
is recommended that this value be no smaller than 100, so as to is recommended that this value be no smaller than 100, so as to
not unnecessarily limit parallelism. not unnecessarily limit parallelism.
SETTINGS_INITIAL_WINDOW_SIZE (7): indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (7): indicates the sender's initial
window size (in bytes) for stream level flow control. window size (in bytes) for stream level flow control.
This settings affects the window size of all streams, including This settings affects the window size of all streams, including
existing streams, see Section 6.9.2. existing streams, see Section 6.9.2.
SETTINGS_FLOW_CONTROL_OPTIONS (10): indicates that streams directed SETTINGS_FLOW_CONTROL_OPTIONS (10): indicates flow control options.
to the sender will not be subject to flow control. The least The least significant bit (0x1) of the value is set to indicate
significant bit (0x1) of the value is set to indicate that new that the sender has disabled all flow control. This bit cannot be
streams are not flow controlled. All other bits are reserved. cleared once set, see Section 6.9.4.
This setting applies to all streams, including existing streams.
These bits cannot be cleared once set, see Section 6.9.4. All bits other than the least significant are reserved.
6.6. PUSH_PROMISE 6.6. PUSH_PROMISE
The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint
in advance of streams the sender intends to initiate. The in advance of streams the sender intends to initiate. The
PUSH_PROMISE frame includes the unsigned 31-bit identifier of the PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
stream the endpoint plans to create along with a minimal set of stream the endpoint plans to create along with a minimal set of
headers that provide additional context for the stream. Section 8.2 headers that provide additional context for the stream. Section 8.2
contains a thorough description of the use of PUSH_PROMISE frames. contains a thorough description of the use of PUSH_PROMISE frames.
skipping to change at page 29, line 8 skipping to change at page 30, line 8
Promised streams are not required to be used in order promised. The Promised streams are not required to be used in order promised. The
PUSH_PROMISE only reserves stream identifiers for later use. PUSH_PROMISE only reserves stream identifiers for later use.
Recipients of PUSH_PROMISE frames can choose to reject promised Recipients of PUSH_PROMISE frames can choose to reject promised
streams by returning a RST_STREAM referencing the promised stream streams by returning a RST_STREAM referencing the promised stream
identifier back to the sender of the PUSH_PROMISE. identifier back to the sender of the PUSH_PROMISE.
The PUSH_PROMISE frame modifies the connection state as defined in The PUSH_PROMISE frame modifies the connection state as defined in
Section 4.3. Section 4.3.
A PUSH_PROMISE frame modifies the connection state in two ways. The
inclusion of a header block (Section 4.3) potentially modifies the
compression state. PUSH_PROMISE also reserves a stream for later
use, causing the promised stream to enter the "reserved" state. A
sender MUST NOT send a PUSH_PROMISE on a stream unless that stream is
either "open" or "half closed (remote)"; the sender MUST ensure that
the promised stream is a valid choice for a new stream identifier
(Section 5.1.1) (that is, the promised stream MUST be in the "idle"
state).
Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame
causes the stream state to become indeterminate. A receiver MUST
treat the receipt of a PUSH_PROMISE on a stream that is neither
"open" nor "half-closed (local)" as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST
treat the receipt of a PUSH_PROMISE that promises an illegal stream
identifier (Section 5.1.1) (that is, an identifier for a stream that
is not currently in the "idle" state) as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
6.7. PING 6.7. PING
The PING frame (type=0x6) is a mechanism for measuring a minimal The PING frame (type=0x6) is a mechanism for measuring a minimal
round-trip time from the sender, as well as determining whether an round-trip time from the sender, as well as determining whether an
idle connection is still functional. PING frames can be sent from idle connection is still functional. PING frames can be sent from
any endpoint. any endpoint.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 30, line 33 skipping to change at page 32, line 4
connection so that the remote can know whether a stream has been connection so that the remote can know whether a stream has been
partially processed or not. For example, if an HTTP client sends a partially processed or not. For example, if an HTTP client sends a
POST at the same time that a server closes a connection, the client POST at the same time that a server closes a connection, the client
cannot know if the server started to process that POST request if the cannot know if the server started to process that POST request if the
server does not send a GOAWAY frame to indicate where it stopped server does not send a GOAWAY frame to indicate where it stopped
working. An endpoint might choose to close a connection without working. An endpoint might choose to close a connection without
sending GOAWAY for misbehaving peers. sending GOAWAY for misbehaving peers.
After sending a GOAWAY frame, the sender can discard frames for new After sending a GOAWAY frame, the sender can discard frames for new
streams. However, any frames that alter connection state cannot be streams. However, any frames that alter connection state cannot be
completely ignored. For instance, HEADERS and PUSH_PROMISE frames completely ignored. For instance, HEADERS, PUSH_PROMISE and
MUST be minimally processed to ensure a consistent compression state CONTINUATION frames MUST be minimally processed to ensure a
(see Section 4.3). consistent compression state (see Section 4.3); similarly DATA frames
MUST be counted toward the connection flow control window.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Last-Stream-ID (31) | |X| Last-Stream-ID (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Additional Debug Data (*) | | Additional Debug Data (*) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
skipping to change at page 31, line 18 skipping to change at page 32, line 37
numbered stream identifier for which the sender of the GOAWAY frame numbered stream identifier for which the sender of the GOAWAY frame
has received frames on and might have taken some action on. All has received frames on and might have taken some action on. All
streams up to and including the identified stream might have been streams up to and including the identified stream might have been
processed in some way. The last stream identifier is set to 0 if no processed in some way. The last stream identifier is set to 0 if no
streams were processed. streams were processed.
Note: In this case, "processed" means that some data from the Note: In this case, "processed" means that some data from the
stream was passed to some higher layer of software that might have stream was passed to some higher layer of software that might have
taken some action as a result. taken some action as a result.
If a connection terminates without a GOAWAY frame, this value is
effectively the highest stream identifier.
On streams with lower or equal numbered identifiers that were not On streams with lower or equal numbered identifiers that were not
closed completely prior to the connection being closed, re-attempting closed completely prior to the connection being closed, re-attempting
requests, transactions, or any protocol activity is not possible requests, transactions, or any protocol activity is not possible
(with the exception of idempotent actions like HTTP GET, PUT, or (with the exception of idempotent actions like HTTP GET, PUT, or
DELETE). Any protocol activity that uses higher numbered streams can DELETE). Any protocol activity that uses higher numbered streams can
be safely retried using a new connection. be safely retried using a new connection.
Activity on streams numbered lower or equal to the last stream Activity on streams numbered lower or equal to the last stream
identifier might still complete successfully. The sender of a GOAWAY identifier might still complete successfully. The sender of a GOAWAY
frame might gracefully shut down a connection by sending a GOAWAY frame might gracefully shut down a connection by sending a GOAWAY
skipping to change at page 32, line 28 skipping to change at page 33, line 51
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
WINDOW_UPDATE Payload Format WINDOW_UPDATE Payload Format
The payload of a WINDOW_UPDATE frame is one reserved bit, plus an The payload of a WINDOW_UPDATE frame is one reserved bit, plus an
unsigned 31-bit integer indicating the number of bytes that the unsigned 31-bit integer indicating the number of bytes that the
sender can transmit in addition to the existing flow control window. sender can transmit in addition to the existing flow control window.
The legal range for the increment to the flow control window is 1 to The legal range for the increment to the flow control window is 1 to
2^31 - 1 (0x7fffffff) bytes. 2^31 - 1 (0x7fffffff) bytes.
The WINDOW_UPDATE frame defines the following flags: The WINDOW_UPDATE frame does not define any flags.
END_FLOW_CONTROL (0x1): Bit 1 being set indicates that flow control
for the identified stream or connection has been ended; subsequent
frames do not need to be flow controlled.
The WINDOW_UPDATE frame can be specific to a stream or to the entire The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the
END_STREAM flag. This means that a receiver could receive a
WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream.
A receiver MUST NOT treat this as an error, see Section 5.1.
A receiver that receives a flow controlled frame MUST always account
for its contribution against the connection flow control window,
unless the receiver treats this as a connection error
(Section 5.4.1). This is necessary even if the frame is in error.
Since the sender counts the frame toward the flow control window, if
the receiver does not, the flow control window at sender and receiver
can become different.
6.9.1. The Flow Control Window 6.9.1. The Flow Control Window
Flow control in HTTP/2.0 is implemented using a window kept by each Flow control in HTTP/2.0 is implemented using a window kept by each
sender on every stream. The flow control window is a simple integer sender on every stream. The flow control window is a simple integer
value that indicates how many bytes of data the sender is permitted value that indicates how many bytes of data the sender is permitted
to transmit; as such, its size is a measure of the buffering to transmit; as such, its size is a measure of the buffering
capability of the receiver. capability of the receiver.
Two flow control windows are applicable; the stream flow control Two flow control windows are applicable: the stream flow control
window and the connection flow control window. The sender MUST NOT window and the connection flow control window. The sender MUST NOT
send a flow controlled frame with a length that exceeds the space send a flow controlled frame with a length that exceeds the space
available in either of the flow control windows advertised by the available in either of the flow control windows advertised by the
receiver. Frames with zero length with the END_STREAM flag set (for receiver. Frames with zero length with the END_STREAM flag set (for
example, an empty data frame) MAY be sent if there is no available example, an empty data frame) MAY be sent if there is no available
space in either flow control window. space in either flow control window.
For flow control calculations, the 8 byte frame header is not For flow control calculations, the 8 byte frame header is not
counted. counted.
skipping to change at page 34, line 12 skipping to change at page 35, line 45
windows that it maintains by the difference between the new value and windows that it maintains by the difference between the new value and
the old value. A SETTINGS frame cannot alter the connection flow the old value. A SETTINGS frame cannot alter the connection flow
control window. control window.
A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available
space in a flow control window to become negative. A sender MUST space in a flow control window to become negative. A sender MUST
track the negative flow control window, and MUST NOT send new flow track the negative flow control window, and MUST NOT send new flow
controlled frames until it receives WINDOW_UPDATE frames that cause controlled frames until it receives WINDOW_UPDATE frames that cause
the flow control window to become positive. the flow control window to become positive.
For example, if the client sends 64KB immediately on connection For example, if the client sends 60KB immediately on connection
establishment, and the server sets the initial window size to be establishment, and the server sets the initial window size to be
16KB, the client will recalculate the available flow control window 16KB, the client will recalculate the available flow control window
to be -48KB on receipt of the SETTINGS frame. The client retains a to be -44KB on receipt of the SETTINGS frame. The client retains a
negative flow control window until WINDOW_UPDATE frames restore the negative flow control window until WINDOW_UPDATE frames restore the
window to being positive, after which the client can resume sending. window to being positive, after which the client can resume sending.
6.9.3. Reducing the Stream Window Size 6.9.3. Reducing the Stream Window Size
A receiver that wishes to use a smaller flow control window than the A receiver that wishes to use a smaller flow control window than the
current size can send a new SETTINGS frame. However, the receiver current size can send a new SETTINGS frame. However, the receiver
MUST be prepared to receive data that exceeds this window size, since MUST be prepared to receive data that exceeds this window size, since
the sender might send data that exceeds the lower limit prior to the sender might send data that exceeds the lower limit prior to
processing the SETTINGS frame. processing the SETTINGS frame.
skipping to change at page 34, line 49 skipping to change at page 36, line 35
sent in the SETTINGS. sent in the SETTINGS.
6.9.4. Ending Flow Control 6.9.4. Ending Flow Control
After a receiver reads in a frame that marks the end of a stream (for After a receiver reads in a frame that marks the end of a stream (for
example, a data stream with a END_STREAM flag set), it MUST cease example, a data stream with a END_STREAM flag set), it MUST cease
transmission of WINDOW_UPDATE frames for that stream. A sender is transmission of WINDOW_UPDATE frames for that stream. A sender is
not obligated to maintain the available flow control window for not obligated to maintain the available flow control window for
streams that it is no longer sending on. streams that it is no longer sending on.
Flow control can be disabled for all streams on the connection using Flow control can be disabled the entire connection using the
the SETTINGS_FLOW_CONTROL_OPTIONS setting. An implementation that SETTINGS_FLOW_CONTROL_OPTIONS setting. This setting ends all forms
does not wish to perform stream flow control can use this in the of flow control. An implementation that does not wish to perform
initial SETTINGS exchange. flow control can use this in the initial SETTINGS exchange.
Flow control can be disabled for an individual stream or the overall
connection by sending a WINDOW_UPDATE with the END_FLOW_CONTROL flag
set. The payload of a WINDOW_UPDATE frame that has the
END_FLOW_CONTROL flag set is ignored.
Flow control cannot be enabled again once disabled. Any attempt to Flow control cannot be enabled again once disabled. Any attempt to
re-enable flow control - by sending a WINDOW_UPDATE or by clearing re-enable flow control - by sending a WINDOW_UPDATE or by clearing
the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
rejected with a FLOW_CONTROL_ERROR error code. rejected with a FLOW_CONTROL_ERROR error code.
6.10. CONTINUATION
The CONTINUATION frame (type=0xA) is used to continue a sequence of
header block fragments (Section 4.3). Any number of CONTINUATION
frames can be sent on an existing stream, as long as the preceding
frame on the same stream is one of HEADERS, PUSH_PROMISE or
CONTINUATION.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Block Fragment (*) ...
+---------------------------------------------------------------+
CONTINUATION Frame Payload
The CONTINUATION frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that this frame is the
last that the endpoint will send for the identified stream.
Setting this flag causes the stream to enter a "half closed" or
"closed" state (Section 5.1).
END_HEADERS (0x2): The END_HEADERS bit indicates that this frame
ends the sequence of header block fragments necessary to provide a
complete set of headers.
The payload for a complete header block is provided by a sequence
that starts with a HEADERS or PUSH_PROMISE frame and zero or more
CONTINUATION frames, terminated by a HEADERS, PUSH_PROMISE, or
CONTINUATION frame with the END_HEADERS flag set. Once the
sequence terminates, the payload of all frames in the sequence are
concatenated and interpreted as a single block.
A HEADERS, PUSH_PROMISE, or CONTINUATION frame without the
END_HEADERS flag set MUST be followed by a CONTINUATION frame for
the same stream. A receiver MUST treat the receipt of any other
type of frame or a frame on a different stream as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
The payload of a CONTINUATION frame contains a header block fragment
(Section 4.3).
The CONTINUATION frame changes the connection state as defined in
Section 4.3.
CONTINUATION frames MUST be associated with a stream. If a
CONTINUATION frame is received whose stream identifier field is 0x0,
the recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR.
header block fragments (Section 4.3). A CONTINUATION frame MUST be
preceded by one of HEADERS, PUSH_PROMISE or CONTINUATION frame. A
recipient that observes violation of this rule MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR.
7. Error Codes 7. Error Codes
Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
frames to convey the reasons for the stream or connection error. frames to convey the reasons for the stream or connection error.
Error codes share a common code space. Some error codes only apply Error codes share a common code space. Some error codes only apply
to specific conditions and have no defined semantics in certain frame to specific conditions and have no defined semantics in certain frame
types. types.
The following error codes are defined: The following error codes are defined:
skipping to change at page 35, line 48 skipping to change at page 38, line 37
FLOW_CONTROL_ERROR (3): The endpoint detected that its peer violated FLOW_CONTROL_ERROR (3): The endpoint detected that its peer violated
the flow control protocol. the flow control protocol.
STREAM_CLOSED (5): The endpoint received a frame after a stream was STREAM_CLOSED (5): The endpoint received a frame after a stream was
half closed. half closed.
FRAME_TOO_LARGE (6): The endpoint received a frame that was larger FRAME_TOO_LARGE (6): The endpoint received a frame that was larger
than the maximum size that it supports. than the maximum size that it supports.
REFUSED_STREAM (7): The endpoint refuses the stream prior to REFUSED_STREAM (7): The endpoint refuses the stream prior to
performing any application processing, see Section 8.1.5 for performing any application processing, see Section 8.1.3 for
details. details.
CANCEL (8): Used by the endpoint to indicate that the stream is no CANCEL (8): Used by the endpoint to indicate that the stream is no
longer needed. longer needed.
COMPRESSION_ERROR (9): The endpoint is unable to maintain the COMPRESSION_ERROR (9): The endpoint is unable to maintain the
compression context for the connection. compression context for the connection.
8. HTTP Message Exchanges 8. HTTP Message Exchanges
skipping to change at page 36, line 30 skipping to change at page 39, line 16
[HTTP-p7]) apply with the changes in the sections below. [HTTP-p7]) apply with the changes in the sections below.
8.1. HTTP Request/Response Exchange 8.1. HTTP Request/Response Exchange
A client sends an HTTP request on a new stream, using a previously A client sends an HTTP request on a new stream, using a previously
unused stream identifier (Section 5.1.1). A server sends an HTTP unused stream identifier (Section 5.1.1). A server sends an HTTP
response on the same stream as the request. response on the same stream as the request.
An HTTP request or response each consist of: An HTTP request or response each consist of:
o one contiguous sequence of HEADERS frames; 1. a HEADERS frame;
o zero or more DATA frames; and 2. one contiguous sequence of zero or more CONTINUATION frames;
o optionally, a contiguous sequence of HEADERS frames 3. zero or more DATA frames; and
4. optionally, a contiguous sequence that starts with a HEADERS
frame, followed by zero or more CONTINUATION frames.
The last frame in the sequence bears an END_STREAM flag. The last frame in the sequence bears an END_STREAM flag.
Other frames, including HEADERS, MAY be interspersed with these Other frames MAY be interspersed with these frames, but those frames
frames, but those frames do not carry HTTP semantics. do not carry HTTP semantics. In particular, HEADERS frames (and any
CONTINUATION frames that follow) other than the first and optional
last frames in this sequence do not carry HTTP semantics.
Trailing header fields are carried in a header block that also Trailing header fields are carried in a header block that also
terminates the stream. That is, a sequence of HEADERS frames that terminates the stream. That is, a sequence starting with a HEADERS
carries an END_STREAM flag on the last frame. Header blocks after frame, followed by zero or more CONTINUATION frames, that carries an
the first that do not terminate the stream are not part of an HTTP END_STREAM flag on the last frame. Header blocks after the first
request or response. that do not terminate the stream are not part of an HTTP request or
response.
An HTTP request/response exchange fully consumes a single stream. A An HTTP request/response exchange fully consumes a single stream. A
request starts with the HEADERS frame that puts the stream into an request starts with the HEADERS frame that puts the stream into an
"open" state and ends with a frame bearing END_STREAM, which causes "open" state and ends with a frame bearing END_STREAM, which causes
the stream to become "half closed" for the client. A response starts the stream to become "half closed" for the client. A response starts
with a HEADERS frame and ends with a frame bearing END_STREAM, which with a HEADERS frame and ends with a frame bearing END_STREAM, which
places the stream in the "closed" state. places the stream in the "closed" state.
8.1.1. Examples 8.1.1. Examples
For example, an HTTP GET request that includes request header fields For example, an HTTP GET request that includes request header fields
and no body, is transmitted as a single contiguous sequence of and no body, is transmitted as a single contiguous sequence of
HEADERS frames containing the serialized block of request header HEADERS frames containing the serialized block of request header
fields. The last HEADERS frame in the sequence has both the fields. The last HEADERS frame in the sequence has both the
END_HEADERS and END_STREAM flag set: END_HEADERS and END_STREAM flag set:
GET /resource HTTP/1.1 HEADERS GET /resource HTTP/1.1 HEADERS
Host: example.org ==> + END_STREAM Host: example.org ==> + END_STREAM
Accept: image/jpeg + END_HEADERS Accept: image/jpeg + END_HEADERS
:method = get :method = GET
:scheme = https :scheme = https
:host = example.org :host = example.org
:path = /resource :path = /resource
accept = image/jpeg accept = image/jpeg
Similarly, a response that includes only response header fields is Similarly, a response that includes only response header fields is
transmitted as a sequence of HEADERS frames containing the serialized transmitted as a sequence of HEADERS frames containing the serialized
block of response header fields. The last HEADERS frame in the block of response header fields. The last HEADERS frame in the
sequence has both the END_HEADERS and END_STREAM flag set: sequence has both the END_HEADERS and END_STREAM flag set:
HTTP/1.1 204 No Content HEADERS HTTP/1.1 204 No Content HEADERS
Content-Length: 0 ===> + END_STREAM Content-Length: 0 ===> + END_STREAM
+ END_HEADERS + END_HEADERS
:status = 204 :status = 204
content-length: 0 content-length: 0
An HTTP POST request that includes request header fields and payload An HTTP POST request that includes request header fields and payload
data is transmitted as one or more HEADERS frames containing the data is transmitted as one HEADERS frame, followed by zero or more
request headers followed by one or more DATA frames, with the last CONTINUATION frames, containing the request headers followed by one
HEADERS frame having the END_HEADERS flag set and the final DATA or more DATA frames, with the last CONTINUATION (or HEADERS) frame
frame having the END_STREAM flag set: having the END_HEADERS flag set and the final DATA frame having the
END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM Host: example.org ==> - END_STREAM
Content-Type: image/jpeg + END_HEADERS Content-Type: image/jpeg + END_HEADERS
Content-Length: 123 :method = post Content-Length: 123 :method = POST
:scheme = https :scheme = https
{binary data} :host = example.org {binary data} :host = example.org
:path = /resource :path = /resource
content-type = image/jpeg content-type = image/jpeg
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
A response that includes header fields and payload data is A response that includes header fields and payload data is
transmitted as one or more HEADERS frames followed by one or more transmitted as a HEADERS frame, followed by zero or more CONTINUATION
DATA frames, with the last DATA frame in the sequence having the frames, followed by one or more DATA frames, with the last DATA frame
END_STREAM flag set: in the sequence having the END_STREAM flag set:
HTTP/1.1 200 OK HEADERS HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS Content-Length: 123 + END_HEADERS
:status = 200 :status = 200
{binary data} content-type = image/jpeg {binary data} content-type = image/jpeg
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
Trailing header fields are sent as a header block after both the Trailing header fields are sent as a header block after both the
request or response header block and all the DATA frames have been request or response header block and all the DATA frames have been
sent. The sequence of HEADERS frames that bears the trailers sent. The sequence of HEADERS/CONTINUATION frames that bears the
includes a terminal frame that has both END_HEADERS and END_STREAM trailers includes a terminal frame that has both END_HEADERS and
flags set. END_STREAM flags set.
HTTP/1.1 200 OK HEADERS HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ===> - END_STREAM Content-Type: image/jpeg ===> - END_STREAM
Content-Length: 123 + END_HEADERS Content-Length: 123 + END_HEADERS
TE: trailers :status = 200 TE: trailers :status = 200
123 content-type = image/jpeg 123 content-type = image/jpeg
{binary data} content-length = 123 {binary data} content-length = 123
0 0
Foo: bar DATA Foo: bar DATA
- END_STREAM - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo: bar foo: bar
8.1.2. Request Header Fields 8.1.2. HTTP Header Fields
The definitions of the request header fields are largely unchanged
relative to HTTP/1.1, with a few notable exceptions:
o The HTTP/1.1 request-line has been split into two separate header
fields named :method and :path, whose values specify the HTTP
method for the request and the request-target, respectively. The
HTTP-version component of the request-line is removed entirely
from the headers.
o The host and optional port portions of the request URI (see
[RFC3986], Section 3.2), are specified using the new :host header
field. [[anchor13: Ed. Note: it needs to be clarified whether or
not this replaces the existing HTTP/1.1 Host header.]]
o A new :scheme header field has been added to specify the scheme
portion of the request-target (e.g. "https")
o All header field names MUST be lowercased, and the definitions of HTTP/2.0 request and response header fields carry information as a
all header field names defined by HTTP/1.1 are updated to be all series of key-value pairs. This includes the target URI for the
lowercase. request, the status code for the response, as well as HTTP header
fields.
o The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer- HTTP header field names are strings of ASCII characters that are
Encoding header fields are no longer valid and MUST NOT be sent. compared in a case-insensitive fashion. Note that header compression
[[anchor14: Ed. Note: And "TE" I presume?]] could cause case information to be lost.
All HTTP Requests MUST include the ":method", ":path", ":host", and The semantics of HTTP header fields are not altered by this
":scheme" header fields. specification, though header fields relating to connection management
or request framing are no longer necessary. An HTTP/2.0 request MUST
NOT include any of the following header fields: Connection, Host,
Keep-Alive, Proxy-Connection, TE, Transfer-Encoding, and Upgrade. A
server MUST treat the presence of any of these header fields as a
stream error (Section 5.4.2) of type PROTOCOL_ERROR.
Header fields whose names begin with ":" (whether defined in this 8.1.2.1. Request Header Fields
document or future extensions to this document) MUST appear before
any other header fields. [[anchor15: Ed. Note: This requirement is
currently pending review. Consider it "on hold" for the moment.]]
All HTTP Requests that include a body SHOULD include the "content- HTTP/2.0 defines a number of headers starting with a ':' character
length" header field. If a server receives a request where the sum that carry information about the request target:
of the DATA frame payload lengths does not equal the value of the
"content-length" header field, the server MUST return a 400 (Bad
Request) error.
If a client omits a mandatory header field from the request, the o The ":method" header field includes the HTTP method ([HTTP-p2],
server MUST reply with a HTTP 400 Bad Request reply. Section 4).
8.1.3. Response Header Fields o The ":scheme" header field includes the scheme portion of the
target URI ([RFC3986], Section 3.1).
The definitions of the response header fields are largely unchanged o The ":host" header field includes the authority portion of the
relative to HTTP/1.1, with a few notable exceptions: target URI ([RFC3986], Section 3.2).
o The response status line has been reduced to a single ":status" o The ":path" header field includes the path and query parts of the
header field whose value specifies only the numeric response target URI (the "path-absolute" production from [RFC3986] and
status code. The status text component of the HTTP/1.1 response optionally a '?' character followed by the "query" production, see
has been dropped entirely. [RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field
MUST NOT be empty; URIs that do not contain a path component MUST
include a value of '/', unless the request is an OPTIONS request
for '*', in which case the ":path" header field MUST include '*'.
o The response MUST contain exactly one :status header field with All HTTP/2.0 requests MUST include exactly one valid value for all of
exactly one response status value. If the client receives an HTTP these header fields. An intermediary MUST ensure that requests that
response that does not include the :status field, or provides it forwards are correct. A server MUST treat the absence of any of
multiple response status code values, it MUST respond with a these header fields, presence of multiple values, or an invalid value
stream error (Section 5.4.2) of type PROTOCOL_ERROR. as a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
o All header field names MUST be lowercased, and the definitions of HTTP/2.0 does not define a way to carry the version identifier that
all header field names defined by HTTP/1.1 are updated to be all is included in the HTTP/1.1 request line.
lowercase.
o The Connection, Keep-Alive, Proxy-Connection, and Transfer- All HTTP Requests that include a body can include a "content-length"
Encoding header fields are not valid and MUST NOT be sent. header field. If a server receives a request where the sum of the
DATA frame payload lengths does not equal the value of the
"content-length" header field, the server MUST return a 400 (Bad
Request) error.
Header fields whose names begin with ":" (whether defined in this 8.1.2.2. Response Header Fields
document or future extensions to this document) MUST appear before
any other header fields. [[anchor16: Ed. Note: This requirement is
currently pending review. Consider it "on hold" for the moment.]]
8.1.4. GZip Content-Encoding A single ":status" header field is defined that carries the HTTP
status code field (see [HTTP-p2], Section 6). This header field MUST
be included in all responses. An intermediary MUST ensure that it
does not forward responses with absent or invalid values. A client
MUST treat the absence of the ":status"" header field, the presence
of multiple values, or an invalid value as a stream error
(Section 5.4.2) of type PROTOCOL_ERROR.
Clients MUST support gzip compression for HTTP response bodies. HTTP/2.0 does not define a way to carry the version or reason phrase
Regardless of the value of the accept-encoding header field, a server that is included in an HTTP/1.1 status line.
MAY send responses with gzip or deflate encoding. A compressed
response MUST still bear an appropriate content-encoding header
field.
8.1.5. Request Reliability Mechanisms in HTTP/2.0 8.1.3. Request Reliability Mechanisms in HTTP/2.0
In HTTP/1.1, an HTTP client is unable to retry a non-idempotent In HTTP/1.1, an HTTP client is unable to retry a non-idempotent
request when an error occurs, because there is no means to determine request when an error occurs, because there is no means to determine
the nature of the error. It is possible that some server processing the nature of the error. It is possible that some server processing
occurred prior to the error, which could result in undesirable occurred prior to the error, which could result in undesirable
effects if the request were reattempted. effects if the request were reattempted.
HTTP/2.0 provides two mechanisms for providing a guarantee to a HTTP/2.0 provides two mechanisms for providing a guarantee to a
client that a request has not been processed: client that a request has not been processed:
skipping to change at page 41, line 29 skipping to change at page 44, line 15
process the originally requested resource. process the originally requested resource.
Pushing additional resources is optional, and is negotiated only Pushing additional resources is optional, and is negotiated only
between individual endpoints. For instance, an intermediary could between individual endpoints. For instance, an intermediary could
receive pushed resources from the server but is not required to receive pushed resources from the server but is not required to
forward those on to the client. How to make use of the pushed forward those on to the client. How to make use of the pushed
resources is up to that intermediary. Equally, the intermediary resources is up to that intermediary. Equally, the intermediary
might choose to push additional resources to the client, without any might choose to push additional resources to the client, without any
action taken by the server. action taken by the server.
8.2.1. Push Requests
Server push is semantically equivalent to a server responding to a Server push is semantically equivalent to a server responding to a
GET request for that resource. The PUSH_PROMISE frame, or frames, request. The PUSH_PROMISE frame, or frames, sent by the server
sent by the server includes a header block that contains the request includes a header block that contains a complete set of request
headers that the server has assumed. headers that the server attributes to the request. It is not
possible to push a response to a request that includes a request
body.
Pushed resources are always associated with an explicit request from Pushed resources are always associated with an explicit request from
a client. The PUSH_PROMISE frames sent by the server are sent on the a client. The PUSH_PROMISE frames sent by the server are sent on the
stream created for the original request. The PUSH_PROMSE frame stream created for the original request. The PUSH_PROMISE frame
includes a promised stream identifier, chosen from the stream includes a promised stream identifier, chosen from the stream
identifiers available to the server (see Section 5.1.1). Any header identifiers available to the server (see Section 5.1.1).
fields that are not specified in the PUSH_PROMISE frames sent by the
server are inherited from the original request sent by the client.
The header fields in PUSH_PROMISE MUST include the ":scheme", ":host"
and ":path" header fields that identify the resource that is being
pushed. A PUSH_PROMISE always implies an HTTP method of GET. If a
client receives a PUSH_PROMISE that does not include these header
fields, or a value for the ":method" header field, it MUST respond
with a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed resource on a new, server-initiated stream that uses the
promised stream identifier. This stream is already implicitly "half
closed" to the client (Section 5.1). The server uses this stream to
transmit an HTTP response, using the same sequence of frames as
defined in Section 8.1.
Once a client receives a PUSH_PROMISE frame and chooses to accept the The header fields in PUSH_PROMISE and any subsequent CONTINUATION
pushed resource, the client SHOULD NOT issue any subsequent GET frames MUST be a valid and complete set of request headers
requests for the promised resource until after the promised stream (Section 8.1.2.1). The server MUST include a method in the ":method"
has closed. header field that is safe (see [HTTP-p2], Section 4.2.1). If a
client receives a PUSH_PROMISE that does not include a complete and
valid set of header fields, or the ":method" header field identifies
a method that is not safe, it MUST respond with a stream error
(Section 5.4.2) of type PROTOCOL_ERROR.
The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to
sending any HEADERS or DATA frames that reference the promised sending any frames that reference the promised resources. This
resources. This avoids a race where clients issue requests for avoids a race where clients issue requests for resources prior to
resources prior to receiving any PUSH_PROMISE frames. receiving any PUSH_PROMISE frames.
For example, if the server receives a request for a document For example, if the server receives a request for a document
containing embedded links to multiple image files, and the server containing embedded links to multiple image files, and the server
chooses to push those additional images to the client, sending push chooses to push those additional images to the client, sending push
promises before the DATA frames that contain the image links ensure promises before the DATA frames that contain the image links ensure
that the client is able to see the promises before discovering the that the client is able to see the promises before discovering the
resources. Likewise, if the server pushes resources referenced by resources. Similarly, if the server pushes resources referenced by
the header block (for instance, in Link header fields), sending the the header block (for instance, in Link header fields), sending the
push promises before sending the header block ensures that clients do push promises before sending the header block ensures that clients do
not request those resources. not request those resources.
PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE
frames can be sent by the server on any stream that was opened by the frames can be sent by the server on any stream that was opened by the
client. They MUST be sent on a stream that is in either the "open" client. They MUST be sent on a stream that is in either the "open"
or "half closed (remote)" to the server. PUSH_PROMISE frames can be or "half closed (remote)" to the server. PUSH_PROMISE frames are
interspersed within the frames that comprise response, with the interspersed with the frames that comprise a response, though they
exception that they cannot be interspersed with HEADERS frames that cannot be interspersed with HEADERS and CONTINUATION frames that
comprise a single header block. comprise a single header block.
8.2.2. Push Responses
After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed resource as a response (Section 8.1.2.2) on a server-
initiated stream that uses the promised stream identifier. The
server uses this stream to transmit an HTTP response, using the same
sequence of frames as defined in Section 8.1. This stream becomes
"half closed" to the client (Section 5.1) after the initial HEADERS
frame is sent.
Once a client receives a PUSH_PROMISE frame and chooses to accept the
pushed resource, the client SHOULD NOT issue any requests for the
promised resource until after the promised stream has closed.
If the client determines, for any reason, that it does not wish to
receive the pushed resource from the server, or if the server takes
too long to begin sending the promised resource, the client can send
an RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
and referencing the pushed stream's identifier.
A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
the number of resources that can be concurrently pushed by a server. the number of resources that can be concurrently pushed by a server.
Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables
server push by preventing the server from creating the necessary server push by preventing the server from creating the necessary
streams. streams. This does not prohibit a server from sending PUSH_PROMISE
frames; clients need to reset any promised streams that are not
The request header fields provided in the PUSH_PROMISE frame SHOULD wanted.
include enough information for a client to determine whether a cached
representation of the resource is already available. If the client
determines, for any reason, that it does not wish to receive the
pushed resource from the server, or if the server takes too long to
begin sending the promised resource, the client can send an
RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
and referencing the pushed stream's identifier.
Clients receiving a pushed response MUST validate that the server is Clients receiving a pushed response MUST validate that the server is
authorized to push the resource using the same-origin policy authorized to push the resource using the same-origin policy
([RFC6454], Section 3). For example, a HTTP/2.0 connection to ([RFC6454], Section 3). For example, a HTTP/2.0 connection to
"example.com" is generally [[anchor17: Ed: weaselly use of "example.com" is generally [[anchor15: Ed: weaselly use of
"generally", needs better definition]] not permitted to push a "generally", needs better definition]] not permitted to push a
response for "www.example.org". response for "www.example.org".
9. Additional HTTP Requirements/Considerations 9. Additional HTTP Requirements/Considerations
TODO: SNI, gzip and deflate Content-Encoding, etc.. This section outlines attributes of the HTTP protocol that improve
interoperability, reduce exposure to known security vulnerabilities,
9.1. Frame Size Limits for HTTP or reduce the potential for implementation variation.
Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
in length, not counting the 8 octet frame header. An endpoint MUST
treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
Section 4.2).
9.2. Connection Management 9.1. Connection Management
HTTP/2.0 connections are persistent. For best performance, it is HTTP/2.0 connections are persistent. For best performance, it is
expected clients will not close connections until it is determined expected clients will not close connections until it is determined
that no further communication with a server is necessary (for that no further communication with a server is necessary (for
example, when a user navigates away from a particular web page), or example, when a user navigates away from a particular web page), or
until the server closes the connection. until the server closes the connection.
Clients SHOULD NOT open more than one HTTP/2.0 connection to a given Clients SHOULD NOT open more than one HTTP/2.0 connection to a given
origin ([RFC6454]) concurrently. A client can create additional origin ([RFC6454]) concurrently. A client can create additional
connections as replacements, either to replace connections that are connections as replacements, either to replace connections that are
skipping to change at page 43, line 44 skipping to change at page 46, line 34
(Section 5.4.1). (Section 5.4.1).
Servers are encouraged to maintain open connections for as long as Servers are encouraged to maintain open connections for as long as
possible, but are permitted to terminate idle connections if possible, but are permitted to terminate idle connections if
necessary. When either endpoint chooses to close the transport-level necessary. When either endpoint chooses to close the transport-level
TCP connection, the terminating endpoint MUST first send a GOAWAY TCP connection, the terminating endpoint MUST first send a GOAWAY
(Section 6.8) frame so that both endpoints can reliably determine (Section 6.8) frame so that both endpoints can reliably determine
whether previously sent frames have been processed and gracefully whether previously sent frames have been processed and gracefully
complete or terminate any necessary remaining tasks. complete or terminate any necessary remaining tasks.
9.2. Use of TLS Features
Implementations of HTTP/2.0 MUST support TLS 1.1 [TLS11]. [[anchor18:
The working group intends to require at least the use of TLS 1.2
[TLS12] prior to publication of this document; negotiating TLS 1.1 is
permitted to enable the creation of interoperable implementations of
early drafts.]]
The TLS implementation MUST support the Server Name Indication (SNI)
[TLS-EXT] extension to TLS. HTTP/2.0 clients MUST indicate the
target domain name when negotiating TLS.
A server that receives a TLS handshake that does not include either
TLS 1.1 or SNI, MUST NOT negotiate HTTP/2.0. Removing HTTP/2.0
protocols from consideration could result in the removal of all
protocols from the set of protocols offered by the client. This
causes protocol negotiation failure, as described in Section 3.2 of
[TLSALPN].
Implementations are encouraged not to negotiate TLS cipher suites
with known vulnerabilities, such as [RC4].
9.3. Frame Size Limits for HTTP
Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
in length, not counting the 8 octet frame header. An endpoint MUST
treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
Section 4.2).
9.4. GZip Content-Encoding
Clients MUST support gzip compression for HTTP response bodies.
Regardless of the value of the accept-encoding header field, a server
MAY send responses with gzip or deflate encoding. A compressed
response MUST still bear an appropriate content-encoding header
field.
10. Security Considerations 10. Security Considerations
10.1. Server Authority and Same-Origin 10.1. Server Authority and Same-Origin
This specification uses the same-origin policy ([RFC6454], Section 3) This specification uses the same-origin policy ([RFC6454], Section 3)
to determine whether an origin server is permitted to provide to determine whether an origin server is permitted to provide
content. content.
A server that is contacted using TLS is authenticated based on the A server that is contacted using TLS is authenticated based on the
certificate that it offers in the TLS handshake (see [RFC2818], certificate that it offers in the TLS handshake (see [RFC2818],
skipping to change at page 46, line 5 skipping to change at page 49, line 20
Frame types are an 8-bit value. When reviewing new frame type Frame types are an 8-bit value. When reviewing new frame type
registrations, special attention is advised for any frame type- registrations, special attention is advised for any frame type-
specific flags that are defined. Frame flags can interact with specific flags that are defined. Frame flags can interact with
existing flags and could prevent the creation of globally applicable existing flags and could prevent the creation of globally applicable
flags. flags.
Initial values for the "HTTP/2.0 Frame Type" registry are shown in Initial values for the "HTTP/2.0 Frame Type" registry are shown in
Table 1. Table 1.
+-----------+---------------+---------------------------------------+ +--------+---------------+---------------------------+--------------+
| Frame | Name | Flags | | Frame | Name | Flags | Section |
| Type | | | | Type | | | |
+-----------+---------------+---------------------------------------+ +--------+---------------+---------------------------+--------------+
| 0 | DATA | END_STREAM(1) | | 0 | DATA | END_STREAM(1) | Section 6.1 |
| 1 | HEADERS | END_STREAM(1), END_HEADERS(4), | | 1 | HEADERS | END_STREAM(1), | Section 6.2 |
| | | PRIORITY(8) | | | | END_HEADERS(4), | |
| 2 | PRIORITY | - | | | | PRIORITY(8) | |
| 3 | RST_STREAM | - | | 2 | PRIORITY | - | Section 6.3 |
| 4 | SETTINGS | - | | 3 | RST_STREAM | - | Section 6.4 |
| 5 | PUSH_PROMISE | END_PUSH_PROMISE(1) | | 4 | SETTINGS | - | Section 6.5 |
| 6 | PING | PONG(1) | | 5 | PUSH_PROMISE | END_PUSH_PROMISE(1) | Section 6.6 |
| 7 | GOAWAY | - | | 6 | PING | PONG(1) | Section 6.7 |
| 9 | WINDOW_UPDATE | END_FLOW_CONTROL(1) | | 7 | GOAWAY | - | Section 6.8 |
+-----------+---------------+---------------------------------------+ | 9 | WINDOW_UPDATE | - | Section 6.9 |
| 10 | CONTINUATION | END_STREAM(1), | Section 6.10 |
| | | END_HEADERS(4) | |
+--------+---------------+---------------------------+--------------+
Table 1 Table 1
12.2. Error Code Registry 12.2. Error Code Registry
This document establishes a registry for HTTP/2.0 error codes. The This document establishes a registry for HTTP/2.0 error codes. The
"HTTP/2.0 Error Code" registry manages a 32-bit space. The "HTTP/2.0 "HTTP/2.0 Error Code" registry manages a 32-bit space. The "HTTP/2.0
Error Code" registry operates under the "Expert Review" policy Error Code" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
skipping to change at page 47, line 49 skipping to change at page 51, line 18
Permanent Message Header Field Registry [BCP90]. Permanent Message Header Field Registry [BCP90].
Header field name: HTTP2-Settings Header field name: HTTP2-Settings
Applicable protocol: http Applicable protocol: http
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): RFC XXXX (this document) Specification document(s): Section 3.2.1 of this document
Related information: This header field is only used by an HTTP/2.0 Related information: This header field is only used by an HTTP/2.0
client for Upgrade-based negotiation. client for Upgrade-based negotiation.
13. Acknowledgements 13. Acknowledgements
This document includes substantial input from the following This document includes substantial input from the following
individuals: individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
skipping to change at page 48, line 35 skipping to change at page 51, line 51
14. References 14. References
14.1. Normative References 14.1. Normative References
[COMPRESSION] Ruellan, H. and R. Peon, "HTTP Header Compression", [COMPRESSION] Ruellan, H. and R. Peon, "HTTP Header Compression",
draft-ietf-httpbis-header-compression-00 (work in draft-ietf-httpbis-header-compression-00 (work in
progress), June 2013. progress), June 2013.
[HTTP-p1] Fielding, R. and J. Reschke, "Hypertext Transfer [HTTP-p1] Fielding, R. and J. Reschke, "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
draft-ietf-httpbis-p1-messaging-22 (work in progress), draft-ietf-httpbis-p1-messaging-23 (work in progress),
February 2013. July 2013.
[HTTP-p2] Fielding, R. and J. Reschke, "Hypertext Transfer [HTTP-p2] Fielding, R. and J. Reschke, "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-22 (work in progress), draft-ietf-httpbis-p2-semantics-23 (work in progress),
February 2013. July 2013.
[HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests", Transfer Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-22 (work in draft-ietf-httpbis-p4-conditional-23 (work in
progress), February 2013. progress), July 2013.
[HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, [HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range
Requests", draft-ietf-httpbis-p5-range-22 (work in Requests", draft-ietf-httpbis-p5-range-23 (work in
progress), February 2013. progress), July 2013.
[HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J. [HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J.
Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1):
Caching", draft-ietf-httpbis-p6-cache-22 (work in Caching", draft-ietf-httpbis-p6-cache-23 (work in
progress), February 2013. progress), July 2013.
[HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication", Transfer Protocol (HTTP/1.1): Authentication",
draft-ietf-httpbis-p7-auth-22 (work in progress), draft-ietf-httpbis-p7-auth-23 (work in progress),
February 2013. July 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
skipping to change at page 49, line 37 skipping to change at page 52, line 52
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008. RFC 5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011. December 2011.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
January 2011.
[TLS11] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.1", RFC 4346,
April 2006.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application Layer "Transport Layer Security (TLS) Application Layer
Protocol Negotiation Extension", Protocol Negotiation Extension",
draft-ietf-tls-applayerprotoneg-01 (work in progress), draft-ietf-tls-applayerprotoneg-01 (work in progress),
April 2013. April 2013.
14.2. Informative References 14.2. Informative References
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004. RFC 3864, September 2004.
[RC4] Rivest, R., "The RC4 encryption algorithm", RSA Data
Security, Inc. , March 1992.
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP
Extensions for High Performance", RFC 1323, May 1992. Extensions for High Performance", RFC 1323, May 1992.
[TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C. [TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
Jackson, "Talking to Yourself for Fun and Profit", Jackson, "Talking to Yourself for Fun and Profit",
2011, <http://w2spconf.com/2011/papers/websocket.pdf>. 2011, <http://w2spconf.com/2011/papers/websocket.pdf>.
Appendix A. Change Log (to be removed by RFC Editor before publication) Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. Since draft-ietf-httpbis-http2-03 A.1. Since draft-ietf-httpbis-http2-04
Added CONTINUATION frame for HEADERS and PUSH_PROMISE.
PUSH_PROMISE is no longer implicitly prohibited if
SETTINGS_MAX_CONCURRENT_STREAMS is zero.
Push expanded to allow all safe methods without a request body.
Clarified the use of HTTP header fields in requests and responses.
Prohibited HTTP/1.1 hop-by-hop header fields.
Requiring that intermediaries not forward requests with missing or
illegal routing :-headers.
Clarified requirements around handling different frames after stream
close, stream reset and GOAWAY.
Added more specific prohibitions for sending of different frame types
in various stream states.
Making the last received setting value the effective value.
Clarified requirements on TLS version, extension and ciphers.
A.2. Since draft-ietf-httpbis-http2-03
Committed major restructuring atrocities. Committed major restructuring atrocities.
Added reference to first header compression draft. Added reference to first header compression draft.
Added more formal description of frame lifecycle. Added more formal description of frame lifecycle.
Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA. Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA.
Removed HEADERS+PRIORITY, added optional priority to HEADERS frame. Removed HEADERS+PRIORITY, added optional priority to HEADERS frame.
Added PRIORITY frame. Added PRIORITY frame.
A.2. Since draft-ietf-httpbis-http2-02 A.3. Since draft-ietf-httpbis-http2-02
Added continuations to frames carrying header blocks. Added continuations to frames carrying header blocks.
Replaced use of "session" with "connection" to avoid confusion with Replaced use of "session" with "connection" to avoid confusion with
other HTTP stateful concepts, like cookies. other HTTP stateful concepts, like cookies.
Removed "message". Removed "message".
Switched to TLS ALPN from NPN. Switched to TLS ALPN from NPN.
Editorial changes. Editorial changes.
A.3. Since draft-ietf-httpbis-http2-01 A.4. Since draft-ietf-httpbis-http2-01
Added IANA considerations section for frame types, error codes and Added IANA considerations section for frame types, error codes and
settings. settings.
Removed data frame compression. Removed data frame compression.
Added PUSH_PROMISE. Added PUSH_PROMISE.
Added globally applicable flags to framing. Added globally applicable flags to framing.
skipping to change at page 51, line 31 skipping to change at page 55, line 31
Restructured frame header. Removed distinction between data and Restructured frame header. Removed distinction between data and
control frames. control frames.
Altered flow control properties to include session-level limits. Altered flow control properties to include session-level limits.
Added note on cacheability of pushed resources and multiple tenant Added note on cacheability of pushed resources and multiple tenant
servers. servers.
Changed protocol label form based on discussions. Changed protocol label form based on discussions.
A.4. Since draft-ietf-httpbis-http2-00 A.5. Since draft-ietf-httpbis-http2-00
Changed title throughout. Changed title throughout.
Removed section on Incompatibilities with SPDY draft#2. Removed section on Incompatibilities with SPDY draft#2.
Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https:// Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https://
groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>. groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.
Replaced abstract and introduction. Replaced abstract and introduction.
Added section on starting HTTP/2.0, including upgrade mechanism. Added section on starting HTTP/2.0, including upgrade mechanism.
Removed unused references. Removed unused references.
Added flow control principles (Section 5.2.1) based on <http:// Added flow control principles (Section 5.2.1) based on <http://
tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>. tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.
A.5. Since draft-mbelshe-httpbis-spdy-00 A.6. Since draft-mbelshe-httpbis-spdy-00
Adopted as base for draft-ietf-httpbis-http2. Adopted as base for draft-ietf-httpbis-http2.
Updated authors/editors list. Updated authors/editors list.
Added status note. Added status note.
Authors' Addresses Authors' Addresses
Mike Belshe Mike Belshe
 End of changes. 130 change blocks. 
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