draft-ietf-httpbis-http2-09.txt   draft-ietf-httpbis-http2-10.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: June 7, 2014 Google, Inc Expires: August 17, 2014 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Microsoft Mozilla
A. Melnikov, Ed. February 13, 2014
Isode Ltd
December 4, 2013
Hypertext Transfer Protocol version 2.0 Hypertext Transfer Protocol version 2
draft-ietf-httpbis-http2-09 draft-ietf-httpbis-http2-10
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). HTTP/2.0 enables a more the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more
efficient use of network resources and a reduced perception of efficient use of network resources and a reduced perception of
latency by introducing header field compression and allowing multiple latency by introducing header field compression and allowing multiple
concurrent messages on the same connection. It also introduces concurrent messages on the same connection. It also introduces
unsolicited push of representations from servers to clients. unsolicited push of representations from servers to 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 syntax. HTTP's existing semantics remain unchanged. HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged.
This version of the draft has been marked for implementation.
Interoperability testing will occur in the HTTP/2.0 interim in
Zurich, CH, starting 2014-01-22. This replaces -08, which was
originally identified as an implementation draft.
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).
skipping to change at page 2, line 15 skipping to change at page 2, line 8
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 June 7, 2014. This Internet-Draft will expire on August 17, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Document Organization . . . . . . . . . . . . . . . . . . 5 1.1. Document Organization . . . . . . . . . . . . . . . . . . 5
1.2. Conventions and Terminology . . . . . . . . . . . . . . . 6 1.2. Conventions and Terminology . . . . . . . . . . . . . . . 6
2. HTTP/2.0 Protocol Overview . . . . . . . . . . . . . . . . . . 6 2. HTTP/2 Protocol Overview . . . . . . . . . . . . . . . . . . . 7
2.1. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 7 3.1. HTTP/2 Version Identification . . . . . . . . . . . . . . 8
3.2. Starting HTTP/2.0 for "http" URIs . . . . . . . . . . . . 8 3.2. Starting HTTP/2 for "http" URIs . . . . . . . . . . . . . 9
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 for "https" URIs . . . . . . . . . . . . . 11
3.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10 3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . . 11
3.5. HTTP/2.0 Connection Header . . . . . . . . . . . . . . . . 11 3.5. HTTP/2 Connection Header . . . . . . . . . . . . . . . . . 11
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . 14
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 15
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 19 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 20
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 19 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 20
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 20 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 20 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 21
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 21 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 22
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 22 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 22
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 22 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 23
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 23 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 23
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 23 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 24
5.4.3. Connection Termination . . . . . . . . . . . . . . . . 24 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 24
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 24 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 24
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 26 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 29
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 27 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 28 6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 31
6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 29 6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 32
6.5.3. Settings Synchronization . . . . . . . . . . . . . . . 30 6.5.3. Settings Synchronization . . . . . . . . . . . . . . . 33
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 30 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 33
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 34 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 38
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 36 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 39
6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 36 6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 40
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 37 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 40
6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 38 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 41
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 38 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 42
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 39 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 44
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 40 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 44
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 40 8.1.1. Informational Responses . . . . . . . . . . . . . . . 45
8.1.1. Informational Responses . . . . . . . . . . . . . . . 41 8.1.2. Examples . . . . . . . . . . . . . . . . . . . . . . . 46
8.1.2. Examples . . . . . . . . . . . . . . . . . . . . . . . 42 8.1.3. HTTP Header Fields . . . . . . . . . . . . . . . . . . 48
8.1.3. HTTP Header Fields . . . . . . . . . . . . . . . . . . 44 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . . 51
8.1.4. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 47 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 52
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 48 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 53
8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 48 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . . 54
8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . . 49 8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . . 54
8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . . 50 9. Additional HTTP Requirements/Considerations . . . . . . . . . 56
9. Additional HTTP Requirements/Considerations . . . . . . . . . 51 9.1. Connection Management . . . . . . . . . . . . . . . . . . 56
9.1. Connection Management . . . . . . . . . . . . . . . . . . 51 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 56
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 52 9.3. GZip Content-Encoding . . . . . . . . . . . . . . . . . . 57
9.3. GZip Content-Encoding . . . . . . . . . . . . . . . . . . 52 10. Security Considerations . . . . . . . . . . . . . . . . . . . 57
10. Security Considerations . . . . . . . . . . . . . . . . . . . 52 10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 57
10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 53 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 58
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 53 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . . 58
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . . 53 10.4. Cacheability of Pushed Resources . . . . . . . . . . . . . 58
10.4. Cacheability of Pushed Resources . . . . . . . . . . . . . 54 10.5. Denial of Service Considerations . . . . . . . . . . . . . 59
10.5. Denial of Service Considerations . . . . . . . . . . . . . 54 10.6. Use of Padding . . . . . . . . . . . . . . . . . . . . . . 60
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 55 11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 60
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 55 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60
12.1. Registration of HTTP/2.0 Identification String . . . . . . 55 12.1. Registration of HTTP/2 Identification String . . . . . . . 61
12.2. Frame Type Registry . . . . . . . . . . . . . . . . . . . 56 12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 61
12.3. Error Code Registry . . . . . . . . . . . . . . . . . . . 56 12.3. HTTP2-Settings Header Field Registration . . . . . . . . . 62
12.4. Settings Registry . . . . . . . . . . . . . . . . . . . . 57 12.4. PRI Method Registration . . . . . . . . . . . . . . . . . 62
12.5. HTTP2-Settings Header Field Registration . . . . . . . . . 58 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 62
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 58 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 58 14.1. Normative References . . . . . . . . . . . . . . . . . . . 63
14.1. Normative References . . . . . . . . . . . . . . . . . . . 58 14.2. Informative References . . . . . . . . . . . . . . . . . . 65
14.2. Informative References . . . . . . . . . . . . . . . . . . 60
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 61 publication) . . . . . . . . . . . . . . . . . . . . 65
A.1. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 61 A.1. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 65
A.2. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 61 A.2. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 66
A.3. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 61 A.3. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 66
A.4. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 61 A.4. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 66
A.5. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 61 A.5. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 66
A.6. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 62 A.6. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 67
A.7. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 62 A.7. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 67
A.8. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 62 A.8. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 67
A.9. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 63 A.9. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 68
A.10. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 63 A.10. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 68
A.11. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 69
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 outstanding at In particular, HTTP/1.0 only allows one request to be outstanding at
skipping to change at page 5, line 43 skipping to change at page 5, line 43
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
The HTTP/2.0 Specification is split into three parts: starting The HTTP/2 specification is split into four parts:
HTTP/2.0 (Section 3), which covers how a HTTP/2.0 connection is
initiated; a framing layer (Section 4), which multiplexes a single o Starting HTTP/2 (Section 3) covers how a HTTP/2 connection is
TCP connection into independent frames of various types; and an HTTP initiated.
layer (Section 8), which specifies the mechanism for expressing HTTP
interactions using the framing layer. While some of the framing o The framing (Section 4) and streams (Section 5) layers describe
layer concepts are isolated from HTTP, building a generic framing the way HTTP/2 frames are structured and formed into multiplexed
layer has not been a goal. The framing layer is tailored to the streams.
needs of the HTTP protocol and server push.
o Frame (Section 6) and error (Section 7) definitions include
details of the frame and error types used in HTTP/2.
o HTTP mappings (Section 8) and additional requirements (Section 9)
describe how HTTP semantics are expressed using the mechanisms
defined.
While some of the frame and stream layer concepts are isolated from
HTTP, the intent is not to define a completely generic framing layer.
The framing and streams layers are tailored to the needs of the HTTP
protocol and server push.
1.2. Conventions and Terminology 1.2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
All numeric values are in network byte order. Values are unsigned All numeric values are in network byte order. Values are unsigned
unless otherwise indicated. Literal values are provided in decimal unless otherwise indicated. Literal values are provided in decimal
or hexadecimal as appropriate. Hexadecimal literals are prefixed or hexadecimal as appropriate. Hexadecimal literals are prefixed
with "0x" to distinguish them from decimal literals. with "0x" to distinguish them from decimal literals.
The following terms are used: The following terms are used:
client: The endpoint initiating the HTTP connection. client: The endpoint initiating the HTTP/2 connection.
connection: A transport-level connection between two endpoints. connection: A transport-level connection between two endpoints.
connection error: An error on the HTTP/2.0 connection. connection error: An error that affects the entire HTTP/2
connection.
endpoint: Either the client or server of the connection. endpoint: Either the client or server of the connection.
frame: The smallest unit of communication within an HTTP/2.0 frame: The smallest unit of communication within an HTTP/2
connection, consisting of a header and a variable-length sequence connection, consisting of a header and a variable-length sequence
of bytes structured according to the frame type. of bytes structured according to the frame type.
peer: An endpoint. When discussing a particular endpoint, "peer" peer: An endpoint. When discussing a particular endpoint, "peer"
refers to the endpoint that is remote to the primary subject of refers to the endpoint that is remote to the primary subject of
discussion. discussion.
receiver: An endpoint that is receiving frames. receiver: An endpoint that is receiving frames.
sender: An endpoint that is transmitting frames. sender: An endpoint that is transmitting frames.
server: The endpoint which did not initiate the HTTP connection. server: The endpoint which did not initiate the HTTP/2 connection.
stream: A bi-directional flow of frames across a virtual channel stream: A bi-directional flow of frames across a virtual channel
within the HTTP/2.0 connection. within the HTTP/2 connection.
stream error: An error on the individual HTTP/2.0 stream. stream error: An error on the individual HTTP/2 stream.
2. HTTP/2.0 Protocol Overview 2. HTTP/2 Protocol Overview
HTTP/2.0 provides an optimized transport for HTTP semantics. HTTP/2 provides an optimized transport for HTTP semantics.
An HTTP/2.0 connection is an application level protocol running on An HTTP/2 connection is an application level protocol running on top
top of a TCP connection ([TCP]). The client is the TCP connection of a TCP connection ([TCP]). The client is the TCP connection
initiator. initiator.
This document describes the HTTP/2.0 protocol using a logical This document describes the HTTP/2 protocol using a logical structure
structure that is formed of three parts: framing, streams, and that is formed of three parts: framing, streams, and application
application mapping. This structure is provided primarily as an aid mapping. This structure is provided primarily as an aid to
to specification, implementations are free to diverge from this specification, implementations are free to diverge from this
structure as necessary. structure as necessary.
2.1. HTTP Frames 2.1. HTTP Frames
HTTP/2.0 provides an efficient serialization of HTTP semantics. HTTP HTTP/2 provides an efficient serialization of HTTP semantics. HTTP
requests and responses are encoded into length-prefixed frames (see requests and responses are encoded into length-prefixed frames (see
Section 4.1). Section 4.1).
HTTP header fields are compressed into a series of frames that HTTP header fields are compressed into a series of frames that
contain header block fragments (see Section 4.3). contain header block fragments (see Section 4.3).
2.2. HTTP Multiplexing 2.2. HTTP Multiplexing
HTTP/2.0 provides the ability to multiplex HTTP requests and HTTP/2 provides the ability to multiplex HTTP requests and responses
responses over a single connection. Multiple requests or responses over a single connection. Multiple requests or responses can be sent
can be sent concurrently on a connection using streams (Section 5). concurrently on a connection using streams (Section 5). In order to
In order to maintain independent streams, flow control and maintain independent streams, flow control and prioritization are
prioritization are necessary. necessary.
2.3. HTTP Semantics 2.3. HTTP Semantics
HTTP/2.0 defines how HTTP requests and responses are mapped to HTTP/2 defines how HTTP requests and responses are mapped to streams
streams (see Section 8.1) and introduces a new interaction model, (see Section 8.1) and introduces a new interaction model, server push
server push (Section 8.2). (Section 8.2).
3. Starting HTTP/2.0 3. Starting HTTP/2
HTTP/2.0 uses the same "http" and "https" URI schemes used by HTTP/2 uses the same "http" and "https" URI schemes used by HTTP/1.1.
HTTP/1.1. HTTP/2.0 shares the same default port numbers: 80 for HTTP/2 shares the same default port numbers: 80 for "http" URIs and
"http" URIs and 443 for "https" URIs. As a result, implementations 443 for "https" URIs. As a result, implementations processing
processing requests for target resource URIs like requests for target resource URIs like "http://example.org/foo" or
"http://example.org/foo" or "https://example.com/bar" are required to "https://example.com/bar" are required to first discover whether the
first discover whether the upstream server (the immediate peer to upstream server (the immediate peer to which the client wishes to
which the client wishes to establish a connection) supports HTTP/2.0. establish a connection) supports HTTP/2.
The means by which support for HTTP/2.0 is determined is different The means by which support for HTTP/2 is determined is different for
for "http" and "https" URIs. Discovery for "http" URIs is described "http" and "https" URIs. Discovery for "http" URIs is described in
in Section 3.2. Discovery for "https" URIs is described in Section 3.2. Discovery for "https" URIs is described in Section 3.3.
Section 3.3.
3.1. HTTP/2.0 Version Identification 3.1. HTTP/2 Version Identification
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 "h2". This identification is used in the HTTP/1.1 Upgrade header
header field, in the TLS application layer protocol negotiation field, in the TLS application layer protocol negotiation extension
extension [TLSALPN] field, and other places where protocol [TLSALPN] field, and other places where protocol identification is
identification is required. required.
Negotiating "HTTP/2.0" implies the use of the transport, security, Negotiating "h2" implies the use of the transport, security, framing
framing and message semantics described in this document. and message semantics described in this document.
[[anchor6: Editor's Note: please remove the remainder of this section [[anchor6: Editor's Note: please remove the remainder of this section
prior to 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 "h2". Until such an RFC exists, implementations MUST
MUST NOT identify themselves using "HTTP/2.0". NOT identify themselves using "h2".
Examples and text throughout the rest of this document use "HTTP/2.0" Examples and text throughout the rest of this document use "h2" as a
as a matter of editorial convenience only. Implementations of draft matter of editorial convenience only. Implementations of draft
versions MUST NOT identify using this string. The exception to this versions MUST NOT identify using this string.
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 "-" and the corresponding draft number to the identifier. For
the separator ('/'). For example, draft-ietf-httpbis-http2-03 is example, draft-ietf-httpbis-http2-09 is identified using the string
identified using the string "HTTP-draft-03/2.0". "h2-09".
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 append the string "-" and a experiment name to the 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-http2-09 might identify itself
as "HTTP-emo-07/2.0". Note that any label MUST conform to the as "h2-09-emo". Note that any label MUST conform to the "token"
"token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters are
are encouraged to coordinate their experiments on the encouraged to coordinate their experiments on the ietf-http-wg@w3.org
ietf-http-wg@w3.org mailing list. mailing list.
3.2. Starting HTTP/2.0 for "http" URIs 3.2. Starting HTTP/2 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 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 with the h2
HTTP/1.1 request MUST include exactly one HTTP2-Settings token. The HTTP/1.1 request MUST include exactly one HTTP2-Settings
(Section 3.2.1) 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: h2
HTTP2-Settings: <base64url encoding of HTTP/2.0 SETTINGS payload> HTTP2-Settings: <base64url encoding of HTTP/2 SETTINGS payload>
Requests that contain an entity body MUST be sent in their entirety Requests that contain an entity body MUST be sent in their entirety
before the client can send HTTP/2.0 frames. This means that a large before the client can send HTTP/2 frames. This means that a large
request entity can block the use of the connection until it is request entity can block the use of the connection until it is
completely sent. completely sent.
If concurrency of an initial request with subsequent requests is If concurrency of an initial request with subsequent requests is
important, a small request can be used to perform the upgrade to important, a small request can be used to perform the upgrade to
HTTP/2.0, at the cost of an additional round-trip. HTTP/2, at the cost of an additional round-trip.
A server that does not support HTTP/2.0 can respond to the request as A server that does not support HTTP/2 can respond to the request as
though the Upgrade header field were absent: though the Upgrade header field were absent:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Length: 243 Content-Length: 243
Content-Type: text/html Content-Type: text/html
... ...
A server that supports HTTP/2.0 can accept the upgrade with a 101 A server that supports HTTP/2 can accept the upgrade with a 101
(Switching Protocols) response. After the empty line that terminates (Switching Protocols) response. After the empty line that terminates
the 101 response, the server can begin sending HTTP/2.0 frames. the 101 response, the server can begin sending HTTP/2 frames. These
These frames MUST include a response to the request that initiated frames MUST include a response to the request that initiated the
the Upgrade. Upgrade.
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: Upgrade Connection: Upgrade
Upgrade: HTTP/2.0 Upgrade: h2
[ HTTP/2.0 connection ... [ HTTP/2 connection ...
The first HTTP/2.0 frame sent by the server is a SETTINGS frame The first HTTP/2 frame sent by the server is a SETTINGS frame
(Section 6.5). Upon receiving the 101 response, the client sends a (Section 6.5). Upon receiving the 101 response, the client sends a
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 assigned stream The HTTP/1.1 request that is sent prior to upgrade is assigned stream
identifier 1 and is assigned the highest possible priority. Stream 1 identifier 1 and is assigned the highest possible priority. Stream 1
is implicitly half closed from the client toward the server, since is 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. the HTTP/2 connection, stream 1 is used for the response.
3.2.1. HTTP2-Settings Header Field 3.2.1. HTTP2-Settings Header Field
A request that upgrades from HTTP/1.1 to HTTP/2.0 MUST include A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly
exactly one "HTTP2-Settings" header field. The "HTTP2-Settings" one "HTTP2-Settings" header field. The "HTTP2-Settings" header field
header field is a hop-by-hop header field that includes settings that is a hop-by-hop header field that includes settings that govern the
govern the HTTP/2.0 connection, provided in anticipation of the HTTP/2 connection, provided in anticipation of the server accepting
server accepting the request to upgrade. A server MUST reject an the request to upgrade. A server MUST reject an attempt to upgrade
attempt to upgrade if this header field is not present. if this header field 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
[RFC5234] production for "token68" is defined in Section 2.1 of [RFC5234] production for "token68" is defined in Section 2.1 of
[HTTP-p7]. [HTTP-p7].
The client MUST include values for the following settings The client MUST include values for the following settings
(Section 6.5.1): (Section 6.5.1):
o SETTINGS_MAX_CONCURRENT_STREAMS o SETTINGS_MAX_CONCURRENT_STREAMS
o SETTINGS_INITIAL_WINDOW_SIZE o SETTINGS_INITIAL_WINDOW_SIZE
As a hop-by-hop header field, the "Connection" header field MUST As a hop-by-hop header field, the "Connection" header field MUST
include a value of "HTTP2-Settings" in addition to "Upgrade" when include a value of "HTTP2-Settings" in addition to "Upgrade" when
upgrading to HTTP/2.0. upgrading to HTTP/2.
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. Acknowledgement of the settings (Section 6.5.3) is
not necessary, since a 101 response serves as implicit
acknowledgment. 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 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 [TLS12] with the knowledge about support for HTTP/2 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 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 by other
other means. A client MAY immediately send HTTP/2.0 frames to a means. For example, [AltSvc] describes a mechanism for advertising
server that is known to support HTTP/2.0, after the connection header this capability in an HTTP header field. A client MAY immediately
(Section 3.5). This only affects the resolution of "http" URIs; send HTTP/2 frames to a server that is known to support HTTP/2, after
servers supporting HTTP/2.0 are required to support protocol the connection header (Section 3.5). A server can identify such a
negotiation in TLS [TLSALPN] for "https" URIs. connection by the use of the "PRI" method in the connection header.
This only affects the resolution of "http" URIs; servers supporting
HTTP/2 are required to support protocol negotiation in TLS [TLSALPN]
for "https" URIs.
Prior support for HTTP/2.0 is not a strong signal that a given server Prior support for HTTP/2 is not a strong signal that a given server
will support HTTP/2.0 for future connections. It is possible for will support HTTP/2 for future connections. It is possible for
server configurations to change or for configurations to differ server configurations to change or for configurations to differ
between instances in clustered server. Interception proxies (a.k.a. between instances in clustered server. Interception proxies (a.k.a.
"transparent" proxies) are another source of variability. "transparent" proxies) are another source of variability.
3.5. HTTP/2.0 Connection Header 3.5. HTTP/2 Connection Header
Upon establishment of a TCP connection and determination that Upon establishment of a TCP connection and determination that HTTP/2
HTTP/2.0 will be used by both peers, each endpoint MUST send a will be used by both peers, each endpoint MUST send a connection
connection header as a final confirmation and to establish the header as a final confirmation and to establish the initial settings
initial settings for the HTTP/2.0 connection. for the HTTP/2 connection.
The client connection header starts with a sequence of 24 octets, The client connection header starts with a sequence of 24 octets,
which in hex notation are: which in hex notation are:
505249202a20485454502f322e300d0a0d0a534d0d0a0d0a 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"). This sequence is (the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"). This sequence is
followed by a SETTINGS frame (Section 6.5). The client sends the followed by a SETTINGS frame (Section 6.5). The client sends the
client connection header immediately upon receipt of a 101 Switching client connection header immediately upon receipt of a 101 Switching
Protocols response (indicating a successful upgrade), or as the first Protocols response (indicating a successful upgrade), or as the first
application data octets of a TLS connection. If starting an HTTP/2.0 application data octets of a TLS connection. If starting an HTTP/2
connection with prior knowledge of server support for the protocol, connection with prior knowledge of server support for the protocol,
the client connection header is sent upon connection establishment. the client 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
HTTP/2.0 connection. HTTP/2 connection.
To avoid unnecessary latency, clients are permitted to send To avoid unnecessary latency, clients are permitted to send
additional frames to the server immediately after sending the client additional frames to the server immediately after sending the client
connection header, without waiting to receive the server connection connection header, without waiting to receive the server connection
header. It is important to note, however, that the server connection header. It is important to note, however, that the server connection
header SETTINGS frame might include parameters that necessarily alter header SETTINGS frame might include parameters that necessarily alter
how a client is expected to communicate with the server. Upon how a client is expected to communicate with the server. Upon
receiving the SETTINGS frame, the client is expected to honor any receiving the SETTINGS frame, the client is expected to honor any
parameters established. parameters established.
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.
4. HTTP Frames 4. HTTP Frames
Once the HTTP/2.0 connection is established, endpoints can begin Once the HTTP/2 connection is established, endpoints can begin
exchanging frames. exchanging frames.
4.1. Frame Format 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 16,383 octets. between 0 and 16,383 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 12, line 35 skipping to change at page 13, line 6
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Frame Payload (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Header Frame Header
The fields of the frame header are defined as: The fields of the frame header are defined as:
R: A reserved 2-bit field. The semantics of these bits are undefined R: A reserved 2-bit field. The semantics of these bits are undefined
and the bit MUST remain unset (0) when sending and MUST be ignored and the bits MUST remain unset (0) when sending and MUST be
when receiving. ignored when receiving.
Length: The length of the frame payload expressed as an unsigned 14- Length: The length of the frame payload expressed as an unsigned 14-
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 frames of unsupported or unrecognized Implementations MUST treat the receipt of an unknown frame type
types. (any frame type not defined in this document) as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
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
and the bit MUST remain unset (0) when sending and MUST be ignored and the bit MUST remain unset (0) when sending and MUST be ignored
skipping to change at page 13, line 30 skipping to change at page 13, line 51
implementations SHOULD be capable of receiving and minimally implementations SHOULD be capable of receiving and minimally
processing frames up to this maximum size. processing frames up to this maximum size.
Certain frame types, such as PING (see Section 6.7), impose Certain frame types, such as PING (see Section 6.7), impose
additional limits on the amount of payload data allowed. Likewise, additional limits on the amount of payload data allowed. Likewise,
additional size limits can be set by specific application uses (see additional size limits can be set by specific application uses (see
Section 9). Section 9).
If a frame size exceeds any defined limit, or is too small to contain If a frame size exceeds any defined limit, or is too small to contain
mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR
error. Frame size errors in frames that affect connection-level error. A frame size error in a frame that affects connection-level
state MUST be treated as a connection error (Section 5.4.1). state MUST be treated as a connection error (Section 5.4.1).
4.3. Header Compression and Decompression 4.3. Header Compression and Decompression
A header field in HTTP/2.0 is a name-value pair with one or more A header field in HTTP/2 is a name-value pair with one or more
associated values. They are used within HTTP request and response associated values. They are used within HTTP request and response
messages as well as server push operations (see Section 8.2). messages as well as server push operations (see Section 8.2).
Header sets are collections of zero or more header fields arranged at Header sets are collections of zero or more header fields. When
the application layer. When transmitted over a connection, a header transmitted over a connection, a header set is serialized into a
set is serialized into a header block using HTTP Header Compression header block using HTTP Header Compression [COMPRESSION]. The
[COMPRESSION]. The serialized header block is then divided into one serialized header block is then divided into one or more octet
or more octet sequences, called header block fragments, and sequences, called header block fragments, and transmitted within the
transmitted within the payload of HEADERS (Section 6.2), PUSH_PROMISE payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or
(Section 6.6) or CONTINUATION (Section 6.10) frames. CONTINUATION (Section 6.10) frames.
HTTP Header Compression does not preserve the relative ordering of HTTP Header Compression does not preserve the relative ordering of
header fields. Header fields with multiple values are encoded into a header fields. Header fields with multiple values are encoded into a
single header field using a special delimiter, see Section 8.1.3.3. single header field using a special delimiter, see Section 8.1.3.3.
The Cookie header field [COOKIE] is treated specially by the HTTP The Cookie header field [COOKIE] is treated specially by the HTTP
mapping, see Section 8.1.3.4. mapping, see Section 8.1.3.4.
A receiving endpoint reassembles the header block by concatenating A receiving endpoint reassembles the header block by concatenating
the individual fragments, then decompresses the block to reconstruct the individual fragments, then decompresses the block to reconstruct
the header set. the header set.
A complete header block consists of either: A complete header block consists of either:
o a single HEADERS or PUSH_PROMISE frame each respectively with the o a single HEADERS or PUSH_PROMISE frame each respectively with the
END_HEADERS or END_PUSH_PROMISE flag set, or END_HEADERS or END_PUSH_PROMISE flag set, or
o a HEADERS or PUSH_PROMISE frame with the END_HEADERS or o a HEADERS or PUSH_PROMISE frame with the END_HEADERS or
END_PUSH_PROMISE flag cleared and one or more CONTINUATION frames, END_PUSH_PROMISE flag cleared and one or more CONTINUATION frames,
where the last CONTINUATION frame has the END_HEADER flag set. where the last CONTINUATION frame has the END_HEADERS flag set.
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 or CONTINUATION stream. The last frame in a sequence of HEADERS or CONTINUATION
frames MUST have the END_HEADERS flag set. The last frame in a frames MUST have the END_HEADERS flag set. The last frame in a
sequence of PUSH_PROMISE or CONTINUATION frames MUST have the sequence of PUSH_PROMISE or CONTINUATION frames MUST have the
END_PUSH_PROMISE or END_HEADERS flag set (respectively). END_PUSH_PROMISE or END_HEADERS flag set (respectively).
Header block fragments can only be sent as the payload of HEADERS, Header block fragments can only be sent as the payload of HEADERS,
PUSH_PROMISE or CONTINUATION frames. HEADERS, PUSH_PROMISE and PUSH_PROMISE or CONTINUATION frames. HEADERS, PUSH_PROMISE and
skipping to change at page 14, line 38 skipping to change at page 15, line 10
context maintained by a receiver. An endpoint receiving HEADERS, context maintained by a receiver. An endpoint receiving HEADERS,
PUSH_PROMISE or CONTINUATION frames MUST reassemble header blocks and PUSH_PROMISE or CONTINUATION frames MUST reassemble header blocks and
perform decompression even if the frames are to be discarded. A perform decompression even if the frames are to be discarded. A
receiver MUST terminate the connection with a connection error receiver MUST terminate the connection with a connection error
(Section 5.4.1) of type COMPRESSION_ERROR, if it does not decompress (Section 5.4.1) of type COMPRESSION_ERROR, if it does not decompress
a header block. a header block.
5. Streams and Multiplexing 5. Streams and Multiplexing
A "stream" is an independent, bi-directional sequence of HEADERS 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
HTTP/2.0 connection. Streams have several important characteristics: connection. Streams have several important characteristics:
o A single HTTP/2.0 connection can contain multiple concurrently o A single HTTP/2 connection can contain multiple concurrently open
open streams, with either endpoint interleaving frames from streams, with either endpoint interleaving frames from multiple
multiple streams. 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.
o Streams can be closed by either endpoint. o Streams can be closed by either endpoint.
o The order in which frames are sent within a stream is significant. o The order in which frames are sent within a stream is significant.
Recipients process frames in the order they are received. Recipients process frames in the order they are received.
o Streams are identified by an integer. Stream identifiers are o Streams are identified by an integer. Stream identifiers are
skipping to change at page 18, line 51 skipping to change at page 19, line 42
MAY choose to limit the period over which it ignores frames and MAY choose to limit the period over which it ignores frames and
treat frames that arrive after this time as being in error. treat frames that arrive after this time as being in error.
Flow controlled frames (i.e., DATA) received after sending Flow controlled frames (i.e., DATA) received after sending
RST_STREAM are counted toward the connection flow control window. RST_STREAM are counted toward the connection flow control window.
Even though these frames might be ignored, because they are sent Even though these frames might be ignored, because they are sent
before the sender receives the RST_STREAM, the sender will before the sender receives the RST_STREAM, the sender will
consider the frames to count against the flow control window. consider the frames to count against the flow control window.
An endpoint might receive a PUSH_PROMISE frame after it sends An endpoint might receive a PUSH_PROMISE frame after it sends
RST_STREAM. PUSH_PROMISE causes a stream to become "reserved". RST_STREAM. PUSH_PROMISE causes a stream to become "reserved"
even if the associated stream has been reset. Therefore, a
The RST_STREAM does not cancel any promised stream. Therefore, if RST_STREAM is needed to close an unwanted promised streams.
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, In the absence of more specific guidance elsewhere in this document,
implementations SHOULD treat the receipt of a message that is not implementations SHOULD treat the receipt of a message that is not
expressly permitted in the description of a state as a connection expressly permitted in the description of a state as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. 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 messages; 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 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). After request which was specified during Upgrade (see Section 3.2). After
the upgrade completes, stream 0x1 is "half closed (local)" to the the upgrade completes, stream 0x1 is "half closed (local)" to the
client. Therefore, stream 0x1 cannot be selected as a new stream client. Therefore, stream 0x1 cannot be selected as a new stream
identifier by a client that upgrades from HTTP/1.1. identifier by a client that upgrades from HTTP/1.1.
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
skipping to change at page 20, line 28 skipping to change at page 21, line 19
promised stream can be successfully used. promised stream can be successfully used.
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 provides for flow control through use of the WINDOW_UPDATE
frame type. frame type.
5.2.1. Flow Control Principles 5.2.1. Flow Control Principles
HTTP/2.0 stream flow control aims to allow for future improvements to HTTP/2 stream flow control aims to allow for future improvements to
flow control algorithms without requiring protocol changes. Flow flow control algorithms without requiring protocol changes. Flow
control in HTTP/2.0 has the following characteristics: control in HTTP/2 has the following characteristics:
1. Flow control is hop-by-hop, not end-to-end. 1. Flow control is hop-by-hop, not end-to-end.
2. Flow control is based on window update frames. Receivers 2. Flow control is based on window update frames. Receivers
advertise how many bytes they are prepared to receive on a stream advertise how many bytes they are prepared to receive on a stream
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 window as a receiver and abide by the flow control limits
limits set by their peer when sending. set by their peer when sending.
4. The initial value for the flow control window is 65,535 bytes for 4. The initial value for the flow control window is 65,535 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 cannot be disabled.
choose to disable both forms of flow control by sending the
SETTINGS_FLOW_CONTROL_OPTIONS setting. See Ending Flow Control
(Section 6.9.4) for more details.
7. HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame 7. HTTP/2 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.
Algorithm choices for these could interact with any flow control Algorithm choices for these could interact with any flow control
algorithm. algorithm.
5.2.2. Appropriate Use of Flow Control 5.2.2. Appropriate Use of Flow Control
Flow control is defined to protect endpoints that are operating under Flow control is defined to protect endpoints that are operating under
resource constraints. For example, a proxy needs to share memory resource constraints. For example, a proxy needs to share memory
between many connections, and also might have a slow upstream between many connections, and also might have a slow upstream
connection and a fast downstream one. Flow control addresses cases connection and a fast downstream one. Flow control addresses cases
where the receiver is unable process data on one stream, yet wants to where the receiver is unable process data on one stream, yet wants to
continue to process other streams in the same connection. continue to process other streams in the same connection.
Deployments that do not require this capability SHOULD disable flow Deployments that do not require this capability can advertise a flow
control for data that is being received. Note that flow control control of the maximum size, incrementing the available space when
cannot be disabled for sending. Sending data is always subject to new data is received. Sending data is always subject to the flow
the flow control window advertised by the receiver. 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 can be difficult. When using flow implementation of flow control can be difficult. When using flow
control, the receive MUST read from the TCP receive buffer in a control, the receiver MUST read from the TCP receive buffer in a
timely fashion. Failure to do so could lead to a deadlock when timely fashion. Failure to do so could lead to a deadlock when
critical frames, such as WINDOW_UPDATE, are not available to critical frames, such as WINDOW_UPDATE, are not available to HTTP/2.
HTTP/2.0. However, flow control can ensure that constrained However, flow control can ensure that constrained resources are
resources are protected without any reduction in connection protected without any reduction in connection utilization.
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 an endpoint to express the The purpose of this value is to allow an endpoint to express the
relative priority of a stream. An endpoint can use this information relative priority of a stream. An endpoint can use this information
to preferentially allocate resources to a stream. Within HTTP/2.0, to preferentially allocate resources to a stream. Within HTTP/2,
priority can be used to select streams for transmitting frames when priority can be used to select streams for transmitting frames when
there is limited capacity for sending. For instance, an endpoint there is limited capacity for sending. For instance, an endpoint
might enqueue frames for all concurrently active streams. As might enqueue frames for all concurrently active streams. As
transmission capacity becomes available, frames from higher priority transmission capacity becomes available, frames from higher priority
streams might be sent before lower priority streams. 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 or transmission order for the stream relative particular processing or transmission order for the stream relative
to any other stream. Nor is there any mechanism provided by which to any other stream. Nor is there any mechanism provided by which
the initiator of a stream can force or require a receiving endpoint the initiator of a stream can force or require a receiving endpoint
skipping to change at page 22, line 43 skipping to change at page 23, line 29
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. stream creation, the default stream priority is 2^30.
Pushed streams (Section 8.2) have a lower priority than their Pushed streams (Section 8.2) have a lower priority than their
associated stream. The promised stream inherits the priority value associated stream. The promised stream inherits the priority value
of the associated stream plus one, up to a maximum of 2^31-1. 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 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
skipping to change at page 24, line 33 skipping to change at page 25, line 17
any given frame. Accordingly, while it is expected that new frame any given frame. Accordingly, while it is expected that new frame
types will be introduced by extensions to this protocol, only frames types will be introduced by extensions to this protocol, only frames
defined by this document are permitted to alter the connection state. defined by this document are permitted to alter the connection state.
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.
DATA frames MAY also contain arbitrary padding. Padding can be added
to DATA frames to hide the size of messages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Pad High(8)] | [Pad Low (8)] | Data (*) .
+---------------+---------------+-------------------------------+
. Data (*) ...
+---------------------------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
DATA Frame Payload
The DATA frame contains the following fields:
Pad High: An 8-bit field containing an amount of padding in units of
256 octets. This field is optional and is only present if the
PAD_HIGH flag is set. This field, in combination with Pad Low,
determines how much padding there is on a frame.
Pad Low: An 8-bit field containing an amount of padding in units of
single octets. This field is optional and is only present if the
PAD_LOW flag is set. This field, in combination with Pad High,
determines how much padding there is on a frame.
Data: Application data. The amount of data is the remainder of the
frame payload after subtracting the length of the other fields
that are present.
Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending and ignored when
receiving.
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 one of "half closed" Setting this flag causes the stream to enter one of the "half
states or "closed" state (Section 5.1). closed" states or the "closed" state (Section 5.1).
RESERVED (0x2): Bit 2 is reserved for future use. END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the
last for the current segment. Intermediaries MUST NOT coalesce
frames across a segment boundary and MUST preserve segment
boundaries when forwarding frames.
PAD_LOW (0x10): Bit 5 being set indicates that the Pad Low field is
present.
PAD_HIGH (0x20): Bit 6 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
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 DATA frames are subject to flow control and can only be sent when a
stream is in the "open" or "half closed (remote)" states. If a DATA stream is in the "open" or "half closed (remote)" states. Padding is
frame is received whose stream is not in "open" or "half closed not excluded from flow control. If a DATA frame is received whose
(local)" state, the recipient MUST respond with a stream error stream is not in "open" or "half closed (local)" state, the recipient
(Section 5.4.2) of type STREAM_CLOSED. MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED.
The total number of padding octets is determined by multiplying the
value of the Pad High field by 256 and adding the value of the Pad
Low field. Both Pad High and Pad Low fields assume a value of zero
if absent. If the length of the padding is greater than the length
of the remainder of the frame payload, the recipient MUST treat this
as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
Note: A frame can be increased in size by one octet by including a
Pad Low field with a value of zero.
Use of padding is a security feature; as such, its use demands some
care, see Section 10.6.
6.2. HEADERS 6.2. HEADERS
The HEADERS frame (type=0x1) carries name-value pairs. It is used to The HEADERS frame (type=0x1) carries name-value pairs. It is used to
open a stream (Section 5.1). HEADERS frames can be sent on a stream open a stream (Section 5.1). HEADERS frames can be sent on a stream
in the "open" or "half closed (remote)" states. 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) | | [Pad High(8)] | [Pad Low (8)] |X| [Priority (31)] ...
+-+-------------------------------------------------------------+ +---------------+---------------+-+-----------------------------+
...[Priority] | Header Block Fragment (*) ...
+-------------------------------+-------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
HEADERS Frame Payload HEADERS Frame Payload
The HEADERS frame payload has the following fields:
Pad High: Padding size high bits. This field is only present if the
PAD_HIGH flag is set.
Pad Low: Padding size low bits. This field is only present if the
PAD_LOW flag is set.
X: A single reserved bit. This field is optional and is only present
if the PRIORITY flag is set.
Priority: Prioritization information for the stream, see
Section 5.3. This field is optional and is only present if the
PRIORITY flag is set.
Header Block Fragment: A header block fragment (Section 4.3).
Padding: Padding octets.
The HEADERS frame defines the following flags: The HEADERS frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that the header block END_STREAM (0x1): Bit 1 being set indicates that the header block
(Section 4.3) is the last that the endpoint will send for the (Section 4.3) is the last that the endpoint will send for the
identified stream. Setting this flag causes the stream to enter identified stream. Setting this flag causes the stream to enter
one of "half closed" states (Section 5.1). one of "half closed" states (Section 5.1).
A HEADERS frame that is followed by CONTINUATION frames carries A HEADERS frame that is followed by CONTINUATION frames carries
the END_STREAM flag that signals the end of a stream. A the END_STREAM flag that signals the end of a stream. A
CONTINUATION frame cannot be used to terminate a stream. CONTINUATION frame cannot be used to terminate a stream.
RESERVED (0x2): Bit 2 is reserved for future use. END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the
last for the current segment. Intermediaries MUST NOT coalesce
frames across a segment boundary and MUST preserve segment
boundaries when forwarding frames.
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): Bit 3 being set indicates that this frame
contains an entire header block (Section 4.3) and is not followed contains an entire header block (Section 4.3) and is not followed
by any CONTINUATION frames. by any CONTINUATION frames.
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 CONTINUATION frame for the same stream. A receiver MUST 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 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 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.
PAD_LOW (0x10): Bit 5 being set indicates that the Pad Low field is
present.
PAD_HIGH (0x20): Bit 6 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
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). A header block that does not fit within a HEADERS (Section 4.3). A header block that does not fit within a HEADERS
frame is continued in a CONTINUATION frame (Section 6.10). 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 described in The HEADERS frame changes the connection state as described in
Section 4.3. Section 4.3.
The HEADERS frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Priority (31) | |X| Priority (31) |
skipping to change at page 28, line 8 skipping to change at page 30, line 48
values for the same setting can be advertised by each peer. For values for the same setting can be advertised by each peer. For
example, a client might set a high initial flow control window, example, a client might set a high initial flow control window,
whereas a server might set a lower value to conserve resources. whereas a server might set a lower value to conserve resources.
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 to this protocol. Unsupported or unrecognized settings
New settings MUST NOT be defined or implemented in a way that MUST be ignored. New settings MUST NOT be defined or implemented in
requires endpoints to understand them in order to communicate a way that requires endpoints to understand them in order to
successfully. communicate successfully.
Each setting in a SETTINGS frame replaces the existing value for that Each setting in a SETTINGS frame replaces the existing value for that
setting. Settings are processed in the order in which they appear, setting. Settings are processed in the order in which they appear,
and a receiver of a SETTINGS frame does not need to maintain any and a receiver of a SETTINGS frame does not need to maintain any
state other than the current value of settings. Therefore, the value state other than the current value of settings. Therefore, the value
of a setting is the last value that is seen by a receiver. This of a setting is the last value that is seen by a receiver. This
permits the inclusion of the same settings multiple times in the same permits the inclusion of the same settings multiple times in the same
SETTINGS frame, though doing so does nothing other than waste SETTINGS frame, though doing so does nothing other than waste
connection capacity. connection capacity.
skipping to change at page 28, line 45 skipping to change at page 31, line 37
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) of type PROTOCOL_ERROR. (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 unsigned 8-bit setting identifier, and an
setting identifier, and an unsigned 32-bit value. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (8) | Setting Identifier (24) | |Identifier (8) | Value (32) ...
+---------------+-----------------------------------------------+ +---------------+-----------------------------------------------+
| Value (32) | ...Value |
+---------------------------------------------------------------+ +---------------+
Setting Format Setting Format
6.5.2. Defined Settings 6.5.2. Defined Settings
The following settings are defined: The following settings are defined:
SETTINGS_HEADER_TABLE_SIZE (1): Allows the sender to inform the SETTINGS_HEADER_TABLE_SIZE (1): Allows the sender to inform the
remote endpoint of the size of the header compression table used remote endpoint of the size of the header compression table used
to decode header blocks. The space available for encoding cannot to decode header blocks. The encoder can reduce this size by
be changed; it is determined by the setting sent by the peer that using signalling specific to the header compression format inside
receives the header blocks. The initial value is 4,096 bytes. a header block. The initial value is 4,096 bytes.
SETTINGS_ENABLE_PUSH (2): This setting can be use to disable server SETTINGS_ENABLE_PUSH (2): This setting can be use to disable server
push (Section 8.2). An endpoint MUST NOT send a PUSH_PROMISE push (Section 8.2). An endpoint MUST NOT send a PUSH_PROMISE
frame if it receives this setting set to a value of 0. The frame if it receives this setting set to a value of 0. An
initial value is 1, which indicates that push is permitted. endpoint that has set this setting to 0 and had it acknowledged
MUST treat the receipt of a PUSH_PROMISE frame as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_CONCURRENT_STREAMS (4): Indicates the maximum number of The initial value is 1, which indicates that push is permitted.
Any value other than 0 or 1 MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_CONCURRENT_STREAMS (3): Indicates the maximum number of
concurrent streams that the sender will allow. This limit is concurrent streams that the sender will allow. This limit is
directional: it applies to the number of streams that the sender directional: it applies to the number of streams that the sender
permits the receiver to create. Initially there is no limit to permits the receiver to create. Initially there is no limit to
this value. It is recommended that this value be no smaller than this value. It is recommended that this value be no smaller than
100, so as to not unnecessarily limit parallelism. 100, so as to not unnecessarily limit parallelism.
SETTINGS_INITIAL_WINDOW_SIZE (7): Indicates the sender's initial A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be
treated as special by endpoints. A zero value does prevent the
creation of new streams, however this can also happen for any
limit that is exhausted with active streams. Servers SHOULD only
set a zero value for short durations; if a server does not wish to
accept requests, closing the connection could be preferable.
SETTINGS_INITIAL_WINDOW_SIZE (4): 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 flow control options. Values above the maximum flow control window size of 2^31 - 1 MUST
The least significant bit (0x1) of the value is set to indicate be treated as a connection error (Section 5.4.1) of type
that the sender has disabled all flow control. This bit cannot be FLOW_CONTROL_ERROR.
cleared once set, see Section 6.9.4.
All bits other than the least significant are reserved. An endpoint that receives a SETTINGS frame with any other setting
identifier MUST treat this as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR.
6.5.3. Settings Synchronization 6.5.3. Settings Synchronization
Most values in SETTINGS benefit from or require an understanding of Most values in SETTINGS benefit from or require an understanding of
when the peer has received and applied the changed setting values. when the peer has received and applied the changed setting values.
In order to provide such synchronization timepoints, the recipient of In order to provide such synchronization timepoints, the recipient of
a SETTINGS frame in which the ACK flag is not set MUST apply the a SETTINGS frame in which the ACK flag is not set MUST apply the
updated settings as soon as possible upon receipt. updated settings as soon as possible upon receipt.
The values in the SETTINGS frame MUST be applied in the order they The values in the SETTINGS frame MUST be applied in the order they
skipping to change at page 31, line 51 skipping to change at page 34, line 51
state). state).
Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame
causes the stream state to become indeterminate. A receiver MUST causes the stream state to become indeterminate. A receiver MUST
treat the receipt of a PUSH_PROMISE on a stream that is neither treat the receipt of a PUSH_PROMISE on a stream that is neither
"open" nor "half-closed (local)" as a connection error "open" nor "half-closed (local)" as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST (Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST
treat the receipt of a PUSH_PROMISE that promises an illegal stream 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 identifier (Section 5.1.1) (that is, an identifier for a stream that
is not currently in the "idle" state) as a connection error is not currently in the "idle" state) as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR, unless the receiver recently (Section 5.4.1) of type PROTOCOL_ERROR.
sent a RST_STREAM frame to cancel the associated stream (see
Section 5.1).
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 32, line 30 skipping to change at page 35, line 28
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PING Payload Format PING Payload Format
In addition to the frame header, PING frames MUST contain 8 octets of In addition to the frame header, PING frames MUST contain 8 octets of
data in the payload. A sender can include any value it chooses and data in the payload. A sender can include any value it chooses and
use those bytes in any fashion. use those bytes in any fashion.
Receivers of a PING frame that does not include a ACK flag MUST send Receivers of a PING frame that does not include a ACK flag MUST send
a PING frame with the ACK flag set in response, with an identical a PING frame with the ACK flag set in response, with an identical
payload. PING responses SHOULD given higher priority than any other payload. PING responses SHOULD be given higher priority than any
frame. other frame.
The PING frame defines the following flags: The PING frame defines the following flags:
ACK (0x1): Bit 1 being set indicates that this PING frame is a PING ACK (0x1): Bit 1 being set indicates that this PING frame is a PING
response. An endpoint MUST set this flag in PING responses. An response. An endpoint MUST set this flag in PING responses. An
endpoint MUST NOT respond to PING frames containing this flag. endpoint MUST NOT respond to PING frames containing this flag.
PING frames are not associated with any individual stream. If a PING PING frames are not associated with any individual stream. If a PING
frame is received with a stream identifier field value other than frame is received with a stream identifier field value other than
0x0, the recipient MUST respond with a connection error 0x0, the recipient MUST respond with a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
Receipt of a PING frame with a length field value other than 8 MUST Receipt of a PING frame with a length field value other than 8 MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR. FRAME_SIZE_ERROR.
6.8. GOAWAY 6.8. GOAWAY
The GOAWAY frame (type=0x7) informs the remote peer to stop creating The GOAWAY frame (type=0x7) informs the remote peer to stop creating
streams on this connection. It can be sent from the client or the streams on this connection. GOAWAY can be sent by either the client
server. Once sent, the sender will ignore frames sent on new streams or the server. Once sent, the sender will ignore frames sent on new
for the remainder of the connection. Receivers of a GOAWAY frame streams for the remainder of the connection. Receivers of a GOAWAY
MUST NOT open additional streams on the connection, although a new frame MUST NOT open additional streams on the connection, although a
connection can be established for new streams. The purpose of this new connection can be established for new streams. The purpose of
frame is to allow an endpoint to gracefully stop accepting new this frame is to allow an endpoint to gracefully stop accepting new
streams (perhaps for a reboot or maintenance), while still finishing streams (perhaps for a reboot or maintenance), while still finishing
processing of previously established streams. processing of previously established streams.
There is an inherent race condition between an endpoint starting new There is an inherent race condition between an endpoint starting new
streams and the remote sending a GOAWAY frame. To deal with this streams and the remote sending a GOAWAY frame. To deal with this
case, the GOAWAY contains the stream identifier of the last stream case, the GOAWAY contains the stream identifier of the last stream
which was processed on the sending endpoint in this connection. If which was processed on the sending endpoint in this connection. If
the receiver of the GOAWAY used streams that are newer than the the receiver of the GOAWAY used streams that are newer than the
indicated stream identifier, they were not processed by the sender indicated stream identifier, they were not processed by the sender
and the receiver may treat the streams as though they had never been and the receiver may treat the streams as though they had never been
skipping to change at page 34, line 6 skipping to change at page 36, line 50
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Additional Debug Data (*) | | Additional Debug Data (*) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
GOAWAY Payload Format GOAWAY Payload Format
The GOAWAY frame does not define any flags. The GOAWAY frame does not define any flags.
The GOAWAY frame applies to the connection, not a specific stream. The GOAWAY frame applies to the connection, not a specific stream.
The stream identifier MUST be zero. An endpoint MUST treat a GOAWAY frame with a stream identifier other
than 0x0 as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
The last stream identifier in the GOAWAY frame contains the highest The last stream identifier in the GOAWAY frame contains the highest
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
skipping to change at page 34, line 37 skipping to change at page 37, line 35
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
frame, maintaining the connection in an open state until all in- frame, maintaining the connection in an open state until all in-
progress streams complete. progress streams complete.
The last stream ID MUST be 0 if no streams were acted upon. The last stream ID MUST be 0 if no streams were acted upon.
If an endpoint maintains the connection and continues to exchange
frames, ignored frames MUST be counted toward flow control limits
(Section 5.2) or update header compression state (Section 4.3).
Otherwise, flow control or header compression state can become
unsynchronized.
The GOAWAY frame also contains a 32-bit error code (Section 7) that The GOAWAY frame also contains a 32-bit error code (Section 7) that
contains the reason for closing the connection. contains the reason for closing the connection.
Endpoints MAY append opaque data to the payload of any GOAWAY frame. Endpoints MAY append opaque data to the payload of any GOAWAY frame.
Additional debug data is intended for diagnostic purposes only and Additional debug data is intended for diagnostic purposes only and
carries no semantic value. Debug data MUST NOT be persistently carries no semantic value. Debug information could contain security-
stored, since it could contain sensitive information. or privacy-sensitive data. Logged or otherwise persistently stored
debug data MUST have adequate safeguards to prevent unauthorized
access.
6.9. WINDOW_UPDATE 6.9. WINDOW_UPDATE
The WINDOW_UPDATE frame (type=0x9) is used to implement flow control. The WINDOW_UPDATE frame (type=0x8) is used to implement flow control.
Flow control operates at two levels: on each individual stream and on Flow control operates at two levels: on each individual stream and on
the entire connection. the entire connection.
Both types of flow control are hop by hop; that is, only between the Both types of flow control are hop by hop; that is, only between the
two endpoints. Intermediaries do not forward WINDOW_UPDATE frames two endpoints. Intermediaries do not forward WINDOW_UPDATE frames
between dependent connections. However, throttling of data transfer between dependent connections. However, throttling of data transfer
by any receiver can indirectly cause the propagation of flow control by any receiver can indirectly cause the propagation of flow control
information toward the original sender. information toward the original sender.
skipping to change at page 36, line 7 skipping to change at page 39, line 15
A receiver that receives a flow controlled frame MUST always account A receiver that receives a flow controlled frame MUST always account
for its contribution against the connection flow control window, for its contribution against the connection flow control window,
unless the receiver treats this as a connection error unless the receiver treats this as a connection error
(Section 5.4.1). This is necessary even if the frame is in 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 Since the sender counts the frame toward the flow control window, if
the receiver does not, the flow control window at sender and receiver the receiver does not, the flow control window at sender and receiver
can become different. 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 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
skipping to change at page 36, line 49 skipping to change at page 40, line 8
sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code; sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code;
for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code.
Flow controlled frames from the sender and WINDOW_UPDATE frames from Flow controlled frames from the sender and WINDOW_UPDATE frames from
the receiver are completely asynchronous with respect to each other. the receiver are completely asynchronous with respect to each other.
This property allows a receiver to aggressively update the window This property allows a receiver to aggressively update the window
size kept by the sender to prevent streams from stalling. size kept by the sender to prevent streams from stalling.
6.9.2. Initial Flow Control Window Size 6.9.2. Initial Flow Control Window Size
When a HTTP/2.0 connection is first established, new streams are When a HTTP/2 connection is first established, new streams are
created with an initial flow control window size of 65,535 bytes. created with an initial flow control window size of 65,535 bytes.
The connection flow control window is 65,535 bytes. Both endpoints The connection flow control window is 65,535 bytes. Both endpoints
can adjust the initial window size for new streams by including a can adjust the initial window size for new streams by including a
value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that
forms part of the connection header. forms part of the connection header.
Prior to receiving a SETTINGS frame that sets a value for Prior to receiving a SETTINGS frame that sets a value for
SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default
initial window size when sending flow controlled frames. Similarly, initial window size when sending flow controlled frames. Similarly,
the connection flow control window is set to the default initial the connection flow control window is set to the default initial
window size until a WINDOW_UPDATE frame is received. window size until a WINDOW_UPDATE frame is received.
A SETTINGS frame can alter the initial flow control window size for A SETTINGS frame can alter the initial flow control window size for
all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE
changes, a receiver MUST adjust the size of all stream flow control changes, a receiver MUST adjust the size of all stream flow control
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 An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that
causes any flow control window to exceed the maximum size as a
connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR.
A change to SETTINGS_INITIAL_WINDOW_SIZE can 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 60KB 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 -44KB 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
skipping to change at page 38, line 7 skipping to change at page 41, line 19
FLOW_CONTROL_ERROR error code for the affected streams. FLOW_CONTROL_ERROR error code for the affected streams.
2. The receiver can accept the streams and tolerate the resulting 2. The receiver can accept the streams and tolerate the resulting
head of line blocking, sending WINDOW_UPDATE frames as it head of line blocking, sending WINDOW_UPDATE frames as it
consumes data. consumes data.
If a receiver decides to accept streams, both sides MUST recompute If a receiver decides to accept streams, both sides MUST recompute
the available flow control window based on the initial window size the available flow control window based on the initial window size
sent in the SETTINGS. sent in the SETTINGS.
6.9.4. Ending Flow Control
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
transmission of WINDOW_UPDATE frames for that stream. A sender is
not obligated to maintain the available flow control window for
streams that it is no longer sending on.
Flow control can be disabled for the entire connection using the
SETTINGS_FLOW_CONTROL_OPTIONS setting. This setting ends all forms
of flow control. An implementation that does not wish to perform
flow control can use this in the initial SETTINGS exchange.
Flow control cannot be enabled again once disabled. Any attempt to
re-enable flow control - by sending a WINDOW_UPDATE or by clearing
the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
rejected with a FLOW_CONTROL_ERROR error code.
6.10. CONTINUATION 6.10. CONTINUATION
The CONTINUATION frame (type=0xA) is used to continue a sequence of The CONTINUATION frame (type=0x9) is used to continue a sequence of
header block fragments (Section 4.3). Any number of CONTINUATION header block fragments (Section 4.3). Any number of CONTINUATION
frames can be sent on an existing stream, as long as the preceding 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 frame on the same stream is one of HEADERS, PUSH_PROMISE or
CONTINUATION without the END_HEADERS or END_PUSH_PROMISE flag set. CONTINUATION without the END_HEADERS or END_PUSH_PROMISE flag set.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Pad High(8)] | [Pad Low (8)] | Header Block Fragment (*) .
+---------------+---------------+-------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
CONTINUATION Frame Payload CONTINUATION Frame Payload
The CONTINUATION frame payload has the following fields:
Pad High: Padding size high bits. This field is only present if the
PAD_HIGH flag is set.
Pad Low: Padding size low bits. This field is only present if the
PAD_LOW flag is set.
Header Block Fragment: A header block fragment (Section 4.3).
Padding: Padding octets.
The CONTINUATION frame defines the following flags: The CONTINUATION frame defines the following flags:
END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a
header block (Section 4.3). header block (Section 4.3).
If the END_HEADERS bit is not set, this frame MUST be followed by If the END_HEADERS bit is not set, this frame MUST be followed by
another CONTINUATION frame. A receiver MUST treat the receipt of another CONTINUATION frame. A receiver MUST treat the receipt of
any other type of frame or a frame on a different stream as a any other type of frame or a frame on a different stream as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
PAD_LOW (0x10): Bit 5 being set indicates that the Pad Low field is
present.
PAD_HIGH (0x20): Bit 6 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
The payload of a CONTINUATION frame contains a header block fragment The payload of a CONTINUATION frame contains a header block fragment
(Section 4.3). (Section 4.3).
The CONTINUATION frame changes the connection state as defined in The CONTINUATION frame changes the connection state as defined in
Section 4.3. Section 4.3.
CONTINUATION frames MUST be associated with a stream. If a CONTINUATION frames MUST be associated with a stream. If a
CONTINUATION frame is received whose stream identifier field is 0x0, CONTINUATION frame is received whose stream identifier field is 0x0,
the recipient MUST respond with a connection error (Section 5.4.1) of the recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or
CONTINUATION frame without the END_HEADERS flag set. A recipient CONTINUATION frame without the END_HEADERS flag set. A recipient
that observes violation of this rule MUST respond with a connection that observes violation of this rule MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
The CONTINUATION frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1).
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 40, line 21 skipping to change at page 43, line 42
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.
CONNECT_ERROR (10): The connection established in response to a CONNECT_ERROR (10): The connection established in response to a
CONNECT request (Section 8.3) was reset or abnormally closed. CONNECT request (Section 8.3) was reset or abnormally closed.
ENHANCE_YOUR_CALM (420): The endpoint detected that its peer is ENHANCE_YOUR_CALM (11): The endpoint detected that its peer is
exhibiting a behavior over a given amount of time that has caused exhibiting a behavior over a given amount of time that has caused
it to refuse to process further frames. it to refuse to process further frames.
INADEQUATE_SECURITY (12): The underlying transport has properties
that do not meet the minimum requirements imposed by this document
(see Section 9.2) or the endpoint.
8. HTTP Message Exchanges 8. HTTP Message Exchanges
HTTP/2.0 is intended to be as compatible as possible with current HTTP/2 is intended to be as compatible as possible with current web-
web-based applications. This means that, from the perspective of the based applications. This means that, from the perspective of the
server business logic or application API, the features of HTTP are server business logic or application API, the features of HTTP are
unchanged. To achieve this, all of the application request and unchanged. To achieve this, all of the application request and
response header semantics are preserved, although the syntax of response header semantics are preserved, although the syntax of
conveying those semantics has changed. Thus, the rules from HTTP/1.1 conveying those semantics has changed. Thus, the rules from HTTP/1.1
([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and ([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and
[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
skipping to change at page 41, line 26 skipping to change at page 45, line 5
terminates the stream. That is, a sequence starting with a HEADERS terminates the stream. That is, a sequence starting with a HEADERS
frame, followed by zero or more CONTINUATION frames, where the frame, followed by zero or more CONTINUATION frames, where the
HEADERS frame bears an END_STREAM flag. Header blocks after the HEADERS frame bears an END_STREAM flag. Header blocks after the
first that do not terminate the stream are not part of an HTTP first that do not terminate the stream are not part of an HTTP
request or response. 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,
places the stream in the "closed" state. optionally followed by CONTINUATION frames, which places the stream
in the "closed" state.
8.1.1. Informational Responses 8.1.1. Informational Responses
The 1xx series of HTTP response status codes ([HTTP-p2], Section 6.2) The 1xx series of HTTP response status codes ([HTTP-p2], Section 6.2)
are not supported in HTTP/2.0. are not supported in HTTP/2.
The most common use case for 1xx is using a Expect header field with The most common use case for 1xx is using a Expect header field with
a "100-continue" token (colloquially, "Expect/continue") to indicate a "100-continue" token (colloquially, "Expect/continue") to indicate
that the client expects a 100 (Continue) non-final response status that the client expects a 100 (Continue) non-final response status
code, receipt of which indicates that the client should continue code, receipt of which indicates that the client should continue
sending the request body if it has not already done so. sending the request body if it has not already done so.
Typically, Expect/continue is used by clients wishing to avoid Typically, Expect/continue is used by clients wishing to avoid
sending a large amount of data in a request body, only to have the sending a large amount of data in a request body, only to have the
request rejected by the origin server. request rejected by the origin server.
HTTP/2.0 does not enable the Expect/continue mechanism; if the server HTTP/2 does not enable the Expect/continue mechanism; if the server
sends a final status code to reject the request, it can do so without sends a final status code to reject the request, it can do so without
making the underlying connection unusable. making the underlying connection unusable.
Note that this means HTTP/2.0 clients sending requests with bodies Note that this means HTTP/2 clients sending requests with bodies may
may waste at least one round trip of sent data when the request is waste at least one round trip of sent data when the request is
rejected. This can be mitigated by restricting the amount of data rejected. This can be mitigated by restricting the amount of data
sent for the first round trip by bandwidth-constrained clients, in sent for the first round trip by bandwidth-constrained clients, in
anticipation of a final status code. anticipation of a final status code.
Other defined 1xx status codes are not applicable to HTTP/2.0; the Other defined 1xx status codes are not applicable to HTTP/2; the
semantics of 101 (Switching Protocols) is better expressed using a semantics of 101 (Switching Protocols) is better expressed using a
distinct frame type, since they apply to the entire connection, not distinct frame type, since they apply to the entire connection, not
just one stream. Likewise, 102 (Processing) is no longer necessary, just one stream. Likewise, 102 (Processing) is no longer necessary,
because HTTP/2.0 has a separate means of keeping the connection because HTTP/2 has a separate means of keeping the connection alive.
alive.
This difference between protocol versions necessitates special This difference between protocol versions necessitates special
handling by intermediaries that translate between them: handling by intermediaries that translate between them:
o An intermediary that gateways HTTP/1.1 to HTTP/2.0 MUST generate a o An intermediary that gateways HTTP/1.1 to HTTP/2 MUST generate a
100 (Continue) response if a received request includes and Expect 100 (Continue) response if a received request includes and Expect
header field with a "100-continue" token ([HTTP-p2], Section header field with a "100-continue" token ([HTTP-p2], Section
5.1.1), unless it can immediately generate a final status code. 5.1.1), unless it can immediately generate a final status code.
It MUST NOT forward the "100-continue" expectation in the request It MUST NOT forward the "100-continue" expectation in the request
header fields. header fields.
o An intermediary that gateways HTTP/2.0 to HTTP/1.1 MAY add an o An intermediary that gateways HTTP/2 to HTTP/1.1 MAY add an Expect
Expect header field with a "100-continue" expectation when header field with a "100-continue" expectation when forwarding a
forwarding a request that has a body; see [HTTP-p2], Section 5.1.1 request that has a body; see [HTTP-p2], Section 5.1.1 for specific
for specific requirements. requirements.
o An intermediary that gateways HTTP/2.0 to HTTP/1.1 MUST discard o An intermediary that gateways HTTP/2 to HTTP/1.1 MUST discard all
all other 1xx informational responses. other 1xx informational responses.
8.1.2. Examples 8.1.2. Examples
This section shows HTTP/1.1 requests and responses, with This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2.0 requests and responses. illustrations of equivalent HTTP/2 requests and responses.
An HTTP GET request includes request header fields and no body and is An HTTP GET request includes request header fields and no body and is
therefore transmitted as a single contiguous sequence of HEADERS therefore transmitted as a single contiguous sequence of HEADERS and
frames containing the serialized block of request header fields. The CONTINUATION frames containing the serialized block of request header
last HEADERS frame in the sequence has both the END_HEADERS and fields. The last HEADERS frame in the sequence has both the
END_STREAM flag set: END_HEADERS and END_STREAM flags 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
:authority = example.org :authority = 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/1.1 304 Not Modified HEADERS
Content-Length: 0 ===> + END_STREAM ETag: "xyzzy" ===> + END_STREAM
+ END_HEADERS Expires: Thu, 23 Jan ... + END_HEADERS
:status = 204 :status = 304
content-length: 0 etag: "xyzzy"
expires: Thu, 23 Jan ...
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 HEADERS frame, followed by zero or more data is transmitted as one HEADERS frame, followed by zero or more
CONTINUATION frames, containing the request header fields followed by CONTINUATION frames containing the request header fields, followed by
one or more DATA frames, with the last CONTINUATION (or HEADERS) one or more DATA frames, with the last CONTINUATION (or HEADERS)
frame having the END_HEADERS flag set and the final DATA frame having frame having the END_HEADERS flag set and the final DATA frame having
the END_STREAM flag set: 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} :authority = example.org {binary data} :authority = example.org
skipping to change at page 44, line 9 skipping to change at page 48, line 7
{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/CONTINUATION frames that bears the sent. The sequence of HEADERS/CONTINUATION frames that bears the
trailers includes a terminal frame that has both END_HEADERS and trailers includes a terminal frame that has both END_HEADERS and
END_STREAM 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 Transfer-Encoding: chunked + END_HEADERS
Transfer-Encoding: chunked :status = 200 TE: trailers :status = 200
TE: trailers content-length = 123 content-length = 123
123 content-type = image/jpeg 123 content-type = image/jpeg
{binary data} {binary data}
0 DATA 0 DATA
Foo: bar - END_STREAM Foo: bar - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo: bar foo: bar
8.1.3. HTTP Header Fields 8.1.3. HTTP Header Fields
HTTP/2.0 request and response header fields carry information as a HTTP/2 request and response header fields carry information as a
series of key-value pairs. This includes the target URI for the series of key-value pairs. This includes the target URI for the
request, the status code for the response, as well as HTTP header request, the status code for the response, as well as HTTP header
fields. fields.
HTTP header field names are strings of ASCII characters that are HTTP header field names are strings of ASCII characters that are
compared in a case-insensitive fashion. Header field names MUST be compared in a case-insensitive fashion. Header field names MUST be
converted to lowercase prior to their encoding in HTTP/2.0. A converted to lowercase prior to their encoding in HTTP/2. A request
request or response containing uppercase header field names MUST be or response containing uppercase header field names MUST be treated
treated as malformed (Section 8.1.3.5). as malformed (Section 8.1.3.5).
The semantics of HTTP header fields are not altered by this HTTP/2 does not use the Connection header field to indicate "hop-by-
specification, though header fields relating to connection management hop" header fields; in this protocol, connection-specific metadata is
or request framing are no longer necessary. An HTTP/2.0 request or conveyed by other means. As such, a HTTP/2 message containing
response MUST NOT include any of the following header fields: Connection MUST be treated as malformed (Section 8.1.3.5).
Connection, Keep-Alive, Proxy-Connection, TE, Transfer-Encoding, and
Upgrade. A request or response containing these header fields MUST
be treated as malformed (Section 8.1.3.5).
Note: HTTP/2.0 purposefully does not support upgrade from HTTP/2.0 This means that an intermediary transforming a HTTP/1.x message to
to another protocol. The handshake methods described in Section 3 HTTP/2 will need to remove any header fields nominated by the
are sufficient to negotiate the use of alternative protocols. Connection header field, along with the Connection header field
itself. Such intermediaries SHOULD also remove other connection-
specific header fields, such as Keep-Alive, Proxy-Connection,
Transfer-Encoding and Upgrade, even if they are not nominated by
Connection.
One exception to this is the TE header field, which MAY be present in
a HTTP/2 request, but when it is MUST NOT contain any value other
than "trailers".
Note: HTTP/2 purposefully does not support upgrade to another
protocol. The handshake methods described in Section 3 are
believed sufficient to negotiate the use of alternative protocols.
8.1.3.1. Request Header Fields 8.1.3.1. Request Header Fields
HTTP/2.0 defines a number of header fields starting with a colon ':' HTTP/2 defines a number of header fields starting with a colon ':'
character that carry information about the request target: character that carry information about the request target:
o The ":method" header field includes the HTTP method ([HTTP-p2], o The ":method" header field includes the HTTP method ([HTTP-p2],
Section 4). Section 4).
o The ":scheme" header field includes the scheme portion of the o The ":scheme" header field includes the scheme portion of the
target URI ([RFC3986], Section 3.1). target URI ([RFC3986], Section 3.1).
o The ":authority" header field includes the authority portion of o The ":authority" header field includes the authority portion of
the target URI ([RFC3986], Section 3.2). the target URI ([RFC3986], Section 3.2). The authority MUST NOT
include the deprecated "userinfo" subcomponent for "http:" or
"https:" URIs.
To ensure that the HTTP/1.1 request line can be reproduced To ensure that the HTTP/1.1 request line can be reproduced
accurately, this header field MUST be omitted when translating accurately, this header field MUST be omitted when translating
from an HTTP/1.1 request that has a request target in origin or from an HTTP/1.1 request that has a request target in origin or
asterisk form (see [HTTP-p1], Section 5.3). Clients that generate asterisk form (see [HTTP-p1], Section 5.3). Clients that generate
HTTP/2.0 requests directly SHOULD instead omit the "Host" header HTTP/2 requests directly SHOULD instead omit the "Host" header
field. An intermediary that converts a request to HTTP/1.1 MUST field. An intermediary that converts a request to HTTP/1.1 MUST
create a "Host" header field if one is not present in a request by create a "Host" header field if one is not present in a request by
copying the value of the ":authority" header field. copying the value of the ":authority" header field.
o The ":path" header field includes the path and query parts of the o The ":path" header field includes the path and query parts of the
target URI (the "path-absolute" production from [RFC3986] and target URI (the "path-absolute" production from [RFC3986] and
optionally a '?' character followed by the "query" production, see optionally a '?' character followed by the "query" production, see
[RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field [RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field
MUST NOT be empty; URIs that do not contain a path component MUST MUST NOT be empty; URIs that do not contain a path component MUST
include a value of '/', unless the request is an OPTIONS in include a value of '/', unless the request is an OPTIONS request
asterisk form, in which case the ":path" header field MUST include in asterisk form, in which case the ":path" header field MUST
'*'. include '*'.
All HTTP/2.0 requests MUST include exactly one valid value for all of All HTTP/2 requests MUST include exactly one valid value for the
these header fields, unless this is a CONNECT request (Section 8.3). ":method", ":scheme", and ":path" header fields, unless this is a
An HTTP request that omits mandatory header fields is malformed CONNECT request (Section 8.3). An HTTP request that omits mandatory
(Section 8.1.3.5). header fields is malformed (Section 8.1.3.5).
Header field names that contain a colon are only valid in the Header field names that start with a colon are only valid in the
HTTP/2.0 context. These are not HTTP header fields. Implementations HTTP/2 context. These are not HTTP header fields. Implementations
MUST NOT generate header fields that start with a colon, but they MUST NOT generate header fields that start with a colon, but they
MUST ignore any header field that starts with a colon. In MUST ignore any header field that starts with a colon. In
particular, header fields with names starting with a colon MUST NOT particular, header fields with names starting with a colon MUST NOT
be exposed as HTTP header fields. be exposed as HTTP header fields.
HTTP/2.0 does not define a way to carry the version identifier that HTTP/2 does not define a way to carry the version identifier that is
is included in the HTTP/1.1 request line. included in the HTTP/1.1 request line.
8.1.3.2. Response Header Fields 8.1.3.2. Response Header Fields
A single ":status" header field is defined that carries the HTTP A single ":status" header field is defined that carries the HTTP
status code field (see [HTTP-p2], Section 6). This header field MUST status code field (see [HTTP-p2], Section 6). This header field MUST
be included in all responses, otherwise the response is malformed be included in all responses, otherwise the response is malformed
(Section 8.1.3.5). (Section 8.1.3.5).
HTTP/2.0 does not define a way to carry the version or reason phrase HTTP/2 does not define a way to carry the version or reason phrase
that is included in an HTTP/1.1 status line. that is included in an HTTP/1.1 status line.
8.1.3.3. Header Field Ordering 8.1.3.3. Header Field Ordering
HTTP Header Compression [COMPRESSION] does not preserve the order of HTTP Header Compression [COMPRESSION] does not preserve the order of
header fields. The relative order of header fields with different header fields. The relative order of header fields with different
names is not important. However, the same header field can be names is not important. However, the same header field can be
repeated to form a comma-separated list (see [HTTP-p1], Section repeated to form a comma-separated list (see [HTTP-p1], Section
3.2.2), where the relative order of header field values is 3.2.2), where the relative order of header field values is
significant. This repetition can occur either as a single header significant. This repetition can occur either as a single header
skipping to change at page 47, line 13 skipping to change at page 51, line 18
prevents cookie-pairs from being separated into different name-value prevents cookie-pairs from being separated into different name-value
pairs. This can significantly reduce compression efficiency as pairs. This can significantly reduce compression efficiency as
individual cookie-pairs are updated. individual cookie-pairs are updated.
To allow for better compression efficiency, the Cookie header field To allow for better compression efficiency, the Cookie header field
MAY be split into separate header fields, each with one or more MAY be split into separate header fields, each with one or more
cookie-pairs. If there are multiple Cookie header fields after cookie-pairs. If there are multiple Cookie header fields after
decompression, these MUST be concatenated into a single octet string decompression, these MUST be concatenated into a single octet string
using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; "). using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; ").
The Cookie header field MAY be split using a zero octet (0x0), as
defined in Section 8.1.3.3. When decoding, zero octets MUST be
replaced with the cookie delimiter ("; ").
8.1.3.5. Malformed Requests and Responses 8.1.3.5. Malformed Requests and Responses
A malformed request or response is one that uses a valid sequence of A malformed request or response is one that uses a valid sequence of
HTTP/2.0 frames, but is otherwise invalid due to the presence of HTTP/2 frames, but is otherwise invalid due to the presence of
prohibited header fields, the absence of mandatory header fields, or prohibited header fields, the absence of mandatory header fields, or
the inclusion of uppercase header field names. the inclusion of uppercase header field names.
A request or response that includes an entity body can include a A request or response that includes an entity body can include a
"content-length" header field. A request or response is also "content-length" header field. A request or response is also
malformed if the value of a "content-length" header field does not malformed if the value of a "content-length" header field does not
equal the sum of the DATA frame payload lengths that form the body. equal the sum of the DATA frame payload lengths that form the body.
Intermediaries that process HTTP requests or responses (i.e., all Intermediaries that process HTTP requests or responses (i.e., all
intermediaries other than those acting as tunnels) MUST NOT forward a intermediaries other than those acting as tunnels) MUST NOT forward a
malformed request or response. malformed request or response.
Implementations that detect malformed requests or responses need to Implementations that detect malformed requests or responses need to
ensure that the stream ends. For malformed requests, a server MAY ensure that the stream ends. For malformed requests, a server MAY
send an HTTP response to prior to closing or resetting the stream. send an HTTP response prior to closing or resetting the stream.
Clients MUST NOT accept a malformed response. Clients MUST NOT accept a malformed response.
8.1.4. Request Reliability Mechanisms in HTTP/2.0 8.1.4. Request Reliability Mechanisms in HTTP/2
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 provides two mechanisms for providing a guarantee to a client
client that a request has not been processed: that a request has not been processed:
o The GOAWAY frame indicates the highest stream number that might o The GOAWAY frame indicates the highest stream number that might
have been processed. Requests on streams with higher numbers are have been processed. Requests on streams with higher numbers are
therefore guaranteed to be safe to retry. therefore guaranteed to be safe to retry.
o The REFUSED_STREAM error code can be included in a RST_STREAM o The REFUSED_STREAM error code can be included in a RST_STREAM
frame to indicate that the stream is being closed prior to any frame to indicate that the stream is being closed prior to any
processing having occurred. Any request that was sent on the processing having occurred. Any request that was sent on the
reset stream can be safely retried. reset stream can be safely retried.
skipping to change at page 48, line 26 skipping to change at page 52, line 34
In addition to these mechanisms, the PING frame provides a way for a In addition to these mechanisms, the PING frame provides a way for a
client to easily test a connection. Connections that remain idle can client to easily test a connection. Connections that remain idle can
become broken as some middleboxes (for instance, network address become broken as some middleboxes (for instance, network address
translators, or load balancers) silently discard connection bindings. translators, or load balancers) silently discard connection bindings.
The PING frame allows a client to safely test whether a connection is The PING frame allows a client to safely test whether a connection is
still active without sending a request. still active without sending a request.
8.2. Server Push 8.2. Server Push
HTTP/2.0 enables a server to pre-emptively send (or "push") multiple HTTP/2 enables a server to pre-emptively send (or "push") multiple
associated resources to a client in response to a single request. associated resources to a client in response to a single request.
This feature becomes particularly helpful when the server knows the This feature becomes particularly helpful when the server knows the
client will need to have those resources available in order to fully client will need to have those resources available in order to fully
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. The SETTINGS_ENABLE_PUSH setting can between individual endpoints. The SETTINGS_ENABLE_PUSH setting can
be set to 0 to indicate that server push is disabled. Even if be set to 0 to indicate that server push is disabled. Even if
enabled, an intermediary could receive pushed resources from the enabled, an intermediary could receive pushed resources from the
server but could choose not to forward those on to the client. How server but could choose not to forward those on to the client. How
to make use of the pushed resources is up to that intermediary. to make use of the pushed resources is up to that intermediary.
Equally, the intermediary might choose to push additional resources Equally, the intermediary might choose to push additional resources
to the client, without any action taken by the server. to the client, without any action taken by the server.
A client cannot push resources. Clients and servers MUST operate as
though the server has disabled PUSH_PROMISE by setting the
SETTINGS_ENABLE_PUSH to 0. As a consequence, servers MUST treat the
receipt of a PUSH_PROMISE frame as a connection error
(Section 5.4.1). Clients MUST reject any attempt to change this
setting by treating the message as a connection error (Section 5.4.1)
of type PROTOCOL_ERROR.
A server can only push requests that are safe (see [HTTP-p2], Section A server can only push requests that are safe (see [HTTP-p2], Section
4.2.1), cacheable (see [HTTP-p6], Section 3) and do not include a 4.2.1), cacheable (see [HTTP-p6], Section 3) and do not include a
request body. request body.
8.2.1. Push Requests 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
request. The PUSH_PROMISE frame, or frames, sent by the server request. The PUSH_PROMISE frame, or frames, sent by the server
includes a header block that contains a complete set of request includes a header block that contains a complete set of request
header fields that the server attributes to the request. It is not header fields that the server attributes to the request. It is not
skipping to change at page 49, line 29 skipping to change at page 53, line 44
PROTOCOL_ERROR. 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 frames that reference the promised resources. This sending any frames that reference the promised resources. This
avoids a race where clients issue requests for resources prior to avoids a race where clients issue requests for 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 ensures
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. Similarly, 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)" state to the server. PUSH_PROMISE frames or "half closed (remote)" state to the server. PUSH_PROMISE frames
skipping to change at page 50, line 26 skipping to change at page 54, line 41
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. This does not prohibit a server from sending PUSH_PROMISE streams. This does not prohibit a server from sending PUSH_PROMISE
frames; clients need to reset any promised streams that are not frames; clients need to reset any promised streams that are not
wanted. wanted.
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 connection to
"example.com" is generally [[anchor15: 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".
8.3. The CONNECT Method 8.3. The CONNECT Method
The HTTP pseudo-method CONNECT ([HTTP-p2], Section 4.3.6) is used to The HTTP pseudo-method CONNECT ([HTTP-p2], Section 4.3.6) is used to
convert an HTTP/1.1 connection into a tunnel to a remote host. convert an HTTP/1.1 connection into a tunnel to a remote host.
CONNECT is primarily used with HTTP proxies to established a TLS CONNECT is primarily used with HTTP proxies to establish a TLS
session with a server for the purposes of interacting with "https" session with a server for the purposes of interacting with "https"
resources. resources.
In HTTP/2.0, the CONNECT method is used to establish a tunnel over a In HTTP/2, the CONNECT method is used to establish a tunnel over a
single HTTP/2.0 stream to a remote host. The HTTP header field single HTTP/2 stream to a remote host. The HTTP header field mapping
mapping works as mostly as defined in Request Header Fields works as mostly as defined in Request Header Fields
(Section 8.1.3.1), with a few differences. Specifically: (Section 8.1.3.1), with a few differences. Specifically:
o The ":method" header field is set to "CONNECT". o The ":method" header field is set to "CONNECT".
o The ":scheme" and ":path" header fields MUST be omitted. o The ":scheme" and ":path" header fields MUST be omitted.
o The ":authority" header field contains the host and port to o The ":authority" header field contains the host and port to
connect to (equivalent to the authority-form of the request-target connect to (equivalent to the authority-form of the request-target
of CONNECT requests, see [HTTP-p1], Section 5.3). of CONNECT requests, see [HTTP-p1], Section 5.3).
skipping to change at page 51, line 35 skipping to change at page 55, line 49
data with the FIN bit set on the last TCP segment. A proxy that data with the FIN bit set on the last TCP segment. A proxy that
receives a TCP segment with the FIN bit set sends a DATA frame with receives a TCP segment with the FIN bit set sends a DATA frame with
the END_STREAM flag set. Note that the final TCP segment or DATA the END_STREAM flag set. Note that the final TCP segment or DATA
frame could be empty. frame could be empty.
A TCP connection error is signaled with RST_STREAM. A proxy treats A TCP connection error is signaled with RST_STREAM. A proxy treats
any error in the TCP connection, which includes receiving a TCP any error in the TCP connection, which includes receiving a TCP
segment with the RST bit set, as a stream error (Section 5.4.2) of segment with the RST bit set, as a stream error (Section 5.4.2) of
type CONNECT_ERROR. Correspondingly, a proxy MUST send a TCP segment type CONNECT_ERROR. Correspondingly, a proxy MUST send a TCP segment
with the RST bit set if it detects an error with the stream or the with the RST bit set if it detects an error with the stream or the
HTTP/2.0 connection. HTTP/2 connection.
9. Additional HTTP Requirements/Considerations 9. Additional HTTP Requirements/Considerations
This section outlines attributes of the HTTP protocol that improve This section outlines attributes of the HTTP protocol that improve
interoperability, reduce exposure to known security vulnerabilities, interoperability, reduce exposure to known security vulnerabilities,
or reduce the potential for implementation variation. or reduce the potential for implementation variation.
9.1. Connection Management 9.1. Connection Management
HTTP/2.0 connections are persistent. For best performance, it is HTTP/2 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 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
near to exhausting the available stream identifiers (Section 5.1.1), near to exhausting the available stream identifiers (Section 5.1.1),
or to replace connections that have encountered errors or to replace connections that have encountered errors
(Section 5.4.1). (Section 5.4.1).
Clients MAY use a single connection for more than one origin when
each origin's hostname resolves to the same IP address, and they
share the same port. For "https" scheme origins, the server's
certificate MUST be valid for each origin's hostname. The
considerations in RFC 6125 [RFC6125] for verification of identity
apply.
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 SHOULD first send a GOAWAY TCP connection, the terminating endpoint SHOULD 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 9.2. Use of TLS Features
Implementations of HTTP/2.0 MUST support TLS 1.1 [TLS11]. [[anchor18: Implementations of HTTP/2 MUST support TLS 1.2 [TLS12]. The general
The working group intends to require at least the use of TLS 1.2 TLS usage guidance in [TLSBCP] SHOULD be followed, with some
[TLS12] prior to publication of this document; negotiating TLS 1.1 is additional restrictions that are specific to HTTP/2.
permitted to enable the creation of interoperable implementations of
early drafts.]]
The TLS implementation MUST support the Server Name Indication (SNI) The TLS implementation MUST support the Server Name Indication (SNI)
[TLS-EXT] extension to TLS. HTTP/2.0 clients MUST indicate the [TLS-EXT] extension to TLS. HTTP/2 clients MUST indicate the target
target domain name when negotiating TLS. domain name when negotiating TLS.
A server that receives a TLS handshake that does not include either The TLS implementation MUST disable compression. TLS compression can
TLS 1.1 or SNI, MUST NOT negotiate HTTP/2.0. Removing HTTP/2.0 lead to the exposure of information that would not otherwise be
protocols from consideration could result in the removal of all revealed [RFC3749]. Generic compression is unnecessary since HTTP/2
protocols from the set of protocols offered by the client. This provides compression features that are more aware of context and
causes protocol negotiation failure, as described in Section 3.2 of therefore likely to be more appropriate for use for performance,
[TLSALPN]. security or other reasons.
Implementations MUST negotiate ephemeral cipher suites (DHE or ECDHE)
with a minimum size of 2048 bits (DHE) or security level of 128 bits
(ECDHE). Clients MUST accept DHE sizes of up to 4096 bits.
An implementation that negotiates a TLS connection that does not meet
the requirements in this section, or any policy-based constraints,
SHOULD NOT negotiate HTTP/2. Removing HTTP/2 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].
Due to implementation limitations, it might not be possible to fail
TLS negotiation based on all of these requirements. An endpoint MUST
terminate a HTTP/2 connection that is opened on a TLS session that
does not meet these minimum requirements with a connection error
(Section 5.4.1) of type INADEQUATE_SECURITY.
Implementations are encouraged not to negotiate TLS cipher suites Implementations are encouraged not to negotiate TLS cipher suites
with known vulnerabilities, such as [RC4]. with known vulnerabilities, such as [RC4].
9.3. GZip Content-Encoding 9.3. GZip Content-Encoding
Clients MUST support gzip compression for HTTP response bodies. Clients MUST support gzip compression for HTTP response bodies.
Regardless of the value of the accept-encoding header field, a server Regardless of the value of the accept-encoding header field, a server
MAY send responses with gzip or deflate encoding. A compressed MAY send responses with gzip or deflate encoding. A compressed
response MUST still bear an appropriate content-encoding header response MUST still bear an appropriate content-encoding header
skipping to change at page 53, line 25 skipping to change at page 58, line 12
A server is considered authoritative for an "http" resource if the A server is considered authoritative for an "http" resource if the
connection is established to a resolved IP address for the domain in connection is established to a resolved IP address for the domain in
the origin of the resource. the origin of the resource.
A client MUST NOT use, in any way, resources provided by a server A client MUST NOT use, in any way, resources provided by a server
that is not authoritative for those resources. that is not authoritative for those resources.
10.2. Cross-Protocol Attacks 10.2. Cross-Protocol Attacks
When using TLS, we believe that HTTP/2.0 introduces no new cross- When using TLS, we believe that HTTP/2 introduces no new cross-
protocol attacks. TLS encrypts the contents of all transmission protocol attacks. TLS encrypts the contents of all transmission
(except the handshake itself), making it difficult for attackers to (except the handshake itself), making it difficult for attackers to
control the data which could be used in a cross-protocol attack. control the data which could be used in a cross-protocol attack.
[[anchor21: Issue: This is no longer true]] [[anchor19: Issue: This is no longer true]]
10.3. Intermediary Encapsulation Attacks 10.3. Intermediary Encapsulation Attacks
HTTP/2.0 header field names and values are encoded as sequences of HTTP/2 header field names and values are encoded as sequences of
octets with a length prefix. This enables HTTP/2.0 to carry any octets with a length prefix. This enables HTTP/2 to carry any string
string of octets as the name or value of a header field. An of octets as the name or value of a header field. An intermediary
intermediary that translates HTTP/2.0 requests or responses into that translates HTTP/2 requests or responses into HTTP/1.1 directly
HTTP/1.1 directly could permit the creation of corrupted HTTP/1.1 could permit the creation of corrupted HTTP/1.1 messages. An
messages. An attacker might exploit this behavior to cause the attacker might exploit this behavior to cause the intermediary to
intermediary to create HTTP/1.1 messages with illegal header fields, create HTTP/1.1 messages with illegal header fields, extra header
extra header fields, or even new messages that are entirely fields, or even new messages that are entirely falsified.
falsified.
An intermediary that performs translation into HTTP/1.1 cannot alter An intermediary that performs translation into HTTP/1.1 cannot alter
the semantics of requests or responses. In particular, header field the semantics of requests or responses. In particular, header field
names or values that contain characters not permitted by HTTP/1.1, names or values that contain characters not permitted by HTTP/1.1,
including carriage return (U+000D) or line feed (U+000A) MUST NOT be including carriage return (U+000D) or line feed (U+000A) MUST NOT be
translated verbatim, as stipulated in [HTTP-p1], Section 3.2.4. translated verbatim, as stipulated in [HTTP-p1], Section 3.2.4.
Translation from HTTP/1.x to HTTP/2.0 does not produce the same Translation from HTTP/1.x to HTTP/2 does not produce the same
opportunity to an attacker. Intermediaries that perform translation opportunity to an attacker. Intermediaries that perform translation
to HTTP/2.0 MUST remove any instances of the "obs-fold" production to HTTP/2 MUST remove any instances of the "obs-fold" production from
from header field values. header field values.
10.4. Cacheability of Pushed Resources 10.4. Cacheability of Pushed Resources
Pushed resources are responses without an explicit request; the Pushed resources are responses without an explicit request from the
request for a pushed resource is synthesized from the request that client. Request header fields are provided by the server in the
triggered the push, plus resource identification information provided PUSH_PROMISE frame. These header fields are provided so that
by the server. Request header fields are necessary for HTTP cache existing HTTP semantics can be applied.
control validations (such as the Vary header field) to work. For
this reason, caches MUST associate the request header fields from the
PUSH_PROMISE frame with the response headers and content delivered on
the pushed stream. This includes the Cookie header field.
Caching resources that are pushed is possible, based on the guidance Caching resources that are pushed is possible based on the guidance
provided by the origin server in the Cache-Control header field. provided by the origin server in the Cache-Control header field.
However, this can cause issues if a single server hosts more than one However, this can cause issues if a single server hosts more than one
tenant. For example, a server might offer multiple users each a tenant. For example, a server might offer multiple users each a
small portion of its URI space. small portion of its URI space.
Where multiple tenants share space on the same server, that server Where multiple tenants share space on the same server, that server
MUST ensure that tenants are not able to push representations of MUST ensure that tenants are not able to push representations of
resources that they do not have authority over. Failure to enforce resources that they do not have authority over. Failure to enforce
this would allow a tenant to provide a representation that would be this would allow a tenant to provide a representation that would be
served out of cache, overriding the actual representation that the served out of cache, overriding the actual representation that the
authoritative tenant provides. authoritative tenant provides.
Pushed resources for which an origin server is not authoritative are Pushed resources for which an origin server is not authoritative are
never cached or used. never cached or used.
10.5. Denial of Service Considerations 10.5. Denial of Service Considerations
An HTTP/2.0 connection can demand a greater commitment of resources An HTTP/2 connection can demand a greater commitment of resources to
to operate than a HTTP/1.1 connection. The use of header compression operate than a HTTP/1.1 connection. The use of header compression
and flow control require that an implementation commit resources for and flow control depend on a commitment of resources for storing a
storing a greater amount of state. Settings for these features greater amount of state. Settings for these features ensure that
ensure that memory commitments for these features are strictly memory commitments for these features are strictly bounded.
bounded. Processing capacity cannot be guarded in the same fashion. Processing capacity cannot be guarded in the same fashion.
The SETTINGS frame can be abused to cause a peer to expend additional The SETTINGS frame can be abused to cause a peer to expend additional
processing time. This might be done by pointlessly changing processing time. This might be done by pointlessly changing
settings, setting multiple undefined settings, or changing the same settings, setting multiple undefined settings, or changing the same
setting multiple times in the same frame. Similarly, WINDOW_UPDATE setting multiple times in the same frame. Similarly, WINDOW_UPDATE
or PRIORITY frames can be abused to cause an unnecessary waste of or PRIORITY frames can be abused to cause an unnecessary waste of
resources. resources.
Large numbers of small or empty frames can be abused to cause a peer Large numbers of small or empty frames can be abused to cause a peer
to expend time processing frame headers. Note however that some uses to expend time processing frame headers. Note however that some uses
are entirely legitimate, such as the sending of an empty DATA frame are entirely legitimate, such as the sending of an empty DATA frame
to end a stream. to end a stream.
Header compression also offers some opportunities to waste processing Header compression also offers some opportunities to waste processing
resources, see [COMPRESSION] for more details on potential abuses. resources, see [COMPRESSION] for more details on potential abuses.
Limits in settings cannot be reduced instantaneously, which leaves an
endpoint exposed to behavior from a peer that could exceed the new
limits. In particular, immediately after establishing a connection,
limits set by a server are not known to clients and could be exceeded
without being an obvious protocol violation.
In all these cases, there are legitimate reasons to use these In all these cases, there are legitimate reasons to use these
protocol mechanisms. These features become a burden only when they protocol mechanisms. These features become a burden only when they
are used unnecessarily or to excess. are used unnecessarily or to excess.
An endpoint that doesn't monitor this behavior exposes itself to a An endpoint that doesn't monitor this behavior exposes itself to a
risk of denial of service attack. Implementations SHOULD track the risk of denial of service attack. Implementations SHOULD track the
use of these types of frames and set limits on their use. An use of these features and set limits on their use. An endpoint MAY
endpoint MAY treat activity that is suspicious as a connection error treat activity that is suspicious as a connection error
(Section 5.4.1) of type ENHANCE_YOUR_CALM. (Section 5.4.1) of type ENHANCE_YOUR_CALM.
10.6. Use of Padding
Padding within HTTP/2 is not intended as a replacement for general
purpose padding, such as might be provided by TLS [TLS12]. Redundant
padding could even be counterproductive. Correct application can
depend on having specific knowledge of the data that is being padded.
To mitigate attacks that rely on compression, disabling compression
might be preferable to padding as a countermeasure.
Padding can be used to obscure the exact size of frame content.
Padding is provided to mitigate specific attacks within HTTP. For
example, attacks where compressed content includes both attacker-
controlled plaintext and secret data (see for example, [BREACH]).
Use of padding can result in less protection than might seem
immediately obvious. At best, padding only makes it more difficult
for an attacker to infer length information by increasing the number
of frames an attacker has to observe. Incorrectly implemented
padding schemes can be easily defeated. In particular, randomized
padding with a predictable distribution provides very little
protection; or padding payloads to a fixed size exposes information
as payload sizes cross the fixed size boundary, which could be
possible if an attacker can control plaintext.
Intermediaries SHOULD NOT remove padding; though an intermediary
could remove padding and add differing amounts if the intent is to
improve the protections padding affords.
11. Privacy Considerations 11. Privacy Considerations
HTTP/2.0 aims to keep connections open longer between clients and HTTP/2 aims to keep connections open longer between clients and
servers in order to reduce the latency when a user makes a request. servers in order to reduce the latency when a user makes a request.
The maintenance of these connections over time could be used to The maintenance of these connections over time could be used to
expose private information. For example, a user using a browser expose private information. For example, a user using a browser
hours after the previous user stopped using that browser may be able hours after the previous user stopped using that browser may be able
to learn about what the previous user was doing. This is a problem to learn about what the previous user was doing. This is a problem
with HTTP in its current form as well, however the short lived with HTTP in its current form as well, however the short lived
connections make it less of a risk. connections make it less of a risk.
12. IANA Considerations 12. IANA Considerations
A string for identifying HTTP/2.0 is entered into the "Application A string for identifying HTTP/2 is entered into the "Application
Layer Protocol Negotiation (ALPN) Protocol IDs" registry established Layer Protocol Negotiation (ALPN) Protocol IDs" registry established
in [TLSALPN]. in [TLSALPN].
This document establishes registries for frame types, error codes and This document establishes registries for error codes. This new
settings. These new registries are entered in a new "Hypertext registry is entered into a new "Hypertext Transfer Protocol (HTTP) 2
Transfer Protocol (HTTP) 2.0 Parameters" section. Parameters" section.
This document registers the "HTTP2-Settings" header field for use in This document registers the "HTTP2-Settings" header field for use in
HTTP. HTTP.
12.1. Registration of HTTP/2.0 Identification String This document registers the "PRI" method for use in HTTP, to avoid
collisions with the connection header (Section 3.5).
This document creates a registration for the identification of
HTTP/2.0 in the "Application Layer Protocol Negotiation (ALPN)
Protocol IDs" registry established in [TLSALPN].
Protocol: HTTP/2.0
Identification Sequence: 0x48 0x54 0x54 0x50 0x2f 0x32 0x2e 0x30
("HTTP/2.0")
Specification: This document (RFCXXXX)
12.2. Frame Type Registry
This document establishes a registry for HTTP/2.0 frame types. The 12.1. Registration of HTTP/2 Identification String
"HTTP/2.0 Frame Type" registry operates under the "IETF Review"
policy [RFC5226].
Frame types are an 8-bit value. When reviewing new frame type This document creates a registration for the identification of HTTP/2
registrations, special attention is advised for any frame type- in the "Application Layer Protocol Negotiation (ALPN) Protocol IDs"
specific flags that are defined. Frame flags can interact with registry established in [TLSALPN].
existing flags and could prevent the creation of globally applicable
flags.
Initial values for the "HTTP/2.0 Frame Type" registry are shown in Protocol: HTTP/2
Table 1.
+--------+---------------+---------------------------+--------------+ Identification Sequence: 0x68 0x32 ("h2")
| Frame | Name | Flags | Section |
| Type | | | |
+--------+---------------+---------------------------+--------------+
| 0 | DATA | END_STREAM(1) | Section 6.1 |
| 1 | HEADERS | END_STREAM(1), | Section 6.2 |
| | | END_HEADERS(4), | |
| | | PRIORITY(8) | |
| 2 | PRIORITY | - | Section 6.3 |
| 3 | RST_STREAM | - | Section 6.4 |
| 4 | SETTINGS | ACK(1) | Section 6.5 |
| 5 | PUSH_PROMISE | END_PUSH_PROMISE(4) | Section 6.6 |
| 6 | PING | ACK(1) | Section 6.7 |
| 7 | GOAWAY | - | Section 6.8 |
| 9 | WINDOW_UPDATE | - | Section 6.9 |
| 10 | CONTINUATION | END_HEADERS(4) | Section 6.10 |
+--------+---------------+---------------------------+--------------+
Table 1 Specification: This document (RFCXXXX)
12.3. 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 error codes. The
"HTTP/2.0 Error Code" registry manages a 32-bit space. The "HTTP/2.0 "HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2
Error Code" registry operates under the "Expert Review" policy Error Code" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
Registrations for error codes are required to include a description Registrations for error codes are required to include a description
of the error code. An expert reviewer is advised to examine new of the error code. An expert reviewer is advised to examine new
registrations for possible duplication with existing error codes. registrations for possible duplication with existing error codes.
Use of existing registrations is to be encouraged, but not mandated. Use of existing registrations is to be encouraged, but not mandated.
New registrations are advised to provide the following information: New registrations are advised to provide the following information:
skipping to change at page 57, line 25 skipping to change at page 62, line 5
optional. optional.
Description: A description of the conditions where the error code is Description: A description of the conditions where the error code is
applicable. applicable.
Specification: An optional reference for a specification that Specification: An optional reference for a specification that
defines the error code. defines the error code.
An initial set of error code registrations can be found in Section 7. An initial set of error code registrations can be found in Section 7.
12.4. Settings Registry 12.3. HTTP2-Settings Header Field Registration
This document establishes a registry for HTTP/2.0 settings. The
"HTTP/2.0 Settings" registry manages a 24-bit space. The "HTTP/2.0
Settings" registry operates under the "Expert Review" policy
[RFC5226].
Registrations for settings are required to include a description of
the setting. An expert reviewer is advised to examine new
registrations for possible duplication with existing settings. Use
of existing registrations is to be encouraged, but not mandated.
New registrations are advised to provide the following information:
Setting: The 24-bit setting value.
Name: A name for the setting. Specifying a name is optional.
Flags: Any setting-specific flags that apply, including their value
and semantics.
Description: A description of the setting. This might include the
range of values, any applicable units and how to act upon a value
when it is provided.
Specification: An optional reference for a specification that
defines the setting.
An initial set of settings registrations can be found in
Section 6.5.2.
12.5. HTTP2-Settings Header Field Registration
This section registers the "HTTP2-Settings" header field in the This section registers the "HTTP2-Settings" header field in the
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): Section 3.2.1 of 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
client for Upgrade-based negotiation. client for Upgrade-based negotiation.
12.4. PRI Method Registration
This section registers the "PRI" method in the HTTP Method Registry
[HTTP-p2].
Method Name: PRI
Safe No
Idempotent No
Specification document(s) Section 3.5 of this document
Related information: This method is never used by an actual client.
This method will appear to be used when an HTTP/1.1 server or
intermediary attempts to parse an HTTP/2 connection header.
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
Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay, Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors). Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism) o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism).
o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
Jitu Padhye, Roberto Peon, Rob Trace (Flow control) Jitu Padhye, Roberto Peon, Rob Trace (Flow control).
o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike
Bishop, Herve Ruellan (Substantial editorial contributions) Bishop, Herve Ruellan (Substantial editorial contributions).
o Alexey Melnikov was an editor of this document during 2013.
o A substantial proportion of Martin's contribution was supported by
Microsoft during his employment there.
14. References 14. References
14.1. Normative References 14.1. Normative References
[COMPRESSION] Ruellan, H. and R. Peon, "HPACK - Header Compression [COMPRESSION] Ruellan, H. and R. Peon, "HPACK - Header Compression
for HTTP/2.0", for HTTP/2", draft-ietf-httpbis-header-compression-06
draft-ietf-httpbis-header-compression-05 (work in (work in progress), February 2014.
progress), December 2013.
[COOKIE] Barth, A., "HTTP State Management Mechanism", [COOKIE] Barth, A., "HTTP State Management Mechanism",
RFC 6265, April 2011. RFC 6265, April 2011.
[HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", draft-ietf-httpbis-p1-messaging-25 (work in Routing", draft-ietf-httpbis-p1-messaging-26 (work in
progress), November 2013. progress), February 2014.
[HTTP-p2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [HTTP-p2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content", Transfer Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-25 (work in progress), draft-ietf-httpbis-p2-semantics-26 (work in progress),
November 2013. February 2014.
[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-25 (work in draft-ietf-httpbis-p4-conditional-26 (work in
progress), November 2013. progress), February 2014.
[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-25 (work in Requests", draft-ietf-httpbis-p5-range-26 (work in
progress), November 2013. progress), February 2014.
[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-25 (work in Caching", draft-ietf-httpbis-p6-cache-26 (work in
progress), November 2013. progress), February 2014.
[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-25 (work in progress), draft-ietf-httpbis-p7-auth-26 (work in progress),
November 2013. February 2014.
[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,
"Uniform Resource Identifier (URI): Generic Syntax", "Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005. STD 66, RFC 3986, January 2005.
[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.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service
Identity within Internet Public Key Infrastructure
Using X.509 (PKIX) Certificates in the Context of
Transport Layer Security (TLS)", RFC 6125, March 2011.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011. December 2011.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, [TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
January 2011. 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 [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008. 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-02 (work in progress), draft-ietf-tls-applayerprotoneg-04 (work in progress),
September 2013. January 2014.
14.2. Informative References 14.2. Informative References
[AltSvc] Nottingham, M., "HTTP Alternate Services",
draft-nottingham-httpbis-alt-svc-01 (work in
progress), December 2013.
[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.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving
the CRIME Attack", July 2013, <http://
breachattack.com/resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[RC4] Rivest, R., "The RC4 encryption algorithm", RSA Data [RC4] Rivest, R., "The RC4 encryption algorithm", RSA Data
Security, Inc. , March 1992. 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.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004.
[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>.
[TLSBCP] Sheffer, Y. and R. Holz, "Recommendations for Secure
Use of TLS and DTLS", draft-sheffer-tls-bcp-01 (work
in progress), September 2013.
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-http2-08 A.1. Since draft-ietf-httpbis-http2-09
Adding padding for data frames.
Renumbering frame types, error codes, and settings.
Adding INADEQUATE_SECURITY error code.
Updating TLS usage requirements to 1.2; forbidding TLS compression.
Removing extensibility for frames and settings.
Changing setting identifier size.
Removing the ability to disable flow control.
Changing the protocol identification token to "h2".
Changing the use of :authority to make it optional and to allow
userinfo in non-HTTP cases.
Allowing split on 0x0 for Cookie.
Reserved PRI method in HTTP/1.1 to avoid possible future collisions.
A.2. Since draft-ietf-httpbis-http2-08
Added cookie crumbling for more efficient header compression. Added cookie crumbling for more efficient header compression.
Added header field ordering with the value-concatenation mechanism. Added header field ordering with the value-concatenation mechanism.
A.2. Since draft-ietf-httpbis-http2-07 A.3. Since draft-ietf-httpbis-http2-07
Marked draft for implementation. Marked draft for implementation.
A.3. Since draft-ietf-httpbis-http2-06 A.4. Since draft-ietf-httpbis-http2-06
Adding definition for CONNECT method. Adding definition for CONNECT method.
Constraining the use of push to safe, cacheable methods with no Constraining the use of push to safe, cacheable methods with no
request body. request body.
Changing from :host to :authority to remove any potential confusion. Changing from :host to :authority to remove any potential confusion.
Adding setting for header compression table size. Adding setting for header compression table size.
Adding settings acknowledgement. Adding settings acknowledgement.
Removing unnecessary and potentially problematic flags from Removing unnecessary and potentially problematic flags from
CONTINUATION. CONTINUATION.
Added denial of service considerations. Added denial of service considerations.
A.4. Since draft-ietf-httpbis-http2-05 A.5. Since draft-ietf-httpbis-http2-05
Marking the draft ready for implementation. Marking the draft ready for implementation.
Renumbering END_PUSH_PROMISE flag. Renumbering END_PUSH_PROMISE flag.
Editorial clarifications and changes. Editorial clarifications and changes.
A.5. Since draft-ietf-httpbis-http2-04 A.6. Since draft-ietf-httpbis-http2-04
Added CONTINUATION frame for HEADERS and PUSH_PROMISE. Added CONTINUATION frame for HEADERS and PUSH_PROMISE.
PUSH_PROMISE is no longer implicitly prohibited if PUSH_PROMISE is no longer implicitly prohibited if
SETTINGS_MAX_CONCURRENT_STREAMS is zero. SETTINGS_MAX_CONCURRENT_STREAMS is zero.
Push expanded to allow all safe methods without a request body. Push expanded to allow all safe methods without a request body.
Clarified the use of HTTP header fields in requests and responses. Clarified the use of HTTP header fields in requests and responses.
Prohibited HTTP/1.1 hop-by-hop header fields. Prohibited HTTP/1.1 hop-by-hop header fields.
Requiring that intermediaries not forward requests with missing or Requiring that intermediaries not forward requests with missing or
illegal routing :-headers. illegal routing :-headers.
Clarified requirements around handling different frames after stream Clarified requirements around handling different frames after stream
close, stream reset and GOAWAY. close, stream reset and GOAWAY.
Added more specific prohibitions for sending of different frame types Added more specific prohibitions for sending of different frame types
in various stream states. in various stream states.
skipping to change at page 62, line 20 skipping to change at page 67, line 30
Clarified requirements around handling different frames after stream Clarified requirements around handling different frames after stream
close, stream reset and GOAWAY. close, stream reset and GOAWAY.
Added more specific prohibitions for sending of different frame types Added more specific prohibitions for sending of different frame types
in various stream states. in various stream states.
Making the last received setting value the effective value. Making the last received setting value the effective value.
Clarified requirements on TLS version, extension and ciphers. Clarified requirements on TLS version, extension and ciphers.
A.6. Since draft-ietf-httpbis-http2-03 A.7. 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.7. Since draft-ietf-httpbis-http2-02 A.8. 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.8. Since draft-ietf-httpbis-http2-01 A.9. 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 63, line 31 skipping to change at page 68, line 42
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.9. Since draft-ietf-httpbis-http2-00 A.10. 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.10. Since draft-mbelshe-httpbis-spdy-00 A.11. 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
Twist Twist
EMail: mbelshe@chromium.org EMail: mbelshe@chromium.org
Roberto Peon Roberto Peon
Google, Inc Google, Inc
EMail: fenix@google.com EMail: fenix@google.com
Martin Thomson (editor) Martin Thomson (editor)
Microsoft Mozilla
3210 Porter Drive Suite 300
Palo Alto 94304 650 Castro Street
Mountain View, CA 94041
US US
EMail: martin.thomson@gmail.com EMail: martin.thomson@gmail.com
Alexey Melnikov (editor)
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com
 End of changes. 228 change blocks. 
560 lines changed or deleted 777 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/