draft-ietf-httpbis-http2-14.txt   draft-ietf-httpbis-http2-15.txt 
HTTPbis Working Group M. Belshe HTTPbis Working Group M. Belshe
Internet-Draft Twist Internet-Draft Twist
Intended status: Standards Track R. Peon Intended status: Standards Track R. Peon
Expires: January 31, 2015 Google, Inc Expires: April 30, 2015 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Mozilla Mozilla
July 30, 2014 October 27, 2014
Hypertext Transfer Protocol version 2 Hypertext Transfer Protocol version 2
draft-ietf-httpbis-http2-14 draft-ietf-httpbis-http2-15
Abstract Abstract
This specification describes an optimized expression of the syntax of This specification describes an optimized expression of the semantics
the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more of 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 specification is an alternative to, but does not obsolete, the This specification 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.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
skipping to change at page 2, line 4 skipping to change at page 2, line 4
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 31, 2015. This Internet-Draft will expire on April 30, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 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
skipping to change at page 2, line 40 skipping to change at page 2, line 40
3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10 3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10
3.3. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 11 3.3. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 11
3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 11 3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 11
3.5. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 11 3.5. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 11
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Header Compression and Decompression . . . . . . . . . . 14 4.3. Header Compression and Decompression . . . . . . . . . . 14
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 15 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 15
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 16 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 16
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 21
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 22 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 22
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 22 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 22
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 24
5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24 5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24
5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25 5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25
5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 25 5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 26
5.3.4. Prioritization State Management . . . . . . . . . . . 26 5.3.4. Prioritization State Management . . . . . . . . . . . 26
5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27 5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 27 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 28
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 28 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 28
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28
5.4.3. Connection Termination . . . . . . . . . . . . . . . 29 5.4.3. Connection Termination . . . . . . . . . . . . . . . 29
5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 29 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 29
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 30 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 30
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 33 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 34
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 34 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 35
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 35 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 36
6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36 6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 37
6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 37 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 37
6.5.3. Settings Synchronization . . . . . . . . . . . . . . 38 6.5.3. Settings Synchronization . . . . . . . . . . . . . . 38
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 39
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 44 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 45
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 45 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 46
6.9.2. Initial Flow Control Window Size . . . . . . . . . . 46 6.9.2. Initial Flow Control Window Size . . . . . . . . . . 47
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 47 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 48
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 48 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 48
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 48 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 49
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 50 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 50
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 50 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 51
8.1.1. Upgrading From HTTP/2 . . . . . . . . . . . . . . . . 51 8.1.1. Upgrading From HTTP/2 . . . . . . . . . . . . . . . . 52
8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 51 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 52
8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 55 8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 56
8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 57 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 59
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 58 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 59
8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 59 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 60
8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 60 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 61
8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 61 8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 62
9. Additional HTTP Requirements/Considerations . . . . . . . . . 62 9. Additional HTTP Requirements/Considerations . . . . . . . . . 63
9.1. Connection Management . . . . . . . . . . . . . . . . . . 62 9.1. Connection Management . . . . . . . . . . . . . . . . . . 64
9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 63 9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 64
9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 63 9.1.2. The 421 (Misdirected Request) Status Code . . . . . . 65
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 65
9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 64 9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 66
9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 65 9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 66
10. Security Considerations . . . . . . . . . . . . . . . . . . . 65 10. Security Considerations . . . . . . . . . . . . . . . . . . . 67
10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 65 10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 67
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 66 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 67
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 66 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 68
10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 67 10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 68
10.5. Denial of Service Considerations . . . . . . . . . . . . 67 10.5. Denial of Service Considerations . . . . . . . . . . . . 68
10.5.1. Limits on Header Block Size . . . . . . . . . . . . 68 10.5.1. Limits on Header Block Size . . . . . . . . . . . . 70
10.6. Use of Compression . . . . . . . . . . . . . . . . . . . 69 10.6. Use of Compression . . . . . . . . . . . . . . . . . . . 70
10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . 69 10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . 71
10.8. Privacy Considerations . . . . . . . . . . . . . . . . . 70 10.8. Privacy Considerations . . . . . . . . . . . . . . . . . 71
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 72
11.1. Registration of HTTP/2 Identification Strings . . . . . 70 11.1. Registration of HTTP/2 Identification Strings . . . . . 72
11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 71 11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 72
11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 72 11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 73
11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 72 11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 74
11.5. HTTP2-Settings Header Field Registration . . . . . . . . 73 11.5. HTTP2-Settings Header Field Registration . . . . . . . . 75
11.6. PRI Method Registration . . . . . . . . . . . . . . . . 74 11.6. PRI Method Registration . . . . . . . . . . . . . . . . 76
11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . 74 11.7. The 421 (Misdirected Request) HTTP Status Code . . . . . 76
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 76
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 75 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 77
13.1. Normative References . . . . . . . . . . . . . . . . . . 75 13.1. Normative References . . . . . . . . . . . . . . . . . . 77
13.2. Informative References . . . . . . . . . . . . . . . . . 77 13.2. Informative References . . . . . . . . . . . . . . . . . 78
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 78 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 79 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 80
A.1. Since draft-ietf-httpbis-http2-13 . . . . . . . . . . . . 79 A.1. Since draft-ietf-httpbis-http2-14 . . . . . . . . . . . . 80
A.2. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 79 A.2. Since draft-ietf-httpbis-http2-13 . . . . . . . . . . . . 80
A.3. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 79 A.3. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 80
A.4. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 80 A.4. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 80
A.5. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 80 A.5. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 81
A.6. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 80 A.6. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 81
A.7. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 81 A.7. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 82
A.8. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 81 A.8. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 82
A.9. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 81 A.9. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 82
A.10. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 81 A.10. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 82
A.11. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 82 A.11. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 82
A.12. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 82 A.12. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 83
A.13. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 82 A.13. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 83
A.14. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 83 A.14. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 83
A.15. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 83 A.15. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 84
A.16. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 84
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 ([RFC7230], protocol. However, the HTTP/1.1 message format ([RFC7230],
Section 3) was designed to be implemented with the tools at hand in Section 3) has several characteristics that have a negative overall
the 1990s, not modern Web application performance. As such it has effect on application performance today.
several characteristics that have a negative overall effect on
application performance today.
In particular, HTTP/1.0 only allows one request to be outstanding at In particular, HTTP/1.0 allowed only one request to be outstanding at
a time on a given connection. HTTP/1.1 pipelining only partially a time on a given TCP connection. HTTP/1.1 added request pipelining,
addressed request concurrency and suffers from head-of-line blocking. but this only partially addressed request concurrency and still
Therefore, clients that need to make many requests typically use suffers from head-of-line blocking. Therefore, HTTP/1.1 clients that
multiple connections to a server in order to reduce latency. need to make many requests typically use multiple connections to a
server in order to achieve concurrency and thereby reduce latency.
Furthermore, HTTP/1.1 header fields are often repetitive and verbose, Furthermore, HTTP header fields are often repetitive and verbose,
which, in addition to generating more or larger network packets, can causing unnecessary network traffic, as well as causing the initial
cause the small initial TCP [TCP] congestion window to quickly fill. TCP [TCP] congestion window to quickly fill. This can result in
This can result in excessive latency when multiple requests are made excessive latency when multiple requests are made on a new TCP
on a single new TCP connection. connection.
This specification addresses these issues by defining an optimized HTTP/2 addresses these issues by defining an optimized mapping of
mapping of HTTP's semantics to an underlying connection. HTTP's semantics to an underlying connection. Specifically, it
Specifically, it allows interleaving of request and response messages allows interleaving of request and response messages on the same
on the same connection and uses an efficient coding for HTTP header connection and uses an efficient coding for HTTP header fields. It
fields. It also allows prioritization of requests, letting more also allows prioritization of requests, letting more important
important requests complete more quickly, further improving requests complete more quickly, further improving performance.
performance.
The resulting protocol is designed to be more friendly to the The resulting protocol is more friendly to the network, because fewer
network, because fewer TCP connections can be used in comparison to TCP connections can be used in comparison to HTTP/1.x. This means
HTTP/1.x. This means less competition with other flows, and longer- less competition with other flows, and longer-lived connections,
lived connections, which in turn leads to better utilization of which in turn leads to better utilization of available network
available network capacity. capacity.
Finally, this encapsulation also enables more efficient processing of Finally, HTTP/2 also enables more efficient processing of messages
messages through use of binary message framing. through use of binary message framing.
2. HTTP/2 Protocol Overview 2. HTTP/2 Protocol Overview
HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2 HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2
supports all of the core features of HTTP/1.1, but aims to be more supports all of the core features of HTTP/1.1, but aims to be more
efficient in several ways. efficient in several ways.
The basic protocol unit in HTTP/2 is a frame (Section 4.1). Each The basic protocol unit in HTTP/2 is a frame (Section 4.1). Each
frame type serves a different purpose. For example, HEADERS and DATA frame type serves a different purpose. For example, HEADERS and DATA
frames form the basis of HTTP requests and responses (Section 8.1); frames form the basis of HTTP requests and responses (Section 8.1);
other frame types like SETTINGS, WINDOW_UPDATE, and PUSH_PROMISE are other frame types like SETTINGS, WINDOW_UPDATE, and PUSH_PROMISE are
used in support of other HTTP/2 features. used in support of other HTTP/2 features.
Multiplexing of requests is achieved by having each HTTP request- Multiplexing of requests is achieved by having each HTTP request-
response exchanged assigned to a single stream (Section 5). Streams response exchange associated with its own stream (Section 5).
are largely independent of each other, so a blocked or stalled Streams are largely independent of each other, so a blocked or
request does not prevent progress on other requests. stalled request or response does not prevent progress on other
streams.
Flow control and prioritization ensure that it is possible to Flow control and prioritization ensure that it is possible to
properly use multiplexed streams. Flow control (Section 5.2) helps efficiently use multiplexed streams. Flow control (Section 5.2)
to ensure that only data that can be used by a receiver is helps to ensure that only data that can be used by a receiver is
transmitted. Prioritization (Section 5.3) ensures that limited transmitted. Prioritization (Section 5.3) ensures that limited
resources can be directed to the most important requests first. resources can be directed to the most important streams first.
HTTP/2 adds a new interaction mode, whereby a server can push HTTP/2 adds a new interaction mode, whereby a server can push
responses to a client (Section 8.2). Server push allows a server to responses to a client (Section 8.2). Server push allows a server to
speculatively send a client data that the server anticipates the speculatively send data to a client that the server anticipates the
client will need, trading off some network usage against a potential client will need, trading off some network usage against a potential
latency gain. The server does this by synthesizing a request, which latency gain. The server does this by synthesizing a request, which
it sends as a PUSH_PROMISE frame. The server is then able to send a it sends as a PUSH_PROMISE frame. The server is then able to send a
response to the synthetic request on a separate stream. response to the synthetic request on a separate stream.
Frames that contain HTTP header fields are compressed (Section 4.3). Frames that contain HTTP header fields are compressed (Section 4.3).
HTTP requests can be highly redundant, so compression can reduce the HTTP requests can be highly redundant, so compression can reduce the
size of requests and responses significantly. size of requests and responses significantly.
2.1. Document Organization 2.1. Document Organization
skipping to change at page 6, line 31 skipping to change at page 6, line 31
streams. streams.
o Frame (Section 6) and error (Section 7) definitions include o Frame (Section 6) and error (Section 7) definitions include
details of the frame and error types used in HTTP/2. details of the frame and error types used in HTTP/2.
o HTTP mappings (Section 8) and additional requirements (Section 9) o HTTP mappings (Section 8) and additional requirements (Section 9)
describe how HTTP semantics are expressed using frames and describe how HTTP semantics are expressed using frames and
streams. streams.
While some of the frame and stream layer concepts are isolated from While some of the frame and stream layer concepts are isolated from
HTTP, the intent is not to define a completely generic framing layer. HTTP, this specification does not define a completely generic framing
The framing and streams layers are tailored to the needs of the HTTP layer. The framing and streams layers are tailored to the needs of
protocol and server push. the HTTP protocol and server push.
2.2. Conventions and Terminology 2.2. 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/2 connection. client: The endpoint initiating the HTTP/2 connection.
connection: A transport-level connection between two endpoints. connection: A transport-layer connection between two endpoints.
connection error: An error that affects the entire HTTP/2 connection error: An error that affects the entire HTTP/2
connection. 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 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 octets 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/2 connection. server: The endpoint which did not initiate the HTTP/2 connection.
skipping to change at page 7, line 34 skipping to change at page 7, line 34
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 connection. within the HTTP/2 connection.
stream error: An error on the individual HTTP/2 stream. stream error: An error on the individual HTTP/2 stream.
Finally, the terms "gateway", "intermediary", "proxy", and "tunnel" Finally, the terms "gateway", "intermediary", "proxy", and "tunnel"
are defined in Section 2.3 of [RFC7230]. are defined in Section 2.3 of [RFC7230].
3. Starting HTTP/2 3. Starting HTTP/2
An HTTP/2 connection is an application level protocol running on top An HTTP/2 connection is an application layer protocol running on 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.
HTTP/2 uses the same "http" and "https" URI schemes used by HTTP/1.1. HTTP/2 uses the same "http" and "https" URI schemes used by HTTP/1.1.
HTTP/2 shares the same default port numbers: 80 for "http" URIs and HTTP/2 shares the same default port numbers: 80 for "http" URIs and
443 for "https" URIs. As a result, implementations processing 443 for "https" URIs. As a result, implementations processing
requests for target resource URIs like "http://example.org/foo" or requests for target resource URIs like "http://example.org/foo" or
"https://example.com/bar" are required to first discover whether the "https://example.com/bar" are required to first discover whether the
upstream server (the immediate peer to which the client wishes to upstream server (the immediate peer to which the client wishes to
establish a connection) supports HTTP/2. establish a connection) supports HTTP/2.
skipping to change at page 8, line 11 skipping to change at page 8, line 11
The means by which support for HTTP/2 is determined is different for The means by which support for HTTP/2 is determined is different for
"http" and "https" URIs. Discovery for "http" URIs is described in "http" and "https" URIs. Discovery for "http" URIs is described in
Section 3.2. Discovery for "https" URIs is described in Section 3.3. Section 3.2. Discovery for "https" URIs is described in Section 3.3.
3.1. HTTP/2 Version Identification 3.1. HTTP/2 Version Identification
The protocol defined in this document has two identifiers. The protocol defined in this document has two identifiers.
o The string "h2" identifies the protocol where HTTP/2 uses TLS o The string "h2" identifies the protocol where HTTP/2 uses TLS
[TLS12]. This identifier is used in the TLS application layer [TLS12]. This identifier is used in the TLS application layer
protocol negotiation extension (ALPN) [TLS-ALPN] field and any protocol negotiation extension (ALPN) [TLS-ALPN] field and in any
place that HTTP/2 over TLS is identified. place where HTTP/2 over TLS is identified.
The "h2" string is serialized into an ALPN protocol identifier as The "h2" string is serialized into an ALPN protocol identifier as
the two octet sequence: 0x68, 0x32. the two octet sequence: 0x68, 0x32.
o The string "h2c" identifies the protocol where HTTP/2 is run over o The string "h2c" identifies the protocol where HTTP/2 is run over
cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade
header field and any place that HTTP/2 over TCP is identified. header field and in any place where HTTP/2 over TCP is identified.
Negotiating "h2" or "h2c" implies the use of the transport, security, Negotiating "h2" or "h2c" implies the use of the transport, security,
framing and message semantics described in this document. framing and message semantics described in this document.
[[CREF1: RFC Editor's Note: please remove the remainder of this [[CREF1: RFC Editor's Note: please remove the remainder of this
section prior to the publication of a final version of this section prior to the publication of a final version of this
document.]] document.]]
Only implementations of the final, published RFC can identify Only implementations of the final, published RFC can identify
themselves as "h2" or "h2c". Until such an RFC exists, themselves as "h2" or "h2c". Until such an RFC exists,
skipping to change at page 9, line 7 skipping to change at page 9, line 7
MUST append the string "-" and an experiment name to the identifier. MUST append the string "-" and an 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-http2-09 might identify itself encoding based on draft-ietf-httpbis-http2-09 might identify itself
as "h2-09-emo". Note that any label MUST conform to the "token" as "h2-09-emo". Note that any label MUST conform to the "token"
syntax defined in Section 3.2.6 of [RFC7230]. Experimenters are syntax defined in Section 3.2.6 of [RFC7230]. Experimenters are
encouraged to coordinate their experiments on the ietf-http-wg@w3.org encouraged to coordinate their experiments on the ietf-http-wg@w3.org
mailing list. mailing list.
3.2. Starting HTTP/2 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 for an "http" URI without prior
knowledge about support for HTTP/2 uses the HTTP Upgrade mechanism knowledge about support for HTTP/2 uses the HTTP Upgrade mechanism
(Section 6.7 of [RFC7230]). The client makes an HTTP/1.1 request (Section 6.7 of [RFC7230]). The client makes an HTTP/1.1 request
that includes an Upgrade header field identifying HTTP/2 with the that includes an Upgrade header field identifying HTTP/2 with the
"h2c" token. The HTTP/1.1 request MUST include exactly one "h2c" token. The HTTP/1.1 request MUST include exactly one
HTTP2-Settings (Section 3.2.1) header field. HTTP2-Settings (Section 3.2.1) header field.
For example: For example:
GET / HTTP/1.1 GET / HTTP/1.1
Host: server.example.com Host: server.example.com
Connection: Upgrade, HTTP2-Settings Connection: Upgrade, HTTP2-Settings
Upgrade: h2c Upgrade: h2c
HTTP2-Settings: <base64url encoding of HTTP/2 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 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, an OPTIONS request can be used to perform the upgrade to
HTTP/2, 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 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
... ...
skipping to change at page 10, line 5 skipping to change at page 10, line 5
A server MUST ignore a "h2" token in an Upgrade header field. A server MUST ignore a "h2" token in an Upgrade header field.
Presence of a token with "h2" implies HTTP/2 over TLS, which is Presence of a token with "h2" implies HTTP/2 over TLS, which is
instead negotiated as described in Section 3.3. instead negotiated as described in Section 3.3.
A server that supports HTTP/2 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 frames. These the 101 response, the server can begin sending HTTP/2 frames. These
frames MUST include a response to the request that initiated the frames MUST include a response to the request that initiated the
Upgrade. Upgrade.
For example:
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: Upgrade Connection: Upgrade
Upgrade: h2c Upgrade: h2c
[ HTTP/2 connection ... [ HTTP/2 connection ...
The first HTTP/2 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) as the server connection preface (Section 3.5). Upon
connection preface (Section 3.5), which includes a SETTINGS frame. receiving the 101 response, the client sends a connection preface
(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 default priority values (Section 5.3.5). identifier 1 and is assigned default priority values (Section 5.3.5).
Stream 1 is implicitly half closed from the client toward the server, Stream 1 is implicitly half closed from the client toward the server,
since the request is completed as an HTTP/1.1 request. After since the request is completed as an HTTP/1.1 request. After
commencing the HTTP/2 connection, stream 1 is used for the response. commencing 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 MUST include exactly A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly
one "HTTP2-Settings" header field. The "HTTP2-Settings" header field one "HTTP2-Settings" header field. The "HTTP2-Settings" header field
is a hop-by-hop header field that includes parameters that govern the is a connection-specific header field that includes parameters that
HTTP/2 connection, provided in anticipation of the server accepting govern the HTTP/2 connection, provided in anticipation of the server
the request to upgrade. accepting the request to upgrade.
HTTP2-Settings = token68 HTTP2-Settings = token68
A server MUST reject an attempt to upgrade if this header field is A server MUST NOT upgrade the connection to HTTP/2 if this header
not present. A server MUST NOT send this header field. field is not present, or if more than one is present. A server MUST
NOT send this header field.
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
[RFC7235]. [RFC7235].
As a hop-by-hop header field, the "Connection" header field MUST Since the upgrade is only intended to apply to the immediate
include a value of "HTTP2-Settings" in addition to "Upgrade" when connection, a client sending "HTTP2-Settings" MUST also send
upgrading to HTTP/2. "HTTP2-Settings" as a connection option in the "Connection" header
field to prevent it from being forwarded (see Section 6.1 of
[RFC7230]).
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. Acknowledgement of the SETTINGS parameters SETTINGS frame. Acknowledgement of the SETTINGS parameters
(Section 6.5.3) is not necessary, since a 101 response serves as (Section 6.5.3) is not necessary, since a 101 response serves as
implicit acknowledgment. Providing these values in the Upgrade implicit acknowledgment. Providing these values in the Upgrade
request ensures that the protocol does not require default values for request gives a client an opportunity to provide parameters prior to
the above SETTINGS parameters, and gives a client an opportunity to receiving any frames from the server.
provide other parameters prior to receiving any frames from the
server.
3.3. Starting HTTP/2 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 uses TLS [TLS12] with
knowledge about support for HTTP/2 uses TLS [TLS12] with the the application layer protocol negotiation extension [TLS-ALPN].
application layer protocol negotiation extension [TLS-ALPN].
HTTP/2 over TLS uses the "h2" application token. The "h2c" token HTTP/2 over TLS uses the "h2" application token. The "h2c" token
MUST NOT be sent by a client or selected by a server. MUST NOT be sent by a client or selected by a server.
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 preface (Section 3.5). a connection preface (Section 3.5).
3.4. Starting HTTP/2 with Prior Knowledge 3.4. Starting HTTP/2 with Prior Knowledge
A client can learn that a particular server supports HTTP/2 by other A client can learn that a particular server supports HTTP/2 by other
means. For example, [ALT-SVC] describes a mechanism for advertising means. For example, [ALT-SVC] describes a mechanism for advertising
this capability. this capability.
A client MAY immediately send HTTP/2 frames to a server that is known A client MAY immediately send HTTP/2 frames to a server that is known
to support HTTP/2, after the connection preface (Section 3.5). A to support HTTP/2, after the connection preface (Section 3.5); a
server can identify such a connection by the use of the "PRI" method server can identify such a connection by the presence of the
in the connection preface. This only affects the establishment of connection preface. This only affects the establishment of HTTP/2
HTTP/2 connections over cleartext TCP; implementations that support connections over cleartext TCP; implementations that support HTTP/2
HTTP/2 over TLS MUST use protocol negotiation in TLS [TLS-ALPN]. over TLS MUST use protocol negotiation in TLS [TLS-ALPN].
Prior support for HTTP/2 is not a strong signal that a given server Without additional information, prior support for HTTP/2 is not a
will support HTTP/2 for future connections. It is possible for strong signal that a given server will support HTTP/2 for future
server configurations to change; for configurations to differ between connections. For example, it is possible for server configurations
instances in clustered server; or network conditions to change. to change, for configurations to differ between instances in
clustered servers, or for network conditions to change.
3.5. HTTP/2 Connection Preface 3.5. HTTP/2 Connection Preface
Upon establishment of a TCP connection and determination that HTTP/2 Upon establishment of a TCP connection and determination that HTTP/2
will be used by both peers, each endpoint MUST send a connection will be used by both peers, each endpoint MUST send a connection
preface as a final confirmation and to establish the initial SETTINGS preface as a final confirmation and to establish the initial SETTINGS
parameters for the HTTP/2 connection. parameters for the HTTP/2 connection. The client and server each
send a different connection preface.
The client connection preface starts with a sequence of 24 octets, The client connection preface starts with a sequence of 24 octets,
which in hex notation are: which in hex notation are:
0x505249202a20485454502f322e300d0a0d0a534d0d0a0d0a 0x505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(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 SETTINGS frame MAY followed by a SETTINGS frame (Section 6.5). The SETTINGS frame MAY
be empty. The client sends the client connection preface immediately be empty. The client sends the client connection preface immediately
upon receipt of a 101 Switching Protocols response (indicating a upon receipt of a 101 Switching Protocols response (indicating a
skipping to change at page 12, line 16 skipping to change at page 12, line 23
The client connection preface is selected so that a large The client connection preface 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 preface consists of a potentially empty The server connection preface consists of a potentially empty
SETTINGS frame (Section 6.5) that MUST be the first frame the server SETTINGS frame (Section 6.5) that MUST be the first frame the server
sends in the HTTP/2 connection. sends in the HTTP/2 connection.
The SETTINGS frames received from a peer as part of the connection
preface MUST be acknowledged (see Section 6.5.3) after sending the
connection preface.
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 preface, without waiting to receive the server connection connection preface, without waiting to receive the server connection
preface. It is important to note, however, that the server preface. It is important to note, however, that the server
connection preface SETTINGS frame might include parameters that connection preface SETTINGS frame might include parameters that
necessarily alter how a client is expected to communicate with the necessarily alter how a client is expected to communicate with the
server. Upon receiving the SETTINGS frame, the client is expected to server. Upon receiving the SETTINGS frame, the client is expected to
honor any parameters established. In some configurations, it is honor any parameters established. In some configurations, it is
possible for the server to transmit SETTINGS before the client, possible for the server to transmit SETTINGS before the client sends
providing an opportunity to avoid this issue. additional frames, providing an opportunity to avoid this issue.
Clients and servers MUST terminate the TCP connection if either peer Clients and servers MUST treat an invalid connection preface as a
does not begin with a valid connection preface. A GOAWAY frame connection error (Section 5.4.1) of type PROTOCOL_ERROR. A GOAWAY
(Section 6.8) can be omitted if it is clear that the peer is not frame (Section 6.8) MAY be omitted in this case, since an invalid
using HTTP/2. preface indicates that the peer is not using HTTP/2.
4. HTTP Frames 4. HTTP Frames
Once the HTTP/2 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 a fixed 9-octet header followed by a variable- All frames begin with a fixed 9-octet header followed by a variable-
length payload. length payload.
skipping to change at page 13, line 17 skipping to change at page 13, line 17
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (24) | | Length (24) |
+---------------+---------------+---------------+ +---------------+---------------+---------------+
| Type (8) | Flags (8) | | Type (8) | Flags (8) |
+-+-+-----------+---------------+-------------------------------+ +-+-+-----------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+=+=============================================================+ +=+=============================================================+
| Frame Payload (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Layout Figure 1: Frame Layout
The fields of the frame header are defined as: The fields of the frame header are defined as:
Length: The length of the frame payload expressed as an unsigned Length: The length of the frame payload expressed as an unsigned
24-bit integer. Values greater than 2^14 (16,384) MUST NOT be 24-bit integer. Values greater than 2^14 (16,384) MUST NOT be
sent unless the receiver has set a larger value for sent unless the receiver has set a larger value for
SETTINGS_MAX_FRAME_SIZE. SETTINGS_MAX_FRAME_SIZE.
The 9 octets of the frame header are not included in this value. The 9 octets of the frame header are not included in this value.
skipping to change at page 14, line 20 skipping to change at page 14, line 20
(16,777,215) octets, inclusive. (16,777,215) octets, inclusive.
All implementations MUST be capable of receiving and minimally All implementations MUST be capable of receiving and minimally
processing frames up to 2^14 octets in length, plus the 9 octet frame processing frames up to 2^14 octets in length, plus the 9 octet frame
header (Section 4.1). The size of the frame header is not included header (Section 4.1). The size of the frame header is not included
when describing frame sizes. when describing frame sizes.
Note: Certain frame types, such as PING (Section 6.7), impose Note: Certain frame types, such as PING (Section 6.7), impose
additional limits on the amount of payload data allowed. additional limits on the amount of payload data allowed.
If a frame size exceeds any defined limit, or is too small to contain An endpoint MUST send a FRAME_SIZE_ERROR error if a frame exceeds the
mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR size defined in SETTINGS_MAX_FRAME_SIZE, any limit defined for the
error. A frame size error in a frame that could alter the state of frame type, or it is too small to contain mandatory frame data. A
the entire connection MUST be treated as a connection error frame size error in a frame that could alter the state of the entire
(Section 5.4.1); this includes any frame carrying a header block connection MUST be treated as a connection error (Section 5.4.1);
(Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), this includes any frame carrying a header block (Section 4.3) (that
SETTINGS, and any WINDOW_UPDATE frame with a stream identifier of 0. is, HEADERS, PUSH_PROMISE, and CONTINUATION), SETTINGS, and any frame
with a stream identifier of 0.
Endpoints are not obligated to use all available space in a frame. Endpoints are not obligated to use all available space in a frame.
Responsiveness can be improved by using frames that are smaller than Responsiveness can be improved by using frames that are smaller than
the permitted maximum size. Sending large frames can result in the permitted maximum size. Sending large frames can result in
delays in sending maintenance frames, such RST_STREAM, WINDOW_UPDATE, delays in sending time-sensitive frames (such RST_STREAM,
or PRIORITY, which if blocked by the transmission of a large frame, WINDOW_UPDATE, or PRIORITY) which if blocked by the transmission of a
could affect performance. large frame, could affect performance.
4.3. Header Compression and Decompression 4.3. Header Compression and Decompression
A header field in HTTP/2 is a name with one or more associated Just as in HTTP/1, a header field in HTTP/2 is a name with one or
values. They are used within HTTP request and response messages as more associated values. They are used within HTTP request and
well as server push operations (see Section 8.2). response messages as well as server push operations (see
Section 8.2).
Header lists are collections of zero or more header fields. When Header lists are collections of zero or more header fields. When
transmitted over a connection, a header list is serialized into a transmitted over a connection, a header list is serialized into a
header block using HTTP Header Compression [COMPRESSION]. The header block using HTTP Header Compression [COMPRESSION]. The
serialized header block is then divided into one or more octet serialized header block is then divided into one or more octet
sequences, called header block fragments, and transmitted within the sequences, called header block fragments, and transmitted within the
payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or
CONTINUATION (Section 6.10) frames. CONTINUATION (Section 6.10) frames.
The Cookie header field [COOKIE] is treated specially by the HTTP The Cookie header field [COOKIE] is treated specially by the HTTP
skipping to change at page 15, line 18 skipping to change at page 15, line 18
A complete header block consists of either: A complete header block consists of either:
o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag
set, or set, or
o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared
and one or more CONTINUATION frames, where the last CONTINUATION and one or more CONTINUATION frames, where the last CONTINUATION
frame has the END_HEADERS flag set. frame has the END_HEADERS flag set.
Header compression is stateful, using a single compression context Header compression is stateful. One compression context and one
for the entire connection. Each header block is processed as a decompression context is used for the entire connection. Each header
discrete unit. Header blocks MUST be transmitted as a contiguous block is processed as a discrete unit. Header blocks MUST be
sequence of frames, with no interleaved frames of any other type or transmitted as a contiguous sequence of frames, with no interleaved
from any other stream. The last frame in a sequence of HEADERS or frames of any other type or from any other stream. The last frame in
CONTINUATION frames MUST have the END_HEADERS flag set. The last a sequence of HEADERS or CONTINUATION frames MUST have the
frame in a sequence of PUSH_PROMISE or CONTINUATION frames MUST have END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE
the END_HEADERS flag set. This allows a header block to be logically or CONTINUATION frames MUST have the END_HEADERS flag set. This
equivalent to a single frame. allows a header block to be logically equivalent to a single frame.
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, because these frames carry data PUSH_PROMISE or CONTINUATION frames, because these frames carry data
that can modify the compression context maintained by a receiver. An that can modify the compression context maintained by a receiver. An
endpoint receiving HEADERS, PUSH_PROMISE or CONTINUATION frames MUST endpoint receiving HEADERS, PUSH_PROMISE or CONTINUATION frames MUST
reassemble header blocks and perform decompression even if the frames reassemble header blocks and perform decompression even if the frames
are to be discarded. A receiver MUST terminate the connection with a are to be discarded. A receiver MUST terminate the connection with a
connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does
not decompress a header block. not decompress a header block.
skipping to change at page 16, line 15 skipping to change at page 16, line 15
o The order in which frames are sent on a stream is significant. o The order in which frames are sent on a stream is significant.
Recipients process frames in the order they are received. In Recipients process frames in the order they are received. In
particular, the order of HEADERS, and DATA frames is semantically particular, the order of HEADERS, and DATA frames is semantically
significant. significant.
o Streams are identified by an integer. Stream identifiers are o Streams are identified by an integer. Stream identifiers are
assigned to streams by the endpoint initiating the stream. assigned to streams by the endpoint initiating the stream.
5.1. Stream States 5.1. Stream States
The lifecycle of a stream is shown in Figure 1. The lifecycle of a stream is shown in Figure 2.
+--------+ +--------+
PP | | PP PP | | PP
,--------| idle |--------. ,--------| idle |--------.
/ | | \ / | | \
v +--------+ v v +--------+ v
+----------+ | +----------+ +----------+ | +----------+
| | | H | | | | | H | |
,---| reserved | | | reserved |---. ,---| reserved | | | reserved |---.
| | (local) | v | (remote) | | | | (local) | v | (remote) | |
skipping to change at page 16, line 48 skipping to change at page 16, line 48
| `----------->| |<-----------' | | `----------->| |<-----------' |
| R | closed | R | | R | closed | R |
`-------------------->| |<--------------------' `-------------------->| |<--------------------'
+--------+ +--------+
H: HEADERS frame (with implied CONTINUATIONs) H: HEADERS frame (with implied CONTINUATIONs)
PP: PUSH_PROMISE frame (with implied CONTINUATIONs) PP: PUSH_PROMISE frame (with implied CONTINUATIONs)
ES: END_STREAM flag ES: END_STREAM flag
R: RST_STREAM frame R: RST_STREAM frame
Figure 1: Stream States Figure 2: Stream States
Note that this diagram shows stream state transitions and frames that Note that this diagram shows stream state transitions and the frames
affect those transitions only. In this regard, CONTINUATION frames and flags that affect those transitions only. In this regard,
do not result in state transitions and are effectively part of the CONTINUATION frames do not result in state transitions; they are
HEADERS or PUSH_PROMISE that they follow. effectively part of the HEADERS or PUSH_PROMISE that they follow.
For this purpose, the END_STREAM flag is processed as a separate
event to the frame that bears it; a HEADERS frame with the END_STREAM
flag set can cause two state transitions.
Both endpoints have a subjective view of the state of a stream that Both endpoints have a subjective view of the state of a stream that
could be different when frames are in transit. Endpoints do not could be different when frames are in transit. Endpoints do not
coordinate the creation of streams; they are created unilaterally by coordinate the creation of streams; they are created unilaterally by
either endpoint. The negative consequences of a mismatch in states either endpoint. The negative consequences of a mismatch in states
are limited to the "closed" state after sending RST_STREAM, where are limited to the "closed" state after sending RST_STREAM, where
frames might be received for some time after closing. frames might be received for some time after closing.
Streams have the following states: Streams have the following states:
skipping to change at page 17, line 38 skipping to change at page 17, line 41
stream to immediately become "half closed". stream to immediately become "half closed".
* Sending a PUSH_PROMISE frame marks the associated stream for * Sending a PUSH_PROMISE frame marks the associated stream for
later use. The stream state for the reserved stream later use. The stream state for the reserved stream
transitions to "reserved (local)". transitions to "reserved (local)".
* Receiving a PUSH_PROMISE frame marks the associated stream as * Receiving a PUSH_PROMISE frame marks the associated stream as
reserved by the remote peer. The state of the stream becomes reserved by the remote peer. The state of the stream becomes
"reserved (remote)". "reserved (remote)".
Receiving any frames other than HEADERS or PUSH_PROMISE on a
stream in this state MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
reserved (local): reserved (local):
A stream in the "reserved (local)" state is one that has been A stream in the "reserved (local)" state is one that has been
promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame
reserves an idle stream by associating the stream with an open reserves an idle stream by associating the stream with an open
stream that was initiated by the remote peer (see Section 8.2). stream that was initiated by the remote peer (see Section 8.2).
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* The endpoint can send a HEADERS frame. This causes the stream * The endpoint can send a HEADERS frame. This causes the stream
to open in a "half closed (remote)" state. to open in a "half closed (remote)" state.
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This releases the stream reservation.
An endpoint MUST NOT send frames other than HEADERS or RST_STREAM An endpoint MUST NOT send any type of frame other than HEADERS or
in this state. RST_STREAM in this state.
A PRIORITY frame MAY be received in this state. Receiving any A PRIORITY or WINDOW_UPDATE frame MAY be received in this state.
frames other than RST_STREAM, or PRIORITY MUST be treated as a Receiving any type of frame other than RST_STREAM, PRIORITY or
WINDOW_UPDATE on a stream in this state MUST be treated as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
reserved (remote): reserved (remote):
A stream in the "reserved (remote)" state has been reserved by a A stream in the "reserved (remote)" state has been reserved by a
remote peer. remote peer.
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* Receiving a HEADERS frame causes the stream to transition to * Receiving a HEADERS frame causes the stream to transition to
"half closed (local)". "half closed (local)".
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This releases the stream reservation.
An endpoint MAY send a PRIORITY frame in this state to An endpoint MAY send a PRIORITY frame in this state to
reprioritize the reserved stream. An endpoint MUST NOT send any reprioritize the reserved stream. An endpoint MUST NOT send any
other type of frame other than RST_STREAM or PRIORITY. type of frame other than RST_STREAM, WINDOW_UPDATE, or PRIORITY in
this state.
Receiving any other type of frame other than HEADERS or RST_STREAM Receiving any type of frame other than HEADERS or RST_STREAM on a
MUST be treated as a connection error (Section 5.4.1) of type stream in this state MUST be treated as a connection error
PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
open: open:
A stream in the "open" state may be used by both peers to send A stream in the "open" state may be used by both peers to send
frames of any type. In this state, sending peers observe frames of any type. In this state, sending peers observe
advertised stream level flow control limits (Section 5.2). advertised stream level flow control limits (Section 5.2).
From this state either endpoint can send a frame with an From this state either endpoint can send a frame with an
END_STREAM flag set, which causes the stream to transition into END_STREAM flag set, which causes the stream to transition into
one of the "half closed" states: an endpoint sending an END_STREAM one of the "half closed" states: an endpoint sending an END_STREAM
flag causes the stream state to become "half closed (local)"; an flag causes the stream state to become "half closed (local)"; an
skipping to change at page 19, line 39 skipping to change at page 19, line 47
continues to observe advertised stream level flow control limits continues to observe advertised stream level flow control limits
(Section 5.2). (Section 5.2).
A stream can transition from this state to "closed" by sending a A stream can transition from this state to "closed" by sending a
frame that contains an END_STREAM flag, or when either peer sends frame that contains an END_STREAM flag, or when either peer sends
a RST_STREAM frame. a RST_STREAM frame.
closed: closed:
The "closed" state is the terminal state. The "closed" state is the terminal state.
An endpoint MUST NOT send frames on a closed stream. An endpoint An endpoint MUST NOT send frames other than PRIORITY on a closed
that receives any frame other than PRIORITY after receiving a stream. An endpoint that receives any frame other than PRIORITY
RST_STREAM MUST treat that as a stream error (Section 5.4.2) of after receiving a RST_STREAM MUST treat that as a stream error
type STREAM_CLOSED. Similarly, an endpoint that receives any (Section 5.4.2) of type STREAM_CLOSED. Similarly, an endpoint
frames after receiving a frame with the END_STREAM flag set MUST that receives any frames after receiving a frame with the
treat that as a connection error (Section 5.4.1) of type END_STREAM flag set MUST treat that as a connection error
STREAM_CLOSED, unless the frame is permitted as described below. (Section 5.4.1) of type STREAM_CLOSED, unless the frame is
permitted as described below.
WINDOW_UPDATE or RST_STREAM frames can be received in this state WINDOW_UPDATE or RST_STREAM frames can be received in this state
for a short period after a DATA or HEADERS frame containing an for a short period after a DATA or HEADERS frame containing an
END_STREAM flag is sent. Until the remote peer receives and END_STREAM flag is sent. Until the remote peer receives and
processes the frame bearing the END_STREAM flag, it might send processes RST_STREAM or the frame bearing the END_STREAM flag, it
frames of these types. Endpoints MUST ignore WINDOW_UPDATE or might send frames of these types. Endpoints MUST ignore
RST_STREAM frames received in this state, though endpoints MAY WINDOW_UPDATE or RST_STREAM frames received in this state, though
choose to treat frames that arrive a significant time after endpoints MAY choose to treat frames that arrive a significant
sending END_STREAM as a connection error (Section 5.4.1) of type time after sending END_STREAM as a connection error
PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
PRIORITY frames can be sent on closed streams to prioritize PRIORITY frames can be sent on closed streams to prioritize
streams that are dependent on the closed stream. Endpoints SHOULD streams that are dependent on the closed stream. Endpoints SHOULD
process PRIORITY frame, though they can be ignored if the stream process PRIORITY frames, though they can be ignored if the stream
has been removed from the dependency tree (see Section 5.3.4). has been removed from the dependency tree (see Section 5.3.4).
If this state is reached as a result of sending a RST_STREAM If this state is reached as a result of sending a RST_STREAM
frame, the peer that receives the RST_STREAM might have already frame, the peer that receives the RST_STREAM might have already
sent - or enqueued for sending - frames on the stream that cannot sent - or enqueued for sending - frames on the stream that cannot
be withdrawn. An endpoint MUST ignore frames that it receives on be withdrawn. An endpoint MUST ignore frames that it receives on
closed streams after it has sent a RST_STREAM frame. An endpoint closed streams after it has sent a RST_STREAM frame. An endpoint
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.
skipping to change at page 20, line 33 skipping to change at page 20, line 42
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 even if the associated stream has been reset. Therefore, a
RST_STREAM is needed to close an unwanted promised stream. RST_STREAM is needed to close an unwanted promised stream.
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 frame 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. Frame of unknown types
are ignored.
An example of the state transitions for an HTTP request/response An example of the state transitions for an HTTP request/response
exchange can be found in Section 8.1. An example of the state exchange can be found in Section 8.1. An example of the state
transitions for server push can be found in Section 8.2.1 and transitions for server push can be found in Section 8.2.1 and
Section 8.2.2. Section 8.2.2.
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
skipping to change at page 22, line 22 skipping to change at page 22, line 33
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 provides for flow control through use of the WINDOW_UPDATE HTTP/2 provides for flow control through use of the WINDOW_UPDATE
frame (Section 6.9). frame (Section 6.9).
5.2.1. Flow Control Principles 5.2.1. Flow Control Principles
HTTP/2 stream flow control aims to allow for future improvements to HTTP/2 stream flow control aims to allow a variety of flow control
flow control algorithms without requiring protocol changes. Flow algorithms to be used without requiring protocol changes. Flow
control in HTTP/2 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 specific to a connection; i.e., it 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 octets they are prepared to receive on a
and for the entire connection. This is a credit-based scheme. stream 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 window as a receiver and abide by the flow control limits control window as a receiver and abide by the flow control 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 octets
both new streams and the overall connection. for 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 cannot be disabled. 6. Flow control cannot be disabled.
7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE 7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE
frame (Section 6.9). This document does not stipulate how a frame (Section 6.9). This document does not stipulate how a
receiver decides when to send this frame or the value that it receiver decides when to send this frame or the value that it
sends. Nor does it specify how a sender chooses to send packets. sends, nor does it specify how a sender chooses to send packets.
Implementations are able to select any algorithm that suits their Implementations are able to select any algorithm that suits their
needs. 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 to process data on one stream, yet wants
continue to process other streams in the same connection. to continue to process other streams in the same connection.
Deployments that do not require this capability can advertise a flow Deployments that do not require this capability can advertise a flow
control window of the maximum size, incrementing the available space control window of the maximum size, incrementing the available space
when new data is received. This effectively disables flow control when new data is received. This effectively disables flow control
for that receiver. Conversely, a sender is always subject to the for that receiver. Conversely, a sender is always subject to the
flow control window advertised by the receiver. flow control window advertised by the receiver.
Deployments with constrained resources (for example, memory) can Deployments with constrained resources (for example, memory) can
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 [RFC7323]).
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 receiver 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 read and acted upon. critical frames, such as WINDOW_UPDATE, are not read and acted upon.
5.3. Stream priority 5.3. Stream priority
A client can assign a priority for a new stream by including A client can assign a priority for a new stream by including
skipping to change at page 24, line 23 skipping to change at page 24, line 33
relative proportion of available resources that are assigned to relative proportion of available resources that are assigned to
streams dependent on the same stream. streams dependent on the same stream.
Explicitly setting the priority for a stream is input to a Explicitly setting the priority for a stream is input to a
prioritization process. It does not guarantee any particular prioritization process. It does not guarantee any particular
processing or transmission order for the stream relative to any other processing or transmission order for the stream relative to any other
stream. An endpoint cannot force a peer to process concurrent stream. An endpoint cannot force a peer to process concurrent
streams in a particular order using priority. Expressing priority is streams in a particular order using priority. Expressing priority is
therefore only ever a suggestion. therefore only ever a suggestion.
Prioritization information can be specified explicitly for streams as Providing prioritization information is optional, so default values
they are created using the HEADERS frame, or changed using the are used if no explicit indicator is provided (Section 5.3.5).
PRIORITY frame. Providing prioritization information is optional, so
default values are used if no explicit indicator is provided
(Section 5.3.5).
5.3.1. Stream Dependencies 5.3.1. Stream Dependencies
Each stream can be given an explicit dependency on another stream. Each stream can be given an explicit dependency on another stream.
Including a dependency expresses a preference to allocate resources Including a dependency expresses a preference to allocate resources
to the identified stream rather than to the dependent stream. to the identified stream rather than to the dependent stream.
A stream that is not dependent on any other stream is given a stream A stream that is not dependent on any other stream is given a stream
dependency of 0x0. In other words, the non-existent stream 0 forms dependency of 0x0. In other words, the non-existent stream 0 forms
the root of the tree. the root of the tree.
A stream that depends on another stream is a dependent stream. The A stream that depends on another stream is a dependent stream. The
stream upon which a stream is dependent is a parent stream. A stream upon which a stream is dependent is a parent stream. A
dependency on a stream that is not currently in the tree - such as a dependency on a stream that is not currently in the tree - such as a
stream in the "idle" state - results in the stream being given a stream in the "idle" state - results in that stream being given a
default priority (Section 5.3.5). default priority (Section 5.3.5).
When assigning a dependency on another stream, the stream is added as When assigning a dependency on another stream, the stream is added as
a new dependency of the parent stream. Dependent streams that share a new dependency of the parent stream. Dependent streams that share
the same parent are not ordered with respect to each other. For the same parent are not ordered with respect to each other. For
example, if streams B and C are dependent on stream A, and if stream example, if streams B and C are dependent on stream A, and if stream
D is created with a dependency on stream A, this results in a D is created with a dependency on stream A, this results in a
dependency order of A followed by B, C, and D in any order. dependency order of A followed by B, C, and D in any order.
A A A A
/ \ ==> /|\ / \ ==> /|\
B C B D C B C B D C
Example of Default Dependency Creation Figure 3: Example of Default Dependency Creation
An exclusive flag allows for the insertion of a new level of An exclusive flag allows for the insertion of a new level of
dependencies. The exclusive flag causes the stream to become the dependencies. The exclusive flag causes the stream to become the
sole dependency of its parent stream, causing other dependencies to sole dependency of its parent stream, causing other dependencies to
become dependent on the prioritized stream. In the previous example, become dependent on the exclusive stream. In the previous example,
if stream D is created with an exclusive dependency on stream A, this if stream D is created with an exclusive dependency on stream A, this
results in D becoming the dependency parent of B and C. results in D becoming the dependency parent of B and C.
A A
A | A |
/ \ ==> D / \ ==> D
B C / \ B C / \
B C B C
Example of Exclusive Dependency Creation Figure 4: Example of Exclusive Dependency Creation
Inside the dependency tree, a dependent stream SHOULD only be Inside the dependency tree, a dependent stream SHOULD only be
allocated resources if all of the streams that it depends on (the allocated resources if all of the streams that it depends on (the
chain of parent streams up to 0x0) are either closed, or it is not chain of parent streams up to 0x0) are either closed, or it is not
possible to make progress on them. possible to make progress on them.
A stream cannot depend on itself. An endpoint MUST treat this as a A stream cannot depend on itself. An endpoint MUST treat this as a
stream error (Section 5.4.2) of type PROTOCOL_ERROR. stream error (Section 5.4.2) of type PROTOCOL_ERROR.
5.3.2. Dependency Weighting 5.3.2. Dependency Weighting
All dependent streams are allocated an integer weight between 1 to All dependent streams are allocated an integer weight between 1 and
256 (inclusive). 256 (inclusive).
Streams with the same parent SHOULD be allocated resources Streams with the same parent SHOULD be allocated resources
proportionally based on their weight. Thus, if stream B depends on proportionally based on their weight. Thus, if stream B depends on
stream A with weight 4, and C depends on stream A with weight 12, and stream A with weight 4, and C depends on stream A with weight 12, and
if no progress can be made on A, stream B ideally receives one third if no progress can be made on A, stream B ideally receives one third
of the resources allocated to stream C. of the resources allocated to stream C.
5.3.3. Reprioritization 5.3.3. Reprioritization
skipping to change at page 26, line 29 skipping to change at page 26, line 38
| / \ | | | / \ | |
A D A D D A D A D D
/ \ / / \ / \ | / \ / / \ / \ |
B C ==> F B C ==> F A OR A B C ==> F B C ==> F A OR A
/ \ | / \ /|\ / \ | / \ /|\
D E E B C B C F D E E B C B C F
| | | | | |
F E E F E E
(intermediate) (non-exclusive) (exclusive) (intermediate) (non-exclusive) (exclusive)
Example of Dependency Reordering Figure 5: Example of Dependency Reordering
5.3.4. Prioritization State Management 5.3.4. Prioritization State Management
When a stream is removed from the dependency tree, its dependencies When a stream is removed from the dependency tree, its dependencies
can be moved to become dependent on the parent of the closed stream. can be moved to become dependent on the parent of the closed stream.
The weights of new dependencies are recalculated by distributing the The weights of new dependencies are recalculated by distributing the
weight of the dependency of the closed stream proportionally based on weight of the dependency of the closed stream proportionally based on
the weights of its dependencies. the weights of its dependencies.
Streams that are removed from the dependency tree cause some Streams that are removed from the dependency tree cause some
skipping to change at page 27, line 11 skipping to change at page 27, line 20
streams A and D are unable to proceed, then stream C receives all the streams A and D are unable to proceed, then stream C receives all the
resources dedicated to stream A. If stream A is removed from the resources dedicated to stream A. If stream A is removed from the
tree, the weight of stream A is divided between streams C and D. If tree, the weight of stream A is divided between streams C and D. If
stream D is still unable to proceed, this results in stream C stream D is still unable to proceed, this results in stream C
receiving a reduced proportion of resources. For equal starting receiving a reduced proportion of resources. For equal starting
weights, C receives one third, rather than one half, of available weights, C receives one third, rather than one half, of available
resources. resources.
It is possible for a stream to become closed while prioritization It is possible for a stream to become closed while prioritization
information that creates a dependency on that stream is in transit. information that creates a dependency on that stream is in transit.
If a stream identified in a dependency has had any associated If a stream identified in a dependency has no associated priority
priority information destroyed, then the dependent stream is instead information, then the dependent stream is instead assigned a default
assigned a default priority. This potentially creates suboptimal priority (Section 5.3.5). This potentially creates suboptimal
prioritization, since the stream could be given a priority that is prioritization, since the stream could be given a priority that is
higher than intended. different to what is intended.
To avoid these problems, an endpoint SHOULD retain stream To avoid these problems, an endpoint SHOULD retain stream
prioritization state for a period after streams become closed. The prioritization state for a period after streams become closed. The
longer state is retained, the lower the chance that streams are longer state is retained, the lower the chance that streams are
assigned incorrect or default priority values. assigned incorrect or default priority values.
This could create a large state burden for an endpoint, so this state This could create a large state burden for an endpoint, so this state
MAY be limited. An endpoint MAY apply a fixed upper limit on the MAY be limited. An endpoint MAY apply a fixed upper limit on the
number of closed streams for which prioritization state is tracked to number of closed streams for which prioritization state is tracked to
limit state exposure. The amount of additional state an endpoint limit state exposure. The amount of additional state an endpoint
skipping to change at page 28, line 16 skipping to change at page 28, line 25
5.4.1. Connection Error Handling 5.4.1. Connection Error Handling
A connection error is any error which prevents further processing of A connection error is any error which prevents further processing of
the framing layer, or which corrupts any connection state. the framing layer, or which corrupts any connection state.
An endpoint that encounters a connection error SHOULD first send a An endpoint that encounters a connection error SHOULD first send a
GOAWAY frame (Section 6.8) with the stream identifier of the last GOAWAY frame (Section 6.8) with the stream identifier of the last
stream that it successfully received from its peer. The GOAWAY frame stream that it successfully received from its peer. The GOAWAY frame
includes an error code that indicates why the connection is includes an error code that indicates why the connection is
terminating. After sending the GOAWAY frame, the endpoint MUST close terminating. After sending the GOAWAY frame for an error condition,
the TCP connection. the endpoint MUST close the TCP connection.
It is possible that the GOAWAY will not be reliably received by the It is possible that the GOAWAY will not be reliably received by the
receiving endpoint. In the event of a connection error, GOAWAY only receiving endpoint (see [RFC7230], Section 6.6). In the event of a
provides a best effort attempt to communicate with the peer about why connection error, GOAWAY only provides a best effort attempt to
the connection is being terminated. communicate with the peer about why the connection is being
terminated.
An endpoint can end a connection at any time. In particular, an An endpoint can end a connection at any time. In particular, an
endpoint MAY choose to treat a stream error as a connection error. endpoint MAY choose to treat a stream error as a connection error.
Endpoints SHOULD send a GOAWAY frame when ending a connection, Endpoints SHOULD send a GOAWAY frame when ending a connection,
providing that circumstances permit it. providing that circumstances permit it.
5.4.2. Stream Error Handling 5.4.2. Stream Error Handling
A stream error is an error related to a specific stream that does not A stream error is an error related to a specific stream that does not
affect processing of other streams. affect processing of other streams.
skipping to change at page 29, line 10 skipping to change at page 29, line 18
for any stream. However, an endpoint MAY send additional RST_STREAM for any stream. However, an endpoint MAY send additional RST_STREAM
frames if it receives frames on a closed stream after more than a frames if it receives frames on a closed stream after more than a
round-trip time. This behavior is permitted to deal with misbehaving round-trip time. This behavior is permitted to deal with misbehaving
implementations. implementations.
An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM
frame, to avoid looping. frame, to avoid looping.
5.4.3. Connection Termination 5.4.3. Connection Termination
If the TCP connection is torn down while streams remain in open or If the TCP connection is closed or reset while streams remain in open
half closed states, then the endpoint MUST assume that those streams or half closed states, then the endpoint MUST assume that those
were abnormally interrupted and could be incomplete. streams were abnormally interrupted and could be incomplete.
5.5. Extending HTTP/2 5.5. Extending HTTP/2
HTTP/2 permits extension of the protocol. Protocol extensions can be HTTP/2 permits extension of the protocol. Protocol extensions can be
used to provide additional services or alter any aspect of the used to provide additional services or alter any aspect of the
protocol, within the limitations described in this section. protocol, within the limitations described in this section.
Extensions are effective only within the scope of a single HTTP/2 Extensions are effective only within the scope of a single HTTP/2
connection. connection.
Extensions are permitted to use new frame types (Section 4.1), new Extensions are permitted to use new frame types (Section 4.1), new
settings (Section 6.5.2), or new error codes (Section 7). Registries settings (Section 6.5.2), or new error codes (Section 7). Registries
are established for managing these extension points: frame types are established for managing these extension points: frame types
(Section 11.2), settings (Section 11.3) and error codes (Section 11.2), settings (Section 11.3) and error codes
(Section 11.4). (Section 11.4).
Implementations MUST ignore unknown or unsupported values in all Implementations MUST ignore unknown or unsupported values in all
extensible protocol elements. Implementations MUST discard frames extensible protocol elements. Implementations MUST discard frames
that have unknown or unsupported types. This means that any of these that have unknown or unsupported types. This means that any of these
extension points can be safely used by extensions without prior extension points can be safely used by extensions without prior
arrangement or negotiation. arrangement or negotiation. However, extension frames that appear in
the middle of a header block (Section 4.3) are not permitted; these
MUST be treated as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
However, extensions that could change the semantics of existing However, extensions that could change the semantics of existing
protocol components MUST be negotiated before being used. For protocol components MUST be negotiated before being used. For
example, an extension that changes the layout of the HEADERS frame example, an extension that changes the layout of the HEADERS frame
cannot be used until the peer has given a positive signal that this cannot be used until the peer has given a positive signal that this
is acceptable. In this case, it could also be necessary to is acceptable. In this case, it could also be necessary to
coordinate when the revised layout comes into effect. Note that coordinate when the revised layout comes into effect. Note that
treating any frame other than DATA frames as flow controlled is such treating any frame other than DATA frames as flow controlled is such
a change in semantics, and can only be done through negotiation. a change in semantics, and can only be done through negotiation.
This document doesn't mandate a specific method for negotiating the This document doesn't mandate a specific method for negotiating the
use of an extension, but notes that a setting (Section 6.5.2) could use of an extension, but notes that a setting (Section 6.5.2) could
be used for that purpose. If both peers set a value that indicates be used for that purpose. If both peers set a value that indicates
willingness to use the extension, then the extension can be used. If willingness to use the extension, then the extension can be used. If
a setting is used for extension negotiation, the initial value MUST a setting is used for extension negotiation, the initial value MUST
be defined so that the extension is initially disabled. be defined in such a fashion that the extension is initially
disabled.
6. Frame Definitions 6. Frame Definitions
This specification defines a number of frame types, each identified This specification defines a number of frame types, each identified
by a unique 8-bit type code. Each frame type serves a distinct by a unique 8-bit type code. Each frame type serves a distinct
purpose either in the establishment and management of the connection purpose either in the establishment and management of the connection
as a whole, or of individual streams. as a whole, or of individual streams.
The transmission of specific frame types can alter the state of a The transmission of specific frame types can alter the state of a
connection. If endpoints fail to maintain a synchronized view of the connection. If endpoints fail to maintain a synchronized view of the
skipping to change at page 30, line 38 skipping to change at page 30, line 48
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 Length? (8)| |Pad Length? (8)|
+---------------+-----------------------------------------------+ +---------------+-----------------------------------------------+
| Data (*) ... | Data (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
DATA Frame Payload Figure 6: DATA Frame Payload
The DATA frame contains the following fields: The DATA frame contains the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is optional and is only
present if the PADDED flag is set. present if the PADDED flag is set.
Data: Application data. The amount of data is the remainder of the Data: Application data. The amount of data is the remainder of the
frame payload after subtracting the length of the other fields frame payload after subtracting the length of the other fields
that are present. that are present.
Padding: Padding octets that contain no application semantic value. Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending and ignored when Padding octets MUST be set to zero when sending. A receiver is
receiving. not obligated to verify padding, but MAY treat non-zero padding as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
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 0 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 the "half Setting this flag causes the stream to enter one of the "half
closed" states or the "closed" state (Section 5.1). closed" states or the "closed" state (Section 5.1).
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): Bit 3 being set indicates that the Pad Length field
present. and any padding that it describes is present.
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. The entire stream is in the "open" or "half closed (remote)" states. The entire
DATA frame payload is included in flow control, including Pad Length DATA frame payload is included in flow control, including Pad Length
and Padding fields if present. If a DATA frame is received whose and Padding fields if present. If a DATA frame is received whose
stream is not in "open" or "half closed (local)" state, the recipient stream is not in "open" or "half closed (local)" state, the recipient
MUST respond with a stream error (Section 5.4.2) of type MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED. STREAM_CLOSED.
The total number of padding octets is determined by the value of the The total number of padding octets is determined by the value of the
Pad Length field. If the length of the padding is greater than the Pad Length field. If the length of the padding is the length of the
length of the remainder of the frame payload, the recipient MUST frame payload or greater, the recipient MUST treat this as a
treat this as a connection error (Section 5.4.1) of type connection error (Section 5.4.1) of type PROTOCOL_ERROR.
PROTOCOL_ERROR.
Note: A frame can be increased in size by one octet by including a Note: A frame can be increased in size by one octet by including a
Pad Length field with a value of zero. Pad Length field with a value of zero.
Use of padding is a security feature; as such, its use demands some Padding is a security feature; see Section 10.7.
care, see Section 10.7.
6.2. HEADERS 6.2. HEADERS
The HEADERS frame (type=0x1) carries name-value pairs. It is used to The HEADERS frame (type=0x1) is used to open a stream (Section 5.1),
open a stream (Section 5.1). HEADERS frames can be sent on a stream and additionally carries a header block fragment. HEADERS frames can
in the "open" or "half closed (remote)" states. be sent on a stream 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Pad Length? (8)| |Pad Length? (8)|
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
|E| Stream Dependency? (31) | |E| Stream Dependency? (31) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Weight? (8) | | Weight? (8) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
HEADERS Frame Payload Figure 7: HEADERS Frame Payload
The HEADERS frame payload has the following fields: The HEADERS frame payload has the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is only present if the
present if the PADDED flag is set. PADDED flag is set.
E: A single bit flag indicates that the stream dependency is E: A single bit flag indicates that the stream dependency is
exclusive, see Section 5.3. This field is optional and is only exclusive, see Section 5.3. This field is only present if the
present if the PRIORITY flag is set. PRIORITY flag is set.
Stream Dependency: A 31-bit stream identifier for the stream that Stream Dependency: A 31-bit stream identifier for the stream that
this stream depends on, see Section 5.3. This field is optional this stream depends on, see Section 5.3. This field is only
and is only present if the PRIORITY flag is set. present if the PRIORITY flag is set.
Weight: An 8-bit weight for the stream, see Section 5.3. Add one to Weight: An 8-bit weight for the stream, see Section 5.3. Add one to
the value to obtain a weight between 1 and 256. This field is the value to obtain a weight between 1 and 256. This field is
optional and is only present if the PRIORITY flag is set. only present if the PRIORITY flag is set.
Header Block Fragment: A header block fragment (Section 4.3). Header Block Fragment: A header block fragment (Section 4.3).
Padding: Padding octets. Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending and ignored when
receiving.
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 0 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 carries the END_STREAM flag that signals the end
the END_STREAM flag that signals the end of a stream. A of a stream. However, a HEADERS frame with the END_STREAM flag
CONTINUATION frame cannot be used to terminate a stream. set can be followed by CONTINUATION frames on the same stream.
Logically, the CONTINUATION frames are part of the HEADERS frame.
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): Bit 2 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.
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): Bit 3 being set indicates that the Pad Length field
present. and any padding that it describes is present.
PRIORITY (0x20): Bit 6 being set indicates that the Exclusive Flag PRIORITY (0x20): Bit 5 being set indicates that the Exclusive Flag
(E), Stream Dependency, and Weight fields are present; see (E), Stream Dependency, and Weight fields are present; see
Section 5.3. Section 5.3.
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 The HEADERS frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1). flags are identical to those defined for DATA frames (Section 6.1).
Prioritization information in a HEADERS frame is logically equivalent
to a separate PRIORITY frame, but inclusion in HEADERS avoids the
potential for churn in stream prioritization when new streams are
created. Priorization fields in HEADERS frames subsequent to the
first on a stream reprioritize the stream (Section 5.3.3).
6.3. PRIORITY 6.3. PRIORITY
The PRIORITY frame (type=0x2) specifies the sender-advised priority The PRIORITY frame (type=0x2) specifies the sender-advised priority
of a stream (Section 5.3). It can be sent at any time for an of a stream (Section 5.3). It can be sent at any time for an
existing stream, including closed streams. This enables existing stream, including closed streams. This enables
reprioritization of existing streams. reprioritization 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| Stream Dependency (31) | |E| Stream Dependency (31) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Weight (8) | | Weight (8) |
+-+-------------+ +-+-------------+
PRIORITY Frame Payload Figure 8: PRIORITY Frame Payload
The payload of a PRIORITY frame contains the following fields: The payload of a PRIORITY frame contains the following fields:
E: A single bit flag indicates that the stream dependency is E: A single bit flag indicates that the stream dependency is
exclusive, see Section 5.3. exclusive, see Section 5.3.
Stream Dependency: A 31-bit stream identifier for the stream that Stream Dependency: A 31-bit stream identifier for the stream that
this stream depends on, see Section 5.3. this stream depends on, see Section 5.3.
Weight: An 8-bit weight for the identified stream dependency, see Weight: An 8-bit weight for the identified stream dependency, see
skipping to change at page 34, line 41 skipping to change at page 35, line 9
this frame can only affect processing of the current stream and not this frame can only affect processing of the current stream and not
frame transmission. frame transmission.
The PRIORITY frame is the only frame that can be sent for a stream in The PRIORITY frame is the only frame that can be sent for a stream in
the "closed" state. This allows for the reprioritization of a group the "closed" state. This allows for the reprioritization of a group
of dependent streams by altering the priority of a parent stream, of dependent streams by altering the priority of a parent stream,
which might be closed. However, a PRIORITY frame sent on a closed which might be closed. However, a PRIORITY frame sent on a closed
stream risks being ignored due to the peer having discarded priority stream risks being ignored due to the peer having discarded priority
state information for that stream. state information for that stream.
A PRIORITY frame with a length other than 5 octets MUST be treated as
a stream error (Section 5.4.2) of type FRAME_SIZE_ERROR.
6.4. RST_STREAM 6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for abnormal termination of a The RST_STREAM frame (type=0x3) allows for immediate termination of a
stream. When sent by the initiator of a stream, it indicates that stream. RST_STREAM is sent to request cancellation of a stream, or
they wish to cancel the stream or that an error condition has to indicate that an error condition has occurred.
occurred. When sent by the receiver of a stream, it indicates that
either the receiver is rejecting the stream, requesting that the
stream be cancelled, or that an error condition has occurred.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
RST_STREAM Frame Payload Figure 9: RST_STREAM Frame Payload
The RST_STREAM frame contains a single unsigned, 32-bit integer The RST_STREAM frame contains a single unsigned, 32-bit integer
identifying the error code (Section 7). The error code indicates why identifying the error code (Section 7). The error code indicates why
the stream is being terminated. the stream is being terminated.
The RST_STREAM frame does not define any flags. The RST_STREAM frame does not define any flags.
The RST_STREAM frame fully terminates the referenced stream and The RST_STREAM frame fully terminates the referenced stream and
causes it to enter the closed state. After receiving a RST_STREAM on causes it to enter the closed state. After receiving a RST_STREAM on
a stream, the receiver MUST NOT send additional frames for that a stream, the receiver MUST NOT send additional frames for that
stream. However, after sending the RST_STREAM, the sending endpoint stream, with the exception of PRIORITY. However, after sending the
MUST be prepared to receive and process additional frames sent on the RST_STREAM, the sending endpoint MUST be prepared to receive and
stream that might have been sent by the peer prior to the arrival of process additional frames sent on the stream that might have been
the RST_STREAM. sent by the peer prior to the arrival of the RST_STREAM.
RST_STREAM frames MUST be associated with a stream. If a RST_STREAM RST_STREAM frames MUST be associated with a stream. If a RST_STREAM
frame is received with a stream identifier of 0x0, the recipient MUST frame is received with a stream identifier of 0x0, the recipient MUST
treat this as a connection error (Section 5.4.1) of type treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
RST_STREAM frames MUST NOT be sent for a stream in the "idle" state. RST_STREAM frames MUST NOT be sent for a stream in the "idle" state.
If a RST_STREAM frame identifying an idle stream is received, the If a RST_STREAM frame identifying an idle stream is received, the
recipient MUST treat this as a connection error (Section 5.4.1) of recipient MUST treat this as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
A RST_STREAM frame with a length other than 4 octets MUST be treated
as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.
6.5. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that The SETTINGS frame (type=0x4) conveys configuration parameters that
affect how endpoints communicate, such as preferences and constraints affect how endpoints communicate, such as preferences and constraints
on peer behavior. The SETTINGS frame is also used to acknowledge the on peer behavior. The SETTINGS frame is also used to acknowledge the
receipt of those parameters. Individually, a SETTINGS parameter can receipt of those parameters. Individually, a SETTINGS parameter can
also be referred to as a "setting". also be referred to as a "setting".
SETTINGS parameters are not negotiated; they describe characteristics SETTINGS parameters are not negotiated; they describe characteristics
of the sending peer, which are used by the receiving peer. Different of the sending peer, which are used by the receiving peer. Different
skipping to change at page 36, line 17 skipping to change at page 36, line 34
Each parameter in a SETTINGS frame replaces any existing value for Each parameter in a SETTINGS frame replaces any existing value for
that parameter. Parameters are processed in the order in which they that parameter. Parameters are processed in the order in which they
appear, and a receiver of a SETTINGS frame does not need to maintain appear, and a receiver of a SETTINGS frame does not need to maintain
any state other than the current value of its parameters. Therefore, any state other than the current value of its parameters. Therefore,
the value of a SETTINGS parameter is the last value that is seen by a the value of a SETTINGS parameter is the last value that is seen by a
receiver. receiver.
SETTINGS parameters are acknowledged by the receiving peer. To SETTINGS parameters are acknowledged by the receiving peer. To
enable this, the SETTINGS frame defines the following flag: enable this, the SETTINGS frame defines the following flag:
ACK (0x1): Bit 1 being set indicates that this frame acknowledges ACK (0x1): Bit 0 being set indicates that this frame acknowledges
receipt and application of the peer's SETTINGS frame. When this receipt and application of the peer's SETTINGS frame. When this
bit is set, the payload of the SETTINGS frame MUST be empty. bit is set, the payload of the SETTINGS frame MUST be empty.
Receipt of a SETTINGS frame with the ACK flag set and a length Receipt of a SETTINGS frame with the ACK flag set and a length
field value other than 0 MUST be treated as a connection error field value other than 0 MUST be treated as a connection error
(Section 5.4.1) of type FRAME_SIZE_ERROR. For more info, see (Section 5.4.1) of type FRAME_SIZE_ERROR. For more info, see
Settings Synchronization (Section 6.5.3). Settings Synchronization (Section 6.5.3).
SETTINGS frames always apply to a connection, never a single stream. SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a SETTINGS frame MUST be zero (0x0). If an The stream identifier for a SETTINGS frame MUST be zero (0x0). If an
endpoint receives a SETTINGS frame whose stream identifier field is endpoint receives a SETTINGS frame whose stream identifier field is
anything other than 0x0, the endpoint MUST respond with a connection anything other than 0x0, the endpoint MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
The SETTINGS frame affects connection state. A badly formed or The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error incomplete SETTINGS frame MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
A SETTINGS frame with a length other than a multiple of 6 octets MUST
be treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR.
6.5.1. SETTINGS Format 6.5.1. SETTINGS Format
The payload of a SETTINGS frame consists of zero or more parameters, The payload of a SETTINGS frame consists of zero or more parameters,
each consisting of an unsigned 16-bit setting identifier and an each consisting of an unsigned 16-bit 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier (16) | | Identifier (16) |
+-------------------------------+-------------------------------+ +-------------------------------+-------------------------------+
| Value (32) | | Value (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Setting Format Figure 10: Setting Format
6.5.2. Defined SETTINGS Parameters 6.5.2. Defined SETTINGS Parameters
The following parameters are defined: The following parameters are defined:
SETTINGS_HEADER_TABLE_SIZE (0x1): Allows the sender to inform the SETTINGS_HEADER_TABLE_SIZE (0x1): Allows the sender to inform the
remote endpoint of the maximum size of the header compression remote endpoint of the maximum size of the header compression
table used to decode header blocks. The encoder can select any table used to decode header blocks, in octets. The encoder can
size equal to or less than this value by using signaling specific select any size equal to or less than this value by using
to the header compression format inside a header block. The signaling specific to the header compression format inside a
initial value is 4,096 bytes. header block. The initial value is 4,096 octets.
SETTINGS_ENABLE_PUSH (0x2): This setting can be use to disable SETTINGS_ENABLE_PUSH (0x2): This setting can be use to disable
server push (Section 8.2). An endpoint MUST NOT send a server push (Section 8.2). An endpoint MUST NOT send a
PUSH_PROMISE frame if it receives this parameter set to a value of PUSH_PROMISE frame if it receives this parameter set to a value of
0. An endpoint that has both set this parameter to 0 and had it 0. An endpoint that has both set this parameter to 0 and had it
acknowledged MUST treat the receipt of a PUSH_PROMISE frame as a acknowledged MUST treat the receipt of a PUSH_PROMISE frame as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The initial value is 1, which indicates that server push is The initial value is 1, which indicates that server push is
permitted. Any value other than 0 or 1 MUST be treated as a permitted. Any value other than 0 or 1 MUST be treated as a
skipping to change at page 37, line 42 skipping to change at page 38, line 13
100, so as to not unnecessarily limit parallelism. 100, so as to not unnecessarily limit parallelism.
A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be
treated as special by endpoints. A zero value does prevent the treated as special by endpoints. A zero value does prevent the
creation of new streams, however this can also happen for any creation of new streams, however this can also happen for any
limit that is exhausted with active streams. Servers SHOULD only limit that is exhausted with active streams. Servers SHOULD only
set a zero value for short durations; if a server does not wish to set a zero value for short durations; if a server does not wish to
accept requests, closing the connection could be preferable. accept requests, closing the connection could be preferable.
SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial
window size (in bytes) for stream level flow control. The initial window size (in octets) for stream level flow control. The
value is 2^16-1 (65,535) octets. initial value is 2^16-1 (65,535) octets.
This setting affects the window size of all streams, including This setting affects the window size of all streams, including
existing streams, see Section 6.9.2. existing streams, see Section 6.9.2.
Values above the maximum flow control window size of 2^31-1 MUST Values above the maximum flow control window size of 2^31-1 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
FLOW_CONTROL_ERROR. FLOW_CONTROL_ERROR.
SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest
frame payload that a receiver is willing to accept. frame payload that the sender is willing to receive, in octets.
The initial value is 2^14 (16,384) octets. The value advertised The initial value is 2^14 (16,384) octets. The value advertised
by an endpoint MUST be between this initial value and the maximum by an endpoint MUST be between this initial value and the maximum
allowed frame size (2^24-1 or 16,777,215 octets), inclusive. allowed frame size (2^24-1 or 16,777,215 octets), inclusive.
Values outside this range MUST be treated as a connection error Values outside this range MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a
peer of the maximum size of header list that the sender is peer of the maximum size of header list that the sender is
prepared to accept. The value is based on the uncompressed size prepared to accept, in octets. The value is based on the
of header fields, including the length of the name and value in uncompressed size of header fields, including the length of the
octets plus an overhead of 32 octets for each header field. name and value in octets plus an overhead of 32 octets for each
header field.
For any given request, a lower limit than what is advertised MAY For any given request, a lower limit than what is advertised MAY
be enforced. The initial value of this setting is unlimited. be enforced. The initial value of this setting is unlimited.
An endpoint that receives a SETTINGS frame with any unknown or An endpoint that receives a SETTINGS frame with any unknown or
unsupported identifier MUST ignore that setting. unsupported identifier MUST ignore that setting.
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
skipping to change at page 39, line 19 skipping to change at page 39, line 38
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Pad Length? (8)| |Pad Length? (8)|
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
|R| Promised Stream ID (31) | |R| Promised Stream ID (31) |
+-+-----------------------------+-------------------------------+ +-+-----------------------------+-------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PUSH_PROMISE Payload Format Figure 11: PUSH_PROMISE Payload Format
The PUSH_PROMISE frame payload has the following fields: The PUSH_PROMISE frame payload has the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is only present if the
present if the PADDED flag is set. PADDED flag is set.
R: A single reserved bit. R: A single reserved bit.
Promised Stream ID: This unsigned 31-bit integer identifies the Promised Stream ID: An unsigned 31-bit integer that identifies the
stream the endpoint intends to start sending frames for. The stream that is reserved by the PUSH_PROMISE. The promised stream
promised stream identifier MUST be a valid choice for the next identifier MUST be a valid choice for the next stream sent by the
stream sent by the sender (see new stream identifier sender (see new stream identifier (Section 5.1.1)).
(Section 5.1.1)).
Header Block Fragment: A header block fragment (Section 4.3) Header Block Fragment: A header block fragment (Section 4.3)
containing request header fields. containing request header fields.
Padding: Padding octets. Padding: Padding octets.
The PUSH_PROMISE frame defines the following flags: The PUSH_PROMISE frame defines the following flags:
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): Bit 2 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 PUSH_PROMISE frame without the END_HEADERS flag set MUST be A PUSH_PROMISE frame without the END_HEADERS flag set MUST be
followed by a CONTINUATION frame for the same stream. A receiver followed by a CONTINUATION frame for the same stream. A receiver
MUST treat the receipt of any other type of frame or a frame on a MUST treat the receipt of any other type of frame or a frame on a
different stream as a connection error (Section 5.4.1) of type different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): Bit 3 being set indicates that the Pad Length field
present. and any padding that it describes is present.
PUSH_PROMISE frames MUST be associated with an existing, peer- PUSH_PROMISE frames MUST be associated with an existing, peer-
initiated stream. The stream identifier of a PUSH_PROMISE frame initiated stream. The stream identifier of a PUSH_PROMISE frame
indicates the stream it is associated with. If the stream identifier indicates the stream it is associated with. If the stream identifier
field specifies the value 0x0, a recipient MUST respond with a field specifies the value 0x0, a recipient MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
Promised streams are not required to be used in the order they are Promised streams are not required to be used in the order they are
promised. The PUSH_PROMISE only reserves stream identifiers for promised. The PUSH_PROMISE only reserves stream identifiers for
later use. later use.
skipping to change at page 40, line 42 skipping to change at page 41, line 11
"reserved" state. A sender MUST NOT send a PUSH_PROMISE on a stream "reserved" state. A sender MUST NOT send a PUSH_PROMISE on a stream
unless that stream is either "open" or "half closed (remote)"; the unless that stream is either "open" or "half closed (remote)"; the
sender MUST ensure that the promised stream is a valid choice for a sender MUST ensure that the promised stream is a valid choice for a
new stream identifier (Section 5.1.1) (that is, the promised stream new stream identifier (Section 5.1.1) (that is, the promised stream
MUST be in the "idle" state). MUST be in the "idle" 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. However, an endpoint that
treat the receipt of a PUSH_PROMISE that promises an illegal stream has sent RST_STREAM on the associated stream MUST handle PUSH_PROMISE
identifier (Section 5.1.1) (that is, an identifier for a stream that frames that might have been created before the RST_STREAM frame is
is not currently in the "idle" state) as a connection error received and processed.
(Section 5.4.1) of type PROTOCOL_ERROR.
A receiver MUST treat the receipt of a PUSH_PROMISE that promises an
illegal stream identifier (Section 5.1.1) (that is, an identifier for
a stream that is not currently in the "idle" state) as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
The PUSH_PROMISE frame includes optional padding. Padding fields and The PUSH_PROMISE frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1). flags are identical to those defined for DATA frames (Section 6.1).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Opaque Data (64) | | Opaque Data (64) |
| | | |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PING Payload Format Figure 12: 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 octets in any fashion.
Receivers of a PING frame that does not include an ACK flag MUST send Receivers of a PING frame that does not include an 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 be given higher priority than any payload. PING responses SHOULD be given higher priority than any
other 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 0 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
skipping to change at page 42, line 10 skipping to change at page 42, line 31
streams on this connection. GOAWAY can be sent by either the client streams on this connection. GOAWAY can be sent by either the client
or the server. Once sent, the sender will ignore frames sent on any or the server. Once sent, the sender will ignore frames sent on any
new streams with identifiers higher than the included last stream new streams with identifiers higher than the included last stream
identifier. Receivers of a GOAWAY frame MUST NOT open additional identifier. Receivers of a GOAWAY frame MUST NOT open additional
streams on the connection, although a new connection can be streams on the connection, although a new connection can be
established for new streams. established for new streams.
The purpose of this frame is to allow an endpoint to gracefully stop The purpose of this frame is to allow an endpoint to gracefully stop
accepting new streams, while still finishing processing of previously accepting new streams, while still finishing processing of previously
established streams. This enables administrative actions, like established streams. This enables administrative actions, like
server maintainence. server maintainance.
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 peer- case, the GOAWAY contains the stream identifier of the last peer-
initiated stream which was or might be processed on the sending initiated stream which was or might be processed on the sending
endpoint in this connection. For instance, if the server sends a endpoint in this connection. For instance, if the server sends a
GOAWAY frame, the identifed stream is the highest numbered stream GOAWAY frame, the identified stream is the highest numbered stream
initiated by the client. initiated by the client.
If the receiver of the GOAWAY has sent data on streams with a higher If the receiver of the GOAWAY has sent data on streams with a higher
stream identifier than what is indicated in the GOAWAY frame, those stream identifier than what is indicated in the GOAWAY frame, those
streams are not or will not be processed. The receiver of the GOAWAY streams are not or will not be processed. The receiver of the GOAWAY
frame can treat the streams as though they had never been created at frame can treat the streams as though they had never been created at
all, thereby allowing those streams to be retried later on a new all, thereby allowing those streams to be retried later on a new
connection. connection.
Endpoints SHOULD always send a GOAWAY frame before closing a Endpoints SHOULD always send a GOAWAY frame before closing a
skipping to change at page 42, line 48 skipping to change at page 43, line 20
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Last-Stream-ID (31) | |R| Last-Stream-ID (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Additional Debug Data (*) | | Additional Debug Data (*) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
GOAWAY Payload Format Figure 13: 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.
An endpoint MUST treat a GOAWAY frame with a stream identifier other An endpoint MUST treat a GOAWAY frame with a stream identifier other
than 0x0 as a connection error (Section 5.4.1) of type than 0x0 as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. 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
skipping to change at page 45, line 11 skipping to change at page 45, line 34
respond with a stream error (Section 5.4.2) or connection error respond with a stream error (Section 5.4.2) or connection error
(Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept (Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept
a frame. a frame.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Window Size Increment (31) | |R| Window Size Increment (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
WINDOW_UPDATE Payload Format Figure 14: WINDOW_UPDATE Payload Format
The payload of a WINDOW_UPDATE frame is one reserved bit, plus an The payload of a WINDOW_UPDATE frame is one reserved bit, plus an
unsigned 31-bit integer indicating the number of bytes that the unsigned 31-bit integer indicating the number of octets that the
sender can transmit in addition to the existing flow control window. sender can transmit in addition to the existing flow control window.
The legal range for the increment to the flow control window is 1 to The legal range for the increment to the flow control window is 1 to
2^31-1 (0x7fffffff) bytes. 2^31-1 (2,147,483,647) octets.
The WINDOW_UPDATE frame does not define any flags. The WINDOW_UPDATE frame does not define any flags.
The WINDOW_UPDATE frame can be specific to a stream or to the entire The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
A receiver MUST treat the recipt of a WINDOW_UPDATE frame with an A receiver MUST treat the receipt of a WINDOW_UPDATE frame with an
flow control window increment of 0 as a stream error (Section 5.4.2) flow control window increment of 0 as a stream error (Section 5.4.2)
of type PROTOCOL_ERROR; errors on the connection flow control window of type PROTOCOL_ERROR; errors on the connection flow control window
MUST be treated as a connection error (Section 5.4.1). MUST be treated as a connection error (Section 5.4.1).
WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the
END_STREAM flag. This means that a receiver could receive a END_STREAM flag. This means that a receiver could receive a
WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream. WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream.
A receiver MUST NOT treat this as an error, see Section 5.1. A receiver MUST NOT treat this as an error, see Section 5.1.
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.
A WINDOW_UPDATE frame with a length other than 4 octets MUST be
treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR.
6.9.1. The Flow Control Window 6.9.1. The Flow Control Window
Flow control in HTTP/2 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 octets of data the sender is permitted
to transmit; as such, its size is a measure of the buffering capacity to transmit; as such, its size is a measure of the buffering capacity
of the receiver. 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 (that receiver. Frames with zero length with the END_STREAM flag set (that
is, an empty DATA frame) MAY be sent if there is no available space is, an empty DATA frame) MAY be sent if there is no available space
in either flow control window. in either flow control window.
For flow control calculations, the 8 byte frame header is not For flow control calculations, the 9 octet frame header is not
counted. counted.
After sending a flow controlled frame, the sender reduces the space After sending a flow controlled frame, the sender reduces the space
available in both windows by the length of the transmitted frame. available in both windows by the length of the transmitted frame.
The receiver of a frame sends a WINDOW_UPDATE frame as it consumes The receiver of a frame sends a WINDOW_UPDATE frame as it consumes
data and frees up space in flow control windows. Separate data and frees up space in flow control windows. Separate
WINDOW_UPDATE frames are sent for the stream and connection level WINDOW_UPDATE frames are sent for the stream and connection level
flow control windows. flow control windows.
A sender that receives a WINDOW_UPDATE frame updates the A sender that receives a WINDOW_UPDATE frame updates the
corresponding window by the amount specified in the frame. corresponding window by the amount specified in the frame.
A sender MUST NOT allow a flow control window to exceed 2^31-1 bytes. A sender MUST NOT allow a flow control window to exceed 2^31-1
If a sender receives a WINDOW_UPDATE that causes a flow control octets. If a sender receives a WINDOW_UPDATE that causes a flow
window to exceed this maximum it MUST terminate either the stream or control window to exceed this maximum it MUST terminate either the
the connection, as appropriate. For streams, the sender sends a stream or the connection, as appropriate. For streams, the sender
RST_STREAM with the error code of FLOW_CONTROL_ERROR code; for the sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code;
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 an HTTP/2 connection is first established, new streams are When an 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 octets.
The connection flow control window is 65,535 bytes. Both endpoints The connection flow control window is 65,535 octets. 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 preface. The connection flow control forms part of the connection preface. The connection flow control
window can only be changed using WINDOW_UPDATE frames. window can only be changed using WINDOW_UPDATE frames.
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.
skipping to change at page 48, line 19 skipping to change at page 48, line 42
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 is on the same stream and is a HEADERS, PUSH_PROMISE or frame is on the same stream and is a HEADERS, PUSH_PROMISE or
CONTINUATION frame without the END_HEADERS flag set. CONTINUATION frame without the END_HEADERS 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
CONTINUATION Frame Payload Figure 15: CONTINUATION Frame Payload
The CONTINUATION frame payload contains a header block fragment The CONTINUATION frame payload contains a header block fragment
(Section 4.3). (Section 4.3).
The CONTINUATION frame defines the following flag: The CONTINUATION frame defines the following flag:
END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a END_HEADERS (0x4): Bit 2 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.
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.
skipping to change at page 49, line 32 skipping to change at page 50, line 8
FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer
violated the flow control protocol. violated the flow control protocol.
SETTINGS_TIMEOUT (0x4): The endpoint sent a SETTINGS frame, but did SETTINGS_TIMEOUT (0x4): The endpoint sent a SETTINGS frame, but did
not receive a response in a timely manner. See Settings not receive a response in a timely manner. See Settings
Synchronization (Section 6.5.3). Synchronization (Section 6.5.3).
STREAM_CLOSED (0x5): The endpoint received a frame after a stream STREAM_CLOSED (0x5): The endpoint received a frame after a stream
was half closed. was half closed.
FRAME_SIZE_ERROR (0x6): The endpoint received a frame that was FRAME_SIZE_ERROR (0x6): The endpoint received a frame with an
larger than the maximum size that it supports. invalid size.
REFUSED_STREAM (0x7): The endpoint refuses the stream prior to REFUSED_STREAM (0x7): The endpoint refuses the stream prior to
performing any application processing, see Section 8.1.4 for performing any application processing, see Section 8.1.4 for
details. details.
CANCEL (0x8): Used by the endpoint to indicate that the stream is no CANCEL (0x8): Used by the endpoint to indicate that the stream is no
longer needed. longer needed.
COMPRESSION_ERROR (0x9): The endpoint is unable to maintain the COMPRESSION_ERROR (0x9): The endpoint is unable to maintain the
header compression context for the connection. header compression context for the connection.
CONNECT_ERROR (0xa): The connection established in response to a CONNECT_ERROR (0xa): 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 (0xb): The endpoint detected that its peer is ENHANCE_YOUR_CALM (0xb): The endpoint detected that its peer is
exhibiting a behavior that might be generating excessive load. exhibiting a behavior that might be generating excessive load.
INADEQUATE_SECURITY (0xc): The underlying transport has properties INADEQUATE_SECURITY (0xc): The underlying transport has properties
that do not meet minimum security requirements (see Section 9.2). that do not meet minimum security requirements (see Section 9.2).
HTTP_1_1_REQUIRED (0xd): The endpoint requires that HTTP/1.1 be used
instead of HTTP/2.
Unknown or unsupported error codes MUST NOT trigger any special Unknown or unsupported error codes MUST NOT trigger any special
behavior. These MAY be treated by an implementation as being behavior. These MAY be treated by an implementation as being
equivalent to INTERNAL_ERROR. equivalent to INTERNAL_ERROR.
8. HTTP Message Exchanges 8. HTTP Message Exchanges
HTTP/2 is intended to be as compatible as possible with current uses HTTP/2 is intended to be as compatible as possible with current uses
of HTTP. This means that, from the application perspective, the of HTTP. This means that, from the application perspective, the
features of the protocol are largely unchanged. To achieve this, all features of the protocol are largely unchanged. To achieve this, all
request and response semantics are preserved, although the syntax of request and response semantics are preserved, although the syntax of
skipping to change at page 51, line 8 skipping to change at page 51, line 36
[RFC7230], Section 4.1.2). [RFC7230], Section 4.1.2).
The last frame in the sequence bears an END_STREAM flag, noting that The last frame in the sequence bears an END_STREAM flag, noting that
a HEADERS frame bearing the END_STREAM flag can be followed by a HEADERS frame bearing the END_STREAM flag can be followed by
CONTINUATION frames that carry any remaining portions of the header CONTINUATION frames that carry any remaining portions of the header
block. block.
Other frames (from any stream) MUST NOT occur between either HEADERS Other frames (from any stream) MUST NOT occur between either HEADERS
frame and any CONTINUATION frames that might follow. frame and any CONTINUATION frames that might follow.
A HEADERS frame (and associated CONTINUATION frames) can only appear HTTP/2 uses DATA frames to carry message payloads. The "chunked"
at the start or end of a stream. An endpoint that receives a second transfer encoding defined in Section 4.1 of [RFC7230] MUST NOT be
HEADERS frame without the END_STREAM flag set MUST treat the used in HTTP/2.
corresponding request or response as malformed (Section 8.1.2.6).
Trailing header fields are carried in a header block that also Trailing header fields are carried in a header block that also
terminates the stream. That is, a sequence starting with a HEADERS terminates the stream. Such a header block is a sequence starting
frame, followed by zero or more CONTINUATION frames, where the with a HEADERS frame, followed by zero or more CONTINUATION frames,
HEADERS frame bears an END_STREAM flag. Header blocks after the where the HEADERS frame bears an END_STREAM flag. Header blocks
first that do not terminate the stream are not part of an HTTP after the first that do not terminate the stream are not part of an
request or response. HTTP request or response.
A HEADERS frame (and associated CONTINUATION frames) can only appear
at the start or end of a stream. An endpoint that receives a HEADERS
frame without the END_STREAM flag set after receiving a final (non-
informational) status code MUST treat the corresponding request or
response as malformed (Section 8.1.2.6).
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. The request ends with a frame bearing END_STREAM, "open" state. The request ends with a frame bearing END_STREAM,
which causes the stream to become "half closed (local)" for the which causes the stream to become "half closed (local)" for the
client and "half closed (remote)" for the server. A response starts client and "half closed (remote)" for the server. A response starts
with a HEADERS frame and ends with a frame bearing END_STREAM, which with a HEADERS frame and ends with a frame bearing END_STREAM, which
places the stream in the "closed" state. places the stream in the "closed" state.
An HTTP response is complete after the server sends - or the client
receives - a frame with the END_STREAM flag set (including any
CONTINUATION frames needed to complete a header block). A server can
send a complete response prior to the client sending an entire
request if the response does not depend on any portion of the request
that has not been sent and received. When this is true, a server MAY
request that the client abort transmission of a request without error
by sending a RST_STREAM with an error code of NO_ERROR after sending
a complete response (i.e., a frame with the END_STREAM flag).
Clients MUST NOT discard responses as a result of receiving such a
RST_STREAM, though clients can always discard responses at their
discretion for other reasons.
8.1.1. Upgrading From HTTP/2 8.1.1. Upgrading From HTTP/2
HTTP/2 removes support for the 101 (Switching Protocols) HTTP/2 removes support for the 101 (Switching Protocols)
informational status code ([RFC7231], Section 6.2.2). informational status code ([RFC7231], Section 6.2.2).
The semantics of 101 (Switching Protocols) aren't applicable to a The semantics of 101 (Switching Protocols) aren't applicable to a
multiplexed protocol. Alternative protocols are able to use the same multiplexed protocol. Alternative protocols are able to use the same
mechanisms that HTTP/2 uses to negotiate their use (see Section 3). mechanisms that HTTP/2 uses to negotiate their use (see Section 3).
8.1.2. HTTP Header Fields 8.1.2. HTTP Header Fields
skipping to change at page 51, line 50 skipping to change at page 52, line 48
For a listing of registered HTTP headers, see the Message Header For a listing of registered HTTP headers, see the Message Header
Field Registry maintained at [4]. Field Registry maintained at [4].
8.1.2.1. Pseudo-Header Fields 8.1.2.1. Pseudo-Header Fields
While HTTP/1.x used the message start-line (see [RFC7230], While HTTP/1.x used the message start-line (see [RFC7230],
Section 3.1) to convey the target URI and method of the request, and Section 3.1) to convey the target URI and method of the request, and
the status code for the response, HTTP/2 uses special pseudo-header the status code for the response, HTTP/2 uses special pseudo-header
fields beginning with ':' character (ASCII 0x3a) for this purpose. fields beginning with ':' character (ASCII 0x3a) for this purpose.
Pseudo-header fields are only valid in the HTTP/2 context. These are Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT
not HTTP header fields. Endpoints MUST NOT generate pseudo-header generate pseudo-header fields other than those defined in this
fields other than those defined in this document. document.
Pseudo-header fields are only valid in the context in which they are Pseudo-header fields are only valid in the context in which they are
defined. Pseudo-header fields defined for requests MUST NOT appear defined. Pseudo-header fields defined for requests MUST NOT appear
in responses; pseudo-header fields defined for responses MUST NOT in responses; pseudo-header fields defined for responses MUST NOT
appear in requests. Pseudo-header fields MUST NOT appear in appear in requests. Pseudo-header fields MUST NOT appear in
trailers. Endpoints MUST treat a request or response that contains trailers. Endpoints MUST treat a request or response that contains
undefined or invalid pseudo-header fields as malformed undefined or invalid pseudo-header fields as malformed
(Section 8.1.2.6). (Section 8.1.2.6).
Just as in HTTP/1.x, header field names are strings of ASCII Just as in HTTP/1.x, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion. However, characters that are compared in a case-insensitive fashion. However,
header field names MUST be converted to lowercase prior to their header field names MUST be converted to lowercase prior to their
encoding in HTTP/2. A request or response containing uppercase encoding in HTTP/2. A request or response containing uppercase
header field names MUST be treated as malformed (Section 8.1.2.6). header field names MUST be treated as malformed (Section 8.1.2.6).
All pseudo-header fields MUST appear in the header block before All pseudo-header fields MUST appear in the header block before
regular header fields. Any request or response that contains a regular header fields. Any request or response that contains a
pseudo-header field that appears in a header block after a regular pseudo-header field that appears in a header block after a regular
header field MUST be treated as malformed (Section 8.1.2.6). header field MUST be treated as malformed (Section 8.1.2.6).
8.1.2.2. Hop-by-Hop Header Fields 8.1.2.2. Connection-Specific Header Fields
HTTP/2 does not use the Connection header field to indicate "hop-by- HTTP/2 does not use the "Connection" header field to indicate
hop" header fields; in this protocol, connection-specific metadata is connection-specific header fields; in this protocol, connection-
conveyed by other means. As such, a HTTP/2 message containing specific metadata is conveyed by other means. An endpoint MUST NOT
Connection MUST be treated as malformed (Section 8.1.2.6). generate an HTTP/2 message containing connection-specific header
fields; any message containing connection-specific header fields MUST
be treated as malformed (Section 8.1.2.6).
This means that an intermediary transforming an HTTP/1.x message to This means that an intermediary transforming an HTTP/1.x message to
HTTP/2 will need to remove any header fields nominated by the HTTP/2 will need to remove any header fields nominated by the
Connection header field, along with the Connection header field Connection header field, along with the Connection header field
itself. Such intermediaries SHOULD also remove other connection- itself. Such intermediaries SHOULD also remove other connection-
specific header fields, such as Keep-Alive, Proxy-Connection, specific header fields, such as Keep-Alive, Proxy-Connection,
Transfer-Encoding and Upgrade, even if they are not nominated by Transfer-Encoding and Upgrade, even if they are not nominated by
Connection. Connection.
One exception to this is the TE header field, which MAY be present in One exception to this is the TE header field, which MAY be present in
an HTTP/2 request, but when it is MUST NOT contain any value other an HTTP/2 request, but when it is, it MUST NOT contain any value
than "trailers". other than "trailers".
Note: HTTP/2 purposefully does not support upgrade to another Note: HTTP/2 purposefully does not support upgrade to another
protocol. The handshake methods described in Section 3 are protocol. The handshake methods described in Section 3 are
believed sufficient to negotiate the use of alternative protocols. believed sufficient to negotiate the use of alternative protocols.
8.1.2.3. Request Header Fields 8.1.2.3. Request Pseudo-Header Fields
HTTP/2 defines a number of pseudo header fields starting with a colon The following pseudo-header fields are defined for HTTP/2 requests:
':' character that carry information about the request target:
o The ":method" header field includes the HTTP method ([RFC7231], o The ":method" pseudo-header field includes the HTTP method
Section 4). ([RFC7231], Section 4).
o The ":scheme" header field includes the scheme portion of the o The ":scheme" pseudo-header field includes the scheme portion of
target URI ([RFC3986], Section 3.1). the target URI ([RFC3986], Section 3.1).
":scheme" is not restricted to "http" and "https" schemed URIs. A ":scheme" is not restricted to "http" and "https" schemed URIs. A
proxy or gateway can translate requests for non-HTTP schemes, proxy or gateway can translate requests for non-HTTP schemes,
enabling the use of HTTP to interact with non-HTTP services. enabling the use of HTTP to interact with non-HTTP services.
o The ":authority" header field includes the authority portion of o The ":authority" pseudo-header field includes the authority
the target URI ([RFC3986], Section 3.2). The authority MUST NOT portion of the target URI ([RFC3986], Section 3.2). The authority
include the deprecated "userinfo" subcomponent for "http" or MUST NOT include the deprecated "userinfo" subcomponent for "http"
"https" schemed URIs. or "https" schemed 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 pseudo-header field MUST be omitted when
from an HTTP/1.1 request that has a request target in origin or translating from an HTTP/1.1 request that has a request target in
asterisk form (see [RFC7230], Section 5.3). Clients that generate origin or asterisk form (see [RFC7230], Section 5.3). Clients
HTTP/2 requests directly SHOULD instead omit the "Host" header that generate HTTP/2 requests directly SHOULD use the _:authority_
field. An intermediary that converts an HTTP/2 request to pseudo-header field instead of the "Host" header field. An
HTTP/1.1 MUST create a "Host" header field if one is not present intermediary that converts an HTTP/2 request to HTTP/1.1 MUST
in a request by copying the value of the ":authority" header create a "Host" header field if one is not present in a request by
field. copying the value of the ":authority" pseudo-header field.
o The ":path" header field includes the path and query parts of the o The ":path" pseudo-header field includes the path and query parts
target URI (the "path-absolute" production from [RFC3986] and of the target URI (the "path-absolute" production from [RFC3986]
optionally a '?' character followed by the "query" production, see and optionally a '?' character followed by the "query" production,
[RFC3986], Section 3.3 and [RFC3986], Section 3.4). A request in see [RFC3986], Section 3.3 and [RFC3986], Section 3.4). A request
asterisk form includes the value '*' for the ":path" header field. in asterisk form includes the value '*' for the ":path" pseudo-
header field.
This field MUST NOT be empty for "http" or "https" URIs; "http" or This pseudo-header field MUST NOT be empty for "http" or "https"
"https" URIs that do not contain a path component MUST include a URIs; "http" or "https" URIs that do not contain a path component
value of '/'. The exception to this rule is an OPTIONS request MUST include a value of '/'. The exception to this rule is an
for an "http" or "https" URI that does not include a path OPTIONS request for an "http" or "https" URI that does not include
component; these MUST include a ":path" header field with a value a path component; these MUST include a ":path" pseudo-header field
of '*' (see [RFC7230], Section 5.3.4). with a value of '*' (see [RFC7230], Section 5.3.4).
All HTTP/2 requests MUST include exactly one valid value for the All HTTP/2 requests MUST include exactly one valid value for the
":method", ":scheme", and ":path" header fields, unless this is a ":method", ":scheme", and ":path" pseudo-header fields, unless it is
CONNECT request (Section 8.3). An HTTP request that omits mandatory a CONNECT request (Section 8.3). An HTTP request that omits
header fields is malformed (Section 8.1.2.6). mandatory pseudo-header fields is malformed (Section 8.1.2.6).
HTTP/2 does not define a way to carry the version identifier that is HTTP/2 does not define a way to carry the version identifier that is
included in the HTTP/1.1 request line. included in the HTTP/1.1 request line.
8.1.2.4. Response Header Fields 8.1.2.4. Response Pseudo-Header Fields
A single ":status" header field is defined that carries the HTTP For HTTP/2 responses, a single ":status" pseudo-header field is
status code field (see [RFC7231], Section 6). This header field MUST defined that carries the HTTP status code field (see [RFC7231],
be included in all responses, otherwise the response is malformed Section 6). This pseudo-header field MUST be included in all
(Section 8.1.2.6). responses, otherwise the response is malformed (Section 8.1.2.6).
HTTP/2 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.
8.1.2.5. Compressing the Cookie Header Field 8.1.2.5. Compressing the Cookie Header Field
The Cookie header field [COOKIE] can carry a significant amount of The Cookie header field [COOKIE] can carry a significant amount of
redundant data. redundant data.
The Cookie header field uses a semi-colon (";") to delimit cookie- The Cookie header field uses a semi-colon (";") to delimit cookie-
skipping to change at page 55, line 8 skipping to change at page 56, line 10
A malformed request or response is one that is an otherwise valid A malformed request or response is one that is an otherwise valid
sequence of HTTP/2 frames, but is otherwise invalid due to the sequence of HTTP/2 frames, but is otherwise invalid due to the
presence of extraneous frames, prohibited header fields, the absence presence of extraneous frames, prohibited header fields, the absence
of mandatory header fields, or the inclusion of uppercase header of mandatory header fields, or the inclusion of uppercase header
field names. 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.
with the exception of responses to HEAD requests, which always A response that is defined to have no payload, as described in
contain no DATA frames. [RFC7230], Section 3.3.2, can have a non-zero "content-length" header
field, even though no content is included in DATA frames.
Intermediaries that process HTTP requests or responses (i.e., any Intermediaries that process HTTP requests or responses (i.e., any
intermediary not acting as a tunnel) MUST NOT forward a malformed intermediary not acting as a tunnel) MUST NOT forward a malformed
request or response. Malformed requests or responses that are request or response. Malformed requests or responses that are
detected MUST be treated as a stream error (Section 5.4.2) of type detected MUST be treated as a stream error (Section 5.4.2) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
For malformed requests, a server MAY send an HTTP response prior to For malformed requests, a server MAY send an HTTP response prior to
closing or resetting the stream. Clients MUST NOT accept a malformed closing or resetting the stream. Clients MUST NOT accept a malformed
response. Note that these requirements are intended to protect response. Note that these requirements are intended to protect
skipping to change at page 56, line 24 skipping to change at page 57, line 26
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
:path = /resource :path = /resource
{binary data} content-type = image/jpeg {binary data} :scheme = https
CONTINUATION CONTINUATION
+ END_HEADERS + END_HEADERS
content-type = image/jpeg
host = example.org host = example.org
:scheme = https
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
Note that data contributing to any given header field could be spread Note that data contributing to any given header field could be spread
between header block fragments. The allocation of header fields to between header block fragments. The allocation of header fields to
frames in this example is illustrative only. frames in this example is illustrative only.
skipping to change at page 57, line 16 skipping to change at page 58, line 16
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS Content-Length: 123 + END_HEADERS
:status = 200 :status = 200
{binary data} content-type = image/jpeg {binary data} content-type = image/jpeg
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
An informational response using a 1xx status code other than 101 is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames.
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 HEADERS frame starting the trailers header block has the sent. The HEADERS frame starting the trailers header block has the
END_STREAM flag set. END_STREAM flag set.
The following example includes both a 100 (Continue) status code,
which is sent in response to a request containing a "100-continue"
token in the Expect header field, and trailing header fields:
HTTP/1.1 100 Continue HEADERS
Extension-Field: bar ==> - END_STREAM
+ END_HEADERS
:status = 100
extension-field = bar
HTTP/1.1 200 OK HEADERS HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Transfer-Encoding: chunked + END_HEADERS Transfer-Encoding: chunked + END_HEADERS
Trailer: Foo :status = 200 Trailer: Foo :status = 200
content-length = 123 content-length = 123
123 content-type = image/jpeg 123 content-type = image/jpeg
{binary data} trailer = Foo {binary data} trailer = Foo
0 0
Foo: bar DATA Foo: bar DATA
- END_STREAM - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo = bar foo = bar
An informational response using a 1xx status code other than 101 is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames:
HTTP/1.1 103 BAR HEADERS
Extension-Field: bar ==> - END_STREAM
+ END_HEADERS
:status = 103
extension-field = bar
8.1.4. Request Reliability Mechanisms in HTTP/2 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 provides two mechanisms for providing a guarantee to a client HTTP/2 provides two mechanisms for providing a guarantee to a client
that a request has not been processed: that a request has not been processed:
skipping to change at page 58, line 38 skipping to change at page 59, line 44
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 enables a server to pre-emptively send (or "push") one or more HTTP/2 allows a server to pre-emptively send (or "push") responses
associated responses to a client in response to a single request. (along with corresponding "promised" requests) to a client in
This feature becomes particularly helpful when the server knows the association with a previous client-initiated request. This can be
client will need to have those responses available in order to fully useful when the server knows the client will need to have those
process the response to the original request. responses available in order to fully process the response to the
original request.
Pushing additional responses is optional, and is negotiated between Pushing additional message exchanges in this fashion is optional, and
individual endpoints. The SETTINGS_ENABLE_PUSH setting can be set to is negotiated between individual endpoints. The SETTINGS_ENABLE_PUSH
0 to indicate that server push is disabled. setting can be set to 0 to indicate that server push is disabled.
Because pushing responses is effectively hop-by-hop, an intermediary Promised requests MUST be cacheable (see [RFC7231], Section 4.2.3),
could receive pushed responses from the server and choose not to MUST be safe (see [RFC7231], Section 4.2.1) and MUST NOT include a
forward those on to the client. In other words, how to make use of request body. Clients that receive a promised request that is not
the pushed responses is up to that intermediary. Equally, the cacheable, unsafe or that includes a request body MUST reset the
intermediary might choose to push additional responses to the client, stream with a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
Pushed responses that are cacheable (see [RFC7234], Section 3) can be
stored by the client, if it implements an HTTP cache. Pushed
responses are considered successfully validated on the origin server
(e.g., if the "no-cache" cache response directive [RFC7234],
Section 5.2.2 is present) while the stream identified by the promised
stream ID is still open.
Pushed responses that are not cacheable MUST NOT be stored by any
HTTP cache. They MAY be made available to the application
separately.
An intermediary can receive pushes from the server and choose not to
forward them on to the client. In other words, how to make use of
the pushed information is up to that intermediary. Equally, the
intermediary might choose to make additional pushes to the client,
without any action taken by the server. without any action taken by the server.
A client cannot push. Thus, servers MUST treat the receipt of a A client cannot push. Thus, servers MUST treat the receipt of a
PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PUSH_PROMISE frame as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. Clients MUST reject any attempt to change the PROTOCOL_ERROR. Clients MUST reject any attempt to change the
SETTINGS_ENABLE_PUSH setting to a value other than 0 by treating the SETTINGS_ENABLE_PUSH setting to a value other than 0 by treating the
message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
A server can only push responses that are cacheable (see [RFC7234],
Section 3); promised requests MUST be safe (see [RFC7231],
Section 4.2.1) and MUST NOT include a 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; however, in this case that request is also sent by the request; however, in this case that request is also sent by the
server, as a PUSH_PROMISE frame. server, as a PUSH_PROMISE frame.
The PUSH_PROMISE frame includes a header block that contains a The PUSH_PROMISE frame includes a header block that contains a
complete set of request header fields that the server attributes to complete set of request header fields that the server attributes to
the request. It is not possible to push a response to a request that the request. It is not possible to push a response to a request that
includes a request body. includes a request body.
skipping to change at page 61, line 5 skipping to change at page 62, line 25
and referencing the pushed stream's identifier. and referencing the pushed stream's identifier.
A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
the number of responses that can be concurrently pushed by a server. the number of responses 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 either the
authorized to provide the response, see Section 10.1. For example, a server is authoritative (see Section 10.1), or the proxy that
server that offers a certificate for only the "example.com" DNS-ID or provided the pushed response is configured for the corresponding
Common Name is not permitted to push a response for request. For example, a server that offers a certificate for only
"https://www.example.org/doc". the "example.com" DNS-ID or Common Name is not permitted to push a
response for "https://www.example.org/doc".
The response for a PUSH_PROMISE stream begins with a HEADERS frame, The response for a PUSH_PROMISE stream begins with a HEADERS frame,
which immediately puts the stream into the "half closed (remote)" which immediately puts the stream into the "half closed (remote)"
state for the server and "half closed (local)" state for the client, state for the server and "half closed (local)" state for the client,
and ends with a frame bearing END_STREAM, which places the stream in and ends with a frame bearing END_STREAM, which places the stream in
the "closed" state. the "closed" state.
Note: The client never sends a frame with the END_STREAM flag for a Note: The client never sends a frame with the END_STREAM flag for a
server push. server push.
8.3. The CONNECT Method 8.3. The CONNECT Method
In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is
used to convert an HTTP connection into a tunnel to a remote host. used to convert an HTTP connection into a tunnel to a remote host.
CONNECT is primarily used with HTTP proxies to establish a TLS CONNECT is primarily used with HTTP proxies to establish a TLS
session with an origin server for the purposes of interacting with session with an origin server for the purposes of interacting with
"https" resources. "https" resources.
In HTTP/2, 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 stream to a remote host, for similar purposes. The single HTTP/2 stream to a remote host, for similar purposes. The
HTTP header field mapping works as mostly as defined in Request HTTP header field mapping works as defined in Request Header Fields
Header Fields (Section 8.1.2.3), with a few differences. (Section 8.1.2.3), with a few differences. Specifically:
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 [RFC7230], Section 5.3). of CONNECT requests, see [RFC7230], Section 5.3).
A proxy that supports CONNECT establishes a TCP connection [TCP] to A proxy that supports CONNECT establishes a TCP connection [TCP] to
the server identified in the ":authority" header field. Once this the server identified in the ":authority" header field. Once this
connection is successfully established, the proxy sends a HEADERS connection is successfully established, the proxy sends a HEADERS
frame containing a 2xx series status code to the client, as defined frame containing a 2xx series status code to the client, as defined
in [RFC7231], Section 4.3.6. in [RFC7231], Section 4.3.6.
After the initial HEADERS frame sent by each peer, all subsequent After the initial HEADERS frame sent by each peer, all subsequent
DATA frames correspond to data sent on the TCP connection. The DATA frames correspond to data sent on the TCP connection. The
payload of any DATA frames sent by the client are transmitted by the payload of any DATA frames sent by the client is transmitted by the
proxy to the TCP server; data received from the TCP server is proxy to the TCP server; data received from the TCP server is
assembled into DATA frames by the proxy. Frame types other than DATA assembled into DATA frames by the proxy. Frame types other than DATA
or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY) or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY)
MUST NOT be sent on a connected stream, and MUST be treated as a MUST NOT be sent on a connected stream, and MUST be treated as a
stream error (Section 5.4.2) if received. stream error (Section 5.4.2) if received.
The TCP connection can be closed by either peer. The END_STREAM flag The TCP connection can be closed by either peer. The END_STREAM flag
on a DATA frame is treated as being equivalent to the TCP FIN bit. A on a DATA frame is treated as being equivalent to the TCP FIN bit. A
client is expected to send a DATA frame with the END_STREAM flag set client is expected to send a DATA frame with the END_STREAM flag set
after receiving a frame bearing the END_STREAM flag. A proxy that after receiving a frame bearing the END_STREAM flag. A proxy that
skipping to change at page 63, line 9 skipping to change at page 64, line 30
a TLS connection, or to replace connections that have encountered a TLS connection, or to replace connections that have encountered
errors (Section 5.4.1). errors (Section 5.4.1).
A client MAY open multiple connections to the same IP address and TCP A client MAY open multiple connections to the same IP address and TCP
port using different Server Name Indication [TLS-EXT] values or to port using different Server Name Indication [TLS-EXT] values or to
provide different TLS client certificates, but SHOULD avoid creating provide different TLS client certificates, but SHOULD avoid creating
multiple connections with the same configuration. multiple connections with the same configuration.
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-layer
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.
9.1.1. Connection Reuse 9.1.1. Connection Reuse
Clients MAY use a single server connection to send requests for URIs Connections that are made to an origin servers, either directly or
with multiple different authority components as long as the server is through a tunnel created using the CONNECT method (Section 8.3) MAY
authoritative (Section 10.1). For "http" resources, this depends on be reused for requests with multiple different URI authority
the host having resolved to the same IP address. components. A connection can be reused as long as the origin server
is authoritative (Section 10.1). For "http" resources, this depends
on the host having resolved to the same IP address.
For "https" resources, connection reuse additionally depends on For "https" resources, connection reuse additionally depends on
having a certificate that is valid for the host in the URI. That is having a certificate that is valid for the host in the URI. An
the use of server certificate with multiple "subjectAltName" origin server might offer a certificate with multiple
attributes, or names with wildcards. For example, a certificate with "subjectAltName" attributes, or names with wildcards, one of which is
valid for the authority in the URI. For example, a certificate with
a "subjectAltName" of "*.example.com" might permit the use of the a "subjectAltName" of "*.example.com" might permit the use of the
same connection for "a.example.com" and "b.example.com". same connection for requests to URIs starting with
"https://a.example.com/" and "https://b.example.com/".
In some deployments, reusing a connection for multiple origins can In some deployments, reusing a connection for multiple origins can
result in requests being directed to the wrong origin server. For result in requests being directed to the wrong origin server. For
example, TLS termination might be performed by a middlebox that uses example, TLS termination might be performed by a middlebox that uses
the TLS Server Name Indication (SNI) [TLS-EXT] extension to select the TLS Server Name Indication (SNI) [TLS-EXT] extension to select an
the an origin server. This means that it is possible for clients to origin server. This means that it is possible for clients to send
send confidential information to servers that might not be the confidential information to servers that might not be the intended
intended target for the request, even though the server has valid target for the request, even though the server is otherwise
authentication credentials. authoritative.
A server that does not wish clients to reuse connections can indicate A server that does not wish clients to reuse connections can indicate
that it is not authoritative for a request by sending a 421 (Not that it is not authoritative for a request by sending a 421
Authoritative) status code in response to the request (see (Misdirected Request) status code in response to the request (see
Section 9.1.2). Section 9.1.2).
9.1.2. The 421 (Not Authoritative) Status Code A client that is configured to use a proxy over HTTP/2 directs
requests to that proxy through a single connection. That is, all
requests sent via a proxy reuse the connection to the proxy.
The 421 (Not Authoritative) status code indicates that the current 9.1.2. The 421 (Misdirected Request) Status Code
origin server is not authoritative for the requested resource, in the
sense of [RFC7230], Section 9.1 (see also Section 10.1).
Clients receiving a 421 (Not Authoritative) response from a server The 421 (Misdirected Request) status code indicates that the request
was directed at a server that is not able to produce a response.
This can be sent by a server that is not configured to produce
responses for the combination of scheme and authority that are
included in the request URI.
Clients receiving a 421 (Misdirected Request) response from a server
MAY retry the request - whether the request method is idempotent or MAY retry the request - whether the request method is idempotent or
not - over a different connection. This is possible if a connection not - over a different connection. This is possible if a connection
is reused (Section 9.1.1) or if an alternative service is selected is reused (Section 9.1.1) or if an alternative service is selected
([ALT-SVC]). ([ALT-SVC]).
This status code MUST NOT be generated by proxies. This status code MUST NOT be generated by proxies.
A 421 response is cacheable by default; i.e., unless otherwise A 421 response is cacheable by default; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [RFC7234]).
skipping to change at page 65, line 7 skipping to change at page 66, line 35
of messages the underlying cipher suite can encipher. of messages the underlying cipher suite can encipher.
A client MAY use renegotiation to provide confidentiality protection A client MAY use renegotiation to provide confidentiality protection
for client credentials offered in the handshake, but any for client credentials offered in the handshake, but any
renegotiation MUST occur prior to sending the connection preface. A renegotiation MUST occur prior to sending the connection preface. A
server SHOULD request a client certificate if it sees a renegotiation server SHOULD request a client certificate if it sees a renegotiation
request immediately after establishing a connection. request immediately after establishing a connection.
This effectively prevents the use of renegotiation in response to a This effectively prevents the use of renegotiation in response to a
request for a specific protected resource. A future specification request for a specific protected resource. A future specification
might provide a way to support this use case. might provide a way to support this use case. Alternatively, a
server might use a connection error (Section 5.4.1) of type
HTTP_1_1_REQUIRED to request the client use a protocol which supports
renegotiation.
9.2.2. TLS Cipher Suites 9.2.2. TLS Cipher Suites
The set of TLS cipher suites that are permitted in HTTP/2 is The set of TLS cipher suites that are permitted in HTTP/2 is
restricted. HTTP/2 MUST only be used with cipher suites that have restricted. HTTP/2 MUST only be used with cipher suites that have
ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE) ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE)
[TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral [TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral
key exchange MUST have a minimum size of 2048 bits for DHE or key exchange MUST have a minimum size of 2048 bits for DHE or
security level of 128 bits for ECDHE. Clients MUST accept DHE sizes security level of 128 bits for ECDHE. Clients MUST accept DHE sizes
of up to 4096 bits. HTTP MUST NOT be used with cipher suites that of up to 4096 bits. HTTP MUST NOT be used with cipher suites that
skipping to change at page 65, line 39 skipping to change at page 67, line 22
Clients MAY advertise support of cipher suites that are prohibited by Clients MAY advertise support of cipher suites that are prohibited by
the above restrictions in order to allow for connection to servers the above restrictions in order to allow for connection to servers
that do not support HTTP/2. This enables a fallback to protocols that do not support HTTP/2. This enables a fallback to protocols
without these constraints without the additional latency imposed by without these constraints without the additional latency imposed by
using a separate connection for fallback. using a separate connection for fallback.
10. Security Considerations 10. Security Considerations
10.1. Server Authority 10.1. Server Authority
A client is only able to accept HTTP/2 responses from servers that
are authoritative for those resources. This is particularly
important for server push (Section 8.2), where the client validates
the PUSH_PROMISE before accepting the response.
HTTP/2 relies on the HTTP/1.1 definition of authority for determining HTTP/2 relies on the HTTP/1.1 definition of authority for determining
whether a server is authoritative in providing a given response, see whether a server is authoritative in providing a given response, see
[RFC7230], Section 9.1. This relies on local name resolution for the [RFC7230], Section 9.1. This relies on local name resolution for the
"http" URI scheme, and the authenticated server identity for the "http" URI scheme, and the authenticated server identity for the
"https" scheme (see [RFC2818], Section 3). "https" scheme (see [RFC2818], Section 3).
A client MUST discard responses provided by a server that is not
authoritative for those resources.
10.2. Cross-Protocol Attacks 10.2. Cross-Protocol Attacks
In a cross-protocol attack, an attacker causes a client to initiate a In a cross-protocol attack, an attacker causes a client to initiate a
transaction in one protocol toward a server that understands a transaction in one protocol toward a server that understands a
different protocol. An attacker might be able to cause the different protocol. An attacker might be able to cause the
transaction to appear as valid transaction in the second protocol. transaction to appear as valid transaction in the second protocol.
In combination with the capabilities of the web context, this can be In combination with the capabilities of the web context, this can be
used to interact with poorly protected servers in private networks. used to interact with poorly protected servers in private networks.
Completing a TLS handshake with an ALPN identifier for HTTP/2 can be Completing a TLS handshake with an ALPN identifier for HTTP/2 can be
skipping to change at page 66, line 34 skipping to change at page 68, line 9
The cleartext version of HTTP/2 has minimal protection against cross- The cleartext version of HTTP/2 has minimal protection against cross-
protocol attacks. The connection preface (Section 3.5) contains a protocol attacks. The connection preface (Section 3.5) contains a
string that is designed to confuse HTTP/1.1 servers, but no special string that is designed to confuse HTTP/1.1 servers, but no special
protection is offered for other protocols. A server that is willing protection is offered for other protocols. A server that is willing
to ignore parts of an HTTP/1.1 request containing an Upgrade header to ignore parts of an HTTP/1.1 request containing an Upgrade header
field in addition to the client connection preface could be exposed field in addition to the client connection preface could be exposed
to a cross-protocol attack. to a cross-protocol attack.
10.3. Intermediary Encapsulation Attacks 10.3. Intermediary Encapsulation Attacks
HTTP/2 header field names and values are encoded as sequences of The HTTP/2 header field encoding allows the expression of names that
octets with a length prefix. This enables HTTP/2 to carry any string are not valid field names in the Internet Message Syntax used by
of octets as the name or value of a header field. An intermediary HTTP/1.1. Requests or responses containing invalid header field
that translates HTTP/2 requests or responses into HTTP/1.1 directly names MUST be treated as malformed (Section 8.1.2.6). An
could permit the creation of corrupted HTTP/1.1 messages. An intermediary therefore cannot translate an HTTP/2 request or response
attacker might exploit this behavior to cause the intermediary to containing an invalid field name into an HTTP/1.1 message.
create HTTP/1.1 messages with illegal header fields, extra header
fields, or even new messages that are entirely falsified.
Header field names or values that contain characters not permitted by
HTTP/1.1, including carriage return (ASCII 0xd) or line feed (ASCII
0xa) MUST NOT be translated verbatim by an intermediary, as
stipulated in [RFC7230], Section 3.2.4.
Translation from HTTP/1.x to HTTP/2 does not produce the same Similarly, HTTP/2 allows header field values that are not valid.
opportunity to an attacker. Intermediaries that perform translation While most of the values that can be encoded will not alter header
to HTTP/2 MUST remove any instances of the "obs-fold" production from field parsing, carriage return (CR, ASCII 0xd), line feed (LF, ASCII
header field values. 0xa), and the zero character (NUL, ASCII 0x0) might be exploited by
an attacker if they are translater verbatim. Any request or response
that contains a character not permitted in a header field value MUST
be treated as malformed (Section 8.1.2.6). Valid characters are
defined by the "field-content" ABNF rule in Section 3.2 of [RFC7230].
10.4. Cacheability of Pushed Responses 10.4. Cacheability of Pushed Responses
Pushed responses do not have an explicit request from the client; the Pushed responses do not have an explicit request from the client; the
request is provided by the server in the PUSH_PROMISE frame. request is provided by the server in the PUSH_PROMISE frame.
Caching responses that are pushed is possible based on the guidance Caching responses 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
skipping to change at page 68, line 4 skipping to change at page 69, line 25
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 SETTINGS processing time. This might be done by pointlessly changing SETTINGS
parameters, setting multiple undefined parameters, or changing the parameters, setting multiple undefined parameters, or changing the
same setting multiple times in the same frame. WINDOW_UPDATE or same setting multiple times in the same frame. WINDOW_UPDATE or
PRIORITY frames can be abused to cause an unnecessary waste of 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 or
to end a stream. CONTINUATION frame at the end of a stream.
Header compression also offers some opportunities to waste processing Header compression also offers some opportunities to waste processing
resources; see Section 8 of [COMPRESSION] for more details on resources; see Section 8 of [COMPRESSION] for more details on
potential abuses. potential abuses.
Limits in SETTINGS parameters cannot be reduced instantaneously, Limits in SETTINGS parameters cannot be reduced instantaneously,
which leaves an endpoint exposed to behavior from a peer that could which leaves an endpoint exposed to behavior from a peer that could
exceed the new limits. In particular, immediately after establishing exceed the new limits. In particular, immediately after establishing
a connection, limits set by a server are not known to clients and a connection, limits set by a server are not known to clients and
could be exceeded without being an obvious protocol violation. could be exceeded without being an obvious protocol violation.
skipping to change at page 68, line 30 skipping to change at page 70, line 8
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 features and set limits on their use. An endpoint MAY use of these features and set limits on their use. An 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.
10.5.1. Limits on Header Block Size 10.5.1. Limits on Header Block Size
A large header block (Section 4.3) can cause an implementation to A large header block (Section 4.3) can cause an implementation to
commit a large amount of state. In servers and intermediaries, commit a large amount of state. Header fields that are critical for
header fields that are critical to routing, such as ":authority", routing can appear toward the end of a header block, which prevents
":path", and ":scheme" are not guaranteed to be present early in the streaming of header fields to their ultimate destination. For this
header block. In particular, values that are in the reference set an other reasons, such as ensuring cache correctness, means that an
cannot be emitted until the header block ends. endpoint might need to buffer the entire header block. Since there
is no hard limit to the size of a header block, some endpoints could
This can prevent streaming of the header fields to their ultimate be forced commit a large amount of available memory for header
destination, and forces the endpoint to buffer the entire header fields.
block. Since there is no hard limit to the size of a header block,
an endpoint could be forced to exhaust available memory.
An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to avise peers An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to advise peers
of limits that might apply on the size of header blocks. This of limits that might apply on the size of header blocks. This
setting is only advisory, so endpoints MAY choose to send header setting is only advisory, so endpoints MAY choose to send header
blocks that exceed this limit and risk having the request or response blocks that exceed this limit and risk having the request or response
being treated as malformed. This setting is advertised hop-by-hop, being treated as malformed. This setting specific to a connection,
so any request or response could encounter a hop with a lower, so any request or response could encounter a hop with a lower,
unknown limit. An intermediary can attempt to avoid this problem by unknown limit. An intermediary can attempt to avoid this problem by
passing on values presented by different peers, but they are not passing on values presented by different peers, but they are not
obligated to do so. obligated to do so.
A server that receives a larger header block than it is willing to A server that receives a larger header block than it is willing to
handle can send an HTTP 431 (Request Header Fields Too Large) status handle can send an HTTP 431 (Request Header Fields Too Large) status
code [RFC6585]. A client can discard responses that it cannot code [RFC6585]. A client can discard responses that it cannot
process. The header block MUST be processed to ensure a consistent process. The header block MUST be processed to ensure a consistent
connection state, unless the connection is closed. connection state, unless the connection is closed.
skipping to change at page 69, line 28 skipping to change at page 70, line 50
There are demonstrable attacks on compression that exploit the There are demonstrable attacks on compression that exploit the
characteristics of the web (e.g., [BREACH]). The attacker induces characteristics of the web (e.g., [BREACH]). The attacker induces
multiple requests containing varying plaintext, observing the length multiple requests containing varying plaintext, observing the length
of the resulting ciphertext in each, which reveals a shorter length of the resulting ciphertext in each, which reveals a shorter length
when a guess about the secret is correct. when a guess about the secret is correct.
Implementations communicating on a secure channel MUST NOT compress Implementations communicating on a secure channel MUST NOT compress
content that includes both confidential and attacker-controlled data content that includes both confidential and attacker-controlled data
unless separate compression dictionaries are used for each source of unless separate compression dictionaries are used for each source of
data. Compression MUST NOT be used if the source of data cannot be data. Compression MUST NOT be used if the source of data cannot be
reliably determined. reliably determined. Generic stream compression, such as that
provided by TLS MUST NOT be used with HTTP/2 (Section 9.2.1).
Further considerations regarding the compression of header fields are Further considerations regarding the compression of header fields are
described in [COMPRESSION]. described in [COMPRESSION].
10.7. Use of Padding 10.7. Use of Padding
Padding within HTTP/2 is not intended as a replacement for general Padding within HTTP/2 is not intended as a replacement for general
purpose padding, such as might be provided by TLS [TLS12]. Redundant purpose padding, such as might be provided by TLS [TLS12]. Redundant
padding could even be counterproductive. Correct application can padding could even be counterproductive. Correct application can
depend on having specific knowledge of the data that is being padded. depend on having specific knowledge of the data that is being padded.
skipping to change at page 70, line 38 skipping to change at page 72, line 16
A string for identifying HTTP/2 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 [TLS-ALPN]. in [TLS-ALPN].
This document establishes a registry for frame types, settings, and This document establishes a registry for frame types, settings, and
error codes. These new registries are entered into a new "Hypertext error codes. These new registries are entered into a new "Hypertext
Transfer Protocol (HTTP) 2 Parameters" section. Transfer Protocol (HTTP) 2 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; and the 421 (Not Authoritative) status code. HTTP; and the 421 (Misdirected Request) status code.
This document registers the "PRI" method for use in HTTP, to avoid This document registers the "PRI" method for use in HTTP, to avoid
collisions with the connection preface (Section 3.5). collisions with the connection preface (Section 3.5).
11.1. Registration of HTTP/2 Identification Strings 11.1. Registration of HTTP/2 Identification Strings
This document creates two registrations for the identification of This document creates two registrations for the identification of
HTTP/2 in the "Application Layer Protocol Negotiation (ALPN) Protocol HTTP/2 in the "Application Layer Protocol Negotiation (ALPN) Protocol
IDs" registry established in [TLS-ALPN]. IDs" registry established in [TLS-ALPN].
skipping to change at page 71, line 18 skipping to change at page 72, line 45
The "h2c" string identifies HTTP/2 when used over cleartext TCP: The "h2c" string identifies HTTP/2 when used over cleartext TCP:
Protocol: HTTP/2 over TCP Protocol: HTTP/2 over TCP
Identification Sequence: 0x68 0x32 0x63 ("h2c") Identification Sequence: 0x68 0x32 0x63 ("h2c")
Specification: This document Specification: This document
11.2. Frame Type Registry 11.2. Frame Type Registry
This document establishes a registry for HTTP/2 frame types codes. This document establishes a registry for HTTP/2 frame type codes.
The "HTTP/2 Frame Type" registry manages an 8-bit space. The "HTTP/2 The "HTTP/2 Frame Type" registry manages an 8-bit space. The "HTTP/2
Frame Type" registry operates under either of the "IETF Review" or Frame Type" registry operates under either of the "IETF Review" or
"IESG Approval" policies [RFC5226] for values between 0x00 and 0xef, "IESG Approval" policies [RFC5226] for values between 0x00 and 0xef,
with values between 0xf0 and 0xff being reserved for experimental with values between 0xf0 and 0xff being reserved for experimental
use. use.
New entries in this registry require the following information: New entries in this registry require the following information:
Frame Type: A name or label for the frame type. Frame Type: A name or label for the frame type.
Code: The 8-bit code assigned to the frame type. Code: The 8-bit code assigned to the frame type.
Specification: A reference to a specification that includes a Specification: A reference to a specification that includes a
description of the frame layout, it's semantics and flags that the description of the frame layout, its semantics, and flags that the
frame type uses, including any parts of the frame that are frame type uses, including any parts of the frame that are
conditionally present based on the value of flags. conditionally present based on the value of flags.
The entries in the following table are registered by this document. The entries in the following table are registered by this document.
+---------------+------+--------------+ +---------------+------+--------------+
| Frame Type | Code | Section | | Frame Type | Code | Section |
+---------------+------+--------------+ +---------------+------+--------------+
| DATA | 0x0 | Section 6.1 | | DATA | 0x0 | Section 6.1 |
| HEADERS | 0x1 | Section 6.2 | | HEADERS | 0x1 | Section 6.2 |
skipping to change at page 72, line 22 skipping to change at page 73, line 48
New registrations are advised to provide the following information: New registrations are advised to provide the following information:
Name: A symbolic name for the setting. Specifying a setting name is Name: A symbolic name for the setting. Specifying a setting name is
optional. optional.
Code: The 16-bit code assigned to the setting. Code: The 16-bit code assigned to the setting.
Initial Value: An initial value for the setting. Initial Value: An initial value for the setting.
Specification: A stable reference to a specification that describes Specification: An optional reference to a specification that
the use of the setting. describes the use of the setting.
An initial set of setting registrations can be found in An initial set of setting registrations can be found in
Section 6.5.2. Section 6.5.2.
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| Name | Code | Initial Value | Specification | | Name | Code | Initial Value | Specification |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 | | HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 |
| ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 | | ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 |
| MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 | | MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 |
| INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 | | INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 |
| MAX_FRAME_SIZE | 0x5 | 65536 | Section 6.5.2 | | MAX_FRAME_SIZE | 0x5 | 16384 | Section 6.5.2 |
| MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 | | MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
11.4. Error Code Registry 11.4. Error Code Registry
This document establishes a registry for HTTP/2 error codes. The This document establishes a registry for HTTP/2 error codes. The
"HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2 "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].
skipping to change at page 73, line 43 skipping to change at page 75, line 30
| CANCEL | 0x8 | Stream cancelled | Section 7 | | CANCEL | 0x8 | Stream cancelled | Section 7 |
| COMPRESSION_ERROR | 0x9 | Compression state | Section 7 | | COMPRESSION_ERROR | 0x9 | Compression state | Section 7 |
| | | not updated | | | | | not updated | |
| CONNECT_ERROR | 0xa | TCP connection error | Section 7 | | CONNECT_ERROR | 0xa | TCP connection error | Section 7 |
| | | for CONNECT method | | | | | for CONNECT method | |
| ENHANCE_YOUR_CALM | 0xb | Processing capacity | Section 7 | | ENHANCE_YOUR_CALM | 0xb | Processing capacity | Section 7 |
| | | exceeded | | | | | exceeded | |
| INADEQUATE_SECURITY | 0xc | Negotiated TLS | Section 7 | | INADEQUATE_SECURITY | 0xc | Negotiated TLS | Section 7 |
| | | parameters not | | | | | parameters not | |
| | | acceptable | | | | | acceptable | |
| HTTP_1_1_REQUIRED | 0xc | Use HTTP/1.1 for the | Section 7 |
| | | request | |
+---------------------+------+----------------------+---------------+ +---------------------+------+----------------------+---------------+
11.5. HTTP2-Settings Header Field Registration 11.5. 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
skipping to change at page 74, line 30 skipping to change at page 76, line 22
Safe No Safe No
Idempotent No Idempotent No
Specification document(s) Section 3.5 of this document Specification document(s) Section 3.5 of this document
Related information: This method is never used by an actual client. 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 This method will appear to be used when an HTTP/1.1 server or
intermediary attempts to parse an HTTP/2 connection preface. intermediary attempts to parse an HTTP/2 connection preface.
11.7. The 421 Not Authoritative HTTP Status Code 11.7. The 421 (Misdirected Request) HTTP Status Code
This document registers the 421 (Not Authoritative) HTTP Status code This document registers the 421 (Misdirected Request) HTTP Status
in the Hypertext Transfer Protocol (HTTP) Status Code Registry code in the Hypertext Transfer Protocol (HTTP) Status Code Registry
([RFC7231], Section 8.2). ([RFC7231], Section 8.2).
Status Code: 421 Status Code: 421
Short Description: Not Authoritative Short Description: Misdirected Request
Specification: Section 9.1.2 of this document Specification: Section 9.1.2 of this document
12. Acknowledgements 12. Acknowledgements
This document includes substantial input from the following This document includes substantial input from the following
individuals: individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
skipping to change at page 76, line 40 skipping to change at page 78, line 29
[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981. 793, September 1981.
[TLS-ALPN] [TLS-ALPN]
Friedl, S., Popov, A., Langley, A., and E. Stephan, Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol "Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, July 2014. Negotiation Extension", RFC 7301, July 2014.
[TLS-ECDHE] [TLS-ECDHE]
Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA- Rescorla, E., "TLS Elliptic Curve Cipher Suites with
256/384 and AES Galois Counter Mode (GCM)", RFC 5289, SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008. August 2008.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions: [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
13.2. Informative References 13.2. Informative References
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", draft-ietf-httpbis-alt-svc-01 (work Alternative Services", draft-ietf-httpbis-alt-svc-04 (work
in progress), April 2014. in progress), October 2014.
[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, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004. September 2004.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
CRIME Attack", July 2013, CRIME Attack", July 2013, <http://breachattack.com/
<http://breachattack.com/resources/ resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>. BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E., [HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E.,
O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate
Recommendation CR-html5-20140204, Febuary 2014, Recommendation CR-html5-20140731, July 2014,
<http://www.w3.org/TR/2014/CR-html5-20140204/>. <http://www.w3.org/TR/2014/CR-html5-20140731/>.
Latest version available at [5]. Latest version available at [5].
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, May 1992.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004. Compression Methods", RFC 3749, May 2004.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006. for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008. August 2008.
[RFC6585] Nottingham, N. and R. Fielding, "Additional HTTP Status [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, April 2012. Codes", RFC 6585, April 2012.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, "TCP Extensions for High Performance", RFC
7323, September 2014.
[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", 2011, Jackson, "Talking to Yourself for Fun and Profit", 2011,
<http://w2spconf.com/2011/papers/websocket.pdf>. <http://w2spconf.com/2011/papers/websocket.pdf>.
[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre, [TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", draft- "Recommendations for Secure Use of TLS and DTLS", draft-
sheffer-tls-bcp-02 (work in progress), February 2014. ietf-uta-tls-bcp-01 (work in progress), June 2014.
13.3. URIs 13.3. URIs
[1] https://www.iana.org/assignments/message-headers [1] https://www.iana.org/assignments/message-headers
[2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/ [2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/
cfUef2gL3iU cfUef2gL3iU
[3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc- [3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-
principles-01 principles-01
Appendix A. Change Log Appendix A. Change Log
This section is to be removed by RFC Editor before publication. This section is to be removed by RFC Editor before publication.
A.1. Since draft-ietf-httpbis-http2-13 A.1. Since draft-ietf-httpbis-http2-14
Renamed Not Authoritative status code to Misdirected Request.
A.2. Since draft-ietf-httpbis-http2-13
Pseudo-header fields are now required to appear strictly before Pseudo-header fields are now required to appear strictly before
regular ones. regular ones.
Restored 1xx series status codes, except 101. Restored 1xx series status codes, except 101.
Changed frame length field 24-bits. Expanded frame header to 9 Changed frame length field 24-bits. Expanded frame header to 9
octets. Added a setting to limit the damage. octets. Added a setting to limit the damage.
Added a setting to advise peers of header set size limits. Added a setting to advise peers of header set size limits.
Removed segments. Removed segments.
Made non-semantic-bearing HEADERS frames illegal in the HTTP mapping. Made non-semantic-bearing HEADERS frames illegal in the HTTP mapping.
A.2. Since draft-ietf-httpbis-http2-12 A.3. Since draft-ietf-httpbis-http2-12
Restored extensibility options. Restored extensibility options.
Restricting TLS cipher suites to AEAD only. Restricting TLS cipher suites to AEAD only.
Removing Content-Encoding requirements. Removing Content-Encoding requirements.
Permitting the use of PRIORITY after stream close. Permitting the use of PRIORITY after stream close.
Removed ALTSVC frame. Removed ALTSVC frame.
Removed BLOCKED frame. Removed BLOCKED frame.
Reducing the maximum padding size to 256 octets; removing padding Reducing the maximum padding size to 256 octets; removing padding
from CONTINUATION frames. from CONTINUATION frames.
Removed per-frame GZIP compression. Removed per-frame GZIP compression.
A.3. Since draft-ietf-httpbis-http2-11 A.4. Since draft-ietf-httpbis-http2-11
Added BLOCKED frame (at risk). Added BLOCKED frame (at risk).
Simplified priority scheme. Simplified priority scheme.
Added DATA per-frame GZIP compression. Added DATA per-frame GZIP compression.
A.4. Since draft-ietf-httpbis-http2-10 A.5. Since draft-ietf-httpbis-http2-10
Changed "connection header" to "connection preface" to avoid Changed "connection header" to "connection preface" to avoid
confusion. confusion.
Added dependency-based stream prioritization. Added dependency-based stream prioritization.
Added "h2c" identifier to distinguish between cleartext and secured Added "h2c" identifier to distinguish between cleartext and secured
HTTP/2. HTTP/2.
Adding missing padding to PUSH_PROMISE. Adding missing padding to PUSH_PROMISE.
Integrate ALTSVC frame and supporting text. Integrate ALTSVC frame and supporting text.
Dropping requirement on "deflate" Content-Encoding. Dropping requirement on "deflate" Content-Encoding.
Improving security considerations around use of compression. Improving security considerations around use of compression.
A.5. Since draft-ietf-httpbis-http2-09 A.6. Since draft-ietf-httpbis-http2-09
Adding padding for data frames. Adding padding for data frames.
Renumbering frame types, error codes, and settings. Renumbering frame types, error codes, and settings.
Adding INADEQUATE_SECURITY error code. Adding INADEQUATE_SECURITY error code.
Updating TLS usage requirements to 1.2; forbidding TLS compression. Updating TLS usage requirements to 1.2; forbidding TLS compression.
Removing extensibility for frames and settings. Removing extensibility for frames and settings.
skipping to change at page 80, line 48 skipping to change at page 82, line 5
Changing the protocol identification token to "h2". Changing the protocol identification token to "h2".
Changing the use of :authority to make it optional and to allow Changing the use of :authority to make it optional and to allow
userinfo in non-HTTP cases. userinfo in non-HTTP cases.
Allowing split on 0x0 for Cookie. Allowing split on 0x0 for Cookie.
Reserved PRI method in HTTP/1.1 to avoid possible future collisions. Reserved PRI method in HTTP/1.1 to avoid possible future collisions.
A.6. Since draft-ietf-httpbis-http2-08 A.7. 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.7. Since draft-ietf-httpbis-http2-07 A.8. Since draft-ietf-httpbis-http2-07
Marked draft for implementation. Marked draft for implementation.
A.8. Since draft-ietf-httpbis-http2-06 A.9. 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.9. Since draft-ietf-httpbis-http2-05 A.10. 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.10. Since draft-ietf-httpbis-http2-04 A.11. 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.
skipping to change at page 82, line 12 skipping to change at page 83, line 18
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.11. Since draft-ietf-httpbis-http2-03 A.12. 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.12. Since draft-ietf-httpbis-http2-02 A.13. 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.13. Since draft-ietf-httpbis-http2-01 A.14. 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 83, line 23 skipping to change at page 84, line 29
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.14. Since draft-ietf-httpbis-http2-00 A.15. 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 [6]. Changed INTERNAL_ERROR on GOAWAY to have a value of 2 [6].
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 [7]. Added flow control principles (Section 5.2.1) based on [7].
A.15. Since draft-mbelshe-httpbis-spdy-00 A.16. Since draft-mbelshe-httpbis-spdy-00
Adopted as base for draft-ietf-httpbis-http2. Adopted as base for draft-ietf-httpbis-http2.
Updated authors/editors list. Updated authors/editors list.
Added status note. Added status note.
Authors' Addresses Authors' Addresses
Mike Belshe Mike Belshe
 End of changes. 224 change blocks. 
539 lines changed or deleted 637 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/