< draft-ietf-httpbis-http2-03.txt   draft-ietf-httpbis-http2-04.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: November 30, 2013 Google, Inc Expires: January 9, 2014 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Microsoft Microsoft
A. Melnikov, Ed. A. Melnikov, Ed.
Isode Ltd Isode Ltd
May 29, 2013 July 8, 2013
Hypertext Transfer Protocol version 2.0 Hypertext Transfer Protocol version 2.0
draft-ietf-httpbis-http2-03 draft-ietf-httpbis-http2-04
Abstract Abstract
This specification describes an optimized expression of the syntax of This specification describes an optimized expression of the syntax of
the Hypertext Transfer Protocol (HTTP). The HTTP/2.0 encapsulation the Hypertext Transfer Protocol (HTTP). The HTTP/2.0 encapsulation
enables more efficient use of network resources and reduced enables more efficient use of network resources and reduced
perception of latency by allowing header field compression and perception of latency by allowing header field compression and
multiple concurrent messages on the same connection. It also multiple concurrent messages on the same connection. It also
introduces unsolicited push of representations from servers to introduces unsolicited push of representations from servers to
clients. clients.
This document is an alternative to, but does not obsolete the This document is an alternative to, but does not obsolete the
HTTP/1.1 message format or protocol. HTTP's existing semantics HTTP/1.1 message format or protocol. HTTP's existing semantics
remain unchanged. remain unchanged.
This version of the draft has been marked for implementation.
Interoperability testing will occur in the HTTP/2.0 interim in
Hamburg, DE, starting 2013-08-05.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information and related documents can be found at Working Group information and related documents can be found at
<http://tools.ietf.org/wg/httpbis/> (Wiki) and <http://tools.ietf.org/wg/httpbis/> (Wiki) and
<https://github.com/http2/http2-spec> (source code and issues <https://github.com/http2/http2-spec> (source code and issues
tracker). tracker).
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 30, 2013. This Internet-Draft will expire on January 9, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Document Organization . . . . . . . . . . . . . . . . . . 5 1.1. Document Organization . . . . . . . . . . . . . . . . . . 5
1.2. Conventions and Terminology . . . . . . . . . . . . . . . 6 1.2. Conventions and Terminology . . . . . . . . . . . . . . . 6
2. Starting HTTP/2.0 . . . . . . . . . . . . . . . . . . . . . . 6 2. HTTP/2.0 Protocol Overview . . . . . . . . . . . . . . . . . . 6
2.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 7 2.1. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Starting HTTP/2.0 for "http:" URIs . . . . . . . . . . . . 8 2.2. HTTP Multiplexing . . . . . . . . . . . . . . . . . . . . 7
2.3. Starting HTTP/2.0 for "https:" URIs . . . . . . . . . . . 8 2.3. HTTP Semantics . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 9 3. Starting HTTP/2.0 . . . . . . . . . . . . . . . . . . . . . . 7
3. HTTP/2.0 Framing Layer . . . . . . . . . . . . . . . . . . . . 9 3.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 8
3.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Starting HTTP/2.0 for "http" URIs . . . . . . . . . . . . 8
3.2. Connection Header . . . . . . . . . . . . . . . . . . . . 9 3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10
3.3. Framing . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3. Starting HTTP/2.0 for "https" URIs . . . . . . . . . . . . 10
3.3.1. Frame Header . . . . . . . . . . . . . . . . . . . . . 10 3.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10
3.3.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . 12 3.5. Connection Header . . . . . . . . . . . . . . . . . . . . 11
3.4. Streams . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.1. Stream Creation . . . . . . . . . . . . . . . . . . . 13 4.1. Frame Header . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.2. Stream priority . . . . . . . . . . . . . . . . . . . 13 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4.3. Stream half-close . . . . . . . . . . . . . . . . . . 14 4.3. Header Compression and Decompression . . . . . . . . . . . 13
3.4.4. Stream close . . . . . . . . . . . . . . . . . . . . . 14 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14
3.5. Error Handling . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 14
3.5.1. Connection Error Handling . . . . . . . . . . . . . . 15 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 18
3.5.2. Stream Error Handling . . . . . . . . . . . . . . . . 16 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 18
3.5.3. Error Codes . . . . . . . . . . . . . . . . . . . . . 16 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 18
3.6. Stream Flow Control . . . . . . . . . . . . . . . . . . . 17 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 19
3.6.1. Flow Control Principles . . . . . . . . . . . . . . . 17 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 20
3.6.2. Appropriate Use of Flow Control . . . . . . . . . . . 18 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 20
3.7. Header Blocks . . . . . . . . . . . . . . . . . . . . . . 19 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 21
3.8. Frame Types . . . . . . . . . . . . . . . . . . . . . . . 19 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 21
3.8.1. DATA Frames . . . . . . . . . . . . . . . . . . . . . 20 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 22
3.8.2. HEADERS+PRIORITY . . . . . . . . . . . . . . . . . . . 20 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 22
3.8.3. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . 21 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 22
3.8.4. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . 21 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.8.5. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . 25 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.8.6. PING . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.8.7. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . 26 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 25
3.8.8. HEADERS . . . . . . . . . . . . . . . . . . . . . . . 28 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.8.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . 29 6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 26
4. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 32 6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 27
4.1. Connection Management . . . . . . . . . . . . . . . . . . 32 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 27
4.2. HTTP Request/Response . . . . . . . . . . . . . . . . . . 33 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.1. HTTP Header Fields and HTTP/2.0 Headers . . . . . . . 33 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.2. Request . . . . . . . . . . . . . . . . . . . . . . . 33 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 31
4.2.3. Response . . . . . . . . . . . . . . . . . . . . . . . 34 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 32
4.3. Server Push Transactions . . . . . . . . . . . . . . . . . 35 6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 33
4.3.1. Server implementation . . . . . . . . . . . . . . . . 36 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 34
4.3.2. Client implementation . . . . . . . . . . . . . . . . 37 6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 34
5. Design Rationale and Notes . . . . . . . . . . . . . . . . . . 38 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.1. Separation of Framing Layer and Application Layer . . . . 38 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 36
5.2. Error handling - Framing Layer . . . . . . . . . . . . . . 39 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 36
5.3. One Connection per Domain . . . . . . . . . . . . . . . . 39 8.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 37
5.4. Fixed vs Variable Length Fields . . . . . . . . . . . . . 39 8.1.2. Request Header Fields . . . . . . . . . . . . . . . . 38
5.5. Server Push . . . . . . . . . . . . . . . . . . . . . . . 40 8.1.3. Response Header Fields . . . . . . . . . . . . . . . . 39
6. Security Considerations . . . . . . . . . . . . . . . . . . . 40 8.1.4. GZip Content-Encoding . . . . . . . . . . . . . . . . 40
6.1. Server Authority and Same-Origin . . . . . . . . . . . . . 40 8.1.5. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 40
6.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 40 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 41
6.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 41 9. Additional HTTP Requirements/Considerations . . . . . . . . . 43
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 41 9.1. Frame Size Limits for HTTP . . . . . . . . . . . . . . . . 43
7.1. Long Lived Connections . . . . . . . . . . . . . . . . . . 41 9.2. Connection Management . . . . . . . . . . . . . . . . . . 43
7.2. SETTINGS frame . . . . . . . . . . . . . . . . . . . . . . 41 10. Security Considerations . . . . . . . . . . . . . . . . . . . 43
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 43
8.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 42 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 44
8.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 43 10.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 44
8.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 43 11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 45
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44 12.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 45
10.1. Normative References . . . . . . . . . . . . . . . . . . . 44 12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 46
10.2. Informative References . . . . . . . . . . . . . . . . . . 45 12.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 47
12.4. HTTP2-Settings Header Field Registration . . . . . . . . . 47
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 48
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
14.1. Normative References . . . . . . . . . . . . . . . . . . . 48
14.2. Informative References . . . . . . . . . . . . . . . . . . 50
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 46 publication) . . . . . . . . . . . . . . . . . . . . 50
A.1. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 50
A.1. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 46 A.2. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 50
A.2. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 46 A.3. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 50
A.3. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 47 A.4. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 51
A.4. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 47 A.5. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 51
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 encapsulation ([HTTP-p1], protocol. However, the HTTP/1.1 message format ([HTTP-p1], Section
Section 3) is optimized for implementation simplicity and 3) is optimized for implementation simplicity and accessibility, not
accessibility, not application performance. As such it has several application performance. As such it has several characteristics that
characteristics that have a negative overall effect on application have a negative overall effect on application performance.
performance.
In particular, HTTP/1.0 only allows one request to be delivered at a In particular, HTTP/1.0 only allows one request to be delivered at a
time on a given connection. HTTP/1.1 pipelining only partially time on a given connection. HTTP/1.1 pipelining only partially
addressed request concurrency, and is not widely deployed. addressed request concurrency, and is not widely deployed.
Therefore, clients that need to make many requests (as is common on Therefore, clients that need to make many requests (as is common on
the Web) typically use multiple connections to a server in order to the Web) typically use multiple connections to a server in order to
reduce perceived latency. reduce perceived latency.
Furthermore, HTTP/1.1 header fields are often repetitive and verbose, Furthermore, HTTP/1.1 header fields are often repetitive and verbose,
which, in addition to generating more or larger network packets, can which, in addition to generating more or larger network packets, can
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HTTP/1.x. This means less competition with other flows, and longer- HTTP/1.x. This means less competition with other flows, and longer-
lived connections, which in turn leads to better utilization of lived connections, which in turn leads to better utilization of
available network capacity. available network capacity.
Finally, this encapsulation also enables more scalable processing of Finally, this encapsulation also enables more scalable processing of
messages through use of binary message framing. messages through use of binary message framing.
1.1. Document Organization 1.1. Document Organization
The HTTP/2.0 Specification is split into three parts: starting The HTTP/2.0 Specification is split into three parts: starting
HTTP/2.0 (Section 2), which covers how a HTTP/2.0 connection is HTTP/2.0 (Section 3), which covers how a HTTP/2.0 connection is
initiated; a framing layer (Section 3), which multiplexes a single initiated; a framing layer (Section 4), which multiplexes a single
TCP connection into independent frames of various types; and an HTTP TCP connection into independent frames of various types; and an HTTP
layer (Section 4), which specifies the mechanism for expressing HTTP layer (Section 8), which specifies the mechanism for expressing HTTP
interactions using the framing layer. While some of the framing interactions using the framing layer. While some of the framing
layer concepts are isolated from HTTP, building a generic framing layer concepts are isolated from HTTP, building a generic framing
layer has not been a goal. The framing layer is tailored to the layer has not been a goal. The framing layer is tailored to the
needs of the HTTP protocol and server push. needs of the HTTP protocol and server push.
1.2. Conventions and Terminology 1.2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
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server: The endpoint which did not initiate the HTTP connection. server: The endpoint which did not initiate the HTTP connection.
connection error: An error on the HTTP/2.0 connection. connection error: An error on the HTTP/2.0 connection.
stream: A bi-directional flow of frames across a virtual channel stream: A bi-directional flow of frames across a virtual channel
within the HTTP/2.0 connection. within the HTTP/2.0 connection.
stream error: An error on the individual HTTP/2.0 stream. stream error: An error on the individual HTTP/2.0 stream.
2. Starting HTTP/2.0 2. HTTP/2.0 Protocol Overview
HTTP/2.0 uses the same "http:" and "https:" URI schemes used by HTTP/2.0 provides an optimized transport for HTTP semantics.
HTTP/1.1. As a result, implementations processing requests for
target resource URIs like "http://example.org/foo" or An HTTP/2.0 connection is an application level protocol running on
"https://example.com/bar" are required to first discover whether the top of a TCP connection ([RFC0793]). The client is the TCP
upstream server (the immediate peer to which the client wishes to connection initiator.
establish a connection) supports HTTP/2.0.
This document describes the HTTP/2.0 protocol using a logical
structure that is formed of three parts: framing, streams, and
application mapping. This structure is provided primarily as an aid
to specification, implementations are free to diverge from this
structure as necessary.
2.1. HTTP Frames
HTTP/2.0 provides an efficient serialization of HTTP semantics. HTTP
requests and responses are encoded into length-prefixed frames (see
Section 4.1).
HTTP headers are compressed into a series of frames that contain
header block fragments (see Section 4.3).
2.2. HTTP Multiplexing
HTTP/2.0 provides the ability to multiplex multiple HTTP requests and
responses onto a single connection. Multiple requests or responses
can be sent concurrently on a connection using streams (Section 5).
In order to maintain independent streams, flow control and
prioritization are necessary.
2.3. HTTP Semantics
HTTP/2.0 defines how HTTP requests and responses are mapped to
streams (see Section 8) and introduces a new interaction model,
server push (Section 8.2).
3. Starting HTTP/2.0
HTTP/2.0 uses the same "http" and "https" URI schemes used by
HTTP/1.1. HTTP/2.0 shares the same default port numbers: 80 for
"http" URIs and 443 for "https" URIs. As a result, implementations
processing requests for target resource URIs like
"http://example.org/foo" or "https://example.com/bar" are required to
first discover whether the upstream server (the immediate peer to
which the client wishes to establish a connection) supports HTTP/2.0.
The means by which support for HTTP/2.0 is determined is different The means by which support for HTTP/2.0 is determined is different
for "http" and "https" URIs. Discovery for "https:" URIs is for "http" and "https" URIs. Discovery for "http" URIs is described
described in Section 2.3. Discovery for "http" URIs is described in Section 3.2. Discovery for "https" URIs is described in
here. Section 3.3.
2.1. HTTP/2.0 Version Identification 3.1. HTTP/2.0 Version Identification
The protocol defined in this document is identified using the string The protocol defined in this document is identified using the string
"HTTP/2.0". This identification is used in the HTTP/1.1 Upgrade "HTTP/2.0". This identification is used in the HTTP/1.1 Upgrade
header field, in the TLS application layer protocol negotiation header field, in the TLS application layer protocol negotiation
extension [TLSALPN] field and other places where protocol extension [TLSALPN] field, and other places where protocol
identification is required. identification is required.
Negotiating "HTTP/2.0" implies the use of the transport, security, Negotiating "HTTP/2.0" implies the use of the transport, security,
framing and message semantics described in this document. framing and message semantics described in this document.
[[anchor3: Editor's Note: please remove the following text prior to [[anchor6: Editor's Note: please remove the following text prior to
the publication of a final version of this document.]] the publication of a final version of this document.]]
Only implementations of the final, published RFC can identify Only implementations of the final, published RFC can identify
themselves as "HTTP/2.0". Until such an RFC exists, implementations themselves as "HTTP/2.0". Until such an RFC exists, implementations
MUST NOT identify themselves using "HTTP/2.0". MUST NOT identify themselves using "HTTP/2.0".
Examples and text throughout the rest of this document use "HTTP/2.0" Examples and text throughout the rest of this document use "HTTP/2.0"
as a matter of editorial convenience only. Implementations of draft as a matter of editorial convenience only. Implementations of draft
versions MUST NOT identify using this string. versions MUST NOT identify using this string.
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Non-compatible experiments that are based on these draft versions Non-compatible experiments that are based on these draft versions
MUST instead replace the string "draft" with a different identifier. MUST instead replace the string "draft" with a different identifier.
For example, an experimental implementation of packet mood-based For example, an experimental implementation of packet mood-based
encoding based on draft-ietf-httpbis-http2-07 might identify itself encoding based on draft-ietf-httpbis-http2-07 might identify itself
as "HTTP-emo-07/2.0". Note that any label MUST conform to the as "HTTP-emo-07/2.0". Note that any label MUST conform to the
"token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters "token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters
are encouraged to coordinate their experiments on the are encouraged to coordinate their experiments on the
ietf-http-wg@w3.org mailing list. ietf-http-wg@w3.org mailing list.
2.2. Starting HTTP/2.0 for "http:" URIs 3.2. Starting HTTP/2.0 for "http" URIs
A client that makes a request to an "http:" URI without prior A client that makes a request to an "http" URI without prior
knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism
(Section 6.7 of [HTTP-p1]). The client makes an HTTP/1.1 request (Section 6.7 of [HTTP-p1]). The client makes an HTTP/1.1 request
that includes an Upgrade header field identifying HTTP/2.0. that includes an Upgrade header field identifying HTTP/2.0. The
HTTP/1.1 request MUST include an HTTP2-Settings (Section 3.2.1)
header field.
For example: For example:
GET /default.htm HTTP/1.1 GET /default.htm HTTP/1.1
Host: server.example.com Host: server.example.com
Connection: Upgrade Connection: Upgrade, HTTP2-Settings
Upgrade: HTTP/2.0 Upgrade: HTTP/2.0
HTTP2-Settings: <base64url encoding of HTTP/2.0 SETTINGS payload>
Requests that contain a request entity body MUST be sent in their
entirety before the client can send HTTP/2.0 frames. This means that
a large request entity can block the use of the connection until it
is completely sent.
If concurrency of an initial request with subsequent requests is
important, a small request can be used to perform the upgrade to
HTTP/2.0, at the cost of an additional round trip.
A server that does not support HTTP/2.0 can respond to the request as A server that does not support HTTP/2.0 can respond to the request as
though the Upgrade header field were absent: though the Upgrade header field were absent:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-length: 243 Content-length: 243
Content-type: text/html Content-type: text/html
... ...
A server that supports HTTP/2.0 can accept the upgrade with a 101 A server that supports HTTP/2.0 accepts the upgrade with a 101
(Switching Protocols) status code. After the empty line that (Switching Protocols) status code. After the empty line that
terminates the 101 response, the server can begin sending HTTP/2.0 terminates the 101 response, the server can begin sending HTTP/2.0
frames. These frames MUST include a response to the request that frames. These frames MUST include a response to the request that
initiated the Upgrade. initiated the Upgrade.
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: Upgrade Connection: Upgrade
Upgrade: HTTP/2.0 Upgrade: HTTP/2.0
[ HTTP/2.0 connection ... [ HTTP/2.0 connection ...
The first HTTP/2.0 frame sent by the server is a SETTINGS frame The first HTTP/2.0 frame sent by the server is a SETTINGS frame
(Section 3.8.4). Upon receiving the 101 response, the client sends a (Section 6.5). Upon receiving the 101 response, the client sends a
connection header (Section 3.2), which includes a SETTINGS frame. connection header (Section 3.5), which includes a SETTINGS frame.
2.3. Starting HTTP/2.0 for "https:" URIs The HTTP/1.1 request that is sent prior to upgrade is associated with
stream 1 and is assigned the highest possible priority. Stream 1 is
implicitly half closed from the client toward the server, since the
request is completed as an HTTP/1.1 request. After commencing the
HTTP/2.0 connection, stream 1 is used for the response.
A client that makes a request to an "https:" URI without prior 3.2.1. HTTP2-Settings Header Field
A client that upgrades from HTTP/1.1 to HTTP/2.0 MUST include an
"HTTP2-Settings" header field. The "HTTP2-Settings" header field is
a hop-by-hop header field that includes settings that govern the
HTTP/2.0 connection, provided in anticipation of the server accepting
the request to upgrade. A server MUST reject an attempt to upgrade
if this header is not present.
HTTP2-Settings = token68
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,
the URL- and filename-safe Base64 encoding described in Section 5 of
[RFC4648], with any trailing '=' characters omitted). The ABNF
[RFC5234] production for "token68" is defined in Section 2.1 of
[HTTP-p7].
The client MUST include values for the following settings
(Section 6.5.1):
o SETTINGS_MAX_CONCURRENT_STREAMS
o SETTINGS_INITIAL_WINDOW_SIZE
As a hop-by-hop header field, the "Connection" header field MUST
include a value of "HTTP2-Settings" in addition to "Upgrade" when
upgrading to HTTP/2.0.
A server decodes and interprets these values as it would any other
SETTINGS frame. Providing these values in the Upgrade request
ensures that the protocol does not require default values for the
above settings, and gives a client an opportunity to provide other
settings prior to receiving any frames from the server.
3.3. Starting HTTP/2.0 for "https" URIs
A client that makes a request to an "https" URI without prior
knowledge about support for HTTP/2.0 uses TLS [RFC5246] with the knowledge about support for HTTP/2.0 uses TLS [RFC5246] with the
application layer protocol negotiation extension [TLSALPN]. application layer protocol negotiation extension [TLSALPN].
Once TLS negotiation is complete, both the client and the server send Once TLS negotiation is complete, both the client and the server send
a connection header (Section 3.2). a connection header (Section 3.5).
2.4. Starting HTTP/2.0 with Prior Knowledge 3.4. Starting HTTP/2.0 with Prior Knowledge
A client can learn that a particular server supports HTTP/2.0 by A client can learn that a particular server supports HTTP/2.0 by
other means. A client MAY immediately send HTTP/2.0 frames to a other means. A client MAY immediately send HTTP/2.0 frames to a
server that is known to support HTTP/2.0. This only affects the server that is known to support HTTP/2.0, after the connection header
resolution of "http:" URIs, servers supporting HTTP/2.0 are required (Section 3.5). This only affects the resolution of "http" URIs;
to support protocol negotiation in TLS [TLSALPN] for "https:" URIs. servers supporting HTTP/2.0 are required to support protocol
negotiation in TLS [TLSALPN] for "https" URIs.
Prior support for HTTP/2.0 is not a strong signal that a given server Prior support for HTTP/2.0 is not a strong signal that a given server
will support HTTP/2.0 for future connections. It is possible for will support HTTP/2.0 for future connections. It is possible for
server configurations to change or for configurations to differ server configurations to change or for configurations to differ
between instances in clustered server. Interception proxies (a.k.a. between instances in clustered server. Interception proxies (a.k.a.
"transparent" proxies) are another source of variability. "transparent" proxies) are another source of variability.
3. HTTP/2.0 Framing Layer 3.5. Connection Header
3.1. Connection
The HTTP/2.0 connection is an Application Level protocol running on
top of a TCP connection ([RFC0793]). The client is the TCP
connection initiator.
HTTP/2.0 connections are persistent. That is, for best performance,
it is expected a clients will not close connections until it is
determined that no further communication with a server is necessary
(for example, when a user navigates away from a particular web page),
or until the server closes the connection.
Servers are encouraged to maintain open connections for as long as
possible, but are permitted to terminate idle connections if
necessary. When either endpoint chooses to close the transport-level
TCP connection, the terminating endpoint MUST first send a GOAWAY
(Section 3.8.7) frame so that both endpoints can reliably determine
whether previously sent frames have been processed and gracefully
complete or terminate any necessary remaining tasks.
3.2. Connection Header
Upon establishment of a TCP connection and determination that Upon establishment of a TCP connection and determination that
HTTP/2.0 will be used by both peers to communicate, each endpoint HTTP/2.0 will be used by both peers, each endpoint MUST send a
MUST send a connection header as a final confirmation and to connection header as a final confirmation and to establish the
establish the default parameters for the HTTP/2.0 connection. initial settings for the HTTP/2.0 connection.
The client connection header is a sequence of 24 octets (in hex The client connection header is a sequence of 24 octets, which in hex
notation) notation are:
464f4f202a20485454502f322e300d0a0d0a42410d0a0d0a 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(the string "FOO * HTTP/2.0\r\n\r\nBA\r\n\r\n") followed by a
SETTINGS frame (Section 3.8.4). The client sends the client (the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n") followed by a
connection header immediately upon receipt of a 101 Switching SETTINGS frame (Section 6.5). The client sends the client connection
Protocols response (indicating a successful upgrade), or after header immediately upon receipt of a 101 Switching Protocols response
receiving a TLS Finished message from the server. If starting an (indicating a successful upgrade), or after receiving a TLS Finished
HTTP/2.0 connection with prior knowledge of server support for the message from the server. If starting an HTTP/2.0 connection with
protocol, the client connection header is sent upon connection prior knowledge of server support for the protocol, the client
establishment. connection header is sent upon connection establishment.
The client connection header is selected so that a large The client connection header is selected so that a large
proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do
not attempt to process further frames. Note that this does not not attempt to process further frames. Note that this does not
address the concerns raised in [TALKING]. address the concerns raised in [TALKING].
The server connection header consists of just a SETTINGS frame The server connection header consists of just a SETTINGS frame
(Section 3.8.4) that MUST be the first frame the server sends in the (Section 6.5) that MUST be the first frame the server sends in the
HTTP/2.0 connection. HTTP/2.0 connection.
To avoid unnecessary latency, clients are permitted to send To avoid unnecessary latency, clients are permitted to send
additional frames to the server immediately after sending the client additional frames to the server immediately after sending the client
connection header, without waiting to receive the server connection connection header, without waiting to receive the server connection
header. It is important to note, however, that the server connection header. It is important to note, however, that the server connection
header SETTINGS frame might include parameters that necessarily alter header SETTINGS frame might include parameters that necessarily alter
how a client is expected to communicate with the server. Upon how a client is expected to communicate with the server. Upon
receiving the SETTINGS frame, the client is expected to honor any receiving the SETTINGS frame, the client is expected to honor any
parameters established. parameters established.
Clients and servers MUST terminate the TCP connection if either peer Clients and servers MUST terminate the TCP connection if either peer
does not begin with a valid connection header. A GOAWAY frame does not begin with a valid connection header. A GOAWAY frame
(Section 3.8.7) MAY be omitted if it is clear that the peer is not (Section 6.8) MAY be omitted if it is clear that the peer is not
using HTTP/2.0. using HTTP/2.0.
3.3. Framing 4. HTTP Frames
Once the HTTP/2.0 connection is established, clients and servers can Once the HTTP/2.0 connection is established, endpoints can begin
begin exchanging frames. exchanging frames.
3.3.1. Frame Header 4.1. Frame Header
HTTP/2.0 frames share a common base format consisting of an 8-byte All frames begin with an 8-octet header followed by a payload of
header followed by 0 to 65535 bytes of data. between 0 and 65,535 octets.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (16) | Type (8) | Flags (8) | | Length (16) | Type (8) | Flags (8) |
+-+-------------+---------------+-------------------------------+ +-+-------------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Frame Data (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Header Frame Header
The fields of the frame header are defined as: The fields of the frame header are defined as:
Length: The length of the frame data expressed as an unsigned 16-bit Length: The length of the frame payload expressed as an unsigned 16-
integer. The 8 bytes of the frame header are not included in this bit integer. The 8 octets of the frame header are not included in
value. this value.
Type: The 8-bit type of the frame. The frame type determines how Type: The 8-bit type of the frame. The frame type determines how
the remainder of the frame header and data are interpreted. the remainder of the frame header and payload are interpreted.
Implementations MUST ignore unsupported and unrecognized frame Implementations MUST ignore unsupported and unrecognized frame
types. types.
Flags: An 8-bit field reserved for frame-type specific boolean Flags: An 8-bit field reserved for frame-type specific boolean
flags. flags.
The least significant bit (0x1) - the FINAL bit - is defined for Flags are assigned semantics specific to the indicated frame type.
all frame types as an indication that this frame is the last the Flags that have no defined semantics for a particular frame type
endpoint will send for the identified stream. Setting this flag MUST be ignored, and MUST be left unset (0) when sending.
causes the stream to enter the half-closed state (Section 3.4.3).
Implementations MUST process the FINAL bit for all frames whose
stream identifier field is not 0x0. The FINAL bit MUST NOT be set
on frames that use a stream identifier of 0.
The remaining flags can be assigned semantics specific to the
indicated frame type. Flags that have no defined semantics for a
particular frame type MUST be ignored, and MUST be left unset (0)
when sending.
R: A reserved 1-bit field. The semantics of this bit are undefined R: A reserved 1-bit field. The semantics of this bit are undefined
and the bit MUST remain unset (0) when sending and MUST be ignored and the bit MUST remain unset (0) when sending and MUST be ignored
when receiving. when receiving.
Stream Identifier: A 31-bit stream identifier (see Section 3.4.1). Stream Identifier: A 31-bit stream identifier (see Section 5.1.1).
A value 0 is reserved for frames that are associated with the A value 0 is reserved for frames that are associated with the
connection as a whole as opposed to an individual stream. connection as a whole as opposed to an individual stream.
The structure and content of the remaining frame data is dependent The structure and content of the frame payload is dependent entirely
entirely on the frame type. on the frame type.
3.3.2. Frame Size 4.2. Frame Size
Implementations with limited resources might not be capable of The maximum size of a frame payload varies by frame type and use.
processing large frame sizes. Such implementations MAY choose to The absolute maximum size is 65,535 octets. All implementations
place additional limits on the maximum frame size. However, all SHOULD be capable of receiving and minimally processing frames up to
implementations MUST be capable of receiving and processing frames this size.
containing at least 8192 octets of data. [[anchor6: Ed. Question:
Does this minimum include the 8-byte header or just the frame data?]]
An implementation MUST terminate a stream immediately if it is unable Certain frame types, such as PING (see Section 6.7), impose
to process a frame due it's size. This is done by sending an additional limits on the amount of payload data allowed. Likewise,
RST_STREAM frame (Section 3.8.3) containing the FRAME_TOO_LARGE error additional size limits can be set by specific application uses (see
code. Section 9).
[[anchor7: <https://github.com/http2/http2-spec/issues/28>: Need a If a frame size exceeds any defined limit, or is too small to contain
way to signal the maximum frame size; no way to RST_STREAM on non- mandatory frame data, the endpoint MUST send a FRAME_TOO_LARGE error.
stream-related frames.]] Frame size errors in frames that affect connection-level state MUST
be treated as a connection error (Section 5.4.1).
3.4. Streams 4.3. Header Compression and Decompression
A "stream" is an independent, bi-directional sequence of frames A header in HTTP/2.0 is a name-value pair with one or more associated
exchanged between the client and server within an HTTP/2.0 values. They are used within HTTP request and response messages as
connection. Streams have several important characteristics: well as server push operations (see Section 8.2).
o Streams can be established and used unilaterally or shared by Header sets are logical collections of zero or more header fields
either the client or server. arranged at the application layer. When transmitted over a
connection, the header set is serialized into a header block using
HTTP Header Compression [COMPRESSION]. The serialized header block
is then divided into one or more octet sequences, called header block
fragments, and transmitted within the payload of HEADERS
(Section 6.2) or PUSH_PROMISE (Section 6.6) frames. The receiving
endpoint reassembles the header block by concatenating the individual
fragments, then decompresses the block to reconstruct the header set.
o Streams can be rejected or cancelled by either endpoint. Header block fragments can only be sent as the payload of HEADERS or
PUSH_PROMISE frames.
o Multiple types of frames can be sent by either endpoint within a A compressed and encoded header block is transmitted in one or more
single stream. HEADERS or PUSH_PROMISE frames. If the number of octets in the block
is greater than the space remaining in the frame, the block is
divided into multiple fragments, which are then transmitted in
multiple frames.
o The order in which frames are sent within a stream is significant. Header blocks MUST be transmitted as a contiguous sequence of frames,
Recipients are required to process frames in the order they are with no interleaved frames of any other type, or from any other
received. stream. The last frame in a sequence of HEADERS frames MUST have the
END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE
frames MUST have the END_PUSH_PROMISE flag set.
o Streams optionally carry a set of name-value header pairs that are HEADERS and PUSH_PROMISE frames carry data that can modify the
expressed within the headers block of HEADERS+PRIORITY, HEADERS, compression context maintained by a receiver. An endpoint receiving
or PUSH_PROMISE frames. HEADERS or PUSH_PROMISE frames MUST reassemble header blocks and
perform decompression even if the frames are to be discarded, which
is likely to occur after a stream is reset. A receiver MUST
terminate the connection with a connection error (Section 5.4.1) of
type COMPRESSION_ERROR, if it does not decompress a header block.
5. Streams and Multiplexing
A "stream" is an independent, bi-directional sequence of HEADER and
DATA frames exchanged between the client and server within an
HTTP/2.0 connection. Streams have several important characteristics:
o A single HTTP/2.0 connection can contain multiple concurrently o A single HTTP/2.0 connection can contain multiple concurrently
active streams, with either endpoint interleaving frames from active streams, with either endpoint interleaving frames from
multiple streams. multiple streams.
3.4.1. Stream Creation o Streams can be established and used unilaterally or shared by
either the client or server.
There is no coordination or shared action between the client and
server required to create a stream. Rather, new streams are
established by sending a frame whose stream identifier field
references a previously unused stream identifier.
All streams are identified by an unsigned 31-bit integer. Streams
initiated by a client use odd numbered stream identifiers; those
initiated by the server use even numbered stream identifiers. A
stream identifier of zero MUST NOT be used to establish a new stream.
The identifier of a newly established stream MUST be numerically
greater than all previously established streams from that endpoint
within the HTTP/2.0 connection, unless the identifier has been
reserved using a PUSH_PROMISE (Section 3.8.5) frame. An endpoint
that receives an unexpected stream identifier MUST respond with a
connection error (Section 3.5.1) of type PROTOCOL_ERROR.
A peer can limit the total number of concurrently active streams
using the SETTINGS_MAX_CONCURRENT_STREAMS parameters within a
SETTINGS frame. The maximum concurrent streams setting is specific
to each endpoint and applies only to the peer. That is, clients
specify the maximum number of concurrent streams the server can
initiate, and servers specify the maximum number of concurrent
streams the client can initiate. Peer endpoints MUST NOT exceed this
limit. All concurrently active streams initiated by an endpoint,
including streams that are half-open (Section 3.4.3) in any
direction, count toward that endpoint's limit.
Stream identifiers cannot be reused within a connection. Long-lived
connections can cause an endpoint to exhaust the available range of
stream identifiers. A client that is unable to establish a new
stream identifier can establish a new connection for new streams.
Either endpoint can request the early termination of an unwanted
stream by sending an RST_STREAM frame (Section 3.5.2) with an error
code of either REFUSED_STREAM (if no frames have been processed) or
CANCEL (if at least one frame has been processed). Such termination
might not take effect immediately as the peer might have sent
additional frames on the stream prior to receiving the termination
request.
3.4.2. Stream priority
The endpoint establishing a new stream can assign a priority for the o Streams can be closed by either endpoint.
stream. Priority is represented as an unsigned 31-bit integer. 0
represents the highest priority and 2^31-1 represents the lowest
priority.
The purpose of this value is to allow the initiating endpoint to o The order in which frames are sent within a stream is significant.
request that frames for the stream be processed with higher priority Recipients process frames in the order they are received.
relative to any other concurrently active streams. That is, if an
endpoint receives interleaved frames for multiple streams, the
endpoint ought to make a best-effort attempt at processing frames for
higher priority streams before processing those for lower priority
streams.
Explicitly setting the priority for a stream does not guarantee any o Streams are identified by an integer. Stream identifiers are
particular processing order for the stream relative to any other assigned to streams by the endpoint that initiates a stream.
stream. Nor is there is any mechanism provided by which the
initiator of a stream can force or require a receiving endpoint to
process frames from one stream before processing frames from another.
3.4.3. Stream half-close 5.1. Stream States
When an endpoint sends a frame for a stream with the FINAL flag set, The lifecycle of a stream is shown in Figure 1.
the stream is considered to be half-closed for that endpoint.
Subsequent frames MUST NOT be sent by that endpoint for the half
closed stream for the remaining duration of the HTTP/2.0 connection.
When both endpoints have sent frames with the FINAL flag set, the
stream is considered to be fully closed.
If an endpoint receives additional frames for a stream that was +--------+
previously half-closed by the sending peer, the recipient MUST PP | | PP
respond with a stream error (Section 3.5.2) of type STREAM_CLOSED. ,--------| idle |--------.
/ | | \
v +--------+ v
+----------+ | +----------+
| | | H | |
,---| reserved | | | reserved |---.
| | (local) | v | (remote) | |
| +----------+ +--------+ +----------+ |
| | ES | | ES | |
| | H ,-------| open |-------. | H |
| | / | | \ | |
| v v +--------+ v v |
| +----------+ | +----------+ |
| | half | | | half | |
| | closed | | R | closed | |
| | (remote) | | | (local) | |
| +----------+ | +----------+ |
| | v | |
| | ES / R +--------+ ES / R | |
| `----------->| |<-----------' |
| R | closed | R |
`-------------------->| |<--------------------'
+--------+
An endpoint that has not yet half-closed a stream by sending the Figure 1: Stream States
FINAL flag can continue sending frames on the stream.
It is not necessary for an endpoint to half-close a stream for which Both endpoints have a subjective view of the state of a stream that
it has not sent any frames. This allows endpoints to use fully could be different when frames are in transit. Endpoints do not
unidirectional streams that do not require explicit action or coordinate the creation of streams, they are created unilaterally by
acknowledgement from the receiver. either endpoint. The negative consequences of a mismatch in states
are limited to the "closed" state after sending RST_STREAM, where
frames might be received for some time after closing.
3.4.4. Stream close Streams have the following states:
Streams can be terminated in the following ways: idle:
All streams start in the "idle" state. In this state, no frames
have been exchanged.
Normal termination: Normal stream termination occurs when both The following transitions are valid from this state:
client and server have half-closed the stream by sending a frame
containing a FINAL flag (Section 3.3.1).
Half-close on unidirectional stream: A stream that only has frames * Sending or receiving a HEADERS frame causes the stream to
sent in one direction can be tentatively considered to be closed become "open". The stream identifier is selected as described
once a frame containing a FINAL flag is sent. The active sender in Section 5.1.1.
on the stream MUST be prepared to receive frames after closing the
stream.
Abrupt termination: Either peer can send a RST_STREAM control frame * Sending a PUSH_PROMISE frame marks the associated stream for
at any time to terminate an active stream. RST_STREAM contains an later use. The stream state for the reserved stream
error code to indicate the reason for termination. A RST_STREAM transitions to "reserved (local)".
indicates that the sender will transmit no further data on the
stream and that the receiver is advised to cease transmission on
it.
The sender of a RST_STREAM frame MUST allow for frames that have * Receiving a PUSH_PROMISE frame marks the associated stream as
already been sent by the peer prior to the RST_STREAM being reserved by the remote peer. The state of the stream becomes
processed. If in-transit frames alter connection state, these "reserved (remote)".
frames cannot be safely discarded. See Stream Error Handling
(Section 3.5.2) for more details.
TCP connection teardown: If the TCP connection is torn down while reserved (local):
un-closed streams exist, then the endpoint MUST assume that the A stream in the "reserved (local)" state is one that has been
stream was abnormally interrupted and may be incomplete. promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame
reserves an idle stream by associating the stream with an open
stream that was initiated by the remote peer (see Section 8.2).
3.5. Error Handling In this state, only the following transitions are possible:
HTTP/2.0 framing permits two classes of error: * The endpoint can send a HEADERS frame. This causes the stream
to open in a "half closed (remote)" state.
o An error condition that renders the entire connection unusable is * Either endpoint can send a RST_STREAM frame to cause the stream
a connection error. to become "closed". This releases the stream reservation.
o An error in an individual stream is a stream error. An endpoint MUST NOT send any other type of frame in this state.
3.5.1. Connection Error Handling reserved (remote):
A stream in the "reserved (remote)" state has been reserved by a
remote peer.
A connection error is any error which prevents further processing of In this state, only the following transitions are possible:
the framing layer or which corrupts any connection state.
An endpoint that encounters a connection error MUST first send a * Receiving a HEADERS frame causes the stream to transition to
GOAWAY (Section 3.8.7) frame with the stream identifier of the last "half closed (local)".
stream that it successfully received from its peer. The GOAWAY frame
includes an error code that indicates why the connection is
terminating. After sending the GOAWAY frame, the endpoint MUST close
the TCP connection.
It is possible that the GOAWAY will not be reliably received by the * Either endpoint can send a RST_STREAM frame to cause the stream
receiving endpoint. In the event of a connection error, GOAWAY only to become "closed". This releases the stream reservation.
provides a best-effort attempt to communicate with the peer about why
the connection is being terminated.
An endpoint can end a connection at any time. In particular, an Receiving any other type of frame MUST be treated as a stream
endpoint MAY choose to treat a stream error as a connection error if error (Section 5.4.2) of type PROTOCOL_ERROR.
the error is recurrent. Endpoints SHOULD send a GOAWAY frame when
ending a connection, as long as circumstances permit it.
3.5.2. Stream Error Handling open:
The "open" state is where both peers can send frames. In this
state, sending peers observe advertised stream level flow control
limits (Section 5.2).
A stream error is an error related to a specific stream identifier From this state either endpoint can send a frame with a END_STREAM
that does not affect processing of other streams at the framing flag set, which causes the stream to transition into one of the
layer. "half closed" states: an endpoint sending a END_STREAM flag causes
the stream state to become "half closed (local)"; an endpoint
receiving a END_STREAM flag causes the stream state to become
"half closed (remote)".
An endpoint that detects a stream error sends a RST_STREAM Either endpoint can send a RST_STREAM frame from this state,
(Section 3.8.3) frame that contains the stream identifier of the causing it to transition immediately to "closed".
stream where the error occurred. The RST_STREAM frame includes an
error code that indicates the type of error.
A RST_STREAM is the last frame that an endpoint can send on a stream. half closed (local):
The peer that sends the RST_STREAM frame MUST be prepared to receive A stream that is "half closed (local)" cannot be used for sending
any frames that were sent or enqueued for sending by the remote peer. frames.
These frames can be ignored, except where they modify connection
state (such as the state maintained for header compression
(Section 3.7)).
Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame A stream transitions from this state to "closed" when a frame that
for any stream. However, an endpoint MAY send additional RST_STREAM contains a END_STREAM flag is received, or when either peer sends
frames if it receives frames on a closed stream after more than a a RST_STREAM frame.
round trip time. This behavior is permitted to deal with misbehaving
implementations.
An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM half closed (remote):
frame, to avoid looping. A stream that is "half closed (remote)" is no longer being used by
the peer to send frames. In this state, an endpoint is no longer
obligated to maintain a receiver flow control window if it
performs flow control.
3.5.3. Error Codes If an endpoint receives additional frames for a stream that is in
this state it MUST respond with a stream error (Section 5.4.2) of
type STREAM_CLOSED.
Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY A stream can transition from this state to "closed" by sending a
frames to convey the reasons for the stream or connection error. frame that contains a END_STREAM flag, or when either peer sends a
RST_STREAM frame.
Error codes share a common code space. Some error codes only apply closed:
to specific conditions and have no defined semantics in certain frame The "closed" state is the terminal state.
types.
The following error codes are defined: An endpoint MUST NOT send frames on a closed stream. An endpoint
that receives a frame after receiving a RST_STREAM or a frame
containing a END_STREAM flag on that stream MUST treat that as a
stream error (Section 5.4.2) of type STREAM_CLOSED.
NO_ERROR (0): The associated condition is not as a result of an If this state is reached as a result of sending a RST_STREAM
error. For example, a GOAWAY might include this code to indicate frame, the peer that receives the RST_STREAM might have already
graceful shutdown of a connection. sent - or enqueued for sending - frames on the stream that cannot
be withdrawn. An endpoint that sends a RST_STREAM frame MUST
ignore frames that it receives on closed streams after it has sent
a RST_STREAM frame. An endpoint MAY choose to limit the period
over which it ignores frames and treat frames that arrive after
this time as being in error.
PROTOCOL_ERROR (1): The endpoint detected an unspecific protocol An endpoint might receive a PUSH_PROMISE frame after it sends
error. This error is for use when a more specific error code is RST_STREAM. PUSH_PROMISE causes a stream to become "reserved".
not available. If promised streams are not desired, a RST_STREAM can be used to
close any of those streams.
INTERNAL_ERROR (2): The endpoint encountered an unexpected internal 5.1.1. Stream Identifiers
error.
FLOW_CONTROL_ERROR (3): The endpoint detected that its peer violated Streams are identified with an unsigned 31-bit integer. Streams
the flow control protocol. initiated by a client MUST use odd-numbered stream identifiers; those
initiated by the server MUST use even-numbered stream identifiers. A
stream identifier of zero (0x0) is used for connection control
message; the stream identifier zero MUST NOT be used to establish a
new stream.
INVALID_STREAM (4): The endpoint received a frame for an inactive The identifier of a newly established stream MUST be numerically
stream. greater than all streams that the initiating endpoint has opened or
reserved. This governs streams that are opened using a HEADERS frame
and streams that are reserved using PUSH_PROMISE. An endpoint that
receives an unexpected stream identifier MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR.
STREAM_CLOSED (5): The endpoint received a frame after a stream was Stream identifiers cannot be reused. Long-lived connections can
half-closed. result in endpoint exhausting the available range of stream
identifiers. A client that is unable to establish a new stream
identifier can establish a new connection for new streams.
FRAME_TOO_LARGE (6): The endpoint received a frame that was larger 5.1.2. Stream Concurrency
than the maximum size that it supports.
REFUSED_STREAM (7): The endpoint is refusing the stream before A peer can limit the number of concurrently active streams using the
processing its payload. SETTINGS_MAX_CONCURRENT_STREAMS parameters within a SETTINGS frame.
The maximum concurrent streams setting is specific to each endpoint
and applies only to the peer that receives the setting. That is,
clients specify the maximum number of concurrent streams the server
can initiate, and servers specify the maximum number of concurrent
streams the client can initiate. Endpoints MUST NOT exceed the limit
set by their peer.
CANCEL (8): Used by the creator of a stream to indicate that the Streams that are in the "open" state, or either of the "half closed"
stream is no longer needed. states count toward the maximum number of streams that an endpoint is
permitted to open. Streams in any of these three states count toward
the limit advertised in the SETTINGS_MAX_CONCURRENT_STREAMS setting
(see Section 6.5.2).
COMPRESSION_ERROR (9): The endpoint is unable to maintain the Streams in either of the "reserved" states do not count as open, even
compression context for the connection. if a small amount of application state is retained to ensure that the
promised stream can be successfully used.
3.6. Stream Flow Control 5.2. Flow Control
Using streams for multiplexing introduces contention over use of the Using streams for multiplexing introduces contention over use of the
TCP connection, resulting in blocked streams. A flow control scheme TCP connection, resulting in blocked streams. A flow control scheme
ensures that streams on the same connection do not destructively ensures that streams on the same connection do not destructively
interfere with each other. interfere with each other. Flow control is used for both individual
streams and for the connection as a whole.
HTTP/2.0 provides for flow control through use of the WINDOW_UPDATE HTTP/2.0 provides for flow control through use of the WINDOW_UPDATE
(Section 3.8.9) frame type. (Section 6.9) frame type.
3.6.1. Flow Control Principles 5.2.1. Flow Control Principles
Experience with TCP congestion control has shown that algorithms can Experience with TCP congestion control has shown that algorithms can
evolve over time to become more sophisticated without requiring evolve over time to become more sophisticated without requiring
protocol changes. TCP congestion control and its evolution is protocol changes. TCP congestion control and its evolution is
clearly different from HTTP/2.0 flow control, though the evolution of clearly different from HTTP/2.0 flow control, though the evolution of
TCP congestion control algorithms shows that a similar approach could TCP congestion control algorithms shows that a similar approach could
be feasible for HTTP/2.0 flow control. be feasible for HTTP/2.0 flow control.
HTTP/2.0 stream flow control aims to allow for future improvements to HTTP/2.0 stream flow control aims to allow for future improvements to
flow control algorithms without requiring protocol changes. Flow flow control algorithms without requiring protocol changes. Flow
control in HTTP/2.0 has the following characteristics: control in HTTP/2.0 has the following characteristics:
1. Flow control is hop-by-hop, not end-to-end. 1. Flow control is hop-by-hop, not end-to-end.
2. Flow control is based on window update frames. Receivers 2. Flow control is based on window update frames. Receivers
advertise how many octets they are prepared to receive on a advertise how many bytes they are prepared to receive on a stream
stream. This is a credit-based scheme. and for the entire connection. This is a credit-based scheme.
3. Flow control is directional with overall control provided by the 3. Flow control is directional with overall control provided by the
receiver. A receiver MAY choose to set any window size that it receiver. A receiver MAY choose to set any window size that it
desires for each stream and for the entire connection. A sender desires for each stream and for the entire connection. A sender
MUST respect flow control limits imposed by a receiver. Clients, MUST respect flow control limits imposed by a receiver. Clients,
servers and intermediaries all independently advertise their flow servers and intermediaries all independently advertise their flow
control preferences as a receiver and abide by the flow control control preferences as a receiver and abide by the flow control
limits set by their peer when sending. limits set by their peer when sending.
4. The initial value for the flow control window is 65536 bytes for 4. The initial value for the flow control window is 65536 bytes for
both new streams and the overall connection. both new streams and the overall connection.
5. The frame type determines whether flow control applies to a 5. The frame type determines whether flow control applies to a
frame. Of the frames specified in this document, only data frame. Of the frames specified in this document, only DATA
frames are subject to flow control; all other frame types do not frames are subject to flow control; all other frame types do not
consume space in the advertised flow control window. This consume space in the advertised flow control window. This
ensures that important control frames are not blocked by flow ensures that important control frames are not blocked by flow
control. control.
6. Flow control can be disabled by a receiver. A receiver can 6. Flow control can be disabled by a receiver. A receiver can
choose to either disable flow control for a stream or connection choose to either disable flow control for a stream or connection
by declaring an infinite flow control limit. by sending a window update frame with a specific flag. See
Ending Flow Control (Section 6.9.4) for more details.
7. HTTP/2.0 standardizes only the format of the window update frame 7. HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame
(Section 3.8.9). This does not stipulate how a receiver decides (Section 6.9). This does not stipulate how a receiver decides
when to send this frame or the value that it sends. Nor does it when to send this frame or the value that it sends. Nor does it
specify how a sender chooses to send packets. Implementations specify how a sender chooses to send packets. Implementations
are able to select any algorithm that suits their needs. are able to select any algorithm that suits their needs.
Implementations are also responsible for managing how requests and Implementations are also responsible for managing how requests and
responses are sent based on priority; choosing how to avoid head of responses are sent based on priority; choosing how to avoid head of
line blocking for requests; and managing the creation of new streams. line blocking for requests; and managing the creation of new streams.
Algorithm choices for these could interact with any flow control Algorithm choices for these could interact with any flow control
algorithm. algorithm.
3.6.2. Appropriate Use of Flow Control 5.2.2. Appropriate Use of Flow Control
Flow control is defined to protect endpoints (client, server or Flow control is defined to protect endpoints that are operating under
intermediary) that are operating under resource constraints. For resource constraints. For example, a proxy needs to share memory
example, a proxy needs to share memory between many connections, and between many connections, and also might have a slow upstream
also might have a slow upstream connection and a fast downstream one. connection and a fast downstream one. Flow control addresses cases
Flow control addresses cases where the receiver is unable process where the receiver is unable process data on one stream, yet wants to
data on one stream, yet wants to continue to process other streams in continue to process other streams in the same connection.
the same connection.
Deployments that do not require this capability SHOULD disable flow Deployments that do not require this capability SHOULD disable flow
control for data that is being received. Note that flow control control for data that is being received. Note that flow control
cannot be disabled for sending. Sending data is always subject to cannot be disabled for sending. Sending data is always subject to
the flow control window advertised by the receiver. the flow control window advertised by the receiver.
Deployments with constrained resources (for example, memory) MAY Deployments with constrained resources (for example, memory) MAY
employ flow control to limit the amount of memory a peer can consume. employ flow control to limit the amount of memory a peer can consume.
Note, however, that this can lead to suboptimal use of available Note, however, that this can lead to suboptimal use of available
network resources if flow control is enabled without knowledge of the network resources if flow control is enabled without knowledge of the
bandwidth-delay product (see [RFC1323]). bandwidth-delay product (see [RFC1323]).
Even with full awareness of the current bandwidth-delay product, Even with full awareness of the current bandwidth-delay product,
implementation of flow control is difficult. However, it can ensure implementation of flow control is difficult. However, it can ensure
that constrained resources are protected without any reduction in that constrained resources are protected without any reduction in
connection utilization. connection utilization.
3.7. Header Blocks 5.3. Stream priority
The header block is found in the HEADERS, HEADERS+PRIORITY and The endpoint establishing a new stream can assign a priority for the
PUSH_PROMISE frames. The header block consists of a set of header stream. Priority is represented as an unsigned 31-bit integer. 0
fields, which are name-value pairs. Headers are compressed using represents the highest priority and 2^31-1 represents the lowest
black magic. priority.
Compression of header fields is a work in progress, as is the format The purpose of this value is to allow the initiating endpoint to
of this block. request that frames for the stream be processed with a specified
priority relative to other concurrently active streams. That is, if
an endpoint receives interleaved frames for multiple streams, the
endpoint ought to make a best-effort attempt at processing frames for
higher priority streams before processing those for lower priority
streams.
The contents of header blocks MUST be processed by the compression Explicitly setting the priority for a stream does not guarantee any
context, even if stream has been reset or the frame is discarded. If particular processing order for the stream relative to any other
header blocks cannot be processed, the receiver MUST treat the stream. Nor is there any mechanism provided by which the initiator
connection with a connection error (Section 3.5.1) of type of a stream can force or require a receiving endpoint to process
COMPRESSION_ERROR. frames from one stream before processing frames from another.
3.8. Frame Types Unless explicitly specified in the HEADERS frame (Section 6.2) during
stream creation, the default stream priority is 2^30. Pushed streams
(Section 8.2) are assumed to inherit the priority of the associated
stream plus one (or 2^31-1 if the the associated stream priority is
2^31-1), i.e. they have priority one lower than the associated
stream.
5.4. Error Handling
HTTP/2.0 framing permits two classes of error:
o An error condition that renders the entire connection unusable is
a connection error.
o An error in an individual stream is a stream error.
A list of error codes is included in Section 7.
5.4.1. Connection Error Handling
A connection error is any error which prevents further processing of
the framing layer or which corrupts any connection state.
An endpoint that encounters a connection error SHOULD first send a
GOAWAY (Section 6.8) frame with the stream identifier of the last
stream that it successfully received from its peer. The GOAWAY frame
includes an error code that indicates why the connection is
terminating. After sending the GOAWAY frame, the endpoint MUST close
the TCP connection.
It is possible that the GOAWAY will not be reliably received by the
receiving endpoint. In the event of a connection error, GOAWAY only
provides a best-effort attempt to communicate with the peer about why
the connection is being terminated.
An endpoint can end a connection at any time. In particular, an
endpoint MAY choose to treat a stream error as a connection error if
the error is recurrent. Endpoints SHOULD send a GOAWAY frame when
ending a connection, as long as circumstances permit it.
5.4.2. Stream Error Handling
A stream error is an error related to a specific stream identifier
that does not affect processing of other streams.
An endpoint that detects a stream error sends a RST_STREAM
(Section 6.4) frame that contains the stream identifier of the stream
where the error occurred. The RST_STREAM frame includes an error
code that indicates the type of error.
A RST_STREAM is the last frame that an endpoint can send on a stream.
The peer that sends the RST_STREAM frame MUST be prepared to receive
any frames that were sent or enqueued for sending by the remote peer.
These frames can be ignored, except where they modify connection
state (such as the state maintained for header compression
(Section 4.3)).
Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame
for any stream. However, an endpoint MAY send additional RST_STREAM
frames if it receives frames on a closed stream after more than a
round trip time. This behavior is permitted to deal with misbehaving
implementations.
An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM
frame, to avoid looping.
5.4.3. Connection Termination
If the TCP connection is torn down while streams remain in open or
half closed states, then the endpoint MUST assume that the stream was
abnormally interrupted and could be incomplete.
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
connection state, successful communication within the connection will connection state, successful communication within the connection will
no longer be possible. Therefore, it is important that endpoints no longer be possible. Therefore, it is important that endpoints
have a shared comprehension of how the state is affected by the use have a shared comprehension of how the state is affected by the use
any given frame. Accordingly, while it is expected that new frame any given frame. Accordingly, while it is expected that new frame
types will be introduced by extensions to this protocol, only frames types will be introduced by extensions to this protocol, only frames
defined by this document are permitted to alter the connection state. defined by this document are permitted to alter the connection state.
3.8.1. DATA Frames 6.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of DATA frames (type=0x0) convey arbitrary, variable-length sequences of
octets associated with a stream. One or more DATA frames are used, octets associated with a stream. One or more DATA frames are used,
for instance, to carry HTTP request or response payloads. for instance, to carry HTTP request or response payloads.
The DATA frame does not define any type-specific flags. The DATA frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that this frame is the
last that the endpoint will send for the identified stream.
Setting this flag causes the stream to enter a "half closed" state
(Section 5.1).
RESERVED (0x2): Bit 2 is reserved for future use.
DATA frames MUST be associated with a stream. If a DATA frame is DATA frames MUST be associated with a stream. If a DATA frame is
received whose stream identifier field is 0x0, the recipient MUST received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 3.5.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
3.8.2. HEADERS+PRIORITY 6.2. HEADERS
The HEADERS+PRIORITY frame (type=0x1) allows the sender to set header The HEADERS frame (type=0x1) carries name-value pairs. The HEADERS
fields and stream priority at the same time. is used to open a stream (Section 5.1). Any number of HEADERS frames
can be sent on an existing stream at any time.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Priority (31) | |X| Priority (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Header Block (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
HEADERS+PRIORITY Frame Payload HEADERS Frame Payload
The HEADERS+PRIORITY frame is identical to the HEADERS frame The HEADERS frame defines the following flags:
(Section 3.8.8), preceded by a single reserved bit and a 31-bit
priority; see Section 3.4.2.
HEADERS+PRIORITY uses the same flags as the HEADERS frame, except END_STREAM (0x1): Bit 1 being set indicates that this frame is the
that a HEADERS+PRIORITY frame with a CONTINUES bit MUST be followed last that the endpoint will send for the identified stream.
by another HEADERS+PRIORITY frame. See HEADERS frame (Section 3.8.8) Setting this flag causes the stream to enter a "half closed" state
for any flags. (Section 5.1).
HEADERS+PRIORITY frames MUST be associated with a stream. If a RESERVED (0x2): Bit 2 is reserved for future use.
HEADERS+PRIORITY frame is received whose stream identifier field is
0x0, the recipient MUST respond with a connection error
(Section 3.5.1) of type PROTOCOL_ERROR.
The HEADERS+PRIORITY frame modifies the connection state as defined END_HEADERS (0x4): The END_HEADERS bit indicates that this frame
in Section 3.7. ends the sequence of header block fragments necessary to provide a
complete set of headers.
3.8.3. RST_STREAM The payload for a complete header block is provided by a sequence
of HEADERS frames, terminated by a HEADERS frame with the
END_HEADERS flag set. Once the sequence terminates, the payload
of all HEADERS frames are concatenated and interpreted as a single
block.
A HEADERS frame without the END_HEADERS flag set MUST be followed
by a HEADERS frame for the same stream. A receiver MUST treat the
receipt of any other type of frame or a frame on a different
stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
PRIORITY (0x8): Bit 4 being set indicates that the first four octets
of this frame contain a single reserved bit and a 31-bit priority;
see Section 5.3. If this bit is not set, the four bytes do not
appear and the frame only contains a header block fragment.
The payload of a HEADERS frame contains a header block fragment
(Section 4.3).
HEADERS frames MUST be associated with a stream. If a HEADERS frame
is received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
The HEADERS frame changes the connection state as defined in
Section 4.3.
6.3. PRIORITY
The PRIORITY frame (type=0x2) specifies the sender-advised priority
of a stream. It can be sent at any time for an existing stream.
This enables reprioritisation of existing streams.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Priority (31) |
+-+-------------------------------------------------------------+
PRIORITY Frame Payload
The payload of a PRIORITY frame contains a single reserved bit and a
31-bit priority.
The PRIORITY frame does not define any flags.
The PRIORITY frame is associated with an existing stream. If a
PRIORITY frame is received with a stream identifier of 0x0, the
recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR.
6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for abnormal termination of a The RST_STREAM frame (type=0x3) allows for abnormal termination of a
stream. When sent by the initiator of a stream, it indicates that stream. When sent by the initiator of a stream, it indicates that
they wish to cancel the stream. When sent by the receiver of a they wish to cancel the stream or that an error condition has
stream, it indicates that either the receiver is rejecting the occurred. When sent by the receiver of a stream, it indicates that
stream, requesting that the stream be cancelled or that an error either the receiver is rejecting the stream, requesting that the
condition has occurred. 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 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 3.5.3). The error code indicates identifying the error code (Section 7). The error code indicates why
why the stream is being terminated. the stream is being terminated.
No type-flags are defined. 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. However, after sending the RST_STREAM, the sending endpoint
MUST be prepared to receive and process additional frames sent on the MUST be prepared to receive and process additional frames sent on the
stream that might have been sent by the peer prior to the arrival of stream that might have been sent by the peer prior to the arrival of
the RST_STREAM. the RST_STREAM.
RST_STREAM frames MUST be associated with a stream. If a RST_STREAM RST_STREAM frames MUST be associated with a stream. If a RST_STREAM
frame is received whose stream identifier field is 0x0 the recipient frame is received whose stream identifier field is 0x0 the recipient
MUST respond with a connection error (Section 3.5.1) of type MUST respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
3.8.4. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that The SETTINGS frame (type=0x4) conveys configuration parameters that
affect how endpoints communicate. The parameters are either affect how endpoints communicate. The parameters are either
constraints on peer behavior or preferences. constraints on peer behavior or preferences.
SETTINGS frames MUST be sent at the start of a connection, and MAY be SETTINGS frames MUST be sent at the start of a connection, and MAY be
sent at any other time by either endpoint over the lifetime of the sent at any other time by either endpoint over the lifetime of the
connection. connection.
Implementations MUST support all of the settings defined by this Implementations MUST support all of the settings defined by this
specification and MAY support additional settings defined by specification and MAY support additional settings defined by
extensions. Unsupported or unrecognized settings MUST be ignored. extensions. Unsupported or unrecognized settings MUST be ignored.
New settings MUST NOT be defined or implemented in a way that New settings MUST NOT be defined or implemented in a way that
requires endpoints to understand then in order to communicate requires endpoints to understand them in order to communicate
successfully. successfully.
A SETTINGS frame is not required to include every defined setting; A SETTINGS frame is not required to include every defined setting;
senders can include only those parameters for which it has accurate senders can include only those parameters for which it has accurate
values and a need to convey. When multiple parameters are sent, they values and a need to convey. When multiple parameters are sent, they
SHOULD be sent in order of numerically lowest ID to highest ID. A SHOULD be sent in order of numerically lowest ID to highest ID. A
single SETTINGS frame MUST NOT contain multiple values for the same single SETTINGS frame MUST NOT contain multiple values for the same
ID. If the receiver of a SETTINGS frame discovers multiple values ID. If the receiver of a SETTINGS frame discovers multiple values
for the same ID, it MUST ignore all values for that ID except the for the same ID, it MUST ignore all values for that ID except the
first one. first one.
Over the lifetime of a connection, an endpoint MAY send multiple Over the lifetime of a connection, an endpoint MAY send multiple
SETTINGS frames containing previously unspecified parameters or new SETTINGS frames containing previously unspecified parameters or new
values for parameters whose values have already been established. values for parameters whose values have already been established.
Only the most recent value provided setting value applies. Only the most recent provided setting value applies.
The SETTINGS frame defines the following flag:
CLEAR_PERSISTED (0x2): Bit 2 being set indicates a request to clear The SETTINGS frame does not define any flags.
any previously persisted settings before processing the settings.
Clients MUST NOT set this flag.
SETTINGS frames always apply to a connection, never a single stream. SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a settings frame MUST be zero. If an The stream identifier for a settings frame MUST be zero. If an
endpoint receives a SETTINGS frame whose stream identifier field is endpoint receives a SETTINGS frame whose stream identifier field is
anything other than 0x0, the endpoint MUST respond with a connection anything other than 0x0, the endpoint MUST respond with a connection
error (Section 3.5.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
3.8.4.1. Setting Format The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error
(Section 5.4.1).
6.5.1. Setting Format
The payload of a SETTINGS frame consists of zero or more settings. The payload of a SETTINGS frame consists of zero or more settings.
Each setting consists of an 8-bit flags field specifying per-item Each setting consists of an 8-bit reserved field, an unsigned 24-bit
instructions, an unsigned 24-bit setting identifier, and an unsigned setting identifier, and an unsigned 32-bit value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SettingFlags(8)| Setting Identifier (24) | | Reserved (8) | Setting Identifier (24) |
+---------------+-----------------------------------------------+ +---------------+-----------------------------------------------+
| Value (32) | | Value (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Setting Format
Two flags are defined for the 8-bit flags field:
PERSIST_VALUE (0x1): Bit 1 (the least significant bit) being set
indicates a request from the server to the client to persist this
setting. A client MUST NOT set this flag.
PERSISTED (0x2): Bit 2 being set indicates that this setting is a
persisted setting being returned by the client to the server.
This also indicates that this setting is not a client setting, but
a value previously set by the server. A server MUST NOT set this
flag.
3.8.4.2. Setting Persistence
[[anchor12: Note that persistence of settings is under discussion in
the WG and might be removed in a future version of this document.]]
A server endpoint can request that configuration parameters sent to a
client in a SETTINGS frame are to be persisted by the client across
HTTP/2.0 connections and returned to the server in any new SETTINGS
frame the client sends to the server in the current connection or any
future connections.
Persistence is requested on a per-setting basis by setting the
PERSIST_VALUE flag (0x1).
Client endpoints are not permitted to make such requests. Servers Setting Format
MUST ignore any attempt by clients to request that a server persist
configuration parameters.
Persistence of configuration parameters is done on a per-origin basis
(see [RFC6454]). That is, when a client establishes a connection
with a server, and the server requests that the client maintain
persistent settings, the client SHOULD return the persisted settings
on all future connections to the same origin, IP address and TCP
port.
Whenever the client sends a SETTINGS frame in the current connection,
or establishes a new connection with the same origin, persisted
configuration parameters are sent with the PERSISTED flag (0x2) set
for each persisted parameter.
Persisted settings accumulate until the server requests that all
previously persisted settings are to be cleared by setting the
CLEAR_PERSISTED (0x2) flag on the SETTINGS frame.
For example, if the server sends IDs 1, 2, and 3 with the
FLAG_SETTINGS_PERSIST_VALUE in a first SETTINGS frame, and then sends
IDs 4 and 5 with the FLAG_SETTINGS_PERSIST_VALUE in a subsequent
SETTINGS frame, the client will return values for all 5 settings (1,
2, 3, 4, and 5 in this example) to the server.
3.8.4.3. Defined Settings 6.5.2. Defined Settings
The following settings are defined: The following settings are defined:
SETTINGS_UPLOAD_BANDWIDTH (1): indicates the sender's estimated
upload bandwidth for this connection. The value is an the
integral number of kilobytes per second that the sender predicts
as an expected maximum upload channel capacity.
SETTINGS_DOWNLOAD_BANDWIDTH (2): indicates the sender's estimated
download bandwidth for this connection. The value is an integral
number of kilobytes per second that the sender predicts as an
expected maximum download channel capacity.
SETTINGS_ROUND_TRIP_TIME (3): indicates the sender's estimated
round-trip-time for this connection. The round trip time is
defined as the minimum amount of time to send a control frame from
this client to the remote and receive a response. The value is
represented in milliseconds.
SETTINGS_MAX_CONCURRENT_STREAMS (4): indicates the maximum number of SETTINGS_MAX_CONCURRENT_STREAMS (4): indicates the maximum number of
concurrent streams that the sender will allow. This limit is concurrent streams that the sender will allow. This limit is
directional: it applies to the number of streams that the sender directional: it applies to the number of streams that the sender
permits the receiver to create. By default there is no limit. It permits the receiver to create. By default there is no limit. It
is recommended that this value be no smaller than 100, so as to is recommended that this value be no smaller than 100, so as to
not unnecessarily limit parallelism. not unnecessarily limit parallelism.
SETTINGS_CURRENT_CWND (5): indicates the sender's current TCP CWND
value.
SETTINGS_DOWNLOAD_RETRANS_RATE (6): indicates the sender's
retransmission rate (bytes retransmitted / total bytes
transmitted).
SETTINGS_INITIAL_WINDOW_SIZE (7): indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (7): indicates the sender's initial
stream window size (in bytes) for new streams. window size (in bytes) for stream level flow control.
This settings affects the window size of all streams, including
existing streams, see Section 6.9.2.
SETTINGS_FLOW_CONTROL_OPTIONS (10): indicates that streams directed SETTINGS_FLOW_CONTROL_OPTIONS (10): indicates that streams directed
to the sender will not be subject to flow control. The least to the sender will not be subject to flow control. The least
significant bit (0x1) is set to indicate that new streams are not significant bit (0x1) of the value is set to indicate that new
flow controlled. All other bits are reserved. streams are not flow controlled. All other bits are reserved.
This setting applies to all streams, including existing streams. This setting applies to all streams, including existing streams.
These bits cannot be cleared once set, see Section 3.8.9.4. These bits cannot be cleared once set, see Section 6.9.4.
3.8.5. PUSH_PROMISE 6.6. PUSH_PROMISE
The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint
in advance of streams the sender intends to initiate. The in advance of streams the sender intends to initiate. The
PUSH_PROMISE frame includes the unsigned 31-bit identifier of the PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
stream the endpoint plans to create along with a minimal set of stream the endpoint plans to create along with a minimal set of
headers that provide additional context for the stream. Section 4.3 headers that provide additional context for the stream. Section 8.2
contains a thorough description of the use of PUSH_PROMISE frames. contains a thorough description of the use of PUSH_PROMISE frames.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Promised-Stream-ID (31) | |X| Promised-Stream-ID (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Header Block (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PUSH_PROMISE Payload Format PUSH_PROMISE Payload Format
The payload of a PUSH_PROMISE includes a "Promised-Stream-ID". This The payload of a PUSH_PROMISE includes a "Promised-Stream-ID". This
unsigned 31-bit integer identifies the stream the endpoint intends to unsigned 31-bit integer identifies the stream the endpoint intends to
start sending frames for. The promised stream identifier MUST be a start sending frames for. The promised stream identifier MUST be a
valid choice for the next stream sent by the sender (see new stream valid choice for the next stream sent by the sender (see new stream
identifier (Section 3.4.1)). identifier (Section 5.1.1)).
PUSH_PROMISE frames MUST be associated with an existing stream. If Following the "Promised-Stream-ID" is a header block fragment
the stream identifier field specifies the value 0x0, a recipient MUST (Section 4.3).
respond with a connection error (Section 3.5.1) of type
PROTOCOL_ERROR.
The state of promised streams is bound to the state of the original PUSH_PROMISE frames MUST be associated with an existing, peer-
associated stream on which the PUSH_PROMISE frame were sent. If the initiated stream. If the stream identifier field specifies the value
originating stream state changes to fully closed, all associated 0x0, a recipient MUST respond with a connection error (Section 5.4.1)
promised streams fully close as well. [[anchor13: Ed. Note: We need of type PROTOCOL_ERROR.
clarification on this point. How synchronized are the lifecycles of
streams and associated promised streams?]]
PUSH_PROMISE uses the same flags as the HEADERS frame, except that a The PUSH_PROMISE frame defines the following flags:
PUSH_PROMISE frame with a CONTINUES bit MUST be followed by another
PUSH_PROMISE frame. See HEADERS frame (Section 3.8.8) for any flags. END_PUSH_PROMISE (0x1): The END_PUSH_PROMISE bit indicates that this
frame ends the sequence of header block fragments necessary to
provide a complete set of headers.
The payload for a complete header block is provided by a sequence
of PUSH_PROMISE frames, terminated by a PUSH_PROMISE frame with
the END_PUSH_PROMISE flag set. Once the sequence terminates, the
payload of all PUSH_PROMISE frames are concatenated and
interpreted as a single block.
A PUSH_PROMISE frame without the END_PUSH_PROMISE flag set MUST be
followed by a PUSH_PROMISE frame for the same stream. A receiver
MUST treat the receipt of any other type of frame or a frame on a
different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
Promised streams are not required to be used in order promised. The Promised streams are not required to be used in order promised. The
PUSH_PROMISE only reserves stream identifiers for later use. PUSH_PROMISE only reserves stream identifiers for later use.
Recipients of PUSH_PROMISE frames can choose to reject promised Recipients of PUSH_PROMISE frames can choose to reject promised
streams by returning a RST_STREAM referencing the promised stream streams by returning a RST_STREAM referencing the promised stream
identifier back to the sender of the PUSH_PROMISE. identifier back to the sender of the PUSH_PROMISE.
The PUSH_PROMISE frame modifies the connection state as defined in The PUSH_PROMISE frame modifies the connection state as defined in
Section 3.7. Section 4.3.
3.8.6. 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.
PING frames consist of an arbitrary, variable-length sequence of 0 1 2 3
octets. Receivers of a PING send a response PING frame with the PONG 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
flag set and precisely the same sequence of octets back to the sender +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
as soon as possible. | |
| Opaque Data (64) |
| |
+---------------------------------------------------------------+
Processing of PING frames SHOULD be performed with the highest PING Payload Format
priority if there are additional frames waiting to be processed.
The PING frame defines one type-specific flag: 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
use those bytes in any fashion.
PONG (0x2): Bit 2 being set indicates that this PING frame is a PING Receivers of a PING frame that does not include a PONG flag MUST send
a PING frame with the PONG flag set in response, with an identical
payload. PING responses SHOULD given higher priority than any other
frame.
The PING frame defines the following flags:
PONG (0x1): Bit 1 being set indicates that this PING frame is a PING
response. An endpoint MUST set this flag in PING responses. An response. An endpoint MUST set this flag in PING responses. An
endpoint MUST NOT respond to PING frames containing this flag. endpoint MUST NOT respond to PING frames containing this flag.
PING frames are not associated with any individual stream. If a PING PING frames are not associated with any individual stream. If a PING
frame is received with a stream identifier field value other than frame is received with a stream identifier field value other than
0x0, the recipient MUST respond with a connection error 0x0, the recipient MUST respond with a connection error
(Section 3.5.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
3.8.7. GOAWAY 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
PROTOCOL_ERROR.
6.8. GOAWAY
The GOAWAY frame (type=0x7) informs the remote peer to stop creating The GOAWAY frame (type=0x7) informs the remote peer to stop creating
streams on this connection. It can be sent from the client or the streams on this connection. It can be sent from the client or the
server. Once sent, the sender will ignore frames sent on new streams server. Once sent, the sender will ignore frames sent on new streams
for the remainder of the connection. Receivers of a GOAWAY frame for the remainder of the connection. Receivers of a GOAWAY frame
MUST NOT open additional streams on the connection, although a new MUST NOT open additional streams on the connection, although a new
connection can be established for new streams. The purpose of this connection can be established for new streams. The purpose of this
frame is to allow an endpoint to gracefully stop accepting new frame is to allow an endpoint to gracefully stop accepting new
streams (perhaps for a reboot or maintenance), while still finishing streams (perhaps for a reboot or maintenance), while still finishing
processing of previously established streams. processing of previously established streams.
skipping to change at page 27, line 11 skipping to change at page 30, line 22
There is an inherent race condition between an endpoint starting new There is an inherent race condition between an endpoint starting new
streams and the remote sending a GOAWAY frame. To deal with this streams and the remote sending a GOAWAY frame. To deal with this
case, the GOAWAY contains the stream identifier of the last stream case, the GOAWAY contains the stream identifier of the last stream
which was processed on the sending endpoint in this connection. If which was processed on the sending endpoint in this connection. If
the receiver of the GOAWAY used streams that are newer than the the receiver of the GOAWAY used streams that are newer than the
indicated stream identifier, they were not processed by the sender indicated stream identifier, they were not processed by the sender
and the receiver may treat the streams as though they had never been and the receiver may treat the streams as though they had never been
created at all (hence the receiver may want to re-create the streams created at all (hence the receiver may want to re-create the streams
later on a new connection). later on a new connection).
Endpoints should always send a GOAWAY frame before closing a Endpoints SHOULD always send a GOAWAY frame before closing a
connection so that the remote can know whether a stream has been connection so that the remote can know whether a stream has been
partially processed or not. (For example, if an HTTP client sends a partially processed or not. For example, if an HTTP client sends a
POST at the same time that a server closes a connection, the client POST at the same time that a server closes a connection, the client
cannot know if the server started to process that POST request if the cannot know if the server started to process that POST request if the
server does not send a GOAWAY frame to indicate where it stopped server does not send a GOAWAY frame to indicate where it stopped
working). working. An endpoint might choose to close a connection without
sending GOAWAY for misbehaving peers.
After sending a GOAWAY frame, the sender can ignore frames for new
streams.
[[anchor14: Issue: connection state that is established by those After sending a GOAWAY frame, the sender can discard frames for new
"ignored" frames cannot be ignored without the state in the two peers streams. However, any frames that alter connection state cannot be
becoming unsynchronized.]] completely ignored. For instance, HEADERS and PUSH_PROMISE frames
MUST be minimally processed to ensure a consistent compression state
(see Section 4.3).
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Last-Stream-ID (31) | |X| Last-Stream-ID (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Additional Debug Data (*) |
+---------------------------------------------------------------+
GOAWAY Payload Format GOAWAY Payload Format
The GOAWAY frame does not define any type-specific flags. The GOAWAY frame does not define any flags.
The GOAWAY frame applies to the connection, not a specific stream. The GOAWAY frame applies to the connection, not a specific stream.
The stream identifier MUST be zero. The stream identifier MUST be zero.
The last stream identifier in the GOAWAY frame contains the highest The last stream identifier in the GOAWAY frame contains the highest
numbered stream identifier for which the sender of the GOAWAY frame numbered stream identifier for which the sender of the GOAWAY frame
has received frames on and might have taken some action on. All has received frames on and might have taken some action on. All
streams up to and including the identified stream might have been streams up to and including the identified stream might have been
processed in some way. The last stream identifier is set to 0 if no processed in some way. The last stream identifier is set to 0 if no
streams were processed. streams were processed.
Note: In this case, "processed" means that some data from the Note: In this case, "processed" means that some data from the
skipping to change at page 28, line 5 skipping to change at page 31, line 18
numbered stream identifier for which the sender of the GOAWAY frame numbered stream identifier for which the sender of the GOAWAY frame
has received frames on and might have taken some action on. All has received frames on and might have taken some action on. All
streams up to and including the identified stream might have been streams up to and including the identified stream might have been
processed in some way. The last stream identifier is set to 0 if no processed in some way. The last stream identifier is set to 0 if no
streams were processed. streams were processed.
Note: In this case, "processed" means that some data from the Note: In this case, "processed" means that some data from the
stream was passed to some higher layer of software that might have stream was passed to some higher layer of software that might have
taken some action as a result. taken some action as a result.
On streams with lower or equal numbered identifiers that do not close On streams with lower or equal numbered identifiers that were not
completely prior to the connection being closed, re-attempting closed completely prior to the connection being closed, re-attempting
requests, transactions, or any protocol activity is not possible requests, transactions, or any protocol activity is not possible
(with the exception of idempotent actions like HTTP GET, PUT, or (with the exception of idempotent actions like HTTP GET, PUT, or
DELETE). Any protocol activity that uses higher numbered streams can DELETE). Any protocol activity that uses higher numbered streams can
be safely retried using a new connection. be safely retried using a new connection.
Activity on streams numbered lower or equal to the last stream Activity on streams numbered lower or equal to the last stream
identifier might still complete successfully. The sender of a GOAWAY identifier might still complete successfully. The sender of a GOAWAY
frame gracefully shut down a connection by sending a GOAWAY frame, frame might gracefully shut down a connection by sending a GOAWAY
maintaining the connection in an open state until all in-progress frame, maintaining the connection in an open state until all in-
streams complete. progress streams complete.
The last stream ID MUST be 0 if no streams were acted upon. The last stream ID MUST be 0 if no streams were acted upon.
The GOAWAY frame also contains a 32-bit error code (Section 3.5.3) The GOAWAY frame also contains a 32-bit error code (Section 7) that
that contains the reason for closing the connection. contains the reason for closing the connection.
3.8.8. HEADERS
The HEADERS frame (type=0x8) provides header fields for a stream.
Any number of HEADERS frames can may be sent on an existing stream at
any time.
Additional type-specific flags for the HEADERS frame are:
CONTINUES (0x2): The CONTINUES bit indicates that this frame does
not contain the entire payload necessary to provide a complete set
of headers.
The payload for a complete set of headers is provided by a
sequence of HEADERS frames, terminated by a HEADERS frame without
the CONTINUES bit. Once the sequence terminates, the payload of
all HEADERS frames are concatenated and interpreted as a single
block.
A HEADERS frame that includes a CONTINUES bit MUST be followed by
a HEADERS frame for the same stream. A receiver MUST treat the
receipt of any other type of frame or a frame on a different
stream as a connection error (Section 3.5.1) of type
PROTOCOL_ERROR.
The payload of a HEADERS frame contains a Headers Block
(Section 3.7).
The HEADERS frame is associated with an existing stream. If a
HEADERS frame is received with a stream identifier of 0x0, the
recipient MUST respond with a stream error (Section 3.5.2) of type
PROTOCOL_ERROR.
The HEADERS frame changes the connection state as defined in Endpoints MAY append opaque data to the payload of any GOAWAY frame.
Section 3.7. Additional debug data is intended for diagnostic purposes only and
carries no semantic value. Debug data MUST NOT be persistently
stored, since it could contain sensitive information.
3.8.9. WINDOW_UPDATE 6.9. WINDOW_UPDATE
The WINDOW_UPDATE frame (type=0x9) is used to implement flow control. The WINDOW_UPDATE frame (type=0x9) is used to implement flow control.
Flow control operates at two levels: on each individual stream and on Flow control operates at two levels: on each individual stream and on
the entire connection. the entire connection.
Both types of flow control are hop by hop; that is, only between the Both types of flow control are hop by hop; that is, only between the
two endpoints. Intermediaries do not forward WINDOW_UPDATE frames two endpoints. Intermediaries do not forward WINDOW_UPDATE frames
between dependent connections. However, throttling of data transfer between dependent connections. However, throttling of data transfer
by any receiver can indirectly cause the propagation of flow control by any receiver can indirectly cause the propagation of flow control
information toward the original sender. information toward the original sender.
Flow control only applies to frames that are identified as being Flow control only applies to frames that are identified as being
subject to flow control. Of the frame types defined in this subject to flow control. Of the frame types defined in this
document, this includes only DATA frame. Frames that are exempt from document, this includes only DATA frame. Frames that are exempt from
flow control MUST be accepted and processed, unless the receiver is flow control MUST be accepted and processed, unless the receiver is
unable to assign resources to handling the frame. A receiver MAY unable to assign resources to handling the frame. A receiver MAY
respond with a stream error (Section 3.5.2) or connection error respond with a stream error (Section 5.4.2) or connection error
(Section 3.5.1) of type FLOW_CONTROL_ERROR if it is unable accept a (Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable accept a
frame. frame.
The following additional flags are defined for the WINDOW_UPDATE 0 1 2 3
frame: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Window Size Increment (31) |
+-+-------------------------------------------------------------+
END_FLOW_CONTROL (0x2): Bit 2 being set indicates that flow control WINDOW_UPDATE Payload Format
The payload of a WINDOW_UPDATE frame is one reserved bit, plus an
unsigned 31-bit integer indicating the number of bytes that the
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
2^31 - 1 (0x7fffffff) bytes.
The WINDOW_UPDATE frame defines the following flags:
END_FLOW_CONTROL (0x1): Bit 1 being set indicates that flow control
for the identified stream or connection has been ended; subsequent for the identified stream or connection has been ended; subsequent
frames do not need to be flow controlled. frames do not need to be flow controlled.
The WINDOW_UPDATE frame can be specific to a stream or to the entire The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
The payload of a WINDOW_UPDATE frame is a 32-bit value indicating the 6.9.1. The Flow Control Window
additional number of bytes that the sender can transmit in addition
to the existing flow control window. The legal range for this field
is 1 to 2^31 - 1 (0x7fffffff) bytes; the most significant bit of this
value is reserved.
3.8.9.1. The Flow Control Window
Flow control in HTTP/2.0 is implemented using a window kept by each Flow control in HTTP/2.0 is implemented using a window kept by each
sender on every stream. The flow control window is a simple integer sender on every stream. The flow control window is a simple integer
value that indicates how many bytes of data the sender is permitted value that indicates how many bytes of data the sender is permitted
to transmit; as such, its size is a measure of the buffering to transmit; as such, its size is a measure of the buffering
capability of the receiver. capability of the receiver.
Two flow control windows are applicable; the stream flow control Two flow control windows are applicable; the stream flow control
window and the connection flow control window. The sender MUST NOT window and the connection flow control window. The sender MUST NOT
send a flow controlled frame with a length that exceeds the space send a flow controlled frame with a length that exceeds the space
available in either of the flow control windows advertised by the available in either of the flow control windows advertised by the
receiver. Frames with zero length with the FINAL flag set (for receiver. Frames with zero length with the END_STREAM flag set (for
example, an empty data frame) MAY be sent if there is no available example, an empty data frame) MAY be sent if there is no available
space in either flow control window. space in either flow control window.
For flow control calculations, the 8 byte frame header is not For flow control calculations, the 8 byte frame header is not
counted. counted.
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
skipping to change at page 30, line 47 skipping to change at page 33, line 32
control window to exceed this maximum it MUST terminate either the control window to exceed this maximum it MUST terminate either the
stream or the connection, as appropriate. For streams, the sender stream or the connection, as appropriate. For streams, the sender
sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code; sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code;
for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code.
Flow controlled frames from the sender and WINDOW_UPDATE frames from Flow controlled frames from the sender and WINDOW_UPDATE frames from
the receiver are completely asynchronous with respect to each other. the receiver are completely asynchronous with respect to each other.
This property allows a receiver to aggressively update the window This property allows a receiver to aggressively update the window
size kept by the sender to prevent streams from stalling. size kept by the sender to prevent streams from stalling.
3.8.9.2. Initial Flow Control Window Size 6.9.2. Initial Flow Control Window Size
When a HTTP/2.0 connection is first established, new streams are When a HTTP/2.0 connection is first established, new streams are
created with an initial flow control window size of 65535 bytes. The created with an initial flow control window size of 65535 bytes. The
connection flow control window is 65536 bytes. Both endpoints can connection flow control window is 65535 bytes. Both endpoints can
adjust the initial window size for new streams by including a value adjust the initial window size for new streams by including a value
for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that forms for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that forms
part of the connection header. part of the connection header.
Prior to receiving a SETTINGS frame that sets a value for Prior to receiving a SETTINGS frame that sets a value for
SETTINGS_INITIAL_WINDOW_SIZE, a client can only use the default SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default
initial window size when sending flow controlled frames. Similarly, initial window size when sending flow controlled frames. Similarly,
the connection flow control window is set to the default initial the connection flow control window is set to the default initial
window size until a WINDOW_UPDATE frame is received. window size until a WINDOW_UPDATE frame is received.
A SETTINGS frame can alter the initial flow control window size for A SETTINGS frame can alter the initial flow control window size for
all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE
changes, a receiver MUST adjust the size of all flow control windows changes, a receiver MUST adjust the size of all stream flow control
that it maintains by the difference between the new value and the old windows that it maintains by the difference between the new value and
value. the old value. A SETTINGS frame cannot alter the connection flow
control window.
A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available
space in a flow control window to become negative. A sender MUST space in a flow control window to become negative. A sender MUST
track the negative flow control window, and MUST NOT send new flow track the negative flow control window, and MUST NOT send new flow
controlled frames until it receives WINDOW_UPDATE frames that cause controlled frames until it receives WINDOW_UPDATE frames that cause
the flow control window to become positive. the flow control window to become positive.
For example, if the server sets the initial window size to be 16KB, For example, if the client sends 64KB immediately on connection
and the client sends 64KB immediately on connection establishment, establishment, and the server sets the initial window size to be
the client will recalculate the available flow control window to be 16KB, the client will recalculate the available flow control window
-48KB on receipt of the SETTINGS frame. The client retains a to be -48KB on receipt of the SETTINGS frame. The client retains a
negative flow control window until WINDOW_UPDATE frames restore the negative flow control window until WINDOW_UPDATE frames restore the
window to being positive, after which the client can resume sending. window to being positive, after which the client can resume sending.
3.8.9.3. Reducing the Stream Window Size 6.9.3. Reducing the Stream Window Size
A receiver that wishes to use a smaller flow control window than the A receiver that wishes to use a smaller flow control window than the
current size can send a new SETTINGS frame. However, the receiver current size can send a new SETTINGS frame. However, the receiver
MUST be prepared to receive data that exceeds this window size, since MUST be prepared to receive data that exceeds this window size, since
the sender might send data that exceeds the lower limit prior to the sender might send data that exceeds the lower limit prior to
processing the SETTINGS frame. processing the SETTINGS frame.
A receiver has two options for handling streams that exceed flow A receiver has two options for handling streams that exceed flow
control limits: control limits:
skipping to change at page 32, line 6 skipping to change at page 34, line 41
FLOW_CONTROL_ERROR error code for the affected streams. FLOW_CONTROL_ERROR error code for the affected streams.
2. The receiver can accept the streams and tolerate the resulting 2. The receiver can accept the streams and tolerate the resulting
head of line blocking, sending WINDOW_UPDATE frames as it head of line blocking, sending WINDOW_UPDATE frames as it
consumes data. consumes data.
If a receiver decides to accept streams, both sides MUST recompute If a receiver decides to accept streams, both sides MUST recompute
the available flow control window based on the initial window size the available flow control window based on the initial window size
sent in the SETTINGS. sent in the SETTINGS.
3.8.9.4. Ending Flow Control 6.9.4. Ending Flow Control
After a receiver reads in a frame that marks the end of a stream (for After a receiver reads in a frame that marks the end of a stream (for
example, a data stream with a FINAL flag set), it MUST cease example, a data stream with a END_STREAM flag set), it MUST cease
transmission of WINDOW_UPDATE frames for that stream. A sender is transmission of WINDOW_UPDATE frames for that stream. A sender is
not obligated to maintain the available flow control window for not obligated to maintain the available flow control window for
streams that it is no longer sending on. streams that it is no longer sending on.
Flow control can be disabled for all streams or the connection using Flow control can be disabled for all streams on the connection using
the SETTINGS_FLOW_CONTROL_OPTIONS setting. An implementation that the SETTINGS_FLOW_CONTROL_OPTIONS setting. An implementation that
does not wish to perform flow control can use this in the initial does not wish to perform stream flow control can use this in the
SETTINGS exchange. initial SETTINGS exchange.
Flow control can be disabled for an individual stream or the overall Flow control can be disabled for an individual stream or the overall
connection by sending a WINDOW_UPDATE with the END_FLOW_CONTROL flag connection by sending a WINDOW_UPDATE with the END_FLOW_CONTROL flag
set. The payload of a WINDOW_UPDATE frame that has the set. The payload of a WINDOW_UPDATE frame that has the
END_FLOW_CONTROL flag set is ignored. END_FLOW_CONTROL flag set is ignored.
Flow control cannot be enabled again once disabled. Any attempt to Flow control cannot be enabled again once disabled. Any attempt to
re-enable flow control - by sending a WINDOW_UPDATE or by clearing re-enable flow control - by sending a WINDOW_UPDATE or by clearing
the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
rejected with a FLOW_CONTROL_ERROR error code. rejected with a FLOW_CONTROL_ERROR error code.
4. HTTP Message Exchanges 7. Error Codes
Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
frames to convey the reasons for the stream or connection error.
Error codes share a common code space. Some error codes only apply
to specific conditions and have no defined semantics in certain frame
types.
The following error codes are defined:
NO_ERROR (0): The associated condition is not as a result of an
error. For example, a GOAWAY might include this code to indicate
graceful shutdown of a connection.
PROTOCOL_ERROR (1): The endpoint detected an unspecific protocol
error. This error is for use when a more specific error code is
not available.
INTERNAL_ERROR (2): The endpoint encountered an unexpected internal
error.
FLOW_CONTROL_ERROR (3): The endpoint detected that its peer violated
the flow control protocol.
STREAM_CLOSED (5): The endpoint received a frame after a stream was
half closed.
FRAME_TOO_LARGE (6): The endpoint received a frame that was larger
than the maximum size that it supports.
REFUSED_STREAM (7): The endpoint refuses the stream prior to
performing any application processing, see Section 8.1.5 for
details.
CANCEL (8): Used by the endpoint to indicate that the stream is no
longer needed.
COMPRESSION_ERROR (9): The endpoint is unable to maintain the
compression context for the connection.
8. HTTP Message Exchanges
HTTP/2.0 is intended to be as compatible as possible with current HTTP/2.0 is intended to be as compatible as possible with current
web-based applications. This means that, from the perspective of the web-based applications. This means that, from the perspective of the
server business logic or application API, the features of HTTP are server business logic or application API, the features of HTTP are
unchanged. To achieve this, all of the application request and unchanged. To achieve this, all of the application request and
response header semantics are preserved, although the syntax of response header semantics are preserved, although the syntax of
conveying those semantics has changed. Thus, the rules from HTTP/1.1 conveying those semantics has changed. Thus, the rules from HTTP/1.1
([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and ([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and
[HTTP-p7]) apply with the changes in the sections below. [HTTP-p7]) apply with the changes in the sections below.
4.1. Connection Management 8.1. HTTP Request/Response Exchange
Clients SHOULD NOT open more than one HTTP/2.0 connection to a given A client sends an HTTP request on a new stream, using a previously
origin ([RFC6454]) concurrently. unused stream identifier (Section 5.1.1). A server sends an HTTP
response on the same stream as the request.
Note that it is possible for one HTTP/2.0 connection to be finishing An HTTP request or response each consist of:
(e.g. a GOAWAY frame has been sent, but not all streams have
finished), while another HTTP/2.0 connection is starting.
4.2. HTTP Request/Response o one contiguous sequence of HEADERS frames;
4.2.1. HTTP Header Fields and HTTP/2.0 Headers o zero or more DATA frames; and
At the application level, HTTP uses name-value pairs in its header o optionally, a contiguous sequence of HEADERS frames
fields. Because HTTP/2.0 merges the existing HTTP header fields with
HTTP/2.0 headers, there is a possibility that some HTTP applications
already use a particular header field name. To avoid any conflicts,
all header fields introduced for layering HTTP over HTTP/2.0 are
prefixed with ":". ":" is not a valid sequence in HTTP/1.* header
field naming, preventing any possible conflict.
4.2.2. Request The last frame in the sequence bears an END_STREAM flag.
The client initiates a request by sending a HEADERS+PRIORITY frame. Other frames, including HEADERS, MAY be interspersed with these
Requests that do not contain a body MUST set the FINAL flag, frames, but those frames do not carry HTTP semantics.
indicating that the client intends to send no further data on this
stream, unless the server intends to push resources (see
Section 4.3). HEADERS+PRIORITY frame does not contain the FINAL flag
for requests that contain a body. The body of a request follows as a
series of DATA frames. The last DATA frame sets the FINAL flag to
indicate the end of the body.
The header fields included in the HEADERS+PRIORITY frame contain all Trailing header fields are carried in a header block that also
of the HTTP header fields associated with an HTTP request. The terminates the stream. That is, a sequence of HEADERS frames that
definitions of these headers are largely unchanged relative to carries an END_STREAM flag on the last frame. Header blocks after
HTTP/1.1, with a few notable exceptions: the first that do not terminate the stream are not part of an HTTP
request or response.
An HTTP request/response exchange fully consumes a single stream. A
request starts with the HEADERS frame that puts the stream into an
"open" state and ends with a frame bearing END_STREAM, which causes
the stream to become "half closed" for the client. A response starts
with a HEADERS frame and ends with a frame bearing END_STREAM, which
places the stream in the "closed" state.
8.1.1. Examples
For example, an HTTP GET request that includes request header fields
and no body, is transmitted as a single contiguous sequence of
HEADERS frames containing the serialized block of request header
fields. The last HEADERS frame in the sequence has both the
END_HEADERS and END_STREAM flag set:
GET /resource HTTP/1.1 HEADERS
Host: example.org ==> + END_STREAM
Accept: image/jpeg + END_HEADERS
:method = get
:scheme = https
:host = example.org
:path = /resource
accept = image/jpeg
Similarly, a response that includes only response header fields is
transmitted as a sequence of HEADERS frames containing the serialized
block of response header fields. The last HEADERS frame in the
sequence has both the END_HEADERS and END_STREAM flag set:
HTTP/1.1 204 No Content HEADERS
Content-Length: 0 ===> + END_STREAM
+ END_HEADERS
:status = 204
content-length: 0
An HTTP POST request that includes request header fields and payload
data is transmitted as one or more HEADERS frames containing the
request headers followed by one or more DATA frames, with the last
HEADERS frame having the END_HEADERS flag set and the final DATA
frame having the END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM
Content-Type: image/jpeg + END_HEADERS
Content-Length: 123 :method = post
:scheme = https
{binary data} :host = example.org
:path = /resource
content-type = image/jpeg
content-length = 123
DATA
+ END_STREAM
{binary data}
A response that includes header fields and payload data is
transmitted as one or more HEADERS frames followed by one or more
DATA frames, with the last DATA frame in the sequence having the
END_STREAM flag set:
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS
:status = 200
{binary data} content-type = image/jpeg
content-length = 123
DATA
+ END_STREAM
{binary data}
Trailing header fields are sent as a header block after both the
request or response header block and all the DATA frames have been
sent. The sequence of HEADERS frames that bears the trailers
includes a terminal frame that has both END_HEADERS and END_STREAM
flags set.
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ===> - END_STREAM
Content-Length: 123 + END_HEADERS
TE: trailers :status = 200
123 content-type = image/jpeg
{binary data} content-length = 123
0
Foo: bar DATA
- END_STREAM
{binary data}
HEADERS
+ END_STREAM
+ END_HEADERS
foo: bar
8.1.2. Request Header Fields
The definitions of the request header fields are largely unchanged
relative to HTTP/1.1, with a few notable exceptions:
o The HTTP/1.1 request-line has been split into two separate header o The HTTP/1.1 request-line has been split into two separate header
fields named :method and :path, whose values specify the HTTP fields named :method and :path, whose values specify the HTTP
method for the request and the request-target, respectively. The method for the request and the request-target, respectively. The
HTTP-version component of the request-line is removed entirely HTTP-version component of the request-line is removed entirely
from the headers. from the headers.
o The host and optional port portions of the request URI (see o The host and optional port portions of the request URI (see
[RFC3986], Section 3.2), is specified using the new :host header [RFC3986], Section 3.2), are specified using the new :host header
field. [[anchor21: Ed. Note: it needs to be clarified whether or field. [[anchor13: Ed. Note: it needs to be clarified whether or
not this replaces the existing HTTP/1.1 Host header.]] not this replaces the existing HTTP/1.1 Host header.]]
o A new :scheme header field has been added to specify the scheme o A new :scheme header field has been added to specify the scheme
portion of the request-target (e.g. "https") portion of the request-target (e.g. "https")
o All header field names MUST be lowercased, and the definitions of o All header field names MUST be lowercased, and the definitions of
all header field names defined by HTTP/1.1 are updated to be all all header field names defined by HTTP/1.1 are updated to be all
lowercase. lowercase.
o The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer- o The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
Encoding header fields are no longer valid and MUST not be sent. Encoding header fields are no longer valid and MUST NOT be sent.
[[anchor14: Ed. Note: And "TE" I presume?]]
All HTTP Requests MUST include the ":method", ":path", ":host", and All HTTP Requests MUST include the ":method", ":path", ":host", and
":scheme" header fields. ":scheme" header fields.
Header fields whose names begin with ":" (whether defined in this Header fields whose names begin with ":" (whether defined in this
document or future extensions to this document) MUST appear before document or future extensions to this document) MUST appear before
any other header fields. any other header fields. [[anchor15: Ed. Note: This requirement is
currently pending review. Consider it "on hold" for the moment.]]
If a client sends a HEADERS+PRIORITY frame that omits a mandatory
header, the server MUST reply with a HTTP 400 Bad Request reply.
[[anchor22: Ed: why PROTOCOL_ERROR on missing ":status" in the
response, but HTTP 400 here?]]
If a server receives a request where the sum of the data frame All HTTP Requests that include a body SHOULD include the "content-
payload lengths does not equal the size of the Content-Length header length" header field. If a server receives a request where the sum
field, the server MUST return a 400 (Bad Request) error. of the DATA frame payload lengths does not equal the value of the
"content-length" header field, the server MUST return a 400 (Bad
Request) error.
Although POSTs are inherently chunked, POST requests SHOULD also be If a client omits a mandatory header field from the request, the
accompanied by a Content-Length header field. First, it informs the server MUST reply with a HTTP 400 Bad Request reply.
server of how much data to expect, which the server can use to track
overall progress and provide appropriate user feedback. More
importantly, some HTTP server implementations fail to correctly
process requests that omit the Content-Length header field. Many
existing clients send a Content-Length header field, and some server
implementations have come to depend upon its presence.
A client provides priority in requests as a hint to the server. A 8.1.3. Response Header Fields
server SHOULD attempt to provide responses to higher priority
requests before lower priority requests. A server could send lower
priority responses during periods that higher priority responses are
unavailable to ensure better utilization of a connection.
If the server receives a data frame prior to a HEADERS+PRIORITY frame The definitions of the response header fields are largely unchanged
the server MUST treat this as a stream error (Section 3.5.2) of type relative to HTTP/1.1, with a few notable exceptions:
PROTOCOL_ERROR.
4.2.3. Response o The response status line has been reduced to a single ":status"
header field whose value specifies only the numeric response
status code. The status text component of the HTTP/1.1 response
has been dropped entirely.
The server responds to a client request using the same stream o The response MUST contain exactly one :status header field with
identifier that was used by the request. An HTTP response begins exactly one response status value. If the client receives an HTTP
with a HEADERS frame. An HTTP response body consists of a series of response that does not include the :status field, or provides
DATA frames. The last data frame contains a FINAL flag to indicate multiple response status code values, it MUST respond with a
the end of the response. A response that contains no body (such as a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
204 or 304 response) consists only of a HEADERS frame that contains
the FINAL flag to indicate no further data will be sent on the
stream.
The response status line is unfolded into name-value pairs like o All header field names MUST be lowercased, and the definitions of
other HTTP header fields and must be present: all header field names defined by HTTP/1.1 are updated to be all
lowercase.
":status": The HTTP response status code (e.g. "200" or "200 OK") o The Connection, Keep-Alive, Proxy-Connection, and Transfer-
Encoding header fields are not valid and MUST NOT be sent.
All header field names starting with ":" (whether defined in this Header fields whose names begin with ":" (whether defined in this
document or future extensions to this document) MUST appear before document or future extensions to this document) MUST appear before
any other header fields. any other header fields. [[anchor16: Ed. Note: This requirement is
currently pending review. Consider it "on hold" for the moment.]]
All header field names MUST be all lowercase.
The Connection, Keep-Alive, Proxy-Connection, and Transfer-
Encoding header fields are not valid and MUST not be sent.
Responses MAY be accompanied by a Content-Length header field for
advisory purposes. This allows clients to learn the full size of
an entity prior to receiving all the data frames. This can help
in, for example, reporting progress.
If a client receives a response where the sum of the data frame
payload length does not equal the size of the Content-Length
header field, the client MUST ignore the content length header
field. [[anchor23: Ed: See
<https://github.com/http2/http2-spec/issues/46>.]]
If a client receives a response with an absent or duplicated status
header, the client MUST treat this as a stream error (Section 3.5.2)
of type PROTOCOL_ERROR.
If the client receives a data frame prior to a HEADERS frame the
client MUST treat this as a stream error (Section 3.5.2) of type
PROTOCOL_ERROR.
Clients MUST support gzip compression. Regardless of the value of
the Accept-Encoding header field, a server MAY send responses with
gzip or deflate encoding. A compressed response MUST still bear an
appropriate Content-Encoding header field.
4.3. Server Push Transactions
HTTP/2.0 enables a server to send multiple replies to a client for a
single request. The rationale for this feature is that sometimes a
server knows that it will need to send multiple resources in response
to a single request. Without server push features, the client must
first download the primary resource, then discover the secondary
resource(s), and request them.
Server push is an optional feature. The
SETTINGS_MAX_CONCURRENT_STREAMS setting from the client limits the
number of resources that can be concurrently pushed by a server.
Server push can be disabled by clients that do not wish to receive
pushed resources by advertising a SETTINGS_MAX_CONCURRENT_STREAMS
SETTING (Section 3.8.4) of zero. This prevents servers from creating
the streams necessary to push resources.
Clients receiving a pushed response MUST validate that the server is
authorized to push the resource using the same-origin policy
([RFC6454], Section 3). For example, a HTTP/2.0 connection to
"example.com" is generally [[anchor24: Ed: weaselly use of
"generally", needs better definition]] not permitted to push a
response for "www.example.org".
A client that accepts pushed resources caches those resources as
though they were responses to GET requests.
Pushing of resources avoids the round-trip delay, but also creates a
potential race where a server can be pushing content which a client
is in the process of requesting. The PUSH_PROMISE frame reduces the
chances of this condition occurring, while retaining the performance
benefit.
Pushed responses are associated with a request at the HTTP/2.0
framing layer. The PUSH_PROMISE is sent on the stream for the
associated request, which allows a receiver to correlate the pushed
resource with a request. The pushed stream inherits all of the
request header fields from the associated stream with the exception
of resource identification header fields (":host", ":scheme", and
":path"), which are provided as part of the PUSH_PROMISE frame.
Pushed resources always have an associated ":method" of "GET". A
cache MUST store these inherited and implied request header fields
with the cached resource.
4.3.1. Server implementation
A server pushes resources in association with a request from the
client. Prior to closing the response stream, the server sends a
PUSH_PROMISE for each resource that it intends to push. The
PUSH_PROMISE includes header fields that allow the client to identify
the resource (":scheme", ":host", and ":path").
A server can push multiple resources in response to a request, but
all pushed resources MUST be promised on the response stream for the
associated request. A server cannot send a PUSH_PROMISE on a new
stream or a half-closed stream.
The server SHOULD include any header fields in a PUSH_PROMISE that
would allow a cache to determine if the resource is already cached
(see [HTTP-p6], Section 4).
After sending a PUSH_PROMISE, the server commences transmission of a
pushed resource. A pushed resource uses a server-initiated stream.
The server sends frames on this stream in the same order as an HTTP
response (Section 4.2.3): a HEADERS frame followed by DATA frames.
Many uses of server push are to send content that a client is likely
to discover a need for based on the content of a response
representation. To minimize the chances that a client will make a
request for resources that are being pushed - causing duplicate
copies of a resource to be sent by the server - a PUSH_PROMISE frame
SHOULD be sent prior to any content in the response representation
that might allow a client to discover the pushed resource and request
it.
The server MUST only push resources that could have been returned 8.1.4. GZip Content-Encoding
from a GET request.
Note: A server does not need to have all response header fields Clients MUST support gzip compression for HTTP response bodies.
available at the time it issues a PUSH_PROMISE frame. All remaining Regardless of the value of the accept-encoding header field, a server
header fields are included in the HEADERS frame. The HEADERS frame MAY send responses with gzip or deflate encoding. A compressed
MUST NOT duplicate header fields from the PUSH_PROMISE frames. response MUST still bear an appropriate content-encoding header
field.
4.3.2. Client implementation 8.1.5. Request Reliability Mechanisms in HTTP/2.0
When fetching a resource the client has 3 possibilities: 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
the nature of the error. It is possible that some server processing
occurred prior to the error, which could result in undesirable
effects if the request were reattempted.
1. the resource is not being pushed HTTP/2.0 provides two mechanisms for providing a guarantee to a
client that a request has not been processed:
2. the resource is being pushed, but the data has not yet arrived o The GOAWAY frame indicates the highest stream number that might
have been processed. Requests on streams with higher numbers are
therefore guaranteed to be safe to retry.
3. the resource is being pushed, and the data has started to arrive o The REFUSED_STREAM error code can be included in a RST_STREAM
frame to indicate that the stream is being closed prior to any
processing having occurred. Any request that was sent on the
reset stream can be safely retried.
A client SHOULD NOT issue GET requests for a resource that has been In both cases, clients MAY automatically retry all requests,
promised. A client is instead advised to wait for the pushed including those with non-idempotent methods.
resource to arrive.
When a client receives a PUSH_PROMISE frame from the server without a A server MUST NOT indicate that a stream has not been processed
the ":host", ":scheme", and ":path" header fields, it MUST treat this unless it can guarantee that fact. If frames that are on a stream
as a stream error (Section 3.5.2) of type PROTOCOL_ERROR. are passed to the application layer for any stream, then
REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame
MUST include a stream identifier that is greater than or equal to the
given stream identifier.
To cancel individual server push streams, the client can issue a In addition to these mechanisms, the PING frame provides a way for a
stream error (Section 3.5.2) of type CANCEL. After receiving a client to easily test a connection. Connections that remain idle can
PUSH_PROMISE frame, the client is able to cancel the pushed resource become broken as some middleboxes (for instance, network address
before receiving any frames on the promised stream. The server translators, or load balancers) silently discard connection bindings.
ceases transmission of the pushed resource; if the server has not The PING frame allows a client to safely test whether a connection is
commenced transmission, it does not start. still active without sending a request.
To cancel all server push streams related to a request, the client 8.2. Server Push
may issue a stream error (Section 3.5.2) of type CANCEL on the
associated-stream-id. By cancelling that stream, the server MUST
immediately stop sending frames for any streams with
in-association-to for the original stream. [[anchor27: Ed: Triggering
side-effects on stream reset is going to be problematic for the
framing layer. Purely from a design perspective, it's a layering
violation. More practically speaking, the base request stream might
already be removed. Special handling logic would be required.]]
A client can choose to time out pushed streams if the server does not HTTP/2.0 enables a server to pre-emptively send (or "push") multiple
provide the resource in a timely fashion. A stream error associated resources to a client in response to a single request.
(Section 3.5.2) of type CANCEL can be used to stop a timed out push. This feature becomes particularly helpful when the server knows the
client will need to have those resources available in order to fully
process the originally requested resource.
If the server sends a HEADERS frame containing header fields that Pushing additional resources is optional, and is negotiated only
duplicate values on a previous HEADERS or PUSH_PROMISE frames on the between individual endpoints. For instance, an intermediary could
same stream, the client MUST treat this as a stream error receive pushed resources from the server but is not required to
(Section 3.5.2) of type PROTOCOL_ERROR. forward those on to the client. How to make use of the pushed
resources is up to that intermediary. Equally, the intermediary
might choose to push additional resources to the client, without any
action taken by the server.
If the server sends a HEADERS frame after sending a data frame for Server push is semantically equivalent to a server responding to a
the same stream, the client MAY ignore the HEADERS frame. Ignoring GET request for that resource. The PUSH_PROMISE frame, or frames,
the HEADERS frame after a data frame prevents handling of HTTP's sent by the server includes a header block that contains the request
trailing header fields (Section 4.1.1 of [HTTP-p1]). headers that the server has assumed.
5. Design Rationale and Notes Pushed resources are always associated with an explicit request from
a client. The PUSH_PROMISE frames sent by the server are sent on the
stream created for the original request. The PUSH_PROMSE frame
includes a promised stream identifier, chosen from the stream
identifiers available to the server (see Section 5.1.1). Any header
fields that are not specified in the PUSH_PROMISE frames sent by the
server are inherited from the original request sent by the client.
Authors' notes: The notes in this section have no bearing on the The header fields in PUSH_PROMISE MUST include the ":scheme", ":host"
HTTP/2.0 protocol as specified within this document, and none of and ":path" header fields that identify the resource that is being
these notes should be considered authoritative about how the protocol pushed. A PUSH_PROMISE always implies an HTTP method of GET. If a
works. However, these notes may prove useful in future debates about client receives a PUSH_PROMISE that does not include these header
how to resolve protocol ambiguities or how to evolve the protocol fields, or a value for the ":method" header field, it MUST respond
going forward. They may be removed before the final draft. with a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
5.1. Separation of Framing Layer and Application Layer After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed resource on a new, server-initiated stream that uses the
promised stream identifier. This stream is already implicitly "half
closed" to the client (Section 5.1). The server uses this stream to
transmit an HTTP response, using the same sequence of frames as
defined in Section 8.1.
Readers may note that this specification sometimes blends the framing Once a client receives a PUSH_PROMISE frame and chooses to accept the
layer (Section 3) with requirements of a specific application - HTTP pushed resource, the client SHOULD NOT issue any subsequent GET
(Section 4). This is reflected in the request/response nature of the requests for the promised resource until after the promised stream
streams and the definition of the HEADERS which are very similar to has closed.
HTTP, and other areas as well.
This blending is intentional - the primary goal of this protocol is The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to
to create a low-latency protocol for use with HTTP. Isolating the sending any HEADERS or DATA frames that reference the promised
two layers is convenient for description of the protocol and how it resources. This avoids a race where clients issue requests for
relates to existing HTTP implementations. However, the ability to resources prior to receiving any PUSH_PROMISE frames.
reuse the HTTP/2.0 framing layer is a non goal.
5.2. Error handling - Framing Layer For example, if the server receives a request for a document
containing embedded links to multiple image files, and the server
chooses to push those additional images to the client, sending push
promises before the DATA frames that contain the image links ensure
that the client is able to see the promises before discovering the
resources. Likewise, if the server pushes resources referenced by
the header block (for instance, in Link header fields), sending the
push promises before sending the header block ensures that clients do
not request those resources.
Error handling at the HTTP/2.0 layer splits errors into two groups: PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE
Those that affect an individual HTTP/2.0 stream, and those that do frames can be sent by the server on any stream that was opened by the
not. client. They MUST be sent on a stream that is in either the "open"
or "half closed (remote)" to the server. PUSH_PROMISE frames can be
interspersed within the frames that comprise response, with the
exception that they cannot be interspersed with HEADERS frames that
comprise a single header block.
When an error is confined to a single stream, but general framing is A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
intact, HTTP/2.0 attempts to use the RST_STREAM as a mechanism to the number of resources that can be concurrently pushed by a server.
invalidate the stream but move forward without aborting the Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables
connection altogether. server push by preventing the server from creating the necessary
streams.
For errors occurring outside of a single stream context, HTTP/2.0 The request header fields provided in the PUSH_PROMISE frame SHOULD
assumes the entire connection is hosed. In this case, the endpoint include enough information for a client to determine whether a cached
detecting the error should initiate a connection close. representation of the resource is already available. If the client
determines, for any reason, that it does not wish to receive the
pushed resource from the server, or if the server takes too long to
begin sending the promised resource, the client can send an
RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
and referencing the pushed stream's identifier.
5.3. One Connection per Domain Clients receiving a pushed response MUST validate that the server is
authorized to push the resource using the same-origin policy
([RFC6454], Section 3). For example, a HTTP/2.0 connection to
"example.com" is generally [[anchor17: Ed: weaselly use of
"generally", needs better definition]] not permitted to push a
response for "www.example.org".
HTTP/2.0 attempts to use fewer connections than other protocols have 9. Additional HTTP Requirements/Considerations
traditionally used. The rationale for this behavior is because it is
very difficult to provide a consistent level of service (e.g. TCP
slow-start), prioritization, or optimal compression when the client
is connecting to the server through multiple channels.
Through lab measurements, we have seen consistent latency benefits by TODO: SNI, gzip and deflate Content-Encoding, etc..
using fewer connections from the client. The overall number of
packets sent by HTTP/2.0 can be as much as 40% less than HTTP.
Handling large numbers of concurrent connections on the server also
does become a scalability problem, and HTTP/2.0 reduces this load.
The use of multiple connections is not without benefit, however. 9.1. Frame Size Limits for HTTP
Because HTTP/2.0 multiplexes multiple, independent streams onto a
single stream, it creates a potential for head-of-line blocking
problems at the transport level. In tests so far, the negative
effects of head-of-line blocking (especially in the presence of
packet loss) is outweighed by the benefits of compression and
prioritization.
5.4. Fixed vs Variable Length Fields Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
in length, not counting the 8 octet frame header. An endpoint MUST
treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
Section 4.2).
HTTP/2.0 favors use of fixed length 32bit fields in cases where 9.2. Connection Management
smaller, variable length encodings could have been used. To some,
this seems like a tragic waste of bandwidth. HTTP/2.0 chooses the
simple encoding for speed and simplicity.
The goal of HTTP/2.0 is to reduce latency on the network. The HTTP/2.0 connections are persistent. For best performance, it is
overhead of HTTP/2.0 frames is generally quite low. Each data frame expected clients will not close connections until it is determined
is only an 8 byte overhead for a 1452 byte payload (~0.6%). At the that no further communication with a server is necessary (for
time of this writing, bandwidth is already plentiful, and there is a example, when a user navigates away from a particular web page), or
strong trend indicating that bandwidth will continue to increase. until the server closes the connection.
With an average worldwide bandwidth of 1Mbps, and assuming that a
variable length encoding could reduce the overhead by 50%, the
latency saved by using a variable length encoding would be less than
100 nanoseconds. More interesting are the effects when the larger
encodings force a packet boundary, in which case a round-trip could
be induced. However, by addressing other aspects of HTTP/2.0 and TCP
interactions, we believe this is completely mitigated.
5.5. Server Push Clients SHOULD NOT open more than one HTTP/2.0 connection to a given
origin ([RFC6454]) concurrently. A client can create additional
connections as replacements, either to replace connections that are
near to exhausting the available stream identifiers (Section 5.1.1),
or to replace connections that have encountered errors
(Section 5.4.1).
A subtle but important point is that server push streams must be Servers are encouraged to maintain open connections for as long as
declared before the associated stream is closed. The reason for this possible, but are permitted to terminate idle connections if
is so that proxies have a lifetime for which they can discard necessary. When either endpoint chooses to close the transport-level
information about previous streams. If a pushed stream could TCP connection, the terminating endpoint MUST first send a GOAWAY
associate itself with an already-closed stream, then endpoints would (Section 6.8) frame so that both endpoints can reliably determine
not have a specific lifecycle for when they could disavow knowledge whether previously sent frames have been processed and gracefully
of the streams which went before. complete or terminate any necessary remaining tasks.
6. Security Considerations 10. Security Considerations
6.1. Server Authority and Same-Origin 10.1. Server Authority and Same-Origin
This specification uses the same-origin policy ([RFC6454], Section 3) This specification uses the same-origin policy ([RFC6454], Section 3)
to determine whether an origin server is permitted to provide to determine whether an origin server is permitted to provide
content. content.
A server that is contacted using TLS is authenticated based on the A server that is contacted using TLS is authenticated based on the
certificate that it offers in the TLS handshake (see [RFC2818], certificate that it offers in the TLS handshake (see [RFC2818],
Section 3). A server is considered authoritative for an "https:" Section 3). A server is considered authoritative for an "https"
resource if it has been successfully authenticated for the domain resource if it has been successfully authenticated for the domain
part of the origin of the resource that it is providing. part of the origin of the resource that it is providing.
A server is considered authoritative for an "http:" resource if the A server is considered authoritative for an "http" resource if the
connection is established to a resolved IP address for the domain in connection is established to a resolved IP address for the domain in
the origin of the resource. the origin of the resource.
A client MUST NOT use, in any way, resources provided by a server A client MUST NOT use, in any way, resources provided by a server
that is not authoritative for those resources. that is not authoritative for those resources.
6.2. Cross-Protocol Attacks 10.2. Cross-Protocol Attacks
When using TLS, we believe that HTTP/2.0 introduces no new cross- When using TLS, we believe that HTTP/2.0 introduces no new cross-
protocol attacks. TLS encrypts the contents of all transmission protocol attacks. TLS encrypts the contents of all transmission
(except the handshake itself), making it difficult for attackers to (except the handshake itself), making it difficult for attackers to
control the data which could be used in a cross-protocol attack. control the data which could be used in a cross-protocol attack.
[[anchor23: Issue: This is no longer true]]
[[anchor37: Issue: This is no longer true]] 10.3. Cacheability of Pushed Resources
6.3. Cacheability of Pushed Resources
Pushed resources are synthesized responses without an explicit Pushed resources are responses without an explicit request; the
request; the request for a pushed resource is synthesized from the request for a pushed resource is synthesized from the request that
request that triggered the push, plus resource identification triggered the push, plus resource identification information provided
information provided by the server. Request header fields are by the server. Request header fields are necessary for HTTP cache
necessary for HTTP cache control validations (such as the Vary header control validations (such as the Vary header field) to work. For
field) to work. For this reason, caches MUST inherit request header this reason, caches MUST inherit request header fields from the
fields from the associated stream for the push. This includes the associated stream for the push. This includes the Cookie header
Cookie header field. field.
Caching resources that are pushed is possible, based on the guidance Caching resources that are pushed is possible, based on the guidance
provided by the origin server in the Cache-Control header field. provided by the origin server in the Cache-Control header field.
However, this can cause issues if a single server hosts more than one However, this can cause issues if a single server hosts more than one
tenant. For example, a server might offer multiple users each a tenant. For example, a server might offer multiple users each a
small portion of its URI space. small portion of its URI space.
Where multiple tenants share space on the same server, that server Where multiple tenants share space on the same server, that server
MUST ensure that tenants are not able to push representations of MUST ensure that tenants are not able to push representations of
resources that they do not have authority over. Failure to enforce resources that they do not have authority over. Failure to enforce
this would allow a tenant to provide a representation that would be this would allow a tenant to provide a representation that would be
served out of cache, overriding the actual representation that the served out of cache, overriding the actual representation that the
authoritative tenant provides. authoritative tenant provides.
Pushed resources for which an origin server is not authoritative are Pushed resources for which an origin server is not authoritative are
never cached or used. never cached or used.
7. Privacy Considerations 11. Privacy Considerations
7.1. Long Lived Connections
HTTP/2.0 aims to keep connections open longer between clients and HTTP/2.0 aims to keep connections open longer between clients and
servers in order to reduce the latency when a user makes a request. servers in order to reduce the latency when a user makes a request.
The maintenance of these connections over time could be used to The maintenance of these connections over time could be used to
expose private information. For example, a user using a browser expose private information. For example, a user using a browser
hours after the previous user stopped using that browser may be able hours after the previous user stopped using that browser may be able
to learn about what the previous user was doing. This is a problem to learn about what the previous user was doing. This is a problem
with HTTP in its current form as well, however the short lived with HTTP in its current form as well, however the short lived
connections make it less of a risk. connections make it less of a risk.
7.2. SETTINGS frame 12. IANA Considerations
The HTTP/2.0 SETTINGS frame allows servers to store out-of-band
transmitted information about the communication between client and
server on the client. Although this is intended only to be used to
reduce latency, renegade servers could use it as a mechanism to store
identifying information about the client in future requests.
Clients implementing privacy modes can disable client-persisted
SETTINGS storage.
Clients MUST clear persisted SETTINGS information when clearing the
cookies.
8. IANA Considerations
This document establishes registries for frame types, error codes and This document establishes registries for frame types, error codes and
settings. settings. These new registries are entered in a new "Hypertext
Transfer Protocol (HTTP) 2.0 Parameters" section.
8.1. Frame Type Registry This document also registers the "HTTP2-Settings" header field for
use in HTTP.
12.1. Frame Type Registry
This document establishes a registry for HTTP/2.0 frame types. The This document establishes a registry for HTTP/2.0 frame types. The
"HTTP/2.0 Frame Type" registry operates under the "IETF Review" "HTTP/2.0 Frame Type" registry operates under the "IETF Review"
policy [RFC5226]. policy [RFC5226].
Frame types are an 8-bit value. When reviewing new frame type Frame types are an 8-bit value. When reviewing new frame type
registrations, special attention is advised for any frame type- registrations, special attention is advised for any frame type-
specific flags that are defined. Frame flags can interact with specific flags that are defined. Frame flags can interact with
existing flags and could prevent the creation of globally applicable existing flags and could prevent the creation of globally applicable
flags. flags.
Initial values for the "HTTP/2.0 Frame Type" registry are shown in Initial values for the "HTTP/2.0 Frame Type" registry are shown in
Table 1. Table 1.
+------------+------------------+---------------------+ +-----------+---------------+---------------------------------------+
| Frame Type | Name | Flags | | Frame | Name | Flags |
+------------+------------------+---------------------+ | Type | | |
| 0 | DATA | - | +-----------+---------------+---------------------------------------+
| 1 | HEADERS+PRIORITY | - | | 0 | DATA | END_STREAM(1) |
| 1 | HEADERS | END_STREAM(1), END_HEADERS(4), |
| | | PRIORITY(8) |
| 2 | PRIORITY | - |
| 3 | RST_STREAM | - | | 3 | RST_STREAM | - |
| 4 | SETTINGS | CLEAR_PERSISTED(2) | | 4 | SETTINGS | - |
| 5 | PUSH_PROMISE | - | | 5 | PUSH_PROMISE | END_PUSH_PROMISE(1) |
| 6 | PING | PONG(2) | | 6 | PING | PONG(1) |
| 7 | GOAWAY | - | | 7 | GOAWAY | - |
| 8 | HEADERS | - | | 9 | WINDOW_UPDATE | END_FLOW_CONTROL(1) |
| 9 | WINDOW_UPDATE | END_FLOW_CONTROL(2) | +-----------+---------------+---------------------------------------+
+------------+------------------+---------------------+
Table 1 Table 1
8.2. Error Code Registry 12.2. Error Code Registry
This document establishes a registry for HTTP/2.0 error codes. The This document establishes a registry for HTTP/2.0 error codes. The
"HTTP/2.0 Error Code" registry manages a 32-bit space. The "HTTP/2.0 "HTTP/2.0 Error Code" registry manages a 32-bit space. The "HTTP/2.0
Error Code" registry operates under the "Expert Review" policy Error Code" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
Registrations for error codes are required to include a description Registrations for error codes are required to include a description
of the error code. An expert reviewer is advised to examine new of the error code. An expert reviewer is advised to examine new
registrations for possible duplication with existing error codes. registrations for possible duplication with existing error codes.
Use of existing registrations is to be encouraged, but not mandated. Use of existing registrations is to be encouraged, but not mandated.
skipping to change at page 43, line 30 skipping to change at page 46, line 48
Name: A name for the error code. Specifying an error code name is Name: A name for the error code. Specifying an error code name is
optional. optional.
Description: A description of the conditions where the error code is Description: A description of the conditions where the error code is
applicable. applicable.
Specification: An optional reference for a specification that Specification: An optional reference for a specification that
defines the error code. defines the error code.
An initial set of error code registrations can be found in An initial set of error code registrations can be found in Section 7.
Section 3.5.3.
8.3. Settings Registry 12.3. Settings Registry
This document establishes a registry for HTTP/2.0 settings. The This document establishes a registry for HTTP/2.0 settings. The
"HTTP/2.0 Settings" registry manages a 24-bit space. The "HTTP/2.0 "HTTP/2.0 Settings" registry manages a 24-bit space. The "HTTP/2.0
Settings" registry operates under the "Expert Review" policy Settings" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
Registrations for settings are required to include a description of Registrations for settings are required to include a description of
the setting. An expert reviewer is advised to examine new the setting. An expert reviewer is advised to examine new
registrations for possible duplication with existing settings. Use registrations for possible duplication with existing settings. Use
of existing registrations is to be encouraged, but not mandated. of existing registrations is to be encouraged, but not mandated.
skipping to change at page 44, line 16 skipping to change at page 47, line 34
and semantics. and semantics.
Description: A description of the setting. This might include the Description: A description of the setting. This might include the
range of values, any applicable units and how to act upon a value range of values, any applicable units and how to act upon a value
when it is provided. when it is provided.
Specification: An optional reference for a specification that Specification: An optional reference for a specification that
defines the setting. defines the setting.
An initial set of settings registrations can be found in An initial set of settings registrations can be found in
Section 3.8.4.3. Section 6.5.2.
9. Acknowledgements 12.4. HTTP2-Settings Header Field Registration
This section registers the "HTTP2-Settings" header field in the
Permanent Message Header Field Registry [BCP90].
Header field name: HTTP2-Settings
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document(s): RFC XXXX (this document)
Related information: This header field is only used by an HTTP/2.0
client for Upgrade-based negotiation.
13. Acknowledgements
This document includes substantial input from the following This document includes substantial input from the following
individuals: individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay, Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors). Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism) o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism)
o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
Jitu Padhye, Roberto Peon, Rob Trace (Flow control) Jitu Padhye, Roberto Peon, Rob Trace (Flow control)
o Mark Nottingham, Julian Reschke, James Snell (Editorial) o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner
(Substantial editorial contributions)
10. References 14. References
10.1. Normative References 14.1. Normative References
[HTTP-p1] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol [COMPRESSION] Ruellan, H. and R. Peon, "HTTP Header Compression",
(HTTP/1.1): Message Syntax and Routing", draft-ietf-httpbis-header-compression-00 (work in
progress), June 2013.
[HTTP-p1] Fielding, R. and J. Reschke, "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
draft-ietf-httpbis-p1-messaging-22 (work in progress), draft-ietf-httpbis-p1-messaging-22 (work in progress),
February 2013. February 2013.
[HTTP-p2] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol [HTTP-p2] Fielding, R. and J. Reschke, "Hypertext Transfer
(HTTP/1.1): Semantics and Content", Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-22 (work in progress), draft-ietf-httpbis-p2-semantics-22 (work in progress),
February 2013. February 2013.
[HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Protocol (HTTP/1.1): Conditional Requests", Transfer Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-22 (work in progress), draft-ietf-httpbis-p4-conditional-22 (work in
February 2013. progress), February 2013.
[HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests", Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range
draft-ietf-httpbis-p5-range-22 (work in progress), Requests", draft-ietf-httpbis-p5-range-22 (work in
February 2013. progress), February 2013.
[HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J.
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1):
draft-ietf-httpbis-p6-cache-22 (work in progress), Caching", draft-ietf-httpbis-p6-cache-22 (work in
February 2013. progress), February 2013.
[HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Protocol (HTTP/1.1): Authentication", Transfer Protocol (HTTP/1.1): Authentication",
draft-ietf-httpbis-p7-auth-22 (work in progress), draft-ietf-httpbis-p7-auth-22 (work in progress),
February 2013. February 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
Resource Identifier (URI): Generic Syntax", STD 66, "Uniform Resource Identifier (URI): Generic Syntax",
RFC 3986, January 2005. STD 66, RFC 3986, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
IANA Considerations Section in RFCs", BCP 26, RFC 5226, Encodings", RFC 4648, October 2006.
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
(TLS) Protocol Version 1.2", RFC 5246, August 2008. an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011. December 2011.
[TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application Layer Protocol "Transport Layer Security (TLS) Application Layer
Negotiation Extension", draft-ietf-tls-applayerprotoneg-01 Protocol Negotiation Extension",
(work in progress), April 2013. draft-ietf-tls-applayerprotoneg-01 (work in progress),
April 2013.
10.2. Informative References 14.2. Informative References
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
for High Performance", RFC 1323, May 1992. Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C. [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP
Extensions for High Performance", RFC 1323, May 1992.
Jackson, "Talking to Yourself for Fun and Profit", 2011, [TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
<http://w2spconf.com/2011/papers/websocket.pdf>. Jackson, "Talking to Yourself for Fun and Profit",
2011, <http://w2spconf.com/2011/papers/websocket.pdf>.
Appendix A. Change Log (to be removed by RFC Editor before publication) Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. Since draft-ietf-httpbis-http2-02 A.1. Since draft-ietf-httpbis-http2-03
Committed major restructuring atrocities.
Added reference to first header compression draft.
Added more formal description of frame lifecycle.
Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA.
Removed HEADERS+PRIORITY, added optional priority to HEADERS frame.
Added PRIORITY frame.
A.2. 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.2. Since draft-ietf-httpbis-http2-01 A.3. 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 47, line 7 skipping to change at page 51, line 31
Restructured frame header. Removed distinction between data and Restructured frame header. Removed distinction between data and
control frames. control frames.
Altered flow control properties to include session-level limits. Altered flow control properties to include session-level limits.
Added note on cacheability of pushed resources and multiple tenant Added note on cacheability of pushed resources and multiple tenant
servers. servers.
Changed protocol label form based on discussions. Changed protocol label form based on discussions.
A.3. Since draft-ietf-httpbis-http2-00 A.4. Since draft-ietf-httpbis-http2-00
Changed title throughout. Changed title throughout.
Removed section on Incompatibilities with SPDY draft#2. Removed section on Incompatibilities with SPDY draft#2.
Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https:// Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https://
groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>. groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.
Replaced abstract and introduction. Replaced abstract and introduction.
Added section on starting HTTP/2.0, including upgrade mechanism. Added section on starting HTTP/2.0, including upgrade mechanism.
Removed unused references. Removed unused references.
Added flow control principles (Section 3.6.1) based on <http:// Added flow control principles (Section 5.2.1) based on <http://
tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>. tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.
A.4. Since draft-mbelshe-httpbis-spdy-00 A.5. 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. 287 change blocks. 
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