--- 1/draft-ietf-httpbis-http2-04.txt 2013-08-12 18:14:25.179065585 -0700
+++ 2/draft-ietf-httpbis-http2-05.txt 2013-08-12 18:14:25.287068089 -0700
@@ -1,42 +1,38 @@
HTTPbis Working Group M. Belshe
Internet-Draft Twist
Intended status: Standards Track R. Peon
-Expires: January 9, 2014 Google, Inc
+Expires: February 14, 2014 Google, Inc
M. Thomson, Ed.
Microsoft
A. Melnikov, Ed.
Isode Ltd
- July 8, 2013
+ August 13, 2013
Hypertext Transfer Protocol version 2.0
- draft-ietf-httpbis-http2-04
+ draft-ietf-httpbis-http2-05
Abstract
This specification describes an optimized expression of the syntax of
the Hypertext Transfer Protocol (HTTP). The HTTP/2.0 encapsulation
enables more efficient use of network resources and reduced
perception of latency by allowing header field compression and
multiple concurrent messages on the same connection. It also
introduces unsolicited push of representations from servers to
clients.
This document is an alternative to, but does not obsolete the
HTTP/1.1 message format or protocol. HTTP's existing semantics
remain unchanged.
- This version of the draft has been marked for implementation.
- Interoperability testing will occur in the HTTP/2.0 interim in
- Hamburg, DE, starting 2013-08-05.
-
Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
.
Working Group information and related documents can be found at
(Wiki) and
(source code and issues
tracker).
@@ -51,21 +47,21 @@
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
- This Internet-Draft will expire on January 9, 2014.
+ This Internet-Draft will expire on February 14, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
@@ -85,84 +81,88 @@
2.2. HTTP Multiplexing . . . . . . . . . . . . . . . . . . . . 7
2.3. HTTP Semantics . . . . . . . . . . . . . . . . . . . . . . 7
3. Starting HTTP/2.0 . . . . . . . . . . . . . . . . . . . . . . 7
3.1. HTTP/2.0 Version Identification . . . . . . . . . . . . . 8
3.2. Starting HTTP/2.0 for "http" URIs . . . . . . . . . . . . 8
3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10
3.3. Starting HTTP/2.0 for "https" URIs . . . . . . . . . . . . 10
3.4. Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10
3.5. Connection Header . . . . . . . . . . . . . . . . . . . . 11
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
- 4.1. Frame Header . . . . . . . . . . . . . . . . . . . . . . . 12
+ 4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Header Compression and Decompression . . . . . . . . . . . 13
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 18
- 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 18
- 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 18
+ 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 19
+ 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 19
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 19
- 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 20
- 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 20
- 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 21
- 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 21
+ 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 21
+ 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 21
+ 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 22
+ 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 22
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 22
- 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 22
- 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 22
+ 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 23
+ 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 23
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
- 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 23
- 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 24
- 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 25
- 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 26
- 6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 26
- 6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 27
- 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 27
- 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
- 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 29
- 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 31
- 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 32
- 6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 33
- 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 34
- 6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 34
- 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 35
- 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 36
- 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 36
- 8.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 37
- 8.1.2. Request Header Fields . . . . . . . . . . . . . . . . 38
- 8.1.3. Response Header Fields . . . . . . . . . . . . . . . . 39
- 8.1.4. GZip Content-Encoding . . . . . . . . . . . . . . . . 40
- 8.1.5. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 40
- 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 41
- 9. Additional HTTP Requirements/Considerations . . . . . . . . . 43
- 9.1. Frame Size Limits for HTTP . . . . . . . . . . . . . . . . 43
- 9.2. Connection Management . . . . . . . . . . . . . . . . . . 43
- 10. Security Considerations . . . . . . . . . . . . . . . . . . . 43
- 10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 43
- 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 44
- 10.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 44
- 11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 45
- 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
- 12.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 45
- 12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 46
- 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
+ 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 24
+ 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 25
+ 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 26
+ 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 27
+ 6.5.1. Setting Format . . . . . . . . . . . . . . . . . . . . 27
+ 6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . . 28
+ 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 28
+ 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
+ 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 31
+ 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 33
+ 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 34
+ 6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 35
+ 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 36
+ 6.9.4. Ending Flow Control . . . . . . . . . . . . . . . . . 36
+ 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 36
+ 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 38
+ 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 38
+ 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 39
+ 8.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 39
+ 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . . 41
+ 8.1.3. Request Reliability Mechanisms in HTTP/2.0 . . . . . . 43
+ 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 43
+ 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 44
+ 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . . 45
+ 9. Additional HTTP Requirements/Considerations . . . . . . . . . 46
+ 9.1. Connection Management . . . . . . . . . . . . . . . . . . 46
+ 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 46
+ 9.3. Frame Size Limits for HTTP . . . . . . . . . . . . . . . . 47
+ 9.4. GZip Content-Encoding . . . . . . . . . . . . . . . . . . 47
+ 10. Security Considerations . . . . . . . . . . . . . . . . . . . 47
+ 10.1. Server Authority and Same-Origin . . . . . . . . . . . . . 47
+ 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 47
+ 10.3. Cacheability of Pushed Resources . . . . . . . . . . . . . 48
+ 11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 48
+ 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
+ 12.1. Frame Type Registry . . . . . . . . . . . . . . . . . . . 49
+ 12.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 49
+ 12.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 50
+ 12.4. HTTP2-Settings Header Field Registration . . . . . . . . . 51
+ 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51
+ 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 51
+ 14.1. Normative References . . . . . . . . . . . . . . . . . . . 51
+ 14.2. Informative References . . . . . . . . . . . . . . . . . . 53
Appendix A. Change Log (to be removed by RFC Editor before
- publication) . . . . . . . . . . . . . . . . . . . . 50
- A.1. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 50
- A.2. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 50
- A.3. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 50
- A.4. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 51
- A.5. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 51
+ publication) . . . . . . . . . . . . . . . . . . . . 53
+ A.1. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 53
+ A.2. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 54
+ A.3. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 54
+ A.4. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 54
+ A.5. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 55
+ A.6. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 55
1. Introduction
The Hypertext Transfer Protocol (HTTP) is a wildly successful
protocol. However, the HTTP/1.1 message format ([HTTP-p1], Section
3) is optimized for implementation simplicity and accessibility, not
application performance. As such it has several characteristics that
have a negative overall effect on application performance.
In particular, HTTP/1.0 only allows one request to be delivered at a
@@ -179,21 +179,21 @@
single new TCP connection.
This document addresses these issues by defining an optimized mapping
of HTTP's semantics to an underlying connection. Specifically, it
allows interleaving of request and response messages on the same
connection and uses an efficient coding for HTTP header fields. It
also allows prioritization of requests, letting more important
requests complete more quickly, further improving perceived
performance.
- The resulting protocol is designed to have be more friendly to the
+ The resulting protocol is designed to be more friendly to the
network, because fewer TCP connections can be used, in comparison to
HTTP/1.x. This means less competition with other flows, and longer-
lived connections, which in turn leads to better utilization of
available network capacity.
Finally, this encapsulation also enables more scalable processing of
messages through use of binary message framing.
1.1. Document Organization
@@ -274,21 +274,21 @@
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,
+ streams (see Section 8.1) 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
@@ -303,30 +303,33 @@
The protocol defined in this document is identified using the string
"HTTP/2.0". This identification is used in the HTTP/1.1 Upgrade
header field, in the TLS application layer protocol negotiation
extension [TLSALPN] field, and other places where protocol
identification is required.
Negotiating "HTTP/2.0" implies the use of the transport, security,
framing and message semantics described in this document.
- [[anchor6: Editor's Note: please remove the following text prior to
- the publication of a final version of this document.]]
+ [[anchor6: Editor's Note: please remove the remainder of this section
+ prior to the publication of a final version of this document.]]
Only implementations of the final, published RFC can identify
themselves as "HTTP/2.0". Until such an RFC exists, implementations
MUST NOT identify themselves using "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
- versions MUST NOT identify using this string.
+ versions MUST NOT identify using this string. The exception to this
+ rule is the string included in the connection header sent by clients
+ immediately after establishing an HTTP/2.0 connection (see
+ Section 3.5); this fixed length sequence of octets does not change.
Implementations of draft versions of the protocol MUST add the string
"-draft-" and the corresponding draft number to the identifier before
the separator ('/'). For example, draft-ietf-httpbis-http2-03 is
identified using the string "HTTP-draft-03/2.0".
Non-compatible experiments that are based on these draft versions
MUST instead replace the string "draft" with a different identifier.
For example, an experimental implementation of packet mood-based
encoding based on draft-ietf-httpbis-http2-07 might identify itself
@@ -334,22 +337,22 @@
"token" syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters
are encouraged to coordinate their experiments on the
ietf-http-wg@w3.org mailing list.
3.2. Starting HTTP/2.0 for "http" URIs
A client that makes a request to an "http" URI without prior
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
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.
+ HTTP/1.1 request MUST include exactly one HTTP2-Settings
+ (Section 3.2.1) header field.
For example:
GET /default.htm HTTP/1.1
Host: server.example.com
Connection: Upgrade, HTTP2-Settings
Upgrade: HTTP/2.0
HTTP2-Settings:
Requests that contain a request entity body MUST be sent in their
@@ -387,23 +390,23 @@
connection header (Section 3.5), which includes a SETTINGS frame.
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.
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
+ A client that upgrades from HTTP/1.1 to HTTP/2.0 MUST include exactly
+ one "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
@@ -423,21 +426,21 @@
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 [TLS12] with the
application layer protocol negotiation extension [TLSALPN].
Once TLS negotiation is complete, both the client and the server send
a connection header (Section 3.5).
3.4. Starting HTTP/2.0 with Prior Knowledge
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
server that is known to support HTTP/2.0, after the connection header
@@ -459,22 +462,22 @@
initial settings for the HTTP/2.0 connection.
The client connection header is a sequence of 24 octets, which in hex
notation are:
505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n") followed by a
SETTINGS frame (Section 6.5). The client sends the client connection
header immediately upon receipt of a 101 Switching Protocols response
- (indicating a successful upgrade), or after receiving a TLS Finished
- message from the server. If starting an HTTP/2.0 connection with
+ (indicating a successful upgrade), or as the first application data
+ octets of a TLS connection. If starting an HTTP/2.0 connection with
prior knowledge of server support for the protocol, the client
connection header is sent upon connection establishment.
The client connection header is selected so that a large
proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do
not attempt to process further frames. Note that this does not
address the concerns raised in [TALKING].
The server connection header consists of just a SETTINGS frame
(Section 6.5) that MUST be the first frame the server sends in the
@@ -492,21 +495,21 @@
Clients and servers MUST terminate the TCP connection if either peer
does not begin with a valid connection header. A GOAWAY frame
(Section 6.8) MAY be omitted if it is clear that the peer is not
using HTTP/2.0.
4. HTTP Frames
Once the HTTP/2.0 connection is established, endpoints can begin
exchanging frames.
-4.1. Frame Header
+4.1. Frame Format
All frames begin with an 8-octet header followed by a payload of
between 0 and 65,535 octets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (16) | Type (8) | Flags (8) |
+-+-------------+---------------+-------------------------------+
|R| Stream Identifier (31) |
@@ -517,21 +520,21 @@
Frame Header
The fields of the frame header are defined as:
Length: The length of the frame payload expressed as an unsigned 16-
bit integer. The 8 octets of the frame header are not included in
this value.
Type: The 8-bit type of the frame. The frame type determines how
the remainder of the frame header and payload are interpreted.
- Implementations MUST ignore unsupported and unrecognized frame
+ Implementations MUST ignore frames of unsupported or unrecognized
types.
Flags: An 8-bit field reserved for frame-type specific boolean
flags.
Flags are 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
@@ -567,50 +570,53 @@
A header in HTTP/2.0 is a name-value pair with one or more associated
values. They are used within HTTP request and response messages as
well as server push operations (see Section 8.2).
Header sets are logical collections of zero or more header fields
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.
+ (Section 6.2), PUSH_PROMISE (Section 6.6) or CONTINUATION
+ (Section 6.10) frames. The receiving endpoint reassembles the header
+ block by concatenating the individual fragments, then decompresses
+ the block to reconstruct the header set.
- Header block fragments can only be sent as the payload of HEADERS or
- PUSH_PROMISE frames.
+ Header block fragments can only be sent as the payload of HEADERS,
+ PUSH_PROMISE or CONTINUATION frames.
- A compressed and encoded header block is transmitted in one or more
- 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.
+ A compressed and encoded header block is transmitted in a HEADERS or
+ PUSH_PROMISE frame, followed by zero or more CONTINUATION 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.
Header blocks MUST be transmitted as a contiguous sequence of frames,
with no interleaved frames of any other type, or from any other
- stream. The last frame in a sequence of HEADERS frames MUST have the
- END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE
- frames MUST have the END_PUSH_PROMISE flag set.
+ stream. The last frame in a sequence of HEADERS/CONTINUATION frames
+ MUST have the END_HEADERS flag set. The last frame in a sequence of
+ PUSH_PROMISE/CONTINUATION frames MUST have the END_PUSH_PROMISE/
+ END_HEADERS flag set (respectively).
- HEADERS and PUSH_PROMISE frames carry data that can modify the
- compression context maintained by a receiver. An endpoint receiving
- 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.
+ HEADERS, PUSH_PROMISE and CONTINUATION frames carry data that can
+ modify the compression context maintained by a receiver. An endpoint
+ receiving HEADERS, PUSH_PROMISE or CONTINUATION 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
+ A "stream" is an independent, bi-directional sequence of HEADERS 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
active streams, with either endpoint interleaving frames from
multiple streams.
o Streams can be established and used unilaterally or shared by
either the client or server.
@@ -686,62 +692,71 @@
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).
In this state, only the following transitions are possible:
* The endpoint can send a HEADERS frame. This causes the stream
to open in a "half closed (remote)" state.
* Either endpoint can send a RST_STREAM frame to cause the stream
- to become "closed". This releases the stream reservation.
+ to become "closed". This also releases the stream reservation.
An endpoint MUST NOT send any other type of frame in this state.
+ Receiving any frame other than RST_STREAM or PRIORITY MUST be
+ treated as a connection error (Section 5.4.1) of type
+ PROTOCOL_ERROR.
reserved (remote):
A stream in the "reserved (remote)" state has been reserved by a
remote peer.
In this state, only the following transitions are possible:
* Receiving a HEADERS frame causes the stream to transition to
"half closed (local)".
* Either endpoint can send a RST_STREAM frame to cause the stream
- to become "closed". This releases the stream reservation.
+ to become "closed". This also releases the stream reservation.
Receiving any other type of frame MUST be treated as a stream
- error (Section 5.4.2) of type PROTOCOL_ERROR.
+ error (Section 5.4.2) of type PROTOCOL_ERROR. An endpoint MAY
+ send RST_STREAM or PRIORITY frames in this state to cancel or
+ reprioritize the reserved stream.
open:
- 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).
+ The "open" state is where both peers can send frames of any type.
+ In this state, sending peers observe advertised stream level flow
+ control limits (Section 5.2).
From this state either endpoint can send a frame with a END_STREAM
flag set, which causes the stream to transition into one of the
"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)".
Either endpoint can send a RST_STREAM frame from this state,
causing it to transition immediately to "closed".
half closed (local):
A stream that is "half closed (local)" cannot be used for sending
frames.
A stream transitions from this state to "closed" when a frame that
contains a END_STREAM flag is received, or when either peer sends
a RST_STREAM frame.
+ A receiver can ignore WINDOW_UPDATE or PRIORITY frames in this
+ state. These frame types might arrive for a short period after a
+ frame bearing the END_STREAM flag is sent.
+
half closed (remote):
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.
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.
@@ -750,50 +765,77 @@
RST_STREAM frame.
closed:
The "closed" state is the terminal state.
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.
+ WINDOW_UPDATE or PRIORITY frames can be received in this state for
+ a short period after a a frame containing an END_STREAM flag is
+ sent. Until the remote peer receives and processes the frame
+ bearing the END_STREAM flag, it might send either frame type.
+
+ Endpoints MUST ignore WINDOW_UPDATE frames received in this state,
+ though endpoints MAY choose to treat WINDOW_UPDATE frames that
+ arrive a significant time after sending END_STREAM as a connection
+ error (Section 5.4.1) of type PROTOCOL_ERROR.
+
If this state is reached as a result of sending a RST_STREAM
frame, the peer that receives the RST_STREAM might have already
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.
+ be withdrawn. An endpoint 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.
- An endpoint might receive a PUSH_PROMISE frame after it sends
- RST_STREAM. PUSH_PROMISE causes a stream to become "reserved".
- If promised streams are not desired, a RST_STREAM can be used to
- close any of those streams.
+ Flow controlled frames (i.e., DATA) received after sending
+ RST_STREAM are counted toward the connection flow control window.
+ Even though these frames might be ignored, because they are sent
+ before the sender receives the RST_STREAM, the sender will
+ consider the frames to count against the flow control window.
+
+ An endpoint might receive a PUSH_PROMISE or a CONTINUATION frame
+ after it sends RST_STREAM. PUSH_PROMISE causes a stream to become
+ "reserved". If promised streams are not desired, a RST_STREAM can
+ be used to close any of those streams.
+
+ In the absence of more specific guidance elsewhere in this document,
+ implementations SHOULD treat the receipt of a message that is not
+ expressly permitted in the description of a state as a connection
+ error (Section 5.4.1) of type PROTOCOL_ERROR.
5.1.1. Stream Identifiers
Streams are identified with an unsigned 31-bit integer. Streams
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.
+ new stream. A stream identifier of one (0x1) is used to respond to
+ the HTTP/1.1 request which was specified during Upgrade (see
+ Section 3.2); the stream identifier one MUST NOT be used to establish
+ a new stream.
The identifier of a newly established stream MUST be numerically
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.
+ The first use of a new stream identifier implicitly closes all idle
+ streams that might have been initiated by that peer with a lower-
+ valued stream identifier.
+
Stream identifiers cannot be reused. Long-lived connections can
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.
5.1.2. Stream Concurrency
A peer can limit the 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
@@ -815,21 +857,21 @@
5.2. Flow Control
Using streams for multiplexing introduces contention over use of the
TCP connection, resulting in blocked streams. A flow control scheme
ensures that streams on the same connection do not destructively
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
- (Section 6.9) frame type.
+ frame type.
5.2.1. Flow Control Principles
Experience with TCP congestion control has shown that algorithms can
evolve over time to become more sophisticated without requiring
protocol changes. TCP congestion control and its evolution is
clearly different from HTTP/2.0 flow control, though the evolution of
TCP congestion control algorithms shows that a similar approach could
be feasible for HTTP/2.0 flow control.
@@ -844,34 +886,34 @@
and for the entire connection. This is a credit-based scheme.
3. Flow control is directional with overall control provided by the
receiver. A receiver MAY choose to set any window size that it
desires for each stream and for the entire connection. A sender
MUST respect flow control limits imposed by a receiver. Clients,
servers and intermediaries all independently advertise their flow
control preferences as a receiver and abide by the flow control
limits set by their peer when sending.
- 4. The initial value for the flow control window is 65536 bytes for
+ 4. The initial value for the flow control window is 65535 bytes for
both new streams and the overall connection.
5. The frame type determines whether flow control applies to a
frame. Of the frames specified in this document, only DATA
frames are subject to flow control; all other frame types do not
consume space in the advertised flow control window. This
ensures that important control frames are not blocked by flow
control.
6. Flow control can be disabled by a receiver. A receiver can
- choose to either disable flow control for a stream or connection
- by sending a window update frame with a specific flag. See
- Ending Flow Control (Section 6.9.4) for more details.
+ choose to disable both forms of flow control by sending the
+ SETTINGS_FLOW_CONTROL_OPTIONS setting. See Ending Flow Control
+ (Section 6.9.4) for more details.
7. HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame
(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
specify how a sender chooses to send packets. Implementations
are able to select any algorithm that suits their needs.
Implementations are also responsible for managing how requests and
responses are sent based on priority; choosing how to avoid head of
line blocking for requests; and managing the creation of new streams.
@@ -892,94 +934,99 @@
cannot be disabled for sending. Sending data is always subject to
the flow control window advertised by the receiver.
Deployments with constrained resources (for example, memory) MAY
employ flow control to limit the amount of memory a peer can consume.
Note, however, that this can lead to suboptimal use of available
network resources if flow control is enabled without knowledge of the
bandwidth-delay product (see [RFC1323]).
Even with full awareness of the current bandwidth-delay product,
- implementation of flow control is difficult. However, it can ensure
- that constrained resources are protected without any reduction in
- connection utilization.
+ implementation of flow control can be difficult. When using flow
+ control, the receive MUST read from the TCP receive buffer in a
+ timely fashion. Failure to do so could lead to a deadlock when
+ critical frames, such as WINDOW_UPDATE, are not available to
+ HTTP/2.0. However, flow control can ensure that constrained
+ resources are protected without any reduction in connection
+ utilization.
5.3. Stream priority
The endpoint establishing a new stream can assign a priority for the
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
- 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 purpose of this value is to allow an endpoint to express the
+ relative priority of a stream. An endpoint can use this information
+ to preferentially allocate resources to a stream. Within HTTP/2.0,
+ priority can be used to select streams for transmitting frames when
+ there is limited capacity for sending. For instance, an endpoint
+ might enqueue frames for all concurrently active streams. As
+ transmission capacity becomes available, frames from higher priority
+ streams might be sent before lower priority streams.
Explicitly setting the priority for a stream does not guarantee any
- particular processing order for the stream relative to any other
- stream. Nor is there 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.
+ particular processing or transmision order for the stream relative to
+ any other stream. Nor is there any mechanism provided by which the
+ initiator of a stream can force or require a receiving endpoint to
+ process concurrent streams in a particular order.
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.
+ stream creation, the default stream priority is 2^30.
+
+ Pushed streams (Section 8.2) have a lower priority than their
+ associated stream. The promised stream inherits the priority value
+ of the associated stream plus one, up to a maximum of 2^31-1.
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
+ GOAWAY frame (Section 6.8) 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.
+ endpoint MAY choose to treat a stream error as a connection error.
+ 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.
+ An endpoint that detects a stream error sends a RST_STREAM frame
+ (Section 6.4) 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
@@ -1015,35 +1062,38 @@
6.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of
octets associated with a stream. One or more DATA frames are used,
for instance, to carry HTTP request or response payloads.
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).
+ Setting this flag causes the stream to enter a "half closed" or
+ "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
received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
+ DATA frames are subject to flow control and can only be sent when a
+ stream is in the "open" or "half closed (remote)" states.
+
6.2. HEADERS
- The HEADERS frame (type=0x1) carries name-value pairs. The HEADERS
- is used to open a stream (Section 5.1). Any number of HEADERS frames
- can be sent on an existing stream at any time.
+ The HEADERS frame (type=0x1) carries name-value pairs. It is used to
+ open a stream (Section 5.1). HEADERS frames can be sent on a stream
+ in the "open" or "half closed (remote)" states.
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) |
+-+-------------------------------------------------------------+
| Header Block Fragment (*) ...
+---------------------------------------------------------------+
HEADERS Frame Payload
@@ -1055,45 +1105,47 @@
Setting this flag causes the stream to enter a "half closed" state
(Section 5.1).
RESERVED (0x2): Bit 2 is reserved for future use.
END_HEADERS (0x4): The END_HEADERS bit indicates that this frame
ends the sequence of header block fragments necessary to provide a
complete set of headers.
The payload for a complete header block is provided by a sequence
- 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.
+ of that starts with a HEADERS frame, followed by zero or more
+ CONTINUATION frames. The sequence is terminated by a frame with
+ the END_HEADERS flag set. Once the sequence terminates, the
+ payload of all HEADERS and CONTINUATION frames are concatenated
+ and interpreted as a single block.
A HEADERS frame without the END_HEADERS flag set MUST be followed
- 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
+ by a CONTINUATION frame for the same stream. A receiver MUST
+ treat the receipt of any other type of frame or a frame on a
+ different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
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).
+ (Section 4.3). A header block that does not fit within a HEADERS
+ frame is continued in a CONTINUATION frame (Section 6.10).
HEADERS frames MUST be associated with a stream. If a HEADERS frame
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
+ The HEADERS frame changes the connection state as described 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
@@ -1106,20 +1158,29 @@
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.
+ The PRIORITY frame can be sent on a stream in any of the "reserved
+ (remote)", "open", "half-closed (local)", or "half closed (remote)"
+ states, though it cannot be sent between consecutive frames that
+ comprise a single header block (Section 4.3). Note that this frame
+ could arrive after processing or frame sending has completed, which
+ would cause it to have no effect. For a stream that is in the "half
+ closed (remote)" state, this frame can only affect processing of the
+ stream and not frame transmission.
+
6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for abnormal termination of a
stream. When sent by the initiator of a stream, it indicates that
they wish to cancel the stream or that an error condition has
occurred. When sent by the receiver of a stream, it indicates that
either the receiver is rejecting the stream, requesting that the
stream be cancelled or that an error condition has occurred.
0 1 2 3
@@ -1138,66 +1199,66 @@
The RST_STREAM frame fully terminates the referenced stream and
causes it to enter the closed state. After receiving a RST_STREAM on
a stream, the receiver MUST NOT send additional frames for that
stream. However, after sending the RST_STREAM, the sending endpoint
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
the 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
- MUST respond with a connection error (Section 5.4.1) of type
+ frame is received with a stream identifier of 0x0, the recipient MUST
+ treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
+ RST_STREAM frames MUST NOT be sent for a stream in the "idle" state.
+ If a RST_STREAM frame identifying an idle stream is received, the
+ recipient MUST treat this as a connection error (Section 5.4.1) of
+ type PROTOCOL_ERROR.
+
6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that
affect how endpoints communicate. The parameters are either
constraints on peer behavior or preferences.
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
connection.
Implementations MUST support all of the settings defined by this
specification and MAY support additional settings defined by
extensions. Unsupported or unrecognized settings MUST be ignored.
New settings MUST NOT be defined or implemented in a way that
requires endpoints to understand them in order to communicate
successfully.
- A SETTINGS frame is not required to include every defined setting;
- senders can include only those parameters for which it has accurate
- 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
- single SETTINGS frame MUST NOT contain multiple values for the same
- 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
- first one.
-
- Over the lifetime of a connection, an endpoint MAY send multiple
- SETTINGS frames containing previously unspecified parameters or new
- values for parameters whose values have already been established.
- Only the most recent provided setting value applies.
+ Each setting in a SETTINGS frame replaces the existing value for that
+ setting. Settings are processed in the order in which they appear,
+ and a receiver of a SETTINGS frame does not need to maintain any
+ state other than the current value of settings. Therefore, the value
+ of a setting is the last value that is seen by a receiver. This
+ permits the inclusion of the same settings multiple times in the same
+ SETTINGS frame, though doing so does nothing other than waste
+ connection capacity.
The SETTINGS frame does not define any flags.
SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a settings frame MUST be zero. If an
endpoint receives a SETTINGS frame whose stream identifier field is
anything other than 0x0, the endpoint MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error
- (Section 5.4.1).
+ (Section 5.4.1) of type PROTOCOL_ERROR.
6.5.1. Setting Format
The payload of a SETTINGS frame consists of zero or more settings.
Each setting consists of an 8-bit reserved field, an unsigned 24-bit
setting identifier, and an unsigned 32-bit value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -1218,28 +1279,26 @@
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
not unnecessarily limit parallelism.
SETTINGS_INITIAL_WINDOW_SIZE (7): indicates the sender's initial
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
- to the sender will not be subject to flow control. The least
- significant bit (0x1) of the value is set to indicate that new
- streams are not flow controlled. All other bits are reserved.
-
- This setting applies to all streams, including existing streams.
+ SETTINGS_FLOW_CONTROL_OPTIONS (10): indicates flow control options.
+ The least significant bit (0x1) of the value is set to indicate
+ that the sender has disabled all flow control. This bit cannot be
+ cleared once set, see Section 6.9.4.
- These bits cannot be cleared once set, see Section 6.9.4.
+ All bits other than the least significant are reserved.
6.6. PUSH_PROMISE
The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint
in advance of streams the sender intends to initiate. The
PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
stream the endpoint plans to create along with a minimal set of
headers that provide additional context for the stream. Section 8.2
contains a thorough description of the use of PUSH_PROMISE frames.
@@ -1288,20 +1347,40 @@
Promised streams are not required to be used in order promised. The
PUSH_PROMISE only reserves stream identifiers for later use.
Recipients of PUSH_PROMISE frames can choose to reject promised
streams by returning a RST_STREAM referencing the promised stream
identifier back to the sender of the PUSH_PROMISE.
The PUSH_PROMISE frame modifies the connection state as defined in
Section 4.3.
+ A PUSH_PROMISE frame modifies the connection state in two ways. The
+ inclusion of a header block (Section 4.3) potentially modifies the
+ compression state. PUSH_PROMISE also reserves a stream for later
+ use, causing the promised stream to enter the "reserved" state. A
+ sender MUST NOT send a PUSH_PROMISE on a stream unless that stream is
+ either "open" or "half closed (remote)"; the sender MUST ensure that
+ the promised stream is a valid choice for a new stream identifier
+ (Section 5.1.1) (that is, the promised stream MUST be in the "idle"
+ state).
+
+ Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame
+ causes the stream state to become indeterminate. A receiver MUST
+ treat the receipt of a PUSH_PROMISE on a stream that is neither
+ "open" nor "half-closed (local)" as a connection error
+ (Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST
+ treat the receipt of a PUSH_PROMISE that promises an illegal stream
+ identifier (Section 5.1.1) (that is, an identifier for a stream that
+ is not currently in the "idle" state) as a connection error
+ (Section 5.4.1) of type PROTOCOL_ERROR.
+
6.7. PING
The PING frame (type=0x6) is a mechanism for measuring a minimal
round-trip time from the sender, as well as determining whether an
idle connection is still functional. PING frames can be sent from
any endpoint.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -1362,23 +1441,24 @@
connection so that the remote can know whether a stream has been
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
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
working. An endpoint might choose to close a connection without
sending GOAWAY for misbehaving peers.
After sending a GOAWAY frame, the sender can discard frames for new
streams. However, any frames that alter connection state cannot be
- completely ignored. For instance, HEADERS and PUSH_PROMISE frames
- MUST be minimally processed to ensure a consistent compression state
- (see Section 4.3).
+ completely ignored. For instance, HEADERS, PUSH_PROMISE and
+ CONTINUATION frames MUST be minimally processed to ensure a
+ consistent compression state (see Section 4.3); similarly DATA frames
+ MUST be counted toward the connection flow control window.
0 1 2 3
0 1 2 3 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) |
+-+-------------------------------------------------------------+
| Error Code (32) |
+---------------------------------------------------------------+
| Additional Debug Data (*) |
+---------------------------------------------------------------+
@@ -1395,20 +1474,23 @@
numbered stream identifier for which the sender of the GOAWAY frame
has received frames on and might have taken some action on. All
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
streams were processed.
Note: In this case, "processed" means that some data from the
stream was passed to some higher layer of software that might have
taken some action as a result.
+ If a connection terminates without a GOAWAY frame, this value is
+ effectively the highest stream identifier.
+
On streams with lower or equal numbered identifiers that were not
closed completely prior to the connection being closed, re-attempting
requests, transactions, or any protocol activity is not possible
(with the exception of idempotent actions like HTTP GET, PUT, or
DELETE). Any protocol activity that uses higher numbered streams can
be safely retried using a new connection.
Activity on streams numbered lower or equal to the last stream
identifier might still complete successfully. The sender of a GOAWAY
frame might gracefully shut down a connection by sending a GOAWAY
@@ -1454,40 +1536,49 @@
+-+-------------------------------------------------------------+
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
- frames do not need to be flow controlled.
+ The WINDOW_UPDATE frame does not define any flags.
The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame.
+ WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the
+ END_STREAM flag. This means that a receiver could receive a
+ WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream.
+ A receiver MUST NOT treat this as an error, see Section 5.1.
+
+ A receiver that receives a flow controlled frame MUST always account
+ for its contribution against the connection flow control window,
+ unless the receiver treats this as a connection error
+ (Section 5.4.1). This is necessary even if the frame is in error.
+ Since the sender counts the frame toward the flow control window, if
+ the receiver does not, the flow control window at sender and receiver
+ can become different.
+
6.9.1. The Flow Control Window
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
value that indicates how many bytes of data the sender is permitted
to transmit; as such, its size is a measure of the buffering
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
send a flow controlled frame with a length that exceeds the space
available in either of the flow control windows advertised by the
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
space in either flow control window.
For flow control calculations, the 8 byte frame header is not
counted.
@@ -1535,24 +1626,24 @@
windows that it maintains by the difference between the new value and
the old value. A SETTINGS frame cannot alter the connection flow
control window.
A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available
space in a flow control window to become negative. A sender MUST
track the negative flow control window, and MUST NOT send new flow
controlled frames until it receives WINDOW_UPDATE frames that cause
the flow control window to become positive.
- For example, if the client sends 64KB immediately on connection
+ For example, if the client sends 60KB immediately on connection
establishment, and the server sets the initial window size to be
16KB, the client will recalculate the available flow control window
- to be -48KB on receipt of the SETTINGS frame. The client retains a
+ to be -44KB on receipt of the SETTINGS frame. The client retains a
negative flow control window until WINDOW_UPDATE frames restore the
window to being positive, after which the client can resume sending.
6.9.3. Reducing the Stream Window Size
A receiver that wishes to use a smaller flow control window than the
current size can send a new SETTINGS frame. However, the receiver
MUST be prepared to receive data that exceeds this window size, since
the sender might send data that exceeds the lower limit prior to
processing the SETTINGS frame.
@@ -1572,35 +1663,86 @@
sent in the SETTINGS.
6.9.4. Ending Flow Control
After a receiver reads in a frame that marks the end of a stream (for
example, a data stream with a END_STREAM flag set), it MUST cease
transmission of WINDOW_UPDATE frames for that stream. A sender is
not obligated to maintain the available flow control window for
streams that it is no longer sending on.
- Flow control can be disabled for all streams on the connection using
- the SETTINGS_FLOW_CONTROL_OPTIONS setting. An implementation that
- does not wish to perform stream flow control can use this in the
- initial SETTINGS exchange.
-
- Flow control can be disabled for an individual stream or the overall
- connection by sending a WINDOW_UPDATE with the END_FLOW_CONTROL flag
- set. The payload of a WINDOW_UPDATE frame that has the
- END_FLOW_CONTROL flag set is ignored.
+ Flow control can be disabled the entire connection using the
+ SETTINGS_FLOW_CONTROL_OPTIONS setting. This setting ends all forms
+ of flow control. An implementation that does not wish to perform
+ flow control can use this in the initial SETTINGS exchange.
Flow control cannot be enabled again once disabled. Any attempt to
re-enable flow control - by sending a WINDOW_UPDATE or by clearing
the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
rejected with a FLOW_CONTROL_ERROR error code.
+6.10. CONTINUATION
+
+ The CONTINUATION frame (type=0xA) is used to continue a sequence of
+ header block fragments (Section 4.3). Any number of CONTINUATION
+ frames can be sent on an existing stream, as long as the preceding
+ frame on the same stream is one of HEADERS, PUSH_PROMISE or
+ CONTINUATION.
+
+ 0 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Header Block Fragment (*) ...
+ +---------------------------------------------------------------+
+
+ CONTINUATION Frame Payload
+
+ The CONTINUATION frame defines the following flags:
+
+ END_STREAM (0x1): Bit 1 being set indicates that this frame is the
+ last that the endpoint will send for the identified stream.
+ Setting this flag causes the stream to enter a "half closed" or
+ "closed" state (Section 5.1).
+
+ END_HEADERS (0x2): The END_HEADERS bit indicates that this frame
+ ends the sequence of header block fragments necessary to provide a
+ complete set of headers.
+
+ The payload for a complete header block is provided by a sequence
+ that starts with a HEADERS or PUSH_PROMISE frame and zero or more
+ CONTINUATION frames, terminated by a HEADERS, PUSH_PROMISE, or
+ CONTINUATION frame with the END_HEADERS flag set. Once the
+ sequence terminates, the payload of all frames in the sequence are
+ concatenated and interpreted as a single block.
+
+ A HEADERS, PUSH_PROMISE, or CONTINUATION frame without the
+ END_HEADERS flag set MUST be followed by a CONTINUATION frame for
+ the same stream. A receiver MUST treat the receipt of any other
+ type of frame or a frame on a different stream as a connection
+ error (Section 5.4.1) of type PROTOCOL_ERROR.
+
+ The payload of a CONTINUATION frame contains a header block fragment
+ (Section 4.3).
+
+ The CONTINUATION frame changes the connection state as defined in
+ Section 4.3.
+
+ CONTINUATION frames MUST be associated with a stream. If a
+ CONTINUATION frame is received whose stream identifier field is 0x0,
+ the recipient MUST respond with a connection error (Section 5.4.1) of
+ type PROTOCOL_ERROR.
+
+ header block fragments (Section 4.3). A CONTINUATION frame MUST be
+ preceded by one of HEADERS, PUSH_PROMISE or CONTINUATION frame. A
+ recipient that observes violation of this rule MUST respond with a
+ connection error (Section 5.4.1) of type PROTOCOL_ERROR.
+
7. Error Codes
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:
@@ -1619,21 +1761,21 @@
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
+ performing any application processing, see Section 8.1.3 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
@@ -1647,211 +1789,207 @@
[HTTP-p7]) apply with the changes in the sections below.
8.1. HTTP Request/Response Exchange
A client sends an HTTP request on a new stream, using a previously
unused stream identifier (Section 5.1.1). A server sends an HTTP
response on the same stream as the request.
An HTTP request or response each consist of:
- o one contiguous sequence of HEADERS frames;
+ 1. a HEADERS frame;
- o zero or more DATA frames; and
+ 2. one contiguous sequence of zero or more CONTINUATION frames;
- o optionally, a contiguous sequence of HEADERS frames
+ 3. zero or more DATA frames; and
+
+ 4. optionally, a contiguous sequence that starts with a HEADERS
+ frame, followed by zero or more CONTINUATION frames.
The last frame in the sequence bears an END_STREAM flag.
- Other frames, including HEADERS, MAY be interspersed with these
- frames, but those frames do not carry HTTP semantics.
+ Other frames MAY be interspersed with these frames, but those frames
+ do not carry HTTP semantics. In particular, HEADERS frames (and any
+ CONTINUATION frames that follow) other than the first and optional
+ last frames in this sequence do not carry HTTP semantics.
Trailing header fields are carried in a header block that also
- terminates the stream. That is, a sequence of HEADERS frames that
- carries an END_STREAM flag on the last frame. Header blocks after
- the first that do not terminate the stream are not part of an HTTP
- request or response.
+ terminates the stream. That is, a sequence starting with a HEADERS
+ frame, followed by zero or more CONTINUATION frames, that carries an
+ END_STREAM flag on the last frame. Header blocks after 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
+ :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:
+ data is transmitted as one HEADERS frame, followed by zero or more
+ CONTINUATION frames, containing the request headers followed by one
+ or more DATA frames, with the last CONTINUATION (or 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
+ 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:
+ transmitted as a HEADERS frame, followed by zero or more CONTINUATION
+ 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.
+ sent. The sequence of HEADERS/CONTINUATION 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
- fields named :method and :path, whose values specify the HTTP
- method for the request and the request-target, respectively. The
- HTTP-version component of the request-line is removed entirely
- from the headers.
-
- o The host and optional port portions of the request URI (see
- [RFC3986], Section 3.2), are specified using the new :host header
- field. [[anchor13: Ed. Note: it needs to be clarified whether or
- not this replaces the existing HTTP/1.1 Host header.]]
-
- o A new :scheme header field has been added to specify the scheme
- portion of the request-target (e.g. "https")
+8.1.2. HTTP Header Fields
- 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
- lowercase.
+ HTTP/2.0 request and response header fields carry information as a
+ series of key-value pairs. This includes the target URI for the
+ request, the status code for the response, as well as HTTP header
+ fields.
- o The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
- Encoding header fields are no longer valid and MUST NOT be sent.
- [[anchor14: Ed. Note: And "TE" I presume?]]
+ HTTP header field names are strings of ASCII characters that are
+ compared in a case-insensitive fashion. Note that header compression
+ could cause case information to be lost.
- All HTTP Requests MUST include the ":method", ":path", ":host", and
- ":scheme" header fields.
+ The semantics of HTTP header fields are not altered by this
+ specification, though header fields relating to connection management
+ or request framing are no longer necessary. An HTTP/2.0 request MUST
+ NOT include any of the following header fields: Connection, Host,
+ Keep-Alive, Proxy-Connection, TE, Transfer-Encoding, and Upgrade. A
+ server MUST treat the presence of any of these header fields as a
+ stream error (Section 5.4.2) of type PROTOCOL_ERROR.
- Header fields whose names begin with ":" (whether defined in this
- document or future extensions to this document) MUST appear before
- any other header fields. [[anchor15: Ed. Note: This requirement is
- currently pending review. Consider it "on hold" for the moment.]]
+8.1.2.1. Request Header Fields
- All HTTP Requests that include a body SHOULD include the "content-
- length" header field. If a server receives a request where the sum
- of the DATA frame payload lengths does not equal the value of the
- "content-length" header field, the server MUST return a 400 (Bad
- Request) error.
+ HTTP/2.0 defines a number of headers starting with a ':' character
+ that carry information about the request target:
- If a client omits a mandatory header field from the request, the
- server MUST reply with a HTTP 400 Bad Request reply.
+ o The ":method" header field includes the HTTP method ([HTTP-p2],
+ Section 4).
-8.1.3. Response Header Fields
+ o The ":scheme" header field includes the scheme portion of the
+ target URI ([RFC3986], Section 3.1).
- The definitions of the response header fields are largely unchanged
- relative to HTTP/1.1, with a few notable exceptions:
+ o The ":host" header field includes the authority portion of the
+ target URI ([RFC3986], Section 3.2).
- 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.
+ o The ":path" header field includes the path and query parts of the
+ target URI (the "path-absolute" production from [RFC3986] and
+ optionally a '?' character followed by the "query" production, see
+ [RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field
+ MUST NOT be empty; URIs that do not contain a path component MUST
+ include a value of '/', unless the request is an OPTIONS request
+ for '*', in which case the ":path" header field MUST include '*'.
- o The response MUST contain exactly one :status header field with
- exactly one response status value. If the client receives an HTTP
- response that does not include the :status field, or provides
- multiple response status code values, it MUST respond with a
- stream error (Section 5.4.2) of type PROTOCOL_ERROR.
+ All HTTP/2.0 requests MUST include exactly one valid value for all of
+ these header fields. An intermediary MUST ensure that requests that
+ it forwards are correct. A server MUST treat the absence of any of
+ these header fields, presence of multiple values, or an invalid value
+ as a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
- 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
- lowercase.
+ HTTP/2.0 does not define a way to carry the version identifier that
+ is included in the HTTP/1.1 request line.
- o The Connection, Keep-Alive, Proxy-Connection, and Transfer-
- Encoding header fields are not valid and MUST NOT be sent.
+ All HTTP Requests that include a body can include a "content-length"
+ header field. If a server receives a request where the sum of the
+ DATA frame payload lengths does not equal the value of the
+ "content-length" header field, the server MUST return a 400 (Bad
+ Request) error.
- Header fields whose names begin with ":" (whether defined in this
- document or future extensions to this document) MUST appear before
- any other header fields. [[anchor16: Ed. Note: This requirement is
- currently pending review. Consider it "on hold" for the moment.]]
+8.1.2.2. Response Header Fields
-8.1.4. GZip Content-Encoding
+ A single ":status" header field is defined that carries the HTTP
+ status code field (see [HTTP-p2], Section 6). This header field MUST
+ be included in all responses. An intermediary MUST ensure that it
+ does not forward responses with absent or invalid values. A client
+ MUST treat the absence of the ":status"" header field, the presence
+ of multiple values, or an invalid value as a stream error
+ (Section 5.4.2) of type PROTOCOL_ERROR.
- Clients MUST support gzip compression for HTTP response bodies.
- 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.
+ HTTP/2.0 does not define a way to carry the version or reason phrase
+ that is included in an HTTP/1.1 status line.
-8.1.5. Request Reliability Mechanisms in HTTP/2.0
+8.1.3. Request Reliability Mechanisms in HTTP/2.0
In HTTP/1.1, an HTTP client is unable to retry a non-idempotent
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.
HTTP/2.0 provides two mechanisms for providing a guarantee to a
client that a request has not been processed:
@@ -1890,109 +2028,109 @@
process the originally requested resource.
Pushing additional resources is optional, and is negotiated only
between individual endpoints. For instance, an intermediary could
receive pushed resources from the server but is not required to
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.
+8.2.1. Push Requests
+
Server push is semantically equivalent to a server responding to a
- GET request for that resource. The PUSH_PROMISE frame, or frames,
- sent by the server includes a header block that contains the request
- headers that the server has assumed.
+ request. The PUSH_PROMISE frame, or frames, sent by the server
+ includes a header block that contains a complete set of request
+ headers that the server attributes to the request. It is not
+ possible to push a response to a request that includes a request
+ body.
Pushed resources are always associated with an explicit request from
a client. The PUSH_PROMISE frames sent by the server are sent on the
- stream created for the original request. The PUSH_PROMSE frame
+ stream created for the original request. The PUSH_PROMISE frame
includes a promised stream identifier, chosen from the stream
- 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.
-
- The header fields in PUSH_PROMISE MUST include the ":scheme", ":host"
- and ":path" header fields that identify the resource that is being
- pushed. A PUSH_PROMISE always implies an HTTP method of GET. If a
- client receives a PUSH_PROMISE that does not include these header
- fields, or a value for the ":method" header field, it MUST respond
- with a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
-
- After sending the PUSH_PROMISE frame, the server can begin delivering
- the pushed resource on a new, server-initiated stream that uses the
- promised stream identifier. This stream is already implicitly "half
- closed" to the client (Section 5.1). The server uses this stream to
- transmit an HTTP response, using the same sequence of frames as
- defined in Section 8.1.
+ identifiers available to the server (see Section 5.1.1).
- Once a client receives a PUSH_PROMISE frame and chooses to accept the
- pushed resource, the client SHOULD NOT issue any subsequent GET
- requests for the promised resource until after the promised stream
- has closed.
+ The header fields in PUSH_PROMISE and any subsequent CONTINUATION
+ frames MUST be a valid and complete set of request headers
+ (Section 8.1.2.1). The server MUST include a method in the ":method"
+ header field that is safe (see [HTTP-p2], Section 4.2.1). If a
+ client receives a PUSH_PROMISE that does not include a complete and
+ valid set of header fields, or the ":method" header field identifies
+ a method that is not safe, it MUST respond with a stream error
+ (Section 5.4.2) of type PROTOCOL_ERROR.
The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to
- sending any HEADERS or DATA frames that reference the promised
- resources. This avoids a race where clients issue requests for
- resources prior to receiving any PUSH_PROMISE frames.
+ sending any frames that reference the promised resources. This
+ avoids a race where clients issue requests for resources prior to
+ receiving any PUSH_PROMISE frames.
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
+ resources. Similarly, 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.
PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE
frames can be sent by the server on any stream that was opened by the
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
+ or "half closed (remote)" to the server. PUSH_PROMISE frames are
+ interspersed with the frames that comprise a response, though they
+ cannot be interspersed with HEADERS and CONTINUATION frames that
comprise a single header block.
+8.2.2. Push Responses
+
+ After sending the PUSH_PROMISE frame, the server can begin delivering
+ the pushed resource as a response (Section 8.1.2.2) on a server-
+ initiated stream that uses the promised stream identifier. The
+ server uses this stream to transmit an HTTP response, using the same
+ sequence of frames as defined in Section 8.1. This stream becomes
+ "half closed" to the client (Section 5.1) after the initial HEADERS
+ frame is sent.
+
+ Once a client receives a PUSH_PROMISE frame and chooses to accept the
+ pushed resource, the client SHOULD NOT issue any requests for the
+ promised resource until after the promised stream has closed.
+
+ If the client determines, for any reason, that it does not wish to
+ receive the pushed resource from the server, or if the server takes
+ too long to begin sending the promised resource, the client can send
+ an RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
+ and referencing the pushed stream's identifier.
+
A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
the number of resources that can be concurrently pushed by a server.
Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables
server push by preventing the server from creating the necessary
- streams.
-
- The request header fields provided in the PUSH_PROMISE frame SHOULD
- include enough information for a client to determine whether a cached
- representation of the resource is already available. If the client
- determines, for any reason, that it does not wish to receive the
- pushed resource from the server, or if the server takes too long to
- begin sending the promised resource, the client can send an
- RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
- and referencing the pushed stream's identifier.
+ streams. This does not prohibit a server from sending PUSH_PROMISE
+ frames; clients need to reset any promised streams that are not
+ wanted.
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
+ "example.com" is generally [[anchor15: Ed: weaselly use of
"generally", needs better definition]] not permitted to push a
response for "www.example.org".
9. Additional HTTP Requirements/Considerations
- TODO: SNI, gzip and deflate Content-Encoding, etc..
-
-9.1. Frame Size Limits for HTTP
-
- Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
- in length, not counting the 8 octet frame header. An endpoint MUST
- treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
- Section 4.2).
+ This section outlines attributes of the HTTP protocol that improve
+ interoperability, reduce exposure to known security vulnerabilities,
+ or reduce the potential for implementation variation.
-9.2. Connection Management
+9.1. Connection Management
HTTP/2.0 connections are persistent. For best performance, it is
expected 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.
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
@@ -2001,20 +2139,57 @@
(Section 5.4.1).
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 6.8) frame so that both endpoints can reliably determine
whether previously sent frames have been processed and gracefully
complete or terminate any necessary remaining tasks.
+9.2. Use of TLS Features
+
+ Implementations of HTTP/2.0 MUST support TLS 1.1 [TLS11]. [[anchor18:
+ The working group intends to require at least the use of TLS 1.2
+ [TLS12] prior to publication of this document; negotiating TLS 1.1 is
+ permitted to enable the creation of interoperable implementations of
+ early drafts.]]
+
+ The TLS implementation MUST support the Server Name Indication (SNI)
+ [TLS-EXT] extension to TLS. HTTP/2.0 clients MUST indicate the
+ target domain name when negotiating TLS.
+
+ A server that receives a TLS handshake that does not include either
+ TLS 1.1 or SNI, MUST NOT negotiate HTTP/2.0. Removing HTTP/2.0
+ protocols from consideration could result in the removal of all
+ protocols from the set of protocols offered by the client. This
+ causes protocol negotiation failure, as described in Section 3.2 of
+ [TLSALPN].
+
+ Implementations are encouraged not to negotiate TLS cipher suites
+ with known vulnerabilities, such as [RC4].
+
+9.3. Frame Size Limits for HTTP
+
+ Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
+ in length, not counting the 8 octet frame header. An endpoint MUST
+ treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
+ Section 4.2).
+
+9.4. GZip Content-Encoding
+
+ Clients MUST support gzip compression for HTTP response bodies.
+ Regardless of the value of the accept-encoding header field, a server
+ MAY send responses with gzip or deflate encoding. A compressed
+ response MUST still bear an appropriate content-encoding header
+ field.
+
10. Security Considerations
10.1. Server Authority and Same-Origin
This specification uses the same-origin policy ([RFC6454], Section 3)
to determine whether an origin server is permitted to provide
content.
A server that is contacted using TLS is authenticated based on the
certificate that it offers in the TLS handshake (see [RFC2818],
@@ -2092,35 +2267,38 @@
Frame types are an 8-bit value. When reviewing new frame type
registrations, special attention is advised for any frame type-
specific flags that are defined. Frame flags can interact with
existing flags and could prevent the creation of globally applicable
flags.
Initial values for the "HTTP/2.0 Frame Type" registry are shown in
Table 1.
- +-----------+---------------+---------------------------------------+
- | Frame | Name | Flags |
- | Type | | |
- +-----------+---------------+---------------------------------------+
- | 0 | DATA | END_STREAM(1) |
- | 1 | HEADERS | END_STREAM(1), END_HEADERS(4), |
- | | | PRIORITY(8) |
- | 2 | PRIORITY | - |
- | 3 | RST_STREAM | - |
- | 4 | SETTINGS | - |
- | 5 | PUSH_PROMISE | END_PUSH_PROMISE(1) |
- | 6 | PING | PONG(1) |
- | 7 | GOAWAY | - |
- | 9 | WINDOW_UPDATE | END_FLOW_CONTROL(1) |
- +-----------+---------------+---------------------------------------+
+ +--------+---------------+---------------------------+--------------+
+ | Frame | Name | Flags | Section |
+ | Type | | | |
+ +--------+---------------+---------------------------+--------------+
+ | 0 | DATA | END_STREAM(1) | Section 6.1 |
+ | 1 | HEADERS | END_STREAM(1), | Section 6.2 |
+ | | | END_HEADERS(4), | |
+ | | | PRIORITY(8) | |
+ | 2 | PRIORITY | - | Section 6.3 |
+ | 3 | RST_STREAM | - | Section 6.4 |
+ | 4 | SETTINGS | - | Section 6.5 |
+ | 5 | PUSH_PROMISE | END_PUSH_PROMISE(1) | Section 6.6 |
+ | 6 | PING | PONG(1) | Section 6.7 |
+ | 7 | GOAWAY | - | Section 6.8 |
+ | 9 | WINDOW_UPDATE | - | Section 6.9 |
+ | 10 | CONTINUATION | END_STREAM(1), | Section 6.10 |
+ | | | END_HEADERS(4) | |
+ +--------+---------------+---------------------------+--------------+
Table 1
12.2. Error Code Registry
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
Error Code" registry operates under the "Expert Review" policy
[RFC5226].
@@ -2181,21 +2359,22 @@
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)
+ Specification document(s): Section 3.2.1 of 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
individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
@@ -2213,47 +2392,47 @@
14. References
14.1. Normative References
[COMPRESSION] Ruellan, H. and R. Peon, "HTTP Header Compression",
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),
- February 2013.
+ draft-ietf-httpbis-p1-messaging-23 (work in progress),
+ July 2013.
[HTTP-p2] Fielding, R. and J. Reschke, "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content",
- draft-ietf-httpbis-p2-semantics-22 (work in progress),
- February 2013.
+ draft-ietf-httpbis-p2-semantics-23 (work in progress),
+ July 2013.
[HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests",
- draft-ietf-httpbis-p4-conditional-22 (work in
- progress), February 2013.
+ draft-ietf-httpbis-p4-conditional-23 (work in
+ progress), July 2013.
[HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range
- Requests", draft-ietf-httpbis-p5-range-22 (work in
- progress), February 2013.
+ Requests", draft-ietf-httpbis-p5-range-23 (work in
+ progress), July 2013.
[HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J.
Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1):
- Caching", draft-ietf-httpbis-p6-cache-22 (work in
- progress), February 2013.
+ Caching", draft-ietf-httpbis-p6-cache-23 (work in
+ progress), July 2013.
[HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication",
- draft-ietf-httpbis-p7-auth-22 (work in progress),
- February 2013.
+ draft-ietf-httpbis-p7-auth-23 (work in progress),
+ July 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
@@ -2263,76 +2442,113 @@
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
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,
December 2011.
+ [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS)
+ Extensions: Extension Definitions", RFC 6066,
+ January 2011.
+
+ [TLS11] Dierks, T. and E. Rescorla, "The Transport Layer
+ Security (TLS) Protocol Version 1.1", RFC 4346,
+ April 2006.
+
+ [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer
+ Security (TLS) Protocol Version 1.2", RFC 5246,
+ August 2008.
+
[TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application Layer
Protocol Negotiation Extension",
draft-ietf-tls-applayerprotoneg-01 (work in progress),
April 2013.
14.2. Informative References
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
+ [RC4] Rivest, R., "The RC4 encryption algorithm", RSA Data
+ Security, Inc. , March 1992.
+
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP
Extensions for High Performance", RFC 1323, May 1992.
[TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
Jackson, "Talking to Yourself for Fun and Profit",
2011, .
Appendix A. Change Log (to be removed by RFC Editor before publication)
-A.1. Since draft-ietf-httpbis-http2-03
+A.1. Since draft-ietf-httpbis-http2-04
+
+ Added CONTINUATION frame for HEADERS and PUSH_PROMISE.
+
+ PUSH_PROMISE is no longer implicitly prohibited if
+ SETTINGS_MAX_CONCURRENT_STREAMS is zero.
+
+ Push expanded to allow all safe methods without a request body.
+
+ Clarified the use of HTTP header fields in requests and responses.
+
+ Prohibited HTTP/1.1 hop-by-hop header fields.
+
+ Requiring that intermediaries not forward requests with missing or
+ illegal routing :-headers.
+
+ Clarified requirements around handling different frames after stream
+ close, stream reset and GOAWAY.
+
+ Added more specific prohibitions for sending of different frame types
+ in various stream states.
+
+ Making the last received setting value the effective value.
+
+ Clarified requirements on TLS version, extension and ciphers.
+
+A.2. Since draft-ietf-httpbis-http2-03
Committed major restructuring atrocities.
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
+A.3. Since draft-ietf-httpbis-http2-02
Added continuations to frames carrying header blocks.
Replaced use of "session" with "connection" to avoid confusion with
other HTTP stateful concepts, like cookies.
Removed "message".
Switched to TLS ALPN from NPN.
Editorial changes.
-A.3. Since draft-ietf-httpbis-http2-01
+A.4. Since draft-ietf-httpbis-http2-01
Added IANA considerations section for frame types, error codes and
settings.
Removed data frame compression.
Added PUSH_PROMISE.
Added globally applicable flags to framing.
@@ -2351,39 +2567,39 @@
Restructured frame header. Removed distinction between data and
control frames.
Altered flow control properties to include session-level limits.
Added note on cacheability of pushed resources and multiple tenant
servers.
Changed protocol label form based on discussions.
-A.4. Since draft-ietf-httpbis-http2-00
+A.5. Since draft-ietf-httpbis-http2-00
Changed title throughout.
Removed section on Incompatibilities with SPDY draft#2.
Changed INTERNAL_ERROR on GOAWAY to have a value of 2 .
Replaced abstract and introduction.
Added section on starting HTTP/2.0, including upgrade mechanism.
Removed unused references.
Added flow control principles (Section 5.2.1) based on .
-A.5. Since draft-mbelshe-httpbis-spdy-00
+A.6. Since draft-mbelshe-httpbis-spdy-00
Adopted as base for draft-ietf-httpbis-http2.
Updated authors/editors list.
Added status note.
Authors' Addresses
Mike Belshe