draft-ietf-httpbis-http2bis-07.txt   draft-ietf-httpbis-http2bis-latest.txt 
HTTPbis Working Group M. Thomson, Ed. Internet Engineering Task Force (IETF) M. Thomson, Ed.
Internet-Draft Mozilla Request for Comments: 9113 Mozilla
Obsoletes: 7540, 8740 (if approved) C. Benfield, Ed. Obsoletes: 7540, 8740 C. Benfield, Ed.
Intended status: Standards Track Apple Inc. Category: Standards Track Apple Inc.
Expires: July 28, 2022 January 24, 2022 ISSN: 2070-1721 May 2022
HTTP/2 HTTP/2
draft-ietf-httpbis-http2bis-07
Abstract Abstract
This specification describes an optimized expression of the semantics This specification describes an optimized expression of the semantics
of the Hypertext Transfer Protocol (HTTP), referred to as HTTP of the Hypertext Transfer Protocol (HTTP), referred to as HTTP
version 2 (HTTP/2). HTTP/2 enables a more efficient use of network version 2 (HTTP/2). HTTP/2 enables a more efficient use of network
resources and a reduced latency by introducing field compression and resources and a reduced latency by introducing field compression and
allowing multiple concurrent exchanges on the same connection. allowing multiple concurrent exchanges on the same connection.
This document obsoletes RFC 7540 and RFC 8740. This document obsoletes RFCs 7540 and 8740.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the HTTPBIS Working Group
mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Source for this draft and an issue tracker can be found at
<https://github.com/httpwg/http2-spec>.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
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 https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on July 28, 2022. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9113.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
2. HTTP/2 Protocol Overview . . . . . . . . . . . . . . . . . . 5 2. HTTP/2 Protocol Overview
2.1. Document Organization . . . . . . . . . . . . . . . . . . 6 2.1. Document Organization
2.2. Conventions and Terminology . . . . . . . . . . . . . . . 6 2.2. Conventions and Terminology
3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 7 3. Starting HTTP/2
3.1. HTTP/2 Version Identification . . . . . . . . . . . . . . 8 3.1. HTTP/2 Version Identification
3.2. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 8 3.2. Starting HTTP/2 for "https" URIs
3.3. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 8 3.3. Starting HTTP/2 with Prior Knowledge
3.4. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 9 3.4. HTTP/2 Connection Preface
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. HTTP Frames
4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Frame Format
4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Frame Size
4.3. Field Section Compression and Decompression . . . . . . . 12 4.3. Field Section Compression and Decompression
4.3.1. Compression State . . . . . . . . . . . . . . . . . . 13 4.3.1. Compression State
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 14 5. Streams and Multiplexing
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 14 5.1. Stream States
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20 5.1.1. Stream Identifiers
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21 5.1.2. Stream Concurrency
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 21 5.2. Flow Control
5.2.1. Flow-Control Principles . . . . . . . . . . . . . . . 21 5.2.1. Flow-Control Principles
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23 5.2.2. Appropriate Use of Flow Control
5.2.3. Flow Control Performance . . . . . . . . . . . . . . 23 5.2.3. Flow-Control Performance
5.3. Prioritization . . . . . . . . . . . . . . . . . . . . . 24 5.3. Prioritization
5.3.1. Background on Priority in RFC 7540 . . . . . . . . . 24 5.3.1. Background on Priority in RFC 7540
5.3.2. Priority Signaling in this Document . . . . . . . . . 24 5.3.2. Priority Signaling in This Document
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 25 5.4. Error Handling
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 26 5.4.1. Connection Error Handling
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 26 5.4.2. Stream Error Handling
5.4.3. Connection Termination . . . . . . . . . . . . . . . 27 5.4.3. Connection Termination
5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 27 5.5. Extending HTTP/2
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 28 6. Frame Definitions
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.1. DATA
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.2. HEADERS
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 32 6.3. PRIORITY
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 33 6.4. RST_STREAM
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 34 6.5. SETTINGS
6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 35 6.5.1. SETTINGS Format
6.5.2. Defined Settings . . . . . . . . . . . . . . . . . . 36 6.5.2. Defined Settings
6.5.3. Settings Synchronization . . . . . . . . . . . . . . 38 6.5.3. Settings Synchronization
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38 6.6. PUSH_PROMISE
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.7. PING
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 42 6.8. GOAWAY
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 45 6.9. WINDOW_UPDATE
6.9.1. The Flow-Control Window . . . . . . . . . . . . . . . 47 6.9.1. The Flow-Control Window
6.9.2. Initial Flow-Control Window Size . . . . . . . . . . 48 6.9.2. Initial Flow-Control Window Size
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 49 6.9.3. Reducing the Stream Window Size
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 49 6.10. CONTINUATION
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 50 7. Error Codes
8. Expressing HTTP Semantics in HTTP/2 . . . . . . . . . . . . . 51 8. Expressing HTTP Semantics in HTTP/2
8.1. HTTP Message Framing . . . . . . . . . . . . . . . . . . 51 8.1. HTTP Message Framing
8.1.1. Malformed Messages . . . . . . . . . . . . . . . . . 53 8.1.1. Malformed Messages
8.2. HTTP Fields . . . . . . . . . . . . . . . . . . . . . . . 54 8.2. HTTP Fields
8.2.1. Field Validity . . . . . . . . . . . . . . . . . . . 54 8.2.1. Field Validity
8.2.2. Connection-Specific Header Fields . . . . . . . . . . 55 8.2.2. Connection-Specific Header Fields
8.2.3. Compressing the Cookie Header Field . . . . . . . . . 56 8.2.3. Compressing the Cookie Header Field
8.3. HTTP Control Data . . . . . . . . . . . . . . . . . . . . 56 8.3. HTTP Control Data
8.3.1. Request Pseudo-Header Fields . . . . . . . . . . . . 57 8.3.1. Request Pseudo-Header Fields
8.3.2. Response Pseudo-Header Fields . . . . . . . . . . . . 59 8.3.2. Response Pseudo-Header Fields
8.4. Server Push . . . . . . . . . . . . . . . . . . . . . . . 59 8.4. Server Push
8.4.1. Push Requests . . . . . . . . . . . . . . . . . . . . 60 8.4.1. Push Requests
8.4.2. Push Responses . . . . . . . . . . . . . . . . . . . 62 8.4.2. Push Responses
8.5. The CONNECT Method . . . . . . . . . . . . . . . . . . . 63 8.5. The CONNECT Method
8.6. The Upgrade Header Field . . . . . . . . . . . . . . . . 64 8.6. The Upgrade Header Field
8.7. Request Reliability . . . . . . . . . . . . . . . . . . . 64 8.7. Request Reliability
8.8. Examples . . . . . . . . . . . . . . . . . . . . . . . . 65 8.8. Examples
8.8.1. Simple Request . . . . . . . . . . . . . . . . . . . 65 8.8.1. Simple Request
8.8.2. Simple Response . . . . . . . . . . . . . . . . . . . 65 8.8.2. Simple Response
8.8.3. Complex Request . . . . . . . . . . . . . . . . . . . 66 8.8.3. Complex Request
8.8.4. Response with Body . . . . . . . . . . . . . . . . . 66 8.8.4. Response with Body
8.8.5. Informational Responses . . . . . . . . . . . . . . . 67 8.8.5. Informational Responses
9. HTTP/2 Connections . . . . . . . . . . . . . . . . . . . . . 68 9. HTTP/2 Connections
9.1. Connection Management . . . . . . . . . . . . . . . . . . 68 9.1. Connection Management
9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 68 9.1.1. Connection Reuse
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 69 9.2. Use of TLS Features
9.2.1. TLS 1.2 Features . . . . . . . . . . . . . . . . . . 70 9.2.1. TLS 1.2 Features
9.2.2. TLS 1.2 Cipher Suites . . . . . . . . . . . . . . . . 71 9.2.2. TLS 1.2 Cipher Suites
9.2.3. TLS 1.3 Features . . . . . . . . . . . . . . . . . . 71 9.2.3. TLS 1.3 Features
10. Security Considerations . . . . . . . . . . . . . . . . . . . 72 10. Security Considerations
10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 72 10.1. Server Authority
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 72 10.2. Cross-Protocol Attacks
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 73 10.3. Intermediary Encapsulation Attacks
10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 73 10.4. Cacheability of Pushed Responses
10.5. Denial-of-Service Considerations . . . . . . . . . . . . 74 10.5. Denial-of-Service Considerations
10.5.1. Limits on Field Block Size . . . . . . . . . . . . . 75 10.5.1. Limits on Field Block Size
10.5.2. CONNECT Issues . . . . . . . . . . . . . . . . . . . 76 10.5.2. CONNECT Issues
10.6. Use of Compression . . . . . . . . . . . . . . . . . . . 76 10.6. Use of Compression
10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . 77 10.7. Use of Padding
10.8. Privacy Considerations . . . . . . . . . . . . . . . . . 77 10.8. Privacy Considerations
10.9. Remote Timing Attacks . . . . . . . . . . . . . . . . . 78 10.9. Remote Timing Attacks
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 78 11. IANA Considerations
11.1. HTTP2-Settings Header Field Registration . . . . . . . . 79 11.1. HTTP2-Settings Header Field Registration
11.2. The h2c Upgrade Token . . . . . . . . . . . . . . . . . 79 11.2. The h2c Upgrade Token
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 79 12. References
12.1. Normative References . . . . . . . . . . . . . . . . . . 79 12.1. Normative References
12.2. Informative References . . . . . . . . . . . . . . . . . 81 12.2. Informative References
Appendix A. Prohibited TLS 1.2 Cipher Suites . . . . . . . . . . 83 Appendix A. Prohibited TLS 1.2 Cipher Suites
Appendix B. Changes from RFC 7540 . . . . . . . . . . . . . . . 89 Appendix B. Changes from RFC 7540
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Acknowledgments
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 90 Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 91 Authors' Addresses
1. Introduction 1. Introduction
The performance of applications using the Hypertext Transfer Protocol The performance of applications using the Hypertext Transfer Protocol
(HTTP, [HTTP]) is linked to how each version of HTTP uses the (HTTP, [HTTP]) is linked to how each version of HTTP uses the
underlying transport, and the conditions under which the transport underlying transport, and the conditions under which the transport
operates. operates.
Making multiple concurrent requests can reduce latency and improve Making multiple concurrent requests can reduce latency and improve
application performance. HTTP/1.0 allowed only one request to be application performance. HTTP/1.0 allowed only one request to be
outstanding at a time on a given TCP [TCP] connection. HTTP/1.1 outstanding at a time on a given TCP [TCP] connection. HTTP/1.1
([HTTP11]) added request pipelining, but this only partially [HTTP/1.1] added request pipelining, but this only partially
addressed request concurrency and still suffers from application- addressed request concurrency and still suffers from application-
layer head-of-line blocking. Therefore, HTTP/1.0 and HTTP/1.1 layer head-of-line blocking. Therefore, HTTP/1.0 and HTTP/1.1
clients use multiple connections to a server to make concurrent clients use multiple connections to a server to make concurrent
requests. requests.
Furthermore, HTTP fields are often repetitive and verbose, causing Furthermore, HTTP fields are often repetitive and verbose, causing
unnecessary network traffic as well as causing the initial TCP unnecessary network traffic as well as causing the initial TCP
congestion window to quickly fill. This can result in excessive congestion window to quickly fill. This can result in excessive
latency when multiple requests are made on a new TCP connection. latency when multiple requests are made on a new TCP connection.
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The resulting protocol is more friendly to the network because fewer The resulting protocol is more friendly to the network because fewer
TCP connections can be used in comparison to HTTP/1.x. This means TCP connections can be used in comparison to HTTP/1.x. This means
less competition with other flows and longer-lived connections, which less competition with other flows and longer-lived connections, which
in turn lead to better utilization of available network capacity. in turn lead to better utilization of available network capacity.
Note, however, that TCP head-of-line blocking is not addressed by Note, however, that TCP head-of-line blocking is not addressed by
this protocol. this protocol.
Finally, HTTP/2 also enables more efficient processing of messages Finally, HTTP/2 also enables more efficient processing of messages
through use of binary message framing. through use of binary message framing.
This document obsoletes RFC 7540 [RFC7540] and RFC 8740 [RFC8740]. This document obsoletes RFCs 7540 and 8740. Appendix B lists notable
Appendix B lists notable changes. changes.
2. HTTP/2 Protocol Overview 2. HTTP/2 Protocol Overview
HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2 HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2
supports all of the core features of HTTP but aims to be more supports all of the core features of HTTP but aims to be more
efficient than HTTP/1.1. efficient than HTTP/1.1.
HTTP/2 is a connection-oriented application-layer protocol that runs HTTP/2 is a connection-oriented application-layer protocol that runs
over a TCP connection ([TCP]). The client is the TCP connection over a TCP connection ([TCP]). The client is the TCP connection
initiator. initiator.
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way HTTP/2 frames are structured and formed into multiplexed way HTTP/2 frames are structured and formed into multiplexed
streams. streams.
o Frame (Section 6) and error (Section 7) definitions include o Frame (Section 6) and error (Section 7) definitions include
details of the frame and error types used in HTTP/2. details of the frame and error types used in HTTP/2.
o HTTP mappings (Section 8) and additional requirements (Section 9) o HTTP mappings (Section 8) and additional requirements (Section 9)
describe how HTTP semantics are expressed using frames and describe how HTTP semantics are expressed using frames and
streams. streams.
While some of the frame and stream layer concepts are isolated from While some of the frame- and stream-layer concepts are isolated from
HTTP, this specification does not define a completely generic frame HTTP, this specification does not define a completely generic frame
layer. The frame and stream layers are tailored to the needs of the layer. The frame and stream layers are tailored to the needs of
HTTP protocol. HTTP.
2.2. Conventions and Terminology 2.2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
All numeric values are in network byte order. Values are unsigned All numeric values are in network byte order. Values are unsigned
unless otherwise indicated. Literal values are provided in decimal unless otherwise indicated. Literal values are provided in decimal
or hexadecimal as appropriate. Hexadecimal literals are prefixed or hexadecimal as appropriate. Hexadecimal literals are prefixed
with "0x" to distinguish them from decimal literals. with "0x" to distinguish them from decimal literals.
This specification describes binary formats using the convention This specification describes binary formats using the conventions
described in RFC 9000 [QUIC]. Note that this format uses network described in RFC 9000 [QUIC]. Note that this format uses network
byte order and high-valued bits are listed before low-valued bits. byte order and that high-valued bits are listed before low-valued
bits.
The following terms are used: The following terms are used:
client: The endpoint that initiates an HTTP/2 connection. Clients client: The endpoint that initiates an HTTP/2 connection. Clients
send HTTP requests and receive HTTP responses. send HTTP requests and receive HTTP responses.
connection: A transport-layer connection between two endpoints. connection: A transport-layer connection between two endpoints.
connection error: An error that affects the entire HTTP/2 connection error: An error that affects the entire HTTP/2
connection. connection.
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The term "content" as it applies to message bodies is defined in The term "content" as it applies to message bodies is defined in
Section 6.4 of [HTTP]. Section 6.4 of [HTTP].
3. Starting HTTP/2 3. Starting HTTP/2
Implementations that generate HTTP requests need to discover whether Implementations that generate HTTP requests need to discover whether
a server supports HTTP/2. a server supports HTTP/2.
HTTP/2 uses the "http" and "https" URI schemes defined in Section 4.2 HTTP/2 uses the "http" and "https" URI schemes defined in Section 4.2
of [HTTP], with the same default port numbers as HTTP/1.1 ([HTTP11]). of [HTTP], with the same default port numbers as HTTP/1.1 [HTTP/1.1].
These URIs do not include any indication about what HTTP versions an These URIs do not include any indication about what HTTP versions an
upstream server (the immediate peer to which the client wishes to upstream server (the immediate peer to which the client wishes to
establish a connection) supports. establish a connection) supports.
The means by which support for HTTP/2 is determined is different for The means by which support for HTTP/2 is determined is different for
"http" and "https" URIs. Discovery for "https" URIs is described in "http" and "https" URIs. Discovery for "https" URIs is described in
Section 3.2. HTTP/2 support for "http" URIs can only be discovered Section 3.2. HTTP/2 support for "http" URIs can only be discovered
by out-of-band means, and requires prior knowledge of the support as by out-of-band means and requires prior knowledge of the support as
described in Section 3.3. described in Section 3.3.
3.1. HTTP/2 Version Identification 3.1. HTTP/2 Version Identification
The protocol defined in this document has two identifiers. Creating The protocol defined in this document has two identifiers. Creating
a connection based on either implies the use of the transport, a connection based on either implies the use of the transport,
framing, and message semantics described in this document. framing, and message semantics described in this document.
o The string "h2" identifies the protocol where HTTP/2 uses o The string "h2" identifies the protocol where HTTP/2 uses
Transport Layer Security (TLS); see Section 9.2. This identifier Transport Layer Security (TLS); see Section 9.2. This identifier
is used in the TLS application-layer protocol negotiation (ALPN) is used in the TLS Application-Layer Protocol Negotiation (ALPN)
extension [TLS-ALPN] field and in any place where HTTP/2 over TLS extension [TLS-ALPN] field and in any place where HTTP/2 over TLS
is identified. is identified.
The "h2" string is serialized into an ALPN protocol identifier as The "h2" string is serialized into an ALPN protocol identifier as
the two-octet sequence: 0x68, 0x32. the two-octet sequence: 0x68, 0x32.
o The "h2c" string was previously used as a token for use in the o The "h2c" string was previously used as a token for use in the
HTTP Upgrade mechanism's Upgrade header field (Section 7.8 of HTTP Upgrade mechanism's Upgrade header field (Section 7.8 of
[HTTP]). This usage was never widely deployed and is deprecated [HTTP]). This usage was never widely deployed and is deprecated
by this document. The same apples to the HTTP2-Settings header by this document. The same applies to the HTTP2-Settings header
field, which was used with the upgrade to "h2c". field, which was used with the upgrade to "h2c".
3.2. Starting HTTP/2 for "https" URIs 3.2. Starting HTTP/2 for "https" URIs
A client that makes a request to an "https" URI uses TLS [TLS13] with A client that makes a request to an "https" URI uses TLS [TLS13] with
the application-layer protocol negotiation (ALPN) extension the ALPN extension [TLS-ALPN].
[TLS-ALPN].
HTTP/2 over TLS uses the "h2" protocol identifier. The "h2c" HTTP/2 over TLS uses the "h2" protocol identifier. The "h2c"
protocol identifier MUST NOT be sent by a client or selected by a protocol identifier MUST NOT be sent by a client or selected by a
server; the "h2c" protocol identifier describes a protocol that does server; the "h2c" protocol identifier describes a protocol that does
not use TLS. not use TLS.
Once TLS negotiation is complete, both the client and the server MUST Once TLS negotiation is complete, both the client and the server MUST
send a connection preface (Section 3.4). send a connection preface (Section 3.4).
3.3. Starting HTTP/2 with Prior Knowledge 3.3. Starting HTTP/2 with Prior Knowledge
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format and semantics of the frame. Frames defined in this format and semantics of the frame. Frames defined in this
document are listed in Section 6. Implementations MUST ignore and document are listed in Section 6. Implementations MUST ignore and
discard frames of unknown types. discard frames of unknown types.
Flags: An 8-bit field reserved for boolean flags specific to the Flags: An 8-bit field reserved for boolean flags specific to the
frame type. frame type.
Flags are assigned semantics specific to the indicated frame type. Flags are assigned semantics specific to the indicated frame type.
Unused flags are those that have no defined semantics for a Unused flags are those that have no defined semantics for a
particular frame type. Unused flags MUST be ignored on receipt particular frame type. Unused flags MUST be ignored on receipt
and MUST be left unset (0x0) when sending. and MUST be left unset (0x00) when sending.
Reserved: A reserved 1-bit field. The semantics of this bit are Reserved: A reserved 1-bit field. The semantics of this bit are
undefined, and the bit MUST remain unset (0x0) when sending and undefined, and the bit MUST remain unset (0x00) when sending and
MUST be ignored when receiving. MUST be ignored when receiving.
Stream Identifier: A stream identifier (see Section 5.1.1) expressed Stream Identifier: A stream identifier (see Section 5.1.1) expressed
as an unsigned 31-bit integer. The value 0x0 is reserved for as an unsigned 31-bit integer. The value 0x00 is reserved for
frames that are associated with the connection as a whole as frames that are associated with the connection as a whole as
opposed to an individual stream. opposed to an individual stream.
The structure and content of the frame payload is dependent entirely The structure and content of the frame payload are dependent entirely
on the frame type. on the frame type.
4.2. Frame Size 4.2. Frame Size
The size of a frame payload is limited by the maximum size that a The size of a frame payload is limited by the maximum size that a
receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This
setting can have any value between 2^14 (16,384) and 2^24-1 setting can have any value between 2^14 (16,384) and 2^24-1
(16,777,215) octets, inclusive. (16,777,215) octets, inclusive.
All implementations MUST be capable of receiving and minimally All implementations MUST be capable of receiving and minimally
skipping to change at page 11, line 51 skipping to change at line 515
| Note: Certain frame types, such as PING (Section 6.7), impose | Note: Certain frame types, such as PING (Section 6.7), impose
| additional limits on the amount of frame payload data allowed. | additional limits on the amount of frame payload data allowed.
An endpoint MUST send an error code of FRAME_SIZE_ERROR if a frame An endpoint MUST send an error code of FRAME_SIZE_ERROR if a frame
exceeds the size defined in SETTINGS_MAX_FRAME_SIZE, exceeds any exceeds the size defined in SETTINGS_MAX_FRAME_SIZE, exceeds any
limit defined for the frame type, or is too small to contain limit defined for the frame type, or is too small to contain
mandatory frame data. A frame size error in a frame that could alter mandatory frame data. A frame size error in a frame that could alter
the state of the entire connection MUST be treated as a connection the state of the entire connection MUST be treated as a connection
error (Section 5.4.1); this includes any frame carrying a field block error (Section 5.4.1); this includes any frame carrying a field block
(Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), (Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), a
SETTINGS, and any frame with a stream identifier of 0. SETTINGS frame, and any frame with a stream identifier of 0.
Endpoints are not obligated to use all available space in a frame. Endpoints are not obligated to use all available space in a frame.
Responsiveness can be improved by using frames that are smaller than Responsiveness can be improved by using frames that are smaller than
the permitted maximum size. Sending large frames can result in the permitted maximum size. Sending large frames can result in
delays in sending time-sensitive frames (such as RST_STREAM, delays in sending time-sensitive frames (such as RST_STREAM,
WINDOW_UPDATE, or PRIORITY), which, if blocked by the transmission of WINDOW_UPDATE, or PRIORITY), which, if blocked by the transmission of
a large frame, could affect performance. a large frame, could affect performance.
4.3. Field Section Compression and Decompression 4.3. Field Section Compression and Decompression
Field section compression is the process of compressing a set of Field section compression is the process of compressing a set of
field lines (Section 5.2 of [HTTP]) to form a field block. Field field lines (Section 5.2 of [HTTP]) to form a field block. Field
section decompression is the process of decoding a field block into a section decompression is the process of decoding a field block into a
set of field lines. Details of HTTP/2 field section compression and set of field lines. Details of HTTP/2 field section compression and
decompression is defined in [COMPRESSION], which, for historical decompression are defined in [COMPRESSION], which, for historical
reasons, refers to these processes as header compression and reasons, refers to these processes as header compression and
decompression. decompression.
Each field block carries all of the compressed field lines of a Each field block carries all of the compressed field lines of a
single field section. Header sections also include control data single field section. Header sections also include control data
associated with the message in the form of pseudo-header fields associated with the message in the form of pseudo-header fields
(Section 8.3) that use the same format as a field line. (Section 8.3) that use the same format as a field line.
| Note: RFC 7540 [RFC7540] used the term "header block" in place | Note: RFC 7540 [RFC7540] used the term "header block" in place
| of the more generic "field block". | of the more generic "field block".
Field blocks carry control data and header sections for requests, Field blocks carry control data and header sections for requests,
responses, promised requests, and pushed responses (see Section 8.4). responses, promised requests, and pushed responses (see Section 8.4).
All these messages, except for interim responses and requests All these messages, except for interim responses and requests
contained in PUSH_PROMISE (Section 6.6) frames, can optionally contained in PUSH_PROMISE (Section 6.6) frames, can optionally
include a field block that carries a trailer section. include a field block that carries a trailer section.
A field section is a collection of field lines. Each of the field A field section is a collection of field lines. Each of the field
lines in a field block carry a single value. The serialized field lines in a field block carries a single value. The serialized field
block is then divided into one or more octet sequences, called field block is then divided into one or more octet sequences, called field
block fragments. The first field block fragment is transmitted block fragments. The first field block fragment is transmitted
within the frame payload of HEADERS (Section 6.2) or PUSH_PROMISE within the frame payload of HEADERS (Section 6.2) or PUSH_PROMISE
(Section 6.6), each of which could be followed by CONTINUATION (Section 6.6), each of which could be followed by CONTINUATION
(Section 6.10) frames to carry subsequent field block fragments. (Section 6.10) frames to carry subsequent field block fragments.
The Cookie header field [COOKIE] is treated specially by the HTTP The Cookie header field [COOKIE] is treated specially by the HTTP
mapping (see Section 8.2.3). mapping (see Section 8.2.3).
A receiving endpoint reassembles the field block by concatenating its A receiving endpoint reassembles the field block by concatenating its
skipping to change at page 15, line 21 skipping to change at line 674
| | | send H / | | | | | send H / | |
,------+ reserved | | recv H | reserved +------. ,------+ reserved | | recv H | reserved +------.
| | (local) | | | (remote) | | | | (local) | | | (remote) | |
| +---+------+ v +------+---+ | | +---+------+ v +------+---+ |
| | +--------+ | | | | +--------+ | |
| | recv ES | | send ES | | | | recv ES | | send ES | |
| send H | ,-------+ open +-------. | recv H | | send H | ,-------+ open +-------. | recv H |
| | / | | \ | | | | / | | \ | |
| v v +---+----+ v v | | v v +---+----+ v v |
| +----------+ | +----------+ | | +----------+ | +----------+ |
| | half | | | half | | | | half- | | | half- | |
| | closed | | send R / | closed | | | | closed | | send R / | closed | |
| | (remote) | | recv R | (local) | | | | (remote) | | recv R | (local) | |
| +----+-----+ | +-----+----+ | | +----+-----+ | +-----+----+ |
| | | | | | | | | |
| | send ES / | recv ES / | | | | send ES / | recv ES / | |
| | send R / v send R / | | | | send R / v send R / | |
| | recv R +--------+ recv R | | | | recv R +--------+ recv R | |
| send R / `----------->| |<-----------' send R / | | send R / `----------->| |<-----------' send R / |
| recv R | closed | recv R | | recv R | closed | recv R |
`----------------------->| |<-----------------------' `----------------------->| |<-----------------------'
skipping to change at page 16, line 44 skipping to change at line 744
o Note that the PUSH_PROMISE frame is not sent on the idle stream o Note that the PUSH_PROMISE frame is not sent on the idle stream
but references the newly reserved stream in the Promised Stream but references the newly reserved stream in the Promised Stream
ID field. ID field.
o Opening a stream with a higher-valued stream identifier causes o Opening a stream with a higher-valued stream identifier causes
the stream to transition immediately to a "closed" state; note the stream to transition immediately to a "closed" state; note
that this transition is not shown in the diagram. that this transition is not shown in the diagram.
Receiving any frame other than HEADERS or PRIORITY on a stream in Receiving any frame other than HEADERS or PRIORITY on a stream in
this state MUST be treated as a connection error (Section 5.4.1) this state MUST be treated as a connection error (Section 5.4.1)
of type PROTOCOL_ERROR. If this stream is server-initiated, as of type PROTOCOL_ERROR. If this stream is initiated by the
described in Section 5.1.1, then receiving a HEADERS frame MUST server, as described in Section 5.1.1, then receiving a HEADERS
also be treated as a connection error (Section 5.4.1) of type frame MUST also be treated as a connection error (Section 5.4.1)
PROTOCOL_ERROR. of type PROTOCOL_ERROR.
reserved (local): A stream in the "reserved (local)" state is one reserved (local): A stream in the "reserved (local)" state is one
that has been promised by sending a PUSH_PROMISE frame. A that has been promised by sending a PUSH_PROMISE frame. A
PUSH_PROMISE frame reserves an idle stream by associating the PUSH_PROMISE frame reserves an idle stream by associating the
stream with an open stream that was initiated by the remote peer stream with an open stream that was initiated by the remote peer
(see Section 8.4). (see Section 8.4).
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
o The endpoint can send a HEADERS frame. This causes the stream o The endpoint can send a HEADERS frame. This causes the stream
skipping to change at page 19, line 26 skipping to change at line 862
RST_STREAM frame might receive a WINDOW_UPDATE or RST_STREAM frame RST_STREAM frame might receive a WINDOW_UPDATE or RST_STREAM frame
from its peer in the time before the peer receives and processes from its peer in the time before the peer receives and processes
the frame that closes the stream. the frame that closes the stream.
An endpoint that sends a RST_STREAM frame on a stream that is in An endpoint that sends a RST_STREAM frame on a stream that is in
the "open" or "half-closed (local)" state could receive any type the "open" or "half-closed (local)" state could receive any type
of frame. The peer might have sent or enqueued for sending these of frame. The peer might have sent or enqueued for sending these
frames before processing the RST_STREAM frame. An endpoint MUST frames before processing the RST_STREAM frame. An endpoint MUST
minimally process and then discard any frames it receives in this minimally process and then discard any frames it receives in this
state. This means updating header compression state for HEADERS state. This means updating header compression state for HEADERS
and PUSH_PROMISE frames; PUSH_PROMISE frames also cause the and PUSH_PROMISE frames. Receiving a PUSH_PROMISE frame also
promised stream to become "reserved", even when the PUSH_PROMISE causes the promised stream to become "reserved (remote)", even
frame is received on a closed stream; and, the content of DATA when the PUSH_PROMISE frame is received on a closed stream.
frames count toward the connection flow-control window. Additionally, the content of DATA frames counts toward the
connection flow-control window.
An endpoint can perform this minimal processing for all streams An endpoint can perform this minimal processing for all streams
that are in the "closed" state. Endpoints MAY use other signals that are in the "closed" state. Endpoints MAY use other signals
to detect that a peer has received the frames that caused the to detect that a peer has received the frames that caused the
stream to enter the "closed" state and treat receipt of any frame stream to enter the "closed" state and treat receipt of any frame
other than PRIORITY as a connection error (Section 5.4.1) of type other than PRIORITY as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. Endpoints can use frames that indicate that the PROTOCOL_ERROR. Endpoints can use frames that indicate that the
peer has received the closing signal to drive this. Endpoints peer has received the closing signal to drive this. Endpoints
SHOULD NOT use timers for this purpose. For example, an endpoint SHOULD NOT use timers for this purpose. For example, an endpoint
that sends a SETTINGS frame after closing a stream can safely that sends a SETTINGS frame after closing a stream can safely
skipping to change at page 20, line 7 skipping to change at line 891
after closing the stream. after closing the stream.
In the absence of more specific rules, implementations SHOULD treat In the absence of more specific rules, implementations SHOULD treat
the receipt of a frame that is not expressly permitted in the the receipt of a frame that is not expressly permitted in the
description of a state as a connection error (Section 5.4.1) of type description of a state as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. Note that PRIORITY can be sent and received in any PROTOCOL_ERROR. Note that PRIORITY can be sent and received in any
stream state. stream state.
The rules in this section only apply to frames defined in this The rules in this section only apply to frames defined in this
document. Receipt of frames for which the semantics are unknown document. Receipt of frames for which the semantics are unknown
cannot be treated as an error as the conditions for sending and cannot be treated as an error, as the conditions for sending and
receiving those frames are also unknown; see Section 5.5. receiving those frames are also unknown; see Section 5.5.
An example of the state transitions for an HTTP request/response An example of the state transitions for an HTTP request/response
exchange can be found in Section 8.8. An example of the state exchange can be found in Section 8.8. An example of the state
transitions for server push can be found in Sections 8.4.1 and 8.4.2. transitions for server push can be found in Sections 8.4.1 and 8.4.2.
5.1.1. Stream Identifiers 5.1.1. Stream Identifiers
Streams are identified by an unsigned 31-bit integer. Streams Streams are identified by an unsigned 31-bit integer. Streams
initiated by a client MUST use odd-numbered stream identifiers; those initiated by a client MUST use odd-numbered stream identifiers; those
initiated by the server MUST use even-numbered stream identifiers. A initiated by the server MUST use even-numbered stream identifiers. A
stream identifier of zero (0x0) is used for connection control stream identifier of zero (0x00) is used for connection control
messages; the stream identifier of zero cannot be used to establish a messages; the stream identifier of zero cannot be used to establish a
new stream. new stream.
The identifier of a newly established stream MUST be numerically The identifier of a newly established stream MUST be numerically
greater than all streams that the initiating endpoint has opened or greater than all streams that the initiating endpoint has opened or
reserved. This governs streams that are opened using a HEADERS frame reserved. This governs streams that are opened using a HEADERS frame
and streams that are reserved using PUSH_PROMISE. An endpoint that and streams that are reserved using PUSH_PROMISE. An endpoint that
receives an unexpected stream identifier MUST respond with a receives an unexpected stream identifier MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
A HEADERS frame will transition the client-initiated stream A HEADERS frame will transition the client-initiated stream
identified by the stream identifier in the frame header from "idle" identified by the stream identifier in the frame header from "idle"
to "open". A PUSH_PROMISE frame will transition the server-initiated to "open". A PUSH_PROMISE frame will transition the server-initiated
stream identified by the "Promised Stream ID" field in the frame stream identified by the Promised Stream ID field in the frame
payload from "idle" to "reserved". When a stream transitions out of payload from "idle" to "reserved (local)" or "reserved (remote)".
the "idle" state, all "idle" streams that might have been opened by When a stream transitions out of the "idle" state, all streams in the
the peer with a lower-valued stream identifier immediately transition "idle" state that might have been opened by the peer with a lower-
to "closed". That is, an endpoint may skip a stream identifier, with valued stream identifier immediately transition to "closed". That
the effect being that the skipped stream is immediately closed. is, an endpoint may skip a stream identifier, with the effect being
that the skipped stream is immediately closed.
Stream identifiers cannot be reused. Long-lived connections can Stream identifiers cannot be reused. Long-lived connections can
result in an endpoint exhausting the available range of stream result in an endpoint exhausting the available range of stream
identifiers. A client that is unable to establish a new stream identifiers. A client that is unable to establish a new stream
identifier can establish a new connection for new streams. A server identifier can establish a new connection for new streams. A server
that is unable to establish a new stream identifier can send a GOAWAY that is unable to establish a new stream identifier can send a GOAWAY
frame so that the client is forced to open a new connection for new frame so that the client is forced to open a new connection for new
streams. streams.
5.1.2. Stream Concurrency 5.1.2. Stream Concurrency
skipping to change at page 21, line 40 skipping to change at line 968
SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current
number of open streams can either close streams that exceed the new number of open streams can either close streams that exceed the new
value or allow streams to complete. value or allow streams to complete.
5.2. Flow Control 5.2. Flow Control
Using streams for multiplexing introduces contention over use of the Using streams for multiplexing introduces contention over use of the
TCP connection, resulting in blocked streams. A flow-control scheme TCP connection, resulting in blocked streams. A flow-control scheme
ensures that streams on the same connection do not destructively ensures that streams on the same connection do not destructively
interfere with each other. Flow control is used for both individual interfere with each other. Flow control is used for both individual
streams and for the connection as a whole. streams and the connection as a whole.
HTTP/2 provides for flow control through use of the WINDOW_UPDATE HTTP/2 provides for flow control through use of the WINDOW_UPDATE
frame (Section 6.9). frame (Section 6.9).
5.2.1. Flow-Control Principles 5.2.1. Flow-Control Principles
HTTP/2 stream flow control aims to allow a variety of flow-control HTTP/2 stream flow control aims to allow a variety of flow-control
algorithms to be used without requiring protocol changes. Flow algorithms to be used without requiring protocol changes. Flow
control in HTTP/2 has the following characteristics: control in HTTP/2 has the following characteristics:
skipping to change at page 22, line 33 skipping to change at line 1007
for both new streams and the overall connection. for both new streams and the overall connection.
5. The frame type determines whether flow control applies to a 5. The frame type determines whether flow control applies to a
frame. Of the frames specified in this document, only DATA frame. Of the frames specified in this document, only DATA
frames are subject to flow control; all other frame types do not frames are subject to flow control; all other frame types do not
consume space in the advertised flow-control window. This consume space in the advertised flow-control window. This
ensures that important control frames are not blocked by flow ensures that important control frames are not blocked by flow
control. control.
6. An endpoint can choose to disable its own flow control, but an 6. An endpoint can choose to disable its own flow control, but an
endpoint cannot ignore flow control signals from its peer. endpoint cannot ignore flow-control signals from its peer.
7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE 7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE
frame (Section 6.9). This document does not stipulate how a frame (Section 6.9). This document does not stipulate how a
receiver decides when to send this frame or the value that it receiver decides when to send this frame or the value that it
sends, nor does it specify how a sender chooses to send packets. sends, nor does it specify how a sender chooses to send packets.
Implementations are able to select any algorithm that suits their Implementations are able to select any algorithm that suits their
needs. needs.
Implementations are also responsible for prioritizing the sending of Implementations are also responsible for prioritizing the sending of
requests and responses, choosing how to avoid head-of-line blocking requests and responses, choosing how to avoid head-of-line blocking
skipping to change at page 23, line 25 skipping to change at line 1041
control window of the maximum size (2^31-1) and can maintain this control window of the maximum size (2^31-1) and can maintain this
window by sending a WINDOW_UPDATE frame when any data is received. window by sending a WINDOW_UPDATE frame when any data is received.
This effectively disables flow control for that receiver. This effectively disables flow control for that receiver.
Conversely, a sender is always subject to the flow-control window Conversely, a sender is always subject to the flow-control window
advertised by the receiver. advertised by the receiver.
Deployments with constrained resources (for example, memory) can Deployments with constrained resources (for example, memory) can
employ flow control to limit the amount of memory a peer can consume. employ flow control to limit the amount of memory a peer can consume.
Note, however, that this can lead to suboptimal use of available Note, however, that this can lead to suboptimal use of available
network resources if flow control is enabled without knowledge of the network resources if flow control is enabled without knowledge of the
bandwidth-delay product (see [RFC7323]). bandwidth * delay product (see [RFC7323]).
Even with full awareness of the current bandwidth-delay product, Even with full awareness of the current bandwidth * delay product,
implementation of flow control can be difficult. Endpoints MUST read implementation of flow control can be difficult. Endpoints MUST read
and process HTTP/2 frames from the TCP receive buffer as soon as data and process HTTP/2 frames from the TCP receive buffer as soon as data
is available. Failure to read promptly could lead to a deadlock when is available. Failure to read promptly could lead to a deadlock when
critical frames, such as WINDOW_UPDATE, are not read and acted upon. critical frames, such as WINDOW_UPDATE, are not read and acted upon.
Reading frames promptly does not expose endpoints to resource Reading frames promptly does not expose endpoints to resource
exhaustion attacks as HTTP/2 flow control limits resource exhaustion attacks, as HTTP/2 flow control limits resource
commitments. commitments.
5.2.3. Flow Control Performance 5.2.3. Flow-Control Performance
If an endpoint cannot ensure that its peer always has available flow If an endpoint cannot ensure that its peer always has available flow-
control window space that is greater than the peer's bandwidth-delay control window space that is greater than the peer's bandwidth *
product on this connection, its receive throughput will be limited by delay product on this connection, its receive throughput will be
HTTP/2 flow control. This will result in degraded performance. limited by HTTP/2 flow control. This will result in degraded
performance.
Sending timely WINDOW_UPDATE frames can improve performance. Sending timely WINDOW_UPDATE frames can improve performance.
Endpoints will want to balance the need to improve receive throughput Endpoints will want to balance the need to improve receive throughput
with the need to manage resource exhaustion risks, and should take with the need to manage resource exhaustion risks and should take
careful note of Section 10.5 in defining their strategy to manage careful note of Section 10.5 in defining their strategy to manage
window sizes. window sizes.
5.3. Prioritization 5.3. Prioritization
In a multiplexed protocol like HTTP/2, prioritizing allocation of In a multiplexed protocol like HTTP/2, prioritizing allocation of
bandwidth and computation resources to streams can be critical to bandwidth and computation resources to streams can be critical to
attaining good performance. A poor prioritization scheme can result attaining good performance. A poor prioritization scheme can result
in HTTP/2 providing poor performance. With no parallelism at the TCP in HTTP/2 providing poor performance. With no parallelism at the TCP
layer, performance could be significantly worse than HTTP/1.1. layer, performance could be significantly worse than HTTP/1.1.
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A good prioritization scheme benefits from the application of A good prioritization scheme benefits from the application of
contextual knowledge such as the content of resources, how resources contextual knowledge such as the content of resources, how resources
are interrelated, and how those resources will be used by a peer. In are interrelated, and how those resources will be used by a peer. In
particular, clients can possess knowledge about the priority of particular, clients can possess knowledge about the priority of
requests that is relevant to server prioritization. In those cases, requests that is relevant to server prioritization. In those cases,
having clients provide priority information can improve performance. having clients provide priority information can improve performance.
5.3.1. Background on Priority in RFC 7540 5.3.1. Background on Priority in RFC 7540
RFC 7540 defined a rich system for signaling priority of requests. RFC 7540 defined a rich system for signaling priority of requests.
However, this system proved to be complex and it was not uniformly However, this system proved to be complex, and it was not uniformly
implemented. implemented.
The flexible scheme meant that it was possible for clients to express The flexible scheme meant that it was possible for clients to express
priorities in very different ways, with little consistency in the priorities in very different ways, with little consistency in the
approaches that were adopted. For servers, implementing generic approaches that were adopted. For servers, implementing generic
support for the scheme was complex. Implementation of priorities was support for the scheme was complex. Implementation of priorities was
uneven in both clients and servers. Many server deployments ignored uneven in both clients and servers. Many server deployments ignored
client signals when prioritizing their handling of requests. client signals when prioritizing their handling of requests.
In short, the prioritization signaling in RFC7540 [RFC7540] was not In short, the prioritization signaling in RFC 7540 [RFC7540] was not
successful. successful.
5.3.2. Priority Signaling in this Document 5.3.2. Priority Signaling in This Document
This update to HTTP/2 deprecates the priority signaling defined in This update to HTTP/2 deprecates the priority signaling defined in
RFC 7540 [RFC7540]. The bulk of the text related to priority signals RFC 7540 [RFC7540]. The bulk of the text related to priority signals
is not included in this document. The description of frame fields is not included in this document. The description of frame fields
and some of the mandatory handling is retained to ensure that and some of the mandatory handling is retained to ensure that
implementations of this document remain interoperable with implementations of this document remain interoperable with
implementations that use the priority signaling described in RFC implementations that use the priority signaling described in RFC
7540. 7540.
A thorough description of the RFC 7540 priority scheme remains in A thorough description of the RFC 7540 priority scheme remains in
Section 5.3 of [RFC7540]. Section 5.3 of [RFC7540].
Signaling priority information is necessary to attain good Signaling priority information is necessary to attain good
performance in many cases. Where signaling priority information is performance in many cases. Where signaling priority information is
important, endpoints are encouraged to use an alternative scheme, important, endpoints are encouraged to use an alternative scheme,
such as [I-D.ietf-httpbis-priority]. such as the scheme described in [HTTP-PRIORITY].
Though the priority signaling from RFC 7540 was not widely adopted, Though the priority signaling from RFC 7540 was not widely adopted,
the information it provides can still be useful in the absence of the information it provides can still be useful in the absence of
better information. Endpoints that receive priority signals in better information. Endpoints that receive priority signals in
HEADERS or PRIORITY frames can benefit from applying that HEADERS or PRIORITY frames can benefit from applying that
information. In particular, implementations that consume these information. In particular, implementations that consume these
signals would not benefit from discarding these priority signals in signals would not benefit from discarding these priority signals in
the absence of alternatives. the absence of alternatives.
Servers SHOULD use other contextual information in determining Servers SHOULD use other contextual information in determining
priority of requests in the absence of any priority signals. Servers priority of requests in the absence of any priority signals. Servers
MAY interpret the complete absence of signals as an indication that MAY interpret the complete absence of signals as an indication that
the client has not implemented the feature. The defaults described the client has not implemented the feature. The defaults described
in Section 5.3.5 of [RFC7540] are known to have poor performance in Section 5.3.5 of [RFC7540] are known to have poor performance
under most conditions and their use is unlikely to be deliberate. under most conditions, and their use is unlikely to be deliberate.
5.4. Error Handling 5.4. Error Handling
HTTP/2 framing permits two classes of error: HTTP/2 framing permits two classes of errors:
o An error condition that renders the entire connection unusable is o An error condition that renders the entire connection unusable is
a connection error. a connection error.
o An error in an individual stream is a stream error. o An error in an individual stream is a stream error.
A list of error codes is included in Section 7. A list of error codes is included in Section 7.
It is possible that an endpoint will encounter frames that would It is possible that an endpoint will encounter frames that would
cause multiple errors. Implementations MAY discover multiple errors cause multiple errors. Implementations MAY discover multiple errors
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used for that purpose. If both peers set a value that indicates used for that purpose. If both peers set a value that indicates
willingness to use the extension, then the extension can be used. If willingness to use the extension, then the extension can be used. If
a setting is used for extension negotiation, the initial value MUST a setting is used for extension negotiation, the initial value MUST
be defined in such a fashion that the extension is initially be defined in such a fashion that the extension is initially
disabled. disabled.
6. Frame Definitions 6. Frame Definitions
This specification defines a number of frame types, each identified This specification defines a number of frame types, each identified
by a unique 8-bit type code. Each frame type serves a distinct by a unique 8-bit type code. Each frame type serves a distinct
purpose in the establishment and management either of the connection purpose in the establishment and management of either the connection
as a whole or of individual streams. as a whole or individual streams.
The transmission of specific frame types can alter the state of a The transmission of specific frame types can alter the state of a
connection. If endpoints fail to maintain a synchronized view of the connection. If endpoints fail to maintain a synchronized view of the
connection state, successful communication within the connection will connection state, successful communication within the connection will
no longer be possible. Therefore, it is important that endpoints no longer be possible. Therefore, it is important that endpoints
have a shared comprehension of how the state is affected by the use have a shared comprehension of how the state is affected by the use
of any given frame. of any given frame.
6.1. DATA 6.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of DATA frames (type=0x00) convey arbitrary, variable-length sequences
octets associated with a stream. One or more DATA frames are used, of octets associated with a stream. One or more DATA frames are
for instance, to carry HTTP request or response message contents. used, for instance, to carry HTTP request or response message
contents.
DATA frames MAY also contain padding. Padding can be added to DATA DATA frames MAY also contain padding. Padding can be added to DATA
frames to obscure the size of messages. Padding is a security frames to obscure the size of messages. Padding is a security
feature; see Section 10.7. feature; see Section 10.7.
DATA Frame { DATA Frame {
Length (24), Length (24),
Type (8) = 0x0, Type (8) = 0x00,
Unused Flags (4), Unused Flags (4),
PADDED Flag (1), PADDED Flag (1),
Unused Flags (2), Unused Flags (2),
END_STREAM Flag (1), END_STREAM Flag (1),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
[Pad Length (8)], [Pad Length (8)],
skipping to change at page 29, line 25 skipping to change at line 1329
frame payload after subtracting the length of the other fields frame payload after subtracting the length of the other fields
that are present. that are present.
Padding: Padding octets that contain no application semantic value. Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending. A receiver is Padding octets MUST be set to zero when sending. A receiver is
not obligated to verify padding but MAY treat non-zero padding as not obligated to verify padding but MAY treat non-zero padding as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR. a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The DATA frame defines the following flags: The DATA frame defines the following flags:
PADDED (0x8): When set, the PADDED flag indicates that the Pad PADDED (0x08): When set, the PADDED flag indicates that the Pad
Length field and any padding that it describes are present. Length field and any padding that it describes are present.
END_STREAM (0x1): When set, the END_STREAM flag indicates that this END_STREAM (0x01): When set, the END_STREAM flag indicates that this
frame is the last that the endpoint will send for the identified frame is the last that the endpoint will send for the identified
stream. Setting this flag causes the stream to enter one of the stream. Setting this flag causes the stream to enter one of the
"half-closed" states or the "closed" state (Section 5.1). "half-closed" states or the "closed" state (Section 5.1).
| Note: An endpoint that learns of stream closure after sending | Note: An endpoint that learns of stream closure after sending
| all data can close a stream by sending a STREAM frame with a | all data can close a stream by sending a STREAM frame with a
| zero-length Data field and the END_STREAM flag set. This is | zero-length Data field and the END_STREAM flag set. This is
| only possible if the endpoint does not send trailers as the | only possible if the endpoint does not send trailers, as the
| END_STREAM flag appears on a HEADERS frame in that case; see | END_STREAM flag appears on a HEADERS frame in that case; see
| Section 8.1. | Section 8.1.
DATA frames MUST be associated with a stream. If a DATA frame is DATA frames MUST be associated with a stream. If a DATA frame is
received whose stream identifier field is 0x0, the recipient MUST received whose Stream Identifier field is 0x00, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
DATA frames are subject to flow control and can only be sent when a DATA frames are subject to flow control and can only be sent when a
stream is in the "open" or "half-closed (remote)" state. The entire stream is in the "open" or "half-closed (remote)" state. The entire
DATA frame payload is included in flow control, including the Pad DATA frame payload is included in flow control, including the Pad
Length and Padding fields if present. If a DATA frame is received Length and Padding fields if present. If a DATA frame is received
whose stream is not in "open" or "half-closed (local)" state, the whose stream is not in the "open" or "half-closed (local)" state, the
recipient MUST respond with a stream error (Section 5.4.2) of type recipient MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED. STREAM_CLOSED.
The total number of padding octets is determined by the value of the The total number of padding octets is determined by the value of the
Pad Length field. If the length of the padding is the length of the Pad Length field. If the length of the padding is the length of the
frame payload or greater, the recipient MUST treat this as a frame payload or greater, the recipient MUST treat this as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
| Note: A frame can be increased in size by one octet by | Note: A frame can be increased in size by one octet by
| including a Pad Length field with a value of zero. | including a Pad Length field with a value of zero.
6.2. HEADERS 6.2. HEADERS
The HEADERS frame (type=0x1) is used to open a stream (Section 5.1), The HEADERS frame (type=0x01) is used to open a stream (Section 5.1),
and additionally carries a field block fragment. Despite the name, a and additionally carries a field block fragment. Despite the name, a
HEADERS frame can carry a header section or a trailer section. HEADERS frame can carry a header section or a trailer section.
HEADERS frames can be sent on a stream in the "idle", "reserved HEADERS frames can be sent on a stream in the "idle", "reserved
(local)", "open", or "half-closed (remote)" state. (local)", "open", or "half-closed (remote)" state.
HEADERS Frame { HEADERS Frame {
Length (24), Length (24),
Type (8) = 0x1, Type (8) = 0x01,
Unused Flags (2), Unused Flags (2),
PRIORITY Flag (1), PRIORITY Flag (1),
Unused Flag (1), Unused Flag (1),
PADDED Flag (1), PADDED Flag (1),
END_HEADERS Flag (1), END_HEADERS Flag (1),
Unused Flag (1), Unused Flag (1),
END_STREAM Flag (1), END_STREAM Flag (1),
Reserved (1), Reserved (1),
skipping to change at page 31, line 27 skipping to change at line 1428
Padding: Padding octets that contain no application semantic value. Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending. A receiver is Padding octets MUST be set to zero when sending. A receiver is
not obligated to verify padding but MAY treat non-zero padding as not obligated to verify padding but MAY treat non-zero padding as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR. a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The HEADERS frame defines the following flags: The HEADERS frame defines the following flags:
PRIORITY (0x20): When set, the PRIORITY flag indicates that the PRIORITY (0x20): When set, the PRIORITY flag indicates that the
Exclusive, Stream Dependency, and Weight fields are present. Exclusive, Stream Dependency, and Weight fields are present.
PADDED (0x8): When set, the PADDED flag indicates that the Pad PADDED (0x08): When set, the PADDED flag indicates that the Pad
Length field and any padding that it describes are present. Length field and any padding that it describes are present.
END_HEADERS (0x4): When set, the END_HEADERS flag indicates that END_HEADERS (0x04): When set, the END_HEADERS flag indicates that
this frame contains an entire field block (Section 4.3) and is not this frame contains an entire field block (Section 4.3) and is not
followed by any CONTINUATION frames. followed by any CONTINUATION frames.
A HEADERS frame without the END_HEADERS flag set MUST be followed A HEADERS frame without the END_HEADERS flag set MUST be followed
by a CONTINUATION frame for the same stream. A receiver MUST by a CONTINUATION frame for the same stream. A receiver MUST
treat the receipt of any other type of frame or a frame on a treat the receipt of any other type of frame or a frame on a
different stream as a connection error (Section 5.4.1) of type different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
END_STREAM (0x1): When set, the END_STREAM flag indicates that the END_STREAM (0x01): When set, the END_STREAM flag indicates that the
field block (Section 4.3) is the last that the endpoint will send field block (Section 4.3) is the last that the endpoint will send
for the identified stream. for the identified stream.
A HEADERS frame with the END_STREAM flag set signals the end of a A HEADERS frame with the END_STREAM flag set signals the end of a
stream. However, a HEADERS frame with the END_STREAM flag set can stream. However, a HEADERS frame with the END_STREAM flag set can
be followed by CONTINUATION frames on the same stream. Logically, be followed by CONTINUATION frames on the same stream. Logically,
the CONTINUATION frames are part of the HEADERS frame. the CONTINUATION frames are part of the HEADERS frame.
The frame payload of a HEADERS frame contains a field block fragment The frame payload of a HEADERS frame contains a field block fragment
(Section 4.3). A field block that does not fit within a HEADERS (Section 4.3). A field block that does not fit within a HEADERS
frame is continued in a CONTINUATION frame (Section 6.10). frame is continued in a CONTINUATION frame (Section 6.10).
HEADERS frames MUST be associated with a stream. If a HEADERS frame HEADERS frames MUST be associated with a stream. If a HEADERS frame
is received whose stream identifier field is 0x0, the recipient MUST is received whose Stream Identifier field is 0x00, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
The HEADERS frame changes the connection state as described in The HEADERS frame changes the connection state as described in
Section 4.3. Section 4.3.
The total number of padding octets is determined by the value of the The total number of padding octets is determined by the value of the
Pad Length field. If the length of the padding is the length of the Pad Length field. If the length of the padding is the length of the
frame payload or greater, the recipient MUST treat this as a frame payload or greater, the recipient MUST treat this as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
| Note: A frame can be increased in size by one octet by | Note: A frame can be increased in size by one octet by
| including a Pad Length field with a value of zero. | including a Pad Length field with a value of zero.
6.3. PRIORITY 6.3. PRIORITY
The PRIORITY frame (type=0x2) is deprecated; see Section 5.3.2. A The PRIORITY frame (type=0x02) is deprecated; see Section 5.3.2. A
PRIORITY frame can be sent in any stream state, including idle or PRIORITY frame can be sent in any stream state, including idle or
closed streams. closed streams.
PRIORITY Frame { PRIORITY Frame {
Length (24) = 0x5, Length (24) = 0x05,
Type (8) = 0x2, Type (8) = 0x02,
Unused Flags (8), Unused Flags (8),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
Exclusive (1), Exclusive (1),
Stream Dependency (31), Stream Dependency (31),
Weight (8), Weight (8),
} }
skipping to change at page 33, line 8 skipping to change at line 1505
Exclusive: A single-bit flag. Exclusive: A single-bit flag.
Stream Dependency: A 31-bit stream identifier. Stream Dependency: A 31-bit stream identifier.
Weight: An unsigned 8-bit integer. Weight: An unsigned 8-bit integer.
The PRIORITY frame does not define any flags. The PRIORITY frame does not define any flags.
The PRIORITY frame always identifies a stream. If a PRIORITY frame The PRIORITY frame always identifies a stream. If a PRIORITY frame
is received with a stream identifier of 0x0, the recipient MUST is received with a stream identifier of 0x00, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
Sending or receiving a PRIORITY frame does not affect the state of Sending or receiving a PRIORITY frame does not affect the state of
any stream (Section 5.1). The PRIORITY frame can be sent on a stream any stream (Section 5.1). The PRIORITY frame can be sent on a stream
in any state, including "idle" or "closed". A PRIORITY frame cannot in any state, including "idle" or "closed". A PRIORITY frame cannot
be sent between consecutive frames that comprise a single field block be sent between consecutive frames that comprise a single field block
(Section 4.3). (Section 4.3).
A PRIORITY frame with a length other than 5 octets MUST be treated as A PRIORITY frame with a length other than 5 octets MUST be treated as
a stream error (Section 5.4.2) of type FRAME_SIZE_ERROR. a stream error (Section 5.4.2) of type FRAME_SIZE_ERROR.
6.4. RST_STREAM 6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for immediate termination of a The RST_STREAM frame (type=0x03) allows for immediate termination of
stream. RST_STREAM is sent to request cancellation of a stream or to a stream. RST_STREAM is sent to request cancellation of a stream or
indicate that an error condition has occurred. to indicate that an error condition has occurred.
RST_STREAM Frame { RST_STREAM Frame {
Length (24) = 0x4, Length (24) = 0x04,
Type (8) = 0x3, Type (8) = 0x03,
Unused Flags (8), Unused Flags (8),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
Error Code (32), Error Code (32),
} }
Figure 6: RST_STREAM Frame Format Figure 6: RST_STREAM Frame Format
skipping to change at page 34, line 9 skipping to change at line 1555
The RST_STREAM frame fully terminates the referenced stream and The RST_STREAM frame fully terminates the referenced stream and
causes it to enter the "closed" state. After receiving a RST_STREAM causes it to enter the "closed" state. After receiving a RST_STREAM
on a stream, the receiver MUST NOT send additional frames for that on a stream, the receiver MUST NOT send additional frames for that
stream, except for PRIORITY. However, after sending the RST_STREAM, stream, except for PRIORITY. However, after sending the RST_STREAM,
the sending endpoint MUST be prepared to receive and process the sending endpoint MUST be prepared to receive and process
additional frames sent on the stream that might have been sent by the additional frames sent on the stream that might have been sent by the
peer prior to the arrival of the RST_STREAM. peer prior to the arrival of the RST_STREAM.
RST_STREAM frames MUST be associated with a stream. If a RST_STREAM RST_STREAM frames MUST be associated with a stream. If a RST_STREAM
frame is received with a stream identifier of 0x0, the recipient MUST frame is received with a stream identifier of 0x00, the recipient
treat this as a connection error (Section 5.4.1) of type MUST treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
RST_STREAM frames MUST NOT be sent for a stream in the "idle" state. RST_STREAM frames MUST NOT be sent for a stream in the "idle" state.
If a RST_STREAM frame identifying an idle stream is received, the If a RST_STREAM frame identifying an idle stream is received, the
recipient MUST treat this as a connection error (Section 5.4.1) of recipient MUST treat this as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
A RST_STREAM frame with a length other than 4 octets MUST be treated A RST_STREAM frame with a length other than 4 octets MUST be treated
as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR. as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.
6.5. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that The SETTINGS frame (type=0x04) conveys configuration parameters that
affect how endpoints communicate, such as preferences and constraints affect how endpoints communicate, such as preferences and constraints
on peer behavior. The SETTINGS frame is also used to acknowledge the on peer behavior. The SETTINGS frame is also used to acknowledge the
receipt of those settings. Individually, a configuration parameter receipt of those settings. Individually, a configuration parameter
from a SETTINGS frame is referred to as a "setting". from a SETTINGS frame is referred to as a "setting".
Settings are not negotiated; they describe characteristics of the Settings are not negotiated; they describe characteristics of the
sending peer, which are used by the receiving peer. Different values sending peer, which are used by the receiving peer. Different values
for the same setting can be advertised by each peer. For example, a for the same setting can be advertised by each peer. For example, a
client might set a high initial flow-control window, whereas a server client might set a high initial flow-control window, whereas a server
might set a lower value to conserve resources. might set a lower value to conserve resources.
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Each parameter in a SETTINGS frame replaces any existing value for Each parameter in a SETTINGS frame replaces any existing value for
that parameter. Settings are processed in the order in which they that parameter. Settings are processed in the order in which they
appear, and a receiver of a SETTINGS frame does not need to maintain appear, and a receiver of a SETTINGS frame does not need to maintain
any state other than the current value of each setting. Therefore, any state other than the current value of each setting. Therefore,
the value of a SETTINGS parameter is the last value that is seen by a the value of a SETTINGS parameter is the last value that is seen by a
receiver. receiver.
SETTINGS frames are acknowledged by the receiving peer. To enable SETTINGS frames are acknowledged by the receiving peer. To enable
this, the SETTINGS frame defines the ACK flag: this, the SETTINGS frame defines the ACK flag:
ACK (0x1): When set, the ACK flag indicates that this frame ACK (0x01): When set, the ACK flag indicates that this frame
acknowledges receipt and application of the peer's SETTINGS frame. acknowledges receipt and application of the peer's SETTINGS frame.
When this bit is set, the frame payload of the SETTINGS frame MUST When this bit is set, the frame payload of the SETTINGS frame MUST
be empty. Receipt of a SETTINGS frame with the ACK flag set and a be empty. Receipt of a SETTINGS frame with the ACK flag set and a
length field value other than 0 MUST be treated as a connection length field value other than 0 MUST be treated as a connection
error (Section 5.4.1) of type FRAME_SIZE_ERROR. For more error (Section 5.4.1) of type FRAME_SIZE_ERROR. For more
information, see Section 6.5.3 ("Settings Synchronization"). information, see Section 6.5.3 ("Settings Synchronization").
SETTINGS frames always apply to a connection, never a single stream. SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a SETTINGS frame MUST be zero (0x0). If an The stream identifier for a SETTINGS frame MUST be zero (0x00). If
endpoint receives a SETTINGS frame whose stream identifier field is an endpoint receives a SETTINGS frame whose Stream Identifier field
anything other than 0x0, the endpoint MUST respond with a connection is anything other than 0x00, the endpoint MUST respond with a
error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The SETTINGS frame affects connection state. A badly formed or The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error incomplete SETTINGS frame MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
A SETTINGS frame with a length other than a multiple of 6 octets MUST A SETTINGS frame with a length other than a multiple of 6 octets MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR. FRAME_SIZE_ERROR.
6.5.1. SETTINGS Format 6.5.1. SETTINGS Format
The frame payload of a SETTINGS frame consists of zero or more The frame payload of a SETTINGS frame consists of zero or more
settings, each consisting of an unsigned 16-bit setting identifier settings, each consisting of an unsigned 16-bit setting identifier
and an unsigned 32-bit value. and an unsigned 32-bit value.
SETTINGS Frame { SETTINGS Frame {
Length (24), Length (24),
Type (8) = 0x4, Type (8) = 0x04,
Unused Flags (7), Unused Flags (7),
ACK Flag (1), ACK Flag (1),
Reserved (1), Reserved (1),
Stream Identifier (31) = 0, Stream Identifier (31) = 0,
Setting (48) ..., Setting (48) ...,
} }
skipping to change at page 36, line 18 skipping to change at line 1657
of: of:
Identifier: A 16-bit setting identifier; see Section 6.5.2. Identifier: A 16-bit setting identifier; see Section 6.5.2.
Value: A 32-bit value for the setting. Value: A 32-bit value for the setting.
6.5.2. Defined Settings 6.5.2. Defined Settings
The following settings are defined: The following settings are defined:
SETTINGS_HEADER_TABLE_SIZE (0x1): Allows the sender to inform the SETTINGS_HEADER_TABLE_SIZE (0x01): This setting allows the sender to
remote endpoint of the maximum size of the compression table used inform the remote endpoint of the maximum size of the compression
to decode field blocks, in units of octets. The encoder can table used to decode field blocks, in units of octets. The
select any size equal to or less than this value by using encoder can select any size equal to or less than this value by
signaling specific to the compression format inside a field block using signaling specific to the compression format inside a field
(see [COMPRESSION]). The initial value is 4,096 octets. block (see [COMPRESSION]). The initial value is 4,096 octets.
SETTINGS_ENABLE_PUSH (0x2): This setting can be used to disable SETTINGS_ENABLE_PUSH (0x02): This setting can be used to enable or
server push (Section 8.4). A server MUST NOT send a PUSH_PROMISE disable server push. A server MUST NOT send a PUSH_PROMISE frame
frame if it receives this parameter set to a value of 0. A client if it receives this parameter set to a value of 0; see
that has both set this parameter to 0 and had it acknowledged MUST Section 8.4. A client that has both set this parameter to 0 and
treat the receipt of a PUSH_PROMISE frame as a connection error had it acknowledged MUST treat the receipt of a PUSH_PROMISE frame
(Section 5.4.1) of type PROTOCOL_ERROR. as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The initial value of SETTINGS_ENABLE_PUSH is 1. For a client this The initial value of SETTINGS_ENABLE_PUSH is 1. For a client,
value indicates that it is willing to receive PUSH_PROMISE frames. this value indicates that it is willing to receive PUSH_PROMISE
For a server this initial value has no effect, and is equivalent frames. For a server, this initial value has no effect, and is
to the value 0. Any value other than 0 or 1 MUST be treated as a equivalent to the value 0. Any value other than 0 or 1 MUST be
connection error (Section 5.4.1) of type PROTOCOL_ERROR. treated as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
A server MUST NOT explicitly set this value to 1. A server MAY A server MUST NOT explicitly set this value to 1. A server MAY
choose to omit this setting when it sends a SETTINGS frame, but if choose to omit this setting when it sends a SETTINGS frame, but if
a server does include a value it MUST be 0. A client MUST treat a server does include a value, it MUST be 0. A client MUST treat
receipt of a SETTINGS frame with SETTINGS_ENABLE_PUSH set to 1 as receipt of a SETTINGS frame with SETTINGS_ENABLE_PUSH set to 1 as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR. a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_CONCURRENT_STREAMS (0x3): Indicates the maximum number SETTINGS_MAX_CONCURRENT_STREAMS (0x03): This setting indicates the
of concurrent streams that the sender will allow. This limit is maximum number of concurrent streams that the sender will allow.
directional: it applies to the number of streams that the sender This limit is directional: it applies to the number of streams
permits the receiver to create. Initially, there is no limit to that the sender permits the receiver to create. Initially, there
this value. It is recommended that this value be no smaller than is no limit to this value. It is recommended that this value be
100, so as to not unnecessarily limit parallelism. no smaller than 100, so as to not unnecessarily limit parallelism.
A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be
treated as special by endpoints. A zero value does prevent the treated as special by endpoints. A zero value does prevent the
creation of new streams; however, this can also happen for any creation of new streams; however, this can also happen for any
limit that is exhausted with active streams. Servers SHOULD only limit that is exhausted with active streams. Servers SHOULD only
set a zero value for short durations; if a server does not wish to set a zero value for short durations; if a server does not wish to
accept requests, closing the connection is more appropriate. accept requests, closing the connection is more appropriate.
SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (0x04): This setting indicates the
window size (in units of octets) for stream-level flow control. sender's initial window size (in units of octets) for stream-level
The initial value is 2^16-1 (65,535) octets. flow control. The initial value is 2^16-1 (65,535) octets.
This setting affects the window size of all streams (see This setting affects the window size of all streams (see
Section 6.9.2). Section 6.9.2).
Values above the maximum flow-control window size of 2^31-1 MUST Values above the maximum flow-control window size of 2^31-1 MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FLOW_CONTROL_ERROR. FLOW_CONTROL_ERROR.
SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest SETTINGS_MAX_FRAME_SIZE (0x05): This setting indicates the size of
frame payload that the sender is willing to receive, in units of the largest frame payload that the sender is willing to receive,
octets. in units of octets.
The initial value is 2^14 (16,384) octets. The value advertised The initial value is 2^14 (16,384) octets. The value advertised
by an endpoint MUST be between this initial value and the maximum by an endpoint MUST be between this initial value and the maximum
allowed frame size (2^24-1 or 16,777,215 octets), inclusive. allowed frame size (2^24-1 or 16,777,215 octets), inclusive.
Values outside this range MUST be treated as a connection error Values outside this range MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a SETTINGS_MAX_HEADER_LIST_SIZE (0x06): This advisory setting informs
peer of the maximum size of field section that the sender is a peer of the maximum field section size that the sender is
prepared to accept, in units of octets. The value is based on the prepared to accept, in units of octets. The value is based on the
uncompressed size of field lines, including the length of the name uncompressed size of field lines, including the length of the name
and value in units of octets plus an overhead of 32 octets for and value in units of octets plus an overhead of 32 octets for
each field line. each field line.
For any given request, a lower limit than what is advertised MAY For any given request, a lower limit than what is advertised MAY
be enforced. The initial value of this setting is unlimited. be enforced. The initial value of this setting is unlimited.
An endpoint that receives a SETTINGS frame with any unknown or An endpoint that receives a SETTINGS frame with any unknown or
unsupported identifier MUST ignore that setting. unsupported identifier MUST ignore that setting.
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settings MUST be ignored. Once all values have been processed, the settings MUST be ignored. Once all values have been processed, the
recipient MUST immediately emit a SETTINGS frame with the ACK flag recipient MUST immediately emit a SETTINGS frame with the ACK flag
set. Upon receiving a SETTINGS frame with the ACK flag set, the set. Upon receiving a SETTINGS frame with the ACK flag set, the
sender of the altered settings can rely on the values from the oldest sender of the altered settings can rely on the values from the oldest
unacknowledged SETTINGS frame having been applied. unacknowledged SETTINGS frame having been applied.
If the sender of a SETTINGS frame does not receive an acknowledgment If the sender of a SETTINGS frame does not receive an acknowledgment
within a reasonable amount of time, it MAY issue a connection error within a reasonable amount of time, it MAY issue a connection error
(Section 5.4.1) of type SETTINGS_TIMEOUT. In setting a timeout, some (Section 5.4.1) of type SETTINGS_TIMEOUT. In setting a timeout, some
allowance needs to be made for processing delays at the peer; a allowance needs to be made for processing delays at the peer; a
timeout that is solely based on the round trip time between endpoints timeout that is solely based on the round-trip time between endpoints
might result in spurious errors. might result in spurious errors.
6.6. PUSH_PROMISE 6.6. PUSH_PROMISE
The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint The PUSH_PROMISE frame (type=0x05) is used to notify the peer
in advance of streams the sender intends to initiate. The endpoint in advance of streams the sender intends to initiate. The
PUSH_PROMISE frame includes the unsigned 31-bit identifier of the PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
stream the endpoint plans to create along with a field section that stream the endpoint plans to create along with a field section that
provides additional context for the stream. Section 8.4 contains a provides additional context for the stream. Section 8.4 contains a
thorough description of the use of PUSH_PROMISE frames. thorough description of the use of PUSH_PROMISE frames.
PUSH_PROMISE Frame { PUSH_PROMISE Frame {
Length (24), Length (24),
Type (8) = 0x5, Type (8) = 0x05,
Unused Flags (4), Unused Flags (4),
PADDED Flag (1), PADDED Flag (1),
END_HEADERS Flag (1), END_HEADERS Flag (1),
Unused Flags (2), Unused Flags (2),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
[Pad Length (8)], [Pad Length (8)],
skipping to change at page 39, line 34 skipping to change at line 1794
Figure 8: PUSH_PROMISE Frame Format Figure 8: PUSH_PROMISE Frame Format
The Length, Type, Unused Flag(s), Reserved, and Stream Identifier The Length, Type, Unused Flag(s), Reserved, and Stream Identifier
fields are described in Section 4. The PUSH_PROMISE frame payload fields are described in Section 4. The PUSH_PROMISE frame payload
has the following additional fields: has the following additional fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is only present if the padding in units of octets. This field is only present if the
PADDED flag is set. PADDED flag is set.
Reserved: A single reserved bit.
Promised Stream ID: An unsigned 31-bit integer that identifies the Promised Stream ID: An unsigned 31-bit integer that identifies the
stream that is reserved by the PUSH_PROMISE. The promised stream stream that is reserved by the PUSH_PROMISE. The promised stream
identifier MUST be a valid choice for the next stream sent by the identifier MUST be a valid choice for the next stream sent by the
sender (see "new stream identifier" in Section 5.1.1). sender (see "new stream identifier" in Section 5.1.1).
Field Block Fragment: A field block fragment (Section 4.3) Field Block Fragment: A field block fragment (Section 4.3)
containing request control data and header section. containing the request control data and a header section.
Padding: Padding octets that contain no application semantic value. Padding: Padding octets that contain no application semantic value.
Padding octets MUST be set to zero when sending. A receiver is Padding octets MUST be set to zero when sending. A receiver is
not obligated to verify padding but MAY treat non-zero padding as not obligated to verify padding but MAY treat non-zero padding as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR. a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The PUSH_PROMISE frame defines the following flags: The PUSH_PROMISE frame defines the following flags:
PADDED (0x8): When set, the PADDED flag indicates that the Pad PADDED (0x08): When set, the PADDED flag indicates that the Pad
Length field and any padding that it describes are present. Length field and any padding that it describes are present.
END_HEADERS (0x4): When set, the END_HEADERS flag indicates that END_HEADERS (0x04): When set, the END_HEADERS flag indicates that
this frame contains an entire field block (Section 4.3) and is not this frame contains an entire field block (Section 4.3) and is not
followed by any CONTINUATION frames. followed by any CONTINUATION frames.
A PUSH_PROMISE frame without the END_HEADERS flag set MUST be A PUSH_PROMISE frame without the END_HEADERS flag set MUST be
followed by a CONTINUATION frame for the same stream. A receiver followed by a CONTINUATION frame for the same stream. A receiver
MUST treat the receipt of any other type of frame or a frame on a MUST treat the receipt of any other type of frame or a frame on a
different stream as a connection error (Section 5.4.1) of type different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
PUSH_PROMISE frames MUST only be sent on a peer-initiated stream that PUSH_PROMISE frames MUST only be sent on a peer-initiated stream that
is in either the "open" or "half-closed (remote)" state. The stream is in either the "open" or "half-closed (remote)" state. The stream
identifier of a PUSH_PROMISE frame indicates the stream it is identifier of a PUSH_PROMISE frame indicates the stream it is
associated with. If the stream identifier field specifies the value associated with. If the Stream Identifier field specifies the value
0x0, a recipient MUST respond with a connection error (Section 5.4.1) 0x00, a recipient MUST respond with a connection error
of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
Promised streams are not required to be used in the order they are Promised streams are not required to be used in the order they are
promised. The PUSH_PROMISE only reserves stream identifiers for promised. The PUSH_PROMISE only reserves stream identifiers for
later use. later use.
PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH setting of PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH setting of
the peer endpoint is set to 0. An endpoint that has set this setting the peer endpoint is set to 0. An endpoint that has set this setting
and has received acknowledgment MUST treat the receipt of a and has received acknowledgment MUST treat the receipt of a
PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PUSH_PROMISE frame as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
Recipients of PUSH_PROMISE frames can choose to reject promised Recipients of PUSH_PROMISE frames can choose to reject promised
streams by returning a RST_STREAM referencing the promised stream streams by returning a RST_STREAM referencing the promised stream
identifier back to the sender of the PUSH_PROMISE. identifier back to the sender of the PUSH_PROMISE.
A PUSH_PROMISE frame modifies the connection state in two ways. A PUSH_PROMISE frame modifies the connection state in two ways.
First, the inclusion of a field block (Section 4.3) potentially First, the inclusion of a field block (Section 4.3) potentially
modifies the state maintained for field section compression. Second, modifies the state maintained for field section compression. Second,
PUSH_PROMISE also reserves a stream for later use, causing the PUSH_PROMISE also reserves a stream for later use, causing the
promised stream to enter the "reserved" state. A sender MUST NOT promised stream to enter the "reserved (local)" or "reserved
send a PUSH_PROMISE on a stream unless that stream is either "open" (remote)" state. A sender MUST NOT send a PUSH_PROMISE on a stream
or "half-closed (remote)"; the sender MUST ensure that the promised unless that stream is either "open" or "half-closed (remote)"; the
stream is a valid choice for a new stream identifier (Section 5.1.1) sender MUST ensure that the promised stream is a valid choice for a
(that is, the promised stream MUST be in the "idle" state). 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 Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame
causes the stream state to become indeterminate. A receiver MUST causes the stream state to become indeterminate. A receiver MUST
treat the receipt of a PUSH_PROMISE on a stream that is neither treat the receipt of a PUSH_PROMISE on a stream that is neither
"open" nor "half-closed (local)" as a connection error "open" nor "half-closed (local)" as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. However, an endpoint that (Section 5.4.1) of type PROTOCOL_ERROR. However, an endpoint that
has sent RST_STREAM on the associated stream MUST handle PUSH_PROMISE has sent RST_STREAM on the associated stream MUST handle PUSH_PROMISE
frames that might have been created before the RST_STREAM frame is frames that might have been created before the RST_STREAM frame is
received and processed. received and processed.
skipping to change at page 41, line 30 skipping to change at line 1879
The total number of padding octets is determined by the value of the The total number of padding octets is determined by the value of the
Pad Length field. If the length of the padding is the length of the Pad Length field. If the length of the padding is the length of the
frame payload or greater, the recipient MUST treat this as a frame payload or greater, the recipient MUST treat this as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
| Note: A frame can be increased in size by one octet by | Note: A frame can be increased in size by one octet by
| including a Pad Length field with a value of zero. | including a Pad Length field with a value of zero.
6.7. PING 6.7. PING
The PING frame (type=0x6) is a mechanism for measuring a minimal The PING frame (type=0x06) is a mechanism for measuring a minimal
round-trip time from the sender, as well as determining whether an round-trip time from the sender, as well as determining whether an
idle connection is still functional. PING frames can be sent from idle connection is still functional. PING frames can be sent from
any endpoint. any endpoint.
PING Frame { PING Frame {
Length (24) = 0x8, Length (24) = 0x08,
Type (8) = 0x6, Type (8) = 0x06,
Unused Flags (7), Unused Flags (7),
ACK Flag (1), ACK Flag (1),
Reserved (1), Reserved (1),
Stream Identifier (31) = 0, Stream Identifier (31) = 0,
Opaque Data (64), Opaque Data (64),
} }
skipping to change at page 42, line 16 skipping to change at line 1913
opaque data in the frame payload. A sender can include any value it opaque data in the frame payload. A sender can include any value it
chooses and use those octets in any fashion. chooses and use those octets in any fashion.
Receivers of a PING frame that does not include an ACK flag MUST send Receivers of a PING frame that does not include an ACK flag MUST send
a PING frame with the ACK flag set in response, with an identical a PING frame with the ACK flag set in response, with an identical
frame payload. PING responses SHOULD be given higher priority than frame payload. PING responses SHOULD be given higher priority than
any other frame. any other frame.
The PING frame defines the following flags: The PING frame defines the following flags:
ACK (0x1): When set, the ACK flag indicates that this PING frame is ACK (0x01): When set, the ACK flag indicates that this PING frame is
a PING response. An endpoint MUST set this flag in PING a PING response. An endpoint MUST set this flag in PING
responses. An endpoint MUST NOT respond to PING frames containing responses. An endpoint MUST NOT respond to PING frames containing
this flag. this flag.
PING frames are not associated with any individual stream. If a PING PING frames are not associated with any individual stream. If a PING
frame is received with a stream identifier field value other than frame is received with a Stream Identifier field value other than
0x0, the recipient MUST respond with a connection error 0x00, the recipient MUST respond with a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
Receipt of a PING frame with a length field value other than 8 MUST Receipt of a PING frame with a length field value other than 8 MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR. FRAME_SIZE_ERROR.
6.8. GOAWAY 6.8. GOAWAY
The GOAWAY frame (type=0x7) is used to initiate shutdown of a The GOAWAY frame (type=0x07) is used to initiate shutdown of a
connection or to signal serious error conditions. GOAWAY allows an connection or to signal serious error conditions. GOAWAY allows an
endpoint to gracefully stop accepting new streams while still endpoint to gracefully stop accepting new streams while still
finishing processing of previously established streams. This enables finishing processing of previously established streams. This enables
administrative actions, like server maintenance. administrative actions, like server maintenance.
There is an inherent race condition between an endpoint starting new There is an inherent race condition between an endpoint starting new
streams and the remote sending a GOAWAY frame. To deal with this streams and the remote peer sending a GOAWAY frame. To deal with
case, the GOAWAY contains the stream identifier of the last peer- this case, the GOAWAY contains the stream identifier of the last
initiated stream that was or might be processed on the sending peer-initiated stream that was or might be processed on the sending
endpoint in this connection. For instance, if the server sends a endpoint in this connection. For instance, if the server sends a
GOAWAY frame, the identified stream is the highest-numbered stream GOAWAY frame, the identified stream is the highest-numbered stream
initiated by the client. initiated by the client.
Once sent, the sender will ignore frames sent on streams initiated by Once the GOAWAY is sent, the sender will ignore frames sent on
the receiver if the stream has an identifier higher than the included streams initiated by the receiver if the stream has an identifier
last stream identifier. Receivers of a GOAWAY frame MUST NOT open higher than the included last stream identifier. Receivers of a
additional streams on the connection, although a new connection can GOAWAY frame MUST NOT open additional streams on the connection,
be established for new streams. although a new connection can be established for new streams.
If the receiver of the GOAWAY has sent data on streams with a higher If the receiver of the GOAWAY has sent data on streams with a higher
stream identifier than what is indicated in the GOAWAY frame, those stream identifier than what is indicated in the GOAWAY frame, those
streams are not or will not be processed. The receiver of the GOAWAY streams are not or will not be processed. The receiver of the GOAWAY
frame can treat the streams as though they had never been created at frame can treat the streams as though they had never been created at
all, thereby allowing those streams to be retried later on a new all, thereby allowing those streams to be retried later on a new
connection. connection.
Endpoints SHOULD always send a GOAWAY frame before closing a Endpoints SHOULD always send a GOAWAY frame before closing a
connection so that the remote peer can know whether a stream has been connection so that the remote peer can know whether a stream has been
skipping to change at page 43, line 30 skipping to change at line 1974
An endpoint might choose to close a connection without sending a An endpoint might choose to close a connection without sending a
GOAWAY for misbehaving peers. GOAWAY for misbehaving peers.
A GOAWAY frame might not immediately precede closing of the A GOAWAY frame might not immediately precede closing of the
connection; a receiver of a GOAWAY that has no more use for the connection; a receiver of a GOAWAY that has no more use for the
connection SHOULD still send a GOAWAY frame before terminating the connection SHOULD still send a GOAWAY frame before terminating the
connection. connection.
GOAWAY Frame { GOAWAY Frame {
Length (24), Length (24),
Type (8) = 0x7, Type (8) = 0x07,
Unused Flags (8), Unused Flags (8),
Reserved (1), Reserved (1),
Stream Identifier (31) = 0, Stream Identifier (31) = 0,
Reserved (1), Reserved (1),
Last-Stream-ID (31), Last-Stream-ID (31),
Error Code (32), Error Code (32),
Additional Debug Data (..), Additional Debug Data (..),
skipping to change at page 44, line 7 skipping to change at line 1996
Figure 10: GOAWAY Frame Format Figure 10: GOAWAY Frame Format
The Length, Type, Unused Flag(s), Reserved, and Stream Identifier The Length, Type, Unused Flag(s), Reserved, and Stream Identifier
fields are described in Section 4. fields are described in Section 4.
The GOAWAY frame does not define any flags. The GOAWAY frame does not define any flags.
The GOAWAY frame applies to the connection, not a specific stream. The GOAWAY frame applies to the connection, not a specific stream.
An endpoint MUST treat a GOAWAY frame with a stream identifier other An endpoint MUST treat a GOAWAY frame with a stream identifier other
than 0x0 as a connection error (Section 5.4.1) of type than 0x00 as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
The last stream identifier in the GOAWAY frame contains the highest- The last stream identifier in the GOAWAY frame contains the highest-
numbered stream identifier for which the sender of the GOAWAY frame numbered stream identifier for which the sender of the GOAWAY frame
might have taken some action on or might yet take action on. All might have taken some action on or might yet take action on. All
streams up to and including the identified stream might have been streams up to and including the identified stream might have been
processed in some way. The last stream identifier can be set to 0 if processed in some way. The last stream identifier can be set to 0 if
no streams were processed. no streams were processed.
| Note: In this context, "processed" means that some data from | Note: In this context, "processed" means that some data from
skipping to change at page 44, line 31 skipping to change at line 2020
If a connection terminates without a GOAWAY frame, the last stream If a connection terminates without a GOAWAY frame, the last stream
identifier is effectively the highest possible stream identifier. identifier is effectively the highest possible stream identifier.
On streams with lower- or equal-numbered identifiers that were not On streams with lower- or equal-numbered identifiers that were not
closed completely prior to the connection being closed, reattempting closed completely prior to the connection being closed, reattempting
requests, transactions, or any protocol activity is not possible, requests, transactions, or any protocol activity is not possible,
except for idempotent actions like HTTP GET, PUT, or DELETE. Any except for idempotent actions like HTTP GET, PUT, or DELETE. Any
protocol activity that uses higher-numbered streams can be safely protocol activity that uses higher-numbered streams can be safely
retried using a new connection. retried using a new connection.
Activity on streams numbered lower or equal to the last stream Activity on streams numbered lower than or equal to the last stream
identifier might still complete successfully. The sender of a GOAWAY identifier might still complete successfully. The sender of a GOAWAY
frame might gracefully shut down a connection by sending a GOAWAY frame might gracefully shut down a connection by sending a GOAWAY
frame, maintaining the connection in an "open" state until all in- frame, maintaining the connection in an "open" state until all in-
progress streams complete. progress streams complete.
An endpoint MAY send multiple GOAWAY frames if circumstances change. An endpoint MAY send multiple GOAWAY frames if circumstances change.
For instance, an endpoint that sends GOAWAY with NO_ERROR during For instance, an endpoint that sends GOAWAY with NO_ERROR during
graceful shutdown could subsequently encounter a condition that graceful shutdown could subsequently encounter a condition that
requires immediate termination of the connection. The last stream requires immediate termination of the connection. The last stream
identifier from the last GOAWAY frame received indicates which identifier from the last GOAWAY frame received indicates which
skipping to change at page 45, line 14 skipping to change at line 2052
requests is prohibited. After allowing time for any in-flight stream requests is prohibited. After allowing time for any in-flight stream
creation (at least one round-trip time), the server MAY send another creation (at least one round-trip time), the server MAY send another
GOAWAY frame with an updated last stream identifier. This ensures GOAWAY frame with an updated last stream identifier. This ensures
that a connection can be cleanly shut down without losing requests. that a connection can be cleanly shut down without losing requests.
After sending a GOAWAY frame, the sender can discard frames for After sending a GOAWAY frame, the sender can discard frames for
streams initiated by the receiver with identifiers higher than the streams initiated by the receiver with identifiers higher than the
identified last stream. However, any frames that alter connection identified last stream. However, any frames that alter connection
state cannot be completely ignored. For instance, HEADERS, state cannot be completely ignored. For instance, HEADERS,
PUSH_PROMISE, and CONTINUATION frames MUST be minimally processed to PUSH_PROMISE, and CONTINUATION frames MUST be minimally processed to
ensure the state maintained for field section compression is ensure that the state maintained for field section compression is
consistent (see Section 4.3); similarly, DATA frames MUST be counted consistent (see Section 4.3); similarly, DATA frames MUST be counted
toward the connection flow-control window. Failure to process these toward the connection flow-control window. Failure to process these
frames can cause flow control or field section compression state to frames can cause flow control or field section compression state to
become unsynchronized. become unsynchronized.
The GOAWAY frame also contains a 32-bit error code (Section 7) that The GOAWAY frame also contains a 32-bit error code (Section 7) that
contains the reason for closing the connection. contains the reason for closing the connection.
Endpoints MAY append opaque data to the frame payload of any GOAWAY Endpoints MAY append opaque data to the frame payload of any GOAWAY
frame. Additional debug data is intended for diagnostic purposes frame. Additional debug data is intended for diagnostic purposes
only and carries no semantic value. Debug information could contain only and carries no semantic value. Debug information could contain
security- or privacy-sensitive data. Logged or otherwise security- or privacy-sensitive data. Logged or otherwise
persistently stored debug data MUST have adequate safeguards to persistently stored debug data MUST have adequate safeguards to
prevent unauthorized access. prevent unauthorized access.
6.9. WINDOW_UPDATE 6.9. WINDOW_UPDATE
The WINDOW_UPDATE frame (type=0x8) is used to implement flow control; The WINDOW_UPDATE frame (type=0x08) is used to implement flow
see Section 5.2 for an overview. control; see Section 5.2 for an overview.
Flow control operates at two levels: on each individual stream and on Flow control operates at two levels: on each individual stream and on
the entire connection. the entire connection.
Both types of flow control are hop by hop, that is, only between the Both types of flow control are hop by hop, that is, only between the
two endpoints. Intermediaries do not forward WINDOW_UPDATE frames two endpoints. Intermediaries do not forward WINDOW_UPDATE frames
between dependent connections. However, throttling of data transfer between dependent connections. However, throttling of data transfer
by any receiver can indirectly cause the propagation of flow-control by any receiver can indirectly cause the propagation of flow-control
information toward the original sender. information toward the original sender.
Flow control only applies to frames that are identified as being Flow control only applies to frames that are identified as being
subject to flow control. Of the frame types defined in this subject to flow control. Of the frame types defined in this
document, this includes only DATA frames. Frames that are exempt document, this includes only DATA frames. Frames that are exempt
from flow control MUST be accepted and processed, unless the receiver from flow control MUST be accepted and processed, unless the receiver
is unable to assign resources to handling the frame. A receiver MAY is unable to assign resources to handling the frame. A receiver MAY
respond with a stream error (Section 5.4.2) or connection error respond with a stream error (Section 5.4.2) or connection error
(Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept (Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept
a frame. a frame.
WINDOW_UPDATE Frame { WINDOW_UPDATE Frame {
Length (24) = 0x4, Length (24) = 0x04,
Type (8) = 0x8, Type (8) = 0x08,
Unused Flags (8), Unused Flags (8),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
Reserved (1), Reserved (1),
Window Size Increment (31), Window Size Increment (31),
} }
skipping to change at page 46, line 42 skipping to change at line 2128
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
A receiver MUST treat the receipt of a WINDOW_UPDATE frame with a A receiver MUST treat the receipt of a WINDOW_UPDATE frame with a
flow-control window increment of 0 as a stream error (Section 5.4.2) flow-control window increment of 0 as a stream error (Section 5.4.2)
of type PROTOCOL_ERROR; errors on the connection flow-control window of type PROTOCOL_ERROR; errors on the connection flow-control window
MUST be treated as a connection error (Section 5.4.1). MUST be treated as a connection error (Section 5.4.1).
WINDOW_UPDATE can be sent by a peer that has sent a frame with the WINDOW_UPDATE can be sent by a peer that has sent a frame with the
END_STREAM flag set. This means that a receiver could receive a END_STREAM flag set. This means that a receiver could receive a
WINDOW_UPDATE frame on a "half-closed (remote)" or "closed" stream. WINDOW_UPDATE frame on a stream in a "half-closed (remote)" or
A receiver MUST NOT treat this as an error (see Section 5.1). "closed" state. A receiver MUST NOT treat this as an error (see
Section 5.1).
A receiver that receives a flow-controlled frame MUST always account A receiver that receives a flow-controlled frame MUST always account
for its contribution against the connection flow-control window, for its contribution against the connection flow-control window,
unless the receiver treats this as a connection error unless the receiver treats this as a connection error
(Section 5.4.1). This is necessary even if the frame is in error. (Section 5.4.1). This is necessary even if the frame is in error.
The sender counts the frame toward the flow-control window, but if The sender counts the frame toward the flow-control window, but if
the receiver does not, the flow-control window at the sender and the receiver does not, the flow-control window at the sender and
receiver can become different. receiver can become different.
A WINDOW_UPDATE frame with a length other than 4 octets MUST be A WINDOW_UPDATE frame with a length other than 4 octets MUST be
skipping to change at page 49, line 24 skipping to change at line 2251
window size, a receiver MAY continue to process streams that exceed window size, a receiver MAY continue to process streams that exceed
flow-control limits. Allowing streams to continue does not allow the flow-control limits. Allowing streams to continue does not allow the
receiver to immediately reduce the space it reserves for flow-control receiver to immediately reduce the space it reserves for flow-control
windows. Progress on these streams can also stall, since windows. Progress on these streams can also stall, since
WINDOW_UPDATE frames are needed to allow the sender to resume WINDOW_UPDATE frames are needed to allow the sender to resume
sending. The receiver MAY instead send a RST_STREAM with an error sending. The receiver MAY instead send a RST_STREAM with an error
code of FLOW_CONTROL_ERROR for the affected streams. code of FLOW_CONTROL_ERROR for the affected streams.
6.10. CONTINUATION 6.10. CONTINUATION
The CONTINUATION frame (type=0x9) is used to continue a sequence of The CONTINUATION frame (type=0x09) is used to continue a sequence of
field block fragments (Section 4.3). Any number of CONTINUATION field block fragments (Section 4.3). Any number of CONTINUATION
frames can be sent, as long as the preceding frame is on the same frames can be sent, as long as the preceding frame is on the same
stream and is a HEADERS, PUSH_PROMISE, or CONTINUATION frame without stream and is a HEADERS, PUSH_PROMISE, or CONTINUATION frame without
the END_HEADERS flag set. the END_HEADERS flag set.
CONTINUATION Frame { CONTINUATION Frame {
Length (24), Length (24),
Type (8) = 0x9, Type (8) = 0x09,
Unused Flags (5), Unused Flags (5),
END_HEADERS Flag (1), END_HEADERS Flag (1),
Unused Flags (2), Unused Flags (2),
Reserved (1), Reserved (1),
Stream Identifier (31), Stream Identifier (31),
Field Block Fragment (..), Field Block Fragment (..),
} }
Figure 12: CONTINUATION Frame Format Figure 12: CONTINUATION Frame Format
The Length, Type, Unused Flag(s), Reserved, and Stream Identifier The Length, Type, Unused Flag(s), Reserved, and Stream Identifier
fields are described in Section 4. The CONTINUATION frame payload fields are described in Section 4. The CONTINUATION frame payload
contains a field block fragment (Section 4.3). contains a field block fragment (Section 4.3).
The CONTINUATION frame defines the following flag: The CONTINUATION frame defines the following flag:
END_HEADERS (0x4): When set, the END_HEADERS flag indicates that END_HEADERS (0x04): When set, the END_HEADERS flag indicates that
this frame ends a field block (Section 4.3). this frame ends a field block (Section 4.3).
If the END_HEADERS flag is not set, this frame MUST be followed by If the END_HEADERS flag is not set, this frame MUST be followed by
another CONTINUATION frame. A receiver MUST treat the receipt of another CONTINUATION frame. A receiver MUST treat the receipt of
any other type of frame or a frame on a different stream as a any other type of frame or a frame on a different stream as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The CONTINUATION frame changes the connection state as defined in The CONTINUATION frame changes the connection state as defined in
Section 4.3. Section 4.3.
CONTINUATION frames MUST be associated with a stream. If a CONTINUATION frames MUST be associated with a stream. If a
CONTINUATION frame is received whose stream identifier field is 0x0, CONTINUATION frame is received with a Stream Identifier field of
the recipient MUST respond with a connection error (Section 5.4.1) of 0x00, the recipient MUST respond with a connection error
type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or
CONTINUATION frame without the END_HEADERS flag set. A recipient CONTINUATION frame without the END_HEADERS flag set. A recipient
that observes violation of this rule MUST respond with a connection that observes violation of this rule MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
7. Error Codes 7. Error Codes
Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
frames to convey the reasons for the stream or connection error. frames to convey the reasons for the stream or connection error.
Error codes share a common code space. Some error codes apply only Error codes share a common code space. Some error codes apply only
to either streams or the entire connection and have no defined to either streams or the entire connection and have no defined
semantics in the other context. semantics in the other context.
The following error codes are defined: The following error codes are defined:
NO_ERROR (0x0): The associated condition is not a result of an NO_ERROR (0x00): The associated condition is not a result of an
error. For example, a GOAWAY might include this code to indicate error. For example, a GOAWAY might include this code to indicate
graceful shutdown of a connection. graceful shutdown of a connection.
PROTOCOL_ERROR (0x1): The endpoint detected an unspecific protocol PROTOCOL_ERROR (0x01): The endpoint detected an unspecific protocol
error. This error is for use when a more specific error code is error. This error is for use when a more specific error code is
not available. not available.
INTERNAL_ERROR (0x2): The endpoint encountered an unexpected INTERNAL_ERROR (0x02): The endpoint encountered an unexpected
internal error. internal error.
FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer FLOW_CONTROL_ERROR (0x03): The endpoint detected that its peer
violated the flow-control protocol. violated the flow-control protocol.
SETTINGS_TIMEOUT (0x4): The endpoint sent a SETTINGS frame but did SETTINGS_TIMEOUT (0x04): The endpoint sent a SETTINGS frame but did
not receive a response in a timely manner. See Section 6.5.3 not receive a response in a timely manner. See Section 6.5.3
("Settings Synchronization"). ("Settings Synchronization").
STREAM_CLOSED (0x5): The endpoint received a frame after a stream STREAM_CLOSED (0x05): The endpoint received a frame after a stream
was half-closed. was half-closed.
FRAME_SIZE_ERROR (0x6): The endpoint received a frame with an FRAME_SIZE_ERROR (0x06): The endpoint received a frame with an
invalid size. invalid size.
REFUSED_STREAM (0x7): The endpoint refused the stream prior to REFUSED_STREAM (0x07): The endpoint refused the stream prior to
performing any application processing (see Section 8.7 for performing any application processing (see Section 8.7 for
details). details).
CANCEL (0x8): Used by the endpoint to indicate that the stream is no CANCEL (0x08): The endpoint uses this error code to indicate that
longer needed. the stream is no longer needed.
COMPRESSION_ERROR (0x9): The endpoint is unable to maintain the COMPRESSION_ERROR (0x09): The endpoint is unable to maintain the
field section compression context for the connection. field section compression context for the connection.
CONNECT_ERROR (0xa): The connection established in response to a CONNECT_ERROR (0x0a): The connection established in response to a
CONNECT request (Section 8.5) was reset or abnormally closed. CONNECT request (Section 8.5) was reset or abnormally closed.
ENHANCE_YOUR_CALM (0xb): The endpoint detected that its peer is ENHANCE_YOUR_CALM (0x0b): The endpoint detected that its peer is
exhibiting a behavior that might be generating excessive load. exhibiting a behavior that might be generating excessive load.
INADEQUATE_SECURITY (0xc): The underlying transport has properties INADEQUATE_SECURITY (0x0c): The underlying transport has properties
that do not meet minimum security requirements (see Section 9.2). that do not meet minimum security requirements (see Section 9.2).
HTTP_1_1_REQUIRED (0xd): The endpoint requires that HTTP/1.1 be used HTTP_1_1_REQUIRED (0x0d): The endpoint requires that HTTP/1.1 be
instead of HTTP/2. used instead of HTTP/2.
Unknown or unsupported error codes MUST NOT trigger any special Unknown or unsupported error codes MUST NOT trigger any special
behavior. These MAY be treated by an implementation as being behavior. These MAY be treated by an implementation as being
equivalent to INTERNAL_ERROR. equivalent to INTERNAL_ERROR.
8. Expressing HTTP Semantics in HTTP/2 8. Expressing HTTP Semantics in HTTP/2
HTTP/2 is an instantiation of the HTTP message abstraction (Section 6 HTTP/2 is an instantiation of the HTTP message abstraction (Section 6
of [HTTP]). of [HTTP]).
skipping to change at page 52, line 29 skipping to change at line 2401
The last frame in the sequence bears an END_STREAM flag, noting that The last frame in the sequence bears an END_STREAM flag, noting that
a HEADERS frame with the END_STREAM flag set can be followed by a HEADERS frame with the END_STREAM flag set can be followed by
CONTINUATION frames that carry any remaining fragments of the field CONTINUATION frames that carry any remaining fragments of the field
block. block.
Other frames (from any stream) MUST NOT occur between the HEADERS Other frames (from any stream) MUST NOT occur between the HEADERS
frame and any CONTINUATION frames that might follow. frame and any CONTINUATION frames that might follow.
HTTP/2 uses DATA frames to carry message content. The chunked HTTP/2 uses DATA frames to carry message content. The chunked
transfer encoding defined in Section 7.1 of [HTTP11] cannot be used transfer encoding defined in Section 7.1 of [HTTP/1.1] cannot be used
in HTTP/2; see Section 8.2.2. in HTTP/2; see Section 8.2.2.
Trailer fields are carried in a field block that also terminates the Trailer fields are carried in a field block that also terminates the
stream. That is, trailer fields comprise a sequence starting with a stream. That is, trailer fields comprise a sequence starting with a
HEADERS frame, followed by zero or more CONTINUATION frames, where HEADERS frame, followed by zero or more CONTINUATION frames, where
the HEADERS frame bears an END_STREAM flag. Trailers MUST NOT the HEADERS frame bears an END_STREAM flag. Trailers MUST NOT
include pseudo-header fields (Section 8.3). An endpoint that include pseudo-header fields (Section 8.3). An endpoint that
receives pseudo-header fields in trailers MUST treat the request or receives pseudo-header fields in trailers MUST treat the request or
response as malformed (Section 8.1.1). response as malformed (Section 8.1.1).
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[COMPRESSION]. [COMPRESSION].
Field names MUST be converted to lowercase when constructing an Field names MUST be converted to lowercase when constructing an
HTTP/2 message. HTTP/2 message.
8.2.1. Field Validity 8.2.1. Field Validity
The definitions of field names and values in HTTP prohibit some The definitions of field names and values in HTTP prohibit some
characters that HPACK might be able to convey. HTTP/2 characters that HPACK might be able to convey. HTTP/2
implementations SHOULD validate field names and values according to implementations SHOULD validate field names and values according to
their definitions in Sections 5.1 and 5.5 of [HTTP] respectively and their definitions in Sections 5.1 and 5.5 of [HTTP], respectively,
treat messages that contain prohibited characters as malformed and treat messages that contain prohibited characters as malformed
(Section 8.1.1). (Section 8.1.1).
Failure to validate fields can be exploited for request smuggling Failure to validate fields can be exploited for request smuggling
attacks. In particular, unvalidated fields might enable attacks when attacks. In particular, unvalidated fields might enable attacks when
messages are forwarded using HTTP 1.1 [HTTP11], where characters such messages are forwarded using HTTP/1.1 [HTTP/1.1], where characters
as CR, LF, and COLON are used as delimiters. Implementations MUST such as carriage return (CR), line feed (LF), and COLON are used as
perform the following minimal validation of field names and values: delimiters. Implementations MUST perform the following minimal
validation of field names and values:
o A field name MUST NOT contain characters in the ranges 0x00-0x20, o A field name MUST NOT contain characters in the ranges 0x00-0x20,
0x41-0x5a, or 0x7f-0xff (all ranges inclusive). This specifically 0x41-0x5a, or 0x7f-0xff (all ranges inclusive). This specifically
excludes all non-visible ASCII characters, ASCII SP (0x20), and excludes all non-visible ASCII characters, ASCII SP (0x20), and
uppercase characters ('A' to 'Z', ASCII 0x41 to 0x5a). uppercase characters ('A' to 'Z', ASCII 0x41 to 0x5a).
o With the exception of pseudo-header fields (Section 8.3), which o With the exception of pseudo-header fields (Section 8.3), which
have a name that starts with a single colon, field names MUST NOT have a name that starts with a single colon, field names MUST NOT
include a colon (ASCII COLON, 0x3a). include a colon (ASCII COLON, 0x3a).
o A field value MUST NOT contain the zero value (ASCII NUL, 0x0), o A field value MUST NOT contain the zero value (ASCII NUL, 0x00),
line feed (ASCII LF, 0xa), or carriage return (ASCII CR, 0xd) at line feed (ASCII LF, 0x0a), or carriage return (ASCII CR, 0x0d) at
any position. any position.
o A field value MUST NOT start or end with an ASCII whitespace o A field value MUST NOT start or end with an ASCII whitespace
character (ASCII SP or HTAB, 0x20 or 0x9). character (ASCII SP or HTAB, 0x20 or 0x09).
| Note: An implementation that validates fields according the | Note: An implementation that validates fields according to the
| definitions in Sections 5.1 and 5.5 of [HTTP] only needs an | definitions in Sections 5.1 and 5.5 of [HTTP] only needs an
| additional check that field names do not include uppercase | additional check that field names do not include uppercase
| characters. | characters.
A request or response that contains a field that violates any of A request or response that contains a field that violates any of
these conditions MUST be treated as malformed (Section 8.1.1). In these conditions MUST be treated as malformed (Section 8.1.1). In
particular, an intermediary that does not process fields when particular, an intermediary that does not process fields when
forwarding messages MUST NOT forward fields that contain any of the forwarding messages MUST NOT forward fields that contain any of the
values that are listed as prohibited above. values that are listed as prohibited above.
skipping to change at page 56, line 19 skipping to change at line 2573
| Note: HTTP/2 purposefully does not support upgrade to another | Note: HTTP/2 purposefully does not support upgrade to another
| protocol. The handshake methods described in Section 3 are | protocol. The handshake methods described in Section 3 are
| believed sufficient to negotiate the use of alternative | believed sufficient to negotiate the use of alternative
| protocols. | protocols.
8.2.3. Compressing the Cookie Header Field 8.2.3. Compressing the Cookie Header Field
The Cookie header field [COOKIE] uses a semicolon (";") to delimit The Cookie header field [COOKIE] uses a semicolon (";") to delimit
cookie-pairs (or "crumbs"). This header field contains multiple cookie-pairs (or "crumbs"). This header field contains multiple
values, but does not use a COMMA (",") as a separator, which prevents values, but does not use a COMMA (",") as a separator, thereby
cookie-pairs from being sent on multiple field lines (see Section 5.2 preventing cookie-pairs from being sent on multiple field lines (see
of [HTTP]). This can significantly reduce compression efficiency as Section 5.2 of [HTTP]). This can significantly reduce compression
updates to individual cookie-pairs would invalidate any field lines efficiency, as updates to individual cookie-pairs would invalidate
that are stored in the HPACK table. any field lines that are stored in the HPACK table.
To allow for better compression efficiency, the Cookie header field To allow for better compression efficiency, the Cookie header field
MAY be split into separate header fields, each with one or more MAY be split into separate header fields, each with one or more
cookie-pairs. If there are multiple Cookie header fields after cookie-pairs. If there are multiple Cookie header fields after
decompression, these MUST be concatenated into a single octet string decompression, these MUST be concatenated into a single octet string
using the two-octet delimiter of 0x3b, 0x20 (the ASCII string "; ") using the two-octet delimiter of 0x3b, 0x20 (the ASCII string "; ")
before being passed into a non-HTTP/2 context, such as an HTTP/1.1 before being passed into a non-HTTP/2 context, such as an HTTP/1.1
connection, or a generic HTTP server application. connection, or a generic HTTP server application.
Therefore, the following two lists of Cookie header fields are Therefore, the following two lists of Cookie header fields are
semantically equivalent. semantically equivalent.
cookie: a=b; c=d; e=f cookie: a=b; c=d; e=f
cookie: a=b cookie: a=b
cookie: c=d cookie: c=d
cookie: e=f cookie: e=f
8.3. HTTP Control Data 8.3. HTTP Control Data
HTTP/2 uses special pseudo-header fields beginning with ':' character HTTP/2 uses special pseudo-header fields beginning with a ':'
(ASCII 0x3a) to convey message control data (see Section 6.2 of character (ASCII 0x3a) to convey message control data (see
[HTTP]). Section 6.2 of [HTTP]).
Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT
generate pseudo-header fields other than those defined in this generate pseudo-header fields other than those defined in this
document. Note that an extension could negotiate the use of document. Note that an extension could negotiate the use of
additional pseudo-header fields; see Section 5.5. additional pseudo-header fields; see Section 5.5.
Pseudo-header fields are only valid in the context in which they are Pseudo-header fields are only valid in the context in which they are
defined. Pseudo-header fields defined for requests MUST NOT appear defined. Pseudo-header fields defined for requests MUST NOT appear
in responses; pseudo-header fields defined for responses MUST NOT in responses; pseudo-header fields defined for responses MUST NOT
appear in requests. Pseudo-header fields MUST NOT appear in a appear in requests. Pseudo-header fields MUST NOT appear in a
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The same pseudo-header field name MUST NOT appear more than once in a The same pseudo-header field name MUST NOT appear more than once in a
field block. A field block for an HTTP request or response that field block. A field block for an HTTP request or response that
contains a repeated pseudo-header field name MUST be treated as contains a repeated pseudo-header field name MUST be treated as
malformed (Section 8.1.1). malformed (Section 8.1.1).
8.3.1. Request Pseudo-Header Fields 8.3.1. Request Pseudo-Header Fields
The following pseudo-header fields are defined for HTTP/2 requests: The following pseudo-header fields are defined for HTTP/2 requests:
o The :method pseudo-header field includes the HTTP method o The ":method" pseudo-header field includes the HTTP method
(Section 9 of [HTTP]). (Section 9 of [HTTP]).
o The :scheme pseudo-header field includes the scheme portion of the o The ":scheme" pseudo-header field includes the scheme portion of
request target. The scheme is taken from the target URI the request target. The scheme is taken from the target URI
(Section 3.1 of [RFC3986]) when generating a request directly, or (Section 3.1 of [RFC3986]) when generating a request directly, or
from the scheme of a translated request (for example, see from the scheme of a translated request (for example, see
Section 3.3 of [HTTP11]). Scheme is omitted for CONNECT requests Section 3.3 of [HTTP/1.1]). Scheme is omitted for CONNECT
(Section 8.5). requests (Section 8.5).
:scheme is not restricted to http and https schemed URIs. A proxy ":scheme" is not restricted to "http" and "https" schemed URIs. A
or gateway can translate requests for non-HTTP schemes, enabling proxy or gateway can translate requests for non-HTTP schemes,
the use of HTTP to interact with non-HTTP services. enabling the use of HTTP to interact with non-HTTP services.
o The :authority pseudo-header field conveys the authority portion o The ":authority" pseudo-header field conveys the authority portion
(Section 3.2 of [RFC3986]) of the target URI (Section 7.1 of (Section 3.2 of [RFC3986]) of the target URI (Section 7.1 of
[HTTP]). The recipient of a HTTP/2 request MUST NOT use the Host [HTTP]). The recipient of an HTTP/2 request MUST NOT use the Host
header field to determine the target URI if :authority is present. header field to determine the target URI if ":authority" is
present.
Clients that generate HTTP/2 requests directly MUST use the Clients that generate HTTP/2 requests directly MUST use the
:authority pseudo-header field to convey authority information, ":authority" pseudo-header field to convey authority information,
unless there is no authority information to convey (in which case unless there is no authority information to convey (in which case
it MUST NOT generate :authority). it MUST NOT generate ":authority").
Clients MUST NOT generate a request with a Host header field that Clients MUST NOT generate a request with a Host header field that
differs from the :authority pseudo-header field. A server SHOULD differs from the ":authority" pseudo-header field. A server
treat a request as malformed if it contains a Host header field SHOULD treat a request as malformed if it contains a Host header
that identifies a different entity to the :authority pseudo-header field that identifies an entity that differs from the entity in
field. The values of fields need to be normalized to compare them the ":authority" pseudo-header field. The values of fields need
(see Section 6.2 of [RFC3986]). An origin server can apply any to be normalized to compare them (see Section 6.2 of [RFC3986]).
normalization method, whereas other servers MUST perform scheme- An origin server can apply any normalization method, whereas other
based normalization (see Section 6.2.3 of [RFC3986]) of the two servers MUST perform scheme-based normalization (see Section 6.2.3
fields. of [RFC3986]) of the two fields.
An intermediary that forwards a request over HTTP/2 MUST construct An intermediary that forwards a request over HTTP/2 MUST construct
an :authority pseudo-header field using the authority information an ":authority" pseudo-header field using the authority
from the control data of the original request, unless the original information from the control data of the original request, unless
request's target URI does not contain authority information (in the original request's target URI does not contain authority
which case it MUST NOT generate :authority). Note that the Host information (in which case it MUST NOT generate ":authority").
header field is not the sole source of this information; see Note that the Host header field is not the sole source of this
Section 7.2 of [HTTP]. information; see Section 7.2 of [HTTP].
An intermediary that needs to generate a Host header field (which An intermediary that needs to generate a Host header field (which
might be necessary to construct an HTTP/1.1 request) MUST use the might be necessary to construct an HTTP/1.1 request) MUST use the
value from the :authority pseudo-header field as the value of the value from the ":authority" pseudo-header field as the value of
Host field, unless the intermediary also changes the request the Host field, unless the intermediary also changes the request
target. This replaces any existing Host field to avoid potential target. This replaces any existing Host field to avoid potential
vulnerabilities in HTTP routing. vulnerabilities in HTTP routing.
An intermediary that forwards a request over HTTP/2 MAY retain any An intermediary that forwards a request over HTTP/2 MAY retain any
Host header field. Host header field.
Note that request targets for CONNECT or asterisk-form OPTIONS Note that request targets for CONNECT or asterisk-form OPTIONS
requests never include authority information; see Section 7.1 of requests never include authority information; see Sections 7.1 and
[HTTP]. 7.2 of [HTTP].
:authority MUST NOT include the deprecated userinfo subcomponent ":authority" MUST NOT include the deprecated userinfo subcomponent
for http or https schemed URIs. for "http" or "https" schemed URIs.
o The :path pseudo-header field includes the path and query parts of o The ":path" pseudo-header field includes the path and query parts
the target URI (the absolute-path production and optionally a '?' of the target URI (the absolute-path production and, optionally, a
character followed by the query production; see Section 4.1 of '?' character followed by the query production; see Section 4.1 of
[HTTP]). A request in asterisk form (for OPTIONS) includes the [HTTP]). A request in asterisk form (for OPTIONS) includes the
value '*' for the :path pseudo-header field. value '*' for the ":path" pseudo-header field.
This pseudo-header field MUST NOT be empty for http or https URIs; This pseudo-header field MUST NOT be empty for "http" or "https"
http or https URIs that do not contain a path component MUST URIs; "http" or "https" URIs that do not contain a path component
include a value of '/'. The exceptions to this rule are: MUST include a value of '/'. The exceptions to this rule are:
* an OPTIONS request for an http or https URI that does not * an OPTIONS request for an "http" or "https" URI that does not
include a path component; these MUST include a :path pseudo- include a path component; these MUST include a ":path" pseudo-
header field with a value of '*' (see Section 7.1 of [HTTP]) header field with a value of '*' (see Section 7.1 of [HTTP]).
* CONNECT requests (Section 8.5), where the :path pseudo-header * CONNECT requests (Section 8.5), where the ":path" pseudo-header
field is omitted. field is omitted.
All HTTP/2 requests MUST include exactly one valid value for the All HTTP/2 requests MUST include exactly one valid value for the
:method, :scheme, and :path pseudo-header fields, unless it is a ":method", ":scheme", and ":path" pseudo-header fields, unless they
CONNECT request (Section 8.5). An HTTP request that omits mandatory are CONNECT requests (Section 8.5). An HTTP request that omits
pseudo-header fields is malformed (Section 8.1.1). mandatory pseudo-header fields is malformed (Section 8.1.1).
Individual HTTP/2 requests do not carry an explicit indicator of Individual HTTP/2 requests do not carry an explicit indicator of
protocol version. All HTTP/2 requests implicitly have a protocol protocol version. All HTTP/2 requests implicitly have a protocol
version of "2.0" (see Section 6.2 of [HTTP]). version of "2.0" (see Section 6.2 of [HTTP]).
8.3.2. Response Pseudo-Header Fields 8.3.2. Response Pseudo-Header Fields
For HTTP/2 responses, a single :status pseudo-header field is defined For HTTP/2 responses, a single ":status" pseudo-header field is
that carries the HTTP status code field (see Section 15 of [HTTP]). defined that carries the HTTP status code field (see Section 15 of
This pseudo-header field MUST be included in all responses, including [HTTP]). This pseudo-header field MUST be included in all responses,
interim responses; otherwise, the response is malformed including interim responses; otherwise, the response is malformed
(Section 8.1.1). (Section 8.1.1).
HTTP/2 responses implicitly have a protocol version of "2.0". HTTP/2 responses implicitly have a protocol version of "2.0".
8.4. Server Push 8.4. Server Push
HTTP/2 allows a server to preemptively send (or "push") responses HTTP/2 allows a server to preemptively send (or "push") responses
(along with corresponding "promised" requests) to a client in (along with corresponding "promised" requests) to a client in
association with a previous client-initiated request. association with a previous client-initiated request.
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stylesheets and scripts referenced by that page. When these requests stylesheets and scripts referenced by that page. When these requests
are pushed, the client does not need to wait to receive the are pushed, the client does not need to wait to receive the
references to them in the HTML and issue separate requests. references to them in the HTML and issue separate requests.
In practice, server push is difficult to use effectively, because it In practice, server push is difficult to use effectively, because it
requires the server to correctly anticipate the additional requests requires the server to correctly anticipate the additional requests
the client will make, taking into account factors such as caching, the client will make, taking into account factors such as caching,
content negotiation, and user behavior. Errors in prediction can content negotiation, and user behavior. Errors in prediction can
lead to performance degradation, due to the opportunity cost that the lead to performance degradation, due to the opportunity cost that the
additional data on the wire represents. In particular, pushing any additional data on the wire represents. In particular, pushing any
significant amount of data can cause contention issues with more- significant amount of data can cause contention issues with responses
important responses. that are more important.
A client can request that server push be disabled, though this is A client can request that server push be disabled, though this is
negotiated for each hop independently. The SETTINGS_ENABLE_PUSH negotiated for each hop independently. The SETTINGS_ENABLE_PUSH
setting can be set to 0 to indicate that server push is disabled. setting can be set to 0 to indicate that server push is disabled.
Promised requests MUST be safe (see Section 9.2.1 of [HTTP]) and Promised requests MUST be safe (see Section 9.2.1 of [HTTP]) and
cacheable (see Section 9.2.3 of [HTTP]). Promised requests cannot cacheable (see Section 9.2.3 of [HTTP]). Promised requests cannot
include any content or a trailer section. Clients that receive a include any content or a trailer section. Clients that receive a
promised request that is not cacheable, that is not known to be safe, promised request that is not cacheable, that is not known to be safe,
or that indicates the presence of request content MUST reset the or that indicates the presence of request content MUST reset the
promised stream with a stream error (Section 5.4.2) of type promised stream with a stream error (Section 5.4.2) of type
PROTOCOL_ERROR. Note this could result in the promised stream being PROTOCOL_ERROR. Note that this could result in the promised stream
reset if the client does not recognize a newly defined method as being reset if the client does not recognize a newly defined method
being safe. as being safe.
Pushed responses that are cacheable (see Section 3 of [CACHE]) can be Pushed responses that are cacheable (see Section 3 of [CACHING]) can
stored by the client, if it implements an HTTP cache. Pushed be stored by the client, if it implements an HTTP cache. Pushed
responses are considered successfully validated on the origin server responses are considered successfully validated on the origin server
(e.g., if the "no-cache" cache response directive is present; see (e.g., if the "no-cache" cache response directive is present; see
Section 5.2.2.4 of [CACHE]) while the stream identified by the Section 5.2.2.4 of [CACHING]) while the stream identified by the
promised stream ID is still open. promised stream identifier is still open.
Pushed responses that are not cacheable MUST NOT be stored by any Pushed responses that are not cacheable MUST NOT be stored by any
HTTP cache. They MAY be made available to the application HTTP cache. They MAY be made available to the application
separately. separately.
The server MUST include a value in the :authority pseudo-header field The server MUST include a value in the ":authority" pseudo-header
for which the server is authoritative (see Section 10.1). A client field for which the server is authoritative (see Section 10.1). A
MUST treat a PUSH_PROMISE for which the server is not authoritative client MUST treat a PUSH_PROMISE for which the server is not
as a stream error (Section 5.4.2) of type PROTOCOL_ERROR. authoritative as a stream error (Section 5.4.2) of type
PROTOCOL_ERROR.
An intermediary can receive pushes from the server and choose not to An intermediary can receive pushes from the server and choose not to
forward them on to the client. In other words, how to make use of forward them on to the client. In other words, how to make use of
the pushed information is up to that intermediary. Equally, the the pushed information is up to that intermediary. Equally, the
intermediary might choose to make additional pushes to the client, intermediary might choose to make additional pushes to the client,
without any action taken by the server. without any action taken by the server.
A client cannot push. Thus, servers MUST treat the receipt of a A client cannot push. Thus, servers MUST treat the receipt of a
PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PUSH_PROMISE frame as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. A server cannot set the SETTINGS_ENABLE_PUSH setting PROTOCOL_ERROR. A server cannot set the SETTINGS_ENABLE_PUSH setting
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a request that includes message content. a request that includes message content.
Promised requests are always associated with an explicit request from Promised requests are always associated with an explicit request from
the client. The PUSH_PROMISE frames sent by the server are sent on the client. The PUSH_PROMISE frames sent by the server are sent on
that explicit request's stream. The PUSH_PROMISE frame also includes that explicit request's stream. The PUSH_PROMISE frame also includes
a promised stream identifier, chosen from the stream identifiers a promised stream identifier, chosen from the stream identifiers
available to the server (see Section 5.1.1). available to the server (see Section 5.1.1).
The header fields in PUSH_PROMISE and any subsequent CONTINUATION The header fields in PUSH_PROMISE and any subsequent CONTINUATION
frames MUST be a valid and complete set of request header fields frames MUST be a valid and complete set of request header fields
(Section 8.3.1). The server MUST include a method in the :method (Section 8.3.1). The server MUST include a method in the ":method"
pseudo-header field that is safe and cacheable. If a client receives pseudo-header field that is safe and cacheable. If a client receives
a PUSH_PROMISE that does not include a complete and valid set of a PUSH_PROMISE that does not include a complete and valid set of
header fields or the :method pseudo-header field identifies a method header fields or the ":method" pseudo-header field identifies a
that is not safe, it MUST respond on the promised stream with a method that is not safe, it MUST respond on the promised stream with
stream error (Section 5.4.2) of type PROTOCOL_ERROR. a stream error (Section 5.4.2) of type PROTOCOL_ERROR.
The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to
sending any frames that reference the promised responses. This sending any frames that reference the promised responses. This
avoids a race where clients issue requests prior to receiving any avoids a race where clients issue requests prior to receiving any
PUSH_PROMISE frames. PUSH_PROMISE frames.
For example, if the server receives a request for a document For example, if the server receives a request for a document
containing embedded links to multiple image files and the server containing embedded links to multiple image files and the server
chooses to push those additional images to the client, sending chooses to push those additional images to the client, sending
PUSH_PROMISE frames before the DATA frames that contain the image PUSH_PROMISE frames before the DATA frames that contain the image
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Sending a PUSH_PROMISE frame creates a new stream and puts the stream Sending a PUSH_PROMISE frame creates a new stream and puts the stream
into the "reserved (local)" state for the server and the "reserved into the "reserved (local)" state for the server and the "reserved
(remote)" state for the client. (remote)" state for the client.
8.4.2. Push Responses 8.4.2. Push Responses
After sending the PUSH_PROMISE frame, the server can begin delivering After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed response as a response (Section 8.3.2) on a server- the pushed response as a response (Section 8.3.2) on a server-
initiated stream that uses the promised stream identifier. The initiated stream that uses the promised stream identifier. The
server uses this stream to transmit an HTTP response, using the same server uses this stream to transmit an HTTP response, using the same
sequence of frames as defined in Section 8.1. This stream becomes sequence of frames as that defined in Section 8.1. This stream
"half-closed" to the client (Section 5.1) after the initial HEADERS becomes "half-closed" to the client (Section 5.1) after the initial
frame is sent. HEADERS frame is sent.
Once a client receives a PUSH_PROMISE frame and chooses to accept the Once a client receives a PUSH_PROMISE frame and chooses to accept the
pushed response, the client SHOULD NOT issue any requests for the pushed response, the client SHOULD NOT issue any requests for the
promised response until after the promised stream has closed. promised response until after the promised stream has closed.
If the client determines, for any reason, that it does not wish to If the client determines, for any reason, that it does not wish to
receive the pushed response from the server or if the server takes receive the pushed response from the server or if the server takes
too long to begin sending the promised response, the client can send too long to begin sending the promised response, the client can send
a RST_STREAM frame, using either the CANCEL or REFUSED_STREAM code a RST_STREAM frame, using either the CANCEL or REFUSED_STREAM code
and referencing the pushed stream's identifier. and referencing the pushed stream's identifier.
A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
the number of responses that can be concurrently pushed by a server. the number of responses that can be concurrently pushed by a server.
Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero prevents Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero prevents
the server from opening the streams necessary to push responses. the server from opening the streams necessary to push responses.
However, this does not prevent the server from reserving streams However, this does not prevent the server from reserving streams
using PUSH_PROMISE frames, because "reserved" streams do not count using PUSH_PROMISE frames, because reserved streams do not count
toward the concurrent stream limit. Clients that do not wish to toward the concurrent stream limit. Clients that do not wish to
receive pushed resources need to reset any unwanted reserved streams receive pushed resources need to reset any unwanted reserved streams
or set SETTINGS_ENABLE_PUSH to 0. or set SETTINGS_ENABLE_PUSH to 0.
Clients receiving a pushed response MUST validate that either the Clients receiving a pushed response MUST validate that either the
server is authoritative (see Section 10.1) or the proxy that provided server is authoritative (see Section 10.1) or the proxy that provided
the pushed response is configured for the corresponding request. For the pushed response is configured for the corresponding request. For
example, a server that offers a certificate for only the example.com example, a server that offers a certificate for only the example.com
DNS-ID (see [RFC6125]) is not permitted to push a response for DNS-ID (see [RFC6125]) is not permitted to push a response for
https://www.example.org/doc. <https://www.example.org/doc>.
The response for a PUSH_PROMISE stream begins with a HEADERS frame, The response for a PUSH_PROMISE stream begins with a HEADERS frame,
which immediately puts the stream into the "half-closed (remote)" which immediately puts the stream into the "half-closed (remote)"
state for the server and "half-closed (local)" state for the client, state for the server and "half-closed (local)" state for the client,
and ends with a frame with the END_STREAM flag set, which places the and ends with a frame with the END_STREAM flag set, which places the
stream in the "closed" state. stream in the "closed" state.
| Note: The client never sends a frame with the END_STREAM flag | Note: The client never sends a frame with the END_STREAM flag
| set for a server push. | set for a server push.
8.5. The CONNECT Method 8.5. The CONNECT Method
The CONNECT method (Section 9.3.6 of [HTTP]) is used to convert an The CONNECT method (Section 9.3.6 of [HTTP]) is used to convert an
HTTP connection into a tunnel to a remote host. CONNECT is primarily HTTP connection into a tunnel to a remote host. CONNECT is primarily
used with HTTP proxies to establish a TLS session with an origin used with HTTP proxies to establish a TLS session with an origin
server for the purposes of interacting with https resources. server for the purposes of interacting with "https" resources.
In HTTP/2, the CONNECT method establishes a tunnel over a single In HTTP/2, the CONNECT method establishes a tunnel over a single
HTTP/2 stream to a remote host, rather than converting the entire HTTP/2 stream to a remote host, rather than converting the entire
connection to a tunnel. A CONNECT header section is constructed as connection to a tunnel. A CONNECT header section is constructed as
defined in Section 8.3.1 ("Request Pseudo-Header Fields"), with a few defined in Section 8.3.1 ("Request Pseudo-Header Fields"), with a few
differences. Specifically: differences. Specifically:
o The :method pseudo-header field is set to CONNECT. o The ":method" pseudo-header field is set to CONNECT.
o The :scheme and :path pseudo-header fields MUST be omitted. o The ":scheme" and ":path" pseudo-header fields MUST be omitted.
o The :authority pseudo-header field contains the host and port to o The ":authority" pseudo-header field contains the host and port to
connect to (equivalent to the authority-form of the request-target connect to (equivalent to the authority-form of the request-target
of CONNECT requests; see Section 3.2.3 of [HTTP11]). of CONNECT requests; see Section 3.2.3 of [HTTP/1.1]).
A CONNECT request that does not conform to these restrictions is A CONNECT request that does not conform to these restrictions is
malformed (Section 8.1.1). malformed (Section 8.1.1).
A proxy that supports CONNECT establishes a TCP connection [TCP] to A proxy that supports CONNECT establishes a TCP connection [TCP] to
the host and port identified in the :authority pseudo-header field. the host and port identified in the ":authority" pseudo-header field.
Once this connection is successfully established, the proxy sends a Once this connection is successfully established, the proxy sends a
HEADERS frame containing a 2xx series status code to the client, as HEADERS frame containing a 2xx-series status code to the client, as
defined in Section 9.3.6 of [HTTP]. defined in Section 9.3.6 of [HTTP].
After the initial HEADERS frame sent by each peer, all subsequent After the initial HEADERS frame sent by each peer, all subsequent
DATA frames correspond to data sent on the TCP connection. The frame DATA frames correspond to data sent on the TCP connection. The frame
payload of any DATA frames sent by the client is transmitted by the payload of any DATA frames sent by the client is transmitted by the
proxy to the TCP server; data received from the TCP server is proxy to the TCP server; data received from the TCP server is
assembled into DATA frames by the proxy. Frame types other than DATA assembled into DATA frames by the proxy. Frame types other than DATA
or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY) or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY)
MUST NOT be sent on a connected stream and MUST be treated as a MUST NOT be sent on a connected stream and MUST be treated as a
stream error (Section 5.4.2) if received. stream error (Section 5.4.2) if received.
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with the RST bit set if it detects an error with the stream or the with the RST bit set if it detects an error with the stream or the
HTTP/2 connection. HTTP/2 connection.
8.6. The Upgrade Header Field 8.6. The Upgrade Header Field
HTTP/2 does not support the 101 (Switching Protocols) informational HTTP/2 does not support the 101 (Switching Protocols) informational
status code (Section 15.2.2 of [HTTP]). status code (Section 15.2.2 of [HTTP]).
The semantics of 101 (Switching Protocols) aren't applicable to a The semantics of 101 (Switching Protocols) aren't applicable to a
multiplexed protocol. Similar functionality might be enabled through multiplexed protocol. Similar functionality might be enabled through
the use of extended CONNECT [RFC8441] and other protocols are able to the use of extended CONNECT [RFC8441], and other protocols are able
use the same mechanisms that HTTP/2 uses to negotiate their use (see to use the same mechanisms that HTTP/2 uses to negotiate their use
Section 3). (see Section 3).
8.7. Request Reliability 8.7. Request Reliability
In general, an HTTP client is unable to retry a non-idempotent In general, an HTTP client is unable to retry a non-idempotent
request when an error occurs because there is no means to determine request when an error occurs because there is no means to determine
the nature of the error (see Section 9.2.2 of [HTTP]). It is the nature of the error (see Section 9.2.2 of [HTTP]). It is
possible that some server processing occurred prior to the error, possible that some server processing occurred prior to the error,
which could result in undesirable effects if the request were which could result in undesirable effects if the request were
reattempted. reattempted.
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A server MUST NOT indicate that a stream has not been processed A server MUST NOT indicate that a stream has not been processed
unless it can guarantee that fact. If frames that are on a stream unless it can guarantee that fact. If frames that are on a stream
are passed to the application layer for any stream, then are passed to the application layer for any stream, then
REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame
MUST include a stream identifier that is greater than or equal to the MUST include a stream identifier that is greater than or equal to the
given stream identifier. given stream identifier.
In addition to these mechanisms, the PING frame provides a way for a In addition to these mechanisms, the PING frame provides a way for a
client to easily test a connection. Connections that remain idle can client to easily test a connection. Connections that remain idle can
become broken as some middleboxes (for instance, network address become broken, because some middleboxes (for instance, network
translators or load balancers) silently discard connection bindings. address translators or load balancers) silently discard connection
The PING frame allows a client to safely test whether a connection is bindings. The PING frame allows a client to safely test whether a
still active without sending a request. connection is still active without sending a request.
8.8. Examples 8.8. Examples
This section shows HTTP/1.1 requests and responses, with This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2 requests and responses. illustrations of equivalent HTTP/2 requests and responses.
8.8.1. Simple Request 8.8.1. Simple Request
An HTTP GET request includes control data and a request header with An HTTP GET request includes control data and a request header with
no message content and is therefore transmitted as a single HEADERS no message content and is therefore transmitted as a single HEADERS
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HTTP/1.1 304 Not Modified HEADERS HTTP/1.1 304 Not Modified HEADERS
ETag: "xyzzy" ==> + END_STREAM ETag: "xyzzy" ==> + END_STREAM
Expires: Thu, 23 Jan ... + END_HEADERS Expires: Thu, 23 Jan ... + END_HEADERS
:status = 304 :status = 304
etag = "xyzzy" etag = "xyzzy"
expires = Thu, 23 Jan ... expires = Thu, 23 Jan ...
8.8.3. Complex Request 8.8.3. Complex Request
An HTTP POST request that includes control data and a request header An HTTP POST request that includes control data and a request header
and message content is transmitted as one HEADERS frame, followed by with message content is transmitted as one HEADERS frame, followed by
zero or more CONTINUATION frames containing the request header, zero or more CONTINUATION frames containing the request header,
followed by one or more DATA frames, with the last CONTINUATION (or followed by one or more DATA frames, with the last CONTINUATION (or
HEADERS) frame having the END_HEADERS flag set and the final DATA HEADERS) frame having the END_HEADERS flag set and the final DATA
frame having the END_STREAM flag set: frame having the END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM Host: example.org ==> - END_STREAM
Content-Type: image/jpeg - END_HEADERS Content-Type: image/jpeg - END_HEADERS
Content-Length: 123 :method = POST Content-Length: 123 :method = POST
:authority = example.org :authority = example.org
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DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
Note that data contributing to any given field line could be spread Note that data contributing to any given field line could be spread
between field block fragments. The allocation of field lines to between field block fragments. The allocation of field lines to
frames in this example is illustrative only. frames in this example is illustrative only.
8.8.4. Response with Body 8.8.4. Response with Body
A response that includes control data and a response header and A response that includes control data and a response header with
message content is transmitted as a HEADERS frame, followed by zero message content is transmitted as a HEADERS frame, followed by zero
or more CONTINUATION frames, followed by one or more DATA frames, or more CONTINUATION frames, followed by one or more DATA frames,
with the last DATA frame in the sequence having the END_STREAM flag with the last DATA frame in the sequence having the END_STREAM flag
set: set:
HTTP/1.1 200 OK HEADERS HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS Content-Length: 123 + END_HEADERS
:status = 200 :status = 200
{binary data} content-type = image/jpeg {binary data} content-type = image/jpeg
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Foo: bar - END_STREAM Foo: bar - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo = bar foo = bar
9. HTTP/2 Connections 9. HTTP/2 Connections
This section outlines attributes of the HTTP protocol that improve This section outlines attributes of HTTP that improve
interoperability, reduce exposure to known security vulnerabilities, interoperability, reduce exposure to known security vulnerabilities,
or reduce the potential for implementation variation. or reduce the potential for implementation variation.
9.1. Connection Management 9.1. Connection Management
HTTP/2 connections are persistent. For best performance, it is HTTP/2 connections are persistent. For best performance, it is
expected that clients will not close connections until it is expected that clients will not close connections until it is
determined that no further communication with a server is necessary determined that no further communication with a server is necessary
(for example, when a user navigates away from a particular web page) (for example, when a user navigates away from a particular web page)
or until the server closes the connection. or until the server closes the connection.
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9.1.1. Connection Reuse 9.1.1. Connection Reuse
Connections that are made to an origin server, either directly or Connections that are made to an origin server, either directly or
through a tunnel created using the CONNECT method (Section 8.5), MAY through a tunnel created using the CONNECT method (Section 8.5), MAY
be reused for requests with multiple different URI authority be reused for requests with multiple different URI authority
components. A connection can be reused as long as the origin server components. A connection can be reused as long as the origin server
is authoritative (Section 10.1). For TCP connections without TLS, is authoritative (Section 10.1). For TCP connections without TLS,
this depends on the host having resolved to the same IP address. this depends on the host having resolved to the same IP address.
For https resources, connection reuse additionally depends on having For "https" resources, connection reuse additionally depends on
a certificate that is valid for the host in the URI. The certificate having a certificate that is valid for the host in the URI. The
presented by the server MUST satisfy any checks that the client would certificate presented by the server MUST satisfy any checks that the
perform when forming a new TLS connection for the host in the URI. A client would perform when forming a new TLS connection for the host
single certificate can be used to establish authority for multiple in the URI. A single certificate can be used to establish authority
origins. Section 4.3 of [HTTP] describes how a client determines for multiple origins. Section 4.3 of [HTTP] describes how a client
whether a server is authoritative for a URI. determines whether a server is authoritative for a URI.
In some deployments, reusing a connection for multiple origins can In some deployments, reusing a connection for multiple origins can
result in requests being directed to the wrong origin server. For result in requests being directed to the wrong origin server. For
example, TLS termination might be performed by a middlebox that uses example, TLS termination might be performed by a middlebox that uses
the TLS Server Name Indication (SNI) [TLS-EXT] extension to select an the TLS Server Name Indication [TLS-EXT] extension to select an
origin server. This means that it is possible for clients to send origin server. This means that it is possible for clients to send
requests to servers that might not be the intended target for the requests to servers that might not be the intended target for the
request, even though the server is otherwise authoritative. request, even though the server is otherwise authoritative.
A server that does not wish clients to reuse connections can indicate A server that does not wish clients to reuse connections can indicate
that it is not authoritative for a request by sending a 421 that it is not authoritative for a request by sending a 421
(Misdirected Request) status code in response to the request (see (Misdirected Request) status code in response to the request (see
Section 15.5.20 of [HTTP]). Section 15.5.20 of [HTTP]).
A client that is configured to use a proxy over HTTP/2 directs A client that is configured to use a proxy over HTTP/2 directs
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SHOULD be followed, with some additional restrictions that are SHOULD be followed, with some additional restrictions that are
specific to HTTP/2. specific to HTTP/2.
The TLS implementation MUST support the Server Name Indication (SNI) The TLS implementation MUST support the Server Name Indication (SNI)
[TLS-EXT] extension to TLS. If the server is identified by a domain [TLS-EXT] extension to TLS. If the server is identified by a domain
name [DNS-TERMS], clients MUST send the server_name TLS extension name [DNS-TERMS], clients MUST send the server_name TLS extension
unless an alternative mechanism to indicate the target host is used. unless an alternative mechanism to indicate the target host is used.
Requirements for deployments of HTTP/2 that negotiate TLS 1.3 [TLS13] Requirements for deployments of HTTP/2 that negotiate TLS 1.3 [TLS13]
are included in Section 9.2.3. Deployments of TLS 1.2 are subject to are included in Section 9.2.3. Deployments of TLS 1.2 are subject to
the requirements in Section 9.2.1 and Section 9.2.2. Implementations the requirements in Sections 9.2.1 and 9.2.2. Implementations are
are encouraged to provide defaults that comply, but it is recognized encouraged to provide defaults that comply, but it is recognized that
that deployments are ultimately responsible for compliance. deployments are ultimately responsible for compliance.
9.2.1. TLS 1.2 Features 9.2.1. TLS 1.2 Features
This section describes restrictions on the TLS 1.2 feature set that This section describes restrictions on the TLS 1.2 feature set that
can be used with HTTP/2. Due to deployment limitations, it might not can be used with HTTP/2. Due to deployment limitations, it might not
be possible to fail TLS negotiation when these restrictions are not be possible to fail TLS negotiation when these restrictions are not
met. An endpoint MAY immediately terminate an HTTP/2 connection that met. An endpoint MAY immediately terminate an HTTP/2 connection that
does not meet these TLS requirements with a connection error does not meet these TLS requirements with a connection error
(Section 5.4.1) of type INADEQUATE_SECURITY. (Section 5.4.1) of type INADEQUATE_SECURITY.
A deployment of HTTP/2 over TLS 1.2 MUST disable compression. TLS A deployment of HTTP/2 over TLS 1.2 MUST disable compression. TLS
compression can lead to the exposure of information that would not compression can lead to the exposure of information that would not
otherwise be revealed [RFC3749]. Generic compression is unnecessary otherwise be revealed [RFC3749]. Generic compression is unnecessary,
since HTTP/2 provides compression features that are more aware of since HTTP/2 provides compression features that are more aware of
context and therefore likely to be more appropriate for use for context and therefore likely to be more appropriate for use for
performance, security, or other reasons. performance, security, or other reasons.
A deployment of HTTP/2 over TLS 1.2 MUST disable renegotiation. An A deployment of HTTP/2 over TLS 1.2 MUST disable renegotiation. An
endpoint MUST treat a TLS renegotiation as a connection error endpoint MUST treat a TLS renegotiation as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Note that disabling (Section 5.4.1) of type PROTOCOL_ERROR. Note that disabling
renegotiation can result in long-lived connections becoming unusable renegotiation can result in long-lived connections becoming unusable
due to limits on the number of messages the underlying cipher suite due to limits on the number of messages the underlying cipher suite
can encipher. can encipher.
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An endpoint MAY use renegotiation to provide confidentiality An endpoint MAY use renegotiation to provide confidentiality
protection for client credentials offered in the handshake, but any protection for client credentials offered in the handshake, but any
renegotiation MUST occur prior to sending the connection preface. A renegotiation MUST occur prior to sending the connection preface. A
server SHOULD request a client certificate if it sees a renegotiation server SHOULD request a client certificate if it sees a renegotiation
request immediately after establishing a connection. request immediately after establishing a connection.
This effectively prevents the use of renegotiation in response to a This effectively prevents the use of renegotiation in response to a
request for a specific protected resource. A future specification request for a specific protected resource. A future specification
might provide a way to support this use case. Alternatively, a might provide a way to support this use case. Alternatively, a
server might use an error (Section 5.4) of type HTTP_1_1_REQUIRED to server might use an error (Section 5.4) of type HTTP_1_1_REQUIRED to
request the client use a protocol that supports renegotiation. request that the client use a protocol that supports renegotiation.
Implementations MUST support ephemeral key exchange sizes of at least Implementations MUST support ephemeral key exchange sizes of at least
2048 bits for cipher suites that use ephemeral finite field Diffie- 2048 bits for cipher suites that use ephemeral finite field Diffie-
Hellman (DHE) (Section 8.1.2 of [TLS12] and 224 bits for cipher Hellman (DHE) (Section 8.1.2 of [TLS12]) and 224 bits for cipher
suites that use ephemeral elliptic curve Diffie-Hellman (ECDHE) suites that use ephemeral elliptic curve Diffie-Hellman (ECDHE)
[RFC8422]. Clients MUST accept DHE sizes of up to 4096 bits. [RFC8422]. Clients MUST accept DHE sizes of up to 4096 bits.
Endpoints MAY treat negotiation of key sizes smaller than the lower Endpoints MAY treat negotiation of key sizes smaller than the lower
limits as a connection error (Section 5.4.1) of type limits as a connection error (Section 5.4.1) of type
INADEQUATE_SECURITY. INADEQUATE_SECURITY.
9.2.2. TLS 1.2 Cipher Suites 9.2.2. TLS 1.2 Cipher Suites
A deployment of HTTP/2 over TLS 1.2 SHOULD NOT use any of the cipher A deployment of HTTP/2 over TLS 1.2 SHOULD NOT use any of the
suites that are listed in the list of prohibited cipher suites prohibited cipher suites listed in Appendix A.
(Appendix A).
Endpoints MAY choose to generate a connection error (Section 5.4.1) Endpoints MAY choose to generate a connection error (Section 5.4.1)
of type INADEQUATE_SECURITY if one of the prohibited cipher suites is of type INADEQUATE_SECURITY if one of the prohibited cipher suites is
negotiated. A deployment that chooses to use a prohibited cipher negotiated. A deployment that chooses to use a prohibited cipher
suite risks triggering a connection error unless the set of potential suite risks triggering a connection error unless the set of potential
peers is known to accept that cipher suite. peers is known to accept that cipher suite.
Implementations MUST NOT generate this error in reaction to the Implementations MUST NOT generate this error in reaction to the
negotiation of a cipher suite that is not prohibited. Consequently, negotiation of a cipher suite that is not prohibited. Consequently,
when clients offer a cipher suite that is not prohibited, they have when clients offer a cipher suite that is not prohibited, they have
to be prepared to use that cipher suite with HTTP/2. to be prepared to use that cipher suite with HTTP/2.
The list of prohibited cipher suites includes the cipher suite that The list of prohibited cipher suites includes the cipher suite that
TLS 1.2 makes mandatory, which means that TLS 1.2 deployments could TLS 1.2 makes mandatory, which means that TLS 1.2 deployments could
have non-intersecting sets of permitted cipher suites. To avoid this have non-intersecting sets of permitted cipher suites. To avoid this
problem causing TLS handshake failures, deployments of HTTP/2 that problem, which causes TLS handshake failures, deployments of HTTP/2
use TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 that use TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
[TLS-ECDHE] with the P-256 elliptic curve [RFC8422]. [TLS-ECDHE] with the P-256 elliptic curve [RFC8422].
Note that clients might advertise support of cipher suites that are Note that clients might advertise support of cipher suites that are
prohibited in order to allow for connection to servers that do not prohibited in order to allow for connection to servers that do not
support HTTP/2. This allows servers to select HTTP/1.1 with a cipher support HTTP/2. This allows servers to select HTTP/1.1 with a cipher
suite that is prohibited in HTTP/2. However, this can result in suite that is prohibited in HTTP/2. However, this can result in
HTTP/2 being negotiated with a prohibited cipher suite if the HTTP/2 being negotiated with a prohibited cipher suite if the
application protocol and cipher suite are independently selected. application protocol and cipher suite are independently selected.
9.2.3. TLS 1.3 Features 9.2.3. TLS 1.3 Features
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treated as delimiters in other HTTP versions. An intermediary that treated as delimiters in other HTTP versions. An intermediary that
translates an HTTP/2 request or response MUST validate fields translates an HTTP/2 request or response MUST validate fields
according to the rules in Section 8.2 before translating a message to according to the rules in Section 8.2 before translating a message to
another HTTP version. Translating a field that includes invalid another HTTP version. Translating a field that includes invalid
delimiters could be used to cause recipients to incorrectly interpret delimiters could be used to cause recipients to incorrectly interpret
a message, which could be exploited by an attacker. a message, which could be exploited by an attacker.
Section 8.2 does not include specific rules for validation of pseudo- Section 8.2 does not include specific rules for validation of pseudo-
header fields. If the values of these fields are used, additional header fields. If the values of these fields are used, additional
validation is necessary. This is particularly important where validation is necessary. This is particularly important where
:scheme, :authority, and :path are combined to form a single URI ":scheme", ":authority", and ":path" are combined to form a single
string ([RFC3986]). Similar problems might occur when that URI or URI string [RFC3986]. Similar problems might occur when that URI or
just :path are combined with :method to construct a request line (as just ":path" is combined with ":method" to construct a request line
in Section 3 of [HTTP11]). Simple concatenation is not secure unless (as in Section 3 of [HTTP/1.1]). Simple concatenation is not secure
the input values are fully validated. unless the input values are fully validated.
An intermediary can reject fields that contain invalid field names or An intermediary can reject fields that contain invalid field names or
values for other reasons, in particular those that do not conform to values for other reasons -- in particular, those fields that do not
the HTTP ABNF grammar from Section 5 of [HTTP]. Intermediaries that conform to the HTTP ABNF grammar from Section 5 of [HTTP].
do not perform any validation of fields other than the minimum Intermediaries that do not perform any validation of fields other
required by Section 8.2 could forward messages that contain invalid than the minimum required by Section 8.2 could forward messages that
field names or values. contain invalid field names or values.
An intermediary that receives any field that requires removal before An intermediary that receives any fields that require removal before
forwarding (see Section 7.6.1 of [HTTP]) MUST remove or replace those forwarding (see Section 7.6.1 of [HTTP]) MUST remove or replace those
header fields when forwarding messages. Additionally, intermediaries header fields when forwarding messages. Additionally, intermediaries
should take care when forwarding messages containing Content-Length should take care when forwarding messages containing Content-Length
fields to ensure that the message is well-formed (Section 8.1.1). fields to ensure that the message is well-formed (Section 8.1.1).
This ensures that if the message is translated into HTTP/1.1 at any This ensures that if the message is translated into HTTP/1.1 at any
point the framing will be correct. point, the framing will be correct.
10.4. Cacheability of Pushed Responses 10.4. Cacheability of Pushed Responses
Pushed responses do not have an explicit request from the client; the Pushed responses do not have an explicit request from the client; the
request is provided by the server in the PUSH_PROMISE frame. request is provided by the server in the PUSH_PROMISE frame.
Caching responses that are pushed is possible based on the guidance Caching responses that are pushed is possible based on the guidance
provided by the origin server in the Cache-Control header field. provided by the origin server in the Cache-Control header field.
However, this can cause issues if a single server hosts more than one However, this can cause issues if a single server hosts more than one
tenant. For example, a server might offer multiple users each a tenant. For example, a server might offer multiple users each a
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this would allow a tenant to provide a representation that would be this would allow a tenant to provide a representation that would be
served out of cache, overriding the actual representation that the served out of cache, overriding the actual representation that the
authoritative tenant provides. authoritative tenant provides.
Pushed responses for which an origin server is not authoritative (see Pushed responses for which an origin server is not authoritative (see
Section 10.1) MUST NOT be used or cached. Section 10.1) MUST NOT be used or cached.
10.5. Denial-of-Service Considerations 10.5. Denial-of-Service Considerations
An HTTP/2 connection can demand a greater commitment of resources to An HTTP/2 connection can demand a greater commitment of resources to
operate than an HTTP/1.1 connection. The use of field section operate than an HTTP/1.1 connection. Both field section compression
compression and flow control depend on a commitment of resources for and flow control depend on a commitment of a greater amount of state.
storing a greater amount of state. Settings for these features Settings for these features ensure that memory commitments for these
ensure that memory commitments for these features are strictly features are strictly bounded.
bounded.
The number of PUSH_PROMISE frames is not constrained in the same The number of PUSH_PROMISE frames is not constrained in the same
fashion. A client that accepts server push SHOULD limit the number fashion. A client that accepts server push SHOULD limit the number
of streams it allows to be in the "reserved (remote)" state. An of streams it allows to be in the "reserved (remote)" state. An
excessive number of server push streams can be treated as a stream excessive number of server push streams can be treated as a stream
error (Section 5.4.2) of type ENHANCE_YOUR_CALM. error (Section 5.4.2) of type ENHANCE_YOUR_CALM.
A number of HTTP/2 implementations were found to be vulnerable to A number of HTTP/2 implementations were found to be vulnerable to
denial of service [NFLX-2019-002]. The following lists known ways denial of service [NFLX-2019-002]. Below is a list of known ways
that implementations might be subject to denial of service attack: that implementations might be subject to denial-of-service attacks:
o Inefficient tracking of outstanding outbound frames can lead to o Inefficient tracking of outstanding outbound frames can lead to
overload if an adversary can cause large numbers of frames to be overload if an adversary can cause large numbers of frames to be
enqueued for sending. A peer could use one of several techniques enqueued for sending. A peer could use one of several techniques
to cause large numbers of frames to be generated: to cause large numbers of frames to be generated:
* Providing tiny increments to flow control in WINDOW_UPDATE * Providing tiny increments to flow control in WINDOW_UPDATE
frames can cause a sender to generate a large number of DATA frames can cause a sender to generate a large number of DATA
frames. frames.
* An endpoint is required to respond to a PING frame. * An endpoint is required to respond to a PING frame.
* Each SETTINGS frame requires acknowledgment. * Each SETTINGS frame requires acknowledgment.
* An invalid request (or server push) can cause a peer to send * An invalid request (or server push) can cause a peer to send
RST_STREAM frames in response. RST_STREAM frames in response.
o An attacker can provide large amounts of flow control credit at o An attacker can provide large amounts of flow-control credit at
the HTTP/2 layer, but withhold credit at the TCP layer, preventing the HTTP/2 layer but withhold credit at the TCP layer, preventing
frames from being sent. An endpoint that constructs and remembers frames from being sent. An endpoint that constructs and remembers
frames for sending without considering TCP limits might be subject frames for sending without considering TCP limits might be subject
to resource exhaustion. to resource exhaustion.
o Large numbers of small or empty frames can be abused to cause a o Large numbers of small or empty frames can be abused to cause a
peer to expend time processing frame headers. Caution is required peer to expend time processing frame headers. Caution is required
here as some uses of small frames are entirely legitimate, such as here as some uses of small frames are entirely legitimate, such as
the sending of an empty DATA or CONTINUATION frame at the end of a the sending of an empty DATA or CONTINUATION frame at the end of a
stream. stream.
o The SETTINGS frame might also be abused to cause a peer to expend o The SETTINGS frame might also be abused to cause a peer to expend
additional processing time. This might be done by pointlessly additional processing time. This might be done by pointlessly
changing settings, sending multiple undefined settings, or changing settings, sending multiple undefined settings, or
changing the same setting multiple times in the same frame. changing the same setting multiple times in the same frame.
o Handling reprioritization with PRIORITY frames can require o Handling reprioritization with PRIORITY frames can require
significant processing time and can lead to overload if many significant processing time and can lead to overload if many
PRIORITY frames are sent. PRIORITY frames are sent.
o Field section compression also offers some opportunities to waste o Field section compression also provides opportunities for an
processing resources; see Section 7 of [COMPRESSION] for more attacker to waste processing resources; see Section 7 of
details on potential abuses. [COMPRESSION] for more details on potential abuses.
o Limits in SETTINGS cannot be reduced instantaneously, which leaves o Limits in SETTINGS cannot be reduced instantaneously, which leaves
an endpoint exposed to behavior from a peer that could exceed the an endpoint exposed to behavior from a peer that could exceed the
new limits. In particular, immediately after establishing a new limits. In particular, immediately after establishing a
connection, limits set by a server are not known to clients and connection, limits set by a server are not known to clients and
could be exceeded without being an obvious protocol violation. could be exceeded without being an obvious protocol violation.
Most of the features that might be exploited for denial of service -- Most of the features that might be exploited for denial of service --
i.e., SETTINGS changes, small frames, field section compression -- such as SETTINGS changes, small frames, field section compression --
have legitimate uses. These features become a burden only when they have legitimate uses. These features become a burden only when they
are used unnecessarily or to excess. are used unnecessarily or to excess.
An endpoint that doesn't monitor use of these features exposes itself An endpoint that doesn't monitor use of these features exposes itself
to a risk of denial of service. Implementations SHOULD track the use to a risk of denial of service. Implementations SHOULD track the use
of these features and set limits on their use. An endpoint MAY treat of these features and set limits on their use. An endpoint MAY treat
activity that is suspicious as a connection error (Section 5.4.1) of activity that is suspicious as a connection error (Section 5.4.1) of
type ENHANCE_YOUR_CALM. type ENHANCE_YOUR_CALM.
10.5.1. Limits on Field Block Size 10.5.1. Limits on Field Block Size
skipping to change at page 76, line 41 skipping to change at line 3526
10.6. Use of Compression 10.6. Use of Compression
Compression can allow an attacker to recover secret data when it is Compression can allow an attacker to recover secret data when it is
compressed in the same context as data under attacker control. compressed in the same context as data under attacker control.
HTTP/2 enables compression of field lines (Section 4.3); the HTTP/2 enables compression of field lines (Section 4.3); the
following concerns also apply to the use of HTTP compressed content- following concerns also apply to the use of HTTP compressed content-
codings (Section 8.4.1 of [HTTP]). codings (Section 8.4.1 of [HTTP]).
There are demonstrable attacks on compression that exploit the There are demonstrable attacks on compression that exploit the
characteristics of the web (e.g., [BREACH]). The attacker induces characteristics of the Web (e.g., [BREACH]). The attacker induces
multiple requests containing varying plaintext, observing the length multiple requests containing varying plaintext, observing the length
of the resulting ciphertext in each, which reveals a shorter length of the resulting ciphertext in each, which reveals a shorter length
when a guess about the secret is correct. when a guess about the secret is correct.
Implementations communicating on a secure channel MUST NOT compress Implementations communicating on a secure channel MUST NOT compress
content that includes both confidential and attacker-controlled data content that includes both confidential and attacker-controlled data
unless separate compression dictionaries are used for each source of unless separate compression dictionaries are used for each source of
data. Compression MUST NOT be used if the source of data cannot be data. Compression MUST NOT be used if the source of data cannot be
reliably determined. Generic stream compression, such as that reliably determined. Generic stream compression, such as that
provided by TLS, MUST NOT be used with HTTP/2 (see Section 9.2). provided by TLS, MUST NOT be used with HTTP/2 (see Section 9.2).
skipping to change at page 77, line 19 skipping to change at line 3552
Padding within HTTP/2 is not intended as a replacement for general Padding within HTTP/2 is not intended as a replacement for general
purpose padding, such as that provided by TLS [TLS13]. Redundant purpose padding, such as that provided by TLS [TLS13]. Redundant
padding could even be counterproductive. Correct application can padding could even be counterproductive. Correct application can
depend on having specific knowledge of the data that is being padded. depend on having specific knowledge of the data that is being padded.
To mitigate attacks that rely on compression, disabling or limiting To mitigate attacks that rely on compression, disabling or limiting
compression might be preferable to padding as a countermeasure. compression might be preferable to padding as a countermeasure.
Padding can be used to obscure the exact size of frame content and is Padding can be used to obscure the exact size of frame content and is
provided to mitigate specific attacks within HTTP, for example, provided to mitigate specific attacks within HTTP -- for example,
attacks where compressed content includes both attacker-controlled attacks where compressed content includes both attacker-controlled
plaintext and secret data (e.g., [BREACH]). plaintext and secret data (e.g., [BREACH]).
Use of padding can result in less protection than might seem Use of padding can result in less protection than might seem
immediately obvious. At best, padding only makes it more difficult immediately obvious. At best, padding only makes it more difficult
for an attacker to infer length information by increasing the number for an attacker to infer length information by increasing the number
of frames an attacker has to observe. Incorrectly implemented of frames an attacker has to observe. Incorrectly implemented
padding schemes can be easily defeated. In particular, randomized padding schemes can be easily defeated. In particular, randomized
padding with a predictable distribution provides very little padding with a predictable distribution provides very little
protection; similarly, padding frame payloads to a fixed size exposes protection; similarly, padding frame payloads to a fixed size exposes
information as frame payload sizes cross the fixed-sized boundary, information as frame payload sizes cross the fixed-sized boundary,
which could be possible if an attacker can control plaintext. which could be possible if an attacker can control plaintext.
Intermediaries SHOULD retain padding for DATA frames, but MAY drop Intermediaries SHOULD retain padding for DATA frames but MAY drop
padding for HEADERS and PUSH_PROMISE frames. A valid reason for an padding for HEADERS and PUSH_PROMISE frames. A valid reason for an
intermediary to change the amount of padding of frames is to improve intermediary to change the amount of padding of frames is to improve
the protections that padding provides. the protections that padding provides.
10.8. Privacy Considerations 10.8. Privacy Considerations
Several characteristics of HTTP/2 provide an observer an opportunity Several characteristics of HTTP/2 provide an observer an opportunity
to correlate actions of a single client or server over time. These to correlate actions of a single client or server over time. These
include the value of settings, the manner in which flow-control include the values of settings, the manner in which flow-control
windows are managed, the way priorities are allocated to streams, the windows are managed, the way priorities are allocated to streams, the
timing of reactions to stimulus, and the handling of any features timing of reactions to stimulus, and the handling of any features
that are controlled by settings. that are controlled by settings.
As far as these create observable differences in behavior, they could As far as these create observable differences in behavior, they could
be used as a basis for fingerprinting a specific client, as defined be used as a basis for fingerprinting a specific client, as defined
in Section 3.2 of [PRIVACY]. in Section 3.2 of [PRIVACY].
HTTP/2's preference for using a single TCP connection allows HTTP/2's preference for using a single TCP connection allows
correlation of a user's activity on a site. Reusing connections for correlation of a user's activity on a site. Reusing connections for
skipping to change at page 78, line 25 skipping to change at line 3604
Remote timing attacks extract secrets from servers by observing Remote timing attacks extract secrets from servers by observing
variations in the time that servers take when processing requests variations in the time that servers take when processing requests
that use secrets. HTTP/2 enables concurrent request creation and that use secrets. HTTP/2 enables concurrent request creation and
processing, which can give attackers better control over when request processing, which can give attackers better control over when request
processing commences. Multiple HTTP/2 requests can be included in processing commences. Multiple HTTP/2 requests can be included in
the same IP packet or TLS record. HTTP/2 can therefore make remote the same IP packet or TLS record. HTTP/2 can therefore make remote
timing attacks more efficient by eliminating variability in request timing attacks more efficient by eliminating variability in request
delivery, leaving only request order and the delivery of responses as delivery, leaving only request order and the delivery of responses as
sources of timing variability. sources of timing variability.
Ensuring that processing time is not dependent on the value of Ensuring that processing time is not dependent on the value of a
secrets is the best defense against any form of timing attack. secret is the best defense against any form of timing attack.
11. IANA Considerations 11. IANA Considerations
This revision of the document marks the HTTP2-Settings header field This revision of HTTP/2 marks the HTTP2-Settings header field and the
and the h2c Upgrade token, both defined in [RFC7540], as obsolete. h2c upgrade token, both defined in [RFC7540], as obsolete.
Section 11 of [RFC7540] registered the h2 and h2c ALPN identifiers Section 11 of [RFC7540] registered the h2 and h2c ALPN identifiers
along with the PRI HTTP method. RFC 7540 also established a registry along with the PRI HTTP method. RFC 7540 also established a registry
for frame types, settings, and error codes. These registrations and for frame types, settings, and error codes. These registrations and
registries apply to HTTP/2, but are not redefined in this document. registries apply to HTTP/2, but are not redefined in this document.
IANA is requested to update references to RFC 7540 in the following IANA has updated references to RFC 7540 in the following registries
registries to refer to this document: Application-Layer Protocol to refer to this document: "TLS Application-Layer Protocol
Negotiation (ALPN) Protocol IDs, HTTP/2 Frame Type, HTTP/2 Settings, Negotiation (ALPN) Protocol IDs", "HTTP/2 Frame Type", "HTTP/2
HTTP/2 Error Code, and HTTP Method Registry. The registration of the Settings", "HTTP/2 Error Code", and "HTTP Method Registry". The
PRI method needs to be updated to refer to Section 3.4; all other registration of the PRI method has been updated to refer to
section numbers have not changed. Section 3.4; all other section numbers have not changed.
IANA is requested to change the policy on those portions of the IANA has changed the policy on those portions of the "HTTP/2 Frame
"HTTP/2 Frame Type" and "HTTP/2 Settings" registries that were Type" and "HTTP/2 Settings" registries that were reserved for
reserved for Experimental Use in RFC 7540. These portions of the Experimental Use in RFC 7540. These portions of the registries shall
registry shall operate on the same policy as the remainder of each operate on the same policy as the remainder of each registry.
registry.
11.1. HTTP2-Settings Header Field Registration 11.1. HTTP2-Settings Header Field Registration
This section marks the HTTP2-Settings header field registered by This section marks the HTTP2-Settings header field registered by
Section 11.5 of [RFC7540] in the Hypertext Transfer Protocol (HTTP) Section 11.5 of [RFC7540] in the "Hypertext Transfer Protocol (HTTP)
Field Name Registry as obsolete. This capability has been removed: Field Name Registry" as obsolete. This capability has been removed:
see Section 3.1. The registration is updated to include the details see Section 3.1. The registration is updated to include the details
as required by Section 18.4 of [HTTP]: as required by Section 18.4 of [HTTP]:
Field Name: HTTP2-Settings Field Name: HTTP2-Settings
Status: Standard Status: obsoleted
Ref.: Section 3.2.1 of [RFC7540] Reference: Section 3.2.1 of [RFC7540]
Comments: Obsolete; see Section 11.1 of this document Comments: Obsolete; see Section 11.1 of this document.
11.2. The h2c Upgrade Token 11.2. The h2c Upgrade Token
This section records the h2c upgrade token registered by Section 11.8 This section records the h2c upgrade token registered by Section 11.8
of [RFC7540] in the Hypertext Transfer Protocol (HTTP) Upgrade Token of [RFC7540] in the "Hypertext Transfer Protocol (HTTP) Upgrade Token
Registry as obsolete. This capability has been removed: see Registry" as obsolete. This capability has been removed: see
Section 3.1. The registration is updated as follows: Section 3.1. The registration is updated as follows:
Value: h2c Value: h2c
Description: Hypertext Transfer Protocol version 2 (HTTP/2) Description: (OBSOLETE) Hypertext Transfer Protocol version 2
(HTTP/2)
Expected Version Tokens: None Expected Version Tokens: None
Reference: Section 3.1 of this document Reference: Section 3.1 of this document
12. References 12. References
12.1. Normative References 12.1. Normative References
[CACHE] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [CACHING] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", Work in Progress, Internet-Draft, Ed., "HTTP Caching", RFC 9111, DOI 10.17487/RFC9111, March
draft-ietf-httpbis-cache-18, Internet-Draft, draft-ietf- 2022, <https://www.rfc-editor.org/info/rfc9111>.
httpbis-cache-18, August 18, 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
cache-18>.
[COMPRESSION] [COMPRESSION]
Peon, R. and H. Ruellan, "HPACK: Header Compression for Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, RFC 7541, HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
DOI 10.17487/RFC7541, May 2015, <https://www.rfc-editor.org/info/rfc7541>.
<https://www.rfc-editor.org/rfc/rfc7541>.
[COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265, [COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, RFC 6265, DOI 10.17487/RFC6265, DOI 10.17487/RFC6265, April 2011,
April 2011, <https://www.rfc-editor.org/rfc/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", Work in Progress, Internet-Draft, Ed., "HTTP Semantics", RFC 9110, DOI 10.17487/RFC9110,
draft-ietf-httpbis-semantics-18, Internet-Draft, draft- March 2022, <https://www.rfc-editor.org/info/rfc9110>.
ietf-httpbis-semantics-18, August 18, 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-18>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based [QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000, Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021, DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>. <https://www.rfc-editor.org/info/rfc9000>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, STD 66, RFC 3986, RFC 3986, DOI 10.17487/RFC3986, January 2005,
DOI 10.17487/RFC3986, January 2005, <https://www.rfc-editor.org/info/rfc3986>.
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic [RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
Curve Cryptography (ECC) Cipher Suites for Transport Layer Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier", RFC 8422, Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, RFC 8422, DOI 10.17487/RFC8422, DOI 10.17487/RFC8422, August 2018,
August 2018, <https://www.rfc-editor.org/info/rfc8422>. <https://www.rfc-editor.org/info/rfc8422>.
[RFC8470] Thomson, M., Nottingham, M., and W. Tarreau, "Using Early [RFC8470] Thomson, M., Nottingham, M., and W. Tarreau, "Using Early
Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, RFC 8470, Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September
DOI 10.17487/RFC8470, September 2018, 2018, <https://www.rfc-editor.org/info/rfc8470>.
<https://www.rfc-editor.org/rfc/rfc8470>.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, [TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC793, STD 7, RFC 793, RFC 793, DOI 10.17487/RFC0793, September 1981,
DOI 10.17487/RFC793, September 1981, <https://www.rfc-editor.org/info/rfc793>.
<https://www.rfc-editor.org/rfc/rfc793>.
[TLS-ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [TLS-ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol "Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
RFC 7301, DOI 10.17487/RFC7301, July 2014, July 2014, <https://www.rfc-editor.org/info/rfc7301>.
<https://www.rfc-editor.org/rfc/rfc7301>.
[TLS-ECDHE] [TLS-ECDHE]
Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA- Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289, 256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
DOI 10.17487/RFC5289, RFC 5289, DOI 10.17487/RFC5289, DOI 10.17487/RFC5289, August 2008,
August 2008, <https://www.rfc-editor.org/rfc/rfc5289>. <https://www.rfc-editor.org/info/rfc5289>.
[TLS-EXT] Eastlake 3rd, D., "Transport Layer Security (TLS) [TLS-EXT] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, RFC 6066, DOI 10.17487/RFC6066, DOI 10.17487/RFC6066, January 2011,
January 2011, <https://www.rfc-editor.org/rfc/rfc6066>. <https://www.rfc-editor.org/info/rfc6066>.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, RFC 5246, DOI 10.17487/RFC5246, DOI 10.17487/RFC5246, August 2008,
August 2008, <https://www.rfc-editor.org/rfc/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol [TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, RFC 8446, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>.
<https://www.rfc-editor.org/rfc/rfc8446>.
[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre, [TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, BCP 195, (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
RFC 7525, DOI 10.17487/RFC7525, May 2015, 2015, <https://www.rfc-editor.org/info/rfc7525>.
<https://www.rfc-editor.org/rfc/rfc7525>.
12.2. Informative References 12.2. Informative References
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", RFC 7838, DOI 10.17487/RFC7838, Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
RFC 7838, DOI 10.17487/RFC7838, April 2016, April 2016, <https://www.rfc-editor.org/info/rfc7838>.
<https://www.rfc-editor.org/rfc/rfc7838>.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
CRIME Attack", July 12, 2013, CRIME Attack", July 12, 2013,
<https://breachattack.com/resources/ <https://breachattack.com/resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>. BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[DNS-TERMS] [DNS-TERMS]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, January 2019, <https://www.rfc-editor.org/info/rfc8499>.
<https://www.rfc-editor.org/rfc/rfc8499>.
[HTTP11] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", Work in Progress, Internet-Draft, draft-
ietf-httpbis-messaging-18, Internet-Draft, draft-ietf-
httpbis-messaging-18, August 18, 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
messaging-18>.
[I-D.ietf-httpbis-priority] [HTTP-PRIORITY]
Oku, K. and L. Pardue, "Extensible Prioritization Scheme Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", Work in Progress, Internet-Draft, draft-ietf- for HTTP", RFC 9218, DOI 10.17487/RFC9218, March 2022,
httpbis-priority-12, January 17, 2022, <https://www.rfc-editor.org/info/rfc9218>.
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
priority-12>. [HTTP/1.1] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", RFC 9112, DOI 10.17487/RFC9112, March
2022, <https://www.rfc-editor.org/info/rfc9112>.
[NFLX-2019-002] [NFLX-2019-002]
Netflix, "HTTP/2 Denial of Service Advisory", August 13, Netflix, "HTTP/2 Denial of Service Advisory", August 13,
2019, <https://github.com/Netflix/security- 2019, <https://github.com/Netflix/security-
bulletins/blob/master/advisories/third-party/2019-002.md>. bulletins/blob/master/advisories/third-party/2019-002.md>.
[PRIVACY] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [PRIVACY] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, RFC 6973, DOI 10.17487/RFC6973, July DOI 10.17487/RFC6973, July 2013,
2013, <https://www.rfc-editor.org/rfc/rfc6973>. <https://www.rfc-editor.org/info/rfc6973>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", RFC 1122, DOI 10.17487/RFC1122, Communication Layers", STD 3, RFC 1122,
RFC 1122, DOI 10.17487/RFC1122, October 1989, DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/rfc/rfc1122>. <https://www.rfc-editor.org/info/rfc1122>.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, DOI 10.17487/RFC3749, Compression Methods", RFC 3749, DOI 10.17487/RFC3749, May
RFC 3749, DOI 10.17487/RFC3749, May 2004, 2004, <https://www.rfc-editor.org/info/rfc3749>.
<https://www.rfc-editor.org/rfc/rfc3749>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, RFC 6125, Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
DOI 10.17487/RFC6125, March 2011, 2011, <https://www.rfc-editor.org/info/rfc6125>.
<https://www.rfc-editor.org/info/rfc6125>.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, RFC 6585, Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
DOI 10.17487/RFC6585, April 2012, <https://www.rfc-editor.org/info/rfc6585>.
<https://www.rfc-editor.org/rfc/rfc6585>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R. [RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance", Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, RFC 7323, RFC 7323, DOI 10.17487/RFC7323, September 2014,
DOI 10.17487/RFC7323, September 2014, <https://www.rfc-editor.org/info/rfc7323>.
<https://www.rfc-editor.org/rfc/rfc7323>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, RFC 7540, DOI 10.17487/RFC7540, May DOI 10.17487/RFC7540, May 2015,
2015, <https://www.rfc-editor.org/rfc/rfc7540>. <https://www.rfc-editor.org/info/rfc7540>.
[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2", [RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, RFC 8441, RFC 8441, DOI 10.17487/RFC8441, September 2018,
DOI 10.17487/RFC8441, September 2018, <https://www.rfc-editor.org/info/rfc8441>.
<https://www.rfc-editor.org/rfc/rfc8441>.
[RFC8740] Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740, [RFC8740] Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740,
DOI 10.17487/RFC8740, RFC 8740, DOI 10.17487/RFC8740, DOI 10.17487/RFC8740, February 2020,
February 2020, <https://www.rfc-editor.org/rfc/rfc8740>. <https://www.rfc-editor.org/info/rfc8740>.
[TALKING] Huang, L., Chen, E., Barth, A., Rescorla, E., and C. [TALKING] Huang, L., Chen, E., Barth, A., Rescorla, E., and C.
Jackson, "Talking to Yourself for Fun and Profit", 2011, Jackson, "Talking to Yourself for Fun and Profit", 2011,
<https://www.adambarth.com/papers/2011/huang-chen-barth- <https://www.adambarth.com/papers/2011/huang-chen-barth-
rescorla-jackson.pdf>. rescorla-jackson.pdf>.
Appendix A. Prohibited TLS 1.2 Cipher Suites Appendix A. Prohibited TLS 1.2 Cipher Suites
An HTTP/2 implementation MAY treat the negotiation of any of the An HTTP/2 implementation MAY treat the negotiation of any of the
following cipher suites with TLS 1.2 as a connection error following cipher suites with TLS 1.2 as a connection error
skipping to change at page 89, line 37 skipping to change at line 4116
o TLS_PSK_WITH_AES_256_CCM_8 o TLS_PSK_WITH_AES_256_CCM_8
| Note: This list was assembled from the set of registered TLS | Note: This list was assembled from the set of registered TLS
| cipher suites when [RFC7540] was developed. This list includes | cipher suites when [RFC7540] was developed. This list includes
| those cipher suites that do not offer an ephemeral key exchange | those cipher suites that do not offer an ephemeral key exchange
| and those that are based on the TLS null, stream, or block | and those that are based on the TLS null, stream, or block
| cipher type (as defined in Section 6.2.3 of [TLS12]). | cipher type (as defined in Section 6.2.3 of [TLS12]).
| Additional cipher suites with these properties could be | Additional cipher suites with these properties could be
| defined; these would not be explicitly prohibited. | defined; these would not be explicitly prohibited.
For more details, see Section 9.2.2 For more details, see Section 9.2.2.
Appendix B. Changes from RFC 7540 Appendix B. Changes from RFC 7540
This revision includes the following substantive changes: This revision includes the following substantive changes:
o Use of TLS 1.3 was defined based on RFC 8740, which this document o Use of TLS 1.3 was defined based on [RFC8740], which this document
obsoletes. obsoletes.
o The priority scheme defined in RFC 7540 is deprecated. o The priority scheme defined in RFC 7540 is deprecated.
Definitions for the format of the PRIORITY frame and the priority Definitions for the format of the PRIORITY frame and the priority
fields in the HEADERS frame have been retained, plus the rules fields in the HEADERS frame have been retained, plus the rules
governing when PRIORITY frames can be sent and received, but the governing when PRIORITY frames can be sent and received, but the
semantics of these fields are only described in RFC 7540. The semantics of these fields are only described in RFC 7540. The
priority signaling scheme from RFC 7540 was not successful. Using priority signaling scheme from RFC 7540 was not successful. Using
the simpler successor signaling [I-D.ietf-httpbis-priority] is the simpler signaling in [HTTP-PRIORITY] is recommended.
recommended.
o The HTTP/1.1 Upgrade mechanism is deprecated and no longer o The HTTP/1.1 Upgrade mechanism is deprecated and no longer
specified in this document. It was never widely deployed, with specified in this document. It was never widely deployed, with
plaintext HTTP/2 users choosing to use the prior-knowledge plaintext HTTP/2 users choosing to use the prior-knowledge
implementation instead. implementation instead.
o Validation for field names and values has been narrowed. The o Validation for field names and values has been narrowed. The
validation that is mandatory for intermediaries is precisely validation that is mandatory for intermediaries is precisely
defined and error reporting for requests has been amended to defined, and error reporting for requests has been amended to
encourage sending 400-series status codes. encourage sending 400-series status codes.
o The ranges of codepoints for settings and frame types that were o The ranges of codepoints for settings and frame types that were
reserved for "Experimental Use" are now available for general use. reserved for Experimental Use are now available for general use.
o Connection-specific header fields - which are prohibited - are o Connection-specific header fields -- which are prohibited -- are
more precisely and comprehensively identified. more precisely and comprehensively identified.
o Host and :authority are no longer permitted to disagree. o Host and ":authority" are no longer permitted to disagree.
o Rules for sending Dynamic Table Size Update instructions after o Rules for sending Dynamic Table Size Update instructions after
changes in settings have been clarified in Section 4.3.1. changes in settings have been clarified in Section 4.3.1.
Editorial changes are also included. In particular, changes to Editorial changes are also included. In particular, changes to
terminology and document structure are in response to updates to core terminology and document structure are in response to updates to core
HTTP semantics [HTTP]. Those documents now include some concepts HTTP semantics [HTTP]. Those documents now include some concepts
that were first defined in RFC 7540, such as the 421 status code or that were first defined in RFC 7540, such as the 421 status code or
connection coalescing. connection coalescing.
Contributors
The previous version of this document was authored by Mike Belshe and
Roberto Peon.
Acknowledgments Acknowledgments
Credit for non-trivial input to this document is owed to a large Credit for non-trivial input to this document is owed to a large
number of people who have contributed to the HTTP working group over number of people who have contributed to the HTTP Working Group over
the years. [RFC7540] contains a more extensive list of people that the years. [RFC7540] contains a more extensive list of people that
deserve acknowledgment for their contributions. deserve acknowledgment for their contributions.
Contributors
Mike Belshe and Roberto Peon authored the text that this document is
based on.
Authors' Addresses Authors' Addresses
Martin Thomson (editor) Martin Thomson (editor)
Mozilla Mozilla
Australia Australia
Email: mt@lowentropy.net Email: mt@lowentropy.net
Cory Benfield (editor) Cory Benfield (editor)
Apple Inc. Apple Inc.
Email: cbenfield@apple.com Email: cbenfield@apple.com
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