Internet Engineering Task Force (IETF)                   M. Thomson, Ed.
Request for Comments: 9113                                       Mozilla
Obsoletes: 7540, 8740                                   C. Benfield, Ed.
Category: Standards Track                                     Apple Inc.
ISSN: 2070-1721                                                June 2022





This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced latency by introducing field compression and allowing multiple concurrent exchanges on the same connection.


This document obsoletes RFCs 7540 and 8740.

このドキュメントは、RFCS 7540および8740を廃止します。

Status of This Memo


This is an Internet Standards Track document.


This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

このドキュメントは、インターネットエンジニアリングタスクフォース(IETF)の製品です。IETFコミュニティのコンセンサスを表しています。公開レビューを受けており、インターネットエンジニアリングステアリンググループ(IESG)からの出版が承認されています。インターネット標準の詳細については、RFC 7841のセクション2で入手できます。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.

著作権(c)2022 IETF Trustおよび文書著者として特定された人。全著作権所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

このドキュメントは、BCP 78およびIETFドキュメント(に関連するIETF Trustの法的規定の対象となります。この文書に関するあなたの権利と制限を説明するので、これらの文書を注意深く確認してください。このドキュメントから抽出されたコードコンポーネントには、セクション4.Eで説明されている法的規定のセクション4.Eで説明されており、修正されたBSDライセンスで説明されているように保証なしで提供される修正されたBSDライセンステキストを含める必要があります。

Table of Contents


   1.  Introduction
   2.  HTTP/2 Protocol Overview
     2.1.  Document Organization
     2.2.  Conventions and Terminology
   3.  Starting HTTP/2
     3.1.  HTTP/2 Version Identification
     3.2.  Starting HTTP/2 for "https" URIs
     3.3.  Starting HTTP/2 with Prior Knowledge
     3.4.  HTTP/2 Connection Preface
   4.  HTTP Frames
     4.1.  Frame Format
     4.2.  Frame Size
     4.3.  Field Section Compression and Decompression
       4.3.1.  Compression State
   5.  Streams and Multiplexing
     5.1.  Stream States
       5.1.1.  Stream Identifiers
       5.1.2.  Stream Concurrency
     5.2.  Flow Control
       5.2.1.  Flow-Control Principles
       5.2.2.  Appropriate Use of Flow Control
       5.2.3.  Flow-Control Performance
     5.3.  Prioritization
       5.3.1.  Background on Priority in RFC 7540
       5.3.2.  Priority Signaling in This Document
     5.4.  Error Handling
       5.4.1.  Connection Error Handling
       5.4.2.  Stream Error Handling
       5.4.3.  Connection Termination
     5.5.  Extending HTTP/2
   6.  Frame Definitions
     6.1.  DATA
     6.2.  HEADERS
     6.3.  PRIORITY
     6.4.  RST_STREAM
     6.5.  SETTINGS
       6.5.1.  SETTINGS Format
       6.5.2.  Defined Settings
       6.5.3.  Settings Synchronization
     6.6.  PUSH_PROMISE
     6.7.  PING
     6.8.  GOAWAY
     6.9.  WINDOW_UPDATE
       6.9.1.  The Flow-Control Window
       6.9.2.  Initial Flow-Control Window Size
       6.9.3.  Reducing the Stream Window Size
   7.  Error Codes
   8.  Expressing HTTP Semantics in HTTP/2
     8.1.  HTTP Message Framing
       8.1.1.  Malformed Messages
     8.2.  HTTP Fields
       8.2.1.  Field Validity
       8.2.2.  Connection-Specific Header Fields
       8.2.3.  Compressing the Cookie Header Field
     8.3.  HTTP Control Data
       8.3.1.  Request Pseudo-Header Fields
       8.3.2.  Response Pseudo-Header Fields
     8.4.  Server Push
       8.4.1.  Push Requests
       8.4.2.  Push Responses
     8.5.  The CONNECT Method
     8.6.  The Upgrade Header Field
     8.7.  Request Reliability
     8.8.  Examples
       8.8.1.  Simple Request
       8.8.2.  Simple Response
       8.8.3.  Complex Request
       8.8.4.  Response with Body
       8.8.5.  Informational Responses
   9.  HTTP/2 Connections
     9.1.  Connection Management
       9.1.1.  Connection Reuse
     9.2.  Use of TLS Features
       9.2.1.  TLS 1.2 Features
       9.2.2.  TLS 1.2 Cipher Suites
       9.2.3.  TLS 1.3 Features
   10. Security Considerations
     10.1.  Server Authority
     10.2.  Cross-Protocol Attacks
     10.3.  Intermediary Encapsulation Attacks
     10.4.  Cacheability of Pushed Responses
     10.5.  Denial-of-Service Considerations
       10.5.1.  Limits on Field Block Size
       10.5.2.  CONNECT Issues
     10.6.  Use of Compression
     10.7.  Use of Padding
     10.8.  Privacy Considerations
     10.9.  Remote Timing Attacks
   11. IANA Considerations
     11.1.  HTTP2-Settings Header Field Registration
     11.2.  The h2c Upgrade Token
   12. References
     12.1.  Normative References
     12.2.  Informative References
   Appendix A.  Prohibited TLS 1.2 Cipher Suites
   Appendix B.  Changes from RFC 7540
   Authors' Addresses
1. Introduction
1. はじめに

The performance of applications using the Hypertext Transfer Protocol (HTTP, [HTTP]) is linked to how each version of HTTP uses the underlying transport, and the conditions under which the transport operates.

HyperText Transfer Protocol(HTTP、[HTTP])を使用したアプリケーションのパフォーマンスは、HTTPの各バージョンが基礎となる輸送を使用する方法と、輸送が動作する条件にリンクされています。

Making multiple concurrent requests can reduce latency and improve application performance. HTTP/1.0 allowed only one request to be outstanding at a time on a given TCP [TCP] connection. HTTP/1.1 [HTTP/1.1] added request pipelining, but this only partially addressed request concurrency and still suffers from application-layer head-of-line blocking. Therefore, HTTP/1.0 and HTTP/1.1 clients use multiple connections to a server to make concurrent requests.

複数の同時リクエストを行うと、遅延を軽減し、アプリケーションのパフォーマンスを向上させることができます。HTTP/1.0では、特定のTCP [TCP]接続で一度に1つのリクエストのみが未払いであることを許可しました。http/1.1 [http/1.1]リクエストパイプラインが追加されましたが、これは部分的にのみ対処されたリクエストの並行性のみであり、アプリケーション層のヘッドオブラインブロッキングに苦しんでいます。したがって、HTTP/1.0およびHTTP/1.1クライアントは、サーバーへの複数の接続を使用して、同時リクエストを行います。

Furthermore, HTTP fields are often repetitive and verbose, causing unnecessary network traffic as well as causing the initial TCP congestion window to quickly fill. This can result in excessive latency when multiple requests are made on a new TCP connection.


HTTP/2 addresses these issues by defining an optimized mapping of HTTP's semantics to an underlying connection. Specifically, it allows interleaving of messages on the same connection and uses an efficient coding for HTTP fields. It also allows prioritization of requests, letting more important requests complete more quickly, further improving performance.


The resulting protocol is more friendly to the network because fewer TCP connections can be used in comparison to HTTP/1.x. This means less competition with other flows and longer-lived connections, which in turn lead to better utilization of available network capacity. Note, however, that TCP head-of-line blocking is not addressed by this protocol.


Finally, HTTP/2 also enables more efficient processing of messages through use of binary message framing.


This document obsoletes RFCs 7540 and 8740. Appendix B lists notable changes.

このドキュメントは、RFCS 7540および8740を廃止します。付録Bには顕著な変更が記載されています。

2. HTTP/2 Protocol Overview
2. HTTP/2プロトコルの概要

HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2 supports all of the core features of HTTP but aims to be more efficient than HTTP/1.1.


HTTP/2 is a connection-oriented application-layer protocol that runs over a TCP connection ([TCP]). The client is the TCP connection initiator.


The basic protocol unit in HTTP/2 is a frame (Section 4.1). Each frame type serves a different purpose. For example, HEADERS and DATA frames form the basis of HTTP requests and responses (Section 8.1); other frame types like SETTINGS, WINDOW_UPDATE, and PUSH_PROMISE are used in support of other HTTP/2 features.


Multiplexing of requests is achieved by having each HTTP request/ response exchange associated with its own stream (Section 5). Streams are largely independent of each other, so a blocked or stalled request or response does not prevent progress on other streams.


Effective use of multiplexing depends on flow control and prioritization. Flow control (Section 5.2) ensures that it is possible to efficiently use multiplexed streams by restricting data that is transmitted to what the receiver is able to handle. Prioritization (Section 5.3) ensures that limited resources are used most effectively. This revision of HTTP/2 deprecates the priority signaling scheme from [RFC7540].


Because HTTP fields used in a connection can contain large amounts of redundant data, frames that contain them are compressed (Section 4.3). This has especially advantageous impact upon request sizes in the common case, allowing many requests to be compressed into one packet.


Finally, HTTP/2 adds a new, optional interaction mode whereby a server can push responses to a client (Section 8.4). This is intended to allow a server to speculatively send data to a client that the server anticipates the client will need, trading off some network usage against a potential latency gain. The server does this by synthesizing a request, which it sends as a PUSH_PROMISE frame. The server is then able to send a response to the synthetic request on a separate stream.


2.1. Document Organization
2.1. ドキュメント組織

The HTTP/2 specification is split into four parts:


* Starting HTTP/2 (Section 3) covers how an HTTP/2 connection is initiated.

* HTTP/2の開始(セクション3)は、HTTP/2接続の開始方法をカバーしています。

* The frame (Section 4) and stream (Section 5) layers describe the way HTTP/2 frames are structured and formed into multiplexed streams.

* フレーム(セクション4)およびストリーム(セクション5)レイヤーは、HTTP/2フレームが構造化され、多重化されたストリームに形成される方法を説明しています。

* Frame (Section 6) and error (Section 7) definitions include details of the frame and error types used in HTTP/2.

* フレーム(セクション6)とエラー(セクション7)の定義には、HTTP/2で使用されるフレームとエラータイプの詳細が含まれています。

* HTTP mappings (Section 8) and additional requirements (Section 9) describe how HTTP semantics are expressed using frames and streams.

* HTTPマッピング(セクション8)および追加要件(セクション9)は、HTTPセマンティクスがフレームとストリームを使用してどのように表現されるかについて説明します。

While some of the frame- and stream-layer concepts are isolated from HTTP, this specification does not define a completely generic frame layer. The frame and stream layers are tailored to the needs of HTTP.


2.2. Conventions and Terminology
2.2. 慣習と用語

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

この文書のキーワード "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", および "OPTIONAL" はBCP 14 [RFC2119] [RFC8174]で説明されているように、すべて大文字の場合にのみ解釈されます。

All numeric values are in network byte order. Values are unsigned unless otherwise indicated. Literal values are provided in decimal or hexadecimal as appropriate. Hexadecimal literals are prefixed with "0x" to distinguish them from decimal literals.


This specification describes binary formats using the conventions described in Section 1.3 of RFC 9000 [QUIC]. Note that this format uses network byte order and that high-valued bits are listed before low-valued bits.

この仕様では、RFC 9000 [QUIC]のセクション1.3で説明されている規則を使用して、バイナリ形式について説明します。この形式では、ネットワークバイトの順序を使用し、高価値ビットが低価値ビットの前にリストされていることに注意してください。

The following terms are used:


client: The endpoint that initiates an HTTP/2 connection. Clients send HTTP requests and receive HTTP responses.


connection: A transport-layer connection between two endpoints.


connection error: An error that affects the entire HTTP/2 connection.


endpoint: Either the client or server of the connection.


frame: The smallest unit of communication within an HTTP/2 connection, consisting of a header and a variable-length sequence of octets structured according to the frame type.


peer: An endpoint. When discussing a particular endpoint, "peer" refers to the endpoint that is remote to the primary subject of discussion.


receiver: An endpoint that is receiving frames.


sender: An endpoint that is transmitting frames.


server: The endpoint that accepts an HTTP/2 connection. Servers receive HTTP requests and send HTTP responses.


stream: A bidirectional flow of frames within the HTTP/2 connection.


stream error: An error on the individual HTTP/2 stream.


Finally, the terms "gateway", "intermediary", "proxy", and "tunnel" are defined in Section 3.7 of [HTTP]. Intermediaries act as both client and server at different times.


The term "content" as it applies to message bodies is defined in Section 6.4 of [HTTP].


3. Starting HTTP/2
3. HTTP/2の開始

Implementations that generate HTTP requests need to discover whether a server supports HTTP/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 [HTTP/1.1]. These URIs do not include any indication about what HTTP versions an upstream server (the immediate peer to which the client wishes to establish a connection) supports.

HTTP/2は、[HTTP]のセクション4.2で定義されている「HTTP」および「HTTPS」URIスキームを使用し、HTTP/1.1 [HTTP/1.1]と同じデフォルトポート番号を使用します。これらのURIには、上流サーバー(クライアントが接続の確立を希望する即時のピア)がサポートするHTTPバージョンについての兆候は含まれていません。

The means by which support for HTTP/2 is determined is different for "http" and "https" URIs. Discovery for "https" URIs is described in 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 described in Section 3.3.


3.1. HTTP/2 Version Identification
3.1. HTTP/2バージョン識別

The protocol defined in this document has two identifiers. Creating a connection based on either implies the use of the transport, framing, and message semantics described in this document.


* The string "h2" identifies the protocol where HTTP/2 uses Transport Layer Security (TLS); see Section 9.2. This identifier is used in the TLS Application-Layer Protocol Negotiation (ALPN) extension [TLS-ALPN] field and in any place where HTTP/2 over TLS is identified.

* 文字列「H2」は、HTTP/2がトランスポートレイヤーセキュリティ(TLS)を使用するプロトコルを識別します。セクション9.2を参照してください。この識別子は、TLSアプリケーション層プロトコルネゴシエーション(ALPN)拡張[TLS-ALPN]フィールドおよびTLS上のHTTP/2が識別される任意の場所で使用されます。

The "h2" string is serialized into an ALPN protocol identifier as the two-octet sequence: 0x68, 0x32.


* 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]). This usage was never widely deployed and is deprecated by this document. The same applies to the HTTP2-Settings header field, which was used with the upgrade to "h2c".

* 「H2C」文字列は、以前はHTTPアップグレードメカニズムのアップグレードヘッダーフィールド([HTTP]のセクション7.8)で使用するためのトークンとして使用されていました。この使用は決して広く展開されず、この文書によって非推奨されます。同じことが、「H2C」へのアップグレードとともに使用されたHTTP2-Settingsヘッダーフィールドにも当てはまります。

3.2. Starting HTTP/2 for "https" URIs
3.2. 「https」urisのHTTP/2を開始します

A client that makes a request to an "https" URI uses TLS [TLS13] with the ALPN extension [TLS-ALPN].

「HTTPS」URIにリクエストを行うクライアントは、ALPN拡張[TLS-ALPN]を使用してTLS [TLS13]を使用します。

HTTP/2 over TLS uses the "h2" protocol identifier. The "h2c" protocol identifier MUST NOT be sent by a client or selected by a server; the "h2c" protocol identifier describes a protocol that does not use TLS.

HTTP/2 Over TLSは、「H2」プロトコル識別子を使用します。「H2C」プロトコル識別子は、クライアントによって送信されたり、サーバーによって選択されたりしないでください。「H2C」プロトコル識別子は、TLSを使用しないプロトコルを記述します。

Once TLS negotiation is complete, both the client and the server MUST send a connection preface (Section 3.4).


3.3. Starting HTTP/2 with Prior Knowledge
3.3. 事前知識でHTTP/2を開始します

A client can learn that a particular server supports HTTP/2 by other means. For example, a client could be configured with knowledge that a server supports HTTP/2.


A client that knows that a server supports HTTP/2 can establish a TCP connection and send the connection preface (Section 3.4) followed by HTTP/2 frames. Servers can identify these connections by the presence of the connection preface. This only affects the establishment of HTTP/2 connections over cleartext TCP; HTTP/2 connections over TLS MUST use protocol negotiation in TLS [TLS-ALPN].

サーバーがHTTP/2をサポートしていることを知っているクライアントは、TCP接続を確立し、接続序文(セクション3.4)を送信し、その後HTTP/2フレームを送信できます。サーバーは、接続序文の存在によりこれらの接続を識別できます。これは、クリアテキストTCPを介したHTTP/2接続の確立にのみ影響します。TLSを介したHTTP/2接続は、TLS [TLS-ALPN]でプロトコルネゴシエーションを使用する必要があります。

Likewise, the server MUST send a connection preface (Section 3.4).


Without additional information, prior support for HTTP/2 is not a strong signal that a given server will support HTTP/2 for future connections. For example, it is possible for server configurations to change, for configurations to differ between instances in clustered servers, or for network conditions to change.


3.4. HTTP/2 Connection Preface
3.4. HTTP/2接続序文

In HTTP/2, each endpoint is required to send a connection preface as a final confirmation of the protocol in use and to establish the initial settings for the HTTP/2 connection. The client and server each send a different connection preface.


The client connection preface starts with a sequence of 24 octets, which in hex notation is:



That is, the connection preface starts with the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n". This sequence MUST be followed by a SETTINGS frame (Section 6.5), which MAY be empty. The client sends the client connection preface as the first application data octets of a connection.

つまり、接続序文は文字列「pri * http/2.0 \ r \ n \ r \ nsm \ r \ n \ r \ n "から始まります。このシーケンスの後に、空の設定フレーム(セクション6.5)が続く必要があります。クライアントは、接続の最初のアプリケーションデータオクテットとしてクライアント接続序文を送信します。

Note: The client connection preface is selected so that a large proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do not attempt to process further frames. Note that this does not address the concerns raised in [TALKING].


The server connection preface consists of a potentially empty SETTINGS frame (Section 6.5) that MUST be the first frame the server sends in the HTTP/2 connection.


The SETTINGS frames received from a peer as part of the connection preface MUST be acknowledged (see Section 6.5.3) after sending the connection preface.


To avoid unnecessary latency, clients are permitted to send additional frames to the server immediately after sending the client connection preface, without waiting to receive the server connection preface. It is important to note, however, that the server connection preface SETTINGS frame might include settings that necessarily alter how a client is expected to communicate with the server. Upon receiving the SETTINGS frame, the client is expected to honor any settings established. In some configurations, it is possible for the server to transmit SETTINGS before the client sends additional frames, providing an opportunity to avoid this issue.


Clients and servers MUST treat an invalid connection preface as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. A GOAWAY frame (Section 6.8) MAY be omitted in this case, since an invalid preface indicates that the peer is not using HTTP/2.


4. HTTP Frames
4. HTTPフレーム

Once the HTTP/2 connection is established, endpoints can begin exchanging frames.


4.1. Frame Format
4.1. フレーム形式

All frames begin with a fixed 9-octet header followed by a variable-length frame payload.


HTTP Frame { Length (24), Type (8),


Flags (8),


Reserved (1), Stream Identifier (31),


Frame Payload (..), }


Figure 1: Frame Layout


The fields of the frame header are defined as:


Length: The length of the frame payload expressed as an unsigned 24-bit integer in units of octets. Values greater than 2^14 (16,384) MUST NOT be sent unless the receiver has set a larger value for SETTINGS_MAX_FRAME_SIZE.


The 9 octets of the frame header are not included in this value.


Type: The 8-bit type of the frame. The frame type determines the format and semantics of the frame. Frames defined in this document are listed in Section 6. Implementations MUST ignore and discard frames of unknown types.


Flags: An 8-bit field reserved for boolean flags specific to the frame type.


Flags are assigned semantics specific to the indicated frame type. Unused flags are those that have no defined semantics for a particular frame type. Unused flags MUST be ignored on receipt and MUST be left unset (0x00) when sending.


Reserved: A reserved 1-bit field. The semantics of this bit are undefined, and the bit MUST remain unset (0x00) when sending and MUST be ignored when receiving.


Stream Identifier: A stream identifier (see Section 5.1.1) expressed as an unsigned 31-bit integer. The value 0x00 is reserved for frames that are associated with the connection as a whole as opposed to an individual stream.


The structure and content of the frame payload are dependent entirely on the frame type.


4.2. Frame Size
4.2. フレームサイズ

The size of a frame payload is limited by the maximum size that a receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This setting can have any value between 2^14 (16,384) and 2^24-1 (16,777,215) octets, inclusive.


All implementations MUST be capable of receiving and minimally processing frames up to 2^14 octets in length, plus the 9-octet frame header (Section 4.1). The size of the frame header is not included when describing frame sizes.


Note: Certain frame types, such as PING (Section 6.7), impose additional limits on the amount of frame payload data allowed.


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 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 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 (Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), a SETTINGS frame, and any frame with a stream identifier of 0.


Endpoints are not obligated to use all available space in a frame. Responsiveness can be improved by using frames that are smaller than the permitted maximum size. Sending large frames can result in delays in sending time-sensitive frames (such as RST_STREAM, WINDOW_UPDATE, or PRIORITY), which, if blocked by the transmission of a large frame, could affect performance.


4.3. Field Section Compression and Decompression
4.3. フィールドセクションの圧縮と減圧

Field section compression is the process of compressing a set of 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 set of field lines. Details of HTTP/2 field section compression and decompression are defined in [COMPRESSION], which, for historical reasons, refers to these processes as header compression and decompression.


Each field block carries all of the compressed field lines of a single field section. Header sections also include control data associated with the message in the form of pseudo-header fields (Section 8.3) that use the same format as a field line.


Note: RFC 7540 [RFC7540] used the term "header block" in place of the more generic "field block".

注:RFC 7540 [RFC7540]は、より一般的な「フィールドブロック」の代わりに「ヘッダーブロック」という用語を使用しました。

Field blocks carry control data and header sections for requests, responses, promised requests, and pushed responses (see Section 8.4). All these messages, except for interim responses and requests contained in PUSH_PROMISE (Section 6.6) frames, can optionally include a field block that carries a trailer section.


A field section is a collection of field lines. Each of the 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 fragments. The first field block fragment is transmitted within the frame payload of HEADERS (Section 6.2) or PUSH_PROMISE (Section 6.6), each of which could be followed by CONTINUATION (Section 6.10) frames to carry subsequent field block fragments.


The Cookie header field [COOKIE] is treated specially by the HTTP mapping (see Section 8.2.3).


A receiving endpoint reassembles the field block by concatenating its fragments and then decompresses the block to reconstruct the field section.


A complete field section consists of either:


* a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag set, or

* end_headersフラグが設定された単一のヘッダーまたはpush_promiseフレーム、または

* a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag unset and one or more CONTINUATION frames, where the last CONTINUATION frame has the END_HEADERS flag set.

* End_headersフラグが解消されたヘッダーまたはPush_promiseフレームと1つ以上の継続フレーム。最後の継続フレームにはend_headersフラグが設定されています。

Each field block is processed as a discrete unit. Field blocks MUST be transmitted as a contiguous sequence of frames, with no interleaved frames of any other type or from any other stream. The last frame in a sequence of HEADERS or CONTINUATION frames has the END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE or CONTINUATION frames has the END_HEADERS flag set. This allows a field block to be logically equivalent to a single frame.


Field block fragments can only be sent as the frame payload of HEADERS, PUSH_PROMISE, or CONTINUATION frames because these frames carry data that can modify the compression context maintained by a receiver. An endpoint receiving HEADERS, PUSH_PROMISE, or CONTINUATION frames needs to reassemble field blocks and perform decompression even if the frames are to be discarded. A receiver MUST terminate the connection with a connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does not decompress a field block.


A decoding error in a field block MUST be treated as a connection error (Section 5.4.1) of type COMPRESSION_ERROR.


4.3.1. Compression State
4.3.1. 圧縮状態

Field compression is stateful. Each endpoint has an HPACK encoder context and an HPACK decoder context that are used for encoding and decoding all field blocks on a connection. Section 4 of [COMPRESSION] defines the dynamic table, which is the primary state for each context.


The dynamic table has a maximum size that is set by an HPACK decoder. An endpoint communicates the size chosen by its HPACK decoder context using the SETTINGS_HEADER_TABLE_SIZE setting; see Section 6.5.2. When a connection is established, the dynamic table size for the HPACK decoder and encoder at both endpoints starts at 4,096 bytes, the initial value of the SETTINGS_HEADER_TABLE_SIZE setting.


Any change to the maximum value set using SETTINGS_HEADER_TABLE_SIZE takes effect when the endpoint acknowledges settings (Section 6.5.3). The HPACK encoder at that endpoint can set the dynamic table to any size up to the maximum value set by the decoder. An HPACK encoder declares the size of the dynamic table with a Dynamic Table Size Update instruction (Section 6.3 of [COMPRESSION]).


Once an endpoint acknowledges a change to SETTINGS_HEADER_TABLE_SIZE that reduces the maximum below the current size of the dynamic table, its HPACK encoder MUST start the next field block with a Dynamic Table Size Update instruction that sets the dynamic table to a size that is less than or equal to the reduced maximum; see Section 4.2 of [COMPRESSION]. An endpoint MUST treat a field block that follows an acknowledgment of the reduction to the maximum dynamic table size as a connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does not start with a conformant Dynamic Table Size Update instruction.


      |  Implementers are advised that reducing the value of
      |  SETTINGS_HEADER_TABLE_SIZE is not widely interoperable.  Use of
      |  the connection preface to reduce the value below the initial
      |  value of 4,096 is somewhat better supported, but this might
      |  fail with some implementations.
5. Streams and Multiplexing
5. ストリームと多重化

A "stream" is an independent, bidirectional sequence of frames exchanged between the client and server within an HTTP/2 connection. Streams have several important characteristics:


* A single HTTP/2 connection can contain multiple concurrently open streams, with either endpoint interleaving frames from multiple streams.

* 単一のHTTP/2接続には、複数のストリームからのエンドポイントインターリーブフレームを備えた複数の同時にオープンストリームを含めることができます。

* Streams can be established and used unilaterally or shared by either endpoint.

* ストリームは、一方的に確立および使用するか、いずれかのエンドポイントで共有できます。

* Streams can be closed by either endpoint.

* ストリームは、いずれかのエンドポイントで閉じることができます。

* The order in which frames are sent is significant. Recipients process frames in the order they are received. In particular, the order of HEADERS and DATA frames is semantically significant.

* フレームが送信される順序は重要です。受信者は、受信した順序でフレームを処理します。特に、ヘッダーとデータフレームの順序は意味的に重要です。

* Streams are identified by an integer. Stream identifiers are assigned to streams by the endpoint initiating the stream.

* ストリームは整数によって識別されます。ストリーム識別子は、ストリームを開始するエンドポイントによってストリームに割り当てられます。

5.1. Stream States
5.1. ストリーム状態

The lifecycle of a stream is shown in Figure 2.


                        send PP |        | recv PP
                       ,--------+  idle  +--------.
                      /         |        |         \
                     v          +--------+          v
              +----------+          |           +----------+
              |          |          | send H /  |          |
       ,------+ reserved |          | recv H    | reserved +------.
       |      | (local)  |          |           | (remote) |      |
       |      +---+------+          v           +------+---+      |
       |          |             +--------+             |          |
       |          |     recv ES |        | send ES     |          |
       |   send H |     ,-------+  open  +-------.     | recv H   |
       |          |    /        |        |        \    |          |
       |          v   v         +---+----+         v   v          |
       |      +----------+          |           +----------+      |
       |      |   half-  |          |           |   half-  |      |
       |      |  closed  |          | send R /  |  closed  |      |
       |      | (remote) |          | recv R    | (local)  |      |
       |      +----+-----+          |           +-----+----+      |
       |           |                |                 |           |
       |           | send ES /      |       recv ES / |           |
       |           |  send R /      v        send R / |           |
       |           |  recv R    +--------+   recv R   |           |
       | send R /  `----------->|        |<-----------'  send R / |
       | recv R                 | closed |               recv R   |
       `----------------------->|        |<-----------------------'

Figure 2: Stream States


send: endpoint sends this frame recv: endpoint receives this frame H: HEADERS frame (with implied CONTINUATION frames) ES: END_STREAM flag R: RST_STREAM frame PP: PUSH_PROMISE frame (with implied CONTINUATION frames); state transitions are for the promised stream

送信:エンドポイントはこのフレームを送信しますRecv:エンドポイントはこのフレームH:ヘッダーフレーム(暗黙の継続フレーム)ES:END_STREAM FLAG R:RST_STREAMフレームPP:Push_Promiseフレーム(暗黙の継続フレーム付き);州の移行は、約束されたストリーム用です

Note that this diagram shows stream state transitions and the frames and flags that affect those transitions only. In this regard, CONTINUATION frames do not result in state transitions; they are effectively part of the HEADERS or PUSH_PROMISE that they follow. For the purpose of state transitions, the END_STREAM flag is processed as a separate event to the frame that bears it; a HEADERS frame with the END_STREAM flag set can cause two state transitions.


Both endpoints have a subjective view of the state of a stream that could be different when frames are in transit. Endpoints do not coordinate the creation of streams; they are created unilaterally by either endpoint. The negative consequences of a mismatch in states are limited to the "closed" state after sending RST_STREAM, where frames might be received for some time after closing.


Streams have the following states:


idle: All streams start in the "idle" state.


The following transitions are valid from this state:


* Sending a HEADERS frame as a client, or receiving a HEADERS frame as a server, causes the stream to become "open". The stream identifier is selected as described in Section 5.1.1. The same HEADERS frame can also cause a stream to immediately become "half-closed".

* クライアントとしてヘッダーフレームを送信するか、サーバーとしてヘッダーフレームを受信すると、ストリームが「オープン」になります。ストリーム識別子は、セクション5.1.1で説明されているように選択されます。同じヘッダーフレームは、ストリームをすぐに「半分閉鎖」する可能性があります。

* Sending a PUSH_PROMISE frame on another stream reserves the idle stream that is identified for later use. The stream state for the reserved stream transitions to "reserved (local)". Only a server may send PUSH_PROMISE frames.

* 別のストリームにPush_Promiseフレームを送信すると、後で使用するために識別されるアイドルストリームが予約されます。予約済みのストリームのストリーム状態は、「予約済み(ローカル)」に移行します。Push_promiseフレームを送信できるサーバーのみができます。

* Receiving a PUSH_PROMISE frame on another stream reserves an idle stream that is identified for later use. The stream state for the reserved stream transitions to "reserved (remote)". Only a client may receive PUSH_PROMISE frames.

* 別のストリームでPush_Promiseフレームを受信すると、後で使用するために識別されるアイドルストリームが予約されます。予約済みのストリームのストリーム状態は、「予約済み(リモート)」に移行します。Push_promiseフレームを受信できるのはクライアントのみです。

* Note that the PUSH_PROMISE frame is not sent on the idle stream but references the newly reserved stream in the Promised Stream ID field.

* Push_Promiseフレームはアイドルストリームに送信されないが、約束されたストリームIDフィールドの新しく予約されたストリームを参照することに注意してください。

* Opening a stream with a higher-valued stream identifier causes the stream to transition immediately to a "closed" state; note that this transition is not shown in the diagram.

* 高価値のストリーム識別子でストリームを開くと、ストリームはすぐに「閉じた」状態に移行します。この遷移は図に示されていないことに注意してください。

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) of type PROTOCOL_ERROR. If this stream is initiated by the server, as described in Section 5.1.1, then receiving a HEADERS frame MUST also be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


reserved (local): A stream in the "reserved (local)" state is one that has been promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame reserves an idle stream by associating the stream with an open stream that was initiated by the remote peer (see Section 8.4).


In this state, only the following transitions are possible:


* The endpoint can send a HEADERS frame. This causes the stream to open in a "half-closed (remote)" state.

* エンドポイントはヘッダーフレームを送信できます。これにより、ストリームは「半分閉鎖された(リモート)」状態で開きます。

* Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This releases the stream reservation.

* いずれかのEndPointがRST_STREAMフレームを送信して、ストリームを「閉じた」ようにすることができます。これにより、ストリーム予約がリリースされます。

An endpoint MUST NOT send any type of frame other than HEADERS, RST_STREAM, or PRIORITY in this state.


A PRIORITY or WINDOW_UPDATE frame MAY be received in this state. Receiving any type of frame other than RST_STREAM, PRIORITY, or WINDOW_UPDATE on a stream in this state MUST be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


reserved (remote): A stream in the "reserved (remote)" state has been reserved by a remote peer.


In this state, only the following transitions are possible:


* Receiving a HEADERS frame causes the stream to transition to "half-closed (local)".

* ヘッダーフレームを受信すると、ストリームは「半分閉鎖(ローカル)」に移行します。

* Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This releases the stream reservation.

* いずれかのEndPointがRST_STREAMフレームを送信して、ストリームを「閉じた」ようにすることができます。これにより、ストリーム予約がリリースされます。

An endpoint MUST NOT send any type of frame other than RST_STREAM, WINDOW_UPDATE, or PRIORITY in this state.


Receiving any type of frame other than HEADERS, RST_STREAM, or PRIORITY on a stream in this state MUST be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


open: A stream in the "open" state may be used by both peers to send frames of any type. In this state, sending peers observe advertised stream-level flow-control limits (Section 5.2).


From this state, either endpoint can send a frame with an END_STREAM flag set, which causes the stream to transition into one of the "half-closed" states. An endpoint sending an END_STREAM flag causes the stream state to become "half-closed (local)"; an endpoint receiving an END_STREAM flag causes the stream state to become "half-closed (remote)".


Either endpoint can send a RST_STREAM frame from this state, causing it to transition immediately to "closed".


half-closed (local): A stream that is in the "half-closed (local)" state cannot be used for sending frames other than WINDOW_UPDATE, PRIORITY, and RST_STREAM.


A stream transitions from this state to "closed" when a frame is received with the END_STREAM flag set or when either peer sends a RST_STREAM frame.


An endpoint can receive any type of frame in this state. Providing flow-control credit using WINDOW_UPDATE frames is necessary to continue receiving flow-controlled frames. In this state, a receiver can ignore WINDOW_UPDATE frames, which might arrive for a short period after a frame with the END_STREAM flag set is sent.


PRIORITY frames can be received in this state.


half-closed (remote): A stream that is "half-closed (remote)" is no longer being used by the peer to send frames. In this state, an endpoint is no longer obligated to maintain a receiver flow-control window.


If an endpoint receives additional frames, other than WINDOW_UPDATE, PRIORITY, or RST_STREAM, for a stream that is in this state, it MUST respond with a stream error (Section 5.4.2) of type STREAM_CLOSED.

この状態にあるストリームの場合、window_update、priority、またはrst_stream以外のエンドポイントが追加のフレームを受信する場合、type stream_closedのストリームエラー(セクション5.4.2)で応答する必要があります。

A stream that is "half-closed (remote)" can be used by the endpoint to send frames of any type. In this state, the endpoint continues to observe advertised stream-level flow-control limits (Section 5.2).


A stream can transition from this state to "closed" by sending a frame with the END_STREAM flag set or when either peer sends a RST_STREAM frame.


closed: The "closed" state is the terminal state.


A stream enters the "closed" state after an endpoint both sends and receives a frame with an END_STREAM flag set. A stream also enters the "closed" state after an endpoint either sends or receives a RST_STREAM frame.


An endpoint MUST NOT send frames other than PRIORITY on a closed stream. An endpoint MAY treat receipt of any other type of frame on a closed stream as a connection error (Section 5.4.1) of type STREAM_CLOSED, except as noted below.


An endpoint that sends a frame with the END_STREAM flag set or a RST_STREAM frame might receive a WINDOW_UPDATE or RST_STREAM frame from its peer in the time before the peer receives and processes the frame that closes the stream.


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 of frame. The peer might have sent or enqueued for sending these frames before processing the RST_STREAM frame. An endpoint MUST minimally process and then discard any frames it receives in this state. This means updating header compression state for HEADERS and PUSH_PROMISE frames. Receiving a PUSH_PROMISE frame also causes the promised stream to become "reserved (remote)", even when the PUSH_PROMISE frame is received on a closed stream. Additionally, the content of DATA frames counts toward the connection flow-control window.


An endpoint can perform this minimal processing for all streams that are in the "closed" state. Endpoints MAY use other signals to detect that a peer has received the frames that caused the 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 PROTOCOL_ERROR. Endpoints can use frames that indicate that the peer has received the closing signal to drive this. Endpoints SHOULD NOT use timers for this purpose. For example, an endpoint that sends a SETTINGS frame after closing a stream can safely treat receipt of a DATA frame on that stream as an error after receiving an acknowledgment of the settings. Other things that might be used are PING frames, receiving data on streams that were created after closing the stream, or responses to requests created after closing the stream.


In the absence of more specific rules, implementations SHOULD treat 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 PROTOCOL_ERROR. Note that PRIORITY can be sent and received in any stream state.


The rules in this section only apply to frames defined in this document. Receipt of frames for which the semantics are unknown cannot be treated as an error, as the conditions for sending and receiving those frames are also unknown; see Section 5.5.


An example of the state transitions for an HTTP request/response 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.


5.1.1. Stream Identifiers
5.1.1. ストリーム識別子

Streams are identified by an unsigned 31-bit integer. Streams initiated by a client MUST use odd-numbered stream identifiers; those initiated by the server MUST use even-numbered stream identifiers. A stream identifier of zero (0x00) is used for connection control messages; the stream identifier of zero cannot be used to establish a new stream.


The identifier of a newly established stream MUST be numerically greater than all streams that the initiating endpoint has opened or reserved. This governs streams that are opened using a HEADERS frame and streams that are reserved using PUSH_PROMISE. An endpoint that receives an unexpected stream identifier MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


A HEADERS frame will transition the client-initiated stream identified by the stream identifier in the frame header from "idle" to "open". A PUSH_PROMISE frame will transition the server-initiated stream identified by the Promised Stream ID field in the frame payload from "idle" to "reserved (local)" or "reserved (remote)". When a stream transitions out of the "idle" state, all streams in the "idle" state that might have been opened by the peer with a lower-valued stream identifier immediately transition to "closed". That 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 result in an endpoint exhausting the available range of stream identifiers. A client that is unable to establish a new stream identifier can establish a new connection for new streams. A server 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 streams.


5.1.2. Stream Concurrency
5.1.2. 並行性をストリーミングします

A peer can limit the number of concurrently active streams using the SETTINGS_MAX_CONCURRENT_STREAMS parameter (see Section 6.5.2) within a SETTINGS frame. The maximum concurrent streams setting is specific to each endpoint and applies only to the peer that receives the setting. That is, clients specify the maximum number of concurrent streams the server can initiate, and servers specify the maximum number of concurrent streams the client can initiate.


Streams that are in the "open" state or in either of the "half-closed" states count toward the maximum number of streams that an endpoint is permitted to open. Streams in any of these three states count toward the limit advertised in the SETTINGS_MAX_CONCURRENT_STREAMS setting. Streams in either of the "reserved" states do not count toward the stream limit.


Endpoints MUST NOT exceed the limit set by their peer. An endpoint that receives a HEADERS frame that causes its advertised concurrent stream limit to be exceeded MUST treat this as a stream error (Section 5.4.2) of type PROTOCOL_ERROR or REFUSED_STREAM. The choice of error code determines whether the endpoint wishes to enable automatic retry (see Section 8.7 for details).


An endpoint that wishes to reduce the value of SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current number of open streams can either close streams that exceed the new value or allow streams to complete.


5.2. Flow Control
5.2. フロー制御

Using streams for multiplexing introduces contention over use of the TCP connection, resulting in blocked streams. A flow-control scheme ensures that streams on the same connection do not destructively interfere with each other. Flow control is used for both individual streams and the connection as a whole.


HTTP/2 provides for flow control through use of the WINDOW_UPDATE frame (Section 6.9).


5.2.1. Flow-Control Principles
5.2.1. フロー制御原則

HTTP/2 stream flow control aims to allow a variety of flow-control algorithms to be used without requiring protocol changes. Flow control in HTTP/2 has the following characteristics:


1. Flow control is specific to a connection. HTTP/2 flow control operates between the endpoints of a single hop and not over the entire end-to-end path.

1. フロー制御は接続に固有です。HTTP/2フロー制御は、単一のホップのエンドポイント間で動作し、エンドツーエンドパス全体ではありません。

2. Flow control is based on WINDOW_UPDATE frames. Receivers advertise how many octets they are prepared to receive on a stream and for the entire connection. This is a credit-based scheme.

2. フロー制御は、window_updateフレームに基づいています。レシーバーは、ストリームと接続全体で受信する準備ができているオクテットの数を宣伝します。これはクレジットベースのスキームです。

3. Flow control is directional with overall control provided by the receiver. A receiver MAY choose to set any window size that it desires for each stream and for the entire connection. A sender MUST respect flow-control limits imposed by a receiver. Clients, servers, and intermediaries all independently advertise their flow-control window as a receiver and abide by the flow-control limits set by their peer when sending.

3. フロー制御は、レシーバーが提供する全体的な制御により方向性があります。受信者は、各ストリームと接続全体に必要なウィンドウサイズを設定することを選択できます。送信者は、受信機によって課されるフロー制御制限を尊重する必要があります。クライアント、サーバー、および仲介者はすべて、すべて独立してフロー制御ウィンドウをレシーバーとして宣伝し、送信時にピアが設定したフロー制御制限を順守します。

4. The initial value for the flow-control window is 65,535 octets for both new streams and the overall connection.

4. フローコントロールウィンドウの初期値は、新しいストリームと全体的な接続の両方で65,535オクテットです。

5. The frame type determines whether flow control applies to a frame. Of the frames specified in this document, only DATA frames are subject to flow control; all other frame types do not consume space in the advertised flow-control window. This ensures that important control frames are not blocked by flow control.

5. フレームタイプは、フロー制御がフレームに適用されるかどうかを決定します。このドキュメントで指定されたフレームのうち、データフレームのみがフロー制御の対象となります。他のすべてのフレームタイプは、広告されたフロー制御ウィンドウでスペースを消費しません。これにより、重要な制御フレームがフロー制御によってブロックされないようになります。

6. An endpoint can choose to disable its own flow control, but an endpoint cannot ignore flow-control signals from its peer.

6. エンドポイントは独自のフロー制御を無効にすることを選択できますが、エンドポイントはピアからのフロー制御信号を無視することはできません。

7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE frame (Section 6.9). This document does not stipulate how a receiver decides when to send this frame or the value that it sends, nor does it specify how a sender chooses to send packets. Implementations are able to select any algorithm that suits their needs.

7. HTTP/2は、window_updateフレームの形式とセマンティクスのみを定義します(セクション6.9)。このドキュメントでは、受信者がこのフレームをいつ送信するか、または送信する値を決定する方法を規定していません。また、送信者がパケットを送信する方法を指定しません。実装は、ニーズに合った任意のアルゴリズムを選択できます。

Implementations are also responsible for prioritizing the sending of requests and responses, choosing how to avoid head-of-line blocking for requests, and managing the creation of new streams. Algorithm choices for these could interact with any flow-control algorithm.


5.2.2. Appropriate Use of Flow Control
5.2.2. フロー制御の適切な使用

Flow control is defined to protect endpoints that are operating under resource constraints. For example, a proxy needs to share memory between many connections and also might have a slow upstream connection and a fast downstream one. Flow control addresses cases where the receiver is unable to process data on one stream yet wants to continue to process other streams in the same connection.


Deployments that do not require this capability can advertise a flow-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. This effectively disables flow control for that receiver. Conversely, a sender is always subject to the flow-control window advertised by the receiver.


Deployments with constrained resources (for example, memory) can employ flow control to limit the amount of memory a peer can consume. Note, however, that this can lead to suboptimal use of available network resources if flow control is enabled without knowledge of the bandwidth * delay product (see [RFC7323]).

制約付きリソース(メモリなど)を使用した展開は、フロー制御を使用して、ピアが消費できるメモリの量を制限できます。ただし、これにより、帯域幅 *遅延積の知識なしにフロー制御が有効になっている場合、利用可能なネットワークリソースの以下の使用につながる可能性があることに注意してください([RFC7323]を参照)。

Even with full awareness of the current bandwidth * delay product, implementation of flow control can be difficult. Endpoints MUST read 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 critical frames, such as WINDOW_UPDATE, are not read and acted upon. Reading frames promptly does not expose endpoints to resource exhaustion attacks, as HTTP/2 flow control limits resource commitments.

現在の帯域幅 *遅延製品を完全に認識していても、フロー制御の実装は困難です。エンドポイントは、データが利用可能になったらすぐにバッファを受信したHTTP/2フレームを読み取り、処理する必要があります。window_updateなどのクリティカルフレームが読み取られて行動されていない場合、すぐに読み取れないとデッドロックにつながる可能性があります。HTTP/2のフロー制御がリソースのコミットメントを制限するため、フレームを読み取りにはエンドポイントをリソースの消耗攻撃にさらしません。

5.2.3. Flow-Control Performance
5.2.3. フローコントロールパフォーマンス

If an endpoint cannot ensure that its peer always has available flow-control window space that is greater than the peer's bandwidth * delay product on this connection, its receive throughput will be limited by HTTP/2 flow control. This will result in degraded performance.

エンドポイントが、ピアが常に利用可能なフローコントロールウィンドウスペースを保証できない場合、この接続のピアの帯域幅 *遅延製品よりも大きいフローコントロールウィンドウスペースは、HTTP/2フロー制御によって制限されます。これにより、パフォーマンスが低下します。

Sending timely WINDOW_UPDATE frames can improve performance. Endpoints will want to balance the need to improve receive throughput with the need to manage resource exhaustion risks and should take careful note of Section 10.5 in defining their strategy to manage window sizes.


5.3. Prioritization
5.3. 優先順位付け

In a multiplexed protocol like HTTP/2, prioritizing allocation of bandwidth and computation resources to streams can be critical to attaining good performance. A poor prioritization scheme can result in HTTP/2 providing poor performance. With no parallelism at the TCP layer, performance could be significantly worse than HTTP/1.1.


A good prioritization scheme benefits from the application of contextual knowledge such as the content of resources, how resources are interrelated, and how those resources will be used by a peer. In particular, clients can possess knowledge about the priority of requests that is relevant to server prioritization. In those cases, having clients provide priority information can improve performance.


5.3.1. Background on Priority in RFC 7540
5.3.1. RFC 7540の優先度に関する背景

RFC 7540 defined a rich system for signaling priority of requests. However, this system proved to be complex, and it was not uniformly implemented.

RFC 7540は、リクエストの優先度をシグナル伝えるための豊富なシステムを定義しました。ただし、このシステムは複雑であることが判明し、均一に実装されていませんでした。

The flexible scheme meant that it was possible for clients to express priorities in very different ways, with little consistency in the approaches that were adopted. For servers, implementing generic support for the scheme was complex. Implementation of priorities was uneven in both clients and servers. Many server deployments ignored client signals when prioritizing their handling of requests.


In short, the prioritization signaling in RFC 7540 [RFC7540] was not successful.

要するに、RFC 7540 [RFC7540]の優先順位付けシグナリングは成功しませんでした。

5.3.2. Priority Signaling in This Document
5.3.2. このドキュメントの優先信号

This update to HTTP/2 deprecates the priority signaling defined in RFC 7540 [RFC7540]. The bulk of the text related to priority signals is not included in this document. The description of frame fields and some of the mandatory handling is retained to ensure that implementations of this document remain interoperable with implementations that use the priority signaling described in RFC 7540.

HTTP/2のこの更新は、RFC 7540 [RFC7540]で定義されている優先シグナル伝達を非難します。優先信号に関連するテキストの大部分は、このドキュメントに含まれていません。フレームフィールドの説明と必須の取り扱いの一部は、RFC 7540で説明されている優先シグナル伝達を使用する実装と相互運用可能であることを保証するために保持されます。

A thorough description of the RFC 7540 priority scheme remains in Section 5.3 of [RFC7540].

RFC 7540優先度スキームの徹底的な説明は、[RFC7540]のセクション5.3に残っています。

Signaling priority information is necessary to attain good performance in many cases. Where signaling priority information is important, endpoints are encouraged to use an alternative scheme, such as the scheme described in [HTTP-PRIORITY].


Though the priority signaling from RFC 7540 was not widely adopted, the information it provides can still be useful in the absence of better information. Endpoints that receive priority signals in HEADERS or PRIORITY frames can benefit from applying that information. In particular, implementations that consume these signals would not benefit from discarding these priority signals in the absence of alternatives.

RFC 7540からの優先シグナルは広く採用されていませんでしたが、それが提供する情報は、より良い情報がない場合でも有用です。ヘッダーまたは優先フレームで優先信号を受信するエンドポイントは、その情報を適用することで利益を得ることができます。特に、これらの信号を消費する実装は、代替案がない場合にこれらの優先信号を破棄することから恩恵を受けることはありません。

Servers SHOULD use other contextual information in determining priority of requests in the absence of any priority signals. Servers MAY interpret the complete absence of signals as an indication that the client has not implemented the feature. The defaults described in Section 5.3.5 of [RFC7540] are known to have poor performance under most conditions, and their use is unlikely to be deliberate.


5.4. Error Handling
5.4. エラー処理

HTTP/2 framing permits two classes of errors:


* An error condition that renders the entire connection unusable is a connection error.

* 接続全体を使用できないエラー条件は、接続エラーです。

* An error in an individual stream is a stream error.

* 個々のストリームのエラーは、ストリームエラーです。

A list of error codes is included in Section 7.


It is possible that an endpoint will encounter frames that would cause multiple errors. Implementations MAY discover multiple errors during processing, but they SHOULD report at most one stream and one connection error as a result.


The first stream error reported for a given stream prevents any other errors on that stream from being reported. In comparison, the protocol permits multiple GOAWAY frames, though an endpoint SHOULD report just one type of connection error unless an error is encountered during graceful shutdown. If this occurs, an endpoint MAY send an additional GOAWAY frame with the new error code, in addition to any prior GOAWAY that contained NO_ERROR.


If an endpoint detects multiple different errors, it MAY choose to report any one of those errors. If a frame causes a connection error, that error MUST be reported. Additionally, an endpoint MAY use any applicable error code when it detects an error condition; a generic error code (such as PROTOCOL_ERROR or INTERNAL_ERROR) can always be used in place of more specific error codes.


5.4.1. Connection Error Handling
5.4.1. 接続エラー処理

A connection error is any error that prevents further processing of the frame layer or corrupts any connection state.


An endpoint that encounters a connection error SHOULD first send a GOAWAY frame (Section 6.8) with the stream identifier of the last stream that it successfully received from its peer. The GOAWAY frame includes an error code (Section 7) that indicates why the connection is terminating. After sending the GOAWAY frame for an error condition, the endpoint MUST close the TCP connection.


It is possible that the GOAWAY will not be reliably received by the receiving endpoint. In the event of a connection error, GOAWAY only provides a best-effort attempt to communicate with the peer about why the connection is being terminated.


An endpoint can end a connection at any time. In particular, an endpoint MAY choose to treat a stream error as a connection error. Endpoints SHOULD send a GOAWAY frame when ending a connection, providing that circumstances permit it.


5.4.2. Stream Error Handling
5.4.2. ストリームエラー処理

A stream error is an error related to a specific stream that does not affect processing of other streams.


An endpoint that detects a stream error sends a RST_STREAM frame (Section 6.4) that contains the stream identifier of the stream where the error occurred. The RST_STREAM frame includes an error code that indicates the type of error.


A RST_STREAM is the last frame that an endpoint can send on a stream. The peer that sends the RST_STREAM frame MUST be prepared to receive any frames that were sent or enqueued for sending by the remote peer. These frames can be ignored, except where they modify connection state (such as the state maintained for field section compression (Section 4.3) or flow control).


Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame for any stream. However, an endpoint MAY send additional RST_STREAM frames if it receives frames on a closed stream after more than a round-trip time. This behavior is permitted to deal with misbehaving implementations.


To avoid looping, an endpoint MUST NOT send a RST_STREAM in response to a RST_STREAM frame.


5.4.3. Connection Termination
5.4.3. 接続終了

If the TCP connection is closed or reset while streams remain in the "open" or "half-closed" states, then the affected streams cannot be automatically retried (see Section 8.7 for details).


5.5. Extending HTTP/2
5.5. HTTP/2を拡張します

HTTP/2 permits extension of the protocol. Within the limitations described in this section, protocol extensions can be used to provide additional services or alter any aspect of the protocol. Extensions are effective only within the scope of a single HTTP/2 connection.


This applies to the protocol elements defined in this document. This does not affect the existing options for extending HTTP, such as defining new methods, status codes, or fields (see Section 16 of [HTTP]).


Extensions are permitted to use new frame types (Section 4.1), new settings (Section 6.5), or new error codes (Section 7). Registries for managing these extension points are defined in Section 11 of [RFC7540].


Implementations MUST ignore unknown or unsupported values in all extensible protocol elements. Implementations MUST discard frames that have unknown or unsupported types. This means that any of these extension points can be safely used by extensions without prior arrangement or negotiation. However, extension frames that appear in the middle of a field block (Section 4.3) are not permitted; these MUST be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Extensions SHOULD avoid changing protocol elements defined in this document or elements for which no extension mechanism is defined. This includes changes to the layout of frames, additions or changes to the way that frames are composed into HTTP messages (Section 8.1), the definition of pseudo-header fields, or changes to any protocol element that a compliant endpoint might treat as a connection error (Section 5.4.1).


An extension that changes existing protocol elements or state MUST be negotiated before being used. For example, an extension that changes the layout of the HEADERS frame cannot be used until the peer has given a positive signal that this is acceptable. In this case, it could also be necessary to coordinate when the revised layout comes into effect. For example, treating frames other than DATA frames as flow controlled requires a change in semantics that both endpoints need to understand, so this can only be done through negotiation.


This document doesn't mandate a specific method for negotiating the use of an extension but notes that a setting (Section 6.5.2) could be used for that purpose. If both peers set a value that indicates willingness to use the extension, then the extension can be used. If a setting is used for extension negotiation, the initial value MUST be defined in such a fashion that the extension is initially disabled.


6. Frame Definitions
6. フレーム定義

This specification defines a number of frame types, each identified by a unique 8-bit type code. Each frame type serves a distinct purpose in the establishment and management of either the connection as a whole or individual streams.


The transmission of specific frame types can alter the state of a connection. If endpoints fail to maintain a synchronized view of the connection state, successful communication within the connection will no longer be possible. Therefore, it is important that endpoints have a shared comprehension of how the state is affected by the use of any given frame.


6.1. DATA
6.1. データ

DATA frames (type=0x00) convey arbitrary, variable-length sequences of octets associated with a stream. One or more DATA frames are used, for instance, to carry HTTP request or response message contents.

データフレーム(Type = 0x00)は、ストリームに関連付けられたオクテットの任意の可変長シーケンスを伝えます。たとえば、1つ以上のデータフレームがHTTP要求または応答メッセージの内容を掲載するために使用されます。

DATA frames MAY also contain padding. Padding can be added to DATA frames to obscure the size of messages. Padding is a security feature; see Section 10.7.


DATA Frame { Length (24), Type (8) = 0x00,

データフレーム{長さ(24)、タイプ(8)= 0x00、

Unused Flags (4), PADDED Flag (1), Unused Flags (2), END_STREAM Flag (1),


Reserved (1), Stream Identifier (31),


[Pad Length (8)], Data (..), Padding (..2040), }


Figure 3: DATA Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The DATA frame contains the following additional fields:


Pad Length: An 8-bit field containing the length of the frame padding in units of octets. This field is conditional and is only present if the PADDED flag is set.


Data: Application data. The amount of data is the remainder of the frame payload after subtracting the length of the other fields that are present.


Padding: Padding octets that contain no application semantic value. Padding octets MUST be set to zero when sending. A receiver is not obligated to verify padding but MAY treat non-zero padding as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The DATA frame defines the following flags:


PADDED (0x08): When set, the PADDED flag indicates that the Pad Length field and any padding that it describes are present.


END_STREAM (0x01): When set, the END_STREAM flag indicates that this frame is the last that the endpoint will send for the identified stream. Setting this flag causes the stream to enter one of the "half-closed" states or the "closed" state (Section 5.1).


Note: An endpoint that learns of stream closure after sending 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 only possible if the endpoint does not send trailers, as the END_STREAM flag appears on a HEADERS frame in that case; see Section 8.1.


DATA frames MUST be associated with a stream. If a DATA frame is received whose Stream Identifier field is 0x00, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


DATA frames are subject to flow control and can only be sent when a stream is in the "open" or "half-closed (remote)" state. The entire DATA frame payload is included in flow control, including the Pad Length and Padding fields if present. If a DATA frame is received 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 STREAM_CLOSED.


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 frame payload or greater, the recipient MUST treat this as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Note: A frame can be increased in size by one octet by including a Pad Length field with a value of zero.


6.2. ヘッダー

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 HEADERS frame can carry a header section or a trailer section. HEADERS frames can be sent on a stream in the "idle", "reserved (local)", "open", or "half-closed (remote)" state.

ヘッダーフレーム(Type = 0x01)は、ストリームを開くために使用され(セクション5.1)、さらにフィールドブロックフラグメントが搭載されています。名前にもかかわらず、ヘッダーフレームはヘッダーセクションまたはトレーラーセクションを搭載できます。ヘッダーフレームは、「アイドル」、「予約済み(ローカル)」、「オープン」、または「半分閉鎖(リモート)」状態のストリームで送信できます。

HEADERS Frame { Length (24), Type (8) = 0x01,

ヘッダーフレーム{長さ(24)、タイプ(8)= 0x01、

Unused Flags (2), PRIORITY Flag (1), Unused Flag (1), PADDED Flag (1), END_HEADERS Flag (1), Unused Flag (1), END_STREAM Flag (1),


Reserved (1), Stream Identifier (31),


     [Pad Length (8)],
     [Exclusive (1)],
     [Stream Dependency (31)],
     [Weight (8)],
     Field Block Fragment (..),
     Padding (..2040),

Figure 4: HEADERS Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The HEADERS frame payload has the following additional fields:


Pad Length: An 8-bit field containing the length of the frame padding in units of octets. This field is only present if the PADDED flag is set.


Exclusive: A single-bit flag. This field is only present if the PRIORITY flag is set. Priority signals in HEADERS frames are deprecated; see Section 5.3.2.


Stream Dependency: A 31-bit stream identifier. This field is only present if the PRIORITY flag is set.


Weight: An unsigned 8-bit integer. This field is only present if the PRIORITY flag is set.


Field Block Fragment: A field block fragment (Section 4.3).


Padding: Padding octets that contain no application semantic value. Padding octets MUST be set to zero when sending. A receiver is not obligated to verify padding but MAY treat non-zero padding as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The HEADERS frame defines the following flags:


PRIORITY (0x20): When set, the PRIORITY flag indicates that the Exclusive, Stream Dependency, and Weight fields are present.


PADDED (0x08): When set, the PADDED flag indicates that the Pad Length field and any padding that it describes are present.


END_HEADERS (0x04): When set, the END_HEADERS flag indicates that this frame contains an entire field block (Section 4.3) and is not followed by any CONTINUATION frames.


A HEADERS frame without the END_HEADERS flag set MUST be followed by a CONTINUATION frame for the same stream. A receiver MUST treat the receipt of any other type of frame or a frame on a different stream as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


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 for the identified stream.


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 be followed by CONTINUATION frames on the same stream. Logically, the CONTINUATION frames are part of the HEADERS frame.


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 frame is continued in a CONTINUATION frame (Section 6.10).


HEADERS frames MUST be associated with a stream. If a HEADERS frame is received whose Stream Identifier field is 0x00, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The HEADERS frame changes the connection state as described in Section 4.3.


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 frame payload or greater, the recipient MUST treat this as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Note: A frame can be increased in size by one octet by including a Pad Length field with a value of zero.


6.3. 優先順位

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 closed streams.

優先フレーム(Type = 0x02)は非推奨です。セクション5.3.2を参照してください。IDLEまたは閉じたストリームを含む、任意のストリーム状態で優先フレームを送信できます。

PRIORITY Frame { Length (24) = 0x05, Type (8) = 0x02,

優先フレーム{長さ(24)= 0x05、タイプ(8)= 0x02、

Unused Flags (8),


Reserved (1), Stream Identifier (31),


Exclusive (1), Stream Dependency (31), Weight (8), }


Figure 5: PRIORITY Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The frame payload of a PRIORITY frame contains the following additional fields:


Exclusive: A single-bit flag.


Stream Dependency: A 31-bit stream identifier.


Weight: An unsigned 8-bit integer.


The PRIORITY frame does not define any flags.


The PRIORITY frame always identifies a stream. If a PRIORITY frame is received with a stream identifier of 0x00, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


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 in any state, including "idle" or "closed". A PRIORITY frame cannot be sent between consecutive frames that comprise a single field block (Section 4.3).


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.



The RST_STREAM frame (type=0x03) allows for immediate termination of a stream. RST_STREAM is sent to request cancellation of a stream or to indicate that an error condition has occurred.

RST_STREAMフレーム(Type = 0x03)により、ストリームの即時終了が可能になります。RST_STREAMは、ストリームのキャンセルを要求するか、エラー条件が発生したことを示すために送信されます。

RST_STREAM Frame { Length (24) = 0x04, Type (8) = 0x03,

rst_streamフレーム{length(24)= 0x04、type(8)= 0x03、

Unused Flags (8),


Reserved (1), Stream Identifier (31),


Error Code (32), }


Figure 6: RST_STREAM Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. Additionally, the RST_STREAM frame contains a single unsigned, 32-bit integer identifying the error code (Section 7). The error code indicates why the stream is being terminated.


The RST_STREAM frame does not define any flags.


The RST_STREAM frame fully terminates the referenced stream and causes it to enter the "closed" state. After receiving a RST_STREAM on a stream, the receiver MUST NOT send additional frames for that stream, except for PRIORITY. However, after sending the RST_STREAM, the sending endpoint MUST be prepared to receive and process additional frames sent on the stream that might have been sent by the peer prior to the arrival of the RST_STREAM.


RST_STREAM frames MUST be associated with a stream. If a RST_STREAM frame is received with a stream identifier of 0x00, the recipient MUST treat this as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


RST_STREAM frames MUST NOT be sent for a stream in the "idle" state. If a RST_STREAM frame identifying an idle stream is received, the recipient MUST treat this as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


A RST_STREAM frame with a length other than 4 octets MUST be treated as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.


6.5. 設定

The SETTINGS frame (type=0x04) conveys configuration parameters that affect how endpoints communicate, such as preferences and constraints on peer behavior. The SETTINGS frame is also used to acknowledge the receipt of those settings. Individually, a configuration parameter from a SETTINGS frame is referred to as a "setting".

設定フレーム(Type = 0x04)は、ピアの動作に対する好みや制約など、エンドポイントの通信方法に影響する構成パラメーターを伝えます。設定フレームは、それらの設定の受領を確認するためにも使用されます。個別に、設定フレームからの構成パラメーターは「設定」と呼ばれます。

Settings are not negotiated; they describe characteristics of the sending peer, which are used by the receiving peer. Different values 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 might set a lower value to conserve resources.


A SETTINGS frame MUST be sent by both endpoints at the start of a connection and MAY be sent at any other time by either endpoint over the lifetime of the connection. Implementations MUST support all of the settings defined by this specification.


Each parameter in a SETTINGS frame replaces any existing value for that parameter. Settings are processed in the order in which they appear, and a receiver of a SETTINGS frame does not need to maintain any state other than the current value of each setting. Therefore, the value of a SETTINGS parameter is the last value that is seen by a receiver.


SETTINGS frames are acknowledged by the receiving peer. To enable this, the SETTINGS frame defines the ACK flag:


ACK (0x01): When set, the ACK flag indicates that this frame acknowledges receipt and application of the peer's SETTINGS frame. 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 length field value other than 0 MUST be treated as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR. For more information, see Section 6.5.3 ("Settings Synchronization").


SETTINGS frames always apply to a connection, never a single stream. The stream identifier for a SETTINGS frame MUST be zero (0x00). If an endpoint receives a SETTINGS frame whose Stream Identifier field is anything other than 0x00, the endpoint MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The SETTINGS frame affects connection state. A badly formed or incomplete SETTINGS frame MUST be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


A SETTINGS frame with a length other than a multiple of 6 octets MUST be treated as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.


6.5.1. SETTINGS Format
6.5.1. 設定形式

The frame payload of a SETTINGS frame consists of zero or more settings, each consisting of an unsigned 16-bit setting identifier and an unsigned 32-bit value.


SETTINGS Frame { Length (24), Type (8) = 0x04,

設定フレーム{長さ(24)、タイプ(8)= 0x04、

Unused Flags (7), ACK Flag (1),


Reserved (1), Stream Identifier (31) = 0,

予約済み(1)、ストリーム識別子(31)= 0、

Setting (48) ..., }


   Setting {
     Identifier (16),
     Value (32),

Figure 7: SETTINGS Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The frame payload of a SETTINGS frame contains any number of Setting fields, each of which consists of:


Identifier: A 16-bit setting identifier; see Section 6.5.2.


Value: A 32-bit value for the setting.


6.5.2. Defined Settings
6.5.2. 定義された設定

The following settings are defined:


SETTINGS_HEADER_TABLE_SIZE (0x01): This setting allows the sender to inform the remote endpoint of the maximum size of the compression table used to decode field blocks, in units of octets. The encoder can select any size equal to or less than this value by using signaling specific to the compression format inside a field block (see [COMPRESSION]). The initial value is 4,096 octets.


SETTINGS_ENABLE_PUSH (0x02): This setting can be used to enable or disable server push. A server MUST NOT send a PUSH_PROMISE frame if it receives this parameter set to a value of 0; see Section 8.4. A client that has both set this parameter to 0 and had it acknowledged MUST treat the receipt of a PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The initial value of SETTINGS_ENABLE_PUSH is 1. For a client, this value indicates that it is willing to receive PUSH_PROMISE frames. For a server, this initial value has no effect, and is equivalent to the value 0. Any value other than 0 or 1 MUST be 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 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 receipt of a SETTINGS frame with SETTINGS_ENABLE_PUSH set to 1 as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


SETTINGS_MAX_CONCURRENT_STREAMS (0x03): This setting indicates the maximum number of concurrent streams that the sender will allow. This limit is directional: it applies to the number of streams that the sender permits the receiver to create. Initially, there is no limit to this value. It is recommended that this value be no smaller than 100, so as to not unnecessarily limit parallelism.


A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be treated as special by endpoints. A zero value does prevent the creation of new streams; however, this can also happen for any limit that is exhausted with active streams. Servers SHOULD only set a zero value for short durations; if a server does not wish to accept requests, closing the connection is more appropriate.


SETTINGS_INITIAL_WINDOW_SIZE (0x04): This setting indicates the sender's initial window size (in units of octets) for stream-level flow control. The initial value is 2^16-1 (65,535) octets.


This setting affects the window size of all streams (see Section 6.9.2).


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 FLOW_CONTROL_ERROR.


SETTINGS_MAX_FRAME_SIZE (0x05): This setting indicates the size of the largest frame payload that the sender is willing to receive, in units of octets.


The initial value is 2^14 (16,384) octets. The value advertised by an endpoint MUST be between this initial value and the maximum allowed frame size (2^24-1 or 16,777,215 octets), inclusive. Values outside this range MUST be treated as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


SETTINGS_MAX_HEADER_LIST_SIZE (0x06): This advisory setting informs 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 uncompressed size of field lines, including the length of the name and value in units of octets plus an overhead of 32 octets for each field line.


For any given request, a lower limit than what is advertised MAY be enforced. The initial value of this setting is unlimited.


An endpoint that receives a SETTINGS frame with any unknown or unsupported identifier MUST ignore that setting.


6.5.3. Settings Synchronization
6.5.3. 設定同期

Most values in SETTINGS benefit from or require an understanding of when the peer has received and applied the changed parameter values. In order to provide such synchronization timepoints, the recipient of a SETTINGS frame in which the ACK flag is not set MUST apply the updated settings as soon as possible upon receipt. SETTINGS frames are acknowledged in the order in which they are received.


The values in the SETTINGS frame MUST be processed in the order they appear, with no other frame processing between values. Unsupported settings MUST be ignored. Once all values have been processed, the recipient MUST immediately emit a SETTINGS frame with the ACK flag 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 unacknowledged SETTINGS frame having been applied.


If the sender of a SETTINGS frame does not receive an acknowledgment 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 allowance needs to be made for processing delays at the peer; a timeout that is solely based on the round-trip time between endpoints might result in spurious errors.


6.6. push_promise

The PUSH_PROMISE frame (type=0x05) is used to notify the peer endpoint in advance of streams the sender intends to initiate. The PUSH_PROMISE frame includes the unsigned 31-bit identifier of the stream the endpoint plans to create along with a field section that provides additional context for the stream. Section 8.4 contains a thorough description of the use of PUSH_PROMISE frames.

Push_Promiseフレーム(Type = 0x05)は、送信者が開始する予定のストリームの前にピアエンドポイントに通知するために使用されます。Push_Promiseフレームには、エンドポイントが作成するストリームの署名されていない31ビット識別子と、ストリームの追加コンテキストを提供するフィールドセクションを作成することが含まれます。セクション8.4には、Push_promiseフレームの使用に関する徹底的な説明が含まれています。

PUSH_PROMISE Frame { Length (24), Type (8) = 0x05,

push_promiseフレーム{長さ(24)、タイプ(8)= 0x05、

Unused Flags (4), PADDED Flag (1), END_HEADERS Flag (1), Unused Flags (2),


Reserved (1), Stream Identifier (31),


[Pad Length (8)], Reserved (1), Promised Stream ID (31), Field Block Fragment (..), Padding (..2040), }


Figure 8: PUSH_PROMISE Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The PUSH_PROMISE frame payload has the following additional fields:


Pad Length: An 8-bit field containing the length of the frame padding in units of octets. This field is only present if the PADDED flag is set.


Promised Stream ID: An unsigned 31-bit integer that identifies the stream that is reserved by the PUSH_PROMISE. The promised stream identifier MUST be a valid choice for the next stream sent by the sender (see "new stream identifier" in Section 5.1.1).


Field Block Fragment: A field block fragment (Section 4.3) containing the request control data and a header section.


Padding: Padding octets that contain no application semantic value. Padding octets MUST be set to zero when sending. A receiver is not obligated to verify padding but MAY treat non-zero padding as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The PUSH_PROMISE frame defines the following flags:


PADDED (0x08): When set, the PADDED flag indicates that the Pad Length field and any padding that it describes are present.


END_HEADERS (0x04): When set, the END_HEADERS flag indicates that this frame contains an entire field block (Section 4.3) and is not followed by any CONTINUATION frames.


A PUSH_PROMISE frame without the END_HEADERS flag set MUST be followed by a CONTINUATION frame for the same stream. A receiver MUST treat the receipt of any other type of frame or a frame on a different stream as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


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 identifier of a PUSH_PROMISE frame indicates the stream it is associated with. If the Stream Identifier field specifies the value 0x00, a recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Promised streams are not required to be used in the order they are promised. The PUSH_PROMISE only reserves stream identifiers for later use.


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 and has received acknowledgment MUST treat the receipt of a PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Recipients of PUSH_PROMISE frames can choose to reject promised streams by returning a RST_STREAM referencing the promised stream identifier back to the sender of the PUSH_PROMISE.


A PUSH_PROMISE frame modifies the connection state in two ways. First, the inclusion of a field block (Section 4.3) potentially modifies the state maintained for field section compression. Second, PUSH_PROMISE also reserves a stream for later use, causing the promised stream to enter the "reserved (local)" or "reserved (remote)" state. A sender MUST NOT send a PUSH_PROMISE on a stream unless that stream is either "open" or "half-closed (remote)"; the sender MUST ensure that the promised stream is a valid choice for a new stream identifier (Section 5.1.1) (that is, the promised stream MUST be in the "idle" state).


Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame causes the stream state to become indeterminate. A receiver MUST treat the receipt of a PUSH_PROMISE on a stream that is neither "open" nor "half-closed (local)" as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. However, an endpoint that has sent RST_STREAM on the associated stream MUST handle PUSH_PROMISE frames that might have been created before the RST_STREAM frame is received and processed.


A receiver MUST treat the receipt of a PUSH_PROMISE that promises an illegal stream identifier (Section 5.1.1) as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. Note that an illegal stream identifier is an identifier for a stream that is not currently in the "idle" state.


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 frame payload or greater, the recipient MUST treat this as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


Note: A frame can be increased in size by one octet by including a Pad Length field with a value of zero.


6.7. PING
6.7. ping

The PING frame (type=0x06) is a mechanism for measuring a minimal round-trip time from the sender, as well as determining whether an idle connection is still functional. PING frames can be sent from any endpoint.

Pingフレーム(Type = 0x06)は、送信者からの最小限の往復時間を測定するメカニズムと、アイドル接続がまだ機能しているかどうかを判断するメカニズムです。Pingフレームは、任意のエンドポイントから送信できます。

PING Frame { Length (24) = 0x08, Type (8) = 0x06,

pingフレーム{長さ(24)= 0x08、タイプ(8)= 0x06、

Unused Flags (7), ACK Flag (1),


Reserved (1), Stream Identifier (31) = 0,

予約済み(1)、ストリーム識別子(31)= 0、

Opaque Data (64), }


Figure 9: PING Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4.


In addition to the frame header, PING frames MUST contain 8 octets of opaque data in the frame payload. A sender can include any value it chooses and use those octets in any fashion.


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 frame payload. PING responses SHOULD be given higher priority than any other frame.


The PING frame defines the following flags:


ACK (0x01): When set, the ACK flag indicates that this PING frame is a PING response. An endpoint MUST set this flag in PING responses. An endpoint MUST NOT respond to PING frames containing this flag.


PING frames are not associated with any individual stream. If a PING frame is received with a Stream Identifier field value other than 0x00, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


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 FRAME_SIZE_ERROR.


6.8. どこかに行って

The GOAWAY frame (type=0x07) is used to initiate shutdown of a connection or to signal serious error conditions. GOAWAY allows an endpoint to gracefully stop accepting new streams while still finishing processing of previously established streams. This enables administrative actions, like server maintenance.

Goawayフレーム(Type = 0x07)を使用して、接続のシャットダウンを開始するか、深刻なエラー条件を通知します。Goawayにより、エンドポイントは、以前に確立されたストリームの処理を完了しながら、新しいストリームの受け入れを優雅に停止することができます。これにより、サーバーのメンテナンスなどの管理アクションが可能になります。

There is an inherent race condition between an endpoint starting new streams and the remote peer sending a GOAWAY frame. To deal with this case, the GOAWAY contains the stream identifier of the last peer-initiated stream that was or might be processed on the sending endpoint in this connection. For instance, if the server sends a GOAWAY frame, the identified stream is the highest-numbered stream initiated by the client.


Once the GOAWAY is sent, the sender will ignore frames sent on streams initiated by the receiver if the stream has an identifier higher than the included last stream identifier. Receivers of a GOAWAY frame MUST NOT open additional streams on the connection, although a new connection can be established for new streams.


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 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 all, thereby allowing those streams to be retried later on a new connection.


Endpoints SHOULD always send a GOAWAY frame before closing a connection so that the remote peer can know whether a stream has been partially processed or not. For example, if an HTTP client sends a POST at the same time that a server closes a connection, the client cannot know if the server started to process that POST request if the server does not send a GOAWAY frame to indicate what streams it might have acted on.


An endpoint might choose to close a connection without sending a GOAWAY for misbehaving peers.


A GOAWAY frame might not immediately precede closing of 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.


GOAWAY Frame { Length (24), Type (8) = 0x07,

goaway frame {length(24)、type(8)= 0x07、

Unused Flags (8),


Reserved (1), Stream Identifier (31) = 0,

予約済み(1)、ストリーム識別子(31)= 0、

Reserved (1), Last-Stream-ID (31), Error Code (32), Additional Debug Data (..), }


Figure 10: GOAWAY Frame Format

図10:Goaway Frameフォーマット

The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4.


The GOAWAY frame does not define any flags.


The GOAWAY frame applies to the connection, not a specific stream. An endpoint MUST treat a GOAWAY frame with a stream identifier other than 0x00 as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The last stream identifier in the GOAWAY frame contains the highest-numbered stream identifier for which the sender of the GOAWAY frame might have taken some action on or might yet take action on. All 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 no streams were processed.


Note: In this context, "processed" means that some data from the stream was passed to some higher layer of software that might have taken some action as a result.


If a connection terminates without a GOAWAY frame, the last stream identifier is effectively the highest possible stream identifier.


On streams with lower- or equal-numbered identifiers that were not closed completely prior to the connection being closed, reattempting requests, transactions, or any protocol activity is not possible, except for idempotent actions like HTTP GET, PUT, or DELETE. Any protocol activity that uses higher-numbered streams can be safely retried using a new connection.

接続が閉じられる前に完全に閉じられていない低いまたは等しい識別子を持つストリームでは、HTTP GET、PUT、または削除などの等身アクションを除き、リクエスト、トランザクション、またはプロトコルアクティビティを再試行することは不可能です。より多くのストリームを使用するプロトコルアクティビティは、新しい接続を使用して安全に再試行できます。

Activity on streams numbered lower than or equal to the last stream identifier might still complete successfully. The sender of a GOAWAY frame might gracefully shut down a connection by sending a GOAWAY frame, maintaining the connection in an "open" state until all in-progress streams complete.


An endpoint MAY send multiple GOAWAY frames if circumstances change. For instance, an endpoint that sends GOAWAY with NO_ERROR during graceful shutdown could subsequently encounter a condition that requires immediate termination of the connection. The last stream identifier from the last GOAWAY frame received indicates which streams could have been acted upon. Endpoints MUST NOT increase the value they send in the last stream identifier, since the peers might already have retried unprocessed requests on another connection.


A client that is unable to retry requests loses all requests that are in flight when the server closes the connection. This is especially true for intermediaries that might not be serving clients using HTTP/2. A server that is attempting to gracefully shut down a connection SHOULD send an initial GOAWAY frame with the last stream identifier set to 2^31-1 and a NO_ERROR code. This signals to the client that a shutdown is imminent and that initiating further requests is prohibited. After allowing time for any in-flight stream creation (at least one round-trip time), the server MAY send another GOAWAY frame with an updated last stream identifier. This ensures that a connection can be cleanly shut down without losing requests.


After sending a GOAWAY frame, the sender can discard frames for streams initiated by the receiver with identifiers higher than the identified last stream. However, any frames that alter connection state cannot be completely ignored. For instance, HEADERS, PUSH_PROMISE, and CONTINUATION frames MUST be minimally processed to ensure that the state maintained for field section compression is consistent (see Section 4.3); similarly, DATA frames MUST be counted toward the connection flow-control window. Failure to process these frames can cause flow control or field section compression state to become unsynchronized.


The GOAWAY frame also contains a 32-bit error code (Section 7) that contains the reason for closing the connection.


Endpoints MAY append opaque data to the frame payload of any GOAWAY frame. Additional debug data is intended for diagnostic purposes only and carries no semantic value. Debug information could contain security- or privacy-sensitive data. Logged or otherwise persistently stored debug data MUST have adequate safeguards to prevent unauthorized access.


6.9. window_update

The WINDOW_UPDATE frame (type=0x08) is used to implement flow control; see Section 5.2 for an overview.

window_updateフレーム(type = 0x08)は、フロー制御を実装するために使用されます。概要については、セクション5.2を参照してください。

Flow control operates at two levels: on each individual stream and on the entire connection.


Both types of flow control are hop by hop, that is, only between the two endpoints. Intermediaries do not forward WINDOW_UPDATE frames between dependent connections. However, throttling of data transfer by any receiver can indirectly cause the propagation of flow-control information toward the original sender.


Flow control only applies to frames that are identified as being subject to flow control. Of the frame types defined in this document, this includes only DATA frames. Frames that are exempt from flow control MUST be accepted and processed, unless the receiver is unable to assign resources to handling the frame. A receiver MAY 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 a frame.


WINDOW_UPDATE Frame { Length (24) = 0x04, Type (8) = 0x08,

window_updateフレーム{長さ(24)= 0x04、type(8)= 0x08、

Unused Flags (8),


Reserved (1), Stream Identifier (31),


Reserved (1), Window Size Increment (31), }


Figure 11: WINDOW_UPDATE Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The frame payload of a WINDOW_UPDATE frame is one reserved bit plus an unsigned 31-bit integer indicating the number of octets that the sender can transmit in addition to the existing flow-control window. The legal range for the increment to the flow-control window is 1 to 2^31-1 (2,147,483,647) octets.


The WINDOW_UPDATE frame does not define any flags.


The WINDOW_UPDATE frame can be specific to a stream or to the entire connection. In the former case, the frame's stream identifier indicates the affected stream; in the latter, the value "0" indicates that the entire connection is the subject of the frame.


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) of type PROTOCOL_ERROR; errors on the connection flow-control window 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 END_STREAM flag set. This means that a receiver could receive a WINDOW_UPDATE frame on a stream in a "half-closed (remote)" or "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 for its contribution against the connection flow-control window, unless the receiver treats this as a connection error (Section 5.4.1). This is necessary even if the frame is in error. The sender counts the frame toward the flow-control window, but if the receiver does not, the flow-control window at the sender and receiver can become different.


A WINDOW_UPDATE frame with a length other than 4 octets MUST be treated as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.


6.9.1. The Flow-Control Window
6.9.1. フロー制御ウィンドウ

Flow control in HTTP/2 is implemented using a window kept by each sender on every stream. The flow-control window is a simple integer value that indicates how many octets of data the sender is permitted to transmit; as such, its size is a measure of the buffering capacity of the receiver.


Two flow-control windows are applicable: the stream flow-control window and the connection flow-control window. The sender MUST NOT send a flow-controlled frame with a length that exceeds the space available in either of the flow-control windows advertised by the receiver. Frames with zero length with the END_STREAM flag set (that is, an empty DATA frame) MAY be sent if there is no available space in either flow-control window.


For flow-control calculations, the 9-octet frame header is not counted.


After sending a flow-controlled frame, the sender reduces the space available in both windows by the length of the transmitted frame.


The receiver of a frame sends a WINDOW_UPDATE frame as it consumes data and frees up space in flow-control windows. Separate WINDOW_UPDATE frames are sent for the stream- and connection-level flow-control windows. Receivers are advised to have mechanisms in place to avoid sending WINDOW_UPDATE frames with very small increments; see Section of [RFC1122].

フレームの受信機は、データを消費し、フロー制御ウィンドウでスペースを解放するため、window_updateフレームを送信します。StreamおよびConnection-Level Flow-Control Windowsには、個別のWindow_Updateフレームが送信されます。受信機は、非常に少ない刻みでWindow_Updateフレームを送信しないようにメカニズムを整えることをお勧めします。[RFC1122]のセクション4.2.3.3を参照してください。

A sender that receives a WINDOW_UPDATE frame updates the corresponding window by the amount specified in the frame.


A sender MUST NOT allow a flow-control window to exceed 2^31-1 octets. If a sender receives a WINDOW_UPDATE that causes a flow-control window to exceed this maximum, it MUST terminate either the stream or the connection, as appropriate. For streams, the sender sends a RST_STREAM with an error code of FLOW_CONTROL_ERROR; for the connection, a GOAWAY frame with an error code of FLOW_CONTROL_ERROR is sent.


Flow-controlled frames from the sender and WINDOW_UPDATE frames from the receiver are completely asynchronous with respect to each other. This property allows a receiver to aggressively update the window size kept by the sender to prevent streams from stalling.


6.9.2. Initial Flow-Control Window Size
6.9.2. 初期フローコントロールウィンドウサイズ

When an HTTP/2 connection is first established, new streams are created with an initial flow-control window size of 65,535 octets. The connection flow-control window is also 65,535 octets. Both endpoints can adjust the initial window size for new streams by including a value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame. The connection flow-control window can only be changed using WINDOW_UPDATE frames.


Prior to receiving a SETTINGS frame that sets a value for SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default initial window size when sending flow-controlled frames. Similarly, the connection flow-control window is set based on the default initial window size until a WINDOW_UPDATE frame is received.


In addition to changing the flow-control window for streams that are not yet active, a SETTINGS frame can alter the initial flow-control window size for streams with active flow-control windows (that is, streams in the "open" or "half-closed (remote)" state). When the value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust the size of all stream flow-control windows that it maintains by the difference between the new value and the old value.

まだアクティブではないストリームのフローコントロールウィンドウを変更することに加えて、設定フレームは、アクティブフローコントロールウィンドウ(つまり、「オープン」または「半分」のストリームのストリームの初期フローコントロールウィンドウサイズを変更できます。-closed(remote) "state)。settings_initial_window_sizeの値が変更された場合、レシーバーは、新しい値と古い値の違いによって維持されるすべてのストリームフローコントロールウィンドウのサイズを調整する必要があります。

A change to SETTINGS_INITIAL_WINDOW_SIZE can cause the available space in a flow-control window to become negative. A sender MUST track the negative flow-control window and MUST NOT send new flow-controlled frames until it receives WINDOW_UPDATE frames that cause the flow-control window to become positive.


For example, if the client sends 60 KB immediately on connection establishment and the server sets the initial window size to be 16 KB, the client will recalculate the available flow-control window to be -44 KB on receipt of the SETTINGS frame. The client retains a negative flow-control window until WINDOW_UPDATE frames restore the window to being positive, after which the client can resume sending.

たとえば、クライアントが接続確立ですぐに60 kBを送信し、サーバーが初期ウィンドウサイズを16 kBに設定する場合、クライアントは、設定フレームを受け取ったときに使用可能なフローコントロールウィンドウを-44 kbに再計算します。クライアントは、window_updateフレームがウィンドウを復元するまでネガティブフローコントロールウィンドウを保持します。その後、クライアントは送信を再開できます。

A SETTINGS frame cannot alter the connection flow-control window.


An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that causes any flow-control window to exceed the maximum size as a connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR.


6.9.3. Reducing the Stream Window Size
6.9.3. ストリームウィンドウサイズの縮小

A receiver that wishes to use a smaller flow-control window than the current size can send a new SETTINGS frame. However, the receiver MUST be prepared to receive data that exceeds this window size, since the sender might send data that exceeds the lower limit prior to processing the SETTINGS frame.


After sending a SETTINGS frame that reduces the initial flow-control window size, a receiver MAY continue to process streams that exceed flow-control limits. Allowing streams to continue does not allow the receiver to immediately reduce the space it reserves for flow-control windows. Progress on these streams can also stall, since WINDOW_UPDATE frames are needed to allow the sender to resume sending. The receiver MAY instead send a RST_STREAM with an error code of FLOW_CONTROL_ERROR for the affected streams.


6.10. 継続

The CONTINUATION frame (type=0x09) is used to continue a sequence of field block fragments (Section 4.3). Any number of CONTINUATION 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 the END_HEADERS flag set.

継続フレーム(Type = 0x09)は、フィールドブロックフラグメントのシーケンスを続行するために使用されます(セクション4.3)。前のフレームが同じストリーム上にあり、end_headersフラグが設定されていないヘッダー、push_promise、または継続フレームである限り、任意の数の継続フレームを送信できます。

CONTINUATION Frame { Length (24), Type (8) = 0x09,

継続フレーム{長さ(24)、タイプ(8)= 0x09、

Unused Flags (5), END_HEADERS Flag (1), Unused Flags (2),


Reserved (1), Stream Identifier (31),


Field Block Fragment (..), }


Figure 12: CONTINUATION Frame Format


The Length, Type, Unused Flag(s), Reserved, and Stream Identifier fields are described in Section 4. The CONTINUATION frame payload contains a field block fragment (Section 4.3).


The CONTINUATION frame defines the following flag:


END_HEADERS (0x04): When set, the END_HEADERS flag indicates that this frame ends a field block (Section 4.3).


If the END_HEADERS flag is not set, this frame MUST be followed by another CONTINUATION frame. A receiver MUST treat the receipt of any other type of frame or a frame on a different stream as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


The CONTINUATION frame changes the connection state as defined in Section 4.3.


CONTINUATION frames MUST be associated with a stream. If a CONTINUATION frame is received with a Stream Identifier field of 0x00, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or CONTINUATION frame without the END_HEADERS flag set. A recipient that observes violation of this rule MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR.


7. Error Codes
7. エラーコード

Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY frames to convey the reasons for the stream or connection error.


Error codes share a common code space. Some error codes apply only to either streams or the entire connection and have no defined semantics in the other context.


The following error codes are defined:


NO_ERROR (0x00): The associated condition is not a result of an error. For example, a GOAWAY might include this code to indicate graceful shutdown of a connection.


PROTOCOL_ERROR (0x01): The endpoint detected an unspecific protocol error. This error is for use when a more specific error code is not available.


INTERNAL_ERROR (0x02): The endpoint encountered an unexpected internal error.


FLOW_CONTROL_ERROR (0x03): The endpoint detected that its peer violated the flow-control protocol.


SETTINGS_TIMEOUT (0x04): The endpoint sent a SETTINGS frame but did not receive a response in a timely manner. See Section 6.5.3 ("Settings Synchronization").

settings_timeout(0x04):エンドポイントは設定フレームを送信しましたが、タイムリーな方法で応答を受け取りませんでした。セクション6.5.3( "設定同期")を参照してください。

STREAM_CLOSED (0x05): The endpoint received a frame after a stream was half-closed.


FRAME_SIZE_ERROR (0x06): The endpoint received a frame with an invalid size.


REFUSED_STREAM (0x07): The endpoint refused the stream prior to performing any application processing (see Section 8.7 for details).


CANCEL (0x08): The endpoint uses this error code to indicate that the stream is no longer needed.


COMPRESSION_ERROR (0x09): The endpoint is unable to maintain the field section compression context for the connection.


CONNECT_ERROR (0x0a): The connection established in response to a CONNECT request (Section 8.5) was reset or abnormally closed.


ENHANCE_YOUR_CALM (0x0b): The endpoint detected that its peer is exhibiting a behavior that might be generating excessive load.


INADEQUATE_SECURITY (0x0c): The underlying transport has properties that do not meet minimum security requirements (see Section 9.2).


HTTP_1_1_REQUIRED (0x0d): The endpoint requires that HTTP/1.1 be used instead of HTTP/2.


Unknown or unsupported error codes MUST NOT trigger any special behavior. These MAY be treated by an implementation as being equivalent to INTERNAL_ERROR.


8. Expressing HTTP Semantics in HTTP/2
8. HTTP/2でHTTPセマンティクスを表現します

HTTP/2 is an instantiation of the HTTP message abstraction (Section 6 of [HTTP]).


8.1. HTTP Message Framing
8.1. HTTPメッセージフレーミング

A client sends an HTTP request on a new stream, using a previously unused stream identifier (Section 5.1.1). A server sends an HTTP response on the same stream as the request.


An HTTP message (request or response) consists of:


1. one HEADERS frame (followed by zero or more CONTINUATION frames) containing the header section (see Section 6.3 of [HTTP]),

1. ヘッダーセクションを含む1つのヘッダーフレーム(ゼロ以上の継続フレームが続きます)([http]のセクション6.3を参照)、

2. zero or more DATA frames containing the message content (see Section 6.4 of [HTTP]), and

2. メッセージコンテンツを含むゼロ以上のデータフレーム([http]のセクション6.4を参照)、および

3. optionally, one HEADERS frame (followed by zero or more CONTINUATION frames) containing the trailer section, if present (see Section 6.5 of [HTTP]).

3. オプションで、トレーラーセクションを含む1つのヘッダーフレーム(ゼロ以上の継続フレームが続きます)([http]のセクション6.5を参照)。

For a response only, a server MAY send any number of interim responses before the HEADERS frame containing a final response. An interim response consists of a HEADERS frame (which might be followed by zero or more CONTINUATION frames) containing the control data and header section of an interim (1xx) HTTP response (see Section 15 of [HTTP]). A HEADERS frame with the END_STREAM flag set that carries an informational status code is malformed (Section 8.1.1).


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 CONTINUATION frames that carry any remaining fragments of the field block.


Other frames (from any stream) MUST NOT occur between the HEADERS frame and any CONTINUATION frames that might follow.


HTTP/2 uses DATA frames to carry message content. The chunked transfer encoding defined in Section 7.1 of [HTTP/1.1] cannot be used in HTTP/2; see Section 8.2.2.


Trailer fields are carried in a field block that also terminates the stream. That is, trailer fields comprise a sequence starting with a HEADERS frame, followed by zero or more CONTINUATION frames, where the HEADERS frame bears an END_STREAM flag. Trailers MUST NOT include pseudo-header fields (Section 8.3). An endpoint that receives pseudo-header fields in trailers MUST treat the request or response as malformed (Section 8.1.1).


An endpoint that receives a HEADERS frame without the END_STREAM flag set after receiving the HEADERS frame that opens a request or after receiving a final (non-informational) status code MUST treat the corresponding request or response as malformed (Section 8.1.1).


An HTTP request/response exchange fully consumes a single stream. A request starts with the HEADERS frame that puts the stream into the "open" state. The request ends with a frame with the END_STREAM flag set, which causes the stream to become "half-closed (local)" for the client and "half-closed (remote)" for the server. A response stream starts with zero or more interim responses in HEADERS frames, followed by a HEADERS frame containing a final status code.


An HTTP response is complete after the server sends -- or the client receives -- a frame with the END_STREAM flag set (including any CONTINUATION frames needed to complete a field block). A server can send a complete response prior to the client sending an entire request if the response does not depend on any portion of the request that has not been sent and received. When this is true, a server MAY request that the client abort transmission of a request without error by sending a RST_STREAM with an error code of NO_ERROR after sending a complete response (i.e., a frame with the END_STREAM flag set). Clients MUST NOT discard responses as a result of receiving such a RST_STREAM, though clients can always discard responses at their discretion for other reasons.

サーバーがEND_STREAMフラグセット(フィールドブロックを完了するために必要な継続フレームを含む)を送信する - またはクライアントが受信する(またはクライアントが受信)後にHTTP応答が完了します。サーバーは、送信されて受信されていないリクエストの一部に依存しない場合、クライアントがリクエスト全体を送信する前に完全な応答を送信できます。これが真実である場合、サーバーは、完全な応答を送信した後、no_errorのエラーコードを使用してRST_STREAMを送信することにより、クライアントがエラーなしでリクエストの送信を中止することを要求する場合があります(つまり、END_STREAMフラグセットのあるフレーム)。クライアントは、そのようなRST_STREAMを受け取った結果として応答を破棄してはなりませんが、クライアントは他の理由で常に裁量で回答を廃棄することができます。

8.1.1. Malformed Messages
8.1.1. 不正なメッセージ

A malformed request or response is one that is an otherwise valid sequence of HTTP/2 frames but is invalid due to the presence of extraneous frames, prohibited fields or pseudo-header fields, the absence of mandatory pseudo-header fields, the inclusion of uppercase field names, or invalid field names and/or values (in certain circumstances; see Section 8.2).


A request or response that includes message content can include a content-length header field. A request or response is also malformed if the value of a content-length header field does not equal the sum of the DATA frame payload lengths that form the content, unless the message is defined as having no content. For example, 204 or 304 responses contain no content, as does the response to a HEAD request. A response that is defined to have no content, as described in Section 6.4.1 of [HTTP], MAY have a non-zero content-length header field, even though no content is included in DATA frames.


Intermediaries that process HTTP requests or responses (i.e., any intermediary not acting as a tunnel) MUST NOT forward a malformed request or response. Malformed requests or responses that are detected MUST be treated as a stream error (Section 5.4.2) of type PROTOCOL_ERROR.


For malformed requests, a server MAY send an HTTP response prior to closing or resetting the stream. Clients MUST NOT accept a malformed response.


Endpoints that progressively process messages might have performed some processing before identifying a request or response as malformed. For instance, it might be possible to generate an informational or 404 status code without having received a complete request. Similarly, intermediaries might forward incomplete messages before detecting errors. A server MAY generate a final response before receiving an entire request when the response does not depend on the remainder of the request being correct.


These requirements are intended to protect against several types of common attacks against HTTP; they are deliberately strict because being permissive can expose implementations to these vulnerabilities.


8.2. HTTP Fields
8.2. HTTPフィールド

HTTP fields (Section 5 of [HTTP]) are conveyed by HTTP/2 in the HEADERS, CONTINUATION, and PUSH_PROMISE frames, compressed with HPACK [COMPRESSION].

HTTPフィールド([HTTP]のセクション5)は、HPACK [圧縮]で圧縮されたヘッダー、継続、およびPush_PromiseフレームのHTTP/2によって伝達されます。

Field names MUST be converted to lowercase when constructing an HTTP/2 message.


8.2.1. Field Validity
8.2.1. フィールドの妥当性

The definitions of field names and values in HTTP prohibit some characters that HPACK might be able to convey. HTTP/2 implementations SHOULD validate field names and values according to their definitions in Sections 5.1 and 5.5 of [HTTP], respectively, and treat messages that contain prohibited characters as malformed (Section 8.1.1).


Failure to validate fields can be exploited for request smuggling attacks. In particular, unvalidated fields might enable attacks when messages are forwarded using HTTP/1.1 [HTTP/1.1], where characters such as carriage return (CR), line feed (LF), and COLON are used as delimiters. Implementations MUST perform the following minimal validation of field names and values:

フィールドの検証の失敗は、密輸攻撃を要求するために悪用される可能性があります。特に、http/1.1 [http/1.1]を使用してメッセージが転送されると、攻撃が可能になる場合があります。ここで、キャリッジリターン(CR)、ラインフィード(LF)、コロンなどの文字が区切り文字として使用されます。実装は、フィールド名と値の次の最小限の検証を実行する必要があります。

* A field name MUST NOT contain characters in the ranges 0x00-0x20, 0x41-0x5a, or 0x7f-0xff (all ranges inclusive). This specifically excludes all non-visible ASCII characters, ASCII SP (0x20), and uppercase characters ('A' to 'Z', ASCII 0x41 to 0x5a).

* フィールド名には、範囲0x00-0x20、0x41-0x5a、または0x7f-0xff(すべての範囲を含む)の文字を含めてはなりません。これは、具体的には、すべての訪問不可能なASCII文字、ASCII SP(0x20)、および大文字( 'a' to 'z'、ascii 0x41〜0x5a)を除外します。

* With the exception of pseudo-header fields (Section 8.3), which have a name that starts with a single colon, field names MUST NOT include a colon (ASCII COLON, 0x3a).

* 単一のコロンで始まる名前を持つ擬似ヘッダーフィールド(セクション8.3)を除き、フィールド名はコロン(ASCIIコロン、0x3a)を含めてはなりません。

* A field value MUST NOT contain the zero value (ASCII NUL, 0x00), line feed (ASCII LF, 0x0a), or carriage return (ASCII CR, 0x0d) at any position.

* フィールド値には、任意の位置にゼロ値(ASCII NUL、0X00)、ラインフィード(ASCII LF、0x0A)、またはキャリッジリターン(ASCII CR、0x0D)を含めてはなりません。

* A field value MUST NOT start or end with an ASCII whitespace character (ASCII SP or HTAB, 0x20 or 0x09).

* フィールド値は、ASCII Whitespace文字(ASCII SPまたはHTAB、0x20または0x09)で起動または終了してはなりません。

Note: An implementation that validates fields according to the definitions in Sections 5.1 and 5.5 of [HTTP] only needs an additional check that field names do not include uppercase characters.


A request or response that contains a field that violates any of these conditions MUST be treated as malformed (Section 8.1.1). In particular, an intermediary that does not process fields when forwarding messages MUST NOT forward fields that contain any of the values that are listed as prohibited above.


When a request message violates one of these requirements, an implementation SHOULD generate a 400 (Bad Request) status code (see Section 15.5.1 of [HTTP]), unless a more suitable status code is defined or the status code cannot be sent (e.g., because the error occurs in a trailer field).


Note: Field values that are not valid according to the definition of the corresponding field do not cause a request to be malformed; the requirements above only apply to the generic syntax for fields as defined in Section 5 of [HTTP].


8.2.2. Connection-Specific Header Fields
8.2.2. 接続固有のヘッダーフィールド

HTTP/2 does not use the Connection header field (Section 7.6.1 of [HTTP]) to indicate connection-specific header fields; in this protocol, connection-specific metadata is conveyed by other means. An endpoint MUST NOT generate an HTTP/2 message containing connection-specific header fields. This includes the Connection header field and those listed as having connection-specific semantics in Section 7.6.1 of [HTTP] (that is, Proxy-Connection, Keep-Alive, Transfer-Encoding, and Upgrade). Any message containing connection-specific header fields MUST be treated as malformed (Section 8.1.1).


The only exception to this is the TE header field, which MAY be present in an HTTP/2 request; when it is, it MUST NOT contain any value other than "trailers".


An intermediary transforming an HTTP/1.x message to HTTP/2 MUST remove connection-specific header fields as discussed in Section 7.6.1 of [HTTP], or their messages will be treated by other HTTP/2 endpoints as malformed (Section 8.1.1).


Note: HTTP/2 purposefully does not support upgrade to another protocol. The handshake methods described in Section 3 are believed sufficient to negotiate the use of alternative protocols.


8.2.3. Compressing the Cookie Header Field
8.2.3. Cookieヘッダーフィールドの圧縮

The Cookie header field [COOKIE] uses a semicolon (";") to delimit cookie-pairs (or "crumbs"). This header field contains multiple values, but does not use a COMMA (",") as a separator, thereby preventing cookie-pairs from being sent on multiple field lines (see Section 5.2 of [HTTP]). This can significantly reduce compression efficiency, as updates to individual cookie-pairs would invalidate any field lines that are stored in the HPACK table.

Cookie Headerフィールド[Cookie]は、セミコロン( ";")を使用して、Cookie-Pairs(または「Crumbs」)を区切ります。このヘッダーフィールドには複数の値が含まれていますが、コンマ( "、")をセパレーターとして使用しないため、複数のフィールドラインでクッキーペアが送信されないようにします([http]のセクション5.2を参照)。これにより、個々のクッキーペアの更新がHPACKテーブルに保存されているフィールドラインを無効にするため、圧縮効率を大幅に低下させる可能性があります。

To allow for better compression efficiency, the Cookie header field MAY be split into separate header fields, each with one or more cookie-pairs. If there are multiple Cookie header fields after decompression, these MUST be concatenated into a single octet 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 connection, or a generic HTTP server application.

より良い圧縮効率を可能にするために、Cookieヘッダーフィールドは、それぞれ1つ以上のCookieペアを備えた個別のヘッダーフィールドに分割できます。減圧後に複数のCookieヘッダーフィールドがある場合、これらは、0x3b、0x20(ascii string ";")の2オクテットデリミターを使用して単一のオクテット文字列に連結する必要があります。HTTP/1.1接続、または汎用HTTPサーバーアプリケーションとして。

Therefore, the following two lists of Cookie header fields are semantically equivalent.


   cookie: a=b; c=d; e=f
   cookie: a=b
   cookie: c=d
   cookie: e=f
8.3. HTTP Control Data
8.3. HTTP制御データ

HTTP/2 uses special pseudo-header fields beginning with a ':' character (ASCII 0x3a) to convey message control data (see Section 6.2 of [HTTP]).

HTTP/2は、 ':'文字(ASCII 0x3a)で始まる特別な擬似ヘッダーフィールドを使用して、メッセージ制御データを伝達します([http]のセクション6.2を参照)。

Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT generate pseudo-header fields other than those defined in this document. Note that an extension could negotiate the use of additional pseudo-header fields; see Section 5.5.


Pseudo-header fields are only valid in the context in which they are defined. Pseudo-header fields defined for requests MUST NOT appear in responses; pseudo-header fields defined for responses MUST NOT appear in requests. Pseudo-header fields MUST NOT appear in a trailer section. Endpoints MUST treat a request or response that contains undefined or invalid pseudo-header fields as malformed (Section 8.1.1).


All pseudo-header fields MUST appear in a field block before all regular field lines. Any request or response that contains a pseudo-header field that appears in a field block after a regular field line MUST be treated as malformed (Section 8.1.1).


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 contains a repeated pseudo-header field name MUST be treated as malformed (Section 8.1.1).


8.3.1. Request Pseudo-Header Fields
8.3.1. 擬似ヘッダーフィールドをリクエストします

The following pseudo-header fields are defined for HTTP/2 requests:


* The ":method" pseudo-header field includes the HTTP method (Section 9 of [HTTP]).

* 「:メソッド」疑似ヘッダーフィールドには、HTTPメソッド([HTTP]のセクション9)が含まれます。

* The ":scheme" pseudo-header field includes the scheme portion of the request target. The scheme is taken from the target URI (Section 3.1 of [RFC3986]) when generating a request directly, or from the scheme of a translated request (for example, see Section 3.3 of [HTTP/1.1]). Scheme is omitted for CONNECT requests (Section 8.5).

* 「:スキーム」疑似ヘッダーフィールドには、リクエストターゲットのスキーム部分が含まれます。スキームは、要求を直接生成するとき、または翻訳された要求のスキームからターゲットURI([RFC3986]のセクション3.1)から取得されます(たとえば、[http/1.1]のセクション3.3を参照)。Connectリクエストのスキームは省略されています(セクション8.5)。

":scheme" is not restricted to "http" and "https" schemed URIs. A proxy or gateway can translate requests for non-HTTP schemes, enabling the use of HTTP to interact with non-HTTP services.


* The ":authority" pseudo-header field conveys the authority portion (Section 3.2 of [RFC3986]) of the target URI (Section 7.1 of [HTTP]). The recipient of an HTTP/2 request MUST NOT use the Host header field to determine the target URI if ":authority" is present.

* ターゲットURI([http]のセクション7.1)の権限部分([rfc3986]のセクション3.2)を「[http]のセクション7.1)に「:権限」疑似ヘッダーフィールドが伝えます。http/2要求の受信者は、「:権限」が存在する場合、ホストヘッダーフィールドを使用してターゲットURIを決定してはなりません。

Clients that generate HTTP/2 requests directly MUST use the ":authority" pseudo-header field to convey authority information, unless there is no authority information to convey (in which case it MUST NOT generate ":authority").


Clients MUST NOT generate a request with a Host header field that differs from the ":authority" pseudo-header field. A server SHOULD treat a request as malformed if it contains a Host header field that identifies an entity that differs from the entity in the ":authority" pseudo-header field. The values of fields need to be normalized to compare them (see Section 6.2 of [RFC3986]). An origin server can apply any normalization method, whereas other servers MUST perform scheme-based normalization (see Section 6.2.3 of [RFC3986]) of the two fields.

クライアントは、「:権威」の擬似ヘッダーフィールドとは異なるホストヘッダーフィールドでリクエストを生成してはなりません。サーバーは、「:権限」の擬似ヘッダーフィールドのエンティティとは異なるエンティティを識別するホストヘッダーフィールドを含む場合、要求を奇形として扱う必要があります。フィールドの値は、それらを比較するために正規化する必要があります([RFC3986]のセクション6.2を参照)。Origin Serverは任意の正規化方法を適用できますが、他のサーバーは、2つのフィールドのスキームベースの正規化([RFC3986]のセクション6.2.3を参照)を実行する必要があります。

An intermediary that forwards a request over HTTP/2 MUST construct an ":authority" pseudo-header field using the authority information from the control data of the original request, unless the original request's target URI does not contain authority information (in which case it MUST NOT generate ":authority"). Note that the Host header field is not the sole source of this information; see Section 7.2 of [HTTP].

HTTP/2よりもリクエストを転送する仲介者は、元のリクエストのターゲットURIに権限情報が含まれていない場合を除き、元のリクエストの制御データからの権限情報を使用して「:権限」擬似ヘッダーフィールドを構築する必要があります(この場合はIT生成してはならない ":authority")。ホストヘッダーフィールドは、この情報の唯一のソースではないことに注意してください。[http]のセクション7.2を参照してください。

An intermediary that needs to generate a Host header field (which 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 Host field, unless the intermediary also changes the request target. This replaces any existing Host field to avoid potential vulnerabilities in HTTP routing.


An intermediary that forwards a request over HTTP/2 MAY retain any Host header field.


Note that request targets for CONNECT or asterisk-form OPTIONS requests never include authority information; see Sections 7.1 and 7.2 of [HTTP].


":authority" MUST NOT include the deprecated userinfo subcomponent for "http" or "https" schemed URIs.

":authority"は、「http」または「https」schemed urisの非推奨ユーザーインフェサブコンポーネントを含めてはなりません。

* The ":path" pseudo-header field includes the path and query parts of the target URI (the absolute-path production and, optionally, a '?' character followed by the query production; see Section 4.1 of [HTTP]). A request in asterisk form (for OPTIONS) includes the value '*' for the ":path" pseudo-header field.

* 「:パス」疑似ヘッダーフィールドには、ターゲットURIのパスとクエリ部分(絶対パス生産、およびオプションではクエリ生産が続く「?」文字が含まれます。[http]のセクション4.1を参照)。アスタリスクフォームの要求(オプション用)には、「:パス」疑似ヘッダーフィールドの値「*」が含まれます。

This pseudo-header field MUST NOT be empty for "http" or "https" URIs; "http" or "https" URIs that do not contain a path component MUST include a value of '/'. The exceptions to this rule are:

この擬似ヘッダーフィールドは、「http」または「https」urisの場合は空にしてはなりません。パスコンポーネントを含まない「http」または「https」urisには、 '/'の値を含める必要があります。このルールの例外は次のとおりです。

- an OPTIONS request for an "http" or "https" URI that does not include a path component; these MUST include a ":path" pseudo-header field with a value of '*' (see Section 7.1 of [HTTP]).

- パスコンポーネントを含まない「HTTP」または「HTTPS」URIのオプションリクエスト。これらには、「*」の値を持つ「:パス」疑似ヘッダーフィールドを含める必要があります([http]のセクション7.1を参照)。

- CONNECT requests (Section 8.5), where the ":path" pseudo-header field is omitted.

- 接続要求(セクション8.5)。ここで、「:パス」疑似ヘッダーフィールドが省略されています。

All HTTP/2 requests MUST include exactly one valid value for the ":method", ":scheme", and ":path" pseudo-header fields, unless they are CONNECT requests (Section 8.5). An HTTP request that omits mandatory pseudo-header fields is malformed (Section 8.1.1).


Individual HTTP/2 requests do not carry an explicit indicator of protocol version. All HTTP/2 requests implicitly have a protocol version of "2.0" (see Section 6.2 of [HTTP]).


8.3.2. Response Pseudo-Header Fields
8.3.2. 応答疑似ヘッダーフィールド

For HTTP/2 responses, a single ":status" pseudo-header field is defined that carries the HTTP status code field (see Section 15 of [HTTP]). This pseudo-header field MUST be included in all responses, including interim responses; otherwise, the response is malformed (Section 8.1.1).

HTTP/2応答の場合、HTTPステータスコードフィールドを運ぶ単一の ":status" pseudo-headerフィールドが定義されています([http]のセクション15を参照)。この擬似ヘッダーフィールドは、暫定的な応答を含むすべての応答に含める必要があります。それ以外の場合、応答は奇形です(セクション8.1.1)。

HTTP/2 responses implicitly have a protocol version of "2.0".


8.4. Server Push
8.4. サーバープッシュ

HTTP/2 allows a server to preemptively send (or "push") responses (along with corresponding "promised" requests) to a client in association with a previous client-initiated request.


Server push was designed to allow a server to improve client-perceived performance by predicting what requests will follow those that it receives, thereby removing a round trip for them. For example, a request for HTML is often followed by requests for stylesheets and scripts referenced by that page. When these requests are pushed, the client does not need to wait to receive the references to them in the HTML and issue separate requests.


In practice, server push is difficult to use effectively, because it requires the server to correctly anticipate the additional requests the client will make, taking into account factors such as caching, content negotiation, and user behavior. Errors in prediction can lead to performance degradation, due to the opportunity cost that the additional data on the wire represents. In particular, pushing any significant amount of data can cause contention issues with responses that are more important.


A client can request that server push be disabled, though this is negotiated for each hop independently. The SETTINGS_ENABLE_PUSH 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 cacheable (see Section 9.2.3 of [HTTP]). Promised requests cannot include any content or a trailer section. Clients that receive a promised request that is not cacheable, that is not known to be safe, or that indicates the presence of request content MUST reset the promised stream with a stream error (Section 5.4.2) of type PROTOCOL_ERROR. Note that this could result in the promised stream being reset if the client does not recognize a newly defined method as being safe.


Pushed responses that are cacheable (see Section 3 of [CACHING]) can be stored by the client, if it implements an HTTP cache. Pushed responses are considered successfully validated on the origin server (e.g., if the "no-cache" cache response directive is present; see Section of [CACHING]) while the stream identified by the promised stream identifier is still open.

キャッシュ可能なプッシュされた応答([キャッシュ]のセクション3を参照)は、HTTPキャッシュを実装する場合、クライアントが保存できます。プッシュされた応答は、Origin Serverで正常に検証されていると見なされます(たとえば、「ノーキャッシュ」キャッシュ応答指令が存在する場合、[キャッシュ]のセクション5.2.2.4を参照)、約束されたストリーム識別子によって識別されたストリームがまだ開いています。

Pushed responses that are not cacheable MUST NOT be stored by any HTTP cache. They MAY be made available to the application separately.


The server MUST include a value in the ":authority" pseudo-header field for which the server is authoritative (see Section 10.1). A client MUST treat a PUSH_PROMISE for which the server is not 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 forward them on to the client. In other words, how to make use of the pushed information is up to that intermediary. Equally, the intermediary might choose to make additional pushes to the client, without any action taken by the server.


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 PROTOCOL_ERROR. A server cannot set the SETTINGS_ENABLE_PUSH setting to a value other than 0 (see Section 6.5.2).


8.4.1. Push Requests
8.4.1. リクエストをプッシュします

Server push is semantically equivalent to a server responding to a request; however, in this case, that request is also sent by the server, as a PUSH_PROMISE frame.


The PUSH_PROMISE frame includes a field block that contains control data and a complete set of request header fields that the server attributes to the request. It is not possible to push a response to a request that includes message content.


Promised requests are always associated with an explicit request from the client. The PUSH_PROMISE frames sent by the server are sent on that explicit request's stream. The PUSH_PROMISE frame also includes a promised stream identifier, chosen from the stream identifiers available to the server (see Section 5.1.1).


The header fields in PUSH_PROMISE and any subsequent CONTINUATION 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" 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 header fields or the ":method" pseudo-header field identifies a method that is not safe, it MUST respond on the promised stream with a stream error (Section 5.4.2) of type PROTOCOL_ERROR.


The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to sending any frames that reference the promised responses. This avoids a race where clients issue requests prior to receiving any PUSH_PROMISE frames.


For example, if the server receives a request for a document containing embedded links to multiple image files and the server chooses to push those additional images to the client, sending PUSH_PROMISE frames before the DATA frames that contain the image links ensures that the client is able to see that a resource will be pushed before discovering embedded links. Similarly, if the server pushes resources referenced by the field block (for instance, in Link header fields), sending a PUSH_PROMISE before sending the header ensures that clients do not request those resources.


PUSH_PROMISE frames MUST NOT be sent by the client.


PUSH_PROMISE frames can be sent by the server on any client-initiated stream, but the stream MUST be in either the "open" or "half-closed (remote)" state with respect to the server. PUSH_PROMISE frames are interspersed with the frames that comprise a response, though they cannot be interspersed with HEADERS and CONTINUATION frames that comprise a single field block.


Sending a PUSH_PROMISE frame creates a new stream and puts the stream into the "reserved (local)" state for the server and the "reserved (remote)" state for the client.


8.4.2. Push Responses
8.4.2. 応答をプッシュします

After sending the PUSH_PROMISE frame, the server can begin delivering the pushed response as a response (Section 8.3.2) on a server-initiated stream that uses the promised stream identifier. The server uses this stream to transmit an HTTP response, using the same sequence of frames as that defined in Section 8.1. This stream becomes "half-closed" to the client (Section 5.1) after the initial HEADERS frame is sent.


Once a client receives a PUSH_PROMISE frame and chooses to accept the pushed response, the client SHOULD NOT issue any requests for the promised response until after the promised stream has closed.


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 too long to begin sending the promised response, the client can send a RST_STREAM frame, using either the CANCEL or REFUSED_STREAM code and referencing the pushed stream's identifier.


A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit the number of responses that can be concurrently pushed by a server. Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero prevents the server from opening the streams necessary to push responses. However, this does not prevent the server from reserving streams using PUSH_PROMISE frames, because reserved streams do not count toward the concurrent stream limit. Clients that do not wish to receive pushed resources need to reset any unwanted reserved streams or set SETTINGS_ENABLE_PUSH to 0.

クライアントは、settings_max_concurrent_streams設定を使用して、サーバーによって同時にプッシュできる応答の数を制限できます。settings_max_concurrent_streams zeroのsettings_max_concurrent_streamsの広告は、サーバーが応答をプッシュするために必要なストリームを開くことを防ぎます。ただし、これは、予約済みのストリームが同時ストリームの制限にカウントされないため、Push_promiseフレームを使用してサーバーを予約することを妨げません。プッシュされたリソースを受け取りたくないクライアントは、不要な予約済みのストリームをリセットする必要があります。

Clients receiving a pushed response MUST validate that either the server is authoritative (see Section 10.1) or the proxy that provided the pushed response is configured for the corresponding request. For example, a server that offers a certificate for only the DNS-ID (see [RFC6125]) is not permitted to push a response for <>.


The response for a PUSH_PROMISE stream begins with a HEADERS frame, which immediately puts the stream into the "half-closed (remote)" 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 stream in the "closed" state.


Note: The client never sends a frame with the END_STREAM flag set for a server push.


8.5. The CONNECT Method
8.5. 接続メソッド

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 used with HTTP proxies to establish a TLS session with an origin server for the purposes of interacting with "https" resources.

Connectメソッド([HTTP]のセクション9.3.6)は、HTTP接続をトンネルにリモートホストに変換するために使用されます。Connectは主にHTTPプロキシで使用され、「HTTPS」リソースとの対話を目的として、Origin ServerとTLSセッションを確立します。

In HTTP/2, the CONNECT method establishes a tunnel over a single HTTP/2 stream to a remote host, rather than converting the entire connection to a tunnel. A CONNECT header section is constructed as defined in Section 8.3.1 ("Request Pseudo-Header Fields"), with a few differences. Specifically:

HTTP/2では、Connectメソッドは、接続全体をトンネルに変換するのではなく、単一のHTTP/2ストリームにリモートホストにトンネルを確立します。接続ヘッダーセクションは、セクション8.3.1( "要求の擬似ヘッダーフィールド")で定義されているように構築され、いくつかの違いがあります。具体的には:

* The ":method" pseudo-header field is set to CONNECT.

* 「:メソッド」擬似ヘッダーフィールドは、接続するように設定されています。

* The ":scheme" and ":path" pseudo-header fields MUST be omitted.

* 「:スキーム」と「:パス」疑似ヘッダーフィールドは省略する必要があります。

* The ":authority" pseudo-header field contains the host and port to connect to (equivalent to the authority-form of the request-target of CONNECT requests; see Section 3.2.3 of [HTTP/1.1]).

* 「:authority」疑似ヘッダーフィールドには、接続するホストとポートが含まれています(接続要求の要求標的の権限形式に相当します。[http/1.1]のセクション3.2.3を参照)。

A CONNECT request that does not conform to these restrictions is malformed (Section 8.1.1).


A proxy that supports CONNECT establishes a TCP connection [TCP] to the host and port identified in the ":authority" pseudo-header field. Once this connection is successfully established, the proxy sends a HEADERS frame containing a 2xx-series status code to the client, as defined in Section 9.3.6 of [HTTP].


After the initial HEADERS frame sent by each peer, all subsequent 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 proxy to the TCP server; data received from the TCP server is assembled into DATA frames by the proxy. Frame types other than DATA or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY) MUST NOT be sent on a connected stream and MUST be treated as a stream error (Section 5.4.2) if received.


The TCP connection can be closed by either peer. The END_STREAM flag on a DATA frame is treated as being equivalent to the TCP FIN bit. A client is expected to send a DATA frame with the END_STREAM flag set after receiving a frame with the END_STREAM flag set. A proxy that receives a DATA frame with the END_STREAM flag set sends the attached data with the FIN bit set on the last TCP segment. A proxy that receives a TCP segment with the FIN bit set sends a DATA frame with the END_STREAM flag set. Note that the final TCP segment or DATA frame could be empty.

TCP接続は、いずれかのピアで閉じることができます。データフレームのEND_STREAMフラグは、TCP FINビットと同等であると扱われます。クライアントは、END_STREAMフラグが設定されたフレームを受信した後、END_STREAMフラグが設定されたデータフレームを送信することが期待されます。END_STREAMフラグセットでデータフレームを受信するプロキシは、最後のTCPセグメントにFINビット設定で添付のデータを送信します。FINビットセットを使用してTCPセグメントを受信するプロキシは、END_STREAMフラグセットでデータフレームを送信します。最終的なTCPセグメントまたはデータフレームが空になる可能性があることに注意してください。

A TCP connection error is signaled with RST_STREAM. A proxy treats any error in the TCP connection, which includes receiving a TCP segment with the RST bit set, as a stream error (Section 5.4.2) of type CONNECT_ERROR. Correspondingly, a proxy MUST send a TCP segment with the RST bit set if it detects an error with the stream or the HTTP/2 connection.


8.6. The Upgrade Header Field
8.6. アップグレードヘッダーフィールド

HTTP/2 does not support the 101 (Switching Protocols) informational status code (Section 15.2.2 of [HTTP]).


The semantics of 101 (Switching Protocols) aren't applicable to a multiplexed protocol. Similar functionality might be enabled through the use of extended CONNECT [RFC8441], and other protocols are able to use the same mechanisms that HTTP/2 uses to negotiate their use (see Section 3).


8.7. Request Reliability
8.7. 信頼性を要求します

In general, an HTTP client is unable to retry a non-idempotent request when an error occurs because there is no means to determine the nature of the error (see Section 9.2.2 of [HTTP]). It is possible that some server processing occurred prior to the error, which could result in undesirable effects if the request were reattempted.


HTTP/2 provides two mechanisms for providing a guarantee to a client that a request has not been processed:


* The GOAWAY frame indicates the highest stream number that might have been processed. Requests on streams with higher numbers are therefore guaranteed to be safe to retry.

* Goawayフレームは、処理された可能性のある最高のストリーム数を示します。したがって、より高い数のストリームのリクエストは、再試行するのが安全であることが保証されています。

* The REFUSED_STREAM error code can be included in a RST_STREAM frame to indicate that the stream is being closed prior to any processing having occurred. Any request that was sent on the reset stream can be safely retried.

* Refused_streamエラーコードをRST_STREAMフレームに含めることができ、処理が発生する前にストリームが閉じられていることを示します。リセットストリームで送信されたリクエストは、安全に再試行できます。

Requests that have not been processed have not failed; clients MAY automatically retry them, even those with non-idempotent methods.


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 are passed to the application layer for any stream, then REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame MUST include a stream identifier that is greater than or equal to the given stream identifier.


In addition to these mechanisms, the PING frame provides a way for a client to easily test a connection. Connections that remain idle can become broken, because some middleboxes (for instance, network address translators or load balancers) silently discard connection bindings. The PING frame allows a client to safely test whether a connection is still active without sending a request.


8.8. Examples
8.8. 例

This section shows HTTP/1.1 requests and responses, with illustrations of equivalent HTTP/2 requests and responses.


8.8.1. Simple Request
8.8.1. 簡単なリクエスト

An HTTP GET request includes control data and a request header with no message content and is therefore transmitted as a single HEADERS frame, followed by zero or more CONTINUATION frames containing the serialized block of request header fields. The HEADERS frame in the following has both the END_HEADERS and END_STREAM flags set; no CONTINUATION frames are sent.

HTTP GETリクエストには、コントロールデータとメッセージコンテンツのないリクエストヘッダーが含まれているため、単一のヘッダーフレームとして送信され、その後、リクエストヘッダーフィールドのシリアル化ブロックを含むゼロ以上の継続フレームが続きます。以下のヘッダーフレームには、end_headersとend_streamフラグの両方が設定されています。継続フレームは送信されません。

     GET /resource HTTP/1.1           HEADERS
     Host:          ==>     + END_STREAM
     Accept: image/jpeg                 + END_HEADERS
                                          :method = GET
                                          :scheme = https
                                          :authority =
                                          :path = /resource
                                          host =
                                          accept = image/jpeg
8.8.2. Simple Response
8.8.2. 単純な応答

Similarly, a response that includes only control data and a response header is transmitted as a HEADERS frame (again, followed by zero or more CONTINUATION frames) containing the serialized block of response header fields.


HTTP/1.1 304 Not Modified HEADERS ETag: "xyzzy" ==> + END_STREAM Expires: Thu, 23 Jan ... + END_HEADERS :status = 304 etag = "xyzzy" expires = Thu, 23 Jan ...

http/1.1 304変更されていないヘッダーetag: "xyzzy" ==> end_streamの有効期限:木、1月23日... end_headers:status = 304 etag = "xyzzy" expires = thu、23 Jan ...

8.8.3. Complex Request
8.8.3. 複雑なリクエスト

An HTTP POST request that includes control data and a request header with message content is transmitted as one HEADERS frame, followed by zero or more CONTINUATION frames containing the request header, followed by one or more DATA frames, with the last CONTINUATION (or HEADERS) frame having the END_HEADERS flag set and the final DATA frame having the END_STREAM flag set:

コントロールデータとメッセージコンテンツを含むリクエストヘッダーを含むHTTP POSTリクエストは、1つのヘッダーフレームとして送信され、その後、リクエストヘッダーを含むゼロ以上の継続フレームが続き、その後に1つ以上のデータフレームが続き、最後の継続(またはヘッダー)が続きます。end_headersフラグが設定されているフレームと、end_streamフラグセットを持つ最終データフレームフレーム:

     POST /resource HTTP/1.1          HEADERS
     Host:          ==>     - END_STREAM
     Content-Type: image/jpeg           - END_HEADERS
     Content-Length: 123                  :method = POST
                                          :authority =
                                          :path = /resource
     {binary data}                        :scheme = https

CONTINUATION + END_HEADERS content-type = image/jpeg host = content-length = 123

継続end_headers content-type = image/jpeg host = content-length = 123

DATA + END_STREAM {binary data}

data end_stream {バイナリデータ}

Note that data contributing to any given field line could be spread between field block fragments. The allocation of field lines to frames in this example is illustrative only.


8.8.4. Response with Body
8.8.4. ボディによる応答

A response that includes control data and a response header with message content is transmitted as a HEADERS frame, followed by zero or more CONTINUATION frames, followed by one or more DATA frames, with the last DATA frame in the sequence having the END_STREAM flag set:


     HTTP/1.1 200 OK                  HEADERS
     Content-Type: image/jpeg   ==>     - END_STREAM
     Content-Length: 123                + END_HEADERS
                                          :status = 200
     {binary data}                        content-type = image/jpeg
                                          content-length = 123

DATA + END_STREAM {binary data}

data end_stream {バイナリデータ}

8.8.5. Informational Responses
8.8.5. 情報回答

An informational response using a 1xx status code other than 101 is transmitted as a HEADERS frame, followed by zero or more CONTINUATION frames.


A trailer section is sent as a field block after both the request or response field block and all the DATA frames have been sent. The HEADERS frame starting the field block that comprises the trailer section has the END_STREAM flag set.


The following example includes both a 100 (Continue) status code, which is sent in response to a request containing a "100-continue" token in the Expect header field, and a trailer section:


     HTTP/1.1 100 Continue            HEADERS
     Extension-Field: bar       ==>     - END_STREAM
                                        + END_HEADERS
                                          :status = 100
                                          extension-field = bar
     HTTP/1.1 200 OK                  HEADERS
     Content-Type: image/jpeg   ==>     - END_STREAM
     Transfer-Encoding: chunked         + END_HEADERS
     Trailer: Foo                         :status = 200
                                          content-type = image/jpeg
     123                                  trailer = Foo
     {binary data}
     0                                DATA
     Foo: bar                           - END_STREAM
                                      {binary data}


ヘッダーend_stream end_headers foo = bar

9. HTTP/2 Connections
9. HTTP/2接続

This section outlines attributes of HTTP that improve interoperability, reduce exposure to known security vulnerabilities, or reduce the potential for implementation variation.


9.1. Connection Management
9.1. 接続管理

HTTP/2 connections are persistent. For best performance, it is expected that clients will not close connections until it is determined that no further communication with a server is necessary (for example, when a user navigates away from a particular web page) or until the server closes the connection.


Clients SHOULD NOT open more than one HTTP/2 connection to a given host and port pair, where the host is derived from a URI, a selected alternative service [ALT-SVC], or a configured proxy.


A client can create additional connections as replacements, either to replace connections that are near to exhausting the available stream identifier space (Section 5.1.1), to refresh the keying material for a TLS connection, or to replace connections that have encountered errors (Section 5.4.1).


A client MAY open multiple connections to the same IP address and TCP port using different Server Name Indication [TLS-EXT] values or to provide different TLS client certificates but SHOULD avoid creating multiple connections with the same configuration.


Servers are encouraged to maintain open connections for as long as possible but are permitted to terminate idle connections if necessary. When either endpoint chooses to close the transport-layer TCP connection, the terminating endpoint SHOULD first send a GOAWAY (Section 6.8) frame so that both endpoints can reliably determine whether previously sent frames have been processed and gracefully complete or terminate any necessary remaining tasks.


9.1.1. Connection Reuse
9.1.1. 接続の再利用

Connections that are made to an origin server, either directly or through a tunnel created using the CONNECT method (Section 8.5), MAY be reused for requests with multiple different URI authority components. A connection can be reused as long as the origin server is authoritative (Section 10.1). For TCP connections without TLS, this depends on the host having resolved to the same IP address.

Origin Serverに直接またはConnectメソッド(セクション8.5)を使用して作成されたトンネルを介して作成された接続は、複数の異なるURI機関コンポーネントを含むリクエストに対して再利用できます。Origin Serverが信頼できる限り、接続を再利用できます(セクション10.1)。TLSのないTCP接続の場合、これはホストが同じIPアドレスに解決したことによって異なります。

For "https" resources, connection reuse additionally depends on having a certificate that is valid for the host in the URI. The certificate presented by the server MUST satisfy any checks that the client would perform when forming a new TLS connection for the host in the URI. A single certificate can be used to establish authority for multiple origins. Section 4.3 of [HTTP] describes how a client determines whether a server is authoritative for a URI.


In some deployments, reusing a connection for multiple origins can result in requests being directed to the wrong origin server. For example, TLS termination might be performed by a middlebox that uses the TLS Server Name Indication [TLS-EXT] extension to select an origin server. This means that it is possible for clients to send requests to servers that might not be the intended target for the request, even though the server is otherwise authoritative.

一部の展開では、複数の起源の接続を再利用すると、リクエストが間違ったOriginサーバーに向けられる可能性があります。たとえば、TLS終了は、TLSサーバー名表示[TLS-EXT]拡張機能を使用してOrigin Serverを選択するミドルボックスによって実行される場合があります。これは、サーバーが権威あるものであるにもかかわらず、クライアントがリクエストの意図されたターゲットではない可能性のあるサーバーにリクエストを送信できることを意味します。

A server that does not wish clients to reuse connections can indicate that it is not authoritative for a request by sending a 421 (Misdirected Request) status code in response to the request (see Section 15.5.20 of [HTTP]).


A client that is configured to use a proxy over HTTP/2 directs requests to that proxy through a single connection. That is, all requests sent via a proxy reuse the connection to the proxy.


9.2. Use of TLS Features
9.2. TLS機能の使用

Implementations of HTTP/2 MUST use TLS version 1.2 [TLS12] or higher for HTTP/2 over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be followed, with some additional restrictions that are specific to HTTP/2.

HTTP/2の実装は、TLSを超えるHTTP/2に対してTLSバージョン1.2 [TLS12]以下を使用する必要があります。[TLSBCP]の一般的なTLS使用ガイダンスに従う必要があり、HTTP/2に固有の追加の制限があります。

The TLS implementation MUST support the Server Name Indication (SNI) [TLS-EXT] extension to TLS. If the server is identified by a domain name [DNS-TERMS], clients MUST send the server_name TLS extension unless an alternative mechanism to indicate the target host is used.

TLS実装は、サーバー名表示(SNI)[TLS-EXT] TLSの拡張をサポートする必要があります。サーバーがドメイン名[DNS-TERMS]によって識別される場合、クライアントはターゲットホストを示すための代替メカニズムを使用しない限り、Server_Name TLS拡張機能を送信する必要があります。

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 the requirements in Sections 9.2.1 and 9.2.2. Implementations are encouraged to provide defaults that comply, but it is recognized that deployments are ultimately responsible for compliance.

TLS 1.3 [TLS13]を交渉するHTTP/2の展開の要件は、セクション9.2.3に含まれています。TLS 1.2の展開は、セクション9.2.1および9.2.2の要件の対象となります。実装は、準拠するデフォルトを提供することをお勧めしますが、展開は最終的にコンプライアンスに責任があることが認識されています。

9.2.1. TLS 1.2 Features
9.2.1. TLS 1.2機能

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 be possible to fail TLS negotiation when these restrictions are not met. An endpoint MAY immediately terminate an HTTP/2 connection that does not meet these TLS requirements with a connection error (Section 5.4.1) of type INADEQUATE_SECURITY.

このセクションでは、HTTP/2で使用できるTLS 1.2機能セットの制限について説明します。展開の制限により、これらの制限が満たされない場合、TLS交渉に失敗することはできないかもしれません。エンドポイントは、タイプのInadequate_Securityの接続エラー(セクション5.4.1)でこれらのTLS要件を満たさないHTTP/2接続を直ちに終了する場合があります。

A deployment of HTTP/2 over TLS 1.2 MUST disable compression. TLS compression can lead to the exposure of information that would not otherwise be revealed [RFC3749]. Generic compression is unnecessary, since HTTP/2 provides compression features that are more aware of context and therefore likely to be more appropriate for use for performance, security, or other reasons.

TLS 1.2を介したHTTP/2の展開は、圧縮を無効にする必要があります。TLS圧縮は、そうでなければ明らかにされない情報の露出につながる可能性があります[RFC3749]。HTTP/2は、コンテキストをより認識しているため、パフォーマンス、セキュリティ、またはその他の理由で使用するためにより適切である可能性が高い圧縮機能を提供するため、一般的な圧縮は不要です。

A deployment of HTTP/2 over TLS 1.2 MUST disable renegotiation. An endpoint MUST treat a TLS renegotiation as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. Note that disabling renegotiation can result in long-lived connections becoming unusable due to limits on the number of messages the underlying cipher suite can encipher.

TLS 1.2を介したHTTP/2の展開は、再交渉を無効にする必要があります。エンドポイントは、TLS再交渉をタイプProtocol_Errorの接続エラー(セクション5.4.1)として扱う必要があります。再交渉を無効にすると、基礎となる暗号スイートが吸収できるメッセージの数が制限されているため、長寿命の接続が使用できなくなる可能性があることに注意してください。

An endpoint MAY use renegotiation to provide confidentiality protection for client credentials offered in the handshake, but any renegotiation MUST occur prior to sending the connection preface. A server SHOULD request a client certificate if it sees a renegotiation request immediately after establishing a connection.


This effectively prevents the use of renegotiation in response to a request for a specific protected resource. A future specification 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 request that the client use a protocol that supports renegotiation.


Implementations MUST support ephemeral key exchange sizes of at least 2048 bits for cipher suites that use ephemeral finite field Diffie-Hellman (DHE) (Section 8.1.2 of [TLS12]) and 224 bits for cipher suites that use ephemeral elliptic curve Diffie-Hellman (ECDHE) [RFC8422]. Clients MUST accept DHE sizes of up to 4096 bits. Endpoints MAY treat negotiation of key sizes smaller than the lower limits as a connection error (Section 5.4.1) of type INADEQUATE_SECURITY.


9.2.2. TLS 1.2 Cipher Suites
9.2.2. TLS 1.2暗号スイート

A deployment of HTTP/2 over TLS 1.2 SHOULD NOT use any of the prohibited cipher suites listed in Appendix A.

TLS 1.2を介したHTTP/2の展開は、付録Aにリストされている禁止された暗号スイートのいずれを使用しないでください。

Endpoints MAY choose to generate a connection error (Section 5.4.1) of type INADEQUATE_SECURITY if one of the prohibited cipher suites is negotiated. A deployment that chooses to use a prohibited cipher suite risks triggering a connection error unless the set of potential peers is known to accept that cipher suite.


Implementations MUST NOT generate this error in reaction to the negotiation of a cipher suite that is not prohibited. Consequently, when clients offer a cipher suite that is not prohibited, they have to be prepared to use that cipher suite with HTTP/2.


The list of prohibited cipher suites includes the cipher suite that TLS 1.2 makes mandatory, which means that TLS 1.2 deployments could have non-intersecting sets of permitted cipher suites. To avoid this problem, which causes TLS handshake failures, deployments of HTTP/2 that use TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 [TLS-ECDHE] with the P-256 elliptic curve [RFC8422].

禁止されている暗号スイートのリストには、TLS 1.2が必須になる暗号スイートが含まれています。つまり、TLS 1.2の展開には、許可された暗号スイートの非合成セットがあります。TLSハンドシェイクの障害を引き起こすこの問題を回避するために、TLS 1.2を使用するHTTP/2の展開は、P-256エリプティックカーブ[RFC8422]でTLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 [TLS-ECDHE]をサポートする必要があります。

Note that clients might advertise support of cipher suites that are 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 suite that is prohibited in HTTP/2. However, this can result in HTTP/2 being negotiated with a prohibited cipher suite if the application protocol and cipher suite are independently selected.


9.2.3. TLS 1.3 Features
9.2.3. TLS 1.3機能

TLS 1.3 includes a number of features not available in earlier versions. This section discusses the use of these features.

TLS 1.3には、以前のバージョンでは利用できない多くの機能が含まれています。このセクションでは、これらの機能の使用について説明します。

HTTP/2 servers MUST NOT send post-handshake TLS 1.3 CertificateRequest messages. HTTP/2 clients MUST treat a TLS post-handshake CertificateRequest message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.

HTTP/2サーバーは、ポストハンドシェイクTLS 1.3のcermostaterequestメッセージを送信してはなりません。HTTP/2クライアントは、TLSポストハンドシェイクの証明書登録メッセージをタイプProtocol_Errorの接続エラー(セクション5.4.1)として扱う必要があります。

The prohibition on post-handshake authentication applies even if the client offered the "post_handshake_auth" TLS extension. Post-handshake authentication support might be advertised independently of ALPN [TLS-ALPN]. Clients might offer the capability for use in other protocols, but inclusion of the extension cannot imply support within HTTP/2.

ポストハンドシェイク認証の禁止は、クライアントが「POST_HANDSHAKE_AUTH」TLS拡張機能を提供した場合でも適用されます。ポストハンドシェイク認証サポートは、ALPN [TLS-ALPN]とは無関係に宣伝される場合があります。クライアントは他のプロトコルで使用する機能を提供する場合がありますが、拡張機能を含めることはHTTP/2内でのサポートを意味することはできません。

[TLS13] defines other post-handshake messages, NewSessionTicket and KeyUpdate, which can be used as they have no direct interaction with HTTP/2. Unless the use of a new type of TLS message depends on an interaction with the application-layer protocol, that TLS message can be sent after the handshake completes.


TLS early data MAY be used to send requests, provided that the guidance in [RFC8470] is observed. Clients send requests in early data assuming initial values for all server settings.


10. Security Considerations
10. セキュリティ上の考慮事項

The use of TLS is necessary to provide many of the security properties of this protocol. Many of the claims in this section do not hold unless TLS is used as described in Section 9.2.


10.1. Server Authority
10.1. サーバー当局

HTTP/2 relies on the HTTP definition of authority for determining whether a server is authoritative in providing a given response (see Section 4.3 of [HTTP]). This relies on local name resolution for the "http" URI scheme and the authenticated server identity for the "https" scheme.


10.2. Cross-Protocol Attacks
10.2. クロスプロトコル攻撃

In a cross-protocol attack, an attacker causes a client to initiate a transaction in one protocol toward a server that understands a different protocol. An attacker might be able to cause the transaction to appear as a valid transaction in the second protocol. In combination with the capabilities of the web context, this can be used to interact with poorly protected servers in private networks.


Completing a TLS handshake with an ALPN identifier for HTTP/2 can be considered sufficient protection against cross-protocol attacks. ALPN provides a positive indication that a server is willing to proceed with HTTP/2, which prevents attacks on other TLS-based protocols.


The encryption in TLS makes it difficult for attackers to control the data that could be used in a cross-protocol attack on a cleartext protocol.


The cleartext version of HTTP/2 has minimal protection against cross-protocol attacks. The connection preface (Section 3.4) contains a string that is designed to confuse HTTP/1.1 servers, but no special protection is offered for other protocols.


10.3. Intermediary Encapsulation Attacks
10.3. 中間カプセル化攻撃

HPACK permits encoding of field names and values that might be treated as delimiters in other HTTP versions. An intermediary that translates an HTTP/2 request or response MUST validate fields according to the rules in Section 8.2 before translating a message to another HTTP version. Translating a field that includes invalid delimiters could be used to cause recipients to incorrectly interpret a message, which could be exploited by an attacker.


Section 8.2 does not include specific rules for validation of pseudo-header fields. If the values of these fields are used, additional validation is necessary. This is particularly important where ":scheme", ":authority", and ":path" are combined to form a single URI string [RFC3986]. Similar problems might occur when that URI or just ":path" is combined with ":method" to construct a request line (as in Section 3 of [HTTP/1.1]). Simple concatenation is not secure unless the input values are fully validated.


An intermediary can reject fields that contain invalid field names or values for other reasons -- in particular, those fields that do not conform to the HTTP ABNF grammar from Section 5 of [HTTP]. Intermediaries that do not perform any validation of fields other than the minimum required by Section 8.2 could forward messages that contain invalid field names or values.

仲介者は、他の理由で無効なフィールド名または値を含むフィールド、特に[HTTP]セクション5からHTTP ABNF文法に適合しないフィールドを拒否できます。セクション8.2で必要な最小値以外のフィールドの検証を実行しない仲介者は、無効なフィールド名または値を含むメッセージを転送できます。

An intermediary that receives any fields that require removal before forwarding (see Section 7.6.1 of [HTTP]) MUST remove or replace those header fields when forwarding messages. Additionally, intermediaries should take care when forwarding messages containing Content-Length 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 point, the framing will be correct.


10.4. Cacheability of Pushed Responses
10.4. プッシュされた応答のカキアビリティ

Pushed responses do not have an explicit request from the client; the request is provided by the server in the PUSH_PROMISE frame.


Caching responses that are pushed is possible based on the guidance provided by the origin server in the Cache-Control header field. However, this can cause issues if a single server hosts more than one tenant. For example, a server might offer multiple users each a small portion of its URI space.

プッシュされるキャッシュ応答は、キャッシュコントロールヘッダーフィールドでOrigin Serverが提供するガイダンスに基づいて可能です。ただし、単一のサーバーが複数のテナントをホストしている場合、これは問題を引き起こす可能性があります。たとえば、サーバーは、それぞれそれぞれURIスペースのごく一部を複数のユーザーに提供する場合があります。

Where multiple tenants share space on the same server, that server MUST ensure that tenants are not able to push representations of resources that they do not have authority over. Failure to enforce this would allow a tenant to provide a representation that would be served out of cache, overriding the actual representation that the authoritative tenant provides.


Pushed responses for which an origin server is not authoritative (see Section 10.1) MUST NOT be used or cached.

Origin Serverが信頼できるものではないプッシュされた応答(セクション10.1を参照)を使用またはキャッシュしてはなりません。

10.5. Denial-of-Service Considerations
10.5. サービス拒否の考慮事項

An HTTP/2 connection can demand a greater commitment of resources to operate than an HTTP/1.1 connection. Both field section compression and flow control depend on a commitment of a greater amount of state. Settings for these features ensure that memory commitments for these features are strictly bounded.


The number of PUSH_PROMISE frames is not constrained in the same fashion. A client that accepts server push SHOULD limit the number of streams it allows to be in the "reserved (remote)" state. An excessive number of server push streams can be treated as a stream error (Section 5.4.2) of type ENHANCE_YOUR_CALM.


A number of HTTP/2 implementations were found to be vulnerable to denial of service [NFLX-2019-002]. Below is a list of known ways that implementations might be subject to denial-of-service attacks:


* Inefficient tracking of outstanding outbound frames can lead to overload if an adversary can cause large numbers of frames to be enqueued for sending. A peer could use one of several techniques to cause large numbers of frames to be generated:

* 攻撃者が多数のフレームを送信するためにエンキューをする可能性がある場合、未解決のアウトバウンドフレームの非効率的な追跡は過負荷につながる可能性があります。ピアは、いくつかのテクニックの1つを使用して、多数のフレームを生成することができます。

- Providing tiny increments to flow control in WINDOW_UPDATE frames can cause a sender to generate a large number of DATA frames.

- window_updateフレーム内のフロー制御のために小さな増分を提供すると、送信者が多数のデータフレームを生成することができます。

- An endpoint is required to respond to a PING frame.

- Pingフレームに応答するには、エンドポイントが必要です。

- Each SETTINGS frame requires acknowledgment.

- 各設定フレームには、確認が必要です。

- An invalid request (or server push) can cause a peer to send RST_STREAM frames in response.

- 無効な要求(またはサーバープッシュ)により、ピアがRST_STREAMフレームをそれに応じて送信する可能性があります。

* An attacker can provide large amounts of flow-control credit at the HTTP/2 layer but withhold credit at the TCP layer, preventing frames from being sent. An endpoint that constructs and remembers frames for sending without considering TCP limits might be subject to resource exhaustion.

* 攻撃者は、HTTP/2レイヤーで大量のフローコントロールクレジットを提供できますが、TCPレイヤーでクレジットを保留し、フレームが送信されないようにします。TCPの制限を考慮せずに送信するためのフレームを構築および覚えているエンドポイントは、リソースの疲労の影響を受ける可能性があります。

* Large numbers of small or empty frames can be abused to cause a peer to expend time processing frame headers. Caution is required 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 stream.

* 多数の小型または空のフレームを乱用して、ピアが時間処理フレームヘッダーを消費することができます。ここでは、ストリームの終わりに空のデータや継続フレームの送信など、小さなフレームのいくつかの使用が完全に合法であるため、ここでは注意が必要です。

* The SETTINGS frame might also be abused to cause a peer to expend additional processing time. This might be done by pointlessly changing settings, sending multiple undefined settings, or changing the same setting multiple times in the same frame.

* 設定フレームは、ピアが追加の処理時間を消費するように乱用される可能性があります。これは、セットを無意味に変更したり、複数の未定義の設定を送信したり、同じ設定を同じフレームで複数回変更したりすることで実行される場合があります。

* Handling reprioritization with PRIORITY frames can require significant processing time and can lead to overload if many PRIORITY frames are sent.

* 優先フレームでの再登録を処理するには、かなりの処理時間が必要になる場合があり、多くの優先フレームが送信されると過負荷につながる可能性があります。

* Field section compression also provides opportunities for an attacker to waste processing resources; see Section 7 of [COMPRESSION] for more details on potential abuses.

* フィールドセクション圧縮は、攻撃者が処理リソースを無駄にする機会も提供します。潜在的な虐待の詳細については、[圧縮]のセクション7を参照してください。

* Limits in SETTINGS cannot be reduced instantaneously, which leaves an endpoint exposed to behavior from a peer that could exceed the new limits. In particular, immediately after establishing a connection, limits set by a server are not known to clients and could be exceeded without being an obvious protocol violation.

* 設定の制限を瞬時に減らすことはできません。これにより、エンドポイントは、新しい制限を超える可能性のあるピアからの動作にさらされます。特に、接続を確立した直後に、サーバーによって設定された制限はクライアントに知られておらず、明らかなプロトコル違反にならずに超えることができます。

Most of the features that might be exploited for denial of service -- such as SETTINGS changes, small frames, field section compression -- have legitimate uses. These features become a burden only when they are used unnecessarily or to excess.


An endpoint that doesn't monitor use of these features exposes itself 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 activity that is suspicious as a connection error (Section 5.4.1) of type ENHANCE_YOUR_CALM.


10.5.1. Limits on Field Block Size
10.5.1. フィールドブロックサイズの制限

A large field block (Section 4.3) can cause an implementation to commit a large amount of state. Field lines that are critical for routing can appear toward the end of a field block, which prevents streaming of fields to their ultimate destination. This ordering and other reasons, such as ensuring cache correctness, mean that an endpoint might need to buffer the entire field block. Since there is no hard limit to the size of a field block, some endpoints could be forced to commit a large amount of available memory for field blocks.


An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to advise peers of limits that might apply on the size of uncompressed field blocks. This setting is only advisory, so endpoints MAY choose to send field blocks that exceed this limit and risk the request or response being treated as malformed. This setting is specific to a connection, so any request or response could encounter a hop with a lower, unknown limit. An intermediary can attempt to avoid this problem by passing on values presented by different peers, but they are not obliged to do so.


A server that receives a larger field block than it is willing to handle can send an HTTP 431 (Request Header Fields Too Large) status code [RFC6585]. A client can discard responses that it cannot process. The field block MUST be processed to ensure a consistent connection state, unless the connection is closed.

処理するよりも大きなフィールドブロックを受信するサーバーは、HTTP 431(リクエストヘッダーフィールドが大きすぎる)ステータスコード[RFC6585]を送信できます。クライアントは、処理できない応答を破棄できます。接続が閉じられない限り、一貫した接続状態を確保するために、フィールドブロックを処理する必要があります。

10.5.2. CONNECT Issues
10.5.2. 問題を接続します

The CONNECT method can be used to create disproportionate load on a proxy, since stream creation is relatively inexpensive when compared to the creation and maintenance of a TCP connection. A proxy might also maintain some resources for a TCP connection beyond the closing of the stream that carries the CONNECT request, since the outgoing TCP connection remains in the TIME_WAIT state. Therefore, a proxy cannot rely on SETTINGS_MAX_CONCURRENT_STREAMS alone to limit the resources consumed by CONNECT requests.

Connectメソッドは、TCP接続の作成とメンテナンスと比較するとストリームの作成が比較的安価であるため、プロキシに不均衡な負荷を作成するために使用できます。Proxyは、発信TCP接続がTime_Wait状態に残っているため、Connect Requestを運ぶストリームの閉鎖を超えてTCP接続のリソースを維持する場合があります。したがって、プロキシはsettings_max_concurrent_streamsだけに依存して、接続要求によって消費されるリソースを制限することはできません。

10.6. Use of Compression
10.6. 圧縮の使用

Compression can allow an attacker to recover secret data when it is compressed in the same context as data under attacker control. HTTP/2 enables compression of field lines (Section 4.3); the following concerns also apply to the use of HTTP compressed content-codings (Section 8.4.1 of [HTTP]).


There are demonstrable attacks on compression that exploit the characteristics of the Web (e.g., [BREACH]). The attacker induces multiple requests containing varying plaintext, observing the length of the resulting ciphertext in each, which reveals a shorter length when a guess about the secret is correct.


Implementations communicating on a secure channel MUST NOT compress content that includes both confidential and attacker-controlled data unless separate compression dictionaries are used for each source of data. Compression MUST NOT be used if the source of data cannot be reliably determined. Generic stream compression, such as that provided by TLS, MUST NOT be used with HTTP/2 (see Section 9.2).


Further considerations regarding the compression of header fields are described in [COMPRESSION].


10.7. Use of Padding
10.7. パディングの使用

Padding within HTTP/2 is not intended as a replacement for general purpose padding, such as that provided by TLS [TLS13]. Redundant padding could even be counterproductive. Correct application can depend on having specific knowledge of the data that is being padded.

HTTP/2内のパディングは、TLS [TLS13]によって提供されるような、汎用パディングの代替として意図されていません。冗長なパディングは逆効果になる可能性があります。正しいアプリケーションは、パッドで塗られているデータの特定の知識を持つことに依存します。

To mitigate attacks that rely on compression, disabling or limiting compression might be preferable to padding as a countermeasure.


Padding can be used to obscure the exact size of frame content and is provided to mitigate specific attacks within HTTP -- for example, attacks where compressed content includes both attacker-controlled plaintext and secret data (e.g., [BREACH]).


Use of padding can result in less protection than might seem immediately obvious. At best, padding only makes it more difficult for an attacker to infer length information by increasing the number of frames an attacker has to observe. Incorrectly implemented padding schemes can be easily defeated. In particular, randomized padding with a predictable distribution provides very little protection; similarly, padding frame payloads to a fixed size exposes information as frame payload sizes cross the fixed-sized boundary, which could be possible if an attacker can control plaintext.


Intermediaries SHOULD retain padding for DATA frames but MAY drop padding for HEADERS and PUSH_PROMISE frames. A valid reason for an intermediary to change the amount of padding of frames is to improve the protections that padding provides.


10.8. Privacy Considerations
10.8. プライバシーに関する考慮事項

Several characteristics of HTTP/2 provide an observer an opportunity to correlate actions of a single client or server over time. These include the values of settings, the manner in which flow-control windows are managed, the way priorities are allocated to streams, the timing of reactions to stimulus, and the handling of any features that are controlled by settings.


As far as these create observable differences in behavior, they could be used as a basis for fingerprinting a specific client, as defined in Section 3.2 of [PRIVACY].


HTTP/2's preference for using a single TCP connection allows correlation of a user's activity on a site. Reusing connections for different origins allows tracking across those origins.


Because the PING and SETTINGS frames solicit immediate responses, they can be used by an endpoint to measure latency to their peer. This might have privacy implications in certain scenarios.


10.9. Remote Timing Attacks
10.9. リモートタイミング攻撃

Remote timing attacks extract secrets from servers by observing variations in the time that servers take when processing requests that use secrets. HTTP/2 enables concurrent request creation and processing, which can give attackers better control over when request processing commences. Multiple HTTP/2 requests can be included in the same IP packet or TLS record. HTTP/2 can therefore make remote timing attacks more efficient by eliminating variability in request delivery, leaving only request order and the delivery of responses as sources of timing variability.


Ensuring that processing time is not dependent on the value of a secret is the best defense against any form of timing attack.


11. IANA Considerations
11. IANAの考慮事項

This revision of HTTP/2 marks the HTTP2-Settings header field and the h2c upgrade token, both defined in [RFC7540], as obsolete.


Section 11 of [RFC7540] registered the h2 and h2c ALPN identifiers along with the PRI HTTP method. RFC 7540 also established a registry for frame types, settings, and error codes. These registrations and registries apply to HTTP/2, but are not redefined in this document.

[RFC7540]のセクション11では、PRI HTTPメソッドとともにH2およびH2C ALPN識別子を登録しました。RFC 7540は、フレームタイプ、設定、エラーコードのレジストリも確立しました。これらの登録と登録はHTTP/2に適用されますが、このドキュメントでは再定義されていません。

IANA has updated references to RFC 7540 in the following registries to refer to this document: "TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs", "HTTP/2 Frame Type", "HTTP/2 Settings", "HTTP/2 Error Code", and "HTTP Method Registry". The registration of the PRI method has been updated to refer to Section 3.4; all other section numbers have not changed.

IANAは、次のレジストリでRFC 7540への参照を更新して、このドキュメントを参照しています:「TLSアプリケーションレイヤープロトコル交渉(ALPN)プロトコルID」、「HTTP/2フレームタイプ」、「HTTP/2設定」、「HTTP/2設定」エラーコード "、および「httpメソッドレジストリ」。PRIメソッドの登録は、セクション3.4を参照するように更新されました。他のすべてのセクション番号は変更されていません。

IANA has changed the policy on those portions of the "HTTP/2 Frame Type" and "HTTP/2 Settings" registries that were reserved for Experimental Use in RFC 7540. These portions of the registries shall operate on the same policy as the remainder of each registry.

IANAは、RFC 7540で実験的に使用するために予約されていた「HTTP/2フレームタイプ」および「HTTP/2設定」レジストリの部分に関するポリシーを変更しました。レジストリのこれらの部分は、残りのポリシーと同じポリシーで動作するものとします。各レジストリ。

11.1. HTTP2-Settings Header Field Registration
11.1. HTTP2-Settingsヘッダーフィールド登録

This section marks the HTTP2-Settings header field registered by Section 11.5 of [RFC7540] in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" as obsolete. This capability has been removed: see Section 3.1. The registration is updated to include the details as required by Section 18.4 of [HTTP]:

このセクションでは、[RFC7540]のセクション11.5で登録されたHTTP2-Settingsヘッダーフィールドを、「HyperText Transfer Protocol(HTTP)フィールド名レジストリ」で時代遅れとしてマークします。この機能は削除されました。セクション3.1を参照してください。登録は更新され、[http]のセクション18.4で必要な詳細が含まれています。

Field Name: HTTP2-Settings


Status: obsoleted


Reference: Section 3.2.1 of [RFC7540]


Comments: Obsolete; see Section 11.1 of this document.


11.2. The h2c Upgrade Token
11.2. H2Cアップグレードトークン

This section records the h2c upgrade token registered by Section 11.8 of [RFC7540] in the "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry" as obsolete. This capability has been removed: see Section 3.1. The registration is updated as follows:

このセクションでは、[RFC7540]のセクション11.8で登録されたH2Cアップグレードトークンを「HyperText Transfer Protocol(HTTP)アップグレードトークンレジストリ」に記録します。この機能は削除されました。セクション3.1を参照してください。登録は次のように更新されます。

Value: h2c


Description: (OBSOLETE) Hypertext Transfer Protocol version 2 (HTTP/2)


Expected Version Tokens: None


Reference: Section 3.1 of this document


12. References
12. 参考文献
12.1. Normative References
12.1. 引用文献

[CACHING] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Caching", STD 98, RFC 9111, DOI 10.17487/RFC9111, June 2022, <>.

[キャッシュ]フィールディング、R。、編、ノッティンガム、M.、編、J。レスケ、編、「HTTPキャッシュ」、STD 98、RFC 9111、DOI 10.17487/RFC9111、2022年6月、<>。

[COMPRESSION] Peon, R. and H. Ruellan, "HPACK: Header Compression for HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, <>.

[圧縮] Peon、R。およびH. Ruellan、 "HPack:HTTP/2のヘッダー圧縮、RFC 7541、DOI 10.17487/RFC7541、2015年5月<>。

[COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265, DOI 10.17487/RFC6265, April 2011, <>.

[Cookie] Barth、A。、「HTTP状態管理メカニズム」、RFC 6265、DOI 10.17487/RFC6265、2011年4月、<>。

[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, <>.

[HTTP] Fielding、R.、Ed。、Nottingham、M.、Ed。、およびJ. Reschke、ed。、 "HTTP Semantics"、Std 97、RFC 9110、DOI 10.17487/RFC9110、2022年6月、<>。

[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, <>.

[Quic] Iyengar、J.、ed。and M. Thomson、ed。、「Quic:UDPベースの多重化および安全な輸送」、RFC 9000、DOI 10.17487/RFC9000、2021年5月、<>

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <>.

[RFC2119] Bradner、S。、「要件レベルを示すためにRFCで使用するためのキーワード」、BCP 14、RFC 2119、DOI 10.17487/RFC2119、1997年3月、<>。

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <>.

[RFC3986] Berners-Lee、T.、Fielding、R。、およびL. Masinter、「Uniform Resource Identifier(URI):Generic Syntax」、Std 66、RFC 3986、DOI 10.17487/RFC3986、2005年1月、<>。

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <>.

[RFC8174] Leiba、B。、「RFC 2119キーワードの大文字と小文字のあいまいさ」、BCP 14、RFC 8174、DOI 10.17487/RFC8174、2017年5月、<>。

[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS) Versions 1.2 and Earlier", RFC 8422, DOI 10.17487/RFC8422, August 2018, <>.

[RFC8422] Nir、Y.、Josefsson、S。、およびM. Pegourie-Gonnard、「輸送層セキュリティ(TLS)バージョン(TLS)バージョン用の楕円曲線暗号化(ECC)暗号スイート」、RFC 8422、DOI 10.17487/RFC8422、2018年8月、<>。

[RFC8470] Thomson, M., Nottingham, M., and W. Tarreau, "Using Early Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September 2018, <>.

[RFC8470] Thomson、M.、Nottingham、M.、およびW. Tarreau、「HTTPで初期データを使用」、RFC 8470、DOI 10.17487/RFC8470、2018年9月、<情報/RFC8470>。

[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <>.

[TCP] Postel、J。、「伝送制御プロトコル」、STD 7、RFC 793、DOI 10.17487/RFC0793、1981年9月、<>。

[TLS-ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, July 2014, <>.

[TLS-Alpn] Friedl、S.、Popov、A.、Langley、A。、およびE. Stephan、「輸送層セキュリティ(TLS)アプリケーション層プロトコル交渉拡張」、RFC 7301、DOI 10.17487/RFC7301、2014年7月、<>。

[TLS-ECDHE] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-256/384 and AES Galois Counter Mode (GCM)", RFC 5289, DOI 10.17487/RFC5289, August 2008, <>.

[TLS-Ecdhe] Rescorla、E。、「SHA-256/384およびAES Galoisカウンターモード(GCM)を備えたTLS楕円曲線暗号」、RFC 5289、DOI 10.17487/RFC5289、2008年8月、<HTTPS:// WWW。>。

[TLS-EXT] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, <>.

[TLS-Ext] EastLake 3rd、D。、「輸送層セキュリティ(TLS)拡張:拡張定義」、RFC 6066、DOI 10.17487/RFC6066、2011年1月、<>。

[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <>.

[TLS12] Dierks、T。およびE. Rescorla、「The Transport Layer Security(TLS)プロトコルバージョン1.2」、RFC 5246、DOI 10.17487/RFC5246、2008年8月、<>。

[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <>.

[TLS13] Rescorla、E。、「輸送層セキュリティ(TLS)プロトコルバージョン1.3」、RFC 8446、DOI 10.17487/RFC8446、2018年8月、<>

[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <>.

[TLSBCP] Sheffer、Y.、Holz、R。、およびP. Saint-Andre、「輸送層セキュリティ(TLS)およびデータグラム輸送層セキュリティ(DTLS)の安全な使用に関する推奨事項」、BCP 195、RFC 7525、DOI 10.17487/RFC7525、2015年5月、<>。

12.2. Informative References
12.2. 参考引用

[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP Alternative Services", RFC 7838, DOI 10.17487/RFC7838, April 2016, <>.

[Alt-Svc] Nottingham、M.、McManus、P。、およびJ. Reschke、「HTTP代替サービス」、RFC 7838、DOI 10.17487/RFC7838、2016年4月、<情報/RFC7838>。

[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the CRIME Attack", 12 July 2013, < BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.

[違反] Gluck、Y.、Harris、N.、A。Prado、「違反:犯罪攻撃の復活」、2013年7月12日、< Breach%20-%20SSL、%20gone%20in%2030%20seconds.pdf>。

[DNS-TERMS] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, <>.

[DNS-TERMS] Hoffman、P.、Sullivan、A。、およびK. Fujiwara、「DNS用語」、BCP 219、RFC 8499、DOI 10.17487/RFC8499、2019年1月、<https://www.rfc-editor。org/info/rfc8499>。

[HTTP-PRIORITY] Oku, K. and L. Pardue, "Extensible Prioritization Scheme for HTTP", RFC 9218, DOI 10.17487/RFC9218, June 2022, <>.

[HTTP優先性] Oku、K。およびL. Pardue、「HTTPの拡張可能な優先順位付けスキーム」、RFC 9218、DOI 10.17487/RFC9218、2022年6月、<>。

[HTTP/1.1] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112, June 2022, <>.

[HTTP/1.1] Fielding、R.、ed。、Nottingham、M.、ed。、およびJ. Reschke、ed。、 "Http/1.1"、Std 99、RFC 9112、DOI 10.17487/RFC9112、2022年6月、<<>。

[NFLX-2019-002] Netflix, "HTTP/2 Denial of Service Advisory", 13 August 2019, <>.

[NFLX-2019-002] Netflix、「HTTP/2サービスアドバイザリー拒否」、2019年8月13日、<>。

[PRIVACY] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013, <>.

[プライバシー] Cooper、A.、Tschofenig、H.、Aboba、B.、Peterson、J.、Morris、J.、Hansen、M。、およびR. Smith、「インターネットプロトコルのプライバシーに関する考慮事項」、RFC 6973、doi10.17487/rfc6973、2013年7月、<>。

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, <>.

[RFC1122] Braden、R.、ed。、「インターネットホストの要件 - 通信レイヤー」、STD 3、RFC 1122、DOI 10.17487/RFC1122、1989年10月、<>。

[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol Compression Methods", RFC 3749, DOI 10.17487/RFC3749, May 2004, <>.

[RFC3749] Hollenbeck、S。、「輸送層セキュリティプロトコル圧縮法」、RFC 3749、DOI 10.17487/RFC3749、2004年5月、<>

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 2011, <>.

[RFC6125] Saint-Andre、P。およびJ. Hodges、「輸送層のセキュリティ(TLS)のコンテキストでX.509(PKIX)証明書を使用したインターネット公開キーインフラストラクチャ内のドメインベースのアプリケーションサービスIDの表現と検証」、RFC 6125、DOI 10.17487/RFC6125、2011年3月、<>。

[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, <>.

[RFC6585]ノッティンガム、M。およびR.フィールディング、「追加のHTTPステータスコード」、RFC 6585、DOI 10.17487/RFC6585、2012年4月、<>

[RFC7323] Borman, D., Braden, B., Jacobson, V., and R. Scheffenegger, Ed., "TCP Extensions for High Performance", RFC 7323, DOI 10.17487/RFC7323, September 2014, <>.

[RFC7323] Borman、D.、Braden、B.、Jacobson、V.、およびR. Scheffenegger、ed。、「TCP拡張機能のためのTCP拡張」、RFC 7323、DOI 10.17487/RFC7323、2014年9月、<https://///////>。

[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, <>.

[RFC7540] Belshe、M.、Peon、R。、およびM. Thomson、ed。、「HyperText Transfer Protocolバージョン2(HTTP/2)」、RFC 7540、DOI 10.17487/RFC7540、2015年5月、<https:///>。

[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2", RFC 8441, DOI 10.17487/RFC8441, September 2018, <>.

[RFC8441] McManus、P。、 "HTTP/2でWebStrappetsをブートストラップするWebSocket、RFC 8441、DOI 10.17487/RFC8441、2018年9月、<>。

[RFC8740] Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740, DOI 10.17487/RFC8740, February 2020, <>.

[RFC8740]ベンジャミン、D。、「HTTP/2でTLS 1.3を使用して」、RFC 8740、DOI 10.17487/RFC8740、2020年2月、<>

[TALKING] Huang, L., Chen, E., Barth, A., Rescorla, E., and C. Jackson, "Talking to Yourself for Fun and Profit", 2011, <>.

[話す] Huang、L.、Chen、E.、Barth、A.、Rescorla、E.、およびC. Jackson、「楽しみと利益のために自分自身に話しかける」、2011年、<>。

Appendix A. Prohibited TLS 1.2 Cipher Suites
付録A. TLS 1.2暗号スイートを禁止しました

An HTTP/2 implementation MAY treat the negotiation of any of the following cipher suites with TLS 1.2 as a connection error (Section 5.4.1) of type INADEQUATE_SECURITY:

HTTP/2の実装は、次の暗号スイートのいずれかの交渉を、TLS 1.2との交渉を、型の不自由な_securityの接続エラー(セクション5.4.1)として扱う可能性があります。



Note: This list was assembled from the set of registered TLS cipher suites when [RFC7540] was developed. This list includes those cipher suites that do not offer an ephemeral key exchange and those that are based on the TLS null, stream, or block cipher type (as defined in Section 6.2.3 of [TLS12]). Additional cipher suites with these properties could be defined; these would not be explicitly prohibited.


For more details, see Section 9.2.2.


Appendix B. Changes from RFC 7540
付録B. RFC 7540からの変更

This revision includes the following substantive changes:


* Use of TLS 1.3 was defined based on [RFC8740], which this document obsoletes.

* TLS 1.3の使用は、[RFC8740]に基づいて定義されました。この文書は廃止されました。

* The priority scheme defined in RFC 7540 is deprecated. Definitions for the format of the PRIORITY frame and the priority fields in the HEADERS frame have been retained, plus the rules governing when PRIORITY frames can be sent and received, but the semantics of these fields are only described in RFC 7540. The priority signaling scheme from RFC 7540 was not successful. Using the simpler signaling in [HTTP-PRIORITY] is recommended.

* RFC 7540で定義されている優先スキームは非推奨です。優先順位フレームの形式とヘッダーフレームの優先フィールドの定義が保持されています。さらに、優先順位フレームを送信および受信できる場合に管理する規則がありますが、これらのフィールドのセマンティクスはRFC 7540でのみ説明されています。RFCから7540は成功しませんでした。[http-priority]でより単純なシグナル伝達を使用することをお勧めします。

* The HTTP/1.1 Upgrade mechanism is deprecated and no longer specified in this document. It was never widely deployed, with plaintext HTTP/2 users choosing to use the prior-knowledge implementation instead.

* HTTP/1.1アップグレードメカニズムは非推奨であり、このドキュメントでは指定されなくなりました。プレーンテキストHTTP/2ユーザーが代わりに事前知識実装を使用することを選択しているため、広く展開されることはありませんでした。

* Validation for field names and values has been narrowed. The validation that is mandatory for intermediaries is precisely defined, and error reporting for requests has been amended to encourage sending 400-series status codes.

* フィールド名と値の検証は狭くなっています。仲介者に必須の検証は正確に定義されており、リクエストのエラーレポートが修正され、400シリーズのステータスコードの送信が促進されました。

* The ranges of codepoints for settings and frame types that were reserved for Experimental Use are now available for general use.

* 実験的に使用するために予約されていた設定とフレームタイプのコードポイントの範囲が一般的に使用できるようになりました。

* Connection-specific header fields -- which are prohibited -- are more precisely and comprehensively identified.

* 禁止されている接続固有のヘッダーフィールドは、より正確かつ包括的に識別されます。

* Host and ":authority" are no longer permitted to disagree.

* ホストと「:権威」は、もはや同意しないことは許可されていません。

* Rules for sending Dynamic Table Size Update instructions after changes in settings have been clarified in Section 4.3.1.

* 設定の変更後の動的テーブルサイズの更新手順を送信するためのルールは、セクション4.3.1で明確にされています。

Editorial changes are also included. In particular, changes to terminology and document structure are in response to updates to core HTTP semantics [HTTP]. Those documents now include some concepts that were first defined in RFC 7540, such as the 421 status code or connection coalescing.

編集上の変更も含まれています。特に、用語とドキュメント構造の変更は、Core HTTPセマンティクス[HTTP]の更新に応じています。これらのドキュメントには、421ステータスコードや接続合体など、RFC 7540で最初に定義されたいくつかの概念が含まれています。



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 the years. [RFC7540] contains a more extensive list of people that deserve acknowledgment for their contributions.




Mike Belshe and Roberto Peon authored the text that this document is based on.

Mike BelsheとRoberto Peonは、このドキュメントが基づいているテキストを作成しました。

Authors' Addresses


Martin Thomson (editor) Mozilla Australia Email:

Martin Thomson(編集者)Mozilla Australiaメール

Cory Benfield (editor) Apple Inc. Email:

Cory Benfield(Editor)Apple Inc.メール