このドキュメントは、RFC2616を翻訳したものです。 参考訳ですので、標準としての効力はありません。 RFCとしての詳細は原文を参照してください。 その他制限等は、原文に準じるものとします。 最新版は http://siisise.net/ にて公開します。 Yuuichirou Oka (oka @ csce.kyushu-u.ac.jp)さんのRFC 2068の訳を含んでいます。 ご意見・ご感想等ありましたら、佐藤 雅俊 okome at siisise.net までお願いします。 Network Working Group R. Fielding リクエスト for Comments: 2616 UC Irvine Obsoletes: 2068 J. Gettys Category: Standards Track Compaq/W3C J. Mogul Compaq H. Frystyk W3C/MIT L. Masinter Xerox P. Leach Microsoft T. Berners-Lee W3C/MIT 1999年6月 Hypertext Transfer Protocol -- HTTP/1.1 このメモの状況(Status of this Memo) This document specifies an Internet standards track protocol for the Internet community, and リクエストs discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. このドキュメントは、インターネット共同社会においてのインターネット標準 プロトコルを規定し、改善のための議論や提案を求めるものです。"インターネッ ト・オフィシャル・プロトコル標準" (STD 1)の最新版を参照して、このプロトコ ルの標準の状態や状況を確認するようにしてください。このメモの再配布は制限 しません。 著作権表示(Copyright Notice) Copyright (C) The Internet Society (1999). All Rights Reserved. 概要(Abstract) Hypertext Transfer Protocol (HTTP) は、分散化して協調したハイパーメディア 情報システムのためのアプリケーション層プロトコルです。それは、共通の無国籍( データに依存しない)プロトコルであり、要求メソッド、エラーコードやヘッダを拡 張することで、ネームサーバや分散オブジェクト管理システムのようなハイパーテキ スト以外の多くの処理にも使うことができます[47]。HTTPの機能/特徴は、システム に依存せず、独立してデータ転送するための、データ表現の分類と取り決めです。 HTTPは、World-Wide Web グローバル情報イニシアティブにより1990年から使われて います。この仕様書は、"HTTP/1.1"として参照されるプロトコルについて規定し、 RFC 2068 [33] から更新されました。 Fielding, et al. Standards Track [Page 1] RFC 2616 HTTP/1.1 1999年6月 Table of Contents 1 はじめに .......................................................7 1.1 目的 .........................................................7 1.2 Requirements .................................................8 1.3 Terminology ..................................................8 1.4 Overall Operation ...........................................12 2 Notational Conventions and Generic Grammar ....................14 2.1 Augmented BNF ...............................................14 2.2 基本ルール ..................................................15 3 プロトコル・パラメータ ........................................17 3.1 HTTP Version ................................................17 3.2 Uniform Resource Identifiers ................................18 3.2.1 General Syntax ...........................................19 3.2.2 http URL .................................................19 3.2.3 URI Comparison ...........................................20 3.3 Date/Time Formats ...........................................20 3.3.1 Full Date ................................................20 3.3.2 Delta Seconds ............................................21 3.4 Character Sets ..............................................21 3.4.1 Missing Charset ..........................................22 3.5 Content Codings .............................................23 3.6 Transfer Codings ............................................24 3.6.1 Chunked Transfer Coding ..................................25 3.7 Media Types .................................................26 3.7.1 Canonicalization and Text Defaults .......................27 3.7.2 Multipart Types ..........................................27 3.8 Product Tokens ..............................................28 3.9 Quality Values ..............................................29 3.10 Language Tags ...............................................29 3.11 Entity Tags .................................................30 3.12 Range Units .................................................30 4 HTTP メッセージ ...............................................31 4.1 メッセージ タイプ ...........................................31 4.2 メッセージ ヘッダ ...........................................31 4.3 メッセージ ボディ ...........................................32 4.4 メッセージ長 ................................................33 4.5 General ヘッダ フィールドs .......................................34 5 リクエスト .......................................................35 5.1 リクエスト-Line ................................................35 5.1.1 Method ...................................................36 5.1.2 リクエスト-URI ..............................................36 5.2 The Resource Identified by a リクエスト ........................38 5.3 リクエスト ヘッダ フィールドs .......................................38 6 レスポンス ......................................................39 6.1 Status-Line .................................................39 6.1.1 ステータス コード and Reason Phrase ............................39 6.2 レスポンス ヘッダ フィールドs ......................................41 Fielding, et al. Standards Track [Page 2] RFC 2616 HTTP/1.1 1999年6月 7 Entity ........................................................42 7.1 Entity ヘッダ フィールドs ........................................42 7.2 Entity Body .................................................43 7.2.1 Type .....................................................43 7.2.2 Entity Length ............................................43 8 Connections ...................................................44 8.1 Persistent Connections ......................................44 8.1.1 Purpose ..................................................44 8.1.2 Overall Operation ........................................45 8.1.3 プロキシ(proxy) Servers ............................................46 8.1.4 Practical Considerations .................................46 8.2 Message Transmission Requirements ...........................47 8.2.1 Persistent Connections and Flow Control ..................47 8.2.2 Monitoring Connections for Error Status Messages .........48 8.2.3 Use of the 100 (Continue) Status .........................48 8.2.4 Client Behavior if Server Prematurely Closes Connection ..50 9 Method Definitions ............................................51 9.1 Safe and Idempotent Methods .................................51 9.1.1 Safe Methods .............................................51 9.1.2 Idempotent Methods .......................................51 9.2 OPTIONS .....................................................52 9.3 GET .........................................................53 9.4 HEAD ........................................................54 9.5 POST ........................................................54 9.6 PUT .........................................................55 9.7 DELETE ......................................................56 9.8 TRACE .......................................................56 9.9 CONNECT .....................................................57 10 ステータス コード Definitions ......................................57 10.1 Informational 1xx ...........................................57 10.1.1 100 Continue .............................................58 10.1.2 101 Switching Protocols ..................................58 10.2 成功 2xx ....................................................58 10.2.1 200 OK ...................................................58 10.2.2 201 Created ..............................................59 10.2.3 202 Accepted .............................................59 10.2.4 203 Non-Authoritative Information ........................59 10.2.5 204 No Content ...........................................60 10.2.6 205 Reset Content ........................................60 10.2.7 206 Partial Content ......................................60 10.3 リダイレクション 3xx ........................................61 10.3.1 300 Multiple Choices .....................................61 10.3.2 301 Moved Permanently ....................................62 10.3.3 302 Found ................................................62 10.3.4 303 See Other ............................................63 10.3.5 304 Not Modified .........................................63 10.3.6 305 Use プロキシ .........................................64 10.3.7 306 (Unused) .............................................64 Fielding, et al. Standards Track [Page 3] RFC 2616 HTTP/1.1 1999年6月 10.3.8 307 Temporary Redirect ...................................65 10.4 クライアントエラー 4xx ......................................65 10.4.1 400 Bad リクエスト .........................................65 10.4.2 401 Unauthorized ........................................66 10.4.3 402 Payment Required ....................................66 10.4.4 403 Forbidden ...........................................66 10.4.5 404 Not Found ...........................................66 10.4.6 405 Method Not Allowed ..................................66 10.4.7 406 Not Acceptable ......................................67 10.4.8 407 プロキシ(proxy) 認証 Required .......................67 10.4.9 408 リクエスト Timeout .....................................67 10.4.10 409 Conflict ............................................67 10.4.11 410 Gone ................................................68 10.4.12 411 Length Required .....................................68 10.4.13 412 Precondition Failed .................................68 10.4.14 413 リクエスト Entity Too Large ............................69 10.4.15 414 リクエスト-URI Too Long ................................69 10.4.16 415 Unsupported Media Type ..............................69 10.4.17 416 リクエストed Range Not Satisfiable .....................69 10.4.18 417 Expectation Failed ..................................70 10.5 サーバー エラー 5xx .........................................70 10.5.1 500 Internal Server Error ................................70 10.5.2 501 Not Implemented ......................................70 10.5.3 502 Bad ゲートウェイ ..........................................70 10.5.4 503 Service Unavailable ..................................70 10.5.5 504 ゲートウェイ Timeout ......................................71 10.5.6 505 HTTP Version Not Supported ...........................71 11 アクセス認証 .................................................71 12 Content ネゴシエーション(交渉) ...............................71 12.1 Server-driven ネゴシエーション ..............................72 12.2 Agent-driven ネゴシエーション ...............................73 12.3 透過ネゴシエーション(Transparent Negotiation) ...............74 13 Caching in HTTP ..............................................74 13.1.1 Cache Correctness ........................................75 13.1.2 警告(Warnings) ...........................................76 13.1.3 キャッシュコントロール機構 ...............................77 13.1.4 Explicit ユーザエージェント警告 ..........................78 13.1.5 Exceptions to the Rules and Warnings .....................78 13.1.6 Client-controlled Behavior ...............................79 13.2 Expiration Model ............................................79 13.2.1 Server-Specified Expiration ..............................79 13.2.2 Heuristic Expiration .....................................80 13.2.3 Age Calculations .........................................80 13.2.4 Expiration Calculations ..................................83 13.2.5 Disambiguating Expiration Values .........................84 13.2.6 Disambiguating Multiple レスポンスs ........................84 13.3 Validation Model ............................................85 13.3.1 Last-Modified Dates ......................................86 Fielding, et al. Standards Track [Page 4] RFC 2616 HTTP/1.1 1999年6月 13.3.2 Entity Tag Cache Validators ..............................86 13.3.3 Weak and Strong Validators ...............................86 13.3.4 Rules for When to Use Entity Tags and Last-Modified Dates.89 13.3.5 Non-validating Conditionals ..............................90 13.4 レスポンス Cacheability .......................................91 13.5 Constructing レスポンスs From Caches ..........................92 13.5.1 End-to-end and Hop-by-hop Headers ........................92 13.5.2 Non-modifiable Headers ...................................92 13.5.3 Combining Headers ........................................94 13.5.4 Combining Byte Ranges ....................................95 13.6 Caching Negotiated レスポンスs ................................95 13.7 Shared and Non-Shared Caches ................................96 13.8 Errors or Incomplete レスポンス Cache Behavior ................97 13.9 Side Effects of GET and HEAD ................................97 13.10 Invalidation After Updates or Deletions ...................97 13.11 Write-Through Mandatory ...................................98 13.12 Cache Replacement .........................................99 13.13 History Lists .............................................99 14 ヘッダ フィールド Definitions ....................................100 14.1 Accept .....................................................100 14.2 Accept-Charset .............................................102 14.3 Accept-Encoding ............................................102 14.4 Accept-Language ............................................104 14.5 Accept-Ranges ..............................................105 14.6 Age ........................................................106 14.7 Allow ......................................................106 14.8 Authorization ..............................................107 14.9 Cache-Control ..............................................108 14.9.1 What is Cacheable .......................................109 14.9.2 What May be Stored by Caches ............................110 14.9.3 Modifications of the Basic Expiration Mechanism .........111 14.9.4 Cache Revalidation and Reload Controls ..................113 14.9.5 No-Transform Directive ..................................115 14.9.6 Cache Control Extensions ................................116 14.10 Connection ...............................................117 14.11 Content-Encoding .........................................118 14.12 Content-Language .........................................118 14.13 Content-Length ...........................................119 14.14 Content-Location .........................................120 14.15 Content-MD5 ..............................................121 14.16 Content-Range ............................................122 14.17 Content-Type .............................................124 14.18 Date .....................................................124 14.18.1 Clockless 元のサーバ Operation ......................125 14.19 ETag .....................................................126 14.20 Expect ...................................................126 14.21 Expires ..................................................127 14.22 From .....................................................128 Fielding, et al. Standards Track [Page 5] RFC 2616 HTTP/1.1 1999年6月 14.23 Host .....................................................128 14.24 If-Match .................................................129 14.25 If-Modified-Since ........................................130 14.26 If-None-Match ............................................132 14.27 If-Range .................................................133 14.28 If-Unmodified-Since ......................................134 14.29 Last-Modified ............................................134 14.30 Location .................................................135 14.31 Max-Forwards .............................................136 14.32 Pragma ...................................................136 14.33 Proxy-Authenticate .......................................137 14.34 Proxy-Authorization ......................................137 14.35 Range ....................................................138 14.35.1 Byte Ranges ...........................................138 14.35.2 Range Retrieval リクエストs ..............................139 14.36 Referer ..................................................140 14.37 Retry-After ..............................................141 14.38 Server ...................................................141 14.39 TE .......................................................142 14.40 Trailer ..................................................143 14.41 Transfer-Encoding..........................................143 14.42 Upgrade ..................................................144 14.43 User-Agent ...............................................145 14.44 Vary .....................................................145 14.45 Via ......................................................146 14.46 Warning ..................................................148 14.47 WWW-Authenticate .........................................150 15 Security Considerations .......................................150 15.1 Personal Information....................................151 15.1.1 Abuse of Server Log Information .........................151 15.1.2 Transfer of Sensitive Information .......................151 15.1.3 Encoding Sensitive Information in URI's .................152 15.1.4 Privacy Issues Connected to Accept Headers ..............152 15.2 Attacks Based On File and Path Names .......................153 15.3 DNS Spoofing ...............................................154 15.4 Location Headers and Spoofing ..............................154 15.5 Content-Disposition Issues .................................154 15.6 認証 Credentials and Idle Clients ..........................155 15.7 プロキシ and Caching ........................................155 15.7.1 Denial of Service Attacks on プロキシ....................156 16 謝辞(Acknowledgments) .......................................156 17 参考文献(References) ........................................158 18 著者アドレス(Authors' Addresses) ............................162 19 付録(Appendices) ............................................164 19.1 Internet Media Type message/http and アプリケーション/http .164 19.2 Internet Media Type multipart/byteranges ...................165 19.3 Tolerant アプリケーションs .................................166 19.4 Differences Between HTTP Entities and RFC 2045 Entities ....167 Fielding, et al. Standards Track [Page 6] RFC 2616 HTTP/1.1 1999年6月 19.4.1 MIME-Version ............................................167 19.4.2 Conversion to Canonical Form ............................167 19.4.3 Conversion of Date Formats ..............................168 19.4.4 Introduction of Content-Encoding ........................168 19.4.5 No Content-Transfer-Encoding ............................168 19.4.6 Introduction of Transfer-Encoding .......................169 19.4.7 MHTML and Line Length Limitations .......................169 19.5 Additional Features ........................................169 19.5.1 Content-Disposition .....................................170 19.6 Compatibility with Previous Versions .......................170 19.6.1 Changes from HTTP/1.0 ...................................171 19.6.2 Compatibility with HTTP/1.0 Persistent Connections ......172 19.6.3 Changes from RFC 2068 ...................................172 20 Index .......................................................175 21 Full Copyright Statement ....................................176 1 はじめに(Introduction) 1.1 目的(Purpose) Hypertext Transfer Protocol (HTTP) は、分散化して協調動作するハイパー メディア情報システムのためのアプリケーション層プロトコルです。HTTPは、 World-Wide Web グローバル情報イニシアティブにより、1990年から使われていま す。最初のバージョンのHTTP(HTTP/0.9参照)は、インターネット上で生のデータ を転送するための簡単なプロトコルでした。RFC 1945 [6] で定義された HTTP/1.0は、要求/応答にデータ転送と修正者のメタ情報を含むMIMEライクなメッ セージのフォーマットを支給し、改良したプロトコルです。(再訳必要)しかしな がら、HTTP/1.0は、階層プロキシ、キャッシング、継続接続の必要性、または仮 想ホストの効果に充分に考慮されていなかった。加えて、"HTTP/1.0"対応だと言 っている不完全な実装をしたアプリケーションの増加は、2つの通信アプリケーシ ョンの能力の違いを正しく規定するためにプロトコルバージョンの変更を必要とさ せた。 この仕様書は、"HTTP/1.1"として参照されるプロトコルを定義する。 このプロトコルには、含まれている。 includes more stringent requirements than HTTP/1.0 in order to ensure 信頼できる実装 of its features. Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation. HTTP allows an open-ended set of methods and headers that indicate the purpose of a リクエスト [47]. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) [3], as a location (URL) [4] or name (URN) [20], for indicating the resource to which a Fielding, et al. Standards Track [Page 7] RFC 2616 HTTP/1.1 1999年6月 method is to be applied. Messages are passed in a format similar to that used by Internet mail [9] as defined by the 多目的インターネット・メール拡張 (MIME) [7]. HTTP is also used as a 共通のプロトコル for コミュニケーション between ユーザエージェント and プロキシ/ゲートウェイ to other Internet システム, including those supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2], and WAIS [10] protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse アプリケーションs. 1.2 条件 (Requirements) このドキュメントで使われるキーワード MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, と OPTIONAL は、RFC 2119 [34]で説明されている. 実装がプロトコルの MUST または REQUIRED レベルの要求条件を一つでも満た していないなら、その実装は、プロトコルに準拠していない. An 実装 that satisfies all the MUST or REQUIREDレベル and all the SHOULD レベルの要求条件 for its protocols is said to be "完全準拠"; one that satisfies all the MUST level requirements but not all the SHOULD レベル requirements for its プロトコル is said to be "条件付き準拠." 1.3 専門用語(Terminology) この仕様書 uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP コミュニケーション. コネクション(connection) A トランスポート層 仮想サーキット established between two programs for the purpose of コミュニケーション. メッセージ(message) 基本単位 of HTTP コミュニケーション, consisting of a structured sequence of octets matching the syntax defined in section 4 and transmitted via the connection. リクエスト/要求(リクエスト) セクション5で定義される、HTTP 要求メッセージ. レスポンス/応答(レスポンス) セクション6で定義される、HTTP 応答メッセージ. Fielding, et al. Standards Track [Page 8] RFC 2616 HTTP/1.1 1999年6月 リソース(resource) ネットワーク・データ・オブジェクトまたはサービス that can be identified by a URI, as defined in section 3.2. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or vary in other ways. エンティティ/実在物(entity) The 情報 transferred as the payload of a リクエストまたは レスポンス. An entity consists of metainformation in the form of entity-ヘッダ フィールドs and content in the form of an entity-body, as described in section 7. representation セクション12で記述される、レスポンスを含むエンティティ that is subject to content negotiation. There may exist multiple representations associated with a particular レスポンス status. content negotiation The メカニズムmechanism for selecting the appropriate representation when servicing a リクエスト, as described in section 12. The representation of entities in any レスポンス can be negotiated (including error レスポンスs). variant A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations is termed a `varriant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation. クライアント(client) リクエストを送信する目的で接続を確立するプログラム. ユーザ エージェント(user agent) The クライアント which initiates a リクエスト. These are often browsers, editors, spiders (web-traversing robots), or other end user tools. サーバ(server) An アプリケーション プログラム that accepts connections in order to service リクエストs by sending back レスポンスs. Any given program may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as an 元のサーバ, プロキシ, ゲートウェイ, or tunnel, switching behavior based on the nature of each リクエスト. Fielding, et al. Standards Track [Page 9] RFC 2616 HTTP/1.1 1999年6月 元のサーバ The server on which a given リソース resides or is to be created. プロキシ(proxy) An 中継プログラム which acts as both a server and a client for the purpose of making リクエストs on behalf of other clients. リクエストs are serviced internally or by passing them on, with possible translation, to other servers. A プロキシ MUST implement both the client and server requirements of this specification. A "transparent プロキシ" is a プロキシ that does not modify the リクエスト or レスポンス beyond what is required for プロキシ 認証 and identification. A "non-transparent プロキシ(proxy)" is a プロキシ(proxy) that modifies the リクエスト or レスポンス in order to provide some added service to the user agent, such as group annotation services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent behavior is explicitly stated, the HTTP プロキシ requirements apply to both types of プロキシ. ゲートウェイ(gateway) A サーバ which acts as an intermediary for some other server. Unlike a プロキシ, a ゲートウェイ receives リクエストs as if it were the 元のサーバ for the リクエストed resource; the リクエストing client may not be aware that it is communicating with a gateway. トンネル(tunnel) An 仲介(中継)プログラム which is acting as a blind ふたつのコネクションの間を中継する. Once active, a tunnel is not considered a party to the HTTP コミュニケーション, though the tunnel may have been initiated by an HTTPリクエスト. The tunnel ceases to exist when both ends of the relayed connections are closed. キャッシュ(cache) A プログラムの応答メッセージ保管場所 and the subsystem that controls its message storage, retrieval, and deletion. A cache stores cacheable レスポンスs in order to reduce the レスポンス time and network バンド幅 consumption on future, equivalent リクエストs. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel. キャッシュ可能／キャッシュできる (cachable) キャッシャが後のリクエストのためにレスポンスメッセージのコピーを保持 する事が許される場合、レスポンスはキャッシュ可能である。HTTP レスポン スをキャッシュできるかどうかの判定規則は13章で定義する。リソースが キャッシュできたとしても、キャッシュがあるリクエストにキャッシュされ たコピーを使えるかどうかについて、別の制約があるかもしれない。 Fielding, et al. Standards Track [Page 10] RFC 2616 HTTP/1.1 1999年6月 直接 (first-hand) レスポンスがオリジンサーバから直接、プロキシを経由するような不要な 遅れを含まないで送られてくるとき、レスポンスが直接であるという。 また、その正当性がオリジンサーバと直接チェックされる時も、その レスポンスは直接であるという。 explicit expiration time The time at which the 元のサーバ intends that an entity should no longer be returned by a cache without further validation. 自発的保持期限／有効期限 (heuristic expiration time) 有効期限が明示されていない場合に、キャッシャが指定する有効期限。 経過時間 (age) オリジンサーバから送られてから、またはオリジンサーバによって有効に されてからの時間を レスポンスの 経過時間という。 freshness lifetime The length of time between the generation of a レスポンス and its expiration time. 有効 (fresh) レスポンスの経過時間が、有効時間をまだ超えていない場合、 そのレスポンスは有効であるという。 無効 (stale) レスポンスの経過時間が、有効時間を超えた場合、そのレスポンスは無効で あるという。 （訳注：直訳は「新鮮でない、古い」。もっといい訳語募集中） semantically transparent A cache behaves in a "semantically transparent" manner, with respect to a particular レスポンス, when its use affects neither the リクエストing client nor the 元のサーバ, except to improve performance. When a cache is semantically transparent, the client receives exactly the same レスポンス (except for hop-by-hop headers) that it would have received had its リクエスト been handled directly by the 元のサーバ. validator A protocol element (e.g., an entity tag or a Last-Modified time) that is used to find out whether a cache entry is an equivalent copy of an entity. upstream/downstream Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream. Fielding, et al. Standards Track [Page 11] RFC 2616 HTTP/1.1 1999年6月 inbound/outbound Inbound and outbound refer to the リクエスト and レスポンス paths for messages: "inbound" means "traveling toward the 元のサーバ", and "outbound" means "traveling toward the user agent" 1.4 オーバーロール・オペレーション(作業) HTTPプロトコルは、要求/応答プロトコルである. A クライアントは、 sends a リクエスト to the server in the form of a リクエスト method, URI, and protocol version, followed by a MIME-like message containing リクエスト modifiers, client information, and possible body content over a connection with a server. The server responds with a status line, including the message's protocol version and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body content. The relationship between HTTP and MIME is described in appendix 19.4. Most HTTP コミュニケーション is initiated by a user agent and consists of a リクエスト to be applied to a resource on some 元のサーバ. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the 元のサーバ (O). リクエスト chain ------------------------> UA -------------------v------------------- O <----------------------- レスポンス chain A more 複雑な状況 occurs when one or more 中継者 are present in the リクエスト/レスポンス chain. There are three common forms of intermediary: プロキシ, ゲートウェイ, and トンネル. A プロキシ is a 転送エージェント, receiving リクエストs for a URI in its absolute form, rewriting all or part of the メッセージ, and 転送する the 再フォーマットされたリクエスト toward the サーバ identified by the URI. A ゲートウェイ is a receiving agent, acting as a layer above some other server(s) and, if 必要なら, 翻訳する the リクエストs to the underlying サーバのプロトコル. A トンネルは、メッセージを変えずに2つのコネクションの間を中継する役をつとめる; tunnels are used when the コミュニケーション needs to pass through an 中継者 (ファイアウォールのような) even when the intermediary cannot understand the contents of the messages. リクエスト chain --------------------------------------> UA -----v----- A -----v----- B -----v----- C -----v----- O <------------------------------------- レスポンス chain 上の図では、ユーザエージェントと元のサーバの間に3つの中継者(A, BとC)がいる. A リクエスト or レスポンス メッセージ that travels the whole chain will pass through four separate connections. This distinction is important because some HTTP コミュニケーション options Fielding, et al. Standards Track [Page 12] RFC 2616 HTTP/1.1 1999年6月 may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple, simultaneous コミュニケーションs. For example, B may be receiving リクエストs from many clients other than A, and/or forwarding リクエストs to servers other than C, at the same time that it is handling A's リクエスト. Any party to the コミュニケーション which is not acting as a tunnel may employ an internal cache for handling リクエストs. The effect of a cache is that the リクエスト/レスポンス chain is shortened if one of the participants along the chain has a cached レスポンス applicable to that リクエスト. The following illustrates the resulting chain if B has a cached copy of an earlier レスポンス from O (via C) for a リクエスト which has not been cached by UA or A. リクエスト chain ----------> UA -----v----- A -----v----- B - - - - - - C - - - - - - O <--------- レスポンス chain Not all レスポンスs are usefully cacheable, and some リクエストs may contain modifiers which place special requirements on cache behavior. HTTP requirements for cache behavior and cacheable レスポンスs are defined in セクション 13. In fact, there are a wide variety of architectures and configurations of caches and プロキシ currently being experimented with or deployed across the World Wide Web. These systems include national hierarchies of プロキシ caches to save transoceanic バンド幅, systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so on. HTTP systems are used in corporate intranets over high-バンド幅 links, and for access via PDAs with low-power radio links and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while introducing protocol constructs that meet the needs of those who build web アプリケーションs that require high reliability and, failing that, at least reliable indications of failure. HTTP コミュニケーション usually takes place over TCP/IP connections. The default port is TCP 80 [19], but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the mapping of the HTTP/1.1 リクエスト and レスポンス structures onto the transport data units of the protocol in question is outside the scope of this specification. Fielding, et al. Standards Track [Page 13] RFC 2616 HTTP/1.1 1999年6月 In HTTP/1.0, most implementations used a new connection for each リクエスト/レスポンス exchange. In HTTP/1.1, a connection may be used for one or more リクエスト/レスポンス exchanges, although connections may be closed for a variety of reasons (see section 8.1). 2 Notational Conventions and Generic Grammar 2.1 拡張BNF All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar to that used by RFC 822 [9]. 実装者 will need to be familiar with the notation in order to understand this specification. The augmented BNF includes the following constructs: name = definition The name of a rule is simply the name itself (without any enclosing "<" and ">") and is separated from its definition by the equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule definition that spans more than one line. Certain basic rules are in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names. "リテラル" Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive. rule1 | rule2 Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no. (rule1 rule2) Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences "elem foo elem" and "elem bar elem". *rule The character "*" preceding an element indicates repetition. The full form is "*element" indicating at least and at most occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero; "1*element" requires at least one; and "1*2element" allows one or two. [rule] Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)". Fielding, et al. Standards Track [Page 14] RFC 2616 HTTP/1.1 1999年6月 N rule Specific repetition: "(element)" is equivalent to "*(element)"; that is, exactly occurrences of (element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters. #rule A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "#element" indicating at least and at most elements, each separated by one or more commas (",") and OPTIONAL linear white space (LWS). This makes the usual form of lists very easy; a rule such as ( *LWS element *( *LWS "," *LWS element )) can be shown as 1#element Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is, "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required, at least one non-null element MUST be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at least one; and "1#2element" allows one or two. ; comment A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is a simple way of including useful notes in parallel with the specifications. implied *LWS The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation of a field. At least one delimiter (LWS and/or separators) MUST exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single token. 2.2 基本ルール(Basic Rules) 次のルール are used throughout この仕様書 to describe basic parsing constructs. The US-ASCII coded character set is defined by ANSI X3.4-1986 [21]. Fielding, et al. Standards Track [Page 15] RFC 2616 HTTP/1.1 1999年6月 OCTET = <任意の8ビットの連続データ> CHAR = <任意のUS-ASCII 文字 (octets 0 - 127)> UPALPHA = <任意のUS-ASCII 大文字 "A".."Z"> LOALPHA = <任意のUS-ASCII 小文字 "a".."z"> ALPHA = UPALPHA | LOALPHA DIGIT = <任意の US-ASCII 数字 "0".."9"> CTL = <任意の US-ASCII 制御文字 (octets 0 - 31) and DEL (127)> CR = LF = SP = HT = <"> = HTTP/1.1は、{エンティティボディを除く全プロトコル要素で連続するCR LFは行端マーカである}と定義する。 (付録 19.3 寛容なアプリケーション 参照). The エンティティボディ中の行端マーカは、defined by its associated media type, as described in section 3.7. CRLF = CR LF HTTP/1.1 ヘッダ フィールド values can be folded onto multiple lines if the continuation line begins with a space or horizontal tab. All linear white space, including folding, has the same semantics as SP. A recipient MAY replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream. LWS = [CRLF] 1*( SP | HT ) The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message parser. Words of *TEXT MAY contain characters from character sets other than ISO- 8859-1 [22] only when encoded according to the rules of RFC 2047 [14]. TEXT = A CRLF is allowed in the definition of TEXT only as part of a header field continuation. It is expected that the folding LWS will be replaced with a single SP before interpretation of the TEXT value. Hexadecimal numeric characters are used in several protocol elements. HEX = "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT Fielding, et al. Standards Track [Page 16] RFC 2616 HTTP/1.1 1999年6月 Many HTTP/1.1 ヘッダ フィールド values consist of words separated by LWS or special characters. These special characters MUST be in a quoted string to be used within a parameter value (as defined in section 3.6). token = 1* separators = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" | "\" | <"> | "/" | "[" | "]" | "?" | "=" | "{" | "}" | SP | HT Comments can be included in some HTTP ヘッダ フィールドs by surrounding the comment text with parentheses. Comments are only allowed in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part of the field value. comment = "(" *( ctext | quoted-pair | comment ) ")" ctext = A string of text is parsed as a single word if it is quoted using double-quote marks. quoted-string = ( <"> *(qdtext | quoted-pair ) <"> ) qdtext = > The backslash character ("\") MAY be used as a single-character quoting mechanism only within quoted-string and comment constructs. quoted-pair = "\" CHAR 3 Protocol Parameters 3.1 HTTP バージョン(HTTP Version) HTTP uses a "." 番号付与計画 to indicate versions of the protocol. The protocol versioning policy is intended to allow the sender to indicate the format of a message and its capacity for understanding further HTTP コミュニケーション, rather than the features obtained via that コミュニケーション. No change is made to the version number for the addition of message components which do not affect コミュニケーション behavior or which only add to extensible field values. The number is incremented when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may add to the message semantics and imply additional capabilities of the sender. The number is incremented when the format of a message within the protocol is changed. See RFC 2145 [36] for a fuller explanation. Fielding, et al. Standards Track [Page 17] RFC 2616 HTTP/1.1 1999年6月 HTTPメッセージのバージョン is indicated by an HTTP-Version field in the first line of the message. HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT Note that the major and minor numbers MUST be treated as separate integers and that each MAY be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and MUST NOT be sent. An アプリケーション that sends a リクエスト or レスポンス message that includes HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant with this specification. アプリケーションs that are at least conditionally compliant with this specification SHOULD use an HTTP-Version of "HTTP/1.1" in their messages, and MUST do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, see RFC 2145 [36]. The HTTPバージョン of an アプリケーション is the highest HTTPバージョン for which the アプリケーション is at least conditionally compliant. プロキシ(proxy) and ゲートウェイ アプリケーションs need to be careful when forwarding messages in プロトコル versions different from that of the アプリケーション. Since the プロトコル バージョン indicates the プロトコルの能力 of the sender, a プロキシ(proxy)/ゲートウェイ MUST NOT send a message with a version indicator which is greater than its actual version. If a higher version リクエスト is received, the プロキシ(proxy)/ゲートウェイ MUST either downgrade the リクエスト バージョン, or respond with an エラー, or switch to tunnel behavior. Due to 相互運用問題 with HTTP/1.0 プロキシ discovered since the publication of RFC 2068[33], caching プロキシ MUST, gateways MAY, and tunnels MUST NOT upgrade the リクエスト to the highest version they support. The プロキシ(proxy)/gateway's レスポンス to that リクエスト MUST be in the same major version as the リクエスト. Note: Converting between versions of HTTP may involve modification of ヘッダ フィールドs required or forbidden by the versions involved. 3.2 同一資源識別子(Uniform Resource Identifiers) URIs have been known by many names: WWW アドレス, Universal Document Identifiers, Universal Resource Identifiers [3], and finally the combination of Uniform Resource Locators (URL) [4] and Names (URN) [20]. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location, or any other characteristic--a resource. Fielding, et al. Standards Track [Page 18] RFC 2616 HTTP/1.1 1999年6月 3.2.1 General Syntax URIs in HTTP can be represented in absolute form or relative to some known base URI [11], depending upon the context of their use. The two forms are differentiated by the fact that absolute URIs always begin with a scheme name followed by a colon. For definitive information on URL syntax and semantics, see "Uniform Resource Identifiers (URI): Generic Syntax and Semantics," RFC 2396 [42] (which replaces RFCs 1738 [4] and RFC 1808 [11]). This specification adopts the definitions of "URI-reference", "absoluteURI", "relativeURI", "port", "host","abs_path", "rel_path", and "authority" from that specification. The HTTPプロトコル does not place any a priori limit on the length of a URI. Servers MUST be able to handle the URI of any resource they serve, and SHOULD be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server SHOULD return 414 (リクエスト-URI Too Long) status if a URI is longer than the server can handle (see section 10.4.15). Note: Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or プロキシ(proxy) implementations might not properly support these lengths. 3.2.2 http URL The "http" スキーマ is used to locate network resources via the HTTP プロトコル. このセクション defines the scheme-specific syntax and semantics for http URLs. http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]] If the port is empty or not given, port 80 is assumed. The semantics are that the identified resource is located at the server listening for TCP connections on that port of that host, and the リクエスト-URI for the resource is abs_path (section 5.1.2). The use of IPアドレスes in URLs SHOULD be avoided whenever possible (see RFC 1900 [24]). If the abs_path is not present in the URL, it MUST be given as "/" when used as a リクエスト-URI for a resource (section 5.1.2). If a プロキシ(proxy) receives a host name which is not a fully qualified domain name, it MAY add its domain to the host name it received. If a プロキシ(proxy) receives a fully qualified domain name, the プロキシ(proxy) MUST NOT change the host name. Fielding, et al. Standards Track [Page 19] RFC 2616 HTTP/1.1 1999年6月 3.2.3 URI Comparison When comparing two URIs to decide if they match or not, a client SHOULD use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions: - A port that is empty or not given is equivalent to the default port for that URI-reference; - Comparisons of host names MUST be case-insensitive; - Comparisons of scheme names MUST be case-insensitive; - An empty abs_path is equivalent to an abs_path of "/". Characters other than those in the "reserved" and "unsafe" sets (see RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding. 例えば, 次の３つのURIは、等しい: http://abc.com:80/~smith/home.html http://ABC.com/%7Esmith/home.html http://ABC.com:/%7esmith/home.html 3.3 Date/Time フォーマット 3.3.1 フル Date HTTP アプリケーション have historically allowed ３つの異なるフォーマット for the representation of date/time stamps: Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123 Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036 Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format 最初のフォーマット is preferred as an Internet 標準 and represents a fixed-length subset of that defined by RFC 1123 [8] (an update to RFC 822 [9]). 二つ目のフォーマットは in common use, but is based on the obsolete RFC 850 [12] 日付フォーマット and lacks a four-digit year. HTTP/1.1クライアントとサーバ that parse the date value MUST accept all three formats (for compatibility with HTTP/1.0), though they MUST RFC 1123フォーマットでのみ、生成しなければならない for representing ヘッダフィールドのHTTP-date の値. See section 19.3 for further information. Note: Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP アプリケーションs, as is sometimes the case when retrieving or posting messages via プロキシ/gateways to SMTP or NNTP. Fielding, et al. Standards Track [Page 20] RFC 2616 HTTP/1.1 1999年6月 All HTTP 日時 stamps MUST be represented in グリニッジ標準時(GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for time zone, and MUST be assumed when reading the asctime format. HTTP-date is case sensitive and MUST NOT include additional LWS beyond that specifically included as SP in the grammar. HTTP-date = rfc1123-date | rfc850-date | asctime-date rfc1123-date = wkday "," SP date1 SP time SP "GMT" rfc850-date = weekday "," SP date2 SP time SP "GMT" asctime-date = wkday SP date3 SP time SP 4DIGIT date1 = 2DIGIT SP month SP 4DIGIT ; day month year (e.g., 02 Jun 1982) date2 = 2DIGIT "-" month "-" 2DIGIT ; day-month-year (e.g., 02-Jun-82) date3 = month SP ( 2DIGIT | ( SP 1DIGIT )) ; month day (e.g., Jun 2) time = 2DIGIT ":" 2DIGIT ":" 2DIGIT ; 00:00:00 - 23:59:59 wkday = "Mon" | "Tue" | "Wed" | "Thu" | "Fri" | "Sat" | "Sun" weekday = "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday" month = "Jan" | "Feb" | "Mar" | "Apr" | "May" | "Jun" | "Jul" | "Aug" | "Sep" | "Oct" | "Nov" | "Dec" Note: HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers are not required to use these formats for user presentation, リクエスト logging, etc. 3.3.2 Delta Seconds Some HTTP ヘッダ フィールドs allow a time value to be specified as an integer number of seconds, represented in decimal, after the time that the message was received. delta-seconds = 1*DIGIT 3.4 文字セット(Character Sets) HTTP uses the same definition of the term "character set" as that described for MIME: Fielding, et al. 標準トラック [Page 21] RFC 2616 HTTP/1.1 1999年6月 The term "character set" is used in this document to refer to a この文書中で用語「文字セット」は method used with one or more tables to convert a sequence of octets into a sequence of characters. Note that unconditional conversion in the other direction is not required, in that not all characters may be available in a given character set and a character set may provide more than one sequence of octets to represent a particular character. This definition is intended to allow various kinds of character encoding, from simple single-table mappings such as US-ASCII to complex table switching methods such as those that use ISO-2022's techniques. However, the definition associated with a MIME character set name MUST fully specify the mapping to be performed from octets to characters. In particular, use of external profiling information to determine the exact mapping is not permitted. Note: This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME share the same registry, it is important that the terminology also be shared. HTTP character sets are identified by case-insensitive tokens. The complete set of tokens is defined by the IANA Character Set registry [19]. charset = token Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA Character Set registry [19] MUST represent the character set defined by that registry. アプリケーションs SHOULD limit their use of character sets to those defined by the IANA registry. 実装者 should be aware of IETF character set requirements [38] [41]. 3.4.1 Missing Charset いくつかのHTTP/1.0ソフトウェア has interpreted a Content-Typeヘッダ without charset パラメータ incorrectly to mean "recipient should guess." Senders wishing to defeat this behavior MAY include a charset パラメータ even when the 文字セット is ISO-8859-1 and SHOULD do so when it is known that it will not confuse the recipient. Unfortunately, some 古いHTTP/1.0クライアント did not deal properly with an explicit 文字セットパラメータ. HTTP/1.1 recipients MUST respect the 文字セットラベル provided by the sender; and those user agents that have a provision to "guess" a charset MUST use the charset from the Fielding, et al. Standards Track [Page 22] RFC 2616 HTTP/1.1 1999年6月 content-type field if they support that charset, rather than the recipient's preference, when initially displaying a document. See section 3.7.1. 3.5 Content Codings Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only decoded by the recipient. content-coding = token All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (section 14.3) and Content-Encoding (section 14.11) ヘッダ フィールドs. Although the value describes the content-coding, what is more important is that it indicates what decoding mechanism will be required to remove the encoding. The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry contains the following tokens: gzip An encoding format produced by the ファイル圧縮プログラム "gzip" (GNU zip) as described in RFC 1952 [25]. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC. compress The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch coding (LZW). Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings. Their use here is representative of historical practice, not good design. For compatibility with previous implementations of HTTP, アプリケーションs SHOULD consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively. deflate The "zlib" format defined in RFC 1950 [31] in combination with the "deflate" compression mechanism described in RFC 1951 [29]. Fielding, et al. Standards Track [Page 23] RFC 2616 HTTP/1.1 1999年6月 identity The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept- Encoding header, and SHOULD NOT be used in the Content-Encoding header. New content-coding value tokens SHOULD be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed to implement a new value SHOULD be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in this section. 3.6 Transfer Codings Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding is a property of the message, not of the original entity. transfer-coding = "chunked" | transfer-extension transfer-extension = token *( ";" parameter ) Parameters are in the form of attribute/value pairs. parameter = attribute "=" value attribute = token value = token | quoted-string All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer-coding values in the TE ヘッダ フィールド (section 14.39) and in the Transfer-Encoding ヘッダ フィールド (section 14.41). Whenever a transfer-coding is applied to a message-body, the set of transfer-codings MUST include "chunked", unless the message is terminated by closing the connection. When the "chunked" transfer- coding is used, it MUST be the last transfer-coding applied to the message-body. The "chunked" transfer-coding MUST NOT be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message (section 4.4). Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME [7], which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty in determining the exact body length (section 7.2.2), or the desire to encrypt data over a shared transport. Fielding, et al. Standards Track [Page 24] RFC 2616 HTTP/1.1 1999年6月 The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry contains the following tokens: "chunked" (section 3.6.1), "identity" (section 3.6.2), "gzip" (section 3.5), "compress" (section 3.5), and "deflate" (section 3.5). New transfer-coding value tokens SHOULD be registered in the same way as new content-coding value tokens (section 3.5). A server which receives an entity-body with a transfer-coding it does not understand SHOULD return 501 (Unimplemented), and close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0 client. 3.6.1 Chunked Transfer Coding The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size indicator, followed by an OPTIONAL trailer containing entity-ヘッダ フィールドs. This allows dynamically produced content to be transferred along with the information necessary for the recipient to verify that it has received the full message. Chunked-Body = *chunk last-chunk trailer CRLF chunk = chunk-size [ chunk-extension ] CRLF chunk-data CRLF chunk-size = 1*HEX last-chunk = 1*("0") [ chunk-extension ] CRLF chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] ) chunk-ext-name = token chunk-ext-val = token | quoted-string chunk-data = chunk-size(OCTET) trailer = *(entity-header CRLF) The chunk-size field is a string of hex digits indicating the size of the chunk. The chunked encoding is ended by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line. The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer ヘッダ フィールド can be used to indicate which ヘッダ フィールドs are included in a trailer (see section 14.40). Fielding, et al. Standards Track [Page 25] RFC 2616 HTTP/1.1 1999年6月 A server using chunked transfer-coding in a レスポンス MUST NOT use the trailer for any ヘッダ フィールドs unless at least one of the following is true: a)リクエスト included a TE ヘッダ フィールド that indicates "trailers" is acceptable in the transfer-coding of the レスポンス, as described in section 14.39; or, b)the server is the 元のサーバ for the レスポンス, the trailer fields consist entirely of optional metadata, and the recipient could use the message (in a manner acceptable to the 元のサーバ) without receiving this metadata. In other words, the 元のサーバ is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client. This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) プロキシ(proxy) and forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly infinite buffer on the プロキシ(proxy). An example process for decoding a Chunked-Body is presented in appendix 19.4.6. All HTTP/1.1 アプリケーションs MUST be able to receive and decode the "chunked" transfer-coding, and MUST ignore chunk-extension extensions they do not understand. 3.7 Media Types HTTP uses Internet Media Types [17] in the Content-Type (section 14.17) and Accept (section 14.1) ヘッダ フィールドs in order to provide open and extensible data typing and type negotiation. media-type = type "/" subtype *( ";" parameter ) type = token subtype = token Parameters MAY follow the type/subtype in the form of attribute/value pairs (as defined in section 3.6). The type, subtype, and parameter attribute names are case- insensitive. Parameter values might or might not be case-sensitive, depending on the semantics of the parameter name. Linear white space (LWS) MUST NOT be used between the type and subtype, nor between an attribute and its value. The presence or absence of a parameter might be significant to the processing of a media-type, depending on its definition within the media type registry. Fielding, et al. Standards Track [Page 26] RFC 2616 HTTP/1.1 1999年6月 Note that some older HTTP アプリケーションs do not recognize media type parameters. When sending data to older HTTP アプリケーションs, implementations SHOULD only use media type parameters when they are required by that type/subtype definition. Media-type values are registered with the Internet Assigned Number Authority (IANA [19]). The media type registration process is outlined in RFC 1590 [17]. Use of non-registered media types is discouraged. 3.7.1 Canonicalization and Text Defaults Internet media types are registered with a canonical form. An entity-body transferred via HTTP messages MUST be represented in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next paragraph. When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an entire entity-body. HTTP アプリケーションs MUST accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP. In addition, if the text is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the entity-body; a bare CR or LF MUST NOT be substituted for CRLF within any of the HTTP control structures (such as ヘッダ フィールドs and multipart boundaries). If an entity-body is encoded with a content-coding, the underlying data MUST be in a form defined above prior to being encoded. The "charset" parameter is used with some media types to define the character set (section 3.4) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or its subsets MUST be labeled with an appropriate charset value. See section 3.4.1 for compatibility problems. 3.7.2 Multipart Types MIME provides for a number of "multipart" types -- encapsulations of one or more entities within a single message-body. All multipart types share a common syntax, as defined in section 5.1.1 of RFC 2046 Fielding, et al. Standards Track [Page 27] RFC 2616 HTTP/1.1 1999年6月 [40], and MUST include a boundary parameter as part of the media type value. The message body is itself a protocol element and MUST therefore use only CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the epilogue of any multipart message MUST be empty; HTTP アプリケーションs MUST NOT transmit the epilogue (even if the original multipart contains an epilogue). These restrictions exist in order to preserve the self-delimiting nature of a multipart message- body, wherein the "end" of the message-body is indicated by the ending multipart boundary. In general, HTTP treats a multipart message-body no differently than any other media type: strictly as payload. The one exception is the "multipart/byteranges" type (appendix 19.2) when it appears in a 206 (Partial Content) レスポンス, which will be interpreted by some HTTP caching mechanisms as described in sections 13.5.4 and 14.16. In all other cases, an HTTP user agent SHOULD follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME ヘッダ フィールドs within each body-part of a multipart message- body do not have any significance to HTTP beyond that defined by their MIME semantics. In general, an HTTP user agent SHOULD follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. If an アプリケーション receives an unrecognized multipart subtype, the アプリケーション MUST treat it as being equivalent to "multipart/mixed". Note: The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST リクエスト method, as described in RFC 1867 [15]. 3.8 Product Tokens Product tokens are used to allow communicating アプリケーションs to identify themselves by software name and version. Most fields using product tokens also allow sub-products which form a significant part of the アプリケーション to be listed, separated by white space. By convention, the products are listed in order of their significance for identifying the アプリケーション. product = token ["/" product-version] product-version = token Examples: User-Agent: CERN-LineMode/2.15 libwww/2.17b3 Server: Apache/0.8.4 Fielding, et al. Standards Track [Page 28] RFC 2616 HTTP/1.1 1999年6月 Product tokens SHOULD be short and to the point. They MUST NOT be used for advertising or other non-essential information. Although any token character MAY appear in a product-version, this token SHOULD only be used for a version identifier (i.e., successive versions of the same product SHOULD only differ in the product-version portion of the product value). 3.9 Quality Values HTTP content negotiation (section 12) uses short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has a quality value of 0, then content with this parameter is `not acceptable' for the client. HTTP/1.1 アプリケーションs MUST NOT generate more than three digits after the decimal point. User configuration of these values SHOULD also be limited in this fashion. qvalue = ( "0" [ "." 0*3DIGIT ] ) | ( "1" [ "." 0*3("0") ] ) "Quality values" is a misnomer, since these values merely represent relative degradation in desired quality. 3.10 Language Tags A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for コミュニケーション of information to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and Content- Language fields. The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 [1]. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags: language-tag = primary-tag *( "-" subtag ) primary-tag = 1*8ALPHA subtag = 1*8ALPHA White space is not allowed within the tag and all tags are case- insensitive. The name space of language tags is administered by the IANA. Example tags include: en, en-US, en-cockney, i-cherokee, x-pig-latin Fielding, et al. Standards Track [Page 29] RFC 2616 HTTP/1.1 1999年6月 where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered in future.) 3.11 Entity Tags Entity tags are used for comparing two or more entities from the same リクエストed resource. HTTP/1.1 uses entity tags in the ETag (section 14.19), If-Match (section 14.24), If-None-Match (section 14.26), and If-Range (section 14.27) ヘッダ フィールドs. The definition of how they are used and compared as cache validators is in section 13.3.3. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. entity-tag = [ weak ] opaque-tag weak = "W/" opaque-tag = quoted-string A "strong entity tag" MAY be shared by two entities of a resource only if they are equivalent by octet equality. A "weak entity tag," indicated by the "W/" prefix, MAY be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no significant change in semantics. A weak entity tag can only be used for weak comparison. An entity tag MUST be unique across all versions of all entities associated with a particular resource. A given entity tag value MAY be used for entities obtained by リクエストs on different URIs. The use of the same entity tag value in conjunction with entities obtained by リクエストs on different URIs does not imply the equivalence of those entities. 3.12 Range Units HTTP/1.1 allows a client to リクエスト that only part (a range of) the レスポンス entity be included within the レスポンス. HTTP/1.1 uses range units in the Range (section 14.35) and Content-Range (section 14.16) ヘッダ フィールドs. An entity can be broken down into subranges according to various structural units. range-unit = bytes-unit | other-range-unit bytes-unit = "bytes" other-range-unit = token The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1 implementations MAY ignore ranges specified using other units. Fielding, et al. Standards Track [Page 30] RFC 2616 HTTP/1.1 1999年6月 HTTP/1.1 has been designed to allow implementations of アプリケーションs that do not depend on knowledge of ranges. 4 HTTP Message 4.1 Message Types HTTP messages consist of リクエストs from client to server and レスポンスs from server to client. HTTP-message = リクエスト | レスポンス ; HTTP/1.1 messages リクエスト (section 5) and レスポンス (section 6) messages use the generic message format of RFC 822 [9] for transferring entities (the payload of the message). Both types of message consist of a start-line, zero or more ヘッダ フィールドs (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the ヘッダ フィールドs, and possibly a message-body. generic-message = start-line *(message-header CRLF) CRLF [ message-body ] start-line = リクエスト-Line | Status-Line In the interest of robustness, servers SHOULD ignore any empty line(s) received where a リクエスト-Line is expected. In other words, if the server is reading the protocol stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF. Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST リクエスト. To restate what is explicitly forbidden by the BNF, an HTTP/1.1 client MUST NOT preface or follow a リクエスト with an extra CRLF. 4.2 Message Headers HTTP ヘッダ フィールドs, which include general-header (section 4.5), リクエスト-header (section 5.3), レスポンス-header (section 6.2), and entity-header (section 7.1) fields, follow the same generic format as that given in Section 3.1 of RFC 822 [9]. Each ヘッダ フィールド consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The field value MAY be preceded by any amount of LWS, though a single SP is preferred. ヘッダ フィールドs can be extended over multiple lines by preceding each extra line with at least one SP or HT. アプリケーションs ought to follow "common form", where one is known or indicated, when generating HTTP constructs, since there might exist some implementations that fail to accept anything Fielding, et al. Standards Track [Page 31] RFC 2616 HTTP/1.1 1999年6月 beyond the common forms. message-header = field-name ":" [ field-value ] field-name = token field-value = *( field-content | LWS ) field-content = The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS MAY be removed without changing the semantics of the field value. Any LWS that occurs between field-content MAY be replaced with a single SP before interpreting the field value or forwarding the message downstream. The order in which ヘッダ フィールドs with differing field names are received is not significant. However, it is "good practice" to send general-ヘッダ フィールドs first, followed by リクエスト-header or レスポンス- ヘッダ フィールドs, and ending with the entity-ヘッダ フィールドs. Multiple message-ヘッダ フィールドs with the same field-name MAY be present in a message if and only if the entire field-value for that ヘッダ フィールド is defined as a comma-separated list [i.e., #(values)]. It MUST be possible to combine the multiple ヘッダ フィールドs into one "field-name: field-value" pair, without changing the semantics of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which ヘッダ フィールドs with the same field-name are received is therefore significant to the interpretation of the combined field value, and thus a プロキシ(proxy) MUST NOT change the order of these field values when a message is forwarded. 4.3 Message Body The message-body (if any) of an HTTP message is used to carry the entity-body associated with the リクエスト or レスポンス. The message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding ヘッダ フィールド (section 14.41). message-body = entity-body | Transfer-Encoding MUST be used to indicate any transfer-codings applied by an アプリケーション to ensure safe and proper transfer of the message. Transfer-Encoding is a property of the message, not of the Fielding, et al. Standards Track [Page 32] RFC 2616 HTTP/1.1 1999年6月 entity, and thus MAY be added or removed by any アプリケーション along the リクエスト/レスポンス chain. (However, section 3.6 places restrictions on when certain transfer-codings may be used.) The rules for when a message-body is allowed in a message differ for リクエストs and レスポンスs. The presence of a message-body in a リクエスト is signaled by the inclusion of a Content-Length or Transfer-Encoding ヘッダ フィールド in the リクエスト's message-headers. A message-body MUST NOT be included in a リクエスト if the specification of the リクエスト method (section 5.1.1) does not allow sending an entity-body in リクエストs. A server SHOULD read and forward a message-body on any リクエスト; if the リクエスト method does not include defined semantics for an entity-body, then the message-body SHOULD be ignored when handling the リクエスト. For レスポンス messages, whether or not a message-body is included with a message is dependent on both the リクエスト method and the レスポンス ステータス コード (section 6.1.1). All レスポンスs to the HEAD リクエスト method MUST NOT include a message-body, even though the presence of entity- ヘッダ フィールドs might lead one to believe they do. All 1xx (informational), 204 (no content), and 304 (not modified) レスポンスs MUST NOT include a message-body. All other レスポンスs do include a message-body, although it MAY be of zero length. 4.4 Message Length The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of the following (in order of precedence): 1.Any レスポンス message which "MUST NOT" include a message-body (such as the 1xx, 204, and 304 レスポンスs and any レスポンス to a HEAD リクエスト) is always terminated by the first empty line after the ヘッダ フィールドs, regardless of the entity-ヘッダ フィールドs present in the message. 2.If a Transfer-Encoding ヘッダ フィールド (section 14.41) is present and has any value other than "identity", then the transfer-length is defined by use of the "chunked" transfer-coding (section 3.6), unless the message is terminated by closing the connection. 3.If a Content-Length ヘッダ フィールド (section 14.13) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length ヘッダ フィールド MUST NOT be sent if these two lengths are different (i.e., if a Transfer-Encoding Fielding, et al. Standards Track [Page 33] RFC 2616 HTTP/1.1 1999年6月 ヘッダ フィールド is present). If a message is received with both a Transfer-Encoding ヘッダ フィールド and a Content-Length ヘッダ フィールド, the latter MUST be ignored. 4.If the message uses the media type "multipart/byteranges", and the ransfer-length is not otherwise specified, then this self- elimiting media type defines the transfer-length. This media type UST NOT be used unless the sender knows that the recipient can arse it; the presence in a リクエスト of a Range header with ultiple byte- range specifiers from a 1.1 client implies that the lient can parse multipart/byteranges レスポンスs. A range header might be forwarded by a 1.0 プロキシ(proxy) that does not understand multipart/byteranges; in this case the server MUST delimit the message using methods defined in items 1,3 or 5 of this section. 5.By the server closing the connection. (Closing the connection cannot be used to indicate the end of a リクエスト body, since that would leave no possibility for the server to send back a レスポンス.) For compatibility with HTTP/1.0 アプリケーションs, HTTP/1.1 リクエストs containing a message-body MUST include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a リクエスト contains a message-body and a Content-Length is not given, the server SHOULD respond with 400 (bad リクエスト) if it cannot determine the length of the message, or with 411 (length required) if it wishes to insist on receiving a valid Content-Length. All HTTP/1.1 アプリケーションs that receive entities MUST accept the "chunked" transfer-coding (section 3.6), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance. Messages MUST NOT include both a Content-Length ヘッダ フィールド and a non-identity transfer-coding. If the message does include a non- identity transfer-coding, the Content-Length MUST be ignored. When a Content-Length is given in a message where a message-body is allowed, its field value MUST exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents MUST notify the user when an invalid length is received and detected. 4.5 General ヘッダ フィールドs There are a few ヘッダ フィールドs which have general applicability for both リクエスト and レスポンス messages, but which do not apply to the entity being transferred. These ヘッダ フィールドs apply only to the Fielding, et al. Standards Track [Page 34] RFC 2616 HTTP/1.1 1999年6月 message being transmitted. general-header = Cache-Control ; Section 14.9 | Connection ; Section 14.10 | Date ; Section 14.18 | Pragma ; Section 14.32 | Trailer ; Section 14.40 | Transfer-Encoding ; Section 14.41 | Upgrade ; Section 14.42 | Via ; Section 14.45 | Warning ; Section 14.46 General-ヘッダ フィールド names can be extended reliably only in combination with a change in the protocol version. However, new or experimental ヘッダ フィールドs may be given the semantics of general ヘッダ フィールドs if all parties in the コミュニケーション recognize them to be general-ヘッダ フィールドs. Unrecognized ヘッダ フィールドs are treated as entity-ヘッダ フィールドs. 5 リクエスト A リクエスト message from a client to a server includes, within the first line of that message, the method to be applied to the resource, the identifier of the resource, and the protocol version in use. リクエスト = リクエスト-Line ; Section 5.1 *(( general-header ; Section 4.5 | リクエスト-header ; Section 5.3 | entity-header ) CRLF) ; Section 7.1 CRLF [ message-body ] ; Section 4.3 5.1 リクエスト-Line The リクエスト-Line begins with a method token, followed by the リクエスト-URI and the protocol version, and ending with CRLF. The elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence. リクエスト-Line = Method SP リクエスト-URI SP HTTP-Version CRLF Fielding, et al. Standards Track [Page 35] RFC 2616 HTTP/1.1 1999年6月 5.1.1 Method The Method token indicates the method to be performed on the resource identified by the リクエスト-URI. The method is case-sensitive. Method = "OPTIONS" ; Section 9.2 | "GET" ; Section 9.3 | "HEAD" ; Section 9.4 | "POST" ; Section 9.5 | "PUT" ; Section 9.6 | "DELETE" ; Section 9.7 | "TRACE" ; Section 9.8 | "CONNECT" ; Section 9.9 | extension-method extension-method = token The list of methods allowed by a resource can be specified in an Allow ヘッダ フィールド (section 14.7). The return code of the レスポンス always notifies the client whether a method is currently allowed on a resource, since the set of allowed methods can change dynamically. An 元のサーバ SHOULD return the ステータス コード 405 (Method Not Allowed) if the method is known by the 元のサーバ but not allowed for the リクエストed resource, and 501 (Not Implemented) if the method is unrecognized or not implemented by the 元のサーバ. The methods GET and HEAD MUST be supported by all general-purpose servers. All other methods are OPTIONAL; however, if the above methods are implemented, they MUST be implemented with the same semantics as those specified in section 9. 5.1.2 リクエスト-URI The リクエスト-URI is a Uniform Resource Identifier (section 3.2) and identifies the resource upon which to apply the リクエスト. リクエスト-URI = "*" | absoluteURI | abs_path | authority The four options for リクエスト-URI are dependent on the nature of the リクエスト. The asterisk "*" means that the リクエスト does not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. One example would be OPTIONS * HTTP/1.1 The absoluteURI form is REQUIRED when the リクエスト is being made to a プロキシ(proxy). The プロキシ(proxy) is リクエストed to forward the リクエスト or service it from a valid cache, and return the レスポンス. Note that the プロキシ(proxy) MAY forward the リクエスト on to another プロキシ(proxy) or directly to the server Fielding, et al. Standards Track [Page 36] RFC 2616 HTTP/1.1 1999年6月 specified by the absoluteURI. In order to avoid リクエスト loops, a プロキシ(proxy) MUST be able to recognize all of its server names, including any aliases, local variations, and the numeric IPアドレス. An example リクエスト-Line would be: GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1 To allow for transition to absoluteURIs in all リクエストs in future versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI form in リクエストs, even though HTTP/1.1 clients will only generate them in リクエストs to プロキシ. The authority form is only used by the CONNECT method (section 9.9). The most common form of リクエスト-URI is that used to identify a resource on an 元のサーバ or gateway. In this case the absolute path of the URI MUST be transmitted (see section 3.2.1, abs_path) as the リクエスト-URI, and the network location of the URI (authority) MUST be transmitted in a Host ヘッダ フィールド. For example, a client wishing to retrieve the resource above directly from the 元のサーバ would create a TCP connection to port 80 of the host "www.w3.org" and send the lines: GET /pub/WWW/TheProject.html HTTP/1.1 Host: www.w3.org followed by the remainder of the リクエスト. Note that the absolute path cannot be empty; if none is present in the original URI, it MUST be given as "/" (the server root). The リクエスト-URI is transmitted in the format specified in section 3.2.1. If the リクエスト-URI is encoded using the "% HEX HEX" encoding [42], the 元のサーバ MUST decode the リクエスト-URI in order to properly interpret the リクエスト. Servers SHOULD respond to invalid リクエスト-URIs with an appropriate ステータス コード. A transparent プロキシ(proxy) MUST NOT rewrite the "abs_path" part of the received リクエスト-URI when forwarding it to the next inbound server, except as noted above to replace a null abs_path with "/". Note: The "no rewrite" rule prevents the プロキシ(proxy) from changing the meaning of the リクエスト when the 元のサーバ is improperly using a non-reserved URI character for a reserved purpose. 実装者 should be aware that some pre-HTTP/1.1 プロキシ have been known to rewrite the リクエスト-URI. Fielding, et al. Standards Track [Page 37] RFC 2616 HTTP/1.1 1999年6月 5.2 The Resource Identified by a リクエスト The exact resource identified by an Internet リクエスト is determined by examining both the リクエスト-URI and the Host ヘッダ フィールド. An 元のサーバ that does not allow resources to differ by the リクエストed host MAY ignore the Host ヘッダ フィールド value when determining the resource identified by an HTTP/1.1 リクエスト. (But see section 19.6.1.1 for other requirements on Host support in HTTP/1.1.) An 元のサーバ that does differentiate resources based on the host リクエストed (sometimes referred to as virtual hosts or vanity host names) MUST use the following rules for determining the リクエストed resource on an HTTP/1.1 リクエスト: 1. If リクエスト-URI is an absoluteURI, the host is part of the リクエスト-URI. Any Host ヘッダ フィールド value in the リクエスト MUST be ignored. 2. If the リクエスト-URI is not an absoluteURI, and the リクエスト includes a Host ヘッダ フィールド, the host is determined by the Host header field value. 3. If the host as determined by rule 1 or 2 is not a valid host on the server, the レスポンス MUST be a 400 (Bad リクエスト) error message. Recipients of an HTTP/1.0 リクエスト that lacks a Host ヘッダ フィールド MAY attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine what exact resource is being リクエストed. 5.3 リクエスト ヘッダ フィールドs The リクエスト-ヘッダ フィールドs allow the client to pass additional information about the リクエスト, and about the client itself, to the server. These fields act as リクエスト modifiers, with semantics equivalent to the parameters on a programming language method invocation. リクエスト-header = Accept ; Section 14.1 | Accept-Charset ; Section 14.2 | Accept-Encoding ; Section 14.3 | Accept-Language ; Section 14.4 | Authorization ; Section 14.8 | Expect ; Section 14.20 | From ; Section 14.22 | Host ; Section 14.23 | If-Match ; Section 14.24 Fielding, et al. Standards Track [Page 38] RFC 2616 HTTP/1.1 1999年6月 | If-Modified-Since ; Section 14.25 | If-None-Match ; Section 14.26 | If-Range ; Section 14.27 | If-Unmodified-Since ; Section 14.28 | Max-Forwards ; Section 14.31 | プロキシ(proxy)-Authorization ; Section 14.34 | Range ; Section 14.35 | Referer ; Section 14.36 | TE ; Section 14.39 | User-Agent ; Section 14.43 リクエスト-ヘッダ フィールド names can be extended reliably only in combination with a change in the protocol version. However, new or experimental ヘッダ フィールドs MAY be given the semantics of リクエスト- ヘッダ フィールドs if all parties in the コミュニケーション recognize them to be リクエスト-ヘッダ フィールドs. Unrecognized ヘッダ フィールドs are treated as entity-ヘッダ フィールドs. 6 レスポンス After receiving and interpreting a リクエスト message, a server responds with an HTTP レスポンス message. レスポンス = Status-Line ; Section 6.1 *(( general-header ; Section 4.5 | レスポンス-header ; Section 6.2 | entity-header ) CRLF) ; Section 7.1 CRLF [ message-body ] ; Section 7.2 6.1 Status-Line The first line of a レスポンス message is the Status-Line, consisting of the protocol version followed by a numeric ステータス コード and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final CRLF sequence. Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF 6.1.1 ステータス コード and Reason Phrase The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the リクエスト. These codes are fully defined in section 10. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason- Phrase. Fielding, et al. Standards Track [Page 39] RFC 2616 HTTP/1.1 1999年6月 The first digit of the Status-Code defines the class of レスポンス. The last two digits do not have any categorization role. There are 5 values for the first digit: - 1xx: Informational - リクエスト received, continuing process - 2xx: Success - The action was successfully received, understood, and accepted - 3xx: Redirection - Further action must be taken in order to complete the リクエスト - 4xx: Client Error - The リクエスト contains bad syntax or cannot be fulfilled - 5xx: Server Error - The server failed to fulfill an apparently valid リクエスト The individual values of the numeric ステータス コードs defined for HTTP/1.1, and an example set of corresponding Reason-Phrase's, are presented below. The reason phrases listed here are only recommendations -- they MAY be replaced by local equivalents without affecting the protocol. Status-Code = "100" ; Section 10.1.1: Continue | "101" ; Section 10.1.2: Switching Protocols | "200" ; Section 10.2.1: OK | "201" ; Section 10.2.2: Created | "202" ; Section 10.2.3: Accepted | "203" ; Section 10.2.4: Non-Authoritative Information | "204" ; Section 10.2.5: No Content | "205" ; Section 10.2.6: Reset Content | "206" ; Section 10.2.7: Partial Content | "300" ; Section 10.3.1: Multiple Choices | "301" ; Section 10.3.2: Moved Permanently | "302" ; Section 10.3.3: Found | "303" ; Section 10.3.4: See Other | "304" ; Section 10.3.5: Not Modified | "305" ; Section 10.3.6: Use プロキシ(proxy) | "307" ; Section 10.3.8: Temporary Redirect | "400" ; Section 10.4.1: Bad リクエスト | "401" ; Section 10.4.2: Unauthorized | "402" ; Section 10.4.3: Payment Required | "403" ; Section 10.4.4: Forbidden | "404" ; Section 10.4.5: Not Found | "405" ; Section 10.4.6: Method Not Allowed | "406" ; Section 10.4.7: Not Acceptable Fielding, et al. Standards Track [Page 40] RFC 2616 HTTP/1.1 1999年6月 | "407" ; Section 10.4.8: プロキシ(proxy) 認証 Required | "408" ; Section 10.4.9: リクエスト Time-out | "409" ; Section 10.4.10: Conflict | "410" ; Section 10.4.11: Gone | "411" ; Section 10.4.12: Length Required | "412" ; Section 10.4.13: Precondition Failed | "413" ; Section 10.4.14: リクエスト Entity Too Large | "414" ; Section 10.4.15: リクエスト-URI Too Large | "415" ; Section 10.4.16: Unsupported Media Type | "416" ; Section 10.4.17: リクエストed range not satisfiable | "417" ; Section 10.4.18: Expectation Failed | "500" ; Section 10.5.1: Internal Server Error | "501" ; Section 10.5.2: Not Implemented | "502" ; Section 10.5.3: Bad Gateway | "503" ; Section 10.5.4: Service Unavailable | "504" ; Section 10.5.5: ゲートウェイ Time-out | "505" ; Section 10.5.6: HTTP Version not supported | extension-code extension-code = 3DIGIT Reason-Phrase = * HTTP ステータスコード are extensible. HTTP アプリケーションs are not required to understand the meaning of all registered ステータス コードs, though such understanding is obviously desirable. However, アプリケーションs MUST understand the class of any ステータス コード, as indicated by the first digit, and treat any unrecognized レスポンス as being equivalent to the x00 ステータス コード of that class, with the exception that an unrecognized レスポンス MUST NOT be cached. For example, if an unrecognized ステータス コード of 431 is received by the client, it can safely assume that there was something wrong with its リクエスト and treat the レスポンス as if it had received a 400 ステータス コード. In such cases, user agents SHOULD present to the user the entity returned with the レスポンス, since that entity is likely to include human- readable information which will explain the unusual status. 6.2 レスポンス ヘッダ フィールドs The レスポンス-ヘッダ フィールドs allow the server to pass additional information about the レスポンス which cannot be placed in the Status- Line. These ヘッダ フィールドs give information about the server and about further access to the resource identified by the リクエスト-URI. レスポンス-header = Accept-Ranges ; Section 14.5 | Age ; Section 14.6 | ETag ; Section 14.19 | Location ; Section 14.30 | プロキシ(proxy)-Authenticate ; Section 14.33 Fielding, et al. Standards Track [Page 41] RFC 2616 HTTP/1.1 1999年6月 | Retry-After ; Section 14.37 | Server ; Section 14.38 | Vary ; Section 14.44 | WWW-Authenticate ; Section 14.47 レスポンス-ヘッダ フィールド names can be extended reliably only in combination with a change in the protocol version. However, new or experimental ヘッダ フィールドs MAY be given the semantics of レスポンス- ヘッダ フィールドs if all parties in the コミュニケーション recognize them to be レスポンス-ヘッダ フィールドs. Unrecognized ヘッダ フィールドs are treated as entity-ヘッダ フィールドs. 7 Entity リクエスト and レスポンス messages MAY transfer an entity if not otherwise restricted by the リクエスト method or レスポンス ステータス コード. An entity consists of entity-ヘッダ フィールドs and an entity-body, although some レスポンスs will only include the entity-headers. In this section, both sender and recipient refer to either the client or the server, depending on who sends and who receives the entity. 7.1 Entity ヘッダ フィールドs Entity-ヘッダ フィールドs define metainformation about the entity-body or, if no body is present, about the resource identified by the リクエスト. Some of this metainformation is OPTIONAL; some might be REQUIRED by portions of this specification. entity-header = Allow ; Section 14.7 | Content-Encoding ; Section 14.11 | Content-Language ; Section 14.12 | Content-Length ; Section 14.13 | Content-Location ; Section 14.14 | Content-MD5 ; Section 14.15 | Content-Range ; Section 14.16 | Content-Type ; Section 14.17 | Expires ; Section 14.21 | Last-Modified ; Section 14.29 | extension-header extension-header = message-header The extension-header mechanism allows additional entity-ヘッダ フィールドs to be defined without changing the protocol, but these fields cannot be assumed to be recognizable by the recipient. Unrecognized header fields SHOULD be ignored by the recipient and MUST be forwarded by transparent プロキシ. Fielding, et al. Standards Track [Page 42] RFC 2616 HTTP/1.1 1999年6月 7.2 Entity Body The entity-body (if any) sent with an HTTPリクエスト or レスポンス is in a format and encoding defined by the entity-ヘッダ フィールドs. entity-body = *OCTET An entity-body is only present in a message when a message-body is present, as described in section 4.3. The entity-body is obtained from the message-body by decoding any Transfer-Encoding that might have been applied to ensure safe and proper transfer of the message. 7.2.1 Type When an entity-body is included with a message, the data type of that body is determined via the ヘッダ フィールドs Content-Type and Content- Encoding. These define a two-layer, ordered encoding model: entity-body := Content-Encoding( Content-Type( data ) ) Content-Type specifies the media type of the underlying data. Content-Encoding may be used to indicate any additional content codings applied to the data, usually for the purpose of data compression, that are a property of the リクエストed resource. There is no default encoding. Any HTTP/1.1 message containing an entity-body SHOULD include a Content-Type ヘッダ フィールド defining the media type of that body. If and only if the media type is not given by a Content-Type field, the recipient MAY attempt to guess the media type via inspection of its content and/or the name extension(s) of the URI used to identify the resource. If the media type remains unknown, the recipient SHOULD treat it as type "application/octet-stream". 7.2.2 Entity Length The entity-length of a message is the length of the message-body before any transfer-codings have been applied. Section 4.4 defines how the transfer-length of a message-body is determined. Fielding, et al. Standards Track [Page 43] RFC 2616 HTTP/1.1 1999年6月 8 Connections 8.1 Persistent Connections 8.1.1 Purpose Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP servers and causing congestion on the Internet. The use of inline images and other associated data often require a client to make multiple リクエストs of the same server in a short amount of time. Analysis of these performance problems and results from a prototype implementation are available [26] [30]. Implementation experience and measurements of actual HTTP/1.1 (RFC 2068) implementations show good results [39]. Alternatives have also been explored, for example, T/TCP [27]. Persistent HTTP connections have a number of advantages: - By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, プロキシ, gateways, tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts. - HTTPリクエストs and レスポンスs can be pipelined on a connection. Pipelining allows a client to make multiple リクエストs without waiting for each レスポンス, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time. - Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to determine the congestion state of the network. - Latency on subsequent リクエストs is reduced since there is no time spent in TCP's connection opening handshake. - HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old semantics after an error is reported. HTTP implementations SHOULD implement persistent connections. Fielding, et al. Standards Track [Page 44] RFC 2616 HTTP/1.1 1999年6月 8.1.2 Overall Operation A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior of any HTTP connection. That is, unless otherwise indicated, the client SHOULD assume that the server will maintain a persistent connection, even after error レスポンスs from the server. Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling takes place using the Connection ヘッダ フィールド (section 14.10). Once a close has been signaled, the client MUST NOT send any more リクエストs on that connection. 8.1.2.1 ネゴシエーション(Negotiation) An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token "close" was sent in the リクエスト. If the server chooses to close the connection immediately after sending the レスポンス, it SHOULD send a Connection header including the connection-token close. An HTTP/1.1 client MAY expect a connection to remain open, but would decide to keep it open based on whether the レスポンス from a server contains a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than that リクエスト, it SHOULD send a Connection header including the connection-token close. If either the client or the server sends the close token in the Connection header, that リクエスト becomes the last one for the connection. Clients and servers SHOULD NOT assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See section 19.6.2 for more information on backward compatibility with HTTP/1.0 clients. In order to remain persistent, all messages on the connection MUST have a self-defined message length (i.e., one not defined by closure of the connection), as described in section 4.4. Fielding, et al. Standards Track [Page 45] RFC 2616 HTTP/1.1 1999年6月 8.1.2.2 Pipelining A client that supports persistent connections MAY "pipeline" its リクエストs (i.e., send multiple リクエストs without waiting for each レスポンス). A server MUST send its レスポンスs to those リクエストs in the same order that the リクエストs were received. Clients which assume persistent connections and pipeline immediately after connection establishment SHOULD be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it MUST NOT pipeline before it knows the connection is persistent. Clients MUST also be prepared to resend their リクエストs if the server closes the connection before sending all of the corresponding レスポンスs. Clients SHOULD NOT pipeline リクエストs using non-idempotent methods or non-idempotent sequences of methods (see section 9.1.2). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to send a non-idempotent リクエスト SHOULD wait to send that リクエスト until it has received the レスポンス status for the previous リクエスト. 8.1.3 プロキシ サーバ It is especially important that プロキシ correctly implement the properties of the Connection ヘッダ フィールド as specified in section 14.10. The プロキシ(proxy) server MUST signal persistent connections separately with its clients and the 元のサーバs (or other プロキシ(proxy) servers) that it connects to. Each persistent connection applies to only one transport link. A プロキシ(proxy) server MUST NOT establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see RFC 2068 [33] for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients). 8.1.4 Practical Considerations Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. プロキシ(proxy) servers might make this a higher value since it is likely that the client will be making more connections through the same server. The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client or the server. Fielding, et al. Standards Track [Page 46] RFC 2616 HTTP/1.1 1999年6月 When a client or server wishes to time-out it SHOULD issue a graceful close on the transport connection. Clients and servers SHOULD both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does not detect the other side's close promptly it could cause unnecessary resource drain on the network. A client, server, or プロキシ(proxy) MAY close the transport connection at any time. For example, a client might have started to send a new リクエスト at the same time that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed while it was idle, but from the client's point of view, a リクエスト is in progress. This means that clients, servers, and プロキシ MUST be able to recover from asynchronous close events. Client software SHOULD reopen the transport connection and retransmit the aborted sequence of リクエストs without user interaction so long as the リクエスト sequence is idempotent (see section 9.1.2). Non-idempotent methods or sequences MUST NOT be automatically retried, although user agents MAY offer a human operator the choice of retrying the リクエスト(s). Confirmation by user-agent software with semantic understanding of the アプリケーション MAY substitute for user confirmation. The automatic retry SHOULD NOT be repeated if the second sequence of リクエストs fails. Servers SHOULD always respond to at least one リクエスト per connection, if at all possible. Servers SHOULD NOT close a connection in the middle of transmitting a レスポンス, unless a network or client failure is suspected. Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or プロキシ(proxy). A プロキシ(proxy) SHOULD use up to 2*N connections to another server or プロキシ(proxy), where N is the number of simultaneously active users. These guidelines are intended to improve HTTP レスポンス times and avoid congestion. 8.2 Message Transmission Requirements 8.2.1 Persistent Connections and Flow Control HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating connections with the expectation that clients will retry. The latter technique can exacerbate network congestion. Fielding, et al. Standards Track [Page 47] RFC 2616 HTTP/1.1 1999年6月 8.2.2 Monitoring Connections for Error Status Messages An HTTP/1.1 (or later) client sending a message-body SHOULD monitor the network connection for an error status while it is transmitting the リクエスト. If the client sees an error status, it SHOULD immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (section 3.6), a zero length chunk and empty trailer MAY be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client MUST close the connection. 8.2.3 Use of the 100 (Continue) Status The purpose of the 100 (Continue) status (see section 10.1.1) is to allow a client that is sending a リクエスト message with a リクエスト body to determine if the 元のサーバ is willing to accept the リクエスト (based on the リクエスト headers) before the client sends the リクエスト body. In some cases, it might either be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking at the body. Requirements for HTTP/1.1 clients: - If a client will wait for a 100 (Continue) レスポンス before sending the リクエスト body, it MUST send an Expect リクエスト-header field (section 14.20) with the "100-continue" expectation. - A client MUST NOT send an Expect リクエスト-ヘッダ フィールド (section 14.20) with the "100-continue" expectation if it does not intend to send a リクエスト body. Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect: 100- continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client sends this ヘッダ フィールド to an 元のサーバ (possibly via a プロキシ(proxy)) from which it has never seen a 100 (Continue) status, the client SHOULD NOT wait for an indefinite period before sending the リクエスト body. Requirements for HTTP/1.1 元のサーバs: - Upon receiving a リクエスト which includes an Expect リクエスト-header field with the "100-continue" expectation, an 元のサーバ MUST either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final ステータス コード. The 元のサーバ MUST NOT wait for the リクエスト body before sending the 100 (Continue) レスポンス. If it responds with a final status code, it MAY close the transport connection or it MAY continue Fielding, et al. Standards Track [Page 48] RFC 2616 HTTP/1.1 1999年6月 to read and discard the rest of the リクエスト. It MUST NOT perform the リクエストed method if it returns a final ステータス コード. - An 元のサーバ SHOULD NOT send a 100 (Continue) レスポンス if the リクエスト message does not include an Expect リクエスト-header field with the "100-continue" expectation, and MUST NOT send a 100 (Continue) レスポンス if such a リクエスト comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility with RFC 2068, a server MAY send a 100 (Continue) status in レスポンス to an HTTP/1.1 PUT or POST リクエスト that does not include an Expect リクエスト-ヘッダ フィールド with the "100- continue" expectation. This exception, the purpose of which is to minimize any client processing delays associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 リクエストs, and not to リクエストs with any other HTTP- version value. - An 元のサーバ MAY omit a 100 (Continue) レスポンス if it has already received some or all of the リクエスト body for the corresponding リクエスト. - An 元のサーバ that sends a 100 (Continue) レスポンス MUST ultimately send a final ステータス コード, once the リクエスト body is received and processed, unless it terminates the transport connection prematurely. - If an 元のサーバ receives a リクエスト that does not include an Expect リクエスト-ヘッダ フィールド with the "100-continue" expectation, the リクエスト includes a リクエスト body, and the server responds with a final ステータス コード before reading the entire リクエスト body from the transport connection, then the server SHOULD NOT close the transport connection until it has read the entire リクエスト, or until the client closes the connection. Otherwise, the client might not reliably receive the レスポンス message. However, this requirement is not be construed as preventing a server from defending itself against denial-of-service attacks, or from badly broken client implementations. Requirements for HTTP/1.1 プロキシ: - If a プロキシ(proxy) receives a リクエスト that includes an Expect リクエスト- ヘッダ フィールド with the "100-continue" expectation, and the プロキシ(proxy) either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop server, it MUST forward the リクエスト, including the Expect header field. Fielding, et al. Standards Track [Page 49] RFC 2616 HTTP/1.1 1999年6月 - If the プロキシ(proxy) knows that the version of the next-hop server is HTTP/1.0 or lower, it MUST NOT forward the リクエスト, and it MUST respond with a 417 (Expectation Failed) status. - プロキシ SHOULD maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers. - A プロキシ(proxy) MUST NOT forward a 100 (Continue) レスポンス if the リクエスト message was received from an HTTP/1.0 (or earlier) client and did not include an Expect リクエスト-ヘッダ フィールド with the "100-continue" expectation. This requirement overrides the general rule for forwarding of 1xx レスポンスs (see section 10.1). 8.2.4 Client Behavior if Server Prematurely Closes Connection If an HTTP/1.1 client sends a リクエスト which includes a リクエスト body, but which does not include an Expect リクエスト-ヘッダ フィールド with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 元のサーバ, and if the client sees the connection close before receiving any status from the server, the client SHOULD retry the リクエスト. If the client does retry this リクエスト, it MAY use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable レスポンス: 1. Initiate a new connection to the server 2. Transmit the リクエスト-headers 3. Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection), or to a constant value of 5 seconds if the round- trip time is not available. 4. Compute T = R * (2**N), where N is the number of previous retries of this リクエスト. 5. Wait either for an error レスポンス from the server, or for T seconds (whichever comes first) 6. If no error レスポンス is received, after T seconds transmit the body of the リクエスト. 7. If client sees that the connection is closed prematurely, repeat from step 1 until the リクエスト is accepted, an error レスポンス is received, or the user becomes impatient and terminates the retry process. Fielding, et al. Standards Track [Page 50] RFC 2616 HTTP/1.1 1999年6月 If at any point an error status is received, the client - SHOULD NOT continue and - SHOULD close the connection if it has not completed sending the リクエスト message. 9 Method Definitions The set of common methods for HTTP/1.1 is defined below. Although this set can be expanded, additional methods cannot be assumed to share the same semantics for separately extended clients and servers. The Host リクエスト-ヘッダ フィールド (section 14.23) MUST accompany all HTTP/1.1 リクエストs. 9.1 Safe and Idempotent Methods 9.1.1 Safe Methods 実装者 should be aware that the software represents the user in their interactions over the Internet, and should be careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves or others. In particul