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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 HTTPbis Working Group R. Fielding, Ed. 3 Internet-Draft Day Software 4 Obsoletes: 2616 (if approved) J. Gettys 5 Intended status: Standards Track One Laptop per Child 6 Expires: January 14, 2010 J. Mogul 7 HP 8 H. Frystyk 9 Microsoft 10 L. Masinter 11 Adobe Systems 12 P. Leach 13 Microsoft 14 T. Berners-Lee 15 W3C/MIT 16 Y. Lafon, Ed. 17 W3C 18 J. Reschke, Ed. 19 greenbytes 20 July 13, 2009 22 HTTP/1.1, part 3: Message Payload and Content Negotiation 23 draft-ietf-httpbis-p3-payload-07 25 Status of this Memo 27 This Internet-Draft is submitted to IETF in full conformance with the 28 provisions of BCP 78 and BCP 79. This document may contain material 29 from IETF Documents or IETF Contributions published or made publicly 30 available before November 10, 2008. The person(s) controlling the 31 copyright in some of this material may not have granted the IETF 32 Trust the right to allow modifications of such material outside the 33 IETF Standards Process. Without obtaining an adequate license from 34 the person(s) controlling the copyright in such materials, this 35 document may not be modified outside the IETF Standards Process, and 36 derivative works of it may not be created outside the IETF Standards 37 Process, except to format it for publication as an RFC or to 38 translate it into languages other than English. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF), its areas, and its working groups. Note that 42 other groups may also distribute working documents as Internet- 43 Drafts. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 The list of current Internet-Drafts can be accessed at 50 http://www.ietf.org/ietf/1id-abstracts.txt. 52 The list of Internet-Draft Shadow Directories can be accessed at 53 http://www.ietf.org/shadow.html. 55 This Internet-Draft will expire on January 14, 2010. 57 Copyright Notice 59 Copyright (c) 2009 IETF Trust and the persons identified as the 60 document authors. All rights reserved. 62 This document is subject to BCP 78 and the IETF Trust's Legal 63 Provisions Relating to IETF Documents in effect on the date of 64 publication of this document (http://trustee.ietf.org/license-info). 65 Please review these documents carefully, as they describe your rights 66 and restrictions with respect to this document. 68 Abstract 70 The Hypertext Transfer Protocol (HTTP) is an application-level 71 protocol for distributed, collaborative, hypermedia information 72 systems. HTTP has been in use by the World Wide Web global 73 information initiative since 1990. This document is Part 3 of the 74 seven-part specification that defines the protocol referred to as 75 "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 3 defines 76 HTTP message content, metadata, and content negotiation. 78 Editorial Note (To be removed by RFC Editor) 80 Discussion of this draft should take place on the HTTPBIS working 81 group mailing list (ietf-http-wg@w3.org). The current issues list is 82 at and related 83 documents (including fancy diffs) can be found at 84 . 86 The changes in this draft are summarized in Appendix E.8. 88 Table of Contents 90 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 91 1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5 92 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5 93 1.2.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 6 94 1.2.2. ABNF Rules defined in other Parts of the 95 Specification . . . . . . . . . . . . . . . . . . . . 6 96 2. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 6 97 2.1. Character Sets . . . . . . . . . . . . . . . . . . . . . . 6 98 2.1.1. Missing Charset . . . . . . . . . . . . . . . . . . . 7 99 2.2. Content Codings . . . . . . . . . . . . . . . . . . . . . 7 100 2.3. Media Types . . . . . . . . . . . . . . . . . . . . . . . 9 101 2.3.1. Canonicalization and Text Defaults . . . . . . . . . . 9 102 2.3.2. Multipart Types . . . . . . . . . . . . . . . . . . . 10 103 2.4. Language Tags . . . . . . . . . . . . . . . . . . . . . . 11 104 3. Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 105 3.1. Entity Header Fields . . . . . . . . . . . . . . . . . . . 12 106 3.2. Entity Body . . . . . . . . . . . . . . . . . . . . . . . 12 107 3.2.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 12 108 3.2.2. Entity Length . . . . . . . . . . . . . . . . . . . . 13 109 4. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 13 110 4.1. Server-driven Negotiation . . . . . . . . . . . . . . . . 14 111 4.2. Agent-driven Negotiation . . . . . . . . . . . . . . . . . 15 112 4.3. Transparent Negotiation . . . . . . . . . . . . . . . . . 15 113 5. Header Field Definitions . . . . . . . . . . . . . . . . . . . 16 114 5.1. Accept . . . . . . . . . . . . . . . . . . . . . . . . . . 16 115 5.2. Accept-Charset . . . . . . . . . . . . . . . . . . . . . . 18 116 5.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . . . 19 117 5.4. Accept-Language . . . . . . . . . . . . . . . . . . . . . 20 118 5.5. Content-Encoding . . . . . . . . . . . . . . . . . . . . . 22 119 5.6. Content-Language . . . . . . . . . . . . . . . . . . . . . 23 120 5.7. Content-Location . . . . . . . . . . . . . . . . . . . . . 24 121 5.8. Content-MD5 . . . . . . . . . . . . . . . . . . . . . . . 24 122 5.9. Content-Type . . . . . . . . . . . . . . . . . . . . . . . 26 123 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 124 6.1. Message Header Registration . . . . . . . . . . . . . . . 26 125 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27 126 7.1. Privacy Issues Connected to Accept Headers . . . . . . . . 27 127 7.2. Content-Disposition Issues . . . . . . . . . . . . . . . . 28 128 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 129 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 130 9.1. Normative References . . . . . . . . . . . . . . . . . . . 28 131 9.2. Informative References . . . . . . . . . . . . . . . . . . 30 132 Appendix A. Differences Between HTTP Entities and RFC 2045 133 Entities . . . . . . . . . . . . . . . . . . . . . . 31 134 A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . . 31 135 A.2. Conversion to Canonical Form . . . . . . . . . . . . . . . 32 136 A.3. Conversion of Date Formats . . . . . . . . . . . . . . . . 32 137 A.4. Introduction of Content-Encoding . . . . . . . . . . . . . 32 138 A.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . . 33 139 A.6. Introduction of Transfer-Encoding . . . . . . . . . . . . 33 140 A.7. MHTML and Line Length Limitations . . . . . . . . . . . . 33 141 Appendix B. Additional Features . . . . . . . . . . . . . . . . . 33 142 B.1. Content-Disposition . . . . . . . . . . . . . . . . . . . 34 143 Appendix C. Compatibility with Previous Versions . . . . . . . . 34 144 C.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 34 145 C.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 35 146 Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 35 147 Appendix E. Change Log (to be removed by RFC Editor before 148 publication) . . . . . . . . . . . . . . . . . . . . 37 149 E.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 37 150 E.2. Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . . 37 151 E.3. Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . . 38 152 E.4. Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . . 38 153 E.5. Since draft-ietf-httpbis-p3-payload-03 . . . . . . . . . . 39 154 E.6. Since draft-ietf-httpbis-p3-payload-04 . . . . . . . . . . 39 155 E.7. Since draft-ietf-httpbis-p3-payload-05 . . . . . . . . . . 39 156 E.8. Since draft-ietf-httpbis-p3-payload-06 . . . . . . . . . . 40 157 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 158 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42 160 1. Introduction 162 This document defines HTTP/1.1 message payloads (a.k.a., content), 163 the associated metadata header fields that define how the payload is 164 intended to be interpreted by a recipient, the request header fields 165 that may influence content selection, and the various selection 166 algorithms that are collectively referred to as HTTP content 167 negotiation. 169 This document is currently disorganized in order to minimize the 170 changes between drafts and enable reviewers to see the smaller errata 171 changes. The next draft will reorganize the sections to better 172 reflect the content. In particular, the sections on entities will be 173 renamed payload and moved to the first half of the document, while 174 the sections on content negotiation and associated request header 175 fields will be moved to the second half. The current mess reflects 176 how widely dispersed these topics and associated requirements had 177 become in [RFC2616]. 179 1.1. Requirements 181 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 182 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 183 document are to be interpreted as described in [RFC2119]. 185 An implementation is not compliant if it fails to satisfy one or more 186 of the MUST or REQUIRED level requirements for the protocols it 187 implements. An implementation that satisfies all the MUST or 188 REQUIRED level and all the SHOULD level requirements for its 189 protocols is said to be "unconditionally compliant"; one that 190 satisfies all the MUST level requirements but not all the SHOULD 191 level requirements for its protocols is said to be "conditionally 192 compliant." 194 1.2. Syntax Notation 196 This specification uses the ABNF syntax defined in Section 1.2 of 197 [Part1] (which extends the syntax defined in [RFC5234] with a list 198 rule). Appendix D shows the collected ABNF, with the list rule 199 expanded. 201 The following core rules are included by reference, as defined in 202 [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF 203 (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), 204 HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit 205 sequence of data), SP (space), VCHAR (any visible USASCII character), 206 and WSP (whitespace). 208 1.2.1. Core Rules 210 The core rules below are defined in Section 1.2.2 of [Part1]: 212 quoted-string = 213 token = 214 OWS = 216 1.2.2. ABNF Rules defined in other Parts of the Specification 218 The ABNF rules below are defined in other parts: 220 absolute-URI = 221 Content-Length = 222 message-header = 223 partial-URI = 224 qvalue = 226 Last-Modified = 228 Content-Range = 230 Expires = 232 2. Protocol Parameters 234 2.1. Character Sets 236 HTTP uses the same definition of the term "character set" as that 237 described for MIME: 239 The term "character set" is used in this document to refer to a 240 method used with one or more tables to convert a sequence of octets 241 into a sequence of characters. Note that unconditional conversion in 242 the other direction is not required, in that not all characters may 243 be available in a given character set and a character set may provide 244 more than one sequence of octets to represent a particular character. 245 This definition is intended to allow various kinds of character 246 encoding, from simple single-table mappings such as US-ASCII to 247 complex table switching methods such as those that use ISO-2022's 248 techniques. However, the definition associated with a MIME character 249 set name MUST fully specify the mapping to be performed from octets 250 to characters. In particular, use of external profiling information 251 to determine the exact mapping is not permitted. 253 Note: This use of the term "character set" is more commonly 254 referred to as a "character encoding." However, since HTTP and 255 MIME share the same registry, it is important that the terminology 256 also be shared. 258 HTTP character sets are identified by case-insensitive tokens. The 259 complete set of tokens is defined by the IANA Character Set registry 260 (). 262 charset = token 264 Although HTTP allows an arbitrary token to be used as a charset 265 value, any token that has a predefined value within the IANA 266 Character Set registry MUST represent the character set defined by 267 that registry. Applications SHOULD limit their use of character sets 268 to those defined by the IANA registry. 270 HTTP uses charset in two contexts: within an Accept-Charset request 271 header (in which the charset value is an unquoted token) and as the 272 value of a parameter in a Content-Type header (within a request or 273 response), in which case the parameter value of the charset parameter 274 may be quoted. 276 Implementors should be aware of IETF character set requirements 277 [RFC3629] [RFC2277]. 279 2.1.1. Missing Charset 281 Some HTTP/1.0 software has interpreted a Content-Type header without 282 charset parameter incorrectly to mean "recipient should guess." 283 Senders wishing to defeat this behavior MAY include a charset 284 parameter even when the charset is ISO-8859-1 ([ISO-8859-1]) and 285 SHOULD do so when it is known that it will not confuse the recipient. 287 Unfortunately, some older HTTP/1.0 clients did not deal properly with 288 an explicit charset parameter. HTTP/1.1 recipients MUST respect the 289 charset label provided by the sender; and those user agents that have 290 a provision to "guess" a charset MUST use the charset from the 291 content-type field if they support that charset, rather than the 292 recipient's preference, when initially displaying a document. See 293 Section 2.3.1. 295 2.2. Content Codings 297 Content coding values indicate an encoding transformation that has 298 been or can be applied to an entity. Content codings are primarily 299 used to allow a document to be compressed or otherwise usefully 300 transformed without losing the identity of its underlying media type 301 and without loss of information. Frequently, the entity is stored in 302 coded form, transmitted directly, and only decoded by the recipient. 304 content-coding = token 306 All content-coding values are case-insensitive. HTTP/1.1 uses 307 content-coding values in the Accept-Encoding (Section 5.3) and 308 Content-Encoding (Section 5.5) header fields. Although the value 309 describes the content-coding, what is more important is that it 310 indicates what decoding mechanism will be required to remove the 311 encoding. 313 The Internet Assigned Numbers Authority (IANA) acts as a registry for 314 content-coding value tokens. Initially, the registry contains the 315 following tokens: 317 gzip 319 An encoding format produced by the file compression program "gzip" 320 (GNU zip) as described in [RFC1952]. This format is a Lempel-Ziv 321 coding (LZ77) with a 32 bit CRC. 323 compress 325 The encoding format produced by the common UNIX file compression 326 program "compress". This format is an adaptive Lempel-Ziv-Welch 327 coding (LZW). 329 Use of program names for the identification of encoding formats is 330 not desirable and is discouraged for future encodings. Their use 331 here is representative of historical practice, not good design. 332 For compatibility with previous implementations of HTTP, 333 applications SHOULD consider "x-gzip" and "x-compress" to be 334 equivalent to "gzip" and "compress" respectively. 336 deflate 338 The "zlib" format defined in [RFC1950] in combination with the 339 "deflate" compression mechanism described in [RFC1951]. 341 identity 343 The default (identity) encoding; the use of no transformation 344 whatsoever. This content-coding is used only in the Accept- 345 Encoding header, and SHOULD NOT be used in the Content-Encoding 346 header. 348 New content-coding value tokens SHOULD be registered; to allow 349 interoperability between clients and servers, specifications of the 350 content coding algorithms needed to implement a new value SHOULD be 351 publicly available and adequate for independent implementation, and 352 conform to the purpose of content coding defined in this section. 354 2.3. Media Types 356 HTTP uses Internet Media Types [RFC2046] in the Content-Type 357 (Section 5.9) and Accept (Section 5.1) header fields in order to 358 provide open and extensible data typing and type negotiation. 360 media-type = type "/" subtype *( OWS ";" OWS parameter ) 361 type = token 362 subtype = token 364 Parameters MAY follow the type/subtype in the form of attribute/value 365 pairs. 367 parameter = attribute "=" value 368 attribute = token 369 value = token / quoted-string 371 The type, subtype, and parameter attribute names are case- 372 insensitive. Parameter values might or might not be case-sensitive, 373 depending on the semantics of the parameter name. The presence or 374 absence of a parameter might be significant to the processing of a 375 media-type, depending on its definition within the media type 376 registry. 378 A parameter value that matches the token production may be 379 transmitted as either a token or within a quoted-string. The quoted 380 and unquoted values are equivalent. 382 Note that some older HTTP applications do not recognize media type 383 parameters. When sending data to older HTTP applications, 384 implementations SHOULD only use media type parameters when they are 385 required by that type/subtype definition. 387 Media-type values are registered with the Internet Assigned Number 388 Authority (IANA). The media type registration process is outlined in 389 [RFC4288]. Use of non-registered media types is discouraged. 391 2.3.1. Canonicalization and Text Defaults 393 Internet media types are registered with a canonical form. An 394 entity-body transferred via HTTP messages MUST be represented in the 395 appropriate canonical form prior to its transmission except for 396 "text" types, as defined in the next paragraph. 398 When in canonical form, media subtypes of the "text" type use CRLF as 399 the text line break. HTTP relaxes this requirement and allows the 400 transport of text media with plain CR or LF alone representing a line 401 break when it is done consistently for an entire entity-body. HTTP 402 applications MUST accept CRLF, bare CR, and bare LF as being 403 representative of a line break in text media received via HTTP. In 404 addition, if the text is represented in a character set that does not 405 use octets 13 and 10 for CR and LF respectively, as is the case for 406 some multi-byte character sets, HTTP allows the use of whatever octet 407 sequences are defined by that character set to represent the 408 equivalent of CR and LF for line breaks. This flexibility regarding 409 line breaks applies only to text media in the entity-body; a bare CR 410 or LF MUST NOT be substituted for CRLF within any of the HTTP control 411 structures (such as header fields and multipart boundaries). 413 If an entity-body is encoded with a content-coding, the underlying 414 data MUST be in a form defined above prior to being encoded. 416 The "charset" parameter is used with some media types to define the 417 character set (Section 2.1) of the data. When no explicit charset 418 parameter is provided by the sender, media subtypes of the "text" 419 type are defined to have a default charset value of "ISO-8859-1" when 420 received via HTTP. Data in character sets other than "ISO-8859-1" or 421 its subsets MUST be labeled with an appropriate charset value. See 422 Section 2.1.1 for compatibility problems. 424 2.3.2. Multipart Types 426 MIME provides for a number of "multipart" types -- encapsulations of 427 one or more entities within a single message-body. All multipart 428 types share a common syntax, as defined in Section 5.1.1 of 429 [RFC2046], and MUST include a boundary parameter as part of the media 430 type value. The message body is itself a protocol element and MUST 431 therefore use only CRLF to represent line breaks between body-parts. 432 Unlike in RFC 2046, the epilogue of any multipart message MUST be 433 empty; HTTP applications MUST NOT transmit the epilogue (even if the 434 original multipart contains an epilogue). These restrictions exist 435 in order to preserve the self-delimiting nature of a multipart 436 message-body, wherein the "end" of the message-body is indicated by 437 the ending multipart boundary. 439 In general, HTTP treats a multipart message-body no differently than 440 any other media type: strictly as payload. The one exception is the 441 "multipart/byteranges" type (Appendix A of [Part5]) when it appears 442 in a 206 (Partial Content) response. In all other cases, an HTTP 443 user agent SHOULD follow the same or similar behavior as a MIME user 444 agent would upon receipt of a multipart type. The MIME header fields 445 within each body-part of a multipart message-body do not have any 446 significance to HTTP beyond that defined by their MIME semantics. 448 In general, an HTTP user agent SHOULD follow the same or similar 449 behavior as a MIME user agent would upon receipt of a multipart type. 450 If an application receives an unrecognized multipart subtype, the 451 application MUST treat it as being equivalent to "multipart/mixed". 453 Note: The "multipart/form-data" type has been specifically defined 454 for carrying form data suitable for processing via the POST 455 request method, as described in [RFC2388]. 457 2.4. Language Tags 459 A language tag identifies a natural language spoken, written, or 460 otherwise conveyed by human beings for communication of information 461 to other human beings. Computer languages are explicitly excluded. 462 HTTP uses language tags within the Accept-Language and Content- 463 Language fields. 465 The syntax and registry of HTTP language tags is the same as that 466 defined by [RFC1766]. In summary, a language tag is composed of 1 or 467 more parts: A primary language tag and a possibly empty series of 468 subtags: 470 language-tag = primary-tag *( "-" subtag ) 471 primary-tag = 1*8ALPHA 472 subtag = 1*8ALPHA 474 White space is not allowed within the tag and all tags are case- 475 insensitive. The name space of language tags is administered by the 476 IANA. Example tags include: 478 en, en-US, en-cockney, i-cherokee, x-pig-latin 480 where any two-letter primary-tag is an ISO-639 language abbreviation 481 and any two-letter initial subtag is an ISO-3166 country code. (The 482 last three tags above are not registered tags; all but the last are 483 examples of tags which could be registered in future.) 485 3. Entity 487 Request and Response messages MAY transfer an entity if not otherwise 488 restricted by the request method or response status code. An entity 489 consists of entity-header fields and an entity-body, although some 490 responses will only include the entity-headers. 492 In this section, both sender and recipient refer to either the client 493 or the server, depending on who sends and who receives the entity. 495 3.1. Entity Header Fields 497 Entity-header fields define metainformation about the entity-body or, 498 if no body is present, about the resource identified by the request. 500 entity-header = Content-Encoding ; Section 5.5 501 / Content-Language ; Section 5.6 502 / Content-Length ; [Part1], Section 8.2 503 / Content-Location ; Section 5.7 504 / Content-MD5 ; Section 5.8 505 / Content-Range ; [Part5], Section 5.2 506 / Content-Type ; Section 5.9 507 / Expires ; [Part6], Section 3.3 508 / Last-Modified ; [Part4], Section 6.6 509 / extension-header 511 extension-header = message-header 513 The extension-header mechanism allows additional entity-header fields 514 to be defined without changing the protocol, but these fields cannot 515 be assumed to be recognizable by the recipient. Unrecognized header 516 fields SHOULD be ignored by the recipient and MUST be forwarded by 517 transparent proxies. 519 3.2. Entity Body 521 The entity-body (if any) sent with an HTTP request or response is in 522 a format and encoding defined by the entity-header fields. 524 entity-body = *OCTET 526 An entity-body is only present in a message when a message-body is 527 present, as described in Section 4.3 of [Part1]. The entity-body is 528 obtained from the message-body by decoding any Transfer-Encoding that 529 might have been applied to ensure safe and proper transfer of the 530 message. 532 3.2.1. Type 534 When an entity-body is included with a message, the data type of that 535 body is determined via the header fields Content-Type and Content- 536 Encoding. These define a two-layer, ordered encoding model: 538 entity-body := Content-Encoding( Content-Type( data ) ) 540 Content-Type specifies the media type of the underlying data. Any 541 HTTP/1.1 message containing an entity-body SHOULD include a Content- 542 Type header field defining the media type of that body, unless that 543 information is unknown. If the Content-Type header field is not 544 present, it indicates that the sender does not know the media type of 545 the data; recipients MAY either assume that it is "application/ 546 octet-stream" ([RFC2046], Section 4.5.1) or examine the content to 547 determine its type. 549 Content-Encoding may be used to indicate any additional content 550 codings applied to the data, usually for the purpose of data 551 compression, that are a property of the requested resource. There is 552 no default encoding. 554 Note that neither the interpretation of the data type of a message 555 nor the behaviors caused by it are defined by HTTP; this potentially 556 includes examination of the content to override any indicated type 557 ("sniffing"). 559 3.2.2. Entity Length 561 The entity-length of a message is the length of the message-body 562 before any transfer-codings have been applied. Section 4.4 of 563 [Part1] defines how the transfer-length of a message-body is 564 determined. 566 4. Content Negotiation 568 Most HTTP responses include an entity which contains information for 569 interpretation by a human user. Naturally, it is desirable to supply 570 the user with the "best available" entity corresponding to the 571 request. Unfortunately for servers and caches, not all users have 572 the same preferences for what is "best," and not all user agents are 573 equally capable of rendering all entity types. For that reason, HTTP 574 has provisions for several mechanisms for "content negotiation" -- 575 the process of selecting the best representation for a given response 576 when there are multiple representations available. 578 Note: This is not called "format negotiation" because the 579 alternate representations may be of the same media type, but use 580 different capabilities of that type, be in different languages, 581 etc. 583 Any response containing an entity-body MAY be subject to negotiation, 584 including error responses. 586 There are two kinds of content negotiation which are possible in 587 HTTP: server-driven and agent-driven negotiation. These two kinds of 588 negotiation are orthogonal and thus may be used separately or in 589 combination. One method of combination, referred to as transparent 590 negotiation, occurs when a cache uses the agent-driven negotiation 591 information provided by the origin server in order to provide server- 592 driven negotiation for subsequent requests. 594 4.1. Server-driven Negotiation 596 If the selection of the best representation for a response is made by 597 an algorithm located at the server, it is called server-driven 598 negotiation. Selection is based on the available representations of 599 the response (the dimensions over which it can vary; e.g. language, 600 content-coding, etc.) and the contents of particular header fields in 601 the request message or on other information pertaining to the request 602 (such as the network address of the client). 604 Server-driven negotiation is advantageous when the algorithm for 605 selecting from among the available representations is difficult to 606 describe to the user agent, or when the server desires to send its 607 "best guess" to the client along with the first response (hoping to 608 avoid the round-trip delay of a subsequent request if the "best 609 guess" is good enough for the user). In order to improve the 610 server's guess, the user agent MAY include request header fields 611 (Accept, Accept-Language, Accept-Encoding, etc.) which describe its 612 preferences for such a response. 614 Server-driven negotiation has disadvantages: 616 1. It is impossible for the server to accurately determine what 617 might be "best" for any given user, since that would require 618 complete knowledge of both the capabilities of the user agent and 619 the intended use for the response (e.g., does the user want to 620 view it on screen or print it on paper?). 622 2. Having the user agent describe its capabilities in every request 623 can be both very inefficient (given that only a small percentage 624 of responses have multiple representations) and a potential 625 violation of the user's privacy. 627 3. It complicates the implementation of an origin server and the 628 algorithms for generating responses to a request. 630 4. It may limit a public cache's ability to use the same response 631 for multiple user's requests. 633 HTTP/1.1 includes the following request-header fields for enabling 634 server-driven negotiation through description of user agent 635 capabilities and user preferences: Accept (Section 5.1), Accept- 636 Charset (Section 5.2), Accept-Encoding (Section 5.3), Accept-Language 637 (Section 5.4), and User-Agent (Section 9.9 of [Part2]). However, an 638 origin server is not limited to these dimensions and MAY vary the 639 response based on any aspect of the request, including information 640 outside the request-header fields or within extension header fields 641 not defined by this specification. 643 The Vary header field (Section 3.5 of [Part6]) can be used to express 644 the parameters the server uses to select a representation that is 645 subject to server-driven negotiation. 647 4.2. Agent-driven Negotiation 649 With agent-driven negotiation, selection of the best representation 650 for a response is performed by the user agent after receiving an 651 initial response from the origin server. Selection is based on a 652 list of the available representations of the response included within 653 the header fields or entity-body of the initial response, with each 654 representation identified by its own URI. Selection from among the 655 representations may be performed automatically (if the user agent is 656 capable of doing so) or manually by the user selecting from a 657 generated (possibly hypertext) menu. 659 Agent-driven negotiation is advantageous when the response would vary 660 over commonly-used dimensions (such as type, language, or encoding), 661 when the origin server is unable to determine a user agent's 662 capabilities from examining the request, and generally when public 663 caches are used to distribute server load and reduce network usage. 665 Agent-driven negotiation suffers from the disadvantage of needing a 666 second request to obtain the best alternate representation. This 667 second request is only efficient when caching is used. In addition, 668 this specification does not define any mechanism for supporting 669 automatic selection, though it also does not prevent any such 670 mechanism from being developed as an extension and used within 671 HTTP/1.1. 673 HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable) 674 status codes for enabling agent-driven negotiation when the server is 675 unwilling or unable to provide a varying response using server-driven 676 negotiation. 678 4.3. Transparent Negotiation 680 Transparent negotiation is a combination of both server-driven and 681 agent-driven negotiation. When a cache is supplied with a form of 682 the list of available representations of the response (as in agent- 683 driven negotiation) and the dimensions of variance are completely 684 understood by the cache, then the cache becomes capable of performing 685 server-driven negotiation on behalf of the origin server for 686 subsequent requests on that resource. 688 Transparent negotiation has the advantage of distributing the 689 negotiation work that would otherwise be required of the origin 690 server and also removing the second request delay of agent-driven 691 negotiation when the cache is able to correctly guess the right 692 response. 694 This specification does not define any mechanism for transparent 695 negotiation, though it also does not prevent any such mechanism from 696 being developed as an extension that could be used within HTTP/1.1. 698 5. Header Field Definitions 700 This section defines the syntax and semantics of HTTP/1.1 header 701 fields related to the payload of messages. 703 For entity-header fields, both sender and recipient refer to either 704 the client or the server, depending on who sends and who receives the 705 entity. 707 5.1. Accept 709 The request-header field "Accept" can be used to specify certain 710 media types which are acceptable for the response. Accept headers 711 can be used to indicate that the request is specifically limited to a 712 small set of desired types, as in the case of a request for an in- 713 line image. 715 Accept = "Accept" ":" OWS Accept-v 716 Accept-v = #( media-range [ accept-params ] ) 718 media-range = ( "*/*" 719 / ( type "/" "*" ) 720 / ( type "/" subtype ) 721 ) *( OWS ";" OWS parameter ) 722 accept-params = OWS ";" OWS "q=" qvalue *( accept-ext ) 723 accept-ext = OWS ";" OWS token 724 [ "=" ( token / quoted-string ) ] 726 The asterisk "*" character is used to group media types into ranges, 727 with "*/*" indicating all media types and "type/*" indicating all 728 subtypes of that type. The media-range MAY include media type 729 parameters that are applicable to that range. 731 Each media-range MAY be followed by one or more accept-params, 732 beginning with the "q" parameter for indicating a relative quality 733 factor. The first "q" parameter (if any) separates the media-range 734 parameter(s) from the accept-params. Quality factors allow the user 735 or user agent to indicate the relative degree of preference for that 736 media-range, using the qvalue scale from 0 to 1 (Section 3.5 of 737 [Part1]). The default value is q=1. 739 Note: Use of the "q" parameter name to separate media type 740 parameters from Accept extension parameters is due to historical 741 practice. Although this prevents any media type parameter named 742 "q" from being used with a media range, such an event is believed 743 to be unlikely given the lack of any "q" parameters in the IANA 744 media type registry and the rare usage of any media type 745 parameters in Accept. Future media types are discouraged from 746 registering any parameter named "q". 748 The example 750 Accept: audio/*; q=0.2, audio/basic 752 SHOULD be interpreted as "I prefer audio/basic, but send me any audio 753 type if it is the best available after an 80% mark-down in quality." 755 If no Accept header field is present, then it is assumed that the 756 client accepts all media types. If an Accept header field is 757 present, and if the server cannot send a response which is acceptable 758 according to the combined Accept field value, then the server SHOULD 759 send a 406 (Not Acceptable) response. 761 A more elaborate example is 763 Accept: text/plain; q=0.5, text/html, 764 text/x-dvi; q=0.8, text/x-c 766 Verbally, this would be interpreted as "text/html and text/x-c are 767 the preferred media types, but if they do not exist, then send the 768 text/x-dvi entity, and if that does not exist, send the text/plain 769 entity." 771 Media ranges can be overridden by more specific media ranges or 772 specific media types. If more than one media range applies to a 773 given type, the most specific reference has precedence. For example, 775 Accept: text/*, text/html, text/html;level=1, */* 777 have the following precedence: 779 1. text/html;level=1 781 2. text/html 783 3. text/* 785 4. */* 787 The media type quality factor associated with a given type is 788 determined by finding the media range with the highest precedence 789 which matches that type. For example, 791 Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, 792 text/html;level=2;q=0.4, */*;q=0.5 794 would cause the following values to be associated: 796 +-------------------+---------------+ 797 | Media Type | Quality Value | 798 +-------------------+---------------+ 799 | text/html;level=1 | 1 | 800 | text/html | 0.7 | 801 | text/plain | 0.3 | 802 | image/jpeg | 0.5 | 803 | text/html;level=2 | 0.4 | 804 | text/html;level=3 | 0.7 | 805 +-------------------+---------------+ 807 Note: A user agent might be provided with a default set of quality 808 values for certain media ranges. However, unless the user agent is a 809 closed system which cannot interact with other rendering agents, this 810 default set ought to be configurable by the user. 812 5.2. Accept-Charset 814 The request-header field "Accept-Charset" can be used to indicate 815 what character sets are acceptable for the response. This field 816 allows clients capable of understanding more comprehensive or 817 special-purpose character sets to signal that capability to a server 818 which is capable of representing documents in those character sets. 820 Accept-Charset = "Accept-Charset" ":" OWS 821 Accept-Charset-v 822 Accept-Charset-v = 1#( ( charset / "*" ) 823 [ OWS ";" OWS "q=" qvalue ] ) 825 Character set values are described in Section 2.1. Each charset MAY 826 be given an associated quality value which represents the user's 827 preference for that charset. The default value is q=1. An example 828 is 830 Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 832 The special value "*", if present in the Accept-Charset field, 833 matches every character set (including ISO-8859-1) which is not 834 mentioned elsewhere in the Accept-Charset field. If no "*" is 835 present in an Accept-Charset field, then all character sets not 836 explicitly mentioned get a quality value of 0, except for ISO-8859-1, 837 which gets a quality value of 1 if not explicitly mentioned. 839 If no Accept-Charset header is present, the default is that any 840 character set is acceptable. If an Accept-Charset header is present, 841 and if the server cannot send a response which is acceptable 842 according to the Accept-Charset header, then the server SHOULD send 843 an error response with the 406 (Not Acceptable) status code, though 844 the sending of an unacceptable response is also allowed. 846 5.3. Accept-Encoding 848 The request-header field "Accept-Encoding" is similar to Accept, but 849 restricts the content-codings (Section 2.2) that are acceptable in 850 the response. 852 Accept-Encoding = "Accept-Encoding" ":" OWS 853 Accept-Encoding-v 854 Accept-Encoding-v = 855 #( codings [ OWS ";" OWS "q=" qvalue ] ) 856 codings = ( content-coding / "*" ) 858 Each codings value MAY be given an associated quality value which 859 represents the preference for that encoding. The default value is 860 q=1. 862 Examples of its use are: 864 Accept-Encoding: compress, gzip 865 Accept-Encoding: 866 Accept-Encoding: * 867 Accept-Encoding: compress;q=0.5, gzip;q=1.0 868 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 870 A server tests whether a content-coding is acceptable, according to 871 an Accept-Encoding field, using these rules: 873 1. If the content-coding is one of the content-codings listed in the 874 Accept-Encoding field, then it is acceptable, unless it is 875 accompanied by a qvalue of 0. (As defined in Section 3.5 of 876 [Part1], a qvalue of 0 means "not acceptable.") 878 2. The special "*" symbol in an Accept-Encoding field matches any 879 available content-coding not explicitly listed in the header 880 field. 882 3. If multiple content-codings are acceptable, then the acceptable 883 content-coding with the highest non-zero qvalue is preferred. 885 4. The "identity" content-coding is always acceptable, unless 886 specifically refused because the Accept-Encoding field includes 887 "identity;q=0", or because the field includes "*;q=0" and does 888 not explicitly include the "identity" content-coding. If the 889 Accept-Encoding field-value is empty, then only the "identity" 890 encoding is acceptable. 892 If an Accept-Encoding field is present in a request, and if the 893 server cannot send a response which is acceptable according to the 894 Accept-Encoding header, then the server SHOULD send an error response 895 with the 406 (Not Acceptable) status code. 897 If no Accept-Encoding field is present in a request, the server MAY 898 assume that the client will accept any content coding. In this case, 899 if "identity" is one of the available content-codings, then the 900 server SHOULD use the "identity" content-coding, unless it has 901 additional information that a different content-coding is meaningful 902 to the client. 904 Note: If the request does not include an Accept-Encoding field, 905 and if the "identity" content-coding is unavailable, then content- 906 codings commonly understood by HTTP/1.0 clients (i.e., "gzip" and 907 "compress") are preferred; some older clients improperly display 908 messages sent with other content-codings. The server might also 909 make this decision based on information about the particular user- 910 agent or client. 912 Note: Most HTTP/1.0 applications do not recognize or obey qvalues 913 associated with content-codings. This means that qvalues will not 914 work and are not permitted with x-gzip or x-compress. 916 5.4. Accept-Language 918 The request-header field "Accept-Language" is similar to Accept, but 919 restricts the set of natural languages that are preferred as a 920 response to the request. Language tags are defined in Section 2.4. 922 Accept-Language = "Accept-Language" ":" OWS 923 Accept-Language-v 924 Accept-Language-v = 925 1#( language-range [ OWS ";" OWS "q=" qvalue ] ) 926 language-range = 927 929 Each language-range can be given an associated quality value which 930 represents an estimate of the user's preference for the languages 931 specified by that range. The quality value defaults to "q=1". For 932 example, 934 Accept-Language: da, en-gb;q=0.8, en;q=0.7 936 would mean: "I prefer Danish, but will accept British English and 937 other types of English." 939 For matching, the "Basic Filtering" matching scheme, defined in 940 Section 3.3.1 of [RFC4647], is used: 942 A language range matches a particular language tag if, in a case- 943 insensitive comparison, it exactly equals the tag, or if it 944 exactly equals a prefix of the tag such that the first character 945 following the prefix is "-". 947 The special range "*", if present in the Accept-Language field, 948 matches every tag not matched by any other range present in the 949 Accept-Language field. 951 Note: This use of a prefix matching rule does not imply that 952 language tags are assigned to languages in such a way that it is 953 always true that if a user understands a language with a certain 954 tag, then this user will also understand all languages with tags 955 for which this tag is a prefix. The prefix rule simply allows the 956 use of prefix tags if this is the case. 958 The language quality factor assigned to a language-tag by the Accept- 959 Language field is the quality value of the longest language-range in 960 the field that matches the language-tag. If no language-range in the 961 field matches the tag, the language quality factor assigned is 0. If 962 no Accept-Language header is present in the request, the server 963 SHOULD assume that all languages are equally acceptable. If an 964 Accept-Language header is present, then all languages which are 965 assigned a quality factor greater than 0 are acceptable. 967 It might be contrary to the privacy expectations of the user to send 968 an Accept-Language header with the complete linguistic preferences of 969 the user in every request. For a discussion of this issue, see 970 Section 7.1. 972 As intelligibility is highly dependent on the individual user, it is 973 recommended that client applications make the choice of linguistic 974 preference available to the user. If the choice is not made 975 available, then the Accept-Language header field MUST NOT be given in 976 the request. 978 Note: When making the choice of linguistic preference available to 979 the user, we remind implementors of the fact that users are not 980 familiar with the details of language matching as described above, 981 and should provide appropriate guidance. As an example, users 982 might assume that on selecting "en-gb", they will be served any 983 kind of English document if British English is not available. A 984 user agent might suggest in such a case to add "en" to get the 985 best matching behavior. 987 5.5. Content-Encoding 989 The entity-header field "Content-Encoding" is used as a modifier to 990 the media-type. When present, its value indicates what additional 991 content codings have been applied to the entity-body, and thus what 992 decoding mechanisms must be applied in order to obtain the media-type 993 referenced by the Content-Type header field. Content-Encoding is 994 primarily used to allow a document to be compressed without losing 995 the identity of its underlying media type. 997 Content-Encoding = "Content-Encoding" ":" OWS Content-Encoding-v 998 Content-Encoding-v = 1#content-coding 1000 Content codings are defined in Section 2.2. An example of its use is 1002 Content-Encoding: gzip 1004 The content-coding is a characteristic of the entity identified by 1005 the request-target. Typically, the entity-body is stored with this 1006 encoding and is only decoded before rendering or analogous usage. 1007 However, a non-transparent proxy MAY modify the content-coding if the 1008 new coding is known to be acceptable to the recipient, unless the 1009 "no-transform" cache-control directive is present in the message. 1011 If the content-coding of an entity is not "identity", then the 1012 response MUST include a Content-Encoding entity-header (Section 5.5) 1013 that lists the non-identity content-coding(s) used. 1015 If the content-coding of an entity in a request message is not 1016 acceptable to the origin server, the server SHOULD respond with a 1017 status code of 415 (Unsupported Media Type). 1019 If multiple encodings have been applied to an entity, the content 1020 codings MUST be listed in the order in which they were applied. 1021 Additional information about the encoding parameters MAY be provided 1022 by other entity-header fields not defined by this specification. 1024 5.6. Content-Language 1026 The entity-header field "Content-Language" describes the natural 1027 language(s) of the intended audience for the enclosed entity. Note 1028 that this might not be equivalent to all the languages used within 1029 the entity-body. 1031 Content-Language = "Content-Language" ":" OWS Content-Language-v 1032 Content-Language-v = 1#language-tag 1034 Language tags are defined in Section 2.4. The primary purpose of 1035 Content-Language is to allow a user to identify and differentiate 1036 entities according to the user's own preferred language. Thus, if 1037 the body content is intended only for a Danish-literate audience, the 1038 appropriate field is 1040 Content-Language: da 1042 If no Content-Language is specified, the default is that the content 1043 is intended for all language audiences. This might mean that the 1044 sender does not consider it to be specific to any natural language, 1045 or that the sender does not know for which language it is intended. 1047 Multiple languages MAY be listed for content that is intended for 1048 multiple audiences. For example, a rendition of the "Treaty of 1049 Waitangi," presented simultaneously in the original Maori and English 1050 versions, would call for 1052 Content-Language: mi, en 1054 However, just because multiple languages are present within an entity 1055 does not mean that it is intended for multiple linguistic audiences. 1056 An example would be a beginner's language primer, such as "A First 1057 Lesson in Latin," which is clearly intended to be used by an English- 1058 literate audience. In this case, the Content-Language would properly 1059 only include "en". 1061 Content-Language MAY be applied to any media type -- it is not 1062 limited to textual documents. 1064 5.7. Content-Location 1066 The entity-header field "Content-Location" MAY be used to supply the 1067 resource location for the entity enclosed in the message when that 1068 entity is accessible from a location separate from the requested 1069 resource's URI. A server SHOULD provide a Content-Location for the 1070 variant corresponding to the response entity; especially in the case 1071 where a resource has multiple entities associated with it, and those 1072 entities actually have separate locations by which they might be 1073 individually accessed, the server SHOULD provide a Content-Location 1074 for the particular variant which is returned. 1076 Content-Location = "Content-Location" ":" OWS 1077 Content-Location-v 1078 Content-Location-v = 1079 absolute-URI / partial-URI 1081 The value of Content-Location also defines the base URI for the 1082 entity. 1084 The Content-Location value is not a replacement for the original 1085 requested URI; it is only a statement of the location of the resource 1086 corresponding to this particular entity at the time of the request. 1087 Future requests MAY specify the Content-Location URI as the request- 1088 target if the desire is to identify the source of that particular 1089 entity. 1091 A cache cannot assume that an entity with a Content-Location 1092 different from the URI used to retrieve it can be used to respond to 1093 later requests on that Content-Location URI. However, the Content- 1094 Location can be used to differentiate between multiple entities 1095 retrieved from a single requested resource, as described in Section 1096 2.6 of [Part6]. 1098 If the Content-Location is a relative URI, the relative URI is 1099 interpreted relative to the request-target. 1101 The meaning of the Content-Location header in requests is undefined; 1102 servers are free to ignore it in those cases. 1104 5.8. Content-MD5 1106 The entity-header field "Content-MD5", as defined in [RFC1864], is an 1107 MD5 digest of the entity-body for the purpose of providing an end-to- 1108 end message integrity check (MIC) of the entity-body. (Note: a MIC 1109 is good for detecting accidental modification of the entity-body in 1110 transit, but is not proof against malicious attacks.) 1111 Content-MD5 = "Content-MD5" ":" OWS Content-MD5-v 1112 Content-MD5-v = 1114 The Content-MD5 header field MAY be generated by an origin server or 1115 client to function as an integrity check of the entity-body. Only 1116 origin servers or clients MAY generate the Content-MD5 header field; 1117 proxies and gateways MUST NOT generate it, as this would defeat its 1118 value as an end-to-end integrity check. Any recipient of the entity- 1119 body, including gateways and proxies, MAY check that the digest value 1120 in this header field matches that of the entity-body as received. 1122 The MD5 digest is computed based on the content of the entity-body, 1123 including any content-coding that has been applied, but not including 1124 any transfer-encoding applied to the message-body. If the message is 1125 received with a transfer-encoding, that encoding MUST be removed 1126 prior to checking the Content-MD5 value against the received entity. 1128 This has the result that the digest is computed on the octets of the 1129 entity-body exactly as, and in the order that, they would be sent if 1130 no transfer-encoding were being applied. 1132 HTTP extends RFC 1864 to permit the digest to be computed for MIME 1133 composite media-types (e.g., multipart/* and message/rfc822), but 1134 this does not change how the digest is computed as defined in the 1135 preceding paragraph. 1137 There are several consequences of this. The entity-body for 1138 composite types MAY contain many body-parts, each with its own MIME 1139 and HTTP headers (including Content-MD5, Content-Transfer-Encoding, 1140 and Content-Encoding headers). If a body-part has a Content- 1141 Transfer-Encoding or Content-Encoding header, it is assumed that the 1142 content of the body-part has had the encoding applied, and the body- 1143 part is included in the Content-MD5 digest as is -- i.e., after the 1144 application. The Transfer-Encoding header field is not allowed 1145 within body-parts. 1147 Conversion of all line breaks to CRLF MUST NOT be done before 1148 computing or checking the digest: the line break convention used in 1149 the text actually transmitted MUST be left unaltered when computing 1150 the digest. 1152 Note: while the definition of Content-MD5 is exactly the same for 1153 HTTP as in RFC 1864 for MIME entity-bodies, there are several ways 1154 in which the application of Content-MD5 to HTTP entity-bodies 1155 differs from its application to MIME entity-bodies. One is that 1156 HTTP, unlike MIME, does not use Content-Transfer-Encoding, and 1157 does use Transfer-Encoding and Content-Encoding. Another is that 1158 HTTP more frequently uses binary content types than MIME, so it is 1159 worth noting that, in such cases, the byte order used to compute 1160 the digest is the transmission byte order defined for the type. 1161 Lastly, HTTP allows transmission of text types with any of several 1162 line break conventions and not just the canonical form using CRLF. 1164 5.9. Content-Type 1166 The entity-header field "Content-Type" indicates the media type of 1167 the entity-body sent to the recipient or, in the case of the HEAD 1168 method, the media type that would have been sent had the request been 1169 a GET. 1171 Content-Type = "Content-Type" ":" OWS Content-Type-v 1172 Content-Type-v = media-type 1174 Media types are defined in Section 2.3. An example of the field is 1176 Content-Type: text/html; charset=ISO-8859-4 1178 Further discussion of methods for identifying the media type of an 1179 entity is provided in Section 3.2.1. 1181 6. IANA Considerations 1183 6.1. Message Header Registration 1185 The Message Header Registry located at should be 1187 updated with the permanent registrations below (see [RFC3864]): 1189 +---------------------+----------+----------+--------------+ 1190 | Header Field Name | Protocol | Status | Reference | 1191 +---------------------+----------+----------+--------------+ 1192 | Accept | http | standard | Section 5.1 | 1193 | Accept-Charset | http | standard | Section 5.2 | 1194 | Accept-Encoding | http | standard | Section 5.3 | 1195 | Accept-Language | http | standard | Section 5.4 | 1196 | Content-Disposition | http | | Appendix B.1 | 1197 | Content-Encoding | http | standard | Section 5.5 | 1198 | Content-Language | http | standard | Section 5.6 | 1199 | Content-Location | http | standard | Section 5.7 | 1200 | Content-MD5 | http | standard | Section 5.8 | 1201 | Content-Type | http | standard | Section 5.9 | 1202 | MIME-Version | http | | Appendix A.1 | 1203 +---------------------+----------+----------+--------------+ 1205 The change controller is: "IETF (iesg@ietf.org) - Internet 1206 Engineering Task Force". 1208 7. Security Considerations 1210 This section is meant to inform application developers, information 1211 providers, and users of the security limitations in HTTP/1.1 as 1212 described by this document. The discussion does not include 1213 definitive solutions to the problems revealed, though it does make 1214 some suggestions for reducing security risks. 1216 7.1. Privacy Issues Connected to Accept Headers 1218 Accept request-headers can reveal information about the user to all 1219 servers which are accessed. The Accept-Language header in particular 1220 can reveal information the user would consider to be of a private 1221 nature, because the understanding of particular languages is often 1222 strongly correlated to the membership of a particular ethnic group. 1223 User agents which offer the option to configure the contents of an 1224 Accept-Language header to be sent in every request are strongly 1225 encouraged to let the configuration process include a message which 1226 makes the user aware of the loss of privacy involved. 1228 An approach that limits the loss of privacy would be for a user agent 1229 to omit the sending of Accept-Language headers by default, and to ask 1230 the user whether or not to start sending Accept-Language headers to a 1231 server if it detects, by looking for any Vary response-header fields 1232 generated by the server, that such sending could improve the quality 1233 of service. 1235 Elaborate user-customized accept header fields sent in every request, 1236 in particular if these include quality values, can be used by servers 1237 as relatively reliable and long-lived user identifiers. Such user 1238 identifiers would allow content providers to do click-trail tracking, 1239 and would allow collaborating content providers to match cross-server 1240 click-trails or form submissions of individual users. Note that for 1241 many users not behind a proxy, the network address of the host 1242 running the user agent will also serve as a long-lived user 1243 identifier. In environments where proxies are used to enhance 1244 privacy, user agents ought to be conservative in offering accept 1245 header configuration options to end users. As an extreme privacy 1246 measure, proxies could filter the accept headers in relayed requests. 1247 General purpose user agents which provide a high degree of header 1248 configurability SHOULD warn users about the loss of privacy which can 1249 be involved. 1251 7.2. Content-Disposition Issues 1253 [RFC2183], from which the often implemented Content-Disposition (see 1254 Appendix B.1) header in HTTP is derived, has a number of very serious 1255 security considerations. Content-Disposition is not part of the HTTP 1256 standard, but since it is widely implemented, we are documenting its 1257 use and risks for implementors. See Section 5 of [RFC2183] for 1258 details. 1260 8. Acknowledgments 1262 9. References 1264 9.1. Normative References 1266 [ISO-8859-1] 1267 International Organization for Standardization, 1268 "Information technology -- 8-bit single-byte coded graphic 1269 character sets -- Part 1: Latin alphabet No. 1", ISO/ 1270 IEC 8859-1:1998, 1998. 1272 [Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1273 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1274 and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections, 1275 and Message Parsing", draft-ietf-httpbis-p1-messaging-07 1276 (work in progress), July 2009. 1278 [Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1279 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1280 and J. Reschke, Ed., "HTTP/1.1, part 2: Message 1281 Semantics", draft-ietf-httpbis-p2-semantics-07 (work in 1282 progress), July 2009. 1284 [Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1285 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1286 and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional 1287 Requests", draft-ietf-httpbis-p4-conditional-07 (work in 1288 progress), July 2009. 1290 [Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1291 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1292 and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and 1293 Partial Responses", draft-ietf-httpbis-p5-range-07 (work 1294 in progress), July 2009. 1296 [Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1297 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1298 Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part 1299 6: Caching", draft-ietf-httpbis-p6-cache-07 (work in 1300 progress), July 2009. 1302 [RFC1766] Alvestrand, H., "Tags for the Identification of 1303 Languages", RFC 1766, March 1995. 1305 [RFC1864] Myers, J. and M. Rose, "The Content-MD5 Header Field", 1306 RFC 1864, October 1995. 1308 [RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format 1309 Specification version 3.3", RFC 1950, May 1996. 1311 RFC 1950 is an Informational RFC, thus it may be less 1312 stable than this specification. On the other hand, this 1313 downward reference was present since the publication of 1314 RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to 1315 cause problems in practice. See also [BCP97]. 1317 [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification 1318 version 1.3", RFC 1951, May 1996. 1320 RFC 1951 is an Informational RFC, thus it may be less 1321 stable than this specification. On the other hand, this 1322 downward reference was present since the publication of 1323 RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to 1324 cause problems in practice. See also [BCP97]. 1326 [RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G. 1327 Randers-Pehrson, "GZIP file format specification version 1328 4.3", RFC 1952, May 1996. 1330 RFC 1952 is an Informational RFC, thus it may be less 1331 stable than this specification. On the other hand, this 1332 downward reference was present since the publication of 1333 RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to 1334 cause problems in practice. See also [BCP97]. 1336 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1337 Extensions (MIME) Part One: Format of Internet Message 1338 Bodies", RFC 2045, November 1996. 1340 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1341 Extensions (MIME) Part Two: Media Types", RFC 2046, 1342 November 1996. 1344 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1345 Requirement Levels", BCP 14, RFC 2119, March 1997. 1347 [RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of Language 1348 Tags", BCP 47, RFC 4647, September 2006. 1350 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1351 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1353 9.2. Informative References 1355 [BCP97] Klensin, J. and S. Hartman, "Handling Normative References 1356 to Standards-Track Documents", BCP 97, RFC 4897, 1357 June 2007. 1359 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 1360 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 1362 [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1363 Extensions (MIME) Part Five: Conformance Criteria and 1364 Examples", RFC 2049, November 1996. 1366 [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. 1367 Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", 1368 RFC 2068, January 1997. 1370 [RFC2076] Palme, J., "Common Internet Message Headers", RFC 2076, 1371 February 1997. 1373 [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating 1374 Presentation Information in Internet Messages: The 1375 Content-Disposition Header Field", RFC 2183, August 1997. 1377 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 1378 Languages", BCP 18, RFC 2277, January 1998. 1380 [RFC2388] Masinter, L., "Returning Values from Forms: multipart/ 1381 form-data", RFC 2388, August 1998. 1383 [RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud, 1384 "MIME Encapsulation of Aggregate Documents, such as HTML 1385 (MHTML)", RFC 2557, March 1999. 1387 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 1388 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 1389 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 1391 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1392 10646", RFC 3629, STD 63, November 2003. 1394 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 1395 Procedures for Message Header Fields", BCP 90, RFC 3864, 1396 September 2004. 1398 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 1399 Registration Procedures", BCP 13, RFC 4288, December 2005. 1401 [RFC5322] Resnick, P., "Internet Message Format", RFC 5322, 1402 October 2008. 1404 Appendix A. Differences Between HTTP Entities and RFC 2045 Entities 1406 HTTP/1.1 uses many of the constructs defined for Internet Mail 1407 ([RFC5322]) and the Multipurpose Internet Mail Extensions (MIME 1408 [RFC2045]) to allow entities to be transmitted in an open variety of 1409 representations and with extensible mechanisms. However, RFC 2045 1410 discusses mail, and HTTP has a few features that are different from 1411 those described in RFC 2045. These differences were carefully chosen 1412 to optimize performance over binary connections, to allow greater 1413 freedom in the use of new media types, to make date comparisons 1414 easier, and to acknowledge the practice of some early HTTP servers 1415 and clients. 1417 This appendix describes specific areas where HTTP differs from RFC 1418 2045. Proxies and gateways to strict MIME environments SHOULD be 1419 aware of these differences and provide the appropriate conversions 1420 where necessary. Proxies and gateways from MIME environments to HTTP 1421 also need to be aware of the differences because some conversions 1422 might be required. 1424 A.1. MIME-Version 1426 HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages 1427 MAY include a single MIME-Version general-header field to indicate 1428 what version of the MIME protocol was used to construct the message. 1429 Use of the MIME-Version header field indicates that the message is in 1430 full compliance with the MIME protocol (as defined in [RFC2045]). 1431 Proxies/gateways are responsible for ensuring full compliance (where 1432 possible) when exporting HTTP messages to strict MIME environments. 1434 MIME-Version = "MIME-Version" ":" OWS MIME-Version-v 1435 MIME-Version-v = 1*DIGIT "." 1*DIGIT 1437 MIME version "1.0" is the default for use in HTTP/1.1. However, 1438 HTTP/1.1 message parsing and semantics are defined by this document 1439 and not the MIME specification. 1441 A.2. Conversion to Canonical Form 1443 [RFC2045] requires that an Internet mail entity be converted to 1444 canonical form prior to being transferred, as described in Section 4 1445 of [RFC2049]. Section 2.3.1 of this document describes the forms 1446 allowed for subtypes of the "text" media type when transmitted over 1447 HTTP. [RFC2046] requires that content with a type of "text" 1448 represent line breaks as CRLF and forbids the use of CR or LF outside 1449 of line break sequences. HTTP allows CRLF, bare CR, and bare LF to 1450 indicate a line break within text content when a message is 1451 transmitted over HTTP. 1453 Where it is possible, a proxy or gateway from HTTP to a strict MIME 1454 environment SHOULD translate all line breaks within the text media 1455 types described in Section 2.3.1 of this document to the RFC 2049 1456 canonical form of CRLF. Note, however, that this might be 1457 complicated by the presence of a Content-Encoding and by the fact 1458 that HTTP allows the use of some character sets which do not use 1459 octets 13 and 10 to represent CR and LF, as is the case for some 1460 multi-byte character sets. 1462 Implementors should note that conversion will break any cryptographic 1463 checksums applied to the original content unless the original content 1464 is already in canonical form. Therefore, the canonical form is 1465 recommended for any content that uses such checksums in HTTP. 1467 A.3. Conversion of Date Formats 1469 HTTP/1.1 uses a restricted set of date formats (Section 3.2 of 1470 [Part1]) to simplify the process of date comparison. Proxies and 1471 gateways from other protocols SHOULD ensure that any Date header 1472 field present in a message conforms to one of the HTTP/1.1 formats 1473 and rewrite the date if necessary. 1475 A.4. Introduction of Content-Encoding 1477 RFC 2045 does not include any concept equivalent to HTTP/1.1's 1478 Content-Encoding header field. Since this acts as a modifier on the 1479 media type, proxies and gateways from HTTP to MIME-compliant 1480 protocols MUST either change the value of the Content-Type header 1481 field or decode the entity-body before forwarding the message. (Some 1482 experimental applications of Content-Type for Internet mail have used 1483 a media-type parameter of ";conversions=" to perform 1484 a function equivalent to Content-Encoding. However, this parameter 1485 is not part of RFC 2045). 1487 A.5. No Content-Transfer-Encoding 1489 HTTP does not use the Content-Transfer-Encoding field of RFC 2045. 1490 Proxies and gateways from MIME-compliant protocols to HTTP MUST 1491 remove any Content-Transfer-Encoding prior to delivering the response 1492 message to an HTTP client. 1494 Proxies and gateways from HTTP to MIME-compliant protocols are 1495 responsible for ensuring that the message is in the correct format 1496 and encoding for safe transport on that protocol, where "safe 1497 transport" is defined by the limitations of the protocol being used. 1498 Such a proxy or gateway SHOULD label the data with an appropriate 1499 Content-Transfer-Encoding if doing so will improve the likelihood of 1500 safe transport over the destination protocol. 1502 A.6. Introduction of Transfer-Encoding 1504 HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.7 1505 of [Part1]). Proxies/gateways MUST remove any transfer-coding prior 1506 to forwarding a message via a MIME-compliant protocol. 1508 A.7. MHTML and Line Length Limitations 1510 HTTP implementations which share code with MHTML [RFC2557] 1511 implementations need to be aware of MIME line length limitations. 1512 Since HTTP does not have this limitation, HTTP does not fold long 1513 lines. MHTML messages being transported by HTTP follow all 1514 conventions of MHTML, including line length limitations and folding, 1515 canonicalization, etc., since HTTP transports all message-bodies as 1516 payload (see Section 2.3.2) and does not interpret the content or any 1517 MIME header lines that might be contained therein. 1519 Appendix B. Additional Features 1521 [RFC1945] and [RFC2068] document protocol elements used by some 1522 existing HTTP implementations, but not consistently and correctly 1523 across most HTTP/1.1 applications. Implementors are advised to be 1524 aware of these features, but cannot rely upon their presence in, or 1525 interoperability with, other HTTP/1.1 applications. Some of these 1526 describe proposed experimental features, and some describe features 1527 that experimental deployment found lacking that are now addressed in 1528 the base HTTP/1.1 specification. 1530 A number of other headers, such as Content-Disposition and Title, 1531 from SMTP and MIME are also often implemented (see [RFC2076]). 1533 B.1. Content-Disposition 1535 The Content-Disposition response-header field has been proposed as a 1536 means for the origin server to suggest a default filename if the user 1537 requests that the content is saved to a file. This usage is derived 1538 from the definition of Content-Disposition in [RFC2183]. 1540 content-disposition = "Content-Disposition" ":" OWS 1541 content-disposition-v 1542 content-disposition-v = disposition-type 1543 *( OWS ";" OWS disposition-parm ) 1544 disposition-type = "attachment" / disp-extension-token 1545 disposition-parm = filename-parm / disp-extension-parm 1546 filename-parm = "filename" "=" quoted-string 1547 disp-extension-token = token 1548 disp-extension-parm = token "=" ( token / quoted-string ) 1550 An example is 1552 Content-Disposition: attachment; filename="fname.ext" 1554 The receiving user agent SHOULD NOT respect any directory path 1555 information present in the filename-parm parameter, which is the only 1556 parameter believed to apply to HTTP implementations at this time. 1557 The filename SHOULD be treated as a terminal component only. 1559 If this header is used in a response with the application/ 1560 octet-stream content-type, the implied suggestion is that the user 1561 agent should not display the response, but directly enter a `save 1562 response as...' dialog. 1564 See Section 7.2 for Content-Disposition security issues. 1566 Appendix C. Compatibility with Previous Versions 1568 C.1. Changes from RFC 2068 1570 Transfer-coding and message lengths all interact in ways that 1571 required fixing exactly when chunked encoding is used (to allow for 1572 transfer encoding that may not be self delimiting); it was important 1573 to straighten out exactly how message lengths are computed. 1574 (Section 3.2.2, see also [Part1], [Part5] and [Part6]). 1576 Charset wildcarding is introduced to avoid explosion of character set 1577 names in accept headers. (Section 5.2) 1579 Content-Base was deleted from the specification: it was not 1580 implemented widely, and there is no simple, safe way to introduce it 1581 without a robust extension mechanism. In addition, it is used in a 1582 similar, but not identical fashion in MHTML [RFC2557]. 1584 A content-coding of "identity" was introduced, to solve problems 1585 discovered in caching. (Section 2.2) 1587 The Alternates, Content-Version, Derived-From, Link, URI, Public and 1588 Content-Base header fields were defined in previous versions of this 1589 specification, but not commonly implemented. See Section 19.6.2 of 1590 [RFC2068]. 1592 C.2. Changes from RFC 2616 1594 Clarify contexts that charset is used in. (Section 2.1) 1596 Remove reference to non-existant identity transfer-coding value 1597 tokens. (Appendix A.5) 1599 Appendix D. Collected ABNF 1601 Accept = "Accept:" OWS Accept-v 1602 Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v 1603 Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q=" 1604 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q=" 1605 qvalue ] ] ) 1606 Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v 1607 Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) 1608 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ] 1609 Accept-Language = "Accept-Language:" OWS Accept-Language-v 1610 Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q=" 1611 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ] 1612 ] ) 1613 Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [ 1614 OWS media-range [ accept-params ] ] ) ] 1616 Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v 1617 Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS 1618 content-coding ] ) 1619 Content-Language = "Content-Language:" OWS Content-Language-v 1620 Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS 1621 language-tag ] ) 1622 Content-Length = 1623 Content-Location = "Content-Location:" OWS Content-Location-v 1624 Content-Location-v = absolute-URI / partial-URI 1625 Content-MD5 = "Content-MD5:" OWS Content-MD5-v 1626 Content-MD5-v = 1627 Content-Range = 1628 Content-Type = "Content-Type:" OWS Content-Type-v 1629 Content-Type-v = media-type 1631 Expires = 1633 Last-Modified = 1635 MIME-Version = "MIME-Version:" OWS MIME-Version-v 1636 MIME-Version-v = 1*DIGIT "." 1*DIGIT 1638 OWS = 1640 absolute-URI = 1641 accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ] 1642 accept-params = OWS ";" OWS "q=" qvalue *accept-ext 1643 attribute = token 1645 charset = token 1646 codings = ( content-coding / "*" ) 1647 content-coding = token 1648 content-disposition = "Content-Disposition:" OWS 1649 content-disposition-v 1650 content-disposition-v = disposition-type *( OWS ";" OWS 1651 disposition-parm ) 1653 disp-extension-parm = token "=" ( token / quoted-string ) 1654 disp-extension-token = token 1655 disposition-parm = filename-parm / disp-extension-parm 1656 disposition-type = "attachment" / disp-extension-token 1658 entity-body = *OCTET 1659 entity-header = Content-Encoding / Content-Language / Content-Length 1660 / Content-Location / Content-MD5 / Content-Range / Content-Type / 1661 Expires / Last-Modified / extension-header 1662 extension-header = message-header 1664 filename-parm = "filename=" quoted-string 1666 language-range = 1667 language-tag = primary-tag *( "-" subtag ) 1669 media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS 1670 ";" OWS parameter ) 1671 media-type = type "/" subtype *( OWS ";" OWS parameter ) 1672 message-header = 1674 parameter = attribute "=" value 1675 partial-URI = 1676 primary-tag = 1*8ALPHA 1678 quoted-string = 1679 qvalue = 1681 subtag = 1*8ALPHA 1682 subtype = token 1684 token = 1685 type = token 1687 value = token / quoted-string 1689 ABNF diagnostics: 1691 ; Accept defined but not used 1692 ; Accept-Charset defined but not used 1693 ; Accept-Encoding defined but not used 1694 ; Accept-Language defined but not used 1695 ; MIME-Version defined but not used 1696 ; content-disposition defined but not used 1697 ; entity-body defined but not used 1698 ; entity-header defined but not used 1700 Appendix E. Change Log (to be removed by RFC Editor before publication) 1702 E.1. Since RFC2616 1704 Extracted relevant partitions from [RFC2616]. 1706 E.2. Since draft-ietf-httpbis-p3-payload-00 1708 Closed issues: 1710 o : "Media Type 1711 Registrations" () 1713 o : "Clarification 1714 regarding quoting of charset values" 1715 () 1717 o : "Remove 1718 'identity' token references" 1719 () 1721 o : "Accept- 1722 Encoding BNF" 1724 o : "Normative and 1725 Informative references" 1727 o : "RFC1700 1728 references" 1730 o : "Updating to 1731 RFC4288" 1733 o : "Informative 1734 references" 1736 o : "ISO-8859-1 1737 Reference" 1739 o : "Encoding 1740 References Normative" 1742 o : "Normative up- 1743 to-date references" 1745 E.3. Since draft-ietf-httpbis-p3-payload-01 1747 Ongoing work on ABNF conversion 1748 (): 1750 o Add explicit references to BNF syntax and rules imported from 1751 other parts of the specification. 1753 E.4. Since draft-ietf-httpbis-p3-payload-02 1755 Closed issues: 1757 o : "Quoting 1758 Charsets" 1760 o : 1761 "Classification for Allow header" 1763 o : "missing 1764 default for qvalue in description of Accept-Encoding" 1766 Ongoing work on IANA Message Header Registration 1767 (): 1769 o Reference RFC 3984, and update header registrations for headers 1770 defined in this document. 1772 E.5. Since draft-ietf-httpbis-p3-payload-03 1774 Closed issues: 1776 o : "Quoting 1777 Charsets" 1779 o : "language tag 1780 matching (Accept-Language) vs RFC4647" 1782 o : "RFC 1806 has 1783 been replaced by RFC2183" 1785 Other changes: 1787 o : "Encoding 1788 References Normative" -- rephrase the annotation and reference 1789 [BCP97]. 1791 E.6. Since draft-ietf-httpbis-p3-payload-04 1793 Closed issues: 1795 o : "RFC 2822 is 1796 updated by RFC 5322" 1798 Ongoing work on ABNF conversion 1799 (): 1801 o Use "/" instead of "|" for alternatives. 1803 o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional 1804 whitespace ("OWS") and required whitespace ("RWS"). 1806 o Rewrite ABNFs to spell out whitespace rules, factor out header 1807 value format definitions. 1809 E.7. Since draft-ietf-httpbis-p3-payload-05 1811 Closed issues: 1813 o : "Join 1814 "Differences Between HTTP Entities and RFC 2045 Entities"?" 1816 Final work on ABNF conversion 1817 (): 1819 o Add appendix containing collected and expanded ABNF, reorganize 1820 ABNF introduction. 1822 Other changes: 1824 o Move definition of quality values into Part 1. 1826 E.8. Since draft-ietf-httpbis-p3-payload-06 1828 Closed issues: 1830 o : "Content- 1831 Location isn't special" 1833 o : "Content 1834 Sniffing" 1836 Index 1838 A 1839 Accept header 16 1840 Accept-Charset header 18 1841 Accept-Encoding header 19 1842 Accept-Language header 20 1843 Alternates header 35 1845 C 1846 compress 8 1847 Content Type Sniffing 13 1848 Content-Base header 35 1849 Content-Disposition header 34 1850 Content-Encoding header 22 1851 Content-Language header 23 1852 Content-Location header 24 1853 Content-MD5 header 24 1854 Content-Type header 26 1855 Content-Version header 35 1857 D 1858 deflate 8 1859 Derived-From header 35 1861 G 1862 Grammar 1863 Accept 16 1864 Accept-Charset 18 1865 Accept-Charset-v 18 1866 Accept-Encoding 19 1867 Accept-Encoding-v 19 1868 accept-ext 16 1869 Accept-Language 21 1870 Accept-Language-v 21 1871 accept-params 16 1872 Accept-v 16 1873 attribute 9 1874 charset 7 1875 codings 19 1876 content-coding 8 1877 content-disposition 34 1878 content-disposition-v 34 1879 Content-Encoding 22 1880 Content-Encoding-v 22 1881 Content-Language 23 1882 Content-Language-v 23 1883 Content-Location 24 1884 Content-Location-v 24 1885 Content-MD5 25 1886 Content-MD5-v 25 1887 Content-Type 26 1888 Content-Type-v 26 1889 disp-extension-parm 34 1890 disp-extension-token 34 1891 disposition-parm 34 1892 disposition-type 34 1893 entity-body 12 1894 entity-header 12 1895 extension-header 12 1896 filename-parm 34 1897 language-range 21 1898 language-tag 11 1899 media-range 16 1900 media-type 9 1901 MIME-Version 31 1902 MIME-Version-v 31 1903 parameter 9 1904 primary-tag 11 1905 subtag 11 1906 subtype 9 1907 type 9 1908 value 9 1909 gzip 8 1911 H 1912 Headers 1913 Accept 16 1914 Accept-Charset 18 1915 Accept-Encoding 19 1916 Accept-Language 20 1917 Alternate 35 1918 Content-Base 35 1919 Content-Disposition 34 1920 Content-Encoding 22 1921 Content-Language 23 1922 Content-Location 24 1923 Content-MD5 24 1924 Content-Type 26 1925 Content-Version 35 1926 Derived-From 35 1927 Link 35 1928 MIME-Version 31 1929 Public 35 1930 URI 35 1932 I 1933 identity 8 1935 L 1936 Link header 35 1938 M 1939 MIME-Version header 31 1941 P 1942 Public header 35 1944 U 1945 URI header 35 1947 Authors' Addresses 1949 Roy T. Fielding (editor) 1950 Day Software 1951 23 Corporate Plaza DR, Suite 280 1952 Newport Beach, CA 92660 1953 USA 1955 Phone: +1-949-706-5300 1956 Fax: +1-949-706-5305 1957 Email: fielding@gbiv.com 1958 URI: http://roy.gbiv.com/ 1960 Jim Gettys 1961 One Laptop per Child 1962 21 Oak Knoll Road 1963 Carlisle, MA 01741 1964 USA 1966 Email: jg@laptop.org 1967 URI: http://www.laptop.org/ 1969 Jeffrey C. Mogul 1970 Hewlett-Packard Company 1971 HP Labs, Large Scale Systems Group 1972 1501 Page Mill Road, MS 1177 1973 Palo Alto, CA 94304 1974 USA 1976 Email: JeffMogul@acm.org 1978 Henrik Frystyk Nielsen 1979 Microsoft Corporation 1980 1 Microsoft Way 1981 Redmond, WA 98052 1982 USA 1984 Email: henrikn@microsoft.com 1985 Larry Masinter 1986 Adobe Systems, Incorporated 1987 345 Park Ave 1988 San Jose, CA 95110 1989 USA 1991 Email: LMM@acm.org 1992 URI: http://larry.masinter.net/ 1994 Paul J. Leach 1995 Microsoft Corporation 1996 1 Microsoft Way 1997 Redmond, WA 98052 1999 Email: paulle@microsoft.com 2001 Tim Berners-Lee 2002 World Wide Web Consortium 2003 MIT Computer Science and Artificial Intelligence Laboratory 2004 The Stata Center, Building 32 2005 32 Vassar Street 2006 Cambridge, MA 02139 2007 USA 2009 Email: timbl@w3.org 2010 URI: http://www.w3.org/People/Berners-Lee/ 2012 Yves Lafon (editor) 2013 World Wide Web Consortium 2014 W3C / ERCIM 2015 2004, rte des Lucioles 2016 Sophia-Antipolis, AM 06902 2017 France 2019 Email: ylafon@w3.org 2020 URI: http://www.raubacapeu.net/people/yves/ 2021 Julian F. Reschke (editor) 2022 greenbytes GmbH 2023 Hafenweg 16 2024 Muenster, NW 48155 2025 Germany 2027 Phone: +49 251 2807760 2028 Fax: +49 251 2807761 2029 Email: julian.reschke@greenbytes.de 2030 URI: http://greenbytes.de/tech/webdav/