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4Network Working Group                                   R. Fielding, Ed.
5Internet-Draft                                              Day Software
6Obsoletes: 2616 (if approved)                                  J. Gettys
7Intended status: Standards Track                    One Laptop per Child
8Expires: December 19, 2008                                      J. Mogul
9                                                                      HP
10                                                              H. Frystyk
11                                                               Microsoft
12                                                             L. Masinter
13                                                           Adobe Systems
14                                                                P. Leach
15                                                               Microsoft
16                                                          T. Berners-Lee
17                                                                 W3C/MIT
18                                                           Y. Lafon, Ed.
19                                                                     W3C
20                                                         J. Reschke, Ed.
21                                                              greenbytes
22                                                           June 17, 2008
23
24
25       HTTP/1.1, part 3: Message Payload and Content Negotiation
26                    draft-ietf-httpbis-p3-payload-03
27
28Status of this Memo
29
30   By submitting this Internet-Draft, each author represents that any
31   applicable patent or other IPR claims of which he or she is aware
32   have been or will be disclosed, and any of which he or she becomes
33   aware will be disclosed, in accordance with Section 6 of BCP 79.
34
35   Internet-Drafts are working documents of the Internet Engineering
36   Task Force (IETF), its areas, and its working groups.  Note that
37   other groups may also distribute working documents as Internet-
38   Drafts.
39
40   Internet-Drafts are draft documents valid for a maximum of six months
41   and may be updated, replaced, or obsoleted by other documents at any
42   time.  It is inappropriate to use Internet-Drafts as reference
43   material or to cite them other than as "work in progress."
44
45   The list of current Internet-Drafts can be accessed at
46   http://www.ietf.org/ietf/1id-abstracts.txt.
47
48   The list of Internet-Draft Shadow Directories can be accessed at
49   http://www.ietf.org/shadow.html.
50
51   This Internet-Draft will expire on December 19, 2008.
52
53
54
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57Internet-Draft              HTTP/1.1, Part 3                   June 2008
58
59
60Abstract
61
62   The Hypertext Transfer Protocol (HTTP) is an application-level
63   protocol for distributed, collaborative, hypermedia information
64   systems.  HTTP has been in use by the World Wide Web global
65   information initiative since 1990.  This document is Part 3 of the
66   seven-part specification that defines the protocol referred to as
67   "HTTP/1.1" and, taken together, obsoletes RFC 2616.  Part 3 defines
68   HTTP message content, metadata, and content negotiation.
69
70Editorial Note (To be removed by RFC Editor)
71
72   Discussion of this draft should take place on the HTTPBIS working
73   group mailing list (ietf-http-wg@w3.org).  The current issues list is
74   at <http://www.tools.ietf.org/wg/httpbis/trac/report/11> and related
75   documents (including fancy diffs) can be found at
76   <http://www.tools.ietf.org/wg/httpbis/>.
77
78   The changes in this draft are summarized in Appendix D.4.
79
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113Internet-Draft              HTTP/1.1, Part 3                   June 2008
114
115
116Table of Contents
117
118   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
119     1.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  5
120   2.  Notational Conventions and Generic Grammar . . . . . . . . . .  5
121   3.  Protocol Parameters  . . . . . . . . . . . . . . . . . . . . .  6
122     3.1.  Character Sets . . . . . . . . . . . . . . . . . . . . . .  6
123       3.1.1.  Missing Charset  . . . . . . . . . . . . . . . . . . .  7
124     3.2.  Content Codings  . . . . . . . . . . . . . . . . . . . . .  7
125     3.3.  Media Types  . . . . . . . . . . . . . . . . . . . . . . .  8
126       3.3.1.  Canonicalization and Text Defaults . . . . . . . . . .  9
127       3.3.2.  Multipart Types  . . . . . . . . . . . . . . . . . . . 10
128     3.4.  Quality Values . . . . . . . . . . . . . . . . . . . . . . 11
129     3.5.  Language Tags  . . . . . . . . . . . . . . . . . . . . . . 11
130   4.  Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
131     4.1.  Entity Header Fields . . . . . . . . . . . . . . . . . . . 12
132     4.2.  Entity Body  . . . . . . . . . . . . . . . . . . . . . . . 12
133       4.2.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 13
134       4.2.2.  Entity Length  . . . . . . . . . . . . . . . . . . . . 13
135   5.  Content Negotiation  . . . . . . . . . . . . . . . . . . . . . 13
136     5.1.  Server-driven Negotiation  . . . . . . . . . . . . . . . . 14
137     5.2.  Agent-driven Negotiation . . . . . . . . . . . . . . . . . 15
138     5.3.  Transparent Negotiation  . . . . . . . . . . . . . . . . . 16
139   6.  Header Field Definitions . . . . . . . . . . . . . . . . . . . 16
140     6.1.  Accept . . . . . . . . . . . . . . . . . . . . . . . . . . 16
141     6.2.  Accept-Charset . . . . . . . . . . . . . . . . . . . . . . 18
142     6.3.  Accept-Encoding  . . . . . . . . . . . . . . . . . . . . . 19
143     6.4.  Accept-Language  . . . . . . . . . . . . . . . . . . . . . 20
144     6.5.  Content-Encoding . . . . . . . . . . . . . . . . . . . . . 22
145     6.6.  Content-Language . . . . . . . . . . . . . . . . . . . . . 22
146     6.7.  Content-Location . . . . . . . . . . . . . . . . . . . . . 23
147     6.8.  Content-MD5  . . . . . . . . . . . . . . . . . . . . . . . 24
148     6.9.  Content-Type . . . . . . . . . . . . . . . . . . . . . . . 25
149   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
150     7.1.  Message Header Registration  . . . . . . . . . . . . . . . 26
151   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 26
152     8.1.  Privacy Issues Connected to Accept Headers . . . . . . . . 26
153     8.2.  Content-Disposition Issues . . . . . . . . . . . . . . . . 27
154   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 27
155   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
156     10.1. Normative References . . . . . . . . . . . . . . . . . . . 27
157     10.2. Informative References . . . . . . . . . . . . . . . . . . 29
158   Appendix A.  Differences Between HTTP Entities and RFC 2045
159                Entities  . . . . . . . . . . . . . . . . . . . . . . 30
160     A.1.  MIME-Version . . . . . . . . . . . . . . . . . . . . . . . 31
161     A.2.  Conversion to Canonical Form . . . . . . . . . . . . . . . 31
162     A.3.  Introduction of Content-Encoding . . . . . . . . . . . . . 31
163     A.4.  No Content-Transfer-Encoding . . . . . . . . . . . . . . . 32
164
165
166
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169Internet-Draft              HTTP/1.1, Part 3                   June 2008
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171
172     A.5.  Introduction of Transfer-Encoding  . . . . . . . . . . . . 32
173     A.6.  MHTML and Line Length Limitations  . . . . . . . . . . . . 32
174   Appendix B.  Additional Features . . . . . . . . . . . . . . . . . 32
175     B.1.  Content-Disposition  . . . . . . . . . . . . . . . . . . . 33
176   Appendix C.  Compatibility with Previous Versions  . . . . . . . . 33
177     C.1.  Changes from RFC 2068  . . . . . . . . . . . . . . . . . . 33
178     C.2.  Changes from RFC 2616  . . . . . . . . . . . . . . . . . . 34
179   Appendix D.  Change Log (to be removed by RFC Editor before
180                publication)  . . . . . . . . . . . . . . . . . . . . 34
181     D.1.  Since RFC2616  . . . . . . . . . . . . . . . . . . . . . . 34
182     D.2.  Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . . 34
183     D.3.  Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . . 35
184     D.4.  Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . . 35
185   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
186   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
187   Intellectual Property and Copyright Statements . . . . . . . . . . 41
188
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225Internet-Draft              HTTP/1.1, Part 3                   June 2008
226
227
2281.  Introduction
229
230   This document defines HTTP/1.1 message payloads (a.k.a., content),
231   the associated metadata header fields that define how the payload is
232   intended to be interpreted by a recipient, the request header fields
233   that may influence content selection, and the various selection
234   algorithms that are collectively referred to as HTTP content
235   negotiation.
236
237   This document is currently disorganized in order to minimize the
238   changes between drafts and enable reviewers to see the smaller errata
239   changes.  The next draft will reorganize the sections to better
240   reflect the content.  In particular, the sections on entities will be
241   renamed payload and moved to the first half of the document, while
242   the sections on content negotiation and associated request header
243   fields will be moved to the second half.  The current mess reflects
244   how widely dispersed these topics and associated requirements had
245   become in [RFC2616].
246
2471.1.  Requirements
248
249   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
250   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
251   document are to be interpreted as described in [RFC2119].
252
253   An implementation is not compliant if it fails to satisfy one or more
254   of the MUST or REQUIRED level requirements for the protocols it
255   implements.  An implementation that satisfies all the MUST or
256   REQUIRED level and all the SHOULD level requirements for its
257   protocols is said to be "unconditionally compliant"; one that
258   satisfies all the MUST level requirements but not all the SHOULD
259   level requirements for its protocols is said to be "conditionally
260   compliant."
261
262
2632.  Notational Conventions and Generic Grammar
264
265   This specification uses the ABNF syntax defined in Section 2.1 of
266   [Part1] and the core rules defined in Section 2.2 of [Part1]:
267   [[abnf.dep: ABNF syntax and basic rules will be adopted from RFC
268   5234, see <http://tools.ietf.org/wg/httpbis/trac/ticket/36>.]]
269
270     ALPHA          = <ALPHA, defined in [Part1], Section 2.2>
271     DIGIT          = <DIGIT, defined in [Part1], Section 2.2>
272     OCTET          = <OCTET, defined in [Part1], Section 2.2>
273
274
275     quoted-string  = <quoted-string, defined in [Part1], Section 2.2>
276
277
278
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283
284     token          = <token, defined in [Part1], Section 2.2>
285
286   The ABNF rules below are defined in other parts:
287
288     absoluteURI    = <absoluteURI, defined in [Part1], Section 3.2.1>
289     Content-Length = <Content-Length, defined in [Part1], Section 8.2>
290     relativeURI    = <relativeURI, defined in [Part1], Section 3.2.1>
291     message-header = <message-header, defined in [Part1], Section 4.2>
292
293
294     Last-Modified  = <Last-Modified, defined in [Part4], Section 7.6>
295
296
297     Content-Range  = <Content-Range, defined in [Part5], Section 6.2>
298
299
300     Expires        = <Expires, defined in [Part6], Section 16.3>
301
302
3033.  Protocol Parameters
304
3053.1.  Character Sets
306
307   HTTP uses the same definition of the term "character set" as that
308   described for MIME:
309
310   The term "character set" is used in this document to refer to a
311   method used with one or more tables to convert a sequence of octets
312   into a sequence of characters.  Note that unconditional conversion in
313   the other direction is not required, in that not all characters may
314   be available in a given character set and a character set may provide
315   more than one sequence of octets to represent a particular character.
316   This definition is intended to allow various kinds of character
317   encoding, from simple single-table mappings such as US-ASCII to
318   complex table switching methods such as those that use ISO-2022's
319   techniques.  However, the definition associated with a MIME character
320   set name MUST fully specify the mapping to be performed from octets
321   to characters.  In particular, use of external profiling information
322   to determine the exact mapping is not permitted.
323
324      Note: This use of the term "character set" is more commonly
325      referred to as a "character encoding."  However, since HTTP and
326      MIME share the same registry, it is important that the terminology
327      also be shared.
328
329   HTTP character sets are identified by case-insensitive tokens.  The
330   complete set of tokens is defined by the IANA Character Set registry
331   (<http://www.iana.org/assignments/character-sets>).
332
333
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339
340     charset = token
341
342   Although HTTP allows an arbitrary token to be used as a charset
343   value, any token that has a predefined value within the IANA
344   Character Set registry MUST represent the character set defined by
345   that registry.  Applications SHOULD limit their use of character sets
346   to those defined by the IANA registry.
347
348   HTTP uses charset in two contexts: within an Accept-Charset request
349   header (in which the charset value is an unquoted token) and as the
350   value of a parameter in a Content-Type header (within a request or
351   response), in which case the parameter value of the charset parameter
352   may be quoted.
353
354   Implementors should be aware of IETF character set requirements
355   [RFC3629] [RFC2277].
356
3573.1.1.  Missing Charset
358
359   Some HTTP/1.0 software has interpreted a Content-Type header without
360   charset parameter incorrectly to mean "recipient should guess."
361   Senders wishing to defeat this behavior MAY include a charset
362   parameter even when the charset is ISO-8859-1 ([ISO-8859-1]) and
363   SHOULD do so when it is known that it will not confuse the recipient.
364
365   Unfortunately, some older HTTP/1.0 clients did not deal properly with
366   an explicit charset parameter.  HTTP/1.1 recipients MUST respect the
367   charset label provided by the sender; and those user agents that have
368   a provision to "guess" a charset MUST use the charset from the
369   content-type field if they support that charset, rather than the
370   recipient's preference, when initially displaying a document.  See
371   Section 3.3.1.
372
3733.2.  Content Codings
374
375   Content coding values indicate an encoding transformation that has
376   been or can be applied to an entity.  Content codings are primarily
377   used to allow a document to be compressed or otherwise usefully
378   transformed without losing the identity of its underlying media type
379   and without loss of information.  Frequently, the entity is stored in
380   coded form, transmitted directly, and only decoded by the recipient.
381
382     content-coding   = token
383
384   All content-coding values are case-insensitive.  HTTP/1.1 uses
385   content-coding values in the Accept-Encoding (Section 6.3) and
386   Content-Encoding (Section 6.5) header fields.  Although the value
387   describes the content-coding, what is more important is that it
388
389
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395
396   indicates what decoding mechanism will be required to remove the
397   encoding.
398
399   The Internet Assigned Numbers Authority (IANA) acts as a registry for
400   content-coding value tokens.  Initially, the registry contains the
401   following tokens:
402
403   gzip
404
405      An encoding format produced by the file compression program "gzip"
406      (GNU zip) as described in [RFC1952].  This format is a Lempel-Ziv
407      coding (LZ77) with a 32 bit CRC.
408
409   compress
410
411      The encoding format produced by the common UNIX file compression
412      program "compress".  This format is an adaptive Lempel-Ziv-Welch
413      coding (LZW).
414
415      Use of program names for the identification of encoding formats is
416      not desirable and is discouraged for future encodings.  Their use
417      here is representative of historical practice, not good design.
418      For compatibility with previous implementations of HTTP,
419      applications SHOULD consider "x-gzip" and "x-compress" to be
420      equivalent to "gzip" and "compress" respectively.
421
422   deflate
423
424      The "zlib" format defined in [RFC1950] in combination with the
425      "deflate" compression mechanism described in [RFC1951].
426
427   identity
428
429      The default (identity) encoding; the use of no transformation
430      whatsoever.  This content-coding is used only in the Accept-
431      Encoding header, and SHOULD NOT be used in the Content-Encoding
432      header.
433
434   New content-coding value tokens SHOULD be registered; to allow
435   interoperability between clients and servers, specifications of the
436   content coding algorithms needed to implement a new value SHOULD be
437   publicly available and adequate for independent implementation, and
438   conform to the purpose of content coding defined in this section.
439
4403.3.  Media Types
441
442   HTTP uses Internet Media Types [RFC2046] in the Content-Type
443   (Section 6.9) and Accept (Section 6.1) header fields in order to
444
445
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451
452   provide open and extensible data typing and type negotiation.
453
454     media-type     = type "/" subtype *( ";" parameter )
455     type           = token
456     subtype        = token
457
458   Parameters MAY follow the type/subtype in the form of attribute/value
459   pairs.
460
461     parameter      = attribute "=" value
462     attribute      = token
463     value          = token | quoted-string
464
465   The type, subtype, and parameter attribute names are case-
466   insensitive.  Parameter values might or might not be case-sensitive,
467   depending on the semantics of the parameter name.  Linear white space
468   (LWS) MUST NOT be used between the type and subtype, nor between an
469   attribute and its value.  The presence or absence of a parameter
470   might be significant to the processing of a media-type, depending on
471   its definition within the media type registry.
472
473   All parameters defined as a token are also allowed to occur as
474   quoted-string; both notations are equivalent.
475
476   Note that some older HTTP applications do not recognize media type
477   parameters.  When sending data to older HTTP applications,
478   implementations SHOULD only use media type parameters when they are
479   required by that type/subtype definition.
480
481   Media-type values are registered with the Internet Assigned Number
482   Authority (IANA).  The media type registration process is outlined in
483   [RFC4288].  Use of non-registered media types is discouraged.
484
4853.3.1.  Canonicalization and Text Defaults
486
487   Internet media types are registered with a canonical form.  An
488   entity-body transferred via HTTP messages MUST be represented in the
489   appropriate canonical form prior to its transmission except for
490   "text" types, as defined in the next paragraph.
491
492   When in canonical form, media subtypes of the "text" type use CRLF as
493   the text line break.  HTTP relaxes this requirement and allows the
494   transport of text media with plain CR or LF alone representing a line
495   break when it is done consistently for an entire entity-body.  HTTP
496   applications MUST accept CRLF, bare CR, and bare LF as being
497   representative of a line break in text media received via HTTP.  In
498   addition, if the text is represented in a character set that does not
499   use octets 13 and 10 for CR and LF respectively, as is the case for
500
501
502
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507
508   some multi-byte character sets, HTTP allows the use of whatever octet
509   sequences are defined by that character set to represent the
510   equivalent of CR and LF for line breaks.  This flexibility regarding
511   line breaks applies only to text media in the entity-body; a bare CR
512   or LF MUST NOT be substituted for CRLF within any of the HTTP control
513   structures (such as header fields and multipart boundaries).
514
515   If an entity-body is encoded with a content-coding, the underlying
516   data MUST be in a form defined above prior to being encoded.
517
518   The "charset" parameter is used with some media types to define the
519   character set (Section 3.1) of the data.  When no explicit charset
520   parameter is provided by the sender, media subtypes of the "text"
521   type are defined to have a default charset value of "ISO-8859-1" when
522   received via HTTP.  Data in character sets other than "ISO-8859-1" or
523   its subsets MUST be labeled with an appropriate charset value.  See
524   Section 3.1.1 for compatibility problems.
525
5263.3.2.  Multipart Types
527
528   MIME provides for a number of "multipart" types -- encapsulations of
529   one or more entities within a single message-body.  All multipart
530   types share a common syntax, as defined in Section 5.1.1 of
531   [RFC2046], and MUST include a boundary parameter as part of the media
532   type value.  The message body is itself a protocol element and MUST
533   therefore use only CRLF to represent line breaks between body-parts.
534   Unlike in RFC 2046, the epilogue of any multipart message MUST be
535   empty; HTTP applications MUST NOT transmit the epilogue (even if the
536   original multipart contains an epilogue).  These restrictions exist
537   in order to preserve the self-delimiting nature of a multipart
538   message-body, wherein the "end" of the message-body is indicated by
539   the ending multipart boundary.
540
541   In general, HTTP treats a multipart message-body no differently than
542   any other media type: strictly as payload.  The one exception is the
543   "multipart/byteranges" type (Appendix A of [Part5]) when it appears
544   in a 206 (Partial Content) response.  In all other cases, an HTTP
545   user agent SHOULD follow the same or similar behavior as a MIME user
546   agent would upon receipt of a multipart type.  The MIME header fields
547   within each body-part of a multipart message-body do not have any
548   significance to HTTP beyond that defined by their MIME semantics.
549
550   In general, an HTTP user agent SHOULD follow the same or similar
551   behavior as a MIME user agent would upon receipt of a multipart type.
552   If an application receives an unrecognized multipart subtype, the
553   application MUST treat it as being equivalent to "multipart/mixed".
554
555
556
557
558
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563
564      Note: The "multipart/form-data" type has been specifically defined
565      for carrying form data suitable for processing via the POST
566      request method, as described in [RFC2388].
567
5683.4.  Quality Values
569
570   HTTP content negotiation (Section 5) uses short "floating point"
571   numbers to indicate the relative importance ("weight") of various
572   negotiable parameters.  A weight is normalized to a real number in
573   the range 0 through 1, where 0 is the minimum and 1 the maximum
574   value.  If a parameter has a quality value of 0, then content with
575   this parameter is `not acceptable' for the client.  HTTP/1.1
576   applications MUST NOT generate more than three digits after the
577   decimal point.  User configuration of these values SHOULD also be
578   limited in this fashion.
579
580     qvalue         = ( "0" [ "." 0*3DIGIT ] )
581                    | ( "1" [ "." 0*3("0") ] )
582
583   "Quality values" is a misnomer, since these values merely represent
584   relative degradation in desired quality.
585
5863.5.  Language Tags
587
588   A language tag identifies a natural language spoken, written, or
589   otherwise conveyed by human beings for communication of information
590   to other human beings.  Computer languages are explicitly excluded.
591   HTTP uses language tags within the Accept-Language and Content-
592   Language fields.
593
594   The syntax and registry of HTTP language tags is the same as that
595   defined by [RFC1766].  In summary, a language tag is composed of 1 or
596   more parts: A primary language tag and a possibly empty series of
597   subtags:
598
599     language-tag  = primary-tag *( "-" subtag )
600     primary-tag   = 1*8ALPHA
601     subtag        = 1*8ALPHA
602
603   White space is not allowed within the tag and all tags are case-
604   insensitive.  The name space of language tags is administered by the
605   IANA.  Example tags include:
606
607       en, en-US, en-cockney, i-cherokee, x-pig-latin
608
609   where any two-letter primary-tag is an ISO-639 language abbreviation
610   and any two-letter initial subtag is an ISO-3166 country code.  (The
611   last three tags above are not registered tags; all but the last are
612
613
614
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619
620   examples of tags which could be registered in future.)
621
622
6234.  Entity
624
625   Request and Response messages MAY transfer an entity if not otherwise
626   restricted by the request method or response status code.  An entity
627   consists of entity-header fields and an entity-body, although some
628   responses will only include the entity-headers.
629
630   In this section, both sender and recipient refer to either the client
631   or the server, depending on who sends and who receives the entity.
632
6334.1.  Entity Header Fields
634
635   Entity-header fields define metainformation about the entity-body or,
636   if no body is present, about the resource identified by the request.
637
638     entity-header  = Content-Encoding         ; Section 6.5
639                    | Content-Language         ; Section 6.6
640                    | Content-Length           ; [Part1], Section 8.2
641                    | Content-Location         ; Section 6.7
642                    | Content-MD5              ; Section 6.8
643                    | Content-Range            ; [Part5], Section 6.2
644                    | Content-Type             ; Section 6.9
645                    | Expires                  ; [Part6], Section 16.3
646                    | Last-Modified            ; [Part4], Section 7.6
647                    | extension-header
648
649     extension-header = message-header
650
651   The extension-header mechanism allows additional entity-header fields
652   to be defined without changing the protocol, but these fields cannot
653   be assumed to be recognizable by the recipient.  Unrecognized header
654   fields SHOULD be ignored by the recipient and MUST be forwarded by
655   transparent proxies.
656
6574.2.  Entity Body
658
659   The entity-body (if any) sent with an HTTP request or response is in
660   a format and encoding defined by the entity-header fields.
661
662     entity-body    = *OCTET
663
664   An entity-body is only present in a message when a message-body is
665   present, as described in Section 4.3 of [Part1].  The entity-body is
666   obtained from the message-body by decoding any Transfer-Encoding that
667   might have been applied to ensure safe and proper transfer of the
668
669
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675
676   message.
677
6784.2.1.  Type
679
680   When an entity-body is included with a message, the data type of that
681   body is determined via the header fields Content-Type and Content-
682   Encoding.  These define a two-layer, ordered encoding model:
683
684       entity-body := Content-Encoding( Content-Type( data ) )
685
686   Content-Type specifies the media type of the underlying data.
687   Content-Encoding may be used to indicate any additional content
688   codings applied to the data, usually for the purpose of data
689   compression, that are a property of the requested resource.  There is
690   no default encoding.
691
692   Any HTTP/1.1 message containing an entity-body SHOULD include a
693   Content-Type header field defining the media type of that body.  If
694   and only if the media type is not given by a Content-Type field, the
695   recipient MAY attempt to guess the media type via inspection of its
696   content and/or the name extension(s) of the URI used to identify the
697   resource.  If the media type remains unknown, the recipient SHOULD
698   treat it as type "application/octet-stream".
699
7004.2.2.  Entity Length
701
702   The entity-length of a message is the length of the message-body
703   before any transfer-codings have been applied.  Section 4.4 of
704   [Part1] defines how the transfer-length of a message-body is
705   determined.
706
707
7085.  Content Negotiation
709
710   Most HTTP responses include an entity which contains information for
711   interpretation by a human user.  Naturally, it is desirable to supply
712   the user with the "best available" entity corresponding to the
713   request.  Unfortunately for servers and caches, not all users have
714   the same preferences for what is "best," and not all user agents are
715   equally capable of rendering all entity types.  For that reason, HTTP
716   has provisions for several mechanisms for "content negotiation" --
717   the process of selecting the best representation for a given response
718   when there are multiple representations available.
719
720      Note: This is not called "format negotiation" because the
721      alternate representations may be of the same media type, but use
722      different capabilities of that type, be in different languages,
723      etc.
724
725
726
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731
732   Any response containing an entity-body MAY be subject to negotiation,
733   including error responses.
734
735   There are two kinds of content negotiation which are possible in
736   HTTP: server-driven and agent-driven negotiation.  These two kinds of
737   negotiation are orthogonal and thus may be used separately or in
738   combination.  One method of combination, referred to as transparent
739   negotiation, occurs when a cache uses the agent-driven negotiation
740   information provided by the origin server in order to provide server-
741   driven negotiation for subsequent requests.
742
7435.1.  Server-driven Negotiation
744
745   If the selection of the best representation for a response is made by
746   an algorithm located at the server, it is called server-driven
747   negotiation.  Selection is based on the available representations of
748   the response (the dimensions over which it can vary; e.g. language,
749   content-coding, etc.) and the contents of particular header fields in
750   the request message or on other information pertaining to the request
751   (such as the network address of the client).
752
753   Server-driven negotiation is advantageous when the algorithm for
754   selecting from among the available representations is difficult to
755   describe to the user agent, or when the server desires to send its
756   "best guess" to the client along with the first response (hoping to
757   avoid the round-trip delay of a subsequent request if the "best
758   guess" is good enough for the user).  In order to improve the
759   server's guess, the user agent MAY include request header fields
760   (Accept, Accept-Language, Accept-Encoding, etc.) which describe its
761   preferences for such a response.
762
763   Server-driven negotiation has disadvantages:
764
765   1.  It is impossible for the server to accurately determine what
766       might be "best" for any given user, since that would require
767       complete knowledge of both the capabilities of the user agent and
768       the intended use for the response (e.g., does the user want to
769       view it on screen or print it on paper?).
770
771   2.  Having the user agent describe its capabilities in every request
772       can be both very inefficient (given that only a small percentage
773       of responses have multiple representations) and a potential
774       violation of the user's privacy.
775
776   3.  It complicates the implementation of an origin server and the
777       algorithms for generating responses to a request.
778
779
780
781
782
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787
788   4.  It may limit a public cache's ability to use the same response
789       for multiple user's requests.
790
791   HTTP/1.1 includes the following request-header fields for enabling
792   server-driven negotiation through description of user agent
793   capabilities and user preferences: Accept (Section 6.1), Accept-
794   Charset (Section 6.2), Accept-Encoding (Section 6.3), Accept-Language
795   (Section 6.4), and User-Agent (Section 10.9 of [Part2]).  However, an
796   origin server is not limited to these dimensions and MAY vary the
797   response based on any aspect of the request, including information
798   outside the request-header fields or within extension header fields
799   not defined by this specification.
800
801   The Vary header field (Section 16.5 of [Part6]) can be used to
802   express the parameters the server uses to select a representation
803   that is subject to server-driven negotiation.
804
8055.2.  Agent-driven Negotiation
806
807   With agent-driven negotiation, selection of the best representation
808   for a response is performed by the user agent after receiving an
809   initial response from the origin server.  Selection is based on a
810   list of the available representations of the response included within
811   the header fields or entity-body of the initial response, with each
812   representation identified by its own URI.  Selection from among the
813   representations may be performed automatically (if the user agent is
814   capable of doing so) or manually by the user selecting from a
815   generated (possibly hypertext) menu.
816
817   Agent-driven negotiation is advantageous when the response would vary
818   over commonly-used dimensions (such as type, language, or encoding),
819   when the origin server is unable to determine a user agent's
820   capabilities from examining the request, and generally when public
821   caches are used to distribute server load and reduce network usage.
822
823   Agent-driven negotiation suffers from the disadvantage of needing a
824   second request to obtain the best alternate representation.  This
825   second request is only efficient when caching is used.  In addition,
826   this specification does not define any mechanism for supporting
827   automatic selection, though it also does not prevent any such
828   mechanism from being developed as an extension and used within
829   HTTP/1.1.
830
831   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
832   status codes for enabling agent-driven negotiation when the server is
833   unwilling or unable to provide a varying response using server-driven
834   negotiation.
835
836
837
838
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843
8445.3.  Transparent Negotiation
845
846   Transparent negotiation is a combination of both server-driven and
847   agent-driven negotiation.  When a cache is supplied with a form of
848   the list of available representations of the response (as in agent-
849   driven negotiation) and the dimensions of variance are completely
850   understood by the cache, then the cache becomes capable of performing
851   server-driven negotiation on behalf of the origin server for
852   subsequent requests on that resource.
853
854   Transparent negotiation has the advantage of distributing the
855   negotiation work that would otherwise be required of the origin
856   server and also removing the second request delay of agent-driven
857   negotiation when the cache is able to correctly guess the right
858   response.
859
860   This specification does not define any mechanism for transparent
861   negotiation, though it also does not prevent any such mechanism from
862   being developed as an extension that could be used within HTTP/1.1.
863
864
8656.  Header Field Definitions
866
867   This section defines the syntax and semantics of HTTP/1.1 header
868   fields related to the payload of messages.
869
870   For entity-header fields, both sender and recipient refer to either
871   the client or the server, depending on who sends and who receives the
872   entity.
873
8746.1.  Accept
875
876   The Accept request-header field can be used to specify certain media
877   types which are acceptable for the response.  Accept headers can be
878   used to indicate that the request is specifically limited to a small
879   set of desired types, as in the case of a request for an in-line
880   image.
881
882     Accept         = "Accept" ":"
883                      #( media-range [ accept-params ] )
884
885     media-range    = ( "*/*"
886                      | ( type "/" "*" )
887                      | ( type "/" subtype )
888                      ) *( ";" parameter )
889     accept-params  = ";" "q" "=" qvalue *( accept-extension )
890     accept-extension = ";" token [ "=" ( token | quoted-string ) ]
891
892
893
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899
900   The asterisk "*" character is used to group media types into ranges,
901   with "*/*" indicating all media types and "type/*" indicating all
902   subtypes of that type.  The media-range MAY include media type
903   parameters that are applicable to that range.
904
905   Each media-range MAY be followed by one or more accept-params,
906   beginning with the "q" parameter for indicating a relative quality
907   factor.  The first "q" parameter (if any) separates the media-range
908   parameter(s) from the accept-params.  Quality factors allow the user
909   or user agent to indicate the relative degree of preference for that
910   media-range, using the qvalue scale from 0 to 1 (Section 3.4).  The
911   default value is q=1.
912
913      Note: Use of the "q" parameter name to separate media type
914      parameters from Accept extension parameters is due to historical
915      practice.  Although this prevents any media type parameter named
916      "q" from being used with a media range, such an event is believed
917      to be unlikely given the lack of any "q" parameters in the IANA
918      media type registry and the rare usage of any media type
919      parameters in Accept.  Future media types are discouraged from
920      registering any parameter named "q".
921
922   The example
923
924       Accept: audio/*; q=0.2, audio/basic
925
926   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
927   type if it is the best available after an 80% mark-down in quality."
928
929   If no Accept header field is present, then it is assumed that the
930   client accepts all media types.  If an Accept header field is
931   present, and if the server cannot send a response which is acceptable
932   according to the combined Accept field value, then the server SHOULD
933   send a 406 (Not Acceptable) response.
934
935   A more elaborate example is
936
937       Accept: text/plain; q=0.5, text/html,
938               text/x-dvi; q=0.8, text/x-c
939
940   Verbally, this would be interpreted as "text/html and text/x-c are
941   the preferred media types, but if they do not exist, then send the
942   text/x-dvi entity, and if that does not exist, send the text/plain
943   entity."
944
945   Media ranges can be overridden by more specific media ranges or
946   specific media types.  If more than one media range applies to a
947   given type, the most specific reference has precedence.  For example,
948
949
950
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955
956       Accept: text/*, text/html, text/html;level=1, */*
957
958   have the following precedence:
959
960       1) text/html;level=1
961       2) text/html
962       3) text/*
963       4) */*
964
965   The media type quality factor associated with a given type is
966   determined by finding the media range with the highest precedence
967   which matches that type.  For example,
968
969       Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
970               text/html;level=2;q=0.4, */*;q=0.5
971
972   would cause the following values to be associated:
973
974       text/html;level=1         = 1
975       text/html                 = 0.7
976       text/plain                = 0.3
977       image/jpeg                = 0.5
978       text/html;level=2         = 0.4
979       text/html;level=3         = 0.7
980
981   Note: A user agent might be provided with a default set of quality
982   values for certain media ranges.  However, unless the user agent is a
983   closed system which cannot interact with other rendering agents, this
984   default set ought to be configurable by the user.
985
9866.2.  Accept-Charset
987
988   The Accept-Charset request-header field can be used to indicate what
989   character sets are acceptable for the response.  This field allows
990   clients capable of understanding more comprehensive or special-
991   purpose character sets to signal that capability to a server which is
992   capable of representing documents in those character sets.
993
994     Accept-Charset = "Accept-Charset" ":"
995             1#( ( charset | "*" ) [ ";" "q" "=" qvalue ] )
996
997   Character set values are described in Section 3.1.  Each charset MAY
998   be given an associated quality value which represents the user's
999   preference for that charset.  The default value is q=1.  An example
1000   is
1001
1002      Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1003
1004
1005
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1011
1012   The special value "*", if present in the Accept-Charset field,
1013   matches every character set (including ISO-8859-1) which is not
1014   mentioned elsewhere in the Accept-Charset field.  If no "*" is
1015   present in an Accept-Charset field, then all character sets not
1016   explicitly mentioned get a quality value of 0, except for ISO-8859-1,
1017   which gets a quality value of 1 if not explicitly mentioned.
1018
1019   If no Accept-Charset header is present, the default is that any
1020   character set is acceptable.  If an Accept-Charset header is present,
1021   and if the server cannot send a response which is acceptable
1022   according to the Accept-Charset header, then the server SHOULD send
1023   an error response with the 406 (Not Acceptable) status code, though
1024   the sending of an unacceptable response is also allowed.
1025
10266.3.  Accept-Encoding
1027
1028   The Accept-Encoding request-header field is similar to Accept, but
1029   restricts the content-codings (Section 3.2) that are acceptable in
1030   the response.
1031
1032     Accept-Encoding  = "Accept-Encoding" ":"
1033                        #( codings [ ";" "q" "=" qvalue ] )
1034     codings          = ( content-coding | "*" )
1035
1036   Each codings value MAY be given an associated quality value which
1037   represents the preference for that encoding.  The default value is
1038   q=1.
1039
1040   Examples of its use are:
1041
1042       Accept-Encoding: compress, gzip
1043       Accept-Encoding:
1044       Accept-Encoding: *
1045       Accept-Encoding: compress;q=0.5, gzip;q=1.0
1046       Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1047
1048   A server tests whether a content-coding is acceptable, according to
1049   an Accept-Encoding field, using these rules:
1050
1051   1.  If the content-coding is one of the content-codings listed in the
1052       Accept-Encoding field, then it is acceptable, unless it is
1053       accompanied by a qvalue of 0.  (As defined in Section 3.4, a
1054       qvalue of 0 means "not acceptable.")
1055
1056   2.  The special "*" symbol in an Accept-Encoding field matches any
1057       available content-coding not explicitly listed in the header
1058       field.
1059
1060
1061
1062
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1066
1067
1068   3.  If multiple content-codings are acceptable, then the acceptable
1069       content-coding with the highest non-zero qvalue is preferred.
1070
1071   4.  The "identity" content-coding is always acceptable, unless
1072       specifically refused because the Accept-Encoding field includes
1073       "identity;q=0", or because the field includes "*;q=0" and does
1074       not explicitly include the "identity" content-coding.  If the
1075       Accept-Encoding field-value is empty, then only the "identity"
1076       encoding is acceptable.
1077
1078   If an Accept-Encoding field is present in a request, and if the
1079   server cannot send a response which is acceptable according to the
1080   Accept-Encoding header, then the server SHOULD send an error response
1081   with the 406 (Not Acceptable) status code.
1082
1083   If no Accept-Encoding field is present in a request, the server MAY
1084   assume that the client will accept any content coding.  In this case,
1085   if "identity" is one of the available content-codings, then the
1086   server SHOULD use the "identity" content-coding, unless it has
1087   additional information that a different content-coding is meaningful
1088   to the client.
1089
1090      Note: If the request does not include an Accept-Encoding field,
1091      and if the "identity" content-coding is unavailable, then content-
1092      codings commonly understood by HTTP/1.0 clients (i.e., "gzip" and
1093      "compress") are preferred; some older clients improperly display
1094      messages sent with other content-codings.  The server might also
1095      make this decision based on information about the particular user-
1096      agent or client.
1097
1098      Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1099      associated with content-codings.  This means that qvalues will not
1100      work and are not permitted with x-gzip or x-compress.
1101
11026.4.  Accept-Language
1103
1104   The Accept-Language request-header field is similar to Accept, but
1105   restricts the set of natural languages that are preferred as a
1106   response to the request.  Language tags are defined in Section 3.5.
1107
1108     Accept-Language = "Accept-Language" ":"
1109                       1#( language-range [ ";" "q" "=" qvalue ] )
1110     language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
1111
1112   Each language-range MAY be given an associated quality value which
1113   represents an estimate of the user's preference for the languages
1114   specified by that range.  The quality value defaults to "q=1".  For
1115   example,
1116
1117
1118
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1122
1123
1124       Accept-Language: da, en-gb;q=0.8, en;q=0.7
1125
1126   would mean: "I prefer Danish, but will accept British English and
1127   other types of English."  A language-range matches a language-tag if
1128   it exactly equals the tag, or if it exactly equals a prefix of the
1129   tag such that the first tag character following the prefix is "-".
1130   The special range "*", if present in the Accept-Language field,
1131   matches every tag not matched by any other range present in the
1132   Accept-Language field.
1133
1134      Note: This use of a prefix matching rule does not imply that
1135      language tags are assigned to languages in such a way that it is
1136      always true that if a user understands a language with a certain
1137      tag, then this user will also understand all languages with tags
1138      for which this tag is a prefix.  The prefix rule simply allows the
1139      use of prefix tags if this is the case.
1140
1141   The language quality factor assigned to a language-tag by the Accept-
1142   Language field is the quality value of the longest language-range in
1143   the field that matches the language-tag.  If no language-range in the
1144   field matches the tag, the language quality factor assigned is 0.  If
1145   no Accept-Language header is present in the request, the server
1146   SHOULD assume that all languages are equally acceptable.  If an
1147   Accept-Language header is present, then all languages which are
1148   assigned a quality factor greater than 0 are acceptable.
1149
1150   It might be contrary to the privacy expectations of the user to send
1151   an Accept-Language header with the complete linguistic preferences of
1152   the user in every request.  For a discussion of this issue, see
1153   Section 8.1.
1154
1155   As intelligibility is highly dependent on the individual user, it is
1156   recommended that client applications make the choice of linguistic
1157   preference available to the user.  If the choice is not made
1158   available, then the Accept-Language header field MUST NOT be given in
1159   the request.
1160
1161      Note: When making the choice of linguistic preference available to
1162      the user, we remind implementors of the fact that users are not
1163      familiar with the details of language matching as described above,
1164      and should provide appropriate guidance.  As an example, users
1165      might assume that on selecting "en-gb", they will be served any
1166      kind of English document if British English is not available.  A
1167      user agent might suggest in such a case to add "en" to get the
1168      best matching behavior.
1169
1170
1171
1172
1173
1174
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1178
1179
11806.5.  Content-Encoding
1181
1182   The Content-Encoding entity-header field is used as a modifier to the
1183   media-type.  When present, its value indicates what additional
1184   content codings have been applied to the entity-body, and thus what
1185   decoding mechanisms must be applied in order to obtain the media-type
1186   referenced by the Content-Type header field.  Content-Encoding is
1187   primarily used to allow a document to be compressed without losing
1188   the identity of its underlying media type.
1189
1190     Content-Encoding  = "Content-Encoding" ":" 1#content-coding
1191
1192   Content codings are defined in Section 3.2.  An example of its use is
1193
1194       Content-Encoding: gzip
1195
1196   The content-coding is a characteristic of the entity identified by
1197   the Request-URI.  Typically, the entity-body is stored with this
1198   encoding and is only decoded before rendering or analogous usage.
1199   However, a non-transparent proxy MAY modify the content-coding if the
1200   new coding is known to be acceptable to the recipient, unless the
1201   "no-transform" cache-control directive is present in the message.
1202
1203   If the content-coding of an entity is not "identity", then the
1204   response MUST include a Content-Encoding entity-header (Section 6.5)
1205   that lists the non-identity content-coding(s) used.
1206
1207   If the content-coding of an entity in a request message is not
1208   acceptable to the origin server, the server SHOULD respond with a
1209   status code of 415 (Unsupported Media Type).
1210
1211   If multiple encodings have been applied to an entity, the content
1212   codings MUST be listed in the order in which they were applied.
1213   Additional information about the encoding parameters MAY be provided
1214   by other entity-header fields not defined by this specification.
1215
12166.6.  Content-Language
1217
1218   The Content-Language entity-header field describes the natural
1219   language(s) of the intended audience for the enclosed entity.  Note
1220   that this might not be equivalent to all the languages used within
1221   the entity-body.
1222
1223     Content-Language  = "Content-Language" ":" 1#language-tag
1224
1225   Language tags are defined in Section 3.5.  The primary purpose of
1226   Content-Language is to allow a user to identify and differentiate
1227   entities according to the user's own preferred language.  Thus, if
1228
1229
1230
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1234
1235
1236   the body content is intended only for a Danish-literate audience, the
1237   appropriate field is
1238
1239       Content-Language: da
1240
1241   If no Content-Language is specified, the default is that the content
1242   is intended for all language audiences.  This might mean that the
1243   sender does not consider it to be specific to any natural language,
1244   or that the sender does not know for which language it is intended.
1245
1246   Multiple languages MAY be listed for content that is intended for
1247   multiple audiences.  For example, a rendition of the "Treaty of
1248   Waitangi," presented simultaneously in the original Maori and English
1249   versions, would call for
1250
1251       Content-Language: mi, en
1252
1253   However, just because multiple languages are present within an entity
1254   does not mean that it is intended for multiple linguistic audiences.
1255   An example would be a beginner's language primer, such as "A First
1256   Lesson in Latin," which is clearly intended to be used by an English-
1257   literate audience.  In this case, the Content-Language would properly
1258   only include "en".
1259
1260   Content-Language MAY be applied to any media type -- it is not
1261   limited to textual documents.
1262
12636.7.  Content-Location
1264
1265   The Content-Location entity-header field MAY be used to supply the
1266   resource location for the entity enclosed in the message when that
1267   entity is accessible from a location separate from the requested
1268   resource's URI.  A server SHOULD provide a Content-Location for the
1269   variant corresponding to the response entity; especially in the case
1270   where a resource has multiple entities associated with it, and those
1271   entities actually have separate locations by which they might be
1272   individually accessed, the server SHOULD provide a Content-Location
1273   for the particular variant which is returned.
1274
1275     Content-Location = "Content-Location" ":"
1276                       ( absoluteURI | relativeURI )
1277
1278   The value of Content-Location also defines the base URI for the
1279   entity.
1280
1281   The Content-Location value is not a replacement for the original
1282   requested URI; it is only a statement of the location of the resource
1283   corresponding to this particular entity at the time of the request.
1284
1285
1286
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1290
1291
1292   Future requests MAY specify the Content-Location URI as the request-
1293   URI if the desire is to identify the source of that particular
1294   entity.
1295
1296   A cache cannot assume that an entity with a Content-Location
1297   different from the URI used to retrieve it can be used to respond to
1298   later requests on that Content-Location URI.  However, the Content-
1299   Location can be used to differentiate between multiple entities
1300   retrieved from a single requested resource, as described in Section 8
1301   of [Part6].
1302
1303   If the Content-Location is a relative URI, the relative URI is
1304   interpreted relative to the Request-URI.
1305
1306   The meaning of the Content-Location header in PUT or POST requests is
1307   undefined; servers are free to ignore it in those cases.
1308
13096.8.  Content-MD5
1310
1311   The Content-MD5 entity-header field, as defined in [RFC1864], is an
1312   MD5 digest of the entity-body for the purpose of providing an end-to-
1313   end message integrity check (MIC) of the entity-body.  (Note: a MIC
1314   is good for detecting accidental modification of the entity-body in
1315   transit, but is not proof against malicious attacks.)
1316
1317     Content-MD5   = "Content-MD5" ":" md5-digest
1318     md5-digest    = <base64 of 128 bit MD5 digest as per [RFC1864]>
1319
1320   The Content-MD5 header field MAY be generated by an origin server or
1321   client to function as an integrity check of the entity-body.  Only
1322   origin servers or clients MAY generate the Content-MD5 header field;
1323   proxies and gateways MUST NOT generate it, as this would defeat its
1324   value as an end-to-end integrity check.  Any recipient of the entity-
1325   body, including gateways and proxies, MAY check that the digest value
1326   in this header field matches that of the entity-body as received.
1327
1328   The MD5 digest is computed based on the content of the entity-body,
1329   including any content-coding that has been applied, but not including
1330   any transfer-encoding applied to the message-body.  If the message is
1331   received with a transfer-encoding, that encoding MUST be removed
1332   prior to checking the Content-MD5 value against the received entity.
1333
1334   This has the result that the digest is computed on the octets of the
1335   entity-body exactly as, and in the order that, they would be sent if
1336   no transfer-encoding were being applied.
1337
1338   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1339   composite media-types (e.g., multipart/* and message/rfc822), but
1340
1341
1342
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1346
1347
1348   this does not change how the digest is computed as defined in the
1349   preceding paragraph.
1350
1351   There are several consequences of this.  The entity-body for
1352   composite types MAY contain many body-parts, each with its own MIME
1353   and HTTP headers (including Content-MD5, Content-Transfer-Encoding,
1354   and Content-Encoding headers).  If a body-part has a Content-
1355   Transfer-Encoding or Content-Encoding header, it is assumed that the
1356   content of the body-part has had the encoding applied, and the body-
1357   part is included in the Content-MD5 digest as is -- i.e., after the
1358   application.  The Transfer-Encoding header field is not allowed
1359   within body-parts.
1360
1361   Conversion of all line breaks to CRLF MUST NOT be done before
1362   computing or checking the digest: the line break convention used in
1363   the text actually transmitted MUST be left unaltered when computing
1364   the digest.
1365
1366      Note: while the definition of Content-MD5 is exactly the same for
1367      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1368      in which the application of Content-MD5 to HTTP entity-bodies
1369      differs from its application to MIME entity-bodies.  One is that
1370      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1371      does use Transfer-Encoding and Content-Encoding.  Another is that
1372      HTTP more frequently uses binary content types than MIME, so it is
1373      worth noting that, in such cases, the byte order used to compute
1374      the digest is the transmission byte order defined for the type.
1375      Lastly, HTTP allows transmission of text types with any of several
1376      line break conventions and not just the canonical form using CRLF.
1377
13786.9.  Content-Type
1379
1380   The Content-Type entity-header field indicates the media type of the
1381   entity-body sent to the recipient or, in the case of the HEAD method,
1382   the media type that would have been sent had the request been a GET.
1383
1384     Content-Type   = "Content-Type" ":" media-type
1385
1386   Media types are defined in Section 3.3.  An example of the field is
1387
1388       Content-Type: text/html; charset=ISO-8859-4
1389
1390   Further discussion of methods for identifying the media type of an
1391   entity is provided in Section 4.2.1.
1392
1393
1394
1395
1396
1397
1398
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1402
1403
14047.  IANA Considerations
1405
14067.1.  Message Header Registration
1407
1408   The Message Header Registry located at <http://www.iana.org/
1409   assignments/message-headers/message-header-index.html> should be
1410   updated with the permanent registrations below (see [RFC3864]):
1411
1412       +---------------------+----------+----------+--------------+
1413       | Header Field Name   | Protocol | Status   | Reference    |
1414       +---------------------+----------+----------+--------------+
1415       | Accept              | http     | standard | Section 6.1  |
1416       | Accept-Charset      | http     | standard | Section 6.2  |
1417       | Accept-Encoding     | http     | standard | Section 6.3  |
1418       | Accept-Language     | http     | standard | Section 6.4  |
1419       | Content-Disposition | http     |          | Appendix B.1 |
1420       | Content-Encoding    | http     | standard | Section 6.5  |
1421       | Content-Language    | http     | standard | Section 6.6  |
1422       | Content-Location    | http     | standard | Section 6.7  |
1423       | Content-MD5         | http     | standard | Section 6.8  |
1424       | Content-Type        | http     | standard | Section 6.9  |
1425       +---------------------+----------+----------+--------------+
1426
1427   The change controller is: "IETF (iesg@ietf.org) - Internet
1428   Engineering Task Force".
1429
1430
14318.  Security Considerations
1432
1433   This section is meant to inform application developers, information
1434   providers, and users of the security limitations in HTTP/1.1 as
1435   described by this document.  The discussion does not include
1436   definitive solutions to the problems revealed, though it does make
1437   some suggestions for reducing security risks.
1438
14398.1.  Privacy Issues Connected to Accept Headers
1440
1441   Accept request-headers can reveal information about the user to all
1442   servers which are accessed.  The Accept-Language header in particular
1443   can reveal information the user would consider to be of a private
1444   nature, because the understanding of particular languages is often
1445   strongly correlated to the membership of a particular ethnic group.
1446   User agents which offer the option to configure the contents of an
1447   Accept-Language header to be sent in every request are strongly
1448   encouraged to let the configuration process include a message which
1449   makes the user aware of the loss of privacy involved.
1450
1451   An approach that limits the loss of privacy would be for a user agent
1452
1453
1454
1455Fielding, et al.        Expires December 19, 2008              [Page 26]
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1458
1459
1460   to omit the sending of Accept-Language headers by default, and to ask
1461   the user whether or not to start sending Accept-Language headers to a
1462   server if it detects, by looking for any Vary response-header fields
1463   generated by the server, that such sending could improve the quality
1464   of service.
1465
1466   Elaborate user-customized accept header fields sent in every request,
1467   in particular if these include quality values, can be used by servers
1468   as relatively reliable and long-lived user identifiers.  Such user
1469   identifiers would allow content providers to do click-trail tracking,
1470   and would allow collaborating content providers to match cross-server
1471   click-trails or form submissions of individual users.  Note that for
1472   many users not behind a proxy, the network address of the host
1473   running the user agent will also serve as a long-lived user
1474   identifier.  In environments where proxies are used to enhance
1475   privacy, user agents ought to be conservative in offering accept
1476   header configuration options to end users.  As an extreme privacy
1477   measure, proxies could filter the accept headers in relayed requests.
1478   General purpose user agents which provide a high degree of header
1479   configurability SHOULD warn users about the loss of privacy which can
1480   be involved.
1481
14828.2.  Content-Disposition Issues
1483
1484   [RFC1806], from which the often implemented Content-Disposition (see
1485   Appendix B.1) header in HTTP is derived, has a number of very serious
1486   security considerations.  Content-Disposition is not part of the HTTP
1487   standard, but since it is widely implemented, we are documenting its
1488   use and risks for implementors.  See [RFC2183] (which updates
1489   [RFC1806]) for details.
1490
1491
14929.  Acknowledgments
1493
1494
149510.  References
1496
149710.1.  Normative References
1498
1499   [ISO-8859-1]
1500              International Organization for Standardization,
1501              "Information technology -- 8-bit single-byte coded graphic
1502              character sets -- Part 1: Latin alphabet No. 1", ISO/
1503              IEC 8859-1:1998, 1998.
1504
1505   [Part1]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1506              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1507              and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
1508
1509
1510
1511Fielding, et al.        Expires December 19, 2008              [Page 27]
1512
1513Internet-Draft              HTTP/1.1, Part 3                   June 2008
1514
1515
1516              and Message Parsing", draft-ietf-httpbis-p1-messaging-03
1517              (work in progress), June 2008.
1518
1519   [Part2]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1520              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1521              and J. Reschke, Ed., "HTTP/1.1, part 2: Message
1522              Semantics", draft-ietf-httpbis-p2-semantics-03 (work in
1523              progress), June 2008.
1524
1525   [Part4]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1526              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1527              and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional
1528              Requests", draft-ietf-httpbis-p4-conditional-03 (work in
1529              progress), June 2008.
1530
1531   [Part5]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1532              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1533              and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
1534              Partial Responses", draft-ietf-httpbis-p5-range-03 (work
1535              in progress), June 2008.
1536
1537   [Part6]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1538              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1539              and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
1540              draft-ietf-httpbis-p6-cache-03 (work in progress),
1541              June 2008.
1542
1543   [RFC1766]  Alvestrand, H., "Tags for the Identification of
1544              Languages", RFC 1766, March 1995.
1545
1546   [RFC1864]  Myers, J. and M. Rose, "The Content-MD5 Header Field",
1547              RFC 1864, October 1995.
1548
1549   [RFC1950]  Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
1550              Specification version 3.3", RFC 1950, May 1996.
1551
1552              RFC1950 is an Informational RFC, thus it may be less
1553              stable than this specification.  On the other hand, this
1554              downward reference was present since [RFC2068] (published
1555              in 1997), therefore it is unlikely to cause problems in
1556              practice.
1557
1558   [RFC1951]  Deutsch, P., "DEFLATE Compressed Data Format Specification
1559              version 1.3", RFC 1951, May 1996.
1560
1561              RFC1951 is an Informational RFC, thus it may be less
1562              stable than this specification.  On the other hand, this
1563              downward reference was present since [RFC2068] (published
1564
1565
1566
1567Fielding, et al.        Expires December 19, 2008              [Page 28]
1568
1569Internet-Draft              HTTP/1.1, Part 3                   June 2008
1570
1571
1572              in 1997), therefore it is unlikely to cause problems in
1573              practice.
1574
1575   [RFC1952]  Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
1576              Randers-Pehrson, "GZIP file format specification version
1577              4.3", RFC 1952, May 1996.
1578
1579              RFC1952 is an Informational RFC, thus it may be less
1580              stable than this specification.  On the other hand, this
1581              downward reference was present since [RFC2068] (published
1582              in 1997), therefore it is unlikely to cause problems in
1583              practice.
1584
1585   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
1586              Extensions (MIME) Part One: Format of Internet Message
1587              Bodies", RFC 2045, November 1996.
1588
1589   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
1590              Extensions (MIME) Part Two: Media Types", RFC 2046,
1591              November 1996.
1592
1593   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
1594              Requirement Levels", BCP 14, RFC 2119, March 1997.
1595
159610.2.  Informative References
1597
1598   [RFC1806]  Troost, R. and S. Dorner, "Communicating Presentation
1599              Information in Internet Messages: The Content-Disposition
1600              Header", RFC 1806, June 1995.
1601
1602   [RFC1945]  Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
1603              Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
1604
1605   [RFC2049]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
1606              Extensions (MIME) Part Five: Conformance Criteria and
1607              Examples", RFC 2049, November 1996.
1608
1609   [RFC2068]  Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
1610              Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
1611              RFC 2068, January 1997.
1612
1613   [RFC2076]  Palme, J., "Common Internet Message Headers", RFC 2076,
1614              February 1997.
1615
1616   [RFC2183]  Troost, R., Dorner, S., and K. Moore, "Communicating
1617              Presentation Information in Internet Messages: The
1618              Content-Disposition Header Field", RFC 2183, August 1997.
1619
1620
1621
1622
1623Fielding, et al.        Expires December 19, 2008              [Page 29]
1624
1625Internet-Draft              HTTP/1.1, Part 3                   June 2008
1626
1627
1628   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
1629              Languages", BCP 18, RFC 2277, January 1998.
1630
1631   [RFC2388]  Masinter, L., "Returning Values from Forms:  multipart/
1632              form-data", RFC 2388, August 1998.
1633
1634   [RFC2557]  Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
1635              "MIME Encapsulation of Aggregate Documents, such as HTML
1636              (MHTML)", RFC 2557, March 1999.
1637
1638   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
1639              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
1640              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
1641
1642   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822,
1643              April 2001.
1644
1645   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
1646              10646", RFC 3629, STD 63, November 2003.
1647
1648   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
1649              Procedures for Message Header Fields", BCP 90, RFC 3864,
1650              September 2004.
1651
1652   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
1653              Registration Procedures", BCP 13, RFC 4288, December 2005.
1654
1655
1656Appendix A.  Differences Between HTTP Entities and RFC 2045 Entities
1657
1658   HTTP/1.1 uses many of the constructs defined for Internet Mail
1659   ([RFC2822]) and the Multipurpose Internet Mail Extensions (MIME
1660   [RFC2045]) to allow entities to be transmitted in an open variety of
1661   representations and with extensible mechanisms.  However, RFC 2045
1662   discusses mail, and HTTP has a few features that are different from
1663   those described in RFC 2045.  These differences were carefully chosen
1664   to optimize performance over binary connections, to allow greater
1665   freedom in the use of new media types, to make date comparisons
1666   easier, and to acknowledge the practice of some early HTTP servers
1667   and clients.
1668
1669   This appendix describes specific areas where HTTP differs from RFC
1670   2045.  Proxies and gateways to strict MIME environments SHOULD be
1671   aware of these differences and provide the appropriate conversions
1672   where necessary.  Proxies and gateways from MIME environments to HTTP
1673   also need to be aware of the differences because some conversions
1674   might be required.
1675
1676
1677
1678
1679Fielding, et al.        Expires December 19, 2008              [Page 30]
1680
1681Internet-Draft              HTTP/1.1, Part 3                   June 2008
1682
1683
1684A.1.  MIME-Version
1685
1686   HTTP is not a MIME-compliant protocol.  However, HTTP/1.1 messages
1687   MAY include a single MIME-Version general-header field to indicate
1688   what version of the MIME protocol was used to construct the message.
1689   Use of the MIME-Version header field indicates that the message is in
1690   full compliance with the MIME protocol (as defined in [RFC2045]).
1691   Proxies/gateways are responsible for ensuring full compliance (where
1692   possible) when exporting HTTP messages to strict MIME environments.
1693
1694     MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
1695
1696   MIME version "1.0" is the default for use in HTTP/1.1.  However,
1697   HTTP/1.1 message parsing and semantics are defined by this document
1698   and not the MIME specification.
1699
1700A.2.  Conversion to Canonical Form
1701
1702   [RFC2045] requires that an Internet mail entity be converted to
1703   canonical form prior to being transferred, as described in Section 4
1704   of [RFC2049].  Section 3.3.1 of this document describes the forms
1705   allowed for subtypes of the "text" media type when transmitted over
1706   HTTP.  [RFC2046] requires that content with a type of "text"
1707   represent line breaks as CRLF and forbids the use of CR or LF outside
1708   of line break sequences.  HTTP allows CRLF, bare CR, and bare LF to
1709   indicate a line break within text content when a message is
1710   transmitted over HTTP.
1711
1712   Where it is possible, a proxy or gateway from HTTP to a strict MIME
1713   environment SHOULD translate all line breaks within the text media
1714   types described in Section 3.3.1 of this document to the RFC 2049
1715   canonical form of CRLF.  Note, however, that this might be
1716   complicated by the presence of a Content-Encoding and by the fact
1717   that HTTP allows the use of some character sets which do not use
1718   octets 13 and 10 to represent CR and LF, as is the case for some
1719   multi-byte character sets.
1720
1721   Implementors should note that conversion will break any cryptographic
1722   checksums applied to the original content unless the original content
1723   is already in canonical form.  Therefore, the canonical form is
1724   recommended for any content that uses such checksums in HTTP.
1725
1726A.3.  Introduction of Content-Encoding
1727
1728   RFC 2045 does not include any concept equivalent to HTTP/1.1's
1729   Content-Encoding header field.  Since this acts as a modifier on the
1730   media type, proxies and gateways from HTTP to MIME-compliant
1731   protocols MUST either change the value of the Content-Type header
1732
1733
1734
1735Fielding, et al.        Expires December 19, 2008              [Page 31]
1736
1737Internet-Draft              HTTP/1.1, Part 3                   June 2008
1738
1739
1740   field or decode the entity-body before forwarding the message.  (Some
1741   experimental applications of Content-Type for Internet mail have used
1742   a media-type parameter of ";conversions=<content-coding>" to perform
1743   a function equivalent to Content-Encoding.  However, this parameter
1744   is not part of RFC 2045).
1745
1746A.4.  No Content-Transfer-Encoding
1747
1748   HTTP does not use the Content-Transfer-Encoding field of RFC 2045.
1749   Proxies and gateways from MIME-compliant protocols to HTTP MUST
1750   remove any Content-Transfer-Encoding prior to delivering the response
1751   message to an HTTP client.
1752
1753   Proxies and gateways from HTTP to MIME-compliant protocols are
1754   responsible for ensuring that the message is in the correct format
1755   and encoding for safe transport on that protocol, where "safe
1756   transport" is defined by the limitations of the protocol being used.
1757   Such a proxy or gateway SHOULD label the data with an appropriate
1758   Content-Transfer-Encoding if doing so will improve the likelihood of
1759   safe transport over the destination protocol.
1760
1761A.5.  Introduction of Transfer-Encoding
1762
1763   HTTP/1.1 introduces the Transfer-Encoding header field (Section 8.7
1764   of [Part1]).  Proxies/gateways MUST remove any transfer-coding prior
1765   to forwarding a message via a MIME-compliant protocol.
1766
1767A.6.  MHTML and Line Length Limitations
1768
1769   HTTP implementations which share code with MHTML [RFC2557]
1770   implementations need to be aware of MIME line length limitations.
1771   Since HTTP does not have this limitation, HTTP does not fold long
1772   lines.  MHTML messages being transported by HTTP follow all
1773   conventions of MHTML, including line length limitations and folding,
1774   canonicalization, etc., since HTTP transports all message-bodies as
1775   payload (see Section 3.3.2) and does not interpret the content or any
1776   MIME header lines that might be contained therein.
1777
1778
1779Appendix B.  Additional Features
1780
1781   [RFC1945] and [RFC2068] document protocol elements used by some
1782   existing HTTP implementations, but not consistently and correctly
1783   across most HTTP/1.1 applications.  Implementors are advised to be
1784   aware of these features, but cannot rely upon their presence in, or
1785   interoperability with, other HTTP/1.1 applications.  Some of these
1786   describe proposed experimental features, and some describe features
1787   that experimental deployment found lacking that are now addressed in
1788
1789
1790
1791Fielding, et al.        Expires December 19, 2008              [Page 32]
1792
1793Internet-Draft              HTTP/1.1, Part 3                   June 2008
1794
1795
1796   the base HTTP/1.1 specification.
1797
1798   A number of other headers, such as Content-Disposition and Title,
1799   from SMTP and MIME are also often implemented (see [RFC2076]).
1800
1801B.1.  Content-Disposition
1802
1803   The Content-Disposition response-header field has been proposed as a
1804   means for the origin server to suggest a default filename if the user
1805   requests that the content is saved to a file.  This usage is derived
1806   from the definition of Content-Disposition in [RFC1806].
1807
1808     content-disposition = "Content-Disposition" ":"
1809                           disposition-type *( ";" disposition-parm )
1810     disposition-type = "attachment" | disp-extension-token
1811     disposition-parm = filename-parm | disp-extension-parm
1812     filename-parm = "filename" "=" quoted-string
1813     disp-extension-token = token
1814     disp-extension-parm = token "=" ( token | quoted-string )
1815
1816   An example is
1817
1818        Content-Disposition: attachment; filename="fname.ext"
1819
1820   The receiving user agent SHOULD NOT respect any directory path
1821   information present in the filename-parm parameter, which is the only
1822   parameter believed to apply to HTTP implementations at this time.
1823   The filename SHOULD be treated as a terminal component only.
1824
1825   If this header is used in a response with the application/
1826   octet-stream content-type, the implied suggestion is that the user
1827   agent should not display the response, but directly enter a `save
1828   response as...' dialog.
1829
1830   See Section 8.2 for Content-Disposition security issues.
1831
1832
1833Appendix C.  Compatibility with Previous Versions
1834
1835C.1.  Changes from RFC 2068
1836
1837   Transfer-coding and message lengths all interact in ways that
1838   required fixing exactly when chunked encoding is used (to allow for
1839   transfer encoding that may not be self delimiting); it was important
1840   to straighten out exactly how message lengths are computed.
1841   (Section 4.2.2, see also [Part1], [Part5] and [Part6]).
1842
1843   Charset wildcarding is introduced to avoid explosion of character set
1844
1845
1846
1847Fielding, et al.        Expires December 19, 2008              [Page 33]
1848
1849Internet-Draft              HTTP/1.1, Part 3                   June 2008
1850
1851
1852   names in accept headers.  (Section 6.2)
1853
1854   Content-Base was deleted from the specification: it was not
1855   implemented widely, and there is no simple, safe way to introduce it
1856   without a robust extension mechanism.  In addition, it is used in a
1857   similar, but not identical fashion in MHTML [RFC2557].
1858
1859   A content-coding of "identity" was introduced, to solve problems
1860   discovered in caching.  (Section 3.2)
1861
1862   Quality Values of zero should indicate that "I don't want something"
1863   to allow clients to refuse a representation.  (Section 3.4)
1864
1865   The Alternates, Content-Version, Derived-From, Link, URI, Public and
1866   Content-Base header fields were defined in previous versions of this
1867   specification, but not commonly implemented.  See [RFC2068].
1868
1869C.2.  Changes from RFC 2616
1870
1871   Clarify contexts that charset is used in.  (Section 3.1)
1872
1873   Remove reference to non-existant identity transfer-coding value
1874   tokens.  (Appendix A.4)
1875
1876
1877Appendix D.  Change Log (to be removed by RFC Editor before publication)
1878
1879D.1.  Since RFC2616
1880
1881   Extracted relevant partitions from [RFC2616].
1882
1883D.2.  Since draft-ietf-httpbis-p3-payload-00
1884
1885   Closed issues:
1886
1887   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
1888      Registrations" (<http://purl.org/NET/http-errata#media-reg>)
1889
1890   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/14>:
1891      "Clarification regarding quoting of charset values"
1892      (<http://purl.org/NET/http-errata#charactersets>)
1893
1894   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
1895      'identity' token references"
1896      (<http://purl.org/NET/http-errata#identity>)
1897
1898   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/25>: "Accept-
1899      Encoding BNF"
1900
1901
1902
1903Fielding, et al.        Expires December 19, 2008              [Page 34]
1904
1905Internet-Draft              HTTP/1.1, Part 3                   June 2008
1906
1907
1908   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative
1909      and Informative references"
1910
1911   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
1912      references"
1913
1914   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating
1915      to RFC4288"
1916
1917   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65>:
1918      "Informative references"
1919
1920   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66>:
1921      "ISO-8859-1 Reference"
1922
1923   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/68>: "Encoding
1924      References Normative"
1925
1926   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative
1927      up-to-date references"
1928
1929D.3.  Since draft-ietf-httpbis-p3-payload-01
1930
1931   Ongoing work on ABNF conversion
1932   (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>):
1933
1934   o  Add explicit references to BNF syntax and rules imported from
1935      other parts of the specification.
1936
1937D.4.  Since draft-ietf-httpbis-p3-payload-02
1938
1939   Closed issues:
1940
1941   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/67>: "Quoting
1942      Charsets"
1943
1944   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/105>:
1945      "Classification for Allow header"
1946
1947   o  <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/115>: "missing
1948      default for qvalue in description of Accept-Encoding"
1949
1950   Ongoing work on IANA Message Header Registration
1951   (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40>):
1952
1953   o  Reference RFC 3984, and update header registrations for headers
1954      defined in this document.
1955
1956
1957
1958
1959Fielding, et al.        Expires December 19, 2008              [Page 35]
1960
1961Internet-Draft              HTTP/1.1, Part 3                   June 2008
1962
1963
1964Index
1965
1966   A
1967      Accept header  16
1968      Accept-Charset header  18
1969      Accept-Encoding header  19
1970      Accept-Language header  20
1971      Alternates header  34
1972
1973   C
1974      compress  8
1975      Content-Base header  34
1976      Content-Disposition header  33
1977      Content-Encoding header  22
1978      Content-Language header  22
1979      Content-Location header  23
1980      Content-MD5 header  24
1981      Content-Type header  25
1982      Content-Version header  34
1983
1984   D
1985      deflate  8
1986      Derived-From header  34
1987
1988   G
1989      Grammar
1990         Accept  16
1991         Accept-Charset  18
1992         Accept-Encoding  19
1993         accept-extension  16
1994         Accept-Language  20
1995         accept-params  16
1996         attribute  9
1997         charset  7
1998         codings  19
1999         content-coding  7
2000         content-disposition  33
2001         Content-Encoding  22
2002         Content-Language  22
2003         Content-Location  23
2004         Content-MD5  24
2005         Content-Type  25
2006         disp-extension-parm  33
2007         disp-extension-token  33
2008         disposition-parm  33
2009         disposition-type  33
2010         entity-body  12
2011         entity-header  12
2012
2013
2014
2015Fielding, et al.        Expires December 19, 2008              [Page 36]
2016
2017Internet-Draft              HTTP/1.1, Part 3                   June 2008
2018
2019
2020         extension-header  12
2021         filename-parm  33
2022         language-range  20
2023         language-tag  11
2024         md5-digest  24
2025         media-range  16
2026         media-type  9
2027         MIME-Version  31
2028         parameter  9
2029         primary-tag  11
2030         qvalue  11
2031         subtag  11
2032         subtype  9
2033         type  9
2034         value  9
2035      gzip  8
2036
2037   H
2038      Headers
2039         Accept  16
2040         Accept-Charset  18
2041         Accept-Encoding  19
2042         Accept-Language  20
2043         Alternate  34
2044         Content-Base  34
2045         Content-Disposition  33
2046         Content-Encoding  22
2047         Content-Language  22
2048         Content-Location  23
2049         Content-MD5  24
2050         Content-Type  25
2051         Content-Version  34
2052         Derived-From  34
2053         Link  34
2054         Public  34
2055         URI  34
2056
2057   I
2058      identity  8
2059
2060   L
2061      Link header  34
2062
2063   P
2064      Public header  34
2065
2066   U
2067      URI header  34
2068
2069
2070
2071Fielding, et al.        Expires December 19, 2008              [Page 37]
2072
2073Internet-Draft              HTTP/1.1, Part 3                   June 2008
2074
2075
2076Authors' Addresses
2077
2078   Roy T. Fielding (editor)
2079   Day Software
2080   23 Corporate Plaza DR, Suite 280
2081   Newport Beach, CA  92660
2082   USA
2083
2084   Phone: +1-949-706-5300
2085   Fax:   +1-949-706-5305
2086   Email: fielding@gbiv.com
2087   URI:   http://roy.gbiv.com/
2088
2089
2090   Jim Gettys
2091   One Laptop per Child
2092   21 Oak Knoll Road
2093   Carlisle, MA  01741
2094   USA
2095
2096   Email: jg@laptop.org
2097   URI:   http://www.laptop.org/
2098
2099
2100   Jeffrey C. Mogul
2101   Hewlett-Packard Company
2102   HP Labs, Large Scale Systems Group
2103   1501 Page Mill Road, MS 1177
2104   Palo Alto, CA  94304
2105   USA
2106
2107   Email: JeffMogul@acm.org
2108
2109
2110   Henrik Frystyk Nielsen
2111   Microsoft Corporation
2112   1 Microsoft Way
2113   Redmond, WA  98052
2114   USA
2115
2116   Email: henrikn@microsoft.com
2117
2118
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2120
2121
2122
2123
2124
2125
2126
2127Fielding, et al.        Expires December 19, 2008              [Page 38]
2128
2129Internet-Draft              HTTP/1.1, Part 3                   June 2008
2130
2131
2132   Larry Masinter
2133   Adobe Systems, Incorporated
2134   345 Park Ave
2135   San Jose, CA  95110
2136   USA
2137
2138   Email: LMM@acm.org
2139   URI:   http://larry.masinter.net/
2140
2141
2142   Paul J. Leach
2143   Microsoft Corporation
2144   1 Microsoft Way
2145   Redmond, WA  98052
2146
2147   Email: paulle@microsoft.com
2148
2149
2150   Tim Berners-Lee
2151   World Wide Web Consortium
2152   MIT Computer Science and Artificial Intelligence Laboratory
2153   The Stata Center, Building 32
2154   32 Vassar Street
2155   Cambridge, MA  02139
2156   USA
2157
2158   Email: timbl@w3.org
2159   URI:   http://www.w3.org/People/Berners-Lee/
2160
2161
2162   Yves Lafon (editor)
2163   World Wide Web Consortium
2164   W3C / ERCIM
2165   2004, rte des Lucioles
2166   Sophia-Antipolis, AM  06902
2167   France
2168
2169   Email: ylafon@w3.org
2170   URI:   http://www.raubacapeu.net/people/yves/
2171
2172
2173
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2175
2176
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2178
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2180
2181
2182
2183Fielding, et al.        Expires December 19, 2008              [Page 39]
2184
2185Internet-Draft              HTTP/1.1, Part 3                   June 2008
2186
2187
2188   Julian F. Reschke (editor)
2189   greenbytes GmbH
2190   Hafenweg 16
2191   Muenster, NW  48155
2192   Germany
2193
2194   Phone: +49 251 2807760
2195   Fax:   +49 251 2807761
2196   Email: julian.reschke@greenbytes.de
2197   URI:   http://greenbytes.de/tech/webdav/
2198
2199
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2238
2239Fielding, et al.        Expires December 19, 2008              [Page 40]
2240
2241Internet-Draft              HTTP/1.1, Part 3                   June 2008
2242
2243
2244Full Copyright Statement
2245
2246   Copyright (C) The IETF Trust (2008).
2247
2248   This document is subject to the rights, licenses and restrictions
2249   contained in BCP 78, and except as set forth therein, the authors
2250   retain all their rights.
2251
2252   This document and the information contained herein are provided on an
2253   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
2254   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
2255   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
2256   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
2257   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
2258   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
2259
2260
2261Intellectual Property
2262
2263   The IETF takes no position regarding the validity or scope of any
2264   Intellectual Property Rights or other rights that might be claimed to
2265   pertain to the implementation or use of the technology described in
2266   this document or the extent to which any license under such rights
2267   might or might not be available; nor does it represent that it has
2268   made any independent effort to identify any such rights.  Information
2269   on the procedures with respect to rights in RFC documents can be
2270   found in BCP 78 and BCP 79.
2271
2272   Copies of IPR disclosures made to the IETF Secretariat and any
2273   assurances of licenses to be made available, or the result of an
2274   attempt made to obtain a general license or permission for the use of
2275   such proprietary rights by implementers or users of this
2276   specification can be obtained from the IETF on-line IPR repository at
2277   http://www.ietf.org/ipr.
2278
2279   The IETF invites any interested party to bring to its attention any
2280   copyrights, patents or patent applications, or other proprietary
2281   rights that may cover technology that may be required to implement
2282   this standard.  Please address the information to the IETF at
2283   ietf-ipr@ietf.org.
2284
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2295Fielding, et al.        Expires December 19, 2008              [Page 41]
2296
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