source: draft-ietf-httpbis/latest/p3-payload.xml @ 660

Last change on this file since 660 was 660, checked in by fielding@…, 10 years ago

editorial: move remaining terminology to part 3 for later edit.
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35]>
36<?rfc toc="yes" ?>
37<?rfc symrefs="yes" ?>
38<?rfc sortrefs="yes" ?>
39<?rfc compact="yes"?>
40<?rfc subcompact="no" ?>
41<?rfc linkmailto="no" ?>
42<?rfc editing="no" ?>
43<?rfc comments="yes"?>
44<?rfc inline="yes"?>
45<?rfc-ext allow-markup-in-artwork="yes" ?>
46<?rfc-ext include-references-in-index="yes" ?>
47<rfc obsoletes="2616" category="std" x:maturity-level="draft"
48     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
49     xmlns:x='http://purl.org/net/xml2rfc/ext'>
50<front>
51
52  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
53
54  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
55    <organization abbrev="Day Software">Day Software</organization>
56    <address>
57      <postal>
58        <street>23 Corporate Plaza DR, Suite 280</street>
59        <city>Newport Beach</city>
60        <region>CA</region>
61        <code>92660</code>
62        <country>USA</country>
63      </postal>
64      <phone>+1-949-706-5300</phone>
65      <facsimile>+1-949-706-5305</facsimile>
66      <email>fielding@gbiv.com</email>
67      <uri>http://roy.gbiv.com/</uri>
68    </address>
69  </author>
70
71  <author initials="J." surname="Gettys" fullname="Jim Gettys">
72    <organization>One Laptop per Child</organization>
73    <address>
74      <postal>
75        <street>21 Oak Knoll Road</street>
76        <city>Carlisle</city>
77        <region>MA</region>
78        <code>01741</code>
79        <country>USA</country>
80      </postal>
81      <email>jg@laptop.org</email>
82      <uri>http://www.laptop.org/</uri>
83    </address>
84  </author>
85 
86  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
87    <organization abbrev="HP">Hewlett-Packard Company</organization>
88    <address>
89      <postal>
90        <street>HP Labs, Large Scale Systems Group</street>
91        <street>1501 Page Mill Road, MS 1177</street>
92        <city>Palo Alto</city>
93        <region>CA</region>
94        <code>94304</code>
95        <country>USA</country>
96      </postal>
97      <email>JeffMogul@acm.org</email>
98    </address>
99  </author>
100
101  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
102    <organization abbrev="Microsoft">Microsoft Corporation</organization>
103    <address>
104      <postal>
105        <street>1 Microsoft Way</street>
106        <city>Redmond</city>
107        <region>WA</region>
108        <code>98052</code>
109        <country>USA</country>
110      </postal>
111      <email>henrikn@microsoft.com</email>
112    </address>
113  </author>
114
115  <author initials="L." surname="Masinter" fullname="Larry Masinter">
116    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
117    <address>
118      <postal>
119        <street>345 Park Ave</street>
120        <city>San Jose</city>
121        <region>CA</region>
122        <code>95110</code>
123        <country>USA</country>
124      </postal>
125      <email>LMM@acm.org</email>
126      <uri>http://larry.masinter.net/</uri>
127    </address>
128  </author>
129 
130  <author initials="P." surname="Leach" fullname="Paul J. Leach">
131    <organization abbrev="Microsoft">Microsoft Corporation</organization>
132    <address>
133      <postal>
134        <street>1 Microsoft Way</street>
135        <city>Redmond</city>
136        <region>WA</region>
137        <code>98052</code>
138      </postal>
139      <email>paulle@microsoft.com</email>
140    </address>
141  </author>
142   
143  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
145    <address>
146      <postal>
147        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
148        <street>The Stata Center, Building 32</street>
149        <street>32 Vassar Street</street>
150        <city>Cambridge</city>
151        <region>MA</region>
152        <code>02139</code>
153        <country>USA</country>
154      </postal>
155      <email>timbl@w3.org</email>
156      <uri>http://www.w3.org/People/Berners-Lee/</uri>
157    </address>
158  </author>
159
160  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
161    <organization abbrev="W3C">World Wide Web Consortium</organization>
162    <address>
163      <postal>
164        <street>W3C / ERCIM</street>
165        <street>2004, rte des Lucioles</street>
166        <city>Sophia-Antipolis</city>
167        <region>AM</region>
168        <code>06902</code>
169        <country>France</country>
170      </postal>
171      <email>ylafon@w3.org</email>
172      <uri>http://www.raubacapeu.net/people/yves/</uri>
173    </address>
174  </author>
175
176  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
177    <organization abbrev="greenbytes">greenbytes GmbH</organization>
178    <address>
179      <postal>
180        <street>Hafenweg 16</street>
181        <city>Muenster</city><region>NW</region><code>48155</code>
182        <country>Germany</country>
183      </postal>
184      <phone>+49 251 2807760</phone>
185      <facsimile>+49 251 2807761</facsimile>
186      <email>julian.reschke@greenbytes.de</email>
187      <uri>http://greenbytes.de/tech/webdav/</uri>
188    </address>
189  </author>
190
191  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
192  <workgroup>HTTPbis Working Group</workgroup>
193
194<abstract>
195<t>
196   The Hypertext Transfer Protocol (HTTP) is an application-level
197   protocol for distributed, collaborative, hypermedia information
198   systems. HTTP has been in use by the World Wide Web global information
199   initiative since 1990. This document is Part 3 of the seven-part specification
200   that defines the protocol referred to as "HTTP/1.1" and, taken together,
201   obsoletes RFC 2616.  Part 3 defines HTTP message content,
202   metadata, and content negotiation.
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org). The current issues list is
210    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
211    and related documents (including fancy diffs) can be found at
212    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
213  </t>
214  <t>
215    The changes in this draft are summarized in <xref target="changes.since.07"/>.
216  </t>
217</note>
218</front>
219<middle>
220<section title="Introduction" anchor="introduction">
221<t>
222   This document defines HTTP/1.1 message payloads (a.k.a., content), the
223   associated metadata header fields that define how the payload is intended
224   to be interpreted by a recipient, the request header fields that
225   may influence content selection, and the various selection algorithms
226   that are collectively referred to as HTTP content negotiation.
227</t>
228<t>
229   This document is currently disorganized in order to minimize the changes
230   between drafts and enable reviewers to see the smaller errata changes.
231   The next draft will reorganize the sections to better reflect the content.
232   In particular, the sections on entities will be renamed payload and moved
233   to the first half of the document, while the sections on content negotiation
234   and associated request header fields will be moved to the second half.  The
235   current mess reflects how widely dispersed these topics and associated
236   requirements had become in <xref target="RFC2616"/>.
237</t>
238
239<section title="Terminology" anchor="terminology">
240<t>
241   This specification uses a number of terms to refer to the roles
242   played by participants in, and objects of, the HTTP communication.
243</t>
244<t>
245  <iref item="content negotiation"/>
246  <x:dfn>content negotiation</x:dfn>
247  <list>
248    <t>
249      The mechanism for selecting the appropriate representation when
250      servicing a request. The representation of entities in any response
251      can be negotiated (including error responses).
252    </t>
253  </list>
254</t>
255<t>
256  <iref item="entity"/>
257  <x:dfn>entity</x:dfn>
258  <list>
259    <t>
260      The information transferred as the payload of a request or
261      response. An entity consists of metadata in the form of
262      entity-header fields and content in the form of an entity-body.
263    </t>
264  </list>
265</t>
266<t>
267  <iref item="representation"/>
268  <x:dfn>representation</x:dfn>
269  <list>
270    <t>
271      An entity included with a response that is subject to content
272      negotiation. There may exist multiple
273      representations associated with a particular response status.
274    </t>
275  </list>
276</t>
277<t>
278  <iref item="variant"/>
279  <x:dfn>variant</x:dfn>
280  <list>
281    <t>
282      A resource may have one, or more than one, representation(s)
283      associated with it at any given instant. Each of these
284      representations is termed a `variant'.  Use of the term `variant'
285      does not necessarily imply that the resource is subject to content
286      negotiation.
287    </t>
288  </list>
289</t>
290</section>
291
292<section title="Requirements" anchor="intro.requirements">
293<t>
294   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
295   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
296   document are to be interpreted as described in <xref target="RFC2119"/>.
297</t>
298<t>
299   An implementation is not compliant if it fails to satisfy one or more
300   of the &MUST; or &REQUIRED; level requirements for the protocols it
301   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
302   level and all the &SHOULD; level requirements for its protocols is said
303   to be "unconditionally compliant"; one that satisfies all the &MUST;
304   level requirements but not all the &SHOULD; level requirements for its
305   protocols is said to be "conditionally compliant."
306</t>
307</section>
308
309<section title="Syntax Notation" anchor="notation">
310  <x:anchor-alias value="ALPHA"/>
311  <x:anchor-alias value="CR"/>
312  <x:anchor-alias value="DIGIT"/>
313  <x:anchor-alias value="LF"/>
314  <x:anchor-alias value="OCTET"/>
315  <x:anchor-alias value="VCHAR"/>
316  <x:anchor-alias value="WSP"/>
317<t>
318  This specification uses the ABNF syntax defined in &notation; (which
319  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
320  <xref target="collected.abnf"/> shows the collected ABNF, with the list
321  rule expanded.
322</t>
323<t>
324  The following core rules are included by
325  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
326  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
327  DIGIT (decimal 0-9), DQUOTE (double quote),
328  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
329  OCTET (any 8-bit sequence of data), SP (space),
330  VCHAR (any visible USASCII character),
331  and WSP (whitespace).
332</t>
333
334<section title="Core Rules" anchor="core.rules">
335  <x:anchor-alias value="quoted-string"/>
336  <x:anchor-alias value="token"/>
337  <x:anchor-alias value="OWS"/>
338<t>
339  The core rules below are defined in &basic-rules;:
340</t>
341<figure><artwork type="abnf2616">
342  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
343  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
344  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
345</artwork></figure>
346</section>
347
348<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
349  <x:anchor-alias value="absolute-URI"/>
350  <x:anchor-alias value="Allow"/>
351  <x:anchor-alias value="Content-Length"/>
352  <x:anchor-alias value="Content-Range"/>
353  <x:anchor-alias value="Expires"/>
354  <x:anchor-alias value="Last-Modified"/>
355  <x:anchor-alias value="header-field"/>
356  <x:anchor-alias value="partial-URI"/>
357  <x:anchor-alias value="qvalue"/>
358<t>
359  The ABNF rules below are defined in other parts:
360</t>
361<figure><!--Part1--><artwork type="abnf2616">
362  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
363  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
364  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
365  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
366  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
367</artwork></figure>
368<figure><!--Part4--><artwork type="abnf2616">
369  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
370</artwork></figure>
371<figure><!--Part5--><artwork type="abnf2616">
372  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
373</artwork></figure>
374<figure><!--Part6--><artwork type="abnf2616">
375  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
376</artwork></figure>
377</section>
378
379</section>
380
381</section>
382
383<section title="Protocol Parameters" anchor="protocol.parameters">
384
385<section title="Character Sets" anchor="character.sets">
386<t>
387   HTTP uses the same definition of the term "character set" as that
388   described for MIME:
389</t>
390<t>
391   The term "character set" is used in this document to refer to a
392   method used with one or more tables to convert a sequence of octets
393   into a sequence of characters. Note that unconditional conversion in
394   the other direction is not required, in that not all characters may
395   be available in a given character set and a character set may provide
396   more than one sequence of octets to represent a particular character.
397   This definition is intended to allow various kinds of character
398   encoding, from simple single-table mappings such as US-ASCII to
399   complex table switching methods such as those that use ISO-2022's
400   techniques. However, the definition associated with a MIME character
401   set name &MUST; fully specify the mapping to be performed from octets
402   to characters. In particular, use of external profiling information
403   to determine the exact mapping is not permitted.
404</t>
405<x:note>
406  <t>
407    <x:h>Note:</x:h> This use of the term "character set" is more commonly
408    referred to as a "character encoding." However, since HTTP and
409    MIME share the same registry, it is important that the terminology
410    also be shared.
411  </t>
412</x:note>
413<t anchor="rule.charset">
414  <x:anchor-alias value="charset"/>
415   HTTP character sets are identified by case-insensitive tokens. The
416   complete set of tokens is defined by the IANA Character Set registry
417   (<eref target="http://www.iana.org/assignments/character-sets"/>).
418</t>
419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
420  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
421</artwork></figure>
422<t>
423   Although HTTP allows an arbitrary token to be used as a charset
424   value, any token that has a predefined value within the IANA
425   Character Set registry &MUST; represent the character set defined
426   by that registry. Applications &SHOULD; limit their use of character
427   sets to those defined by the IANA registry.
428</t>
429<t>
430   HTTP uses charset in two contexts: within an Accept-Charset request
431   header (in which the charset value is an unquoted token) and as the
432   value of a parameter in a Content-Type header (within a request or
433   response), in which case the parameter value of the charset parameter
434   may be quoted.
435</t>
436<t>
437   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
438   <xref target="RFC2277"/>.
439</t>
440
441<section title="Missing Charset" anchor="missing.charset">
442<t>
443   Some HTTP/1.0 software has interpreted a Content-Type header without
444   charset parameter incorrectly to mean "recipient should guess."
445   Senders wishing to defeat this behavior &MAY; include a charset
446   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
447   it is known that it will not confuse the recipient.
448</t>
449<t>
450   Unfortunately, some older HTTP/1.0 clients did not deal properly with
451   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
452   charset label provided by the sender; and those user agents that have
453   a provision to "guess" a charset &MUST; use the charset from the
454   content-type field if they support that charset, rather than the
455   recipient's preference, when initially displaying a document. See
456   <xref target="canonicalization.and.text.defaults"/>.
457</t>
458</section>
459</section>
460
461<section title="Content Codings" anchor="content.codings">
462  <x:anchor-alias value="content-coding"/>
463<t>
464   Content coding values indicate an encoding transformation that has
465   been or can be applied to an entity. Content codings are primarily
466   used to allow a document to be compressed or otherwise usefully
467   transformed without losing the identity of its underlying media type
468   and without loss of information. Frequently, the entity is stored in
469   coded form, transmitted directly, and only decoded by the recipient.
470</t>
471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
472  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
473</artwork></figure>
474<t>
475   All content-coding values are case-insensitive. HTTP/1.1 uses
476   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
477   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
478   describes the content-coding, what is more important is that it
479   indicates what decoding mechanism will be required to remove the
480   encoding.
481</t>
482<t>
483   The Internet Assigned Numbers Authority (IANA) acts as a registry for
484   content-coding value tokens. Initially, the registry contains the
485   following tokens:
486</t>
487<t>
488   gzip<iref item="gzip"/>
489  <list>
490    <t>
491        An encoding format produced by the file compression program
492        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
493        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
494    </t>
495  </list>
496</t>
497<t>
498   compress<iref item="compress"/>
499  <list><t>
500        The encoding format produced by the common UNIX file compression
501        program "compress". This format is an adaptive Lempel-Ziv-Welch
502        coding (LZW).
503</t><t>
504        Use of program names for the identification of encoding formats
505        is not desirable and is discouraged for future encodings. Their
506        use here is representative of historical practice, not good
507        design. For compatibility with previous implementations of HTTP,
508        applications &SHOULD; consider "x-gzip" and "x-compress" to be
509        equivalent to "gzip" and "compress" respectively.
510  </t></list>
511</t>
512<t>
513   deflate<iref item="deflate"/>
514  <list><t>
515        The "zlib" format defined in <xref target="RFC1950"/> in combination with
516        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
517  </t></list>
518</t>
519<t>
520   identity<iref item="identity"/>
521  <list><t>
522        The default (identity) encoding; the use of no transformation
523        whatsoever. This content-coding is used only in the Accept-Encoding
524        header, and &SHOULD-NOT;  be used in the Content-Encoding
525        header.
526  </t></list>
527</t>
528<t>
529   New content-coding value tokens &SHOULD; be registered; to allow
530   interoperability between clients and servers, specifications of the
531   content coding algorithms needed to implement a new value &SHOULD; be
532   publicly available and adequate for independent implementation, and
533   conform to the purpose of content coding defined in this section.
534</t>
535</section>
536
537<section title="Media Types" anchor="media.types">
538  <x:anchor-alias value="media-type"/>
539  <x:anchor-alias value="type"/>
540  <x:anchor-alias value="subtype"/>
541<t>
542   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
543   and Accept (<xref target="header.accept"/>) header fields in order to provide
544   open and extensible data typing and type negotiation.
545</t>
546<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
547  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
548  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
549  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
550</artwork></figure>
551<t anchor="rule.parameter">
552  <x:anchor-alias value="attribute"/>
553  <x:anchor-alias value="parameter"/>
554  <x:anchor-alias value="value"/>
555   Parameters &MAY; follow the type/subtype in the form of attribute/value
556   pairs.
557</t>
558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
559  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
560  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
561  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
562</artwork></figure>
563<t>
564   The type, subtype, and parameter attribute names are case-insensitive.
565   Parameter values might or might not be case-sensitive, depending on the
566   semantics of the parameter name.  The presence or absence of a parameter might
567   be significant to the processing of a media-type, depending on its
568   definition within the media type registry.
569</t>
570<t>
571   A parameter value that matches the <x:ref>token</x:ref> production may be
572   transmitted as either a token or within a quoted-string. The quoted and
573   unquoted values are equivalent.
574</t>
575<t>
576   Note that some older HTTP applications do not recognize media type
577   parameters. When sending data to older HTTP applications,
578   implementations &SHOULD; only use media type parameters when they are
579   required by that type/subtype definition.
580</t>
581<t>
582   Media-type values are registered with the Internet Assigned Number
583   Authority (IANA). The media type registration process is
584   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
585   discouraged.
586</t>
587
588<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
589<t>
590   Internet media types are registered with a canonical form. An
591   entity-body transferred via HTTP messages &MUST; be represented in the
592   appropriate canonical form prior to its transmission except for
593   "text" types, as defined in the next paragraph.
594</t>
595<t>
596   When in canonical form, media subtypes of the "text" type use CRLF as
597   the text line break. HTTP relaxes this requirement and allows the
598   transport of text media with plain CR or LF alone representing a line
599   break when it is done consistently for an entire entity-body. HTTP
600   applications &MUST; accept CRLF, bare CR, and bare LF as being
601   representative of a line break in text media received via HTTP. In
602   addition, if the text is represented in a character set that does not
603   use octets 13 and 10 for CR and LF respectively, as is the case for
604   some multi-byte character sets, HTTP allows the use of whatever octet
605   sequences are defined by that character set to represent the
606   equivalent of CR and LF for line breaks. This flexibility regarding
607   line breaks applies only to text media in the entity-body; a bare CR
608   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
609   structures (such as header fields and multipart boundaries).
610</t>
611<t>
612   If an entity-body is encoded with a content-coding, the underlying
613   data &MUST; be in a form defined above prior to being encoded.
614</t>
615<t>
616   The "charset" parameter is used with some media types to define the
617   character set (<xref target="character.sets"/>) of the data. When no explicit charset
618   parameter is provided by the sender, media subtypes of the "text"
619   type are defined to have a default charset value of "ISO-8859-1" when
620   received via HTTP. Data in character sets other than "ISO-8859-1" or
621   its subsets &MUST; be labeled with an appropriate charset value. See
622   <xref target="missing.charset"/> for compatibility problems.
623</t>
624</section>
625
626<section title="Multipart Types" anchor="multipart.types">
627<t>
628   MIME provides for a number of "multipart" types -- encapsulations of
629   one or more entities within a single message-body. All multipart
630   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
631   and &MUST; include a boundary parameter as part of the media type
632   value. The message body is itself a protocol element and &MUST;
633   therefore use only CRLF to represent line breaks between body-parts.
634   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
635   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
636   original multipart contains an epilogue). These restrictions exist in
637   order to preserve the self-delimiting nature of a multipart message-body,
638   wherein the "end" of the message-body is indicated by the
639   ending multipart boundary.
640</t>
641<t>
642   In general, HTTP treats a multipart message-body no differently than
643   any other media type: strictly as payload. The one exception is the
644   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
645   (Partial Content) response.
646   <!-- jre: re-insert removed text pointing to caching? -->
647   In all
648   other cases, an HTTP user agent &SHOULD; follow the same or similar
649   behavior as a MIME user agent would upon receipt of a multipart type.
650   The MIME header fields within each body-part of a multipart message-body
651   do not have any significance to HTTP beyond that defined by
652   their MIME semantics.
653</t>
654<t>
655   In general, an HTTP user agent &SHOULD; follow the same or similar
656   behavior as a MIME user agent would upon receipt of a multipart type.
657   If an application receives an unrecognized multipart subtype, the
658   application &MUST; treat it as being equivalent to "multipart/mixed".
659</t>
660<x:note>
661  <t>
662    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
663    for carrying form data suitable for processing via the POST
664    request method, as described in <xref target="RFC2388"/>.
665  </t>
666</x:note>
667</section>
668</section>
669
670<section title="Language Tags" anchor="language.tags">
671  <x:anchor-alias value="language-tag"/>
672<t>
673   A language tag, as defined in <xref target="RFC4646bis"/>, identifies a
674   natural language spoken, written, or otherwise conveyed by human beings for
675   communication of information to other human beings. Computer languages are
676   explicitly excluded. HTTP uses language tags within the Accept-Language and
677   Content-Language fields.
678</t>
679<t>
680   In summary, a language tag is composed of one or more parts: A primary
681   language subtag followed by a possibly empty series of subtags:
682</t>
683<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
684  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC4646bis" x:sec="2.1"/>&gt;
685</artwork></figure>
686<t>
687   White space is not allowed within the tag and all tags are case-insensitive.
688   The name space of language subtags is administered by the IANA (see
689   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
690</t>
691<figure>
692  <preamble>Example tags include:</preamble>
693<artwork type="example">
694  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
695</artwork>
696</figure>
697<t>
698   See <xref target="RFC4646bis"/> for further information.
699</t>
700</section>
701</section>
702
703<section title="Entity" anchor="entity">
704<t>
705   Request and Response messages &MAY; transfer an entity if not otherwise
706   restricted by the request method or response status code. An entity
707   consists of entity-header fields and an entity-body, although some
708   responses will only include the entity-headers.
709</t>
710<t>
711   In this section, both sender and recipient refer to either the client
712   or the server, depending on who sends and who receives the entity.
713</t>
714
715<section title="Entity Header Fields" anchor="entity.header.fields">
716  <x:anchor-alias value="entity-header"/>
717  <x:anchor-alias value="extension-header"/>
718<t>
719   Entity-header fields define metainformation about the entity-body or,
720   if no body is present, about the resource identified by the request.
721</t>
722<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
723  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
724                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
725                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
726                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
727                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
728                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
729                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
730                 / <x:ref>Expires</x:ref>                  ; &header-expires;
731                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
732                 / <x:ref>extension-header</x:ref>
733 
734  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
735</artwork></figure>
736<t>
737   The extension-header mechanism allows additional entity-header fields
738   to be defined without changing the protocol, but these fields cannot
739   be assumed to be recognizable by the recipient. Unrecognized header
740   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
741   transparent proxies.
742</t>
743</section>
744
745<section title="Entity Body" anchor="entity.body">
746  <x:anchor-alias value="entity-body"/>
747<t>
748   The entity-body (if any) sent with an HTTP request or response is in
749   a format and encoding defined by the entity-header fields.
750</t>
751<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
752  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
753</artwork></figure>
754<t>
755   An entity-body is only present in a message when a message-body is
756   present, as described in &message-body;. The entity-body is obtained
757   from the message-body by decoding any Transfer-Encoding that might
758   have been applied to ensure safe and proper transfer of the message.
759</t>
760
761<section title="Type" anchor="type">
762<t>
763   When an entity-body is included with a message, the data type of that
764   body is determined via the header fields Content-Type and Content-Encoding.
765   These define a two-layer, ordered encoding model:
766</t>
767<figure><artwork type="example">
768  entity-body := Content-Encoding( Content-Type( data ) )
769</artwork></figure>
770<t>
771   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
772   message containing an entity-body &SHOULD; include a Content-Type header
773   field defining the media type of that body, unless that information is
774   unknown.  If the Content-Type header field is not present, it indicates that
775   the sender does not know the media type of the data; recipients &MAY;
776   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
777   or examine the content to determine its type.
778</t>
779<t>
780   Content-Encoding may be used to indicate any additional content
781   codings applied to the data, usually for the purpose of data
782   compression, that are a property of the requested resource.  There is
783   no default encoding.
784</t>
785<t>
786   Note that neither the interpretation of the data type of a message nor
787   the behaviors caused by it are defined by HTTP; this
788   potentially includes examination of the content to override any
789   indicated type ("sniffing")<iref item="Content Type Sniffing"/>.
790</t>
791</section>
792   
793<section title="Entity Length" anchor="entity.length">
794<t>
795   The entity-length of a message is the length of the message-body
796   before any transfer-codings have been applied. &message-length; defines
797   how the transfer-length of a message-body is determined.
798</t>
799</section>
800</section>
801</section>
802
803<section title="Content Negotiation" anchor="content.negotiation">
804<t>
805   Most HTTP responses include an entity which contains information for
806   interpretation by a human user. Naturally, it is desirable to supply
807   the user with the "best available" entity corresponding to the
808   request. Unfortunately for servers and caches, not all users have the
809   same preferences for what is "best," and not all user agents are
810   equally capable of rendering all entity types. For that reason, HTTP
811   has provisions for several mechanisms for "content negotiation" --
812   the process of selecting the best representation for a given response
813   when there are multiple representations available.
814</t>
815<x:note>
816  <t>
817    <x:h>Note:</x:h> This is not called "format negotiation" because the
818    alternate representations may be of the same media type, but use
819    different capabilities of that type, be in different languages,
820    etc.
821  </t>
822</x:note>
823<t>
824   Any response containing an entity-body &MAY; be subject to negotiation,
825   including error responses.
826</t>
827<t>
828   There are two kinds of content negotiation which are possible in
829   HTTP: server-driven and agent-driven negotiation. These two kinds of
830   negotiation are orthogonal and thus may be used separately or in
831   combination. One method of combination, referred to as transparent
832   negotiation, occurs when a cache uses the agent-driven negotiation
833   information provided by the origin server in order to provide
834   server-driven negotiation for subsequent requests.
835</t>
836
837<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
838<t>
839   If the selection of the best representation for a response is made by
840   an algorithm located at the server, it is called server-driven
841   negotiation. Selection is based on the available representations of
842   the response (the dimensions over which it can vary; e.g. language,
843   content-coding, etc.) and the contents of particular header fields in
844   the request message or on other information pertaining to the request
845   (such as the network address of the client).
846</t>
847<t>
848   Server-driven negotiation is advantageous when the algorithm for
849   selecting from among the available representations is difficult to
850   describe to the user agent, or when the server desires to send its
851   "best guess" to the client along with the first response (hoping to
852   avoid the round-trip delay of a subsequent request if the "best
853   guess" is good enough for the user). In order to improve the server's
854   guess, the user agent &MAY; include request header fields (Accept,
855   Accept-Language, Accept-Encoding, etc.) which describe its
856   preferences for such a response.
857</t>
858<t>
859   Server-driven negotiation has disadvantages:
860  <list style="numbers">
861    <t>
862         It is impossible for the server to accurately determine what
863         might be "best" for any given user, since that would require
864         complete knowledge of both the capabilities of the user agent
865         and the intended use for the response (e.g., does the user want
866         to view it on screen or print it on paper?).
867    </t>
868    <t>
869         Having the user agent describe its capabilities in every
870         request can be both very inefficient (given that only a small
871         percentage of responses have multiple representations) and a
872         potential violation of the user's privacy.
873    </t>
874    <t>
875         It complicates the implementation of an origin server and the
876         algorithms for generating responses to a request.
877    </t>
878    <t>
879         It may limit a public cache's ability to use the same response
880         for multiple user's requests.
881    </t>
882  </list>
883</t>
884<t>
885   HTTP/1.1 includes the following request-header fields for enabling
886   server-driven negotiation through description of user agent
887   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
888   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
889   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
890   origin server is not limited to these dimensions and &MAY; vary the
891   response based on any aspect of the request, including information
892   outside the request-header fields or within extension header fields
893   not defined by this specification.
894</t>
895<t>
896   The Vary header field (&header-vary;) can be used to express the parameters the
897   server uses to select a representation that is subject to server-driven
898   negotiation.
899</t>
900</section>
901
902<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
903<t>
904   With agent-driven negotiation, selection of the best representation
905   for a response is performed by the user agent after receiving an
906   initial response from the origin server. Selection is based on a list
907   of the available representations of the response included within the
908   header fields or entity-body of the initial response, with each
909   representation identified by its own URI. Selection from among the
910   representations may be performed automatically (if the user agent is
911   capable of doing so) or manually by the user selecting from a
912   generated (possibly hypertext) menu.
913</t>
914<t>
915   Agent-driven negotiation is advantageous when the response would vary
916   over commonly-used dimensions (such as type, language, or encoding),
917   when the origin server is unable to determine a user agent's
918   capabilities from examining the request, and generally when public
919   caches are used to distribute server load and reduce network usage.
920</t>
921<t>
922   Agent-driven negotiation suffers from the disadvantage of needing a
923   second request to obtain the best alternate representation. This
924   second request is only efficient when caching is used. In addition,
925   this specification does not define any mechanism for supporting
926   automatic selection, though it also does not prevent any such
927   mechanism from being developed as an extension and used within
928   HTTP/1.1.
929</t>
930<t>
931   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
932   status codes for enabling agent-driven negotiation when the server is
933   unwilling or unable to provide a varying response using server-driven
934   negotiation.
935</t>
936</section>
937
938<section title="Transparent Negotiation" anchor="transparent.negotiation">
939<t>
940   Transparent negotiation is a combination of both server-driven and
941   agent-driven negotiation. When a cache is supplied with a form of the
942   list of available representations of the response (as in agent-driven
943   negotiation) and the dimensions of variance are completely understood
944   by the cache, then the cache becomes capable of performing server-driven
945   negotiation on behalf of the origin server for subsequent
946   requests on that resource.
947</t>
948<t>
949   Transparent negotiation has the advantage of distributing the
950   negotiation work that would otherwise be required of the origin
951   server and also removing the second request delay of agent-driven
952   negotiation when the cache is able to correctly guess the right
953   response.
954</t>
955<t>
956   This specification does not define any mechanism for transparent
957   negotiation, though it also does not prevent any such mechanism from
958   being developed as an extension that could be used within HTTP/1.1.
959</t>
960</section>
961</section>
962
963<section title="Header Field Definitions" anchor="header.fields">
964<t>
965   This section defines the syntax and semantics of HTTP/1.1 header fields
966   related to the payload of messages.
967</t>
968<t>
969   For entity-header fields, both sender and recipient refer to either the
970   client or the server, depending on who sends and who receives the entity.
971</t>
972
973<section title="Accept" anchor="header.accept">
974  <iref primary="true" item="Accept header" x:for-anchor=""/>
975  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
976  <x:anchor-alias value="Accept"/>
977  <x:anchor-alias value="Accept-v"/>
978  <x:anchor-alias value="accept-ext"/>
979  <x:anchor-alias value="accept-params"/>
980  <x:anchor-alias value="media-range"/>
981<t>
982   The request-header field "Accept" can be used to specify certain media
983   types which are acceptable for the response. Accept headers can be
984   used to indicate that the request is specifically limited to a small
985   set of desired types, as in the case of a request for an in-line
986   image.
987</t>
988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
989  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
990  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
991 
992  <x:ref>media-range</x:ref>    = ( "*/*"
993                   / ( <x:ref>type</x:ref> "/" "*" )
994                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
995                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
996  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
997  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
998                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
999</artwork></figure>
1000<t>
1001   The asterisk "*" character is used to group media types into ranges,
1002   with "*/*" indicating all media types and "type/*" indicating all
1003   subtypes of that type. The media-range &MAY; include media type
1004   parameters that are applicable to that range.
1005</t>
1006<t>
1007   Each media-range &MAY; be followed by one or more accept-params,
1008   beginning with the "q" parameter for indicating a relative quality
1009   factor. The first "q" parameter (if any) separates the media-range
1010   parameter(s) from the accept-params. Quality factors allow the user
1011   or user agent to indicate the relative degree of preference for that
1012   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1013   default value is q=1.
1014</t>
1015<x:note>
1016  <t>
1017    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1018    parameters from Accept extension parameters is due to historical
1019    practice. Although this prevents any media type parameter named
1020    "q" from being used with a media range, such an event is believed
1021    to be unlikely given the lack of any "q" parameters in the IANA
1022    media type registry and the rare usage of any media type
1023    parameters in Accept. Future media types are discouraged from
1024    registering any parameter named "q".
1025  </t>
1026</x:note>
1027<t>
1028   The example
1029</t>
1030<figure><artwork type="example">
1031  Accept: audio/*; q=0.2, audio/basic
1032</artwork></figure>
1033<t>
1034   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1035   type if it is the best available after an 80% mark-down in quality."
1036</t>
1037<t>
1038   If no Accept header field is present, then it is assumed that the
1039   client accepts all media types. If an Accept header field is present,
1040   and if the server cannot send a response which is acceptable
1041   according to the combined Accept field value, then the server &SHOULD;
1042   send a 406 (Not Acceptable) response.
1043</t>
1044<t>
1045   A more elaborate example is
1046</t>
1047<figure><artwork type="example">
1048  Accept: text/plain; q=0.5, text/html,
1049          text/x-dvi; q=0.8, text/x-c
1050</artwork></figure>
1051<t>
1052   Verbally, this would be interpreted as "text/html and text/x-c are
1053   the preferred media types, but if they do not exist, then send the
1054   text/x-dvi entity, and if that does not exist, send the text/plain
1055   entity."
1056</t>
1057<t>
1058   Media ranges can be overridden by more specific media ranges or
1059   specific media types. If more than one media range applies to a given
1060   type, the most specific reference has precedence. For example,
1061</t>
1062<figure><artwork type="example">
1063  Accept: text/*, text/html, text/html;level=1, */*
1064</artwork></figure>
1065<t>
1066   have the following precedence:
1067   <list style="numbers">
1068    <t>text/html;level=1</t>
1069    <t>text/html</t>
1070    <t>text/*</t>
1071    <t>*/*</t>
1072   </list>
1073</t>
1074<t>
1075   The media type quality factor associated with a given type is
1076   determined by finding the media range with the highest precedence
1077   which matches that type. For example,
1078</t>
1079<figure><artwork type="example">
1080  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1081          text/html;level=2;q=0.4, */*;q=0.5
1082</artwork></figure>
1083<t>
1084   would cause the following values to be associated:
1085</t>
1086<texttable align="left">
1087  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1088  <c>text/html;level=1</c>    <c>1</c>
1089  <c>text/html</c>            <c>0.7</c>
1090  <c>text/plain</c>           <c>0.3</c>
1091  <c>image/jpeg</c>           <c>0.5</c>
1092  <c>text/html;level=2</c>    <c>0.4</c>
1093  <c>text/html;level=3</c>    <c>0.7</c>
1094</texttable>
1095<t>
1096      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1097      values for certain media ranges. However, unless the user agent is
1098      a closed system which cannot interact with other rendering agents,
1099      this default set ought to be configurable by the user.
1100</t>
1101</section>
1102
1103<section title="Accept-Charset" anchor="header.accept-charset">
1104  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1105  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1106  <x:anchor-alias value="Accept-Charset"/>
1107  <x:anchor-alias value="Accept-Charset-v"/>
1108<t>
1109   The request-header field "Accept-Charset" can be used to indicate what
1110   character sets are acceptable for the response. This field allows
1111   clients capable of understanding more comprehensive or special-purpose
1112   character sets to signal that capability to a server which is
1113   capable of representing documents in those character sets.
1114</t>
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1116  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1117          <x:ref>Accept-Charset-v</x:ref>
1118  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1119                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1120</artwork></figure>
1121<t>
1122   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1123   be given an associated quality value which represents the user's
1124   preference for that charset. The default value is q=1. An example is
1125</t>
1126<figure><artwork type="example">
1127  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1128</artwork></figure>
1129<t>
1130   The special value "*", if present in the Accept-Charset field,
1131   matches every character set (including ISO-8859-1) which is not
1132   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1133   in an Accept-Charset field, then all character sets not explicitly
1134   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1135   a quality value of 1 if not explicitly mentioned.
1136</t>
1137<t>
1138   If no Accept-Charset header is present, the default is that any
1139   character set is acceptable. If an Accept-Charset header is present,
1140   and if the server cannot send a response which is acceptable
1141   according to the Accept-Charset header, then the server &SHOULD; send
1142   an error response with the 406 (Not Acceptable) status code, though
1143   the sending of an unacceptable response is also allowed.
1144</t>
1145</section>
1146
1147<section title="Accept-Encoding" anchor="header.accept-encoding">
1148  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1149  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1150  <x:anchor-alias value="Accept-Encoding"/>
1151  <x:anchor-alias value="Accept-Encoding-v"/>
1152  <x:anchor-alias value="codings"/>
1153<t>
1154   The request-header field "Accept-Encoding" is similar to Accept, but
1155   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1156   the response.
1157</t>
1158<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1159  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1160                     <x:ref>Accept-Encoding-v</x:ref>
1161  <x:ref>Accept-Encoding-v</x:ref>  =
1162                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1163  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1164</artwork></figure>
1165<t>
1166   Each codings value &MAY; be given an associated quality value which
1167   represents the preference for that encoding. The default value is q=1.
1168</t>
1169<t>
1170   Examples of its use are:
1171</t>
1172<figure><artwork type="example">
1173  Accept-Encoding: compress, gzip
1174  Accept-Encoding:
1175  Accept-Encoding: *
1176  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1177  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1178</artwork></figure>
1179<t>
1180   A server tests whether a content-coding is acceptable, according to
1181   an Accept-Encoding field, using these rules:
1182  <list style="numbers">
1183      <t>If the content-coding is one of the content-codings listed in
1184         the Accept-Encoding field, then it is acceptable, unless it is
1185         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1186         qvalue of 0 means "not acceptable.")</t>
1187
1188      <t>The special "*" symbol in an Accept-Encoding field matches any
1189         available content-coding not explicitly listed in the header
1190         field.</t>
1191
1192      <t>If multiple content-codings are acceptable, then the acceptable
1193         content-coding with the highest non-zero qvalue is preferred.</t>
1194
1195      <t>The "identity" content-coding is always acceptable, unless
1196         specifically refused because the Accept-Encoding field includes
1197         "identity;q=0", or because the field includes "*;q=0" and does
1198         not explicitly include the "identity" content-coding. If the
1199         Accept-Encoding field-value is empty, then only the "identity"
1200         encoding is acceptable.</t>
1201  </list>
1202</t>
1203<t>
1204   If an Accept-Encoding field is present in a request, and if the
1205   server cannot send a response which is acceptable according to the
1206   Accept-Encoding header, then the server &SHOULD; send an error response
1207   with the 406 (Not Acceptable) status code.
1208</t>
1209<t>
1210   If no Accept-Encoding field is present in a request, the server &MAY;
1211   assume that the client will accept any content coding. In this case,
1212   if "identity" is one of the available content-codings, then the
1213   server &SHOULD; use the "identity" content-coding, unless it has
1214   additional information that a different content-coding is meaningful
1215   to the client.
1216</t>
1217<x:note>
1218  <t>
1219    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1220    and if the "identity" content-coding is unavailable, then
1221    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1222    "gzip" and "compress") are preferred; some older clients
1223    improperly display messages sent with other content-codings.  The
1224    server might also make this decision based on information about
1225    the particular user-agent or client.
1226  </t>
1227</x:note>
1228<x:note>
1229  <t>
1230    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1231    associated with content-codings. This means that qvalues will not
1232    work and are not permitted with x-gzip or x-compress.
1233  </t>
1234</x:note>
1235</section>
1236
1237<section title="Accept-Language" anchor="header.accept-language">
1238  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1239  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1240  <x:anchor-alias value="Accept-Language"/>
1241  <x:anchor-alias value="Accept-Language-v"/>
1242  <x:anchor-alias value="language-range"/>
1243<t>
1244   The request-header field "Accept-Language" is similar to Accept, but
1245   restricts the set of natural languages that are preferred as a
1246   response to the request. Language tags are defined in <xref target="language.tags"/>.
1247</t>
1248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1249  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1250                    <x:ref>Accept-Language-v</x:ref>
1251  <x:ref>Accept-Language-v</x:ref> =
1252                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1253  <x:ref>language-range</x:ref>    =
1254            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1255</artwork></figure>
1256<t>
1257   Each language-range can be given an associated quality value which
1258   represents an estimate of the user's preference for the languages
1259   specified by that range. The quality value defaults to "q=1". For
1260   example,
1261</t>
1262<figure><artwork type="example">
1263  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1264</artwork></figure>
1265<t>
1266   would mean: "I prefer Danish, but will accept British English and
1267   other types of English."
1268</t>
1269<t>
1270   For matching, the "Basic Filtering" matching scheme, defined in
1271   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1272</t>
1273<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1274  <t>
1275     A language range matches a
1276     particular language tag if, in a case-insensitive comparison, it
1277     exactly equals the tag, or if it exactly equals a prefix of the tag
1278     such that the first character following the prefix is "-".
1279  </t>
1280</x:blockquote> 
1281<t>
1282   The special range "*", if present in the Accept-Language field,
1283   matches every tag not matched by any other range present in the
1284   Accept-Language field.
1285</t>
1286<x:note>
1287  <t>
1288    <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1289    language tags are assigned to languages in such a way that it is
1290    always true that if a user understands a language with a certain
1291    tag, then this user will also understand all languages with tags
1292    for which this tag is a prefix. The prefix rule simply allows the
1293    use of prefix tags if this is the case.
1294  </t>
1295</x:note>
1296<t>
1297   The language quality factor assigned to a language-tag by the
1298   Accept-Language field is the quality value of the longest language-range
1299   in the field that matches the language-tag. If no language-range
1300   in the field matches the tag, the language quality factor
1301   assigned is 0. If no Accept-Language header is present in the
1302   request, the server
1303   &SHOULD; assume that all languages are equally acceptable. If an
1304   Accept-Language header is present, then all languages which are
1305   assigned a quality factor greater than 0 are acceptable.
1306</t>
1307<t>
1308   It might be contrary to the privacy expectations of the user to send
1309   an Accept-Language header with the complete linguistic preferences of
1310   the user in every request. For a discussion of this issue, see
1311   <xref target="privacy.issues.connected.to.accept.headers"/>.
1312</t>
1313<t>
1314   As intelligibility is highly dependent on the individual user, it is
1315   recommended that client applications make the choice of linguistic
1316   preference available to the user. If the choice is not made
1317   available, then the Accept-Language header field &MUST-NOT; be given in
1318   the request.
1319</t>
1320<x:note>
1321  <t>
1322    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1323    the user, we remind implementors of  the fact that users are not
1324    familiar with the details of language matching as described above,
1325    and should provide appropriate guidance. As an example, users
1326    might assume that on selecting "en-gb", they will be served any
1327    kind of English document if British English is not available. A
1328    user agent might suggest in such a case to add "en" to get the
1329    best matching behavior.
1330  </t>
1331</x:note>
1332</section>
1333
1334<section title="Content-Encoding" anchor="header.content-encoding">
1335  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1336  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1337  <x:anchor-alias value="Content-Encoding"/>
1338  <x:anchor-alias value="Content-Encoding-v"/>
1339<t>
1340   The entity-header field "Content-Encoding" is used as a modifier to the
1341   media-type. When present, its value indicates what additional content
1342   codings have been applied to the entity-body, and thus what decoding
1343   mechanisms must be applied in order to obtain the media-type
1344   referenced by the Content-Type header field. Content-Encoding is
1345   primarily used to allow a document to be compressed without losing
1346   the identity of its underlying media type.
1347</t>
1348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1349  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1350  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1351</artwork></figure>
1352<t>
1353   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1354</t>
1355<figure><artwork type="example">
1356  Content-Encoding: gzip
1357</artwork></figure>
1358<t>
1359   The content-coding is a characteristic of the entity identified by
1360   the request-target. Typically, the entity-body is stored with this
1361   encoding and is only decoded before rendering or analogous usage.
1362   However, a non-transparent proxy &MAY; modify the content-coding if the
1363   new coding is known to be acceptable to the recipient, unless the
1364   "no-transform" cache-control directive is present in the message.
1365</t>
1366<t>
1367   If the content-coding of an entity is not "identity", then the
1368   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1369   that lists the non-identity content-coding(s) used.
1370</t>
1371<t>
1372   If the content-coding of an entity in a request message is not
1373   acceptable to the origin server, the server &SHOULD; respond with a
1374   status code of 415 (Unsupported Media Type).
1375</t>
1376<t>
1377   If multiple encodings have been applied to an entity, the content
1378   codings &MUST; be listed in the order in which they were applied.
1379   Additional information about the encoding parameters &MAY; be provided
1380   by other entity-header fields not defined by this specification.
1381</t>
1382</section>
1383
1384<section title="Content-Language" anchor="header.content-language">
1385  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1386  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1387  <x:anchor-alias value="Content-Language"/>
1388  <x:anchor-alias value="Content-Language-v"/>
1389<t>
1390   The entity-header field "Content-Language" describes the natural
1391   language(s) of the intended audience for the enclosed entity. Note
1392   that this might not be equivalent to all the languages used within
1393   the entity-body.
1394</t>
1395<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1396  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1397  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1398</artwork></figure>
1399<t>
1400   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1401   Content-Language is to allow a user to identify and differentiate
1402   entities according to the user's own preferred language. Thus, if the
1403   body content is intended only for a Danish-literate audience, the
1404   appropriate field is
1405</t>
1406<figure><artwork type="example">
1407  Content-Language: da
1408</artwork></figure>
1409<t>
1410   If no Content-Language is specified, the default is that the content
1411   is intended for all language audiences. This might mean that the
1412   sender does not consider it to be specific to any natural language,
1413   or that the sender does not know for which language it is intended.
1414</t>
1415<t>
1416   Multiple languages &MAY; be listed for content that is intended for
1417   multiple audiences. For example, a rendition of the "Treaty of
1418   Waitangi," presented simultaneously in the original Maori and English
1419   versions, would call for
1420</t>
1421<figure><artwork type="example">
1422  Content-Language: mi, en
1423</artwork></figure>
1424<t>
1425   However, just because multiple languages are present within an entity
1426   does not mean that it is intended for multiple linguistic audiences.
1427   An example would be a beginner's language primer, such as "A First
1428   Lesson in Latin," which is clearly intended to be used by an
1429   English-literate audience. In this case, the Content-Language would
1430   properly only include "en".
1431</t>
1432<t>
1433   Content-Language &MAY; be applied to any media type -- it is not
1434   limited to textual documents.
1435</t>
1436</section>
1437
1438<section title="Content-Location" anchor="header.content-location">
1439  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1440  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1441  <x:anchor-alias value="Content-Location"/>
1442  <x:anchor-alias value="Content-Location-v"/>
1443<t>
1444   The entity-header field "Content-Location" &MAY; be used to supply the
1445   resource location for the entity enclosed in the message when that
1446   entity is accessible from a location separate from the requested
1447   resource's URI. A server &SHOULD; provide a Content-Location for the
1448   variant corresponding to the response entity; especially in the case
1449   where a resource has multiple entities associated with it, and those
1450   entities actually have separate locations by which they might be
1451   individually accessed, the server &SHOULD; provide a Content-Location
1452   for the particular variant which is returned.
1453</t>
1454<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1455  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1456                    <x:ref>Content-Location-v</x:ref>
1457  <x:ref>Content-Location-v</x:ref> =
1458                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1459</artwork></figure>
1460<t>
1461   The value of Content-Location also defines the base URI for the
1462   entity.
1463</t>
1464<t>
1465   The Content-Location value is not a replacement for the original
1466   requested URI; it is only a statement of the location of the resource
1467   corresponding to this particular entity at the time of the request.
1468   Future requests &MAY; specify the Content-Location URI as the request-target
1469   if the desire is to identify the source of that particular
1470   entity.
1471</t>
1472<t>
1473   A cache cannot assume that an entity with a Content-Location
1474   different from the URI used to retrieve it can be used to respond to
1475   later requests on that Content-Location URI. However, the Content-Location
1476   can be used to differentiate between multiple entities
1477   retrieved from a single requested resource, as described in &caching-neg-resp;.
1478</t>
1479<t>
1480   If the Content-Location is a relative URI, the relative URI is
1481   interpreted relative to the request-target.
1482</t>
1483<t>
1484   The meaning of the Content-Location header in requests is
1485   undefined; servers are free to ignore it in those cases.
1486</t>
1487</section>
1488
1489<section title="Content-MD5" anchor="header.content-md5">
1490  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1491  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1492  <x:anchor-alias value="Content-MD5"/>
1493  <x:anchor-alias value="Content-MD5-v"/>
1494<t>
1495   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1496   an MD5 digest of the entity-body for the purpose of providing an
1497   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1498   MIC is good for detecting accidental modification of the entity-body
1499   in transit, but is not proof against malicious attacks.)
1500</t>
1501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1502  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1503  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1504</artwork></figure>
1505<t>
1506   The Content-MD5 header field &MAY; be generated by an origin server or
1507   client to function as an integrity check of the entity-body. Only
1508   origin servers or clients &MAY; generate the Content-MD5 header field;
1509   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1510   value as an end-to-end integrity check. Any recipient of the entity-body,
1511   including gateways and proxies, &MAY; check that the digest value
1512   in this header field matches that of the entity-body as received.
1513</t>
1514<t>
1515   The MD5 digest is computed based on the content of the entity-body,
1516   including any content-coding that has been applied, but not including
1517   any transfer-encoding applied to the message-body. If the message is
1518   received with a transfer-encoding, that encoding &MUST; be removed
1519   prior to checking the Content-MD5 value against the received entity.
1520</t>
1521<t>
1522   This has the result that the digest is computed on the octets of the
1523   entity-body exactly as, and in the order that, they would be sent if
1524   no transfer-encoding were being applied.
1525</t>
1526<t>
1527   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1528   composite media-types (e.g., multipart/* and message/rfc822), but
1529   this does not change how the digest is computed as defined in the
1530   preceding paragraph.
1531</t>
1532<t>
1533   There are several consequences of this. The entity-body for composite
1534   types &MAY; contain many body-parts, each with its own MIME and HTTP
1535   headers (including Content-MD5, Content-Transfer-Encoding, and
1536   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1537   or Content-Encoding header, it is assumed that the content
1538   of the body-part has had the encoding applied, and the body-part is
1539   included in the Content-MD5 digest as is -- i.e., after the
1540   application. The Transfer-Encoding header field is not allowed within
1541   body-parts.
1542</t>
1543<t>
1544   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1545   computing or checking the digest: the line break convention used in
1546   the text actually transmitted &MUST; be left unaltered when computing
1547   the digest.
1548</t>
1549<x:note>
1550  <t>
1551    <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1552    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1553    in which the application of Content-MD5 to HTTP entity-bodies
1554    differs from its application to MIME entity-bodies. One is that
1555    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1556    does use Transfer-Encoding and Content-Encoding. Another is that
1557    HTTP more frequently uses binary content types than MIME, so it is
1558    worth noting that, in such cases, the byte order used to compute
1559    the digest is the transmission byte order defined for the type.
1560    Lastly, HTTP allows transmission of text types with any of several
1561    line break conventions and not just the canonical form using CRLF.
1562  </t>
1563</x:note>
1564</section>
1565
1566<section title="Content-Type" anchor="header.content-type">
1567  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1568  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1569  <x:anchor-alias value="Content-Type"/>
1570  <x:anchor-alias value="Content-Type-v"/>
1571<t>
1572   The entity-header field "Content-Type" indicates the media type of the
1573   entity-body sent to the recipient or, in the case of the HEAD method,
1574   the media type that would have been sent had the request been a GET.
1575</t>
1576<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1577  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1578  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1579</artwork></figure>
1580<t>
1581   Media types are defined in <xref target="media.types"/>. An example of the field is
1582</t>
1583<figure><artwork type="example">
1584  Content-Type: text/html; charset=ISO-8859-4
1585</artwork></figure>
1586<t>
1587   Further discussion of methods for identifying the media type of an
1588   entity is provided in <xref target="type"/>.
1589</t>
1590</section>
1591
1592</section>
1593
1594<section title="IANA Considerations" anchor="IANA.considerations">
1595<section title="Message Header Registration" anchor="message.header.registration">
1596<t>
1597   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1598   with the permanent registrations below (see <xref target="RFC3864"/>):
1599</t>
1600<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1601<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1602   <ttcol>Header Field Name</ttcol>
1603   <ttcol>Protocol</ttcol>
1604   <ttcol>Status</ttcol>
1605   <ttcol>Reference</ttcol>
1606
1607   <c>Accept</c>
1608   <c>http</c>
1609   <c>standard</c>
1610   <c>
1611      <xref target="header.accept"/>
1612   </c>
1613   <c>Accept-Charset</c>
1614   <c>http</c>
1615   <c>standard</c>
1616   <c>
1617      <xref target="header.accept-charset"/>
1618   </c>
1619   <c>Accept-Encoding</c>
1620   <c>http</c>
1621   <c>standard</c>
1622   <c>
1623      <xref target="header.accept-encoding"/>
1624   </c>
1625   <c>Accept-Language</c>
1626   <c>http</c>
1627   <c>standard</c>
1628   <c>
1629      <xref target="header.accept-language"/>
1630   </c>
1631   <c>Content-Disposition</c>
1632   <c>http</c>
1633   <c/>
1634   <c>
1635      <xref target="content-disposition"/>
1636   </c>
1637   <c>Content-Encoding</c>
1638   <c>http</c>
1639   <c>standard</c>
1640   <c>
1641      <xref target="header.content-encoding"/>
1642   </c>
1643   <c>Content-Language</c>
1644   <c>http</c>
1645   <c>standard</c>
1646   <c>
1647      <xref target="header.content-language"/>
1648   </c>
1649   <c>Content-Location</c>
1650   <c>http</c>
1651   <c>standard</c>
1652   <c>
1653      <xref target="header.content-location"/>
1654   </c>
1655   <c>Content-MD5</c>
1656   <c>http</c>
1657   <c>standard</c>
1658   <c>
1659      <xref target="header.content-md5"/>
1660   </c>
1661   <c>Content-Type</c>
1662   <c>http</c>
1663   <c>standard</c>
1664   <c>
1665      <xref target="header.content-type"/>
1666   </c>
1667   <c>MIME-Version</c>
1668   <c>http</c>
1669   <c/>
1670   <c>
1671      <xref target="mime-version"/>
1672   </c>
1673</texttable>
1674<!--(END)-->
1675<t>
1676   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1677</t>
1678</section>
1679</section>
1680
1681<section title="Security Considerations" anchor="security.considerations">
1682<t>
1683   This section is meant to inform application developers, information
1684   providers, and users of the security limitations in HTTP/1.1 as
1685   described by this document. The discussion does not include
1686   definitive solutions to the problems revealed, though it does make
1687   some suggestions for reducing security risks.
1688</t>
1689
1690<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1691<t>
1692   Accept request-headers can reveal information about the user to all
1693   servers which are accessed. The Accept-Language header in particular
1694   can reveal information the user would consider to be of a private
1695   nature, because the understanding of particular languages is often
1696   strongly correlated to the membership of a particular ethnic group.
1697   User agents which offer the option to configure the contents of an
1698   Accept-Language header to be sent in every request are strongly
1699   encouraged to let the configuration process include a message which
1700   makes the user aware of the loss of privacy involved.
1701</t>
1702<t>
1703   An approach that limits the loss of privacy would be for a user agent
1704   to omit the sending of Accept-Language headers by default, and to ask
1705   the user whether or not to start sending Accept-Language headers to a
1706   server if it detects, by looking for any Vary response-header fields
1707   generated by the server, that such sending could improve the quality
1708   of service.
1709</t>
1710<t>
1711   Elaborate user-customized accept header fields sent in every request,
1712   in particular if these include quality values, can be used by servers
1713   as relatively reliable and long-lived user identifiers. Such user
1714   identifiers would allow content providers to do click-trail tracking,
1715   and would allow collaborating content providers to match cross-server
1716   click-trails or form submissions of individual users. Note that for
1717   many users not behind a proxy, the network address of the host
1718   running the user agent will also serve as a long-lived user
1719   identifier. In environments where proxies are used to enhance
1720   privacy, user agents ought to be conservative in offering accept
1721   header configuration options to end users. As an extreme privacy
1722   measure, proxies could filter the accept headers in relayed requests.
1723   General purpose user agents which provide a high degree of header
1724   configurability &SHOULD; warn users about the loss of privacy which can
1725   be involved.
1726</t>
1727</section>
1728
1729<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1730<t>
1731   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1732   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1733   serious security considerations. Content-Disposition is not part of
1734   the HTTP standard, but since it is widely implemented, we are
1735   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1736   for details.
1737</t>
1738</section>
1739
1740</section>
1741
1742<section title="Acknowledgments" anchor="ack">
1743</section>
1744</middle>
1745<back>
1746
1747<references title="Normative References">
1748
1749<reference anchor="ISO-8859-1">
1750  <front>
1751    <title>
1752     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1753    </title>
1754    <author>
1755      <organization>International Organization for Standardization</organization>
1756    </author>
1757    <date year="1998"/>
1758  </front>
1759  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1760</reference>
1761
1762<reference anchor="Part1">
1763  <front>
1764    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1765    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1766      <organization abbrev="Day Software">Day Software</organization>
1767      <address><email>fielding@gbiv.com</email></address>
1768    </author>
1769    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1770      <organization>One Laptop per Child</organization>
1771      <address><email>jg@laptop.org</email></address>
1772    </author>
1773    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1774      <organization abbrev="HP">Hewlett-Packard Company</organization>
1775      <address><email>JeffMogul@acm.org</email></address>
1776    </author>
1777    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1778      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1779      <address><email>henrikn@microsoft.com</email></address>
1780    </author>
1781    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1782      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1783      <address><email>LMM@acm.org</email></address>
1784    </author>
1785    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1786      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1787      <address><email>paulle@microsoft.com</email></address>
1788    </author>
1789    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1790      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1791      <address><email>timbl@w3.org</email></address>
1792    </author>
1793    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1794      <organization abbrev="W3C">World Wide Web Consortium</organization>
1795      <address><email>ylafon@w3.org</email></address>
1796    </author>
1797    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1798      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1799      <address><email>julian.reschke@greenbytes.de</email></address>
1800    </author>
1801    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1802  </front>
1803  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1804  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1805</reference>
1806
1807<reference anchor="Part2">
1808  <front>
1809    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1810    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1811      <organization abbrev="Day Software">Day Software</organization>
1812      <address><email>fielding@gbiv.com</email></address>
1813    </author>
1814    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1815      <organization>One Laptop per Child</organization>
1816      <address><email>jg@laptop.org</email></address>
1817    </author>
1818    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1819      <organization abbrev="HP">Hewlett-Packard Company</organization>
1820      <address><email>JeffMogul@acm.org</email></address>
1821    </author>
1822    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1823      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1824      <address><email>henrikn@microsoft.com</email></address>
1825    </author>
1826    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1827      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1828      <address><email>LMM@acm.org</email></address>
1829    </author>
1830    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1831      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1832      <address><email>paulle@microsoft.com</email></address>
1833    </author>
1834    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1835      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1836      <address><email>timbl@w3.org</email></address>
1837    </author>
1838    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1839      <organization abbrev="W3C">World Wide Web Consortium</organization>
1840      <address><email>ylafon@w3.org</email></address>
1841    </author>
1842    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1843      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1844      <address><email>julian.reschke@greenbytes.de</email></address>
1845    </author>
1846    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1847  </front>
1848  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1849  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1850</reference>
1851
1852<reference anchor="Part4">
1853  <front>
1854    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1855    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1856      <organization abbrev="Day Software">Day Software</organization>
1857      <address><email>fielding@gbiv.com</email></address>
1858    </author>
1859    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1860      <organization>One Laptop per Child</organization>
1861      <address><email>jg@laptop.org</email></address>
1862    </author>
1863    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1864      <organization abbrev="HP">Hewlett-Packard Company</organization>
1865      <address><email>JeffMogul@acm.org</email></address>
1866    </author>
1867    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1868      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1869      <address><email>henrikn@microsoft.com</email></address>
1870    </author>
1871    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1872      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1873      <address><email>LMM@acm.org</email></address>
1874    </author>
1875    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1876      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1877      <address><email>paulle@microsoft.com</email></address>
1878    </author>
1879    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1880      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1881      <address><email>timbl@w3.org</email></address>
1882    </author>
1883    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1884      <organization abbrev="W3C">World Wide Web Consortium</organization>
1885      <address><email>ylafon@w3.org</email></address>
1886    </author>
1887    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1888      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1889      <address><email>julian.reschke@greenbytes.de</email></address>
1890    </author>
1891    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1892  </front>
1893  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1894  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1895</reference>
1896
1897<reference anchor="Part5">
1898  <front>
1899    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1900    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1901      <organization abbrev="Day Software">Day Software</organization>
1902      <address><email>fielding@gbiv.com</email></address>
1903    </author>
1904    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1905      <organization>One Laptop per Child</organization>
1906      <address><email>jg@laptop.org</email></address>
1907    </author>
1908    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1909      <organization abbrev="HP">Hewlett-Packard Company</organization>
1910      <address><email>JeffMogul@acm.org</email></address>
1911    </author>
1912    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1913      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1914      <address><email>henrikn@microsoft.com</email></address>
1915    </author>
1916    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1917      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1918      <address><email>LMM@acm.org</email></address>
1919    </author>
1920    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1921      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1922      <address><email>paulle@microsoft.com</email></address>
1923    </author>
1924    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1925      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1926      <address><email>timbl@w3.org</email></address>
1927    </author>
1928    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1929      <organization abbrev="W3C">World Wide Web Consortium</organization>
1930      <address><email>ylafon@w3.org</email></address>
1931    </author>
1932    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1933      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1934      <address><email>julian.reschke@greenbytes.de</email></address>
1935    </author>
1936    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1937  </front>
1938  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1939  <x:source href="p5-range.xml" basename="p5-range"/>
1940</reference>
1941
1942<reference anchor="Part6">
1943  <front>
1944    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1945    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1946      <organization abbrev="Day Software">Day Software</organization>
1947      <address><email>fielding@gbiv.com</email></address>
1948    </author>
1949    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1950      <organization>One Laptop per Child</organization>
1951      <address><email>jg@laptop.org</email></address>
1952    </author>
1953    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1954      <organization abbrev="HP">Hewlett-Packard Company</organization>
1955      <address><email>JeffMogul@acm.org</email></address>
1956    </author>
1957    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1958      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1959      <address><email>henrikn@microsoft.com</email></address>
1960    </author>
1961    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1962      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1963      <address><email>LMM@acm.org</email></address>
1964    </author>
1965    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1966      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1967      <address><email>paulle@microsoft.com</email></address>
1968    </author>
1969    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1970      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1971      <address><email>timbl@w3.org</email></address>
1972    </author>
1973    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1974      <organization abbrev="W3C">World Wide Web Consortium</organization>
1975      <address><email>ylafon@w3.org</email></address>
1976    </author>
1977    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1978      <organization />
1979      <address><email>mnot@mnot.net</email></address>
1980    </author>
1981    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1982      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1983      <address><email>julian.reschke@greenbytes.de</email></address>
1984    </author>
1985    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1986  </front>
1987  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1988  <x:source href="p6-cache.xml" basename="p6-cache"/>
1989</reference>
1990
1991<reference anchor="RFC1864">
1992  <front>
1993    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1994    <author initials="J." surname="Myers" fullname="John G. Myers">
1995      <organization>Carnegie Mellon University</organization>
1996      <address><email>jgm+@cmu.edu</email></address>
1997    </author>
1998    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1999      <organization>Dover Beach Consulting, Inc.</organization>
2000      <address><email>mrose@dbc.mtview.ca.us</email></address>
2001    </author>
2002    <date month="October" year="1995"/>
2003  </front>
2004  <seriesInfo name="RFC" value="1864"/>
2005</reference>
2006
2007<reference anchor="RFC1950">
2008  <front>
2009    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2010    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2011      <organization>Aladdin Enterprises</organization>
2012      <address><email>ghost@aladdin.com</email></address>
2013    </author>
2014    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2015      <organization/>
2016    </author>
2017    <date month="May" year="1996"/>
2018  </front>
2019  <seriesInfo name="RFC" value="1950"/>
2020  <annotation>
2021    RFC 1950 is an Informational RFC, thus it may be less stable than
2022    this specification. On the other hand, this downward reference was
2023    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2024    therefore it is unlikely to cause problems in practice. See also
2025    <xref target="BCP97"/>.
2026  </annotation>
2027</reference>
2028
2029<reference anchor="RFC1951">
2030  <front>
2031    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2032    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2033      <organization>Aladdin Enterprises</organization>
2034      <address><email>ghost@aladdin.com</email></address>
2035    </author>
2036    <date month="May" year="1996"/>
2037  </front>
2038  <seriesInfo name="RFC" value="1951"/>
2039  <annotation>
2040    RFC 1951 is an Informational RFC, thus it may be less stable than
2041    this specification. On the other hand, this downward reference was
2042    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2043    therefore it is unlikely to cause problems in practice. See also
2044    <xref target="BCP97"/>.
2045  </annotation>
2046</reference>
2047
2048<reference anchor="RFC1952">
2049  <front>
2050    <title>GZIP file format specification version 4.3</title>
2051    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2052      <organization>Aladdin Enterprises</organization>
2053      <address><email>ghost@aladdin.com</email></address>
2054    </author>
2055    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2056      <organization/>
2057      <address><email>gzip@prep.ai.mit.edu</email></address>
2058    </author>
2059    <author initials="M." surname="Adler" fullname="Mark Adler">
2060      <organization/>
2061      <address><email>madler@alumni.caltech.edu</email></address>
2062    </author>
2063    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2064      <organization/>
2065      <address><email>ghost@aladdin.com</email></address>
2066    </author>
2067    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2068      <organization/>
2069      <address><email>randeg@alumni.rpi.edu</email></address>
2070    </author>
2071    <date month="May" year="1996"/>
2072  </front>
2073  <seriesInfo name="RFC" value="1952"/>
2074  <annotation>
2075    RFC 1952 is an Informational RFC, thus it may be less stable than
2076    this specification. On the other hand, this downward reference was
2077    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2078    therefore it is unlikely to cause problems in practice. See also
2079    <xref target="BCP97"/>.
2080  </annotation>
2081</reference>
2082
2083<reference anchor="RFC2045">
2084  <front>
2085    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2086    <author initials="N." surname="Freed" fullname="Ned Freed">
2087      <organization>Innosoft International, Inc.</organization>
2088      <address><email>ned@innosoft.com</email></address>
2089    </author>
2090    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2091      <organization>First Virtual Holdings</organization>
2092      <address><email>nsb@nsb.fv.com</email></address>
2093    </author>
2094    <date month="November" year="1996"/>
2095  </front>
2096  <seriesInfo name="RFC" value="2045"/>
2097</reference>
2098
2099<reference anchor="RFC2046">
2100  <front>
2101    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2102    <author initials="N." surname="Freed" fullname="Ned Freed">
2103      <organization>Innosoft International, Inc.</organization>
2104      <address><email>ned@innosoft.com</email></address>
2105    </author>
2106    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2107      <organization>First Virtual Holdings</organization>
2108      <address><email>nsb@nsb.fv.com</email></address>
2109    </author>
2110    <date month="November" year="1996"/>
2111  </front>
2112  <seriesInfo name="RFC" value="2046"/>
2113</reference>
2114
2115<reference anchor="RFC2119">
2116  <front>
2117    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2118    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2119      <organization>Harvard University</organization>
2120      <address><email>sob@harvard.edu</email></address>
2121    </author>
2122    <date month="March" year="1997"/>
2123  </front>
2124  <seriesInfo name="BCP" value="14"/>
2125  <seriesInfo name="RFC" value="2119"/>
2126</reference>
2127
2128<reference anchor='RFC4647'>
2129  <front>
2130    <title>Matching of Language Tags</title>
2131    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2132      <organization>Yahoo! Inc.</organization>
2133      <address><email>addison@inter-locale.com</email></address>
2134    </author>
2135    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2136      <organization>Google</organization>
2137      <address><email>mark.davis@macchiato.com</email></address>
2138    </author>
2139    <date year='2006' month='September' />
2140  </front>
2141  <seriesInfo name='BCP' value='47' />
2142  <seriesInfo name='RFC' value='4647' />
2143</reference>
2144
2145<reference anchor="RFC5234">
2146  <front>
2147    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2148    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2149      <organization>Brandenburg InternetWorking</organization>
2150      <address>
2151      <postal>
2152      <street>675 Spruce Dr.</street>
2153      <city>Sunnyvale</city>
2154      <region>CA</region>
2155      <code>94086</code>
2156      <country>US</country></postal>
2157      <phone>+1.408.246.8253</phone>
2158      <email>dcrocker@bbiw.net</email></address> 
2159    </author>
2160    <author initials="P." surname="Overell" fullname="Paul Overell">
2161      <organization>THUS plc.</organization>
2162      <address>
2163      <postal>
2164      <street>1/2 Berkeley Square</street>
2165      <street>99 Berkely Street</street>
2166      <city>Glasgow</city>
2167      <code>G3 7HR</code>
2168      <country>UK</country></postal>
2169      <email>paul.overell@thus.net</email></address>
2170    </author>
2171    <date month="January" year="2008"/>
2172  </front>
2173  <seriesInfo name="STD" value="68"/>
2174  <seriesInfo name="RFC" value="5234"/>
2175</reference>
2176
2177<reference anchor='RFC4646bis'>
2178  <front>
2179    <title>Tags for Identifying Languages</title>
2180    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2181      <organization>Lab126</organization>
2182      <address><email>addison@inter-locale.com</email></address>
2183    </author>
2184    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2185      <organization>Google</organization>
2186      <address><email>mark.davis@google.com</email></address>
2187    </author>
2188    <date month='June' day='11' year='2009' />
2189  </front>
2190  <seriesInfo name='Internet-Draft' value='draft-ietf-ltru-4646bis-23' />
2191</reference>
2192
2193</references>
2194
2195<references title="Informative References">
2196
2197<reference anchor="RFC1945">
2198  <front>
2199    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2200    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2201      <organization>MIT, Laboratory for Computer Science</organization>
2202      <address><email>timbl@w3.org</email></address>
2203    </author>
2204    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2205      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2206      <address><email>fielding@ics.uci.edu</email></address>
2207    </author>
2208    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2209      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2210      <address><email>frystyk@w3.org</email></address>
2211    </author>
2212    <date month="May" year="1996"/>
2213  </front>
2214  <seriesInfo name="RFC" value="1945"/>
2215</reference>
2216
2217<reference anchor="RFC2049">
2218  <front>
2219    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2220    <author initials="N." surname="Freed" fullname="Ned Freed">
2221      <organization>Innosoft International, Inc.</organization>
2222      <address><email>ned@innosoft.com</email></address>
2223    </author>
2224    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2225      <organization>First Virtual Holdings</organization>
2226      <address><email>nsb@nsb.fv.com</email></address>
2227    </author>
2228    <date month="November" year="1996"/>
2229  </front>
2230  <seriesInfo name="RFC" value="2049"/>
2231</reference>
2232
2233<reference anchor="RFC2068">
2234  <front>
2235    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2236    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2237      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2238      <address><email>fielding@ics.uci.edu</email></address>
2239    </author>
2240    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2241      <organization>MIT Laboratory for Computer Science</organization>
2242      <address><email>jg@w3.org</email></address>
2243    </author>
2244    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2245      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2246      <address><email>mogul@wrl.dec.com</email></address>
2247    </author>
2248    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2249      <organization>MIT Laboratory for Computer Science</organization>
2250      <address><email>frystyk@w3.org</email></address>
2251    </author>
2252    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2253      <organization>MIT Laboratory for Computer Science</organization>
2254      <address><email>timbl@w3.org</email></address>
2255    </author>
2256    <date month="January" year="1997"/>
2257  </front>
2258  <seriesInfo name="RFC" value="2068"/>
2259</reference>
2260
2261<reference anchor="RFC2076">
2262  <front>
2263    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2264    <author initials="J." surname="Palme" fullname="Jacob Palme">
2265      <organization>Stockholm University/KTH</organization>
2266      <address><email>jpalme@dsv.su.se</email></address>
2267    </author>
2268    <date month="February" year="1997"/>
2269  </front>
2270  <seriesInfo name="RFC" value="2076"/>
2271</reference>
2272
2273<reference anchor="RFC2183">
2274  <front>
2275    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2276    <author initials="R." surname="Troost" fullname="Rens Troost">
2277      <organization>New Century Systems</organization>
2278      <address><email>rens@century.com</email></address>
2279    </author>
2280    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2281      <organization>QUALCOMM Incorporated</organization>
2282      <address><email>sdorner@qualcomm.com</email></address>
2283    </author>
2284    <author initials="K." surname="Moore" fullname="Keith Moore">
2285      <organization>Department of Computer Science</organization>
2286      <address><email>moore@cs.utk.edu</email></address>
2287    </author>
2288    <date month="August" year="1997"/>
2289  </front>
2290  <seriesInfo name="RFC" value="2183"/>
2291</reference>
2292
2293<reference anchor="RFC2277">
2294  <front>
2295    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2296    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2297      <organization>UNINETT</organization>
2298      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2299    </author>
2300    <date month="January" year="1998"/>
2301  </front>
2302  <seriesInfo name="BCP" value="18"/>
2303  <seriesInfo name="RFC" value="2277"/>
2304</reference>
2305
2306<reference anchor="RFC2388">
2307  <front>
2308    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2309    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2310      <organization>Xerox Palo Alto Research Center</organization>
2311      <address><email>masinter@parc.xerox.com</email></address>
2312    </author>
2313    <date year="1998" month="August"/>
2314  </front>
2315  <seriesInfo name="RFC" value="2388"/>
2316</reference>
2317
2318<reference anchor="RFC2557">
2319  <front>
2320    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2321    <author initials="F." surname="Palme" fullname="Jacob Palme">
2322      <organization>Stockholm University and KTH</organization>
2323      <address><email>jpalme@dsv.su.se</email></address>
2324    </author>
2325    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2326      <organization>Microsoft Corporation</organization>
2327      <address><email>alexhop@microsoft.com</email></address>
2328    </author>
2329    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2330      <organization>Lotus Development Corporation</organization>
2331      <address><email>Shelness@lotus.com</email></address>
2332    </author>
2333    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2334      <organization/>
2335      <address><email>stef@nma.com</email></address>
2336    </author>
2337    <date year="1999" month="March"/>
2338  </front>
2339  <seriesInfo name="RFC" value="2557"/>
2340</reference>
2341
2342<reference anchor="RFC2616">
2343  <front>
2344    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2345    <author initials="R." surname="Fielding" fullname="R. Fielding">
2346      <organization>University of California, Irvine</organization>
2347      <address><email>fielding@ics.uci.edu</email></address>
2348    </author>
2349    <author initials="J." surname="Gettys" fullname="J. Gettys">
2350      <organization>W3C</organization>
2351      <address><email>jg@w3.org</email></address>
2352    </author>
2353    <author initials="J." surname="Mogul" fullname="J. Mogul">
2354      <organization>Compaq Computer Corporation</organization>
2355      <address><email>mogul@wrl.dec.com</email></address>
2356    </author>
2357    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2358      <organization>MIT Laboratory for Computer Science</organization>
2359      <address><email>frystyk@w3.org</email></address>
2360    </author>
2361    <author initials="L." surname="Masinter" fullname="L. Masinter">
2362      <organization>Xerox Corporation</organization>
2363      <address><email>masinter@parc.xerox.com</email></address>
2364    </author>
2365    <author initials="P." surname="Leach" fullname="P. Leach">
2366      <organization>Microsoft Corporation</organization>
2367      <address><email>paulle@microsoft.com</email></address>
2368    </author>
2369    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2370      <organization>W3C</organization>
2371      <address><email>timbl@w3.org</email></address>
2372    </author>
2373    <date month="June" year="1999"/>
2374  </front>
2375  <seriesInfo name="RFC" value="2616"/>
2376</reference>
2377
2378<reference anchor="RFC3629">
2379  <front>
2380    <title>UTF-8, a transformation format of ISO 10646</title>
2381    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2382      <organization>Alis Technologies</organization>
2383      <address><email>fyergeau@alis.com</email></address>
2384    </author>
2385    <date month="November" year="2003"/>
2386  </front>
2387  <seriesInfo name="RFC" value="3629"/>
2388  <seriesInfo name="STD" value="63"/>
2389</reference>
2390
2391<reference anchor='RFC3864'>
2392  <front>
2393    <title>Registration Procedures for Message Header Fields</title>
2394    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2395      <organization>Nine by Nine</organization>
2396      <address><email>GK-IETF@ninebynine.org</email></address>
2397    </author>
2398    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2399      <organization>BEA Systems</organization>
2400      <address><email>mnot@pobox.com</email></address>
2401    </author>
2402    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2403      <organization>HP Labs</organization>
2404      <address><email>JeffMogul@acm.org</email></address>
2405    </author>
2406    <date year='2004' month='September' />
2407  </front>
2408  <seriesInfo name='BCP' value='90' />
2409  <seriesInfo name='RFC' value='3864' />
2410</reference>
2411
2412<reference anchor="RFC4288">
2413  <front>
2414    <title>Media Type Specifications and Registration Procedures</title>
2415    <author initials="N." surname="Freed" fullname="N. Freed">
2416      <organization>Sun Microsystems</organization>
2417      <address>
2418        <email>ned.freed@mrochek.com</email>
2419      </address>
2420    </author>
2421    <author initials="J." surname="Klensin" fullname="J. Klensin">
2422      <organization/>
2423      <address>
2424        <email>klensin+ietf@jck.com</email>
2425      </address>
2426    </author>
2427    <date year="2005" month="December"/>
2428  </front>
2429  <seriesInfo name="BCP" value="13"/>
2430  <seriesInfo name="RFC" value="4288"/>
2431</reference>
2432
2433<reference anchor="RFC5322">
2434  <front>
2435    <title>Internet Message Format</title>
2436    <author initials="P." surname="Resnick" fullname="P. Resnick">
2437      <organization>Qualcomm Incorporated</organization>
2438    </author>
2439    <date year="2008" month="October"/>
2440  </front> 
2441  <seriesInfo name="RFC" value="5322"/>
2442</reference>
2443
2444<reference anchor='BCP97'>
2445  <front>
2446    <title>Handling Normative References to Standards-Track Documents</title>
2447    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2448      <organization />
2449      <address>
2450        <email>klensin+ietf@jck.com</email>
2451      </address>
2452    </author>
2453    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2454      <organization>MIT</organization>
2455      <address>
2456        <email>hartmans-ietf@mit.edu</email>
2457      </address>
2458    </author>
2459    <date year='2007' month='June' />
2460  </front>
2461  <seriesInfo name='BCP' value='97' />
2462  <seriesInfo name='RFC' value='4897' />
2463</reference>
2464
2465
2466</references>
2467
2468<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2469<t>
2470   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2471   allow entities to be transmitted in an open variety of
2472   representations and with extensible mechanisms. However, RFC 2045
2473   discusses mail, and HTTP has a few features that are different from
2474   those described in RFC 2045. These differences were carefully chosen
2475   to optimize performance over binary connections, to allow greater
2476   freedom in the use of new media types, to make date comparisons
2477   easier, and to acknowledge the practice of some early HTTP servers
2478   and clients.
2479</t>
2480<t>
2481   This appendix describes specific areas where HTTP differs from RFC
2482   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2483   aware of these differences and provide the appropriate conversions
2484   where necessary. Proxies and gateways from MIME environments to HTTP
2485   also need to be aware of the differences because some conversions
2486   might be required.
2487</t>
2488
2489<section title="MIME-Version" anchor="mime-version">
2490  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2491  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2492  <x:anchor-alias value="MIME-Version"/>
2493  <x:anchor-alias value="MIME-Version-v"/>
2494<t>
2495   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2496   include a single MIME-Version general-header field to indicate what
2497   version of the MIME protocol was used to construct the message. Use
2498   of the MIME-Version header field indicates that the message is in
2499   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2500   Proxies/gateways are responsible for ensuring full compliance (where
2501   possible) when exporting HTTP messages to strict MIME environments.
2502</t>
2503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2504  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2505  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2506</artwork></figure>
2507<t>
2508   MIME version "1.0" is the default for use in HTTP/1.1. However,
2509   HTTP/1.1 message parsing and semantics are defined by this document
2510   and not the MIME specification.
2511</t>
2512</section>
2513
2514<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2515<t>
2516   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2517   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2518   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2519   allowed for subtypes of the "text" media type when transmitted over
2520   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2521   line breaks as CRLF and forbids the use of CR or LF outside of line
2522   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2523   line break within text content when a message is transmitted over
2524   HTTP.
2525</t>
2526<t>
2527   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2528   environment &SHOULD; translate all line breaks within the text media
2529   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2530   canonical form of CRLF. Note, however, that this might be complicated
2531   by the presence of a Content-Encoding and by the fact that HTTP
2532   allows the use of some character sets which do not use octets 13 and
2533   10 to represent CR and LF, as is the case for some multi-byte
2534   character sets.
2535</t>
2536<t>
2537   Implementors should note that conversion will break any cryptographic
2538   checksums applied to the original content unless the original content
2539   is already in canonical form. Therefore, the canonical form is
2540   recommended for any content that uses such checksums in HTTP.
2541</t>
2542</section>
2543
2544
2545<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2546<t>
2547   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2548   simplify the process of date comparison. Proxies and gateways from
2549   other protocols &SHOULD; ensure that any Date header field present in a
2550   message conforms to one of the HTTP/1.1 formats and rewrite the date
2551   if necessary.
2552</t>
2553</section>
2554
2555<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2556<t>
2557   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2558   Content-Encoding header field. Since this acts as a modifier on the
2559   media type, proxies and gateways from HTTP to MIME-compliant
2560   protocols &MUST; either change the value of the Content-Type header
2561   field or decode the entity-body before forwarding the message. (Some
2562   experimental applications of Content-Type for Internet mail have used
2563   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2564   a function equivalent to Content-Encoding. However, this parameter is
2565   not part of RFC 2045).
2566</t>
2567</section>
2568
2569<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2570<t>
2571   HTTP does not use the Content-Transfer-Encoding field of RFC
2572   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2573   remove any Content-Transfer-Encoding
2574   prior to delivering the response message to an HTTP client.
2575</t>
2576<t>
2577   Proxies and gateways from HTTP to MIME-compliant protocols are
2578   responsible for ensuring that the message is in the correct format
2579   and encoding for safe transport on that protocol, where "safe
2580   transport" is defined by the limitations of the protocol being used.
2581   Such a proxy or gateway &SHOULD; label the data with an appropriate
2582   Content-Transfer-Encoding if doing so will improve the likelihood of
2583   safe transport over the destination protocol.
2584</t>
2585</section>
2586
2587<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2588<t>
2589   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2590   Proxies/gateways &MUST; remove any transfer-coding prior to
2591   forwarding a message via a MIME-compliant protocol.
2592</t>
2593</section>
2594
2595<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2596<t>
2597   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2598   need to be aware of MIME line length limitations. Since HTTP does not
2599   have this limitation, HTTP does not fold long lines. MHTML messages
2600   being transported by HTTP follow all conventions of MHTML, including
2601   line length limitations and folding, canonicalization, etc., since
2602   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2603   does not interpret the content or any MIME header lines that might be
2604   contained therein.
2605</t>
2606</section>
2607</section>
2608
2609<section title="Additional Features" anchor="additional.features">
2610<t>
2611   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2612   existing HTTP implementations, but not consistently and correctly
2613   across most HTTP/1.1 applications. Implementors are advised to be
2614   aware of these features, but cannot rely upon their presence in, or
2615   interoperability with, other HTTP/1.1 applications. Some of these
2616   describe proposed experimental features, and some describe features
2617   that experimental deployment found lacking that are now addressed in
2618   the base HTTP/1.1 specification.
2619</t>
2620<t>
2621   A number of other headers, such as Content-Disposition and Title,
2622   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2623</t>
2624
2625<section title="Content-Disposition" anchor="content-disposition">
2626<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2627<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2628  <x:anchor-alias value="content-disposition"/>
2629  <x:anchor-alias value="content-disposition-v"/>
2630  <x:anchor-alias value="disposition-type"/>
2631  <x:anchor-alias value="disposition-parm"/>
2632  <x:anchor-alias value="disp-extension-parm"/>
2633  <x:anchor-alias value="disp-extension-token"/>
2634  <x:anchor-alias value="filename-parm"/>
2635<t>
2636   The Content-Disposition response-header field has been proposed as a
2637   means for the origin server to suggest a default filename if the user
2638   requests that the content is saved to a file. This usage is derived
2639   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2640</t>
2641<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2642  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2643                        <x:ref>content-disposition-v</x:ref>
2644  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2645                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2646  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2647  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2648  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2649  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2650  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2651</artwork></figure>
2652<t>
2653   An example is
2654</t>
2655<figure><artwork type="example">
2656  Content-Disposition: attachment; filename="fname.ext"
2657</artwork></figure>
2658<t>
2659   The receiving user agent &SHOULD-NOT;  respect any directory path
2660   information present in the filename-parm parameter, which is the only
2661   parameter believed to apply to HTTP implementations at this time. The
2662   filename &SHOULD; be treated as a terminal component only.
2663</t>
2664<t>
2665   If this header is used in a response with the application/octet-stream
2666   content-type, the implied suggestion is that the user agent
2667   should not display the response, but directly enter a `save response
2668   as...' dialog.
2669</t>
2670<t>
2671   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2672</t>
2673</section>
2674</section>
2675
2676<section title="Compatibility with Previous Versions" anchor="compatibility">
2677<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2678<t>
2679   Transfer-coding and message lengths all interact in ways that
2680   required fixing exactly when chunked encoding is used (to allow for
2681   transfer encoding that may not be self delimiting); it was important
2682   to straighten out exactly how message lengths are computed.
2683   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2684   <xref target="Part5"/> and <xref target="Part6"/>).
2685</t>
2686<t>
2687   Charset wildcarding is introduced to avoid explosion of character set
2688   names in accept headers. (<xref target="header.accept-charset"/>)
2689</t>
2690<t>
2691   Content-Base was deleted from the specification: it was not
2692   implemented widely, and there is no simple, safe way to introduce it
2693   without a robust extension mechanism. In addition, it is used in a
2694   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2695</t>
2696<t>
2697   A content-coding of "identity" was introduced, to solve problems
2698   discovered in caching. (<xref target="content.codings"/>)
2699</t>
2700<t>
2701   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2702   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2703   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2704</t>
2705</section>
2706
2707<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2708<t>
2709  Clarify contexts that charset is used in.
2710  (<xref target="character.sets"/>)
2711</t>
2712<t>
2713  Remove reference to non-existant identity transfer-coding value tokens.
2714  (<xref target="no.content-transfer-encoding"/>)
2715</t>
2716</section>
2717
2718</section>
2719
2720<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2721<figure>
2722<artwork type="abnf" name="p3-payload.parsed-abnf">
2723<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2724<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2725<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2726 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2727 qvalue ] ] )
2728<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2729<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2730 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2731<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2732<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2733 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2734 ] )
2735<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2736 OWS media-range [ accept-params ] ] ) ]
2737
2738<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2739<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2740 content-coding ] )
2741<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2742<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2743 language-tag ] )
2744<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 3.2&gt;
2745<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2746<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2747<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2748<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2749<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2750<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2751<x:ref>Content-Type-v</x:ref> = media-type
2752
2753<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2754
2755<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2756
2757<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2758<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2759
2760<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2761
2762<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2763<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2764<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2765<x:ref>attribute</x:ref> = token
2766
2767<x:ref>charset</x:ref> = token
2768<x:ref>codings</x:ref> = ( content-coding / "*" )
2769<x:ref>content-coding</x:ref> = token
2770<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2771 content-disposition-v
2772<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2773 disposition-parm )
2774
2775<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2776<x:ref>disp-extension-token</x:ref> = token
2777<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2778<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2779
2780<x:ref>entity-body</x:ref> = *OCTET
2781<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2782 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2783 Expires / Last-Modified / extension-header
2784<x:ref>extension-header</x:ref> = header-field
2785
2786<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2787
2788<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 2.7.2&gt;
2789
2790<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2791<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC4646bis], Section 2.1&gt;
2792
2793<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2794 ";" OWS parameter )
2795<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2796
2797<x:ref>parameter</x:ref> = attribute "=" value
2798<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2799
2800<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2801<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 2.10.4&gt;
2802
2803<x:ref>subtype</x:ref> = token
2804
2805<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2806<x:ref>type</x:ref> = token
2807
2808<x:ref>value</x:ref> = token / quoted-string
2809</artwork>
2810</figure>
2811<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2812; Accept defined but not used
2813; Accept-Charset defined but not used
2814; Accept-Encoding defined but not used
2815; Accept-Language defined but not used
2816; MIME-Version defined but not used
2817; content-disposition defined but not used
2818; entity-body defined but not used
2819; entity-header defined but not used
2820</artwork></figure></section>
2821
2822<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2823
2824<section title="Since RFC2616">
2825<t>
2826  Extracted relevant partitions from <xref target="RFC2616"/>.
2827</t>
2828</section>
2829
2830<section title="Since draft-ietf-httpbis-p3-payload-00">
2831<t>
2832  Closed issues:
2833  <list style="symbols"> 
2834    <t>
2835      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2836      "Media Type Registrations"
2837      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2838    </t>
2839    <t>
2840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2841      "Clarification regarding quoting of charset values"
2842      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2843    </t>
2844    <t>
2845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2846      "Remove 'identity' token references"
2847      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2848    </t>
2849    <t>
2850      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2851      "Accept-Encoding BNF"
2852    </t>
2853    <t>
2854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2855      "Normative and Informative references"
2856    </t>
2857    <t>
2858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2859      "RFC1700 references"
2860    </t>
2861    <t>
2862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2863      "Updating to RFC4288"
2864    </t>
2865    <t>
2866      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2867      "Informative references"
2868    </t>
2869    <t>
2870      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2871      "ISO-8859-1 Reference"
2872    </t>
2873    <t>
2874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2875      "Encoding References Normative"
2876    </t>
2877    <t>
2878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2879      "Normative up-to-date references"
2880    </t>
2881  </list>
2882</t>
2883</section>
2884
2885<section title="Since draft-ietf-httpbis-p3-payload-01">
2886<t>
2887  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2888  <list style="symbols"> 
2889    <t>
2890      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2891    </t>
2892  </list>
2893</t>
2894</section>
2895
2896<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2897<t>
2898  Closed issues:
2899  <list style="symbols"> 
2900    <t>
2901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2902      "Quoting Charsets"
2903    </t>
2904    <t>
2905      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2906      "Classification for Allow header"
2907    </t>
2908    <t>
2909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2910      "missing default for qvalue in description of Accept-Encoding"
2911    </t>
2912  </list>
2913</t>
2914<t>
2915  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2916  <list style="symbols"> 
2917    <t>
2918      Reference RFC 3984, and update header registrations for headers defined
2919      in this document.
2920    </t>
2921  </list>
2922</t>
2923</section>
2924
2925<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2926<t>
2927  Closed issues:
2928  <list style="symbols"> 
2929    <t>
2930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2931      "Quoting Charsets"
2932    </t>
2933    <t>
2934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2935      "language tag matching (Accept-Language) vs RFC4647"
2936    </t>
2937    <t>
2938      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2939      "RFC 1806 has been replaced by RFC2183"
2940    </t>
2941  </list>
2942</t>
2943<t>
2944  Other changes:
2945  <list style="symbols"> 
2946    <t>
2947      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2948      "Encoding References Normative" -- rephrase the annotation and reference
2949      <xref target="BCP97"/>.
2950    </t>
2951  </list>
2952</t>
2953 </section>
2954
2955<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2956<t>
2957  Closed issues:
2958  <list style="symbols"> 
2959    <t>
2960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2961      "RFC 2822 is updated by RFC 5322"
2962    </t>
2963  </list>
2964</t>
2965<t>
2966  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2967  <list style="symbols"> 
2968    <t>
2969      Use "/" instead of "|" for alternatives.
2970    </t>
2971    <t>
2972      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2973      whitespace ("OWS") and required whitespace ("RWS").
2974    </t>
2975    <t>
2976      Rewrite ABNFs to spell out whitespace rules, factor out
2977      header value format definitions.
2978    </t>
2979  </list>
2980</t>
2981</section>
2982
2983<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2984<t>
2985  Closed issues:
2986  <list style="symbols"> 
2987    <t>
2988      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2989      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2990    </t>
2991  </list>
2992</t>
2993<t>
2994  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2995  <list style="symbols"> 
2996    <t>
2997      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2998    </t>
2999  </list>
3000</t>
3001<t>
3002  Other changes:
3003  <list style="symbols"> 
3004    <t>
3005      Move definition of quality values into Part 1.
3006    </t>
3007  </list>
3008</t>
3009</section>
3010
3011<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3012<t>
3013  Closed issues:
3014  <list style="symbols"> 
3015    <t>
3016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3017      "Content-Location isn't special"
3018    </t>
3019    <t>
3020      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3021      "Content Sniffing"
3022    </t>
3023  </list>
3024</t>
3025</section>
3026
3027<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3028<t>
3029  Closed issues:
3030  <list style="symbols"> 
3031    <t>
3032      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3033      "Updated reference for language tags"
3034    </t>
3035  </list>
3036</t>
3037</section>
3038
3039</section>
3040
3041</back>
3042</rfc>
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