source: draft-ietf-httpbis/latest/p3-payload.xml @ 1153

Last change on this file since 1153 was 1153, checked in by julian.reschke@…, 9 years ago

rephrase MAY for parameters (see #277)

  • Property svn:eol-style set to native
File size: 130.9 KB
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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 "March">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc rfcedstyle="yes"?>
52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
56     xmlns:x='http://purl.org/net/xml2rfc/ext'>
57<front>
58
59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
60
61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
63    <address>
64      <postal>
65        <street>345 Park Ave</street>
66        <city>San Jose</city>
67        <region>CA</region>
68        <code>95110</code>
69        <country>USA</country>
70      </postal>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@freedesktop.org</email>
87      <uri>http://gettys.wordpress.com/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 3 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 3 defines HTTP message content,
207   metadata, and content negotiation.
208</t>
209</abstract>
210
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (ietf-http-wg@w3.org). The current issues list is
215    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
216    and related documents (including fancy diffs) can be found at
217    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.12"/>.
221  </t>
222</note>
223</front>
224<middle>
225<section title="Introduction" anchor="introduction">
226<t>
227   This document defines HTTP/1.1 message payloads (a.k.a., content), the
228   associated metadata header fields that define how the payload is intended
229   to be interpreted by a recipient, the request header fields that
230   might influence content selection, and the various selection algorithms
231   that are collectively referred to as HTTP content negotiation.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   A future draft will reorganize the sections to better reflect the content.
237   In particular, the sections on entities will be renamed payload and moved
238   to the first half of the document, while the sections on content negotiation
239   and associated request header fields will be moved to the second half.  The
240   current mess reflects how widely dispersed these topics and associated
241   requirements had become in <xref target="RFC2616"/>.
242</t>
243
244<section title="Terminology" anchor="terminology">
245<t>
246   This specification uses a number of terms to refer to the roles
247   played by participants in, and objects of, the HTTP communication.
248</t>
249<t>
250  <iref item="content negotiation"/>
251  <x:dfn>content negotiation</x:dfn>
252  <list>
253    <t>
254      The mechanism for selecting the appropriate representation when
255      servicing a request. The representation in any response
256      can be negotiated (including error responses).
257    </t>
258  </list>
259</t>
260</section>
261
262<section title="Requirements" anchor="intro.requirements">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   An implementation is not compliant if it fails to satisfy one or more
270   of the "MUST" or "REQUIRED" level requirements for the protocols it
271   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
272   level and all the "SHOULD" level requirements for its protocols is said
273   to be "unconditionally compliant"; one that satisfies all the "MUST"
274   level requirements but not all the "SHOULD" level requirements for its
275   protocols is said to be "conditionally compliant".
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280  <x:anchor-alias value="ALPHA"/>
281  <x:anchor-alias value="CR"/>
282  <x:anchor-alias value="DIGIT"/>
283  <x:anchor-alias value="LF"/>
284  <x:anchor-alias value="OCTET"/>
285  <x:anchor-alias value="VCHAR"/>
286  <x:anchor-alias value="WSP"/>
287<t>
288  This specification uses the ABNF syntax defined in &notation; (which
289  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
290  <xref target="collected.abnf"/> shows the collected ABNF, with the list
291  rule expanded.
292</t>
293<t>
294  The following core rules are included by
295  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
296  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
297  DIGIT (decimal 0-9), DQUOTE (double quote),
298  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
299  OCTET (any 8-bit sequence of data), SP (space),
300  VCHAR (any visible USASCII character),
301  and WSP (whitespace).
302</t>
303
304<section title="Core Rules" anchor="core.rules">
305  <x:anchor-alias value="token"/>
306  <x:anchor-alias value="word"/>
307  <x:anchor-alias value="OWS"/>
308<t>
309  The core rules below are defined in &basic-rules;:
310</t>
311<figure><artwork type="abnf2616">
312  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
313  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
314  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
315</artwork></figure>
316</section>
317
318<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
319  <x:anchor-alias value="absolute-URI"/>
320  <x:anchor-alias value="Allow"/>
321  <x:anchor-alias value="Content-Length"/>
322  <x:anchor-alias value="Content-Range"/>
323  <x:anchor-alias value="Expires"/>
324  <x:anchor-alias value="Last-Modified"/>
325  <x:anchor-alias value="partial-URI"/>
326  <x:anchor-alias value="qvalue"/>
327<t>
328  The ABNF rules below are defined in other parts:
329</t>
330<figure><!--Part1--><artwork type="abnf2616">
331  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
332  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
333  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
334  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
335</artwork></figure>
336<figure><!--Part4--><artwork type="abnf2616">
337  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
338</artwork></figure>
339<figure><!--Part5--><artwork type="abnf2616">
340  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
341</artwork></figure>
342<figure><!--Part6--><artwork type="abnf2616">
343  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
344</artwork></figure>
345</section>
346
347</section>
348
349</section>
350
351<section title="Protocol Parameters" anchor="protocol.parameters">
352
353<section title="Character Sets" anchor="character.sets">
354<t>
355   HTTP uses the same definition of the term "character set" as that
356   described for MIME:
357</t>
358<t>
359   The term "character set" is used in this document to refer to a
360   method used with one or more tables to convert a sequence of octets
361   into a sequence of characters. Note that unconditional conversion in
362   the other direction is not required, in that not all characters might
363   be available in a given character set and a character set might provide
364   more than one sequence of octets to represent a particular character.
365   This definition is intended to allow various kinds of character
366   encoding, from simple single-table mappings such as US-ASCII to
367   complex table switching methods such as those that use ISO-2022's
368   techniques. However, the definition associated with a MIME character
369   set name &MUST; fully specify the mapping to be performed from octets
370   to characters. In particular, use of external profiling information
371   to determine the exact mapping is not permitted.
372</t>
373<x:note>
374  <t>
375    <x:h>Note:</x:h> This use of the term "character set" is more commonly
376    referred to as a "character encoding". However, since HTTP and
377    MIME share the same registry, it is important that the terminology
378    also be shared.
379  </t>
380</x:note>
381<t anchor="rule.charset">
382  <x:anchor-alias value="charset"/>
383   HTTP character sets are identified by case-insensitive tokens. The
384   complete set of tokens is defined by the IANA Character Set registry
385   (<eref target="http://www.iana.org/assignments/character-sets"/>).
386</t>
387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
388  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
389</artwork></figure>
390<t>
391   Although HTTP allows an arbitrary token to be used as a charset
392   value, any token that has a predefined value within the IANA
393   Character Set registry &MUST; represent the character set defined
394   by that registry. Applications &SHOULD; limit their use of character
395   sets to those defined by the IANA registry.
396</t>
397<t>
398   HTTP uses charset in two contexts: within an Accept-Charset request
399   header field (in which the charset value is an unquoted token) and as the
400   value of a parameter in a Content-Type header field (within a request or
401   response), in which case the parameter value of the charset parameter
402   can be quoted.
403</t>
404<t>
405   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
406   <xref target="RFC2277"/>.
407</t>
408
409<section title="Missing Charset" anchor="missing.charset">
410<t>
411   Some HTTP/1.0 software has interpreted a Content-Type header field without
412   charset parameter incorrectly to mean "recipient should guess".
413   Senders wishing to defeat this behavior &MAY; include a charset
414   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
415   it is known that it will not confuse the recipient.
416</t>
417<t>
418   Unfortunately, some older HTTP/1.0 clients did not deal properly with
419   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
420   charset label provided by the sender; and those user agents that have
421   a provision to "guess" a charset &MUST; use the charset from the
422   content-type field if they support that charset, rather than the
423   recipient's preference, when initially displaying a document. See
424   <xref target="canonicalization.and.text.defaults"/>.
425</t>
426</section>
427</section>
428
429<section title="Content Codings" anchor="content.codings">
430  <x:anchor-alias value="content-coding"/>
431<t>
432   Content coding values indicate an encoding transformation that has
433   been or can be applied to a representation. Content codings are primarily
434   used to allow a representation to be compressed or otherwise usefully
435   transformed without losing the identity of its underlying media type
436   and without loss of information. Frequently, the representation is stored in
437   coded form, transmitted directly, and only decoded by the recipient.
438</t>
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
440  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
441</artwork></figure>
442<t>
443   All content-coding values are case-insensitive. HTTP/1.1 uses
444   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
445   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
446   describes the content-coding, what is more important is that it
447   indicates what decoding mechanism will be required to remove the
448   encoding.
449</t>
450<t>
451   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
452  <list>
453    <t>
454      See &compress-coding;.
455    </t>
456  </list>
457</t>
458<t>
459   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
460  <list>
461    <t>
462      See &deflate-coding;.
463    </t>
464  </list>
465</t>
466<t>
467   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
468  <list>
469    <t>
470      See &gzip-coding;.
471    </t>
472  </list>
473</t>
474<t>
475   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
476  <list><t>
477        The default (identity) encoding; the use of no transformation
478        whatsoever. This content-coding is used only in the Accept-Encoding
479        header field, and &SHOULD-NOT;  be used in the Content-Encoding
480        header field.
481  </t></list>
482</t>
483
484<section title="Content Coding Registry" anchor="content.coding.registry">
485<t>
486   The HTTP Content Coding Registry defines the name space for the content
487   coding names.
488</t>
489<t>
490   Registrations &MUST; include the following fields:
491   <list style="symbols">
492     <t>Name</t>
493     <t>Description</t>
494     <t>Pointer to specification text</t>
495   </list>
496</t>
497<t>
498   Names of content codings &MUST-NOT; overlap with names of transfer codings
499   (&transfer-codings;), unless the encoding transformation is identical (as it
500   is the case for the compression codings defined in
501   &compression-codings;).
502</t>
503<t>
504   Values to be added to this name space require a specification
505   (see "Specification Required" in
506   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
507   conform to the purpose of content coding defined in this section.
508</t>
509<t>
510   The registry itself is maintained at
511   <eref target="http://www.iana.org/assignments/http-parameters"/>.
512</t>
513</section>
514
515</section>
516
517<section title="Media Types" anchor="media.types">
518  <x:anchor-alias value="media-type"/>
519  <x:anchor-alias value="type"/>
520  <x:anchor-alias value="subtype"/>
521<t>
522   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
523   and Accept (<xref target="header.accept"/>) header fields in order to provide
524   open and extensible data typing and type negotiation.
525</t>
526<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"/>
527  <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> )
528  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
529  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
530</artwork></figure>
531<t anchor="rule.parameter">
532  <x:anchor-alias value="attribute"/>
533  <x:anchor-alias value="parameter"/>
534  <x:anchor-alias value="value"/>
535   The type/subtype &MAY; be followed by parameters in the form of
536   attribute/value pairs.
537</t>
538<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"/>
539  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
540  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
541  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
542</artwork></figure>
543<t>
544   The type, subtype, and parameter attribute names are case-insensitive.
545   Parameter values might or might not be case-sensitive, depending on the
546   semantics of the parameter name.  The presence or absence of a parameter might
547   be significant to the processing of a media-type, depending on its
548   definition within the media type registry.
549</t>
550<t>
551   A parameter value that matches the <x:ref>token</x:ref> production can be
552   transmitted as either a token or within a quoted-string. The quoted and
553   unquoted values are equivalent.
554</t>
555<t>
556   Note that some older HTTP applications do not recognize media type
557   parameters. When sending data to older HTTP applications,
558   implementations &SHOULD; only use media type parameters when they are
559   required by that type/subtype definition.
560</t>
561<t>
562   Media-type values are registered with the Internet Assigned Number
563   Authority (IANA). The media type registration process is
564   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
565   discouraged.
566</t>
567
568<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
569<t>
570   Internet media types are registered with a canonical form. A
571   representation transferred via HTTP messages &MUST; be in the
572   appropriate canonical form prior to its transmission except for
573   "text" types, as defined in the next paragraph.
574</t>
575<t>
576   When in canonical form, media subtypes of the "text" type use CRLF as
577   the text line break. HTTP relaxes this requirement and allows the
578   transport of text media with plain CR or LF alone representing a line
579   break when it is done consistently for an entire representation. HTTP
580   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
581   a line break in text media received via HTTP. In
582   addition, if the text is in a character encoding that does not
583   use octets 13 and 10 for CR and LF respectively, as is the case for
584   some multi-byte character encodings, HTTP allows the use of whatever octet
585   sequences are defined by that character encoding to represent the
586   equivalent of CR and LF for line breaks. This flexibility regarding
587   line breaks applies only to text media in the payload body; a bare CR
588   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
589   structures (such as header fields and multipart boundaries).
590</t>
591<t>
592   If a representation is encoded with a content-coding, the underlying
593   data &MUST; be in a form defined above prior to being encoded.
594</t>
595<t>
596   The "charset" parameter is used with some media types to define the
597   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
598   parameter is provided by the sender, media subtypes of the "text"
599   type are defined to have a default charset value of "ISO-8859-1" when
600   received via HTTP. Data in character encodings other than "ISO-8859-1" or
601   its subsets &MUST; be labeled with an appropriate charset value. See
602   <xref target="missing.charset"/> for compatibility problems.
603</t>
604</section>
605
606<section title="Multipart Types" anchor="multipart.types">
607<t>
608   MIME provides for a number of "multipart" types &mdash; encapsulations of
609   one or more representations within a single message-body. All multipart
610   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
611   and &MUST; include a boundary parameter as part of the media type
612   value. The message body is itself a protocol element and &MUST;
613   therefore use only CRLF to represent line breaks between body-parts.
614</t>
615<t>
616   In general, HTTP treats a multipart message-body no differently than
617   any other media type: strictly as payload.  HTTP does not use the
618   multipart boundary as an indicator of message-body length.
619   <!-- jre: re-insert removed text pointing to caching? -->
620   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
621   behavior as a MIME user agent would upon receipt of a multipart type.
622   The MIME header fields within each body-part of a multipart message-body
623   do not have any significance to HTTP beyond that defined by
624   their MIME semantics.
625</t>
626<t>
627   If an application receives an unrecognized multipart subtype, the
628   application &MUST; treat it as being equivalent to "multipart/mixed".
629</t>
630<x:note>
631  <t>
632    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
633    for carrying form data suitable for processing via the POST
634    request method, as described in <xref target="RFC2388"/>.
635  </t>
636</x:note>
637</section>
638</section>
639
640<section title="Language Tags" anchor="language.tags">
641  <x:anchor-alias value="language-tag"/>
642<t>
643   A language tag, as defined in <xref target="RFC5646"/>, identifies a
644   natural language spoken, written, or otherwise conveyed by human beings for
645   communication of information to other human beings. Computer languages are
646   explicitly excluded. HTTP uses language tags within the Accept-Language and
647   Content-Language fields.
648</t>
649<t>
650   In summary, a language tag is composed of one or more parts: A primary
651   language subtag followed by a possibly empty series of subtags:
652</t>
653<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
654  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
655</artwork></figure>
656<t>
657   White space is not allowed within the tag and all tags are case-insensitive.
658   The name space of language subtags is administered by the IANA (see
659   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
660</t>
661<figure>
662  <preamble>Example tags include:</preamble>
663<artwork type="example">
664  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
665</artwork>
666</figure>
667<t>
668   See <xref target="RFC5646"/> for further information.
669</t>
670</section>
671</section>
672
673<section title="Payload" anchor="payload">
674<t>
675   HTTP messages &MAY; transfer a payload if not otherwise restricted by
676   the request method or response status code.  The payload consists of
677   metadata, in the form of header fields, and data, in the form of the
678   sequence of octets in the message-body after any transfer-coding has
679   been decoded.
680</t>
681<iref item="payload"/>
682<t>   
683   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
684   representation of some resource.  We use separate terms for payload
685   and representation because some messages contain only the associated
686   representation's header fields (e.g., responses to HEAD) or only some
687   part(s) of the representation (e.g., the 206 status code).
688</t>
689<section title="Payload Header Fields" anchor="payload.header.fields">
690  <x:anchor-alias value="payload-header"/>
691<t>
692   HTTP header fields that specifically define the payload, rather than the
693   associated representation, are referred to as "payload header fields".
694   The following payload header fields are defined by HTTP/1.1:
695</t>
696<texttable align="left">
697  <ttcol>Header Field Name</ttcol>
698  <ttcol>Defined in...</ttcol>
699
700  <c>Content-Length</c> <c>&header-content-length;</c>
701  <c>Content-MD5</c> <c><xref target="header.content-md5"/></c>
702  <c>Content-Range</c> <c>&header-content-range;</c>
703</texttable>
704</section>
705
706<section title="Payload Body" anchor="payload.body">
707  <x:anchor-alias value="payload-body"/>
708<t>
709   A payload body is only present in a message when a message-body is
710   present, as described in &message-body;. The payload body is obtained
711   from the message-body by decoding any Transfer-Encoding that might
712   have been applied to ensure safe and proper transfer of the message.
713</t>
714</section>
715</section>
716
717<section title="Representation" anchor="representation">
718<iref item="representation"/>
719<t>
720   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
721   communicated from one party to another.  A resource representation
722   is information that reflects the state of that resource, as observed
723   at some point in the past (e.g., in a response to GET) or to be
724   desired at some point in the future (e.g., in a PUT request).
725</t>
726<t>
727   Most, but not all, representations transferred via HTTP are intended
728   to be a representation of the target resource (the resource identified
729   by the effective request URI).  The precise semantics of a representation
730   are determined by the type of message (request or response), the request
731   method, the response status code, and the representation metadata.
732   For example, the above semantic is true for the representation in any
733   200 (OK) response to GET and for the representation in any PUT request.
734   A 200 response to PUT, in contrast, contains either a representation
735   that describes the successful action or a representation of the target
736   resource, with the latter indicated by a Content-Location header field
737   with the same value as the effective request URI.  Likewise, response
738   messages with an error status code usually contain a representation that
739   describes the error and what next steps are suggested for resolving it.
740</t>
741
742<section title="Representation Header Fields" anchor="representation.header.fields">
743  <x:anchor-alias value="representation-header"/>
744<t>
745   Representation header fields define metadata about the representation data
746   enclosed in the message-body or, if no message-body is present, about
747   the representation that would have been transferred in a 200 response
748   to a simultaneous GET request with the same effective request URI.
749</t>
750<t>
751   The following header fields are defined as representation metadata:
752</t>
753<texttable align="left">
754  <ttcol>Header Field Name</ttcol>
755  <ttcol>Defined in...</ttcol>
756
757  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
758  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
759  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
760  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
761  <c>Expires</c> <c>&header-expires;</c>
762  <c>Last-Modified</c> <c>&header-last-modified;</c>
763</texttable>
764</section>
765
766<section title="Representation Data" anchor="representation.data">
767  <x:anchor-alias value="representation-data"/>
768<t>
769   The representation body associated with an HTTP message is
770   either provided as the payload body of the message or
771   referred to by the message semantics and the effective request
772   URI.  The representation data is in a format and encoding defined by
773   the representation metadata header fields.
774</t>
775<t>
776   The data type of the representation data
777   is determined via the header fields Content-Type and Content-Encoding.
778   These define a two-layer, ordered encoding model:
779</t>
780<figure><artwork type="example">
781  representation-data := Content-Encoding( Content-Type( bits ) )
782</artwork></figure>
783<t>
784   Content-Type specifies the media type of the underlying data, which
785   defines both the data format and how that data &SHOULD; be processed
786   by the recipient (within the scope of the request method semantics).
787   Any HTTP/1.1 message containing a payload body &SHOULD; include a
788   Content-Type header field defining the media type of the associated
789   representation unless that metadata is unknown to the sender.
790   If the Content-Type header field is not present, it indicates that
791   the sender does not know the media type of the representation;
792   recipients &MAY; either assume that the media type is
793   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
794   or examine the content to determine its type.
795</t>
796<t>
797   In practice, resource owners do not always properly configure their origin
798   server to provide the correct Content-Type for a given representation,
799   with the result that some clients will examine a response body's content
800   and override the specified type.
801   Clients that do so risk drawing incorrect conclusions, which might expose
802   additional security risks (e.g., "privilege escalation").  Furthermore,
803   it is impossible to determine the sender's intent by examining the data
804   format: many data formats match multiple media types that differ only in
805   processing semantics.  Implementers are encouraged to provide a means of
806   disabling such "content sniffing" when it is used.
807</t>
808<t>
809   Content-Encoding is used to indicate any additional content
810   codings applied to the data, usually for the purpose of data
811   compression, that are a property of the representation.  If
812   Content-Encoding is not present, then there is no additional
813   encoding beyond that defined by the Content-Type.
814</t>
815</section>
816</section>
817
818<section title="Content Negotiation" anchor="content.negotiation">
819<t>
820   HTTP responses include a representation which contains information for
821   interpretation, whether by a human user or for further processing.
822   Often, the server has different ways of representing the
823   same information; for example, in different formats, languages,
824   or using different character encodings.
825</t>
826<t>
827   HTTP clients and their users might have different or variable
828   capabilities, characteristics or preferences which would influence
829   which representation, among those available from the server,
830   would be best for the server to deliver. For this reason, HTTP
831   provides mechanisms for "content negotiation" &mdash; a process of
832   allowing selection of a representation of a given resource,
833   when more than one is available.
834</t>
835<t>
836   This specification defines two patterns of content negotiation;
837   "server-driven", where the server selects the representation based
838   upon the client's stated preferences, and "agent-driven" negotiation,
839   where the server provides a list of representations for the client to
840   choose from, based upon their metadata. In addition,  there are
841   other patterns: some applications use an "active content" pattern,
842   where the server returns active content which runs on the client
843   and, based on client available parameters, selects additional
844   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
845   has also been proposed.
846</t>
847<t>
848   These patterns are all widely used, and have trade-offs in applicability
849   and practicality. In particular, when the number of preferences or
850   capabilities to be expressed by a client are large (such as when many
851   different formats are supported by a user-agent), server-driven
852   negotiation becomes unwieldy, and might not be appropriate. Conversely,
853   when the number of representations to choose from is very large,
854   agent-driven negotiation might not be appropriate.
855</t>
856<t>
857   Note that in all cases, the supplier of representations has the
858   responsibility for determining which representations might be
859   considered to be the "same information".
860</t>
861
862<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
863<t>
864   If the selection of the best representation for a response is made by
865   an algorithm located at the server, it is called server-driven
866   negotiation. Selection is based on the available representations of
867   the response (the dimensions over which it can vary; e.g., language,
868   content-coding, etc.) and the contents of particular header fields in
869   the request message or on other information pertaining to the request
870   (such as the network address of the client).
871</t>
872<t>
873   Server-driven negotiation is advantageous when the algorithm for
874   selecting from among the available representations is difficult to
875   describe to the user agent, or when the server desires to send its
876   "best guess" to the client along with the first response (hoping to
877   avoid the round-trip delay of a subsequent request if the "best
878   guess" is good enough for the user). In order to improve the server's
879   guess, the user agent &MAY; include request header fields (Accept,
880   Accept-Language, Accept-Encoding, etc.) which describe its
881   preferences for such a response.
882</t>
883<t>
884   Server-driven negotiation has disadvantages:
885  <list style="numbers">
886    <t>
887         It is impossible for the server to accurately determine what
888         might be "best" for any given user, since that would require
889         complete knowledge of both the capabilities of the user agent
890         and the intended use for the response (e.g., does the user want
891         to view it on screen or print it on paper?).
892    </t>
893    <t>
894         Having the user agent describe its capabilities in every
895         request can be both very inefficient (given that only a small
896         percentage of responses have multiple representations) and a
897         potential violation of the user's privacy.
898    </t>
899    <t>
900         It complicates the implementation of an origin server and the
901         algorithms for generating responses to a request.
902    </t>
903    <t>
904         It might limit a public cache's ability to use the same response
905         for multiple user's requests.
906    </t>
907  </list>
908</t>
909<t>
910   HTTP/1.1 includes the following request-header fields for enabling
911   server-driven negotiation through description of user agent
912   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
913   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
914   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
915   However, an origin server is not limited to these dimensions and &MAY; vary
916   the response based on any aspect of the request, including information
917   outside the request-header fields or within extension header fields
918   not defined by this specification.
919</t>
920<x:note>
921  <t>
922    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
923    because new clients might not be recognized.
924  </t>
925</x:note>
926<t>
927   The Vary header field (&header-vary;) can be used to express the parameters the
928   server uses to select a representation that is subject to server-driven
929   negotiation.
930</t>
931</section>
932
933<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
934<t>
935   With agent-driven negotiation, selection of the best representation
936   for a response is performed by the user agent after receiving an
937   initial response from the origin server. Selection is based on a list
938   of the available representations of the response included within the
939   header fields or body of the initial response, with each
940   representation identified by its own URI. Selection from among the
941   representations can be performed automatically (if the user agent is
942   capable of doing so) or manually by the user selecting from a
943   generated (possibly hypertext) menu.
944</t>
945<t>
946   Agent-driven negotiation is advantageous when the response would vary
947   over commonly-used dimensions (such as type, language, or encoding),
948   when the origin server is unable to determine a user agent's
949   capabilities from examining the request, and generally when public
950   caches are used to distribute server load and reduce network usage.
951</t>
952<t>
953   Agent-driven negotiation suffers from the disadvantage of needing a
954   second request to obtain the best alternate representation. This
955   second request is only efficient when caching is used. In addition,
956   this specification does not define any mechanism for supporting
957   automatic selection, though it also does not prevent any such
958   mechanism from being developed as an extension and used within
959   HTTP/1.1.
960</t>
961<t>
962   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
963   status codes for enabling agent-driven negotiation when the server is
964   unwilling or unable to provide a varying response using server-driven
965   negotiation.
966</t>
967</section>
968</section>
969
970<section title="Header Field Definitions" anchor="header.fields">
971<t>
972   This section defines the syntax and semantics of HTTP/1.1 header fields
973   related to the payload of messages.
974</t>
975
976<section title="Accept" anchor="header.accept">
977  <iref primary="true" item="Accept header field" x:for-anchor=""/>
978  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
979  <x:anchor-alias value="Accept"/>
980  <x:anchor-alias value="Accept-v"/>
981  <x:anchor-alias value="accept-ext"/>
982  <x:anchor-alias value="accept-params"/>
983  <x:anchor-alias value="media-range"/>
984<t>
985   The "Accept" request-header field can be used by user agents to specify
986   response media types that are acceptable. Accept header fields can be used to
987   indicate that the request is specifically limited to a small set of desired
988   types, as in the case of a request for an in-line image.
989</t>
990<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"/>
991  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
992  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
993 
994  <x:ref>media-range</x:ref>    = ( "*/*"
995                   / ( <x:ref>type</x:ref> "/" "*" )
996                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
997                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
998  <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> )
999  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
1000</artwork></figure>
1001<t>
1002   The asterisk "*" character is used to group media types into ranges,
1003   with "*/*" indicating all media types and "type/*" indicating all
1004   subtypes of that type. The media-range &MAY; include media type
1005   parameters that are applicable to that range.
1006</t>
1007<t>
1008   Each media-range &MAY; be followed by one or more accept-params,
1009   beginning with the "q" parameter for indicating a relative quality
1010   factor. The first "q" parameter (if any) separates the media-range
1011   parameter(s) from the accept-params. Quality factors allow the user
1012   or user agent to indicate the relative degree of preference for that
1013   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1014   default value is q=1.
1015</t>
1016<x:note>
1017  <t>
1018    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1019    parameters from Accept extension parameters is due to historical
1020    practice. Although this prevents any media type parameter named
1021    "q" from being used with a media range, such an event is believed
1022    to be unlikely given the lack of any "q" parameters in the IANA
1023    media type registry and the rare usage of any media type
1024    parameters in Accept. Future media types are discouraged from
1025    registering any parameter named "q".
1026  </t>
1027</x:note>
1028<t>
1029   The example
1030</t>
1031<figure><artwork type="example">
1032  Accept: audio/*; q=0.2, audio/basic
1033</artwork></figure>
1034<t>
1035   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1036   type if it is the best available after an 80% mark-down in quality".
1037</t>
1038<t>
1039   If no Accept header field is present, then it is assumed that the
1040   client accepts all media types. If an Accept header field is present,
1041   and if the server cannot send a response which is acceptable
1042   according to the combined Accept field value, then the server &SHOULD;
1043   send a 406 (Not Acceptable) response.
1044</t>
1045<t>
1046   A more elaborate example is
1047</t>
1048<figure><artwork type="example">
1049  Accept: text/plain; q=0.5, text/html,
1050          text/x-dvi; q=0.8, text/x-c
1051</artwork></figure>
1052<t>
1053   Verbally, this would be interpreted as "text/html and text/x-c are
1054   the preferred media types, but if they do not exist, then send the
1055   text/x-dvi representation, and if that does not exist, send the text/plain
1056   representation".
1057</t>
1058<t>
1059   Media ranges can be overridden by more specific media ranges or
1060   specific media types. If more than one media range applies to a given
1061   type, the most specific reference has precedence. For example,
1062</t>
1063<figure><artwork type="example">
1064  Accept: text/*, text/html, text/html;level=1, */*
1065</artwork></figure>
1066<t>
1067   have the following precedence:
1068   <list style="numbers">
1069    <t>text/html;level=1</t>
1070    <t>text/html</t>
1071    <t>text/*</t>
1072    <t>*/*</t>
1073   </list>
1074</t>
1075<t>
1076   The media type quality factor associated with a given type is
1077   determined by finding the media range with the highest precedence
1078   which matches that type. For example,
1079</t>
1080<figure><artwork type="example">
1081  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1082          text/html;level=2;q=0.4, */*;q=0.5
1083</artwork></figure>
1084<t>
1085   would cause the following values to be associated:
1086</t>
1087<texttable align="left">
1088  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1089  <c>text/html;level=1</c>    <c>1</c>
1090  <c>text/html</c>            <c>0.7</c>
1091  <c>text/plain</c>           <c>0.3</c>
1092  <c>image/jpeg</c>           <c>0.5</c>
1093  <c>text/html;level=2</c>    <c>0.4</c>
1094  <c>text/html;level=3</c>    <c>0.7</c>
1095</texttable>
1096<t>
1097      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1098      values for certain media ranges. However, unless the user agent is
1099      a closed system which cannot interact with other rendering agents,
1100      this default set ought to be configurable by the user.
1101</t>
1102</section>
1103
1104<section title="Accept-Charset" anchor="header.accept-charset">
1105  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1106  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
1107  <x:anchor-alias value="Accept-Charset"/>
1108  <x:anchor-alias value="Accept-Charset-v"/>
1109<t>
1110   The "Accept-Charset" request-header field can be used by user agents to
1111   indicate what response character sets are acceptable. This field allows
1112   clients capable of understanding more comprehensive or special-purpose
1113   character sets to signal that capability to a server which is capable of
1114   representing documents in those character sets.
1115</t>
1116<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1117  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1118          <x:ref>Accept-Charset-v</x:ref>
1119  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1120                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1121</artwork></figure>
1122<t>
1123   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1124   be given an associated quality value which represents the user's
1125   preference for that charset. The default value is q=1. An example is
1126</t>
1127<figure><artwork type="example">
1128  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1129</artwork></figure>
1130<t>
1131   The special value "*", if present in the Accept-Charset field,
1132   matches every character set (including ISO-8859-1) which is not
1133   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1134   in an Accept-Charset field, then all character sets not explicitly
1135   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1136   a quality value of 1 if not explicitly mentioned.
1137</t>
1138<t>
1139   If no Accept-Charset header field is present, the default is that any
1140   character set is acceptable. If an Accept-Charset header field is present,
1141   and if the server cannot send a response which is acceptable
1142   according to the Accept-Charset header field, then the server &SHOULD; send
1143   an error response with the 406 (Not Acceptable) status code, though
1144   the sending of an unacceptable response is also allowed.
1145</t>
1146</section>
1147
1148<section title="Accept-Encoding" anchor="header.accept-encoding">
1149  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1150  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
1151  <x:anchor-alias value="Accept-Encoding"/>
1152  <x:anchor-alias value="Accept-Encoding-v"/>
1153  <x:anchor-alias value="codings"/>
1154<t>
1155   The "Accept-Encoding" request-header field can be used by user agents to
1156   indicate what response content-codings (<xref target="content.codings"/>)
1157   are acceptable in the response.
1158</t>
1159<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"/>
1160  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1161                     <x:ref>Accept-Encoding-v</x:ref>
1162  <x:ref>Accept-Encoding-v</x:ref>  =
1163                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1164  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1165</artwork></figure>
1166<t>
1167   Each codings value &MAY; be given an associated quality value which
1168   represents the preference for that encoding. The default value is q=1.
1169</t>
1170<t>
1171   Examples of its use are:
1172</t>
1173<figure><artwork type="example">
1174  Accept-Encoding: compress, gzip
1175  Accept-Encoding:
1176  Accept-Encoding: *
1177  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1178  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1179</artwork></figure>
1180<t>
1181   A server tests whether a content-coding is acceptable, according to
1182   an Accept-Encoding field, using these rules:
1183  <list style="numbers">
1184      <t>If the content-coding is one of the content-codings listed in
1185         the Accept-Encoding field, then it is acceptable, unless it is
1186         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1187         qvalue of 0 means "not acceptable".)</t>
1188
1189      <t>The special "*" symbol in an Accept-Encoding field matches any
1190         available content-coding not explicitly listed in the header
1191         field.</t>
1192
1193      <t>If multiple content-codings are acceptable, then the acceptable
1194         content-coding with the highest non-zero qvalue is preferred.</t>
1195
1196      <t>The "identity" content-coding is always acceptable, unless
1197         specifically refused because the Accept-Encoding field includes
1198         "identity;q=0", or because the field includes "*;q=0" and does
1199         not explicitly include the "identity" content-coding. If the
1200         Accept-Encoding field-value is empty, then only the "identity"
1201         encoding is acceptable.</t>
1202  </list>
1203</t>
1204<t>
1205   If an Accept-Encoding field is present in a request, and if the
1206   server cannot send a response which is acceptable according to the
1207   Accept-Encoding header field, then the server &SHOULD; send an error response
1208   with the 406 (Not Acceptable) status code.
1209</t>
1210<t>
1211   If no Accept-Encoding field is present in a request, the server &MAY;
1212   assume that the client will accept any content coding. In this case,
1213   if "identity" is one of the available content-codings, then the
1214   server &SHOULD; use the "identity" content-coding, unless it has
1215   additional information that a different content-coding is meaningful
1216   to the client.
1217</t>
1218<x:note>
1219  <t>
1220    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1221    and if the "identity" content-coding is unavailable, then
1222    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1223    "gzip" and "compress") are preferred; some older clients
1224    improperly display messages sent with other content-codings.  The
1225    server might also make this decision based on information about
1226    the particular user-agent or client.
1227  </t>
1228</x:note>
1229<x:note>
1230  <t>
1231    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1232    associated with content-codings. This means that qvalues will not
1233    work and are not permitted with x-gzip or x-compress.
1234  </t>
1235</x:note>
1236</section>
1237
1238<section title="Accept-Language" anchor="header.accept-language">
1239  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1240  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
1241  <x:anchor-alias value="Accept-Language"/>
1242  <x:anchor-alias value="Accept-Language-v"/>
1243  <x:anchor-alias value="language-range"/>
1244<t>
1245   The "Accept-Language" request-header field can be used by user agents to
1246   indicate the set of natural languages that are preferred in the response.
1247   Language tags are defined in <xref target="language.tags"/>.
1248</t>
1249<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"/>
1250  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1251                    <x:ref>Accept-Language-v</x:ref>
1252  <x:ref>Accept-Language-v</x:ref> =
1253                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1254  <x:ref>language-range</x:ref>    =
1255            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1256</artwork></figure>
1257<t>
1258   Each language-range can be given an associated quality value which
1259   represents an estimate of the user's preference for the languages
1260   specified by that range. The quality value defaults to "q=1". For
1261   example,
1262</t>
1263<figure><artwork type="example">
1264  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1265</artwork></figure>
1266<t>
1267   would mean: "I prefer Danish, but will accept British English and
1268   other types of English".
1269   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1270</t>
1271<t>
1272   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1273   several matching schemes. Implementations can offer the most appropriate
1274   matching scheme for their requirements.
1275</t>
1276<x:note>
1277  <t>
1278    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1279    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1280    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1281  </t>
1282</x:note>
1283<t>
1284   It might be contrary to the privacy expectations of the user to send
1285   an Accept-Language header field with the complete linguistic preferences of
1286   the user in every request. For a discussion of this issue, see
1287   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1288</t>
1289<t>
1290   As intelligibility is highly dependent on the individual user, it is
1291   recommended that client applications make the choice of linguistic
1292   preference available to the user. If the choice is not made
1293   available, then the Accept-Language header field &MUST-NOT; be given in
1294   the request.
1295</t>
1296<x:note>
1297  <t>
1298    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1299    the user, we remind implementors of  the fact that users are not
1300    familiar with the details of language matching as described above,
1301    and ought to be provided appropriate guidance. As an example, users
1302    might assume that on selecting "en-gb", they will be served any
1303    kind of English document if British English is not available. A
1304    user agent might suggest in such a case to add "en" to get the
1305    best matching behavior.
1306  </t>
1307</x:note>
1308</section>
1309
1310<section title="Content-Encoding" anchor="header.content-encoding">
1311  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1312  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1313  <x:anchor-alias value="Content-Encoding"/>
1314  <x:anchor-alias value="Content-Encoding-v"/>
1315<t>
1316   The "Content-Encoding" header field indicates what content-codings
1317   have been applied to the representation, and thus what decoding mechanisms
1318   must be applied in order to obtain the media-type referenced by the
1319   Content-Type header field. Content-Encoding is primarily used to allow a
1320   representation to be compressed without losing the identity of its underlying
1321   media type.
1322</t>
1323<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1324  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1325  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1326</artwork></figure>
1327<t>
1328   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1329</t>
1330<figure><artwork type="example">
1331  Content-Encoding: gzip
1332</artwork></figure>
1333<t>
1334   The content-coding is a characteristic of the representation.
1335   Typically, the representation body is stored with this
1336   encoding and is only decoded before rendering or analogous usage.
1337   However, a transforming proxy &MAY; modify the content-coding if the
1338   new coding is known to be acceptable to the recipient, unless the
1339   "no-transform" cache-control directive is present in the message.
1340</t>
1341<t>
1342   If the content-coding of a representation is not "identity", then the
1343   representation metadata &MUST; include a Content-Encoding header
1344   field (<xref target="header.content-encoding"/>)
1345   that lists the non-identity content-coding(s) used.
1346</t>
1347<t>
1348   If the content-coding of a representation in a request message is not
1349   acceptable to the origin server, the server &SHOULD; respond with a
1350   status code of 415 (Unsupported Media Type).
1351</t>
1352<t>
1353   If multiple encodings have been applied to a representation, the content
1354   codings &MUST; be listed in the order in which they were applied.
1355   Additional information about the encoding parameters &MAY; be provided
1356   by other header fields not defined by this specification.
1357</t>
1358</section>
1359
1360<section title="Content-Language" anchor="header.content-language">
1361  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1362  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1363  <x:anchor-alias value="Content-Language"/>
1364  <x:anchor-alias value="Content-Language-v"/>
1365<t>
1366   The "Content-Language" header field describes the natural
1367   language(s) of the intended audience for the representation. Note that this might
1368   not be equivalent to all the languages used within the representation.
1369</t>
1370<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1371  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1372  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1373</artwork></figure>
1374<t>
1375   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1376   Content-Language is to allow a user to identify and differentiate
1377   representations according to the user's own preferred language. Thus, if the
1378   body content is intended only for a Danish-literate audience, the
1379   appropriate field is
1380</t>
1381<figure><artwork type="example">
1382  Content-Language: da
1383</artwork></figure>
1384<t>
1385   If no Content-Language is specified, the default is that the content
1386   is intended for all language audiences. This might mean that the
1387   sender does not consider it to be specific to any natural language,
1388   or that the sender does not know for which language it is intended.
1389</t>
1390<t>
1391   Multiple languages &MAY; be listed for content that is intended for
1392   multiple audiences. For example, a rendition of the "Treaty of
1393   Waitangi", presented simultaneously in the original Maori and English
1394   versions, would call for
1395</t>
1396<figure><artwork type="example">
1397  Content-Language: mi, en
1398</artwork></figure>
1399<t>
1400   However, just because multiple languages are present within a representation
1401   does not mean that it is intended for multiple linguistic audiences.
1402   An example would be a beginner's language primer, such as "A First
1403   Lesson in Latin", which is clearly intended to be used by an
1404   English-literate audience. In this case, the Content-Language would
1405   properly only include "en".
1406</t>
1407<t>
1408   Content-Language &MAY; be applied to any media type &mdash; it is not
1409   limited to textual documents.
1410</t>
1411</section>
1412
1413<section title="Content-Location" anchor="header.content-location">
1414  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1415  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1416  <x:anchor-alias value="Content-Location"/>
1417  <x:anchor-alias value="Content-Location-v"/>
1418<t>
1419   The "Content-Location" header field supplies a URI that can be used
1420   as a specific identifier for the representation in this message.
1421   In other words, if one were to perform a GET on this URI at the time
1422   of this message's generation, then a 200 response would contain the
1423   same representation that is enclosed as payload in this message.
1424</t>
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1426  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1427                    <x:ref>Content-Location-v</x:ref>
1428  <x:ref>Content-Location-v</x:ref> =
1429                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1430</artwork></figure>
1431<t>
1432   The Content-Location value is not a replacement for the effective
1433   Request URI (&effective-request-uri;).  It is representation metadata.
1434   It has the same syntax and semantics as the header field of the same name
1435   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1436   However, its appearance in an HTTP message has some special implications
1437   for HTTP recipients.
1438</t>
1439<t>
1440   If Content-Location is included in a response message and its value
1441   is the same as the effective request URI, then the response payload
1442   &SHOULD; be considered the current representation of that resource.
1443   For a GET or HEAD request, this is the same as the default semantics
1444   when no Content-Location is provided by the server.  For a state-changing
1445   method like PUT or POST, it implies that the server's response contains
1446   the new representation of that resource, thereby distinguishing it from
1447   representations that might only report about the action (e.g., "It worked!").
1448   This allows authoring applications to update their local copies without
1449   the need for a subsequent GET request.
1450</t>
1451<t>
1452   If Content-Location is included in a response message and its value
1453   differs from the effective request URI, then the origin server is
1454   informing recipients that this representation has its own, presumably
1455   more specific, identifier.  For a GET or HEAD request, this is an
1456   indication that the effective request URI identifies a resource that
1457   is subject to content negotiation and the representation selected for
1458   this response can also be found at the identified URI.  For other
1459   methods, such a Content-Location indicates that this representation
1460   contains a report on the action's status and the same report is
1461   available (for future access with GET) at the given URI.  For
1462   example, a purchase transaction made via the POST method might
1463   include a receipt document as the payload of the 200 response;
1464   the Content-Location value provides an identifier for retrieving
1465   a copy of that same receipt in the future.
1466</t>
1467<t>
1468   If Content-Location is included in a request message, then it &MAY;
1469   be interpreted by the origin server as an indication of where the
1470   user agent originally obtained the content of the enclosed
1471   representation (prior to any subsequent modification of the content
1472   by that user agent).  In other words, the user agent is providing
1473   the same representation metadata that it received with the original
1474   representation.  However, such interpretation &MUST-NOT; be used to
1475   alter the semantics of the method requested by the client.  For
1476   example, if a client makes a PUT request on a negotiated resource
1477   and the origin server accepts that PUT (without redirection), then the
1478   new set of values for that resource is expected to be consistent with
1479   the one representation supplied in that PUT; the Content-Location
1480   cannot be used as a form of reverse content selection that
1481   identifies only one of the negotiated representations to be updated.
1482   If the user agent had wanted the latter semantics, it would have applied
1483   the PUT directly to the Content-Location URI.
1484</t>
1485<t>
1486   A Content-Location field received in a request message is transitory
1487   information that &SHOULD-NOT; be saved with other representation
1488   metadata for use in later responses.  The Content-Location's value
1489   might be saved for use in other contexts, such as within source links
1490   or other metadata.
1491</t>
1492<t>
1493   A cache cannot assume that a representation with a Content-Location
1494   different from the URI used to retrieve it can be used to respond to
1495   later requests on that Content-Location URI.
1496</t>
1497<t>
1498   If the Content-Location value is a partial URI, the partial URI is
1499   interpreted relative to the effective request URI.
1500</t>
1501</section>
1502
1503<section title="Content-MD5" anchor="header.content-md5">
1504  <iref primary="true" item="Content-MD5 header field" x:for-anchor=""/>
1505  <iref primary="true" item="Header Fields" subitem="Content-MD5" x:for-anchor=""/>
1506  <x:anchor-alias value="Content-MD5"/>
1507  <x:anchor-alias value="Content-MD5-v"/>
1508<t>
1509   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1510   an MD5 digest of the payload body that provides an end-to-end message
1511   integrity check (MIC) of the payload body (the message-body after any
1512   transfer-coding is decoded). Note that a MIC is good for
1513   detecting accidental modification of the payload body in transit, but is not
1514   proof against malicious attacks.
1515</t>
1516<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1517  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1518  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1519</artwork></figure>
1520<t>
1521   The Content-MD5 header field &MAY; be generated by an origin server or
1522   client to function as an integrity check of the payload body. Only
1523   origin servers or user agents &MAY; generate the Content-MD5 header field;
1524   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1525   value as an end-to-end integrity check. Any recipient &MAY; check that
1526   the digest value in this header field matches a corresponding digest
1527   calculated on payload body as received.
1528</t>
1529<t>
1530   The MD5 digest is computed based on the content of the payload body,
1531   including any content-coding, but not including any transfer-coding
1532   applied to the message-body because such transfer-codings might be
1533   applied or removed anywhere along the request/response chain.
1534   If the message is received with a transfer-coding, that encoding &MUST;
1535   be decoded prior to checking the Content-MD5 value against the received
1536   payload.
1537</t>
1538<t>
1539   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1540   composite media-types (e.g., multipart/* and message/rfc822), but
1541   this does not change how the digest is computed as defined in the
1542   preceding paragraph.
1543</t>
1544<t>
1545   There are several consequences of this. The payload for composite
1546   types &MAY; contain many body-parts, each with its own MIME and HTTP
1547   header fields (including Content-MD5, Content-Transfer-Encoding, and
1548   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1549   or Content-Encoding header field, it is assumed that the content
1550   of the body-part has had the encoding applied, and the body-part is
1551   included in the Content-MD5 digest as is &mdash; i.e., after the
1552   application. The Transfer-Encoding header field is not allowed within
1553   body-parts.
1554</t>
1555<t>
1556   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1557   computing or checking the digest: the line break convention used in
1558   the text actually transmitted &MUST; be left unaltered when computing
1559   the digest.
1560</t>
1561<x:note>
1562  <t>
1563    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1564    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1565    in which the application of Content-MD5 to HTTP entity-bodies
1566    differs from its application to MIME entity-bodies. One is that
1567    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1568    does use Transfer-Encoding and Content-Encoding. Another is that
1569    HTTP more frequently uses binary content types than MIME, so it is
1570    worth noting that, in such cases, the byte order used to compute
1571    the digest is the transmission byte order defined for the type.
1572    Lastly, HTTP allows transmission of text types with any of several
1573    line break conventions and not just the canonical form using CRLF.
1574  </t>
1575</x:note>
1576</section>
1577
1578<section title="Content-Type" anchor="header.content-type">
1579  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1580  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1581  <x:anchor-alias value="Content-Type"/>
1582  <x:anchor-alias value="Content-Type-v"/>
1583<t>
1584   The "Content-Type" header field indicates the media type of the
1585   representation. In the case of responses to the HEAD method, the media type is
1586   that which would have been sent had the request been a GET.
1587</t>
1588<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1589  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1590  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1591</artwork></figure>
1592<t>
1593   Media types are defined in <xref target="media.types"/>. An example of the field is
1594</t>
1595<figure><artwork type="example">
1596  Content-Type: text/html; charset=ISO-8859-4
1597</artwork></figure>
1598<t>
1599   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1600</t>
1601</section>
1602
1603</section>
1604
1605<section title="IANA Considerations" anchor="IANA.considerations">
1606<section title="Header Field Registration" anchor="header.field.registration">
1607<t>
1608   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1609   with the permanent registrations below (see <xref target="RFC3864"/>):
1610</t>
1611<?BEGININC p3-payload.iana-headers ?>
1612<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1613<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1614   <ttcol>Header Field Name</ttcol>
1615   <ttcol>Protocol</ttcol>
1616   <ttcol>Status</ttcol>
1617   <ttcol>Reference</ttcol>
1618
1619   <c>Accept</c>
1620   <c>http</c>
1621   <c>standard</c>
1622   <c>
1623      <xref target="header.accept"/>
1624   </c>
1625   <c>Accept-Charset</c>
1626   <c>http</c>
1627   <c>standard</c>
1628   <c>
1629      <xref target="header.accept-charset"/>
1630   </c>
1631   <c>Accept-Encoding</c>
1632   <c>http</c>
1633   <c>standard</c>
1634   <c>
1635      <xref target="header.accept-encoding"/>
1636   </c>
1637   <c>Accept-Language</c>
1638   <c>http</c>
1639   <c>standard</c>
1640   <c>
1641      <xref target="header.accept-language"/>
1642   </c>
1643   <c>Content-Encoding</c>
1644   <c>http</c>
1645   <c>standard</c>
1646   <c>
1647      <xref target="header.content-encoding"/>
1648   </c>
1649   <c>Content-Language</c>
1650   <c>http</c>
1651   <c>standard</c>
1652   <c>
1653      <xref target="header.content-language"/>
1654   </c>
1655   <c>Content-Location</c>
1656   <c>http</c>
1657   <c>standard</c>
1658   <c>
1659      <xref target="header.content-location"/>
1660   </c>
1661   <c>Content-MD5</c>
1662   <c>http</c>
1663   <c>standard</c>
1664   <c>
1665      <xref target="header.content-md5"/>
1666   </c>
1667   <c>Content-Type</c>
1668   <c>http</c>
1669   <c>standard</c>
1670   <c>
1671      <xref target="header.content-type"/>
1672   </c>
1673   <c>MIME-Version</c>
1674   <c>http</c>
1675   <c>standard</c>
1676   <c>
1677      <xref target="mime-version"/>
1678   </c>
1679</texttable>
1680<!--(END)-->
1681<?ENDINC p3-payload.iana-headers ?>
1682<t>
1683   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1684</t>
1685</section>
1686
1687<section title="Content Coding Registry" anchor="content.coding.registration">
1688<t>
1689   The registration procedure for HTTP Content Codings is now defined
1690   by <xref target="content.coding.registry"/> of this document.
1691</t>
1692<t>
1693   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1694   shall be updated with the registration below:
1695</t>
1696<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1697   <ttcol>Name</ttcol>
1698   <ttcol>Description</ttcol>
1699   <ttcol>Reference</ttcol>
1700   <c>compress</c>
1701   <c>UNIX "compress" program method</c>
1702   <c>
1703      &compress-coding;
1704   </c>
1705   <c>deflate</c>
1706   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1707   the "zlib" data format (<xref target="RFC1950"/>)
1708   </c>
1709   <c>
1710      &deflate-coding;
1711   </c>
1712   <c>gzip</c>
1713   <c>Same as GNU zip <xref target="RFC1952"/></c>
1714   <c>
1715      &gzip-coding;
1716   </c>
1717   <c>identity</c>
1718   <c>No transformation</c>
1719   <c>
1720      <xref target="content.codings"/>
1721   </c>
1722</texttable>
1723</section>
1724
1725</section>
1726
1727<section title="Security Considerations" anchor="security.considerations">
1728<t>
1729   This section is meant to inform application developers, information
1730   providers, and users of the security limitations in HTTP/1.1 as
1731   described by this document. The discussion does not include
1732   definitive solutions to the problems revealed, though it does make
1733   some suggestions for reducing security risks.
1734</t>
1735
1736<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1737<t>
1738   Accept request-headers fields can reveal information about the user to all
1739   servers which are accessed. The Accept-Language header field in particular
1740   can reveal information the user would consider to be of a private
1741   nature, because the understanding of particular languages is often
1742   strongly correlated to the membership of a particular ethnic group.
1743   User agents which offer the option to configure the contents of an
1744   Accept-Language header field to be sent in every request are strongly
1745   encouraged to let the configuration process include a message which
1746   makes the user aware of the loss of privacy involved.
1747</t>
1748<t>
1749   An approach that limits the loss of privacy would be for a user agent
1750   to omit the sending of Accept-Language header fields by default, and to ask
1751   the user whether or not to start sending Accept-Language header fields to a
1752   server if it detects, by looking for any Vary response-header fields
1753   generated by the server, that such sending could improve the quality
1754   of service.
1755</t>
1756<t>
1757   Elaborate user-customized accept header fields sent in every request,
1758   in particular if these include quality values, can be used by servers
1759   as relatively reliable and long-lived user identifiers. Such user
1760   identifiers would allow content providers to do click-trail tracking,
1761   and would allow collaborating content providers to match cross-server
1762   click-trails or form submissions of individual users. Note that for
1763   many users not behind a proxy, the network address of the host
1764   running the user agent will also serve as a long-lived user
1765   identifier. In environments where proxies are used to enhance
1766   privacy, user agents ought to be conservative in offering accept
1767   header configuration options to end users. As an extreme privacy
1768   measure, proxies could filter the accept header fields in relayed requests.
1769   General purpose user agents which provide a high degree of header
1770   configurability &SHOULD; warn users about the loss of privacy which can
1771   be involved.
1772</t>
1773</section>
1774
1775</section>
1776
1777<section title="Acknowledgments" anchor="ack">
1778</section>
1779</middle>
1780<back>
1781
1782<references title="Normative References">
1783
1784<reference anchor="ISO-8859-1">
1785  <front>
1786    <title>
1787     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1788    </title>
1789    <author>
1790      <organization>International Organization for Standardization</organization>
1791    </author>
1792    <date year="1998"/>
1793  </front>
1794  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1795</reference>
1796
1797<reference anchor="Part1">
1798  <front>
1799    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1800    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1801      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1802      <address><email>fielding@gbiv.com</email></address>
1803    </author>
1804    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1805      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1806      <address><email>jg@freedesktop.org</email></address>
1807    </author>
1808    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1809      <organization abbrev="HP">Hewlett-Packard Company</organization>
1810      <address><email>JeffMogul@acm.org</email></address>
1811    </author>
1812    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1813      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1814      <address><email>henrikn@microsoft.com</email></address>
1815    </author>
1816    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1817      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1818      <address><email>LMM@acm.org</email></address>
1819    </author>
1820    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1821      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1822      <address><email>paulle@microsoft.com</email></address>
1823    </author>
1824    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1825      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1826      <address><email>timbl@w3.org</email></address>
1827    </author>
1828    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1829      <organization abbrev="W3C">World Wide Web Consortium</organization>
1830      <address><email>ylafon@w3.org</email></address>
1831    </author>
1832    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1833      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1834      <address><email>julian.reschke@greenbytes.de</email></address>
1835    </author>
1836    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1837  </front>
1838  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1839  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1840</reference>
1841
1842<reference anchor="Part2">
1843  <front>
1844    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1845    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1846      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1847      <address><email>fielding@gbiv.com</email></address>
1848    </author>
1849    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1850      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1851      <address><email>jg@freedesktop.org</email></address>
1852    </author>
1853    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1854      <organization abbrev="HP">Hewlett-Packard Company</organization>
1855      <address><email>JeffMogul@acm.org</email></address>
1856    </author>
1857    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1858      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1859      <address><email>henrikn@microsoft.com</email></address>
1860    </author>
1861    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1862      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1863      <address><email>LMM@acm.org</email></address>
1864    </author>
1865    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1866      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1867      <address><email>paulle@microsoft.com</email></address>
1868    </author>
1869    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1870      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1871      <address><email>timbl@w3.org</email></address>
1872    </author>
1873    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1874      <organization abbrev="W3C">World Wide Web Consortium</organization>
1875      <address><email>ylafon@w3.org</email></address>
1876    </author>
1877    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1878      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1879      <address><email>julian.reschke@greenbytes.de</email></address>
1880    </author>
1881    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1882  </front>
1883  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1884  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1885</reference>
1886
1887<reference anchor="Part4">
1888  <front>
1889    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1890    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1891      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1892      <address><email>fielding@gbiv.com</email></address>
1893    </author>
1894    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1895      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1896      <address><email>jg@freedesktop.org</email></address>
1897    </author>
1898    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1899      <organization abbrev="HP">Hewlett-Packard Company</organization>
1900      <address><email>JeffMogul@acm.org</email></address>
1901    </author>
1902    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1903      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1904      <address><email>henrikn@microsoft.com</email></address>
1905    </author>
1906    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1907      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1908      <address><email>LMM@acm.org</email></address>
1909    </author>
1910    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1911      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1912      <address><email>paulle@microsoft.com</email></address>
1913    </author>
1914    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1915      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1916      <address><email>timbl@w3.org</email></address>
1917    </author>
1918    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1919      <organization abbrev="W3C">World Wide Web Consortium</organization>
1920      <address><email>ylafon@w3.org</email></address>
1921    </author>
1922    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1923      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1924      <address><email>julian.reschke@greenbytes.de</email></address>
1925    </author>
1926    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1927  </front>
1928  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1929  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1930</reference>
1931
1932<reference anchor="Part5">
1933  <front>
1934    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1935    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1936      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1937      <address><email>fielding@gbiv.com</email></address>
1938    </author>
1939    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1940      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1941      <address><email>jg@freedesktop.org</email></address>
1942    </author>
1943    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1944      <organization abbrev="HP">Hewlett-Packard Company</organization>
1945      <address><email>JeffMogul@acm.org</email></address>
1946    </author>
1947    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1948      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1949      <address><email>henrikn@microsoft.com</email></address>
1950    </author>
1951    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1952      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1953      <address><email>LMM@acm.org</email></address>
1954    </author>
1955    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1956      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1957      <address><email>paulle@microsoft.com</email></address>
1958    </author>
1959    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1960      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1961      <address><email>timbl@w3.org</email></address>
1962    </author>
1963    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1964      <organization abbrev="W3C">World Wide Web Consortium</organization>
1965      <address><email>ylafon@w3.org</email></address>
1966    </author>
1967    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1968      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1969      <address><email>julian.reschke@greenbytes.de</email></address>
1970    </author>
1971    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1972  </front>
1973  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1974  <x:source href="p5-range.xml" basename="p5-range"/>
1975</reference>
1976
1977<reference anchor="Part6">
1978  <front>
1979    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1980    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1981      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1982      <address><email>fielding@gbiv.com</email></address>
1983    </author>
1984    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1985      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1986      <address><email>jg@freedesktop.org</email></address>
1987    </author>
1988    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1989      <organization abbrev="HP">Hewlett-Packard Company</organization>
1990      <address><email>JeffMogul@acm.org</email></address>
1991    </author>
1992    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1993      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1994      <address><email>henrikn@microsoft.com</email></address>
1995    </author>
1996    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1997      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1998      <address><email>LMM@acm.org</email></address>
1999    </author>
2000    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2001      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2002      <address><email>paulle@microsoft.com</email></address>
2003    </author>
2004    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2005      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2006      <address><email>timbl@w3.org</email></address>
2007    </author>
2008    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2009      <organization abbrev="W3C">World Wide Web Consortium</organization>
2010      <address><email>ylafon@w3.org</email></address>
2011    </author>
2012    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2013      <address><email>mnot@mnot.net</email></address>
2014    </author>
2015    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2016      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2017      <address><email>julian.reschke@greenbytes.de</email></address>
2018    </author>
2019    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2020  </front>
2021  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2022  <x:source href="p6-cache.xml" basename="p6-cache"/>
2023</reference>
2024
2025<reference anchor="RFC1864">
2026  <front>
2027    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2028    <author initials="J." surname="Myers" fullname="John G. Myers">
2029      <organization>Carnegie Mellon University</organization>
2030      <address><email>jgm+@cmu.edu</email></address>
2031    </author>
2032    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2033      <organization>Dover Beach Consulting, Inc.</organization>
2034      <address><email>mrose@dbc.mtview.ca.us</email></address>
2035    </author>
2036    <date month="October" year="1995"/>
2037  </front>
2038  <seriesInfo name="RFC" value="1864"/>
2039</reference>
2040
2041<reference anchor="RFC1950">
2042  <front>
2043    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2044    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2045      <organization>Aladdin Enterprises</organization>
2046      <address><email>ghost@aladdin.com</email></address>
2047    </author>
2048    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2049    <date month="May" year="1996"/>
2050  </front>
2051  <seriesInfo name="RFC" value="1950"/>
2052  <annotation>
2053    RFC 1950 is an Informational RFC, thus it might be less stable than
2054    this specification. On the other hand, this downward reference was
2055    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2056    therefore it is unlikely to cause problems in practice. See also
2057    <xref target="BCP97"/>.
2058  </annotation>
2059</reference>
2060
2061<reference anchor="RFC1951">
2062  <front>
2063    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2064    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2065      <organization>Aladdin Enterprises</organization>
2066      <address><email>ghost@aladdin.com</email></address>
2067    </author>
2068    <date month="May" year="1996"/>
2069  </front>
2070  <seriesInfo name="RFC" value="1951"/>
2071  <annotation>
2072    RFC 1951 is an Informational RFC, thus it might be less stable than
2073    this specification. On the other hand, this downward reference was
2074    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2075    therefore it is unlikely to cause problems in practice. See also
2076    <xref target="BCP97"/>.
2077  </annotation>
2078</reference>
2079
2080<reference anchor="RFC1952">
2081  <front>
2082    <title>GZIP file format specification version 4.3</title>
2083    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2084      <organization>Aladdin Enterprises</organization>
2085      <address><email>ghost@aladdin.com</email></address>
2086    </author>
2087    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2088      <address><email>gzip@prep.ai.mit.edu</email></address>
2089    </author>
2090    <author initials="M." surname="Adler" fullname="Mark Adler">
2091      <address><email>madler@alumni.caltech.edu</email></address>
2092    </author>
2093    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2094      <address><email>ghost@aladdin.com</email></address>
2095    </author>
2096    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2097      <address><email>randeg@alumni.rpi.edu</email></address>
2098    </author>
2099    <date month="May" year="1996"/>
2100  </front>
2101  <seriesInfo name="RFC" value="1952"/>
2102  <annotation>
2103    RFC 1952 is an Informational RFC, thus it might be less stable than
2104    this specification. On the other hand, this downward reference was
2105    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2106    therefore it is unlikely to cause problems in practice. See also
2107    <xref target="BCP97"/>.
2108  </annotation>
2109</reference>
2110
2111<reference anchor="RFC2045">
2112  <front>
2113    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2114    <author initials="N." surname="Freed" fullname="Ned Freed">
2115      <organization>Innosoft International, Inc.</organization>
2116      <address><email>ned@innosoft.com</email></address>
2117    </author>
2118    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2119      <organization>First Virtual Holdings</organization>
2120      <address><email>nsb@nsb.fv.com</email></address>
2121    </author>
2122    <date month="November" year="1996"/>
2123  </front>
2124  <seriesInfo name="RFC" value="2045"/>
2125</reference>
2126
2127<reference anchor="RFC2046">
2128  <front>
2129    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2130    <author initials="N." surname="Freed" fullname="Ned Freed">
2131      <organization>Innosoft International, Inc.</organization>
2132      <address><email>ned@innosoft.com</email></address>
2133    </author>
2134    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2135      <organization>First Virtual Holdings</organization>
2136      <address><email>nsb@nsb.fv.com</email></address>
2137    </author>
2138    <date month="November" year="1996"/>
2139  </front>
2140  <seriesInfo name="RFC" value="2046"/>
2141</reference>
2142
2143<reference anchor="RFC2119">
2144  <front>
2145    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2146    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2147      <organization>Harvard University</organization>
2148      <address><email>sob@harvard.edu</email></address>
2149    </author>
2150    <date month="March" year="1997"/>
2151  </front>
2152  <seriesInfo name="BCP" value="14"/>
2153  <seriesInfo name="RFC" value="2119"/>
2154</reference>
2155
2156<reference anchor='RFC4647'>
2157  <front>
2158    <title>Matching of Language Tags</title>
2159    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2160      <organization>Yahoo! Inc.</organization>
2161      <address><email>addison@inter-locale.com</email></address>
2162    </author>
2163    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2164      <organization>Google</organization>
2165      <address><email>mark.davis@macchiato.com</email></address>
2166    </author>
2167    <date year='2006' month='September' />
2168  </front>
2169  <seriesInfo name='BCP' value='47' />
2170  <seriesInfo name='RFC' value='4647' />
2171</reference>
2172
2173<reference anchor="RFC5234">
2174  <front>
2175    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2176    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2177      <organization>Brandenburg InternetWorking</organization>
2178      <address>
2179        <email>dcrocker@bbiw.net</email>
2180      </address> 
2181    </author>
2182    <author initials="P." surname="Overell" fullname="Paul Overell">
2183      <organization>THUS plc.</organization>
2184      <address>
2185        <email>paul.overell@thus.net</email>
2186      </address>
2187    </author>
2188    <date month="January" year="2008"/>
2189  </front>
2190  <seriesInfo name="STD" value="68"/>
2191  <seriesInfo name="RFC" value="5234"/>
2192</reference>
2193
2194<reference anchor='RFC5646'>
2195  <front>
2196    <title>Tags for Identifying Languages</title>
2197    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2198      <organization>Lab126</organization>
2199      <address><email>addison@inter-locale.com</email></address>
2200    </author>
2201    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2202      <organization>Google</organization>
2203      <address><email>mark.davis@google.com</email></address>
2204    </author>
2205    <date month='September' year='2009' />
2206  </front>
2207  <seriesInfo name='BCP' value='47' />
2208  <seriesInfo name='RFC' value='5646' />
2209</reference>
2210
2211</references>
2212
2213<references title="Informative References">
2214
2215<reference anchor="RFC1945">
2216  <front>
2217    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2218    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2219      <organization>MIT, Laboratory for Computer Science</organization>
2220      <address><email>timbl@w3.org</email></address>
2221    </author>
2222    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2223      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2224      <address><email>fielding@ics.uci.edu</email></address>
2225    </author>
2226    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2227      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2228      <address><email>frystyk@w3.org</email></address>
2229    </author>
2230    <date month="May" year="1996"/>
2231  </front>
2232  <seriesInfo name="RFC" value="1945"/>
2233</reference>
2234
2235<reference anchor="RFC2049">
2236  <front>
2237    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2238    <author initials="N." surname="Freed" fullname="Ned Freed">
2239      <organization>Innosoft International, Inc.</organization>
2240      <address><email>ned@innosoft.com</email></address>
2241    </author>
2242    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2243      <organization>First Virtual Holdings</organization>
2244      <address><email>nsb@nsb.fv.com</email></address>
2245    </author>
2246    <date month="November" year="1996"/>
2247  </front>
2248  <seriesInfo name="RFC" value="2049"/>
2249</reference>
2250
2251<reference anchor="RFC2068">
2252  <front>
2253    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2254    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2255      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2256      <address><email>fielding@ics.uci.edu</email></address>
2257    </author>
2258    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2259      <organization>MIT Laboratory for Computer Science</organization>
2260      <address><email>jg@w3.org</email></address>
2261    </author>
2262    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2263      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2264      <address><email>mogul@wrl.dec.com</email></address>
2265    </author>
2266    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2267      <organization>MIT Laboratory for Computer Science</organization>
2268      <address><email>frystyk@w3.org</email></address>
2269    </author>
2270    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2271      <organization>MIT Laboratory for Computer Science</organization>
2272      <address><email>timbl@w3.org</email></address>
2273    </author>
2274    <date month="January" year="1997"/>
2275  </front>
2276  <seriesInfo name="RFC" value="2068"/>
2277</reference>
2278
2279<reference anchor="RFC2076">
2280  <front>
2281    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2282    <author initials="J." surname="Palme" fullname="Jacob Palme">
2283      <organization>Stockholm University/KTH</organization>
2284      <address><email>jpalme@dsv.su.se</email></address>
2285    </author>
2286    <date month="February" year="1997"/>
2287  </front>
2288  <seriesInfo name="RFC" value="2076"/>
2289</reference>
2290
2291<reference anchor="RFC2277">
2292  <front>
2293    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2294    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2295      <organization>UNINETT</organization>
2296      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2297    </author>
2298    <date month="January" year="1998"/>
2299  </front>
2300  <seriesInfo name="BCP" value="18"/>
2301  <seriesInfo name="RFC" value="2277"/>
2302</reference>
2303
2304<reference anchor='RFC2295'>
2305  <front>
2306    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2307    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2308      <organization>Technische Universiteit Eindhoven</organization>
2309      <address>
2310        <email>koen@win.tue.nl</email>
2311      </address>
2312    </author>
2313    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2314      <organization>Hewlett-Packard Company</organization>
2315      <address>
2316        <email>mutz@hpl.hp.com</email>
2317      </address>
2318    </author>
2319    <date year='1998' month='March'/>
2320  </front>
2321  <seriesInfo name='RFC' value='2295'/>
2322</reference>
2323
2324<reference anchor="RFC2388">
2325  <front>
2326    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2327    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2328      <organization>Xerox Palo Alto Research Center</organization>
2329      <address><email>masinter@parc.xerox.com</email></address>
2330    </author>
2331    <date year="1998" month="August"/>
2332  </front>
2333  <seriesInfo name="RFC" value="2388"/>
2334</reference>
2335
2336<reference anchor="RFC2557">
2337  <front>
2338    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2339    <author initials="F." surname="Palme" fullname="Jacob Palme">
2340      <organization>Stockholm University and KTH</organization>
2341      <address><email>jpalme@dsv.su.se</email></address>
2342    </author>
2343    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2344      <organization>Microsoft Corporation</organization>
2345      <address><email>alexhop@microsoft.com</email></address>
2346    </author>
2347    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2348      <organization>Lotus Development Corporation</organization>
2349      <address><email>Shelness@lotus.com</email></address>
2350    </author>
2351    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2352      <address><email>stef@nma.com</email></address>
2353    </author>
2354    <date year="1999" month="March"/>
2355  </front>
2356  <seriesInfo name="RFC" value="2557"/>
2357</reference>
2358
2359<reference anchor="RFC2616">
2360  <front>
2361    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2362    <author initials="R." surname="Fielding" fullname="R. Fielding">
2363      <organization>University of California, Irvine</organization>
2364      <address><email>fielding@ics.uci.edu</email></address>
2365    </author>
2366    <author initials="J." surname="Gettys" fullname="J. Gettys">
2367      <organization>W3C</organization>
2368      <address><email>jg@w3.org</email></address>
2369    </author>
2370    <author initials="J." surname="Mogul" fullname="J. Mogul">
2371      <organization>Compaq Computer Corporation</organization>
2372      <address><email>mogul@wrl.dec.com</email></address>
2373    </author>
2374    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2375      <organization>MIT Laboratory for Computer Science</organization>
2376      <address><email>frystyk@w3.org</email></address>
2377    </author>
2378    <author initials="L." surname="Masinter" fullname="L. Masinter">
2379      <organization>Xerox Corporation</organization>
2380      <address><email>masinter@parc.xerox.com</email></address>
2381    </author>
2382    <author initials="P." surname="Leach" fullname="P. Leach">
2383      <organization>Microsoft Corporation</organization>
2384      <address><email>paulle@microsoft.com</email></address>
2385    </author>
2386    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2387      <organization>W3C</organization>
2388      <address><email>timbl@w3.org</email></address>
2389    </author>
2390    <date month="June" year="1999"/>
2391  </front>
2392  <seriesInfo name="RFC" value="2616"/>
2393</reference>
2394
2395<reference anchor="RFC3629">
2396  <front>
2397    <title>UTF-8, a transformation format of ISO 10646</title>
2398    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2399      <organization>Alis Technologies</organization>
2400      <address><email>fyergeau@alis.com</email></address>
2401    </author>
2402    <date month="November" year="2003"/>
2403  </front>
2404  <seriesInfo name="STD" value="63"/>
2405  <seriesInfo name="RFC" value="3629"/>
2406</reference>
2407
2408<reference anchor='RFC3864'>
2409  <front>
2410    <title>Registration Procedures for Message Header Fields</title>
2411    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2412      <organization>Nine by Nine</organization>
2413      <address><email>GK-IETF@ninebynine.org</email></address>
2414    </author>
2415    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2416      <organization>BEA Systems</organization>
2417      <address><email>mnot@pobox.com</email></address>
2418    </author>
2419    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2420      <organization>HP Labs</organization>
2421      <address><email>JeffMogul@acm.org</email></address>
2422    </author>
2423    <date year='2004' month='September' />
2424  </front>
2425  <seriesInfo name='BCP' value='90' />
2426  <seriesInfo name='RFC' value='3864' />
2427</reference>
2428
2429<reference anchor="RFC4288">
2430  <front>
2431    <title>Media Type Specifications and Registration Procedures</title>
2432    <author initials="N." surname="Freed" fullname="N. Freed">
2433      <organization>Sun Microsystems</organization>
2434      <address>
2435        <email>ned.freed@mrochek.com</email>
2436      </address>
2437    </author>
2438    <author initials="J." surname="Klensin" fullname="J. Klensin">
2439      <address>
2440        <email>klensin+ietf@jck.com</email>
2441      </address>
2442    </author>
2443    <date year="2005" month="December"/>
2444  </front>
2445  <seriesInfo name="BCP" value="13"/>
2446  <seriesInfo name="RFC" value="4288"/>
2447</reference>
2448
2449<reference anchor='RFC5226'>
2450  <front>
2451    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2452    <author initials='T.' surname='Narten' fullname='T. Narten'>
2453      <organization>IBM</organization>
2454      <address><email>narten@us.ibm.com</email></address>
2455    </author>
2456    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2457      <organization>Google</organization>
2458      <address><email>Harald@Alvestrand.no</email></address>
2459    </author>
2460    <date year='2008' month='May' />
2461  </front>
2462  <seriesInfo name='BCP' value='26' />
2463  <seriesInfo name='RFC' value='5226' />
2464</reference>
2465
2466<reference anchor="RFC5322">
2467  <front>
2468    <title>Internet Message Format</title>
2469    <author initials="P." surname="Resnick" fullname="P. Resnick">
2470      <organization>Qualcomm Incorporated</organization>
2471    </author>
2472    <date year="2008" month="October"/>
2473  </front> 
2474  <seriesInfo name="RFC" value="5322"/>
2475</reference>
2476
2477<reference anchor='BCP97'>
2478  <front>
2479    <title>Handling Normative References to Standards-Track Documents</title>
2480    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2481      <address>
2482        <email>klensin+ietf@jck.com</email>
2483      </address>
2484    </author>
2485    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2486      <organization>MIT</organization>
2487      <address>
2488        <email>hartmans-ietf@mit.edu</email>
2489      </address>
2490    </author>
2491    <date year='2007' month='June' />
2492  </front>
2493  <seriesInfo name='BCP' value='97' />
2494  <seriesInfo name='RFC' value='4897' />
2495</reference>
2496
2497
2498</references>
2499
2500<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2501<t>
2502   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
2503   allow a message-body to be transmitted in an open variety of
2504   representations and with extensible mechanisms. However, RFC 2045
2505   discusses mail, and HTTP has a few features that are different from
2506   those described in MIME. These differences were carefully chosen
2507   to optimize performance over binary connections, to allow greater
2508   freedom in the use of new media types, to make date comparisons
2509   easier, and to acknowledge the practice of some early HTTP servers
2510   and clients.
2511</t>
2512<t>
2513   This appendix describes specific areas where HTTP differs from MIME.
2514   Proxies and gateways to strict MIME environments &SHOULD; be
2515   aware of these differences and provide the appropriate conversions
2516   where necessary. Proxies and gateways from MIME environments to HTTP
2517   also need to be aware of the differences because some conversions
2518   might be required.
2519</t>
2520
2521<section title="MIME-Version" anchor="mime-version">
2522  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2523  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
2524  <x:anchor-alias value="MIME-Version"/>
2525  <x:anchor-alias value="MIME-Version-v"/>
2526<t>
2527   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2528   include a single MIME-Version general-header field to indicate what
2529   version of the MIME protocol was used to construct the message. Use
2530   of the MIME-Version header field indicates that the message is in
2531   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2532   Proxies/gateways are responsible for ensuring full compliance (where
2533   possible) when exporting HTTP messages to strict MIME environments.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2536  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2537  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2538</artwork></figure>
2539<t>
2540   MIME version "1.0" is the default for use in HTTP/1.1. However,
2541   HTTP/1.1 message parsing and semantics are defined by this document
2542   and not the MIME specification.
2543</t>
2544</section>
2545
2546<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2547<t>
2548   MIME requires that an Internet mail body-part be converted to
2549   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2550   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2551   allowed for subtypes of the "text" media type when transmitted over
2552   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2553   line breaks as CRLF and forbids the use of CR or LF outside of line
2554   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2555   line break within text content when a message is transmitted over
2556   HTTP.
2557</t>
2558<t>
2559   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2560   environment &SHOULD; translate all line breaks within the text media
2561   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2562   canonical form of CRLF. Note, however, that this might be complicated
2563   by the presence of a Content-Encoding and by the fact that HTTP
2564   allows the use of some character sets which do not use octets 13 and
2565   10 to represent CR and LF, as is the case for some multi-byte
2566   character sets.
2567</t>
2568<t>
2569   Conversion will break any cryptographic
2570   checksums applied to the original content unless the original content
2571   is already in canonical form. Therefore, the canonical form is
2572   recommended for any content that uses such checksums in HTTP.
2573</t>
2574</section>
2575
2576
2577<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2578<t>
2579   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2580   simplify the process of date comparison. Proxies and gateways from
2581   other protocols &SHOULD; ensure that any Date header field present in a
2582   message conforms to one of the HTTP/1.1 formats and rewrite the date
2583   if necessary.
2584</t>
2585</section>
2586
2587<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2588<t>
2589   MIME does not include any concept equivalent to HTTP/1.1's
2590   Content-Encoding header field. Since this acts as a modifier on the
2591   media type, proxies and gateways from HTTP to MIME-compliant
2592   protocols &MUST; either change the value of the Content-Type header
2593   field or decode the representation before forwarding the message. (Some
2594   experimental applications of Content-Type for Internet mail have used
2595   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2596   a function equivalent to Content-Encoding. However, this parameter is
2597   not part of the MIME standards).
2598</t>
2599</section>
2600
2601<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2602<t>
2603   HTTP does not use the Content-Transfer-Encoding field of MIME.
2604   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2605   remove any Content-Transfer-Encoding
2606   prior to delivering the response message to an HTTP client.
2607</t>
2608<t>
2609   Proxies and gateways from HTTP to MIME-compliant protocols are
2610   responsible for ensuring that the message is in the correct format
2611   and encoding for safe transport on that protocol, where "safe
2612   transport" is defined by the limitations of the protocol being used.
2613   Such a proxy or gateway &SHOULD; label the data with an appropriate
2614   Content-Transfer-Encoding if doing so will improve the likelihood of
2615   safe transport over the destination protocol.
2616</t>
2617</section>
2618
2619<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2620<t>
2621   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2622   Proxies/gateways &MUST; remove any transfer-coding prior to
2623   forwarding a message via a MIME-compliant protocol.
2624</t>
2625</section>
2626
2627<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2628<t>
2629   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2630   need to be aware of MIME line length limitations. Since HTTP does not
2631   have this limitation, HTTP does not fold long lines. MHTML messages
2632   being transported by HTTP follow all conventions of MHTML, including
2633   line length limitations and folding, canonicalization, etc., since
2634   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2635   does not interpret the content or any MIME header lines that might be
2636   contained therein.
2637</t>
2638</section>
2639</section>
2640
2641<section title="Additional Features" anchor="additional.features">
2642<t>
2643   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2644   existing HTTP implementations, but not consistently and correctly
2645   across most HTTP/1.1 applications. Implementors are advised to be
2646   aware of these features, but cannot rely upon their presence in, or
2647   interoperability with, other HTTP/1.1 applications. Some of these
2648   describe proposed experimental features, and some describe features
2649   that experimental deployment found lacking that are now addressed in
2650   the base HTTP/1.1 specification.
2651</t>
2652<t>
2653   A number of other header fields, such as Content-Disposition and Title,
2654   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2655</t>
2656</section>
2657
2658<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2659<t>
2660  Clarify contexts that charset is used in.
2661  (<xref target="character.sets"/>)
2662</t>
2663<t>
2664  Remove base URI setting semantics for Content-Location due to poor
2665  implementation support, which was caused by too many broken servers emitting
2666  bogus Content-Location header fields, and also the potentially undesirable effect
2667  of potentially breaking relative links in content-negotiated resources.
2668  (<xref target="header.content-location"/>)
2669</t>
2670<t>
2671  Remove reference to non-existant identity transfer-coding value tokens.
2672  (<xref target="no.content-transfer-encoding"/>)
2673</t>
2674</section>
2675
2676<?BEGININC p3-payload.abnf-appendix ?>
2677<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2678<figure>
2679<artwork type="abnf" name="p3-payload.parsed-abnf">
2680<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2681<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2682<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2683 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2684 qvalue ] ] )
2685<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2686<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2687 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2688<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2689<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2690 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2691 ] )
2692<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2693 OWS media-range [ accept-params ] ] ) ]
2694
2695<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2696<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2697 content-coding ] )
2698<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2699<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2700 language-tag ] )
2701<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2702<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2703<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2704<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2705<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2706<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2707<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2708<x:ref>Content-Type-v</x:ref> = media-type
2709
2710<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2711
2712<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2713
2714<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2715<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2716
2717<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2718
2719<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2720<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2721<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2722<x:ref>attribute</x:ref> = token
2723
2724<x:ref>charset</x:ref> = token
2725<x:ref>codings</x:ref> = ( content-coding / "*" )
2726<x:ref>content-coding</x:ref> = token
2727
2728<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2729<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2730
2731<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2732 ";" OWS parameter )
2733<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2734
2735<x:ref>parameter</x:ref> = attribute "=" value
2736<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2737
2738<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2739
2740<x:ref>subtype</x:ref> = token
2741
2742<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2743<x:ref>type</x:ref> = token
2744
2745<x:ref>value</x:ref> = word
2746
2747<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2748</artwork>
2749</figure>
2750<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2751; Accept defined but not used
2752; Accept-Charset defined but not used
2753; Accept-Encoding defined but not used
2754; Accept-Language defined but not used
2755; Content-Encoding defined but not used
2756; Content-Language defined but not used
2757; Content-Length defined but not used
2758; Content-Location defined but not used
2759; Content-MD5 defined but not used
2760; Content-Range defined but not used
2761; Content-Type defined but not used
2762; Expires defined but not used
2763; Last-Modified defined but not used
2764; MIME-Version defined but not used
2765</artwork></figure></section>
2766<?ENDINC p3-payload.abnf-appendix ?>
2767
2768<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2769
2770<section title="Since RFC 2616">
2771<t>
2772  Extracted relevant partitions from <xref target="RFC2616"/>.
2773</t>
2774</section>
2775
2776<section title="Since draft-ietf-httpbis-p3-payload-00">
2777<t>
2778  Closed issues:
2779  <list style="symbols"> 
2780    <t>
2781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2782      "Media Type Registrations"
2783      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2784    </t>
2785    <t>
2786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2787      "Clarification regarding quoting of charset values"
2788      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2789    </t>
2790    <t>
2791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2792      "Remove 'identity' token references"
2793      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2794    </t>
2795    <t>
2796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2797      "Accept-Encoding BNF"
2798    </t>
2799    <t>
2800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2801      "Normative and Informative references"
2802    </t>
2803    <t>
2804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2805      "RFC1700 references"
2806    </t>
2807    <t>
2808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2809      "Updating to RFC4288"
2810    </t>
2811    <t>
2812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2813      "Informative references"
2814    </t>
2815    <t>
2816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2817      "ISO-8859-1 Reference"
2818    </t>
2819    <t>
2820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2821      "Encoding References Normative"
2822    </t>
2823    <t>
2824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2825      "Normative up-to-date references"
2826    </t>
2827  </list>
2828</t>
2829</section>
2830
2831<section title="Since draft-ietf-httpbis-p3-payload-01">
2832<t>
2833  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2834  <list style="symbols"> 
2835    <t>
2836      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2837    </t>
2838  </list>
2839</t>
2840</section>
2841
2842<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2843<t>
2844  Closed issues:
2845  <list style="symbols"> 
2846    <t>
2847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2848      "Quoting Charsets"
2849    </t>
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2852      "Classification for Allow header"
2853    </t>
2854    <t>
2855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2856      "missing default for qvalue in description of Accept-Encoding"
2857    </t>
2858  </list>
2859</t>
2860<t>
2861  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2862  <list style="symbols"> 
2863    <t>
2864      Reference RFC 3984, and update header field registrations for headers defined
2865      in this document.
2866    </t>
2867  </list>
2868</t>
2869</section>
2870
2871<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2872<t>
2873  Closed issues:
2874  <list style="symbols"> 
2875    <t>
2876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2877      "Quoting Charsets"
2878    </t>
2879    <t>
2880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2881      "language tag matching (Accept-Language) vs RFC4647"
2882    </t>
2883    <t>
2884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2885      "RFC 1806 has been replaced by RFC2183"
2886    </t>
2887  </list>
2888</t>
2889<t>
2890  Other changes:
2891  <list style="symbols"> 
2892    <t>
2893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2894      "Encoding References Normative" &mdash; rephrase the annotation and reference
2895      <xref target="BCP97"/>.
2896    </t>
2897  </list>
2898</t>
2899 </section>
2900
2901<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2902<t>
2903  Closed issues:
2904  <list style="symbols"> 
2905    <t>
2906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2907      "RFC 2822 is updated by RFC 5322"
2908    </t>
2909  </list>
2910</t>
2911<t>
2912  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2913  <list style="symbols"> 
2914    <t>
2915      Use "/" instead of "|" for alternatives.
2916    </t>
2917    <t>
2918      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2919      whitespace ("OWS") and required whitespace ("RWS").
2920    </t>
2921    <t>
2922      Rewrite ABNFs to spell out whitespace rules, factor out
2923      header field value format definitions.
2924    </t>
2925  </list>
2926</t>
2927</section>
2928
2929<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2930<t>
2931  Closed issues:
2932  <list style="symbols"> 
2933    <t>
2934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2935      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2936    </t>
2937  </list>
2938</t>
2939<t>
2940  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2941  <list style="symbols"> 
2942    <t>
2943      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2944    </t>
2945  </list>
2946</t>
2947<t>
2948  Other changes:
2949  <list style="symbols"> 
2950    <t>
2951      Move definition of quality values into Part 1.
2952    </t>
2953  </list>
2954</t>
2955</section>
2956
2957<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2958<t>
2959  Closed issues:
2960  <list style="symbols"> 
2961    <t>
2962      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2963      "Content-Location isn't special"
2964    </t>
2965    <t>
2966      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2967      "Content Sniffing"
2968    </t>
2969  </list>
2970</t>
2971</section>
2972
2973<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2974<t>
2975  Closed issues:
2976  <list style="symbols"> 
2977    <t>
2978      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2979      "Updated reference for language tags"
2980    </t>
2981    <t>
2982      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2983      "Clarify rules for determining what entities a response carries"
2984    </t>
2985    <t>
2986      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2987      "Content-Location base-setting problems"
2988    </t>
2989    <t>
2990      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2991      "Content Sniffing"
2992    </t>
2993    <t>
2994      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2995      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2996    </t>
2997    <t>
2998      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2999      "move definitions of gzip/deflate/compress to part 1"
3000    </t>
3001  </list>
3002</t>
3003<t>
3004  Partly resolved issues:
3005  <list style="symbols"> 
3006    <t>
3007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3008      "update IANA requirements wrt Transfer-Coding values" (add the
3009      IANA Considerations subsection)
3010    </t>
3011    <t>
3012      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3013      "update IANA requirements wrt Content-Coding values" (add the
3014      IANA Considerations subsection)
3015    </t>
3016  </list>
3017</t>
3018</section>
3019
3020<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3021<t>
3022  Closed issues:
3023  <list style="symbols"> 
3024    <t>
3025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3026      "Content Negotiation for media types"
3027    </t>
3028    <t>
3029      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3030      "Accept-Language: which RFC4647 filtering?"
3031    </t>
3032  </list>
3033</t>
3034</section>
3035
3036<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3037<t>
3038  Closed issues:
3039  <list style="symbols"> 
3040    <t>
3041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
3042      "MIME-Version not listed in P1, general header fields"
3043    </t>
3044    <t>
3045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3046      "IANA registry for content/transfer encodings"
3047    </t>
3048    <t>
3049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3050      "Content Sniffing"
3051    </t>
3052    <t>
3053      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3054      "use of term "word" when talking about header structure"
3055    </t>
3056  </list>
3057</t>
3058<t>
3059  Partly resolved issues:
3060  <list style="symbols"> 
3061    <t>
3062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3063      "Term for the requested resource's URI"
3064    </t>
3065  </list>
3066</t>
3067</section>
3068
3069<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
3070<t>
3071  Closed issues:
3072  <list style="symbols"> 
3073    <t>
3074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3075      "Clarify 'Requested Variant'"
3076    </t>
3077    <t>
3078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3079      "Content-Location isn't special"
3080    </t>
3081    <t>
3082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3083      "Delimiting messages with multipart/byteranges"
3084    </t>
3085    <t>
3086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3087      "Clarify entity / representation / variant terminology"
3088    </t>
3089    <t>
3090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3091      "confusing req. language for Content-Location"
3092    </t>
3093    <t>
3094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3095      "Content-Location on 304 responses"
3096    </t>
3097    <t>
3098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
3099      "'requested resource' in content-encoding definition"
3100    </t>
3101    <t>
3102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3103      "consider removing the 'changes from 2068' sections"
3104    </t>
3105  </list>
3106</t>
3107<t>
3108  Partly resolved issues:
3109  <list style="symbols"> 
3110    <t>
3111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3112      "Content-MD5 and partial responses"
3113    </t>
3114  </list>
3115</t>
3116</section>
3117
3118<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3119<t>
3120  Closed issues:
3121  <list style="symbols"> 
3122    <t>
3123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3124      "Factor out Content-Disposition"
3125    </t>
3126  </list>
3127</t>
3128</section>
3129
3130<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3131<t>
3132  Closed issues:
3133  <list style="symbols"> 
3134    <t>
3135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
3136      "potentially misleading MAY in media-type def"
3137    </t>
3138  </list>
3139</t>
3140</section>
3141
3142</section>
3143
3144</back>
3145</rfc>
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