source: draft-ietf-httpbis/latest/p3-payload.xml @ 814

Last change on this file since 814 was 814, checked in by julian.reschke@…, 10 years ago

latest version of rfc2629.xslt, bump up document dates

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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 "May">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!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="Day Software">Day Software</organization>
63    <address>
64      <postal>
65        <street>23 Corporate Plaza DR, Suite 280</street>
66        <city>Newport Beach</city>
67        <region>CA</region>
68        <code>92660</code>
69        <country>USA</country>
70      </postal>
71      <phone>+1-949-706-5300</phone>
72      <facsimile>+1-949-706-5305</facsimile>
73      <email>fielding@gbiv.com</email>
74      <uri>http://roy.gbiv.com/</uri>
75    </address>
76  </author>
77
78  <author initials="J." surname="Gettys" fullname="Jim Gettys">
79    <organization>One Laptop per Child</organization>
80    <address>
81      <postal>
82        <street>21 Oak Knoll Road</street>
83        <city>Carlisle</city>
84        <region>MA</region>
85        <code>01741</code>
86        <country>USA</country>
87      </postal>
88      <email>jg@laptop.org</email>
89      <uri>http://www.laptop.org/</uri>
90    </address>
91  </author>
92 
93  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
94    <organization abbrev="HP">Hewlett-Packard Company</organization>
95    <address>
96      <postal>
97        <street>HP Labs, Large Scale Systems Group</street>
98        <street>1501 Page Mill Road, MS 1177</street>
99        <city>Palo Alto</city>
100        <region>CA</region>
101        <code>94304</code>
102        <country>USA</country>
103      </postal>
104      <email>JeffMogul@acm.org</email>
105    </address>
106  </author>
107
108  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
109    <organization abbrev="Microsoft">Microsoft Corporation</organization>
110    <address>
111      <postal>
112        <street>1 Microsoft Way</street>
113        <city>Redmond</city>
114        <region>WA</region>
115        <code>98052</code>
116        <country>USA</country>
117      </postal>
118      <email>henrikn@microsoft.com</email>
119    </address>
120  </author>
121
122  <author initials="L." surname="Masinter" fullname="Larry Masinter">
123    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
124    <address>
125      <postal>
126        <street>345 Park Ave</street>
127        <city>San Jose</city>
128        <region>CA</region>
129        <code>95110</code>
130        <country>USA</country>
131      </postal>
132      <email>LMM@acm.org</email>
133      <uri>http://larry.masinter.net/</uri>
134    </address>
135  </author>
136 
137  <author initials="P." surname="Leach" fullname="Paul J. Leach">
138    <organization abbrev="Microsoft">Microsoft Corporation</organization>
139    <address>
140      <postal>
141        <street>1 Microsoft Way</street>
142        <city>Redmond</city>
143        <region>WA</region>
144        <code>98052</code>
145      </postal>
146      <email>paulle@microsoft.com</email>
147    </address>
148  </author>
149   
150  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
151    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
152    <address>
153      <postal>
154        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
155        <street>The Stata Center, Building 32</street>
156        <street>32 Vassar Street</street>
157        <city>Cambridge</city>
158        <region>MA</region>
159        <code>02139</code>
160        <country>USA</country>
161      </postal>
162      <email>timbl@w3.org</email>
163      <uri>http://www.w3.org/People/Berners-Lee/</uri>
164    </address>
165  </author>
166
167  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
168    <organization abbrev="W3C">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>W3C / ERCIM</street>
172        <street>2004, rte des Lucioles</street>
173        <city>Sophia-Antipolis</city>
174        <region>AM</region>
175        <code>06902</code>
176        <country>France</country>
177      </postal>
178      <email>ylafon@w3.org</email>
179      <uri>http://www.raubacapeu.net/people/yves/</uri>
180    </address>
181  </author>
182
183  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
184    <organization abbrev="greenbytes">greenbytes GmbH</organization>
185    <address>
186      <postal>
187        <street>Hafenweg 16</street>
188        <city>Muenster</city><region>NW</region><code>48155</code>
189        <country>Germany</country>
190      </postal>
191      <phone>+49 251 2807760</phone>
192      <facsimile>+49 251 2807761</facsimile>
193      <email>julian.reschke@greenbytes.de</email>
194      <uri>http://greenbytes.de/tech/webdav/</uri>
195    </address>
196  </author>
197
198  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
199  <workgroup>HTTPbis Working Group</workgroup>
200
201<abstract>
202<t>
203   The Hypertext Transfer Protocol (HTTP) is an application-level
204   protocol for distributed, collaborative, hypermedia information
205   systems. HTTP has been in use by the World Wide Web global information
206   initiative since 1990. This document is Part 3 of the seven-part specification
207   that defines the protocol referred to as "HTTP/1.1" and, taken together,
208   obsoletes RFC 2616.  Part 3 defines HTTP message content,
209   metadata, and content negotiation.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.09"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   This document defines HTTP/1.1 message payloads (a.k.a., content), the
230   associated metadata header fields that define how the payload is intended
231   to be interpreted by a recipient, the request header fields that
232   may influence content selection, and the various selection algorithms
233   that are collectively referred to as HTTP content negotiation.
234</t>
235<t>
236   This document is currently disorganized in order to minimize the changes
237   between drafts and enable reviewers to see the smaller errata changes.
238   The next draft will reorganize the sections to better reflect the content.
239   In particular, the sections on entities will be renamed payload and moved
240   to the first half of the document, while the sections on content negotiation
241   and associated request header fields will be moved to the second half.  The
242   current mess reflects how widely dispersed these topics and associated
243   requirements had become in <xref target="RFC2616"/>.
244</t>
245
246<section title="Terminology" anchor="terminology">
247<t>
248   This specification uses a number of terms to refer to the roles
249   played by participants in, and objects of, the HTTP communication.
250</t>
251<t>
252  <iref item="content negotiation"/>
253  <x:dfn>content negotiation</x:dfn>
254  <list>
255    <t>
256      The mechanism for selecting the appropriate representation when
257      servicing a request. The representation of entities in any response
258      can be negotiated (including error responses).
259    </t>
260  </list>
261</t>
262<t>
263  <iref item="entity"/>
264  <x:dfn>entity</x:dfn>
265  <list>
266    <t>
267      The information transferred as the payload of a request or
268      response. An entity consists of metadata in the form of
269      entity-header fields and content in the form of an entity-body.
270    </t>
271  </list>
272</t>
273<t>
274  <iref item="representation"/>
275  <x:dfn>representation</x:dfn>
276  <list>
277    <t>
278      An entity included with a response that is subject to content
279      negotiation. There may exist multiple
280      representations associated with a particular response status.
281    </t>
282  </list>
283</t>
284<t>
285  <iref item="variant"/>
286  <x:dfn>variant</x:dfn>
287  <list>
288    <t>
289      A resource may have one, or more than one, representation(s)
290      associated with it at any given instant. Each of these
291      representations is termed a "variant".  Use of the term "variant"
292      does not necessarily imply that the resource is subject to content
293      negotiation.
294    </t>
295  </list>
296</t>
297</section>
298
299<section title="Requirements" anchor="intro.requirements">
300<t>
301   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
302   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
303   document are to be interpreted as described in <xref target="RFC2119"/>.
304</t>
305<t>
306   An implementation is not compliant if it fails to satisfy one or more
307   of the &MUST; or &REQUIRED; level requirements for the protocols it
308   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
309   level and all the &SHOULD; level requirements for its protocols is said
310   to be "unconditionally compliant"; one that satisfies all the &MUST;
311   level requirements but not all the &SHOULD; level requirements for its
312   protocols is said to be "conditionally compliant."
313</t>
314</section>
315
316<section title="Syntax Notation" anchor="notation">
317  <x:anchor-alias value="ALPHA"/>
318  <x:anchor-alias value="CR"/>
319  <x:anchor-alias value="DIGIT"/>
320  <x:anchor-alias value="LF"/>
321  <x:anchor-alias value="OCTET"/>
322  <x:anchor-alias value="VCHAR"/>
323  <x:anchor-alias value="WSP"/>
324<t>
325  This specification uses the ABNF syntax defined in &notation; (which
326  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
327  <xref target="collected.abnf"/> shows the collected ABNF, with the list
328  rule expanded.
329</t>
330<t>
331  The following core rules are included by
332  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334  DIGIT (decimal 0-9), DQUOTE (double quote),
335  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336  OCTET (any 8-bit sequence of data), SP (space),
337  VCHAR (any visible USASCII character),
338  and WSP (whitespace).
339</t>
340
341<section title="Core Rules" anchor="core.rules">
342  <x:anchor-alias value="quoted-string"/>
343  <x:anchor-alias value="token"/>
344  <x:anchor-alias value="word"/>
345  <x:anchor-alias value="OWS"/>
346<t>
347  The core rules below are defined in &basic-rules;:
348</t>
349<figure><artwork type="abnf2616">
350  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
351  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
352  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
353  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
354</artwork></figure>
355</section>
356
357<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
358  <x:anchor-alias value="absolute-URI"/>
359  <x:anchor-alias value="Allow"/>
360  <x:anchor-alias value="Content-Length"/>
361  <x:anchor-alias value="Content-Range"/>
362  <x:anchor-alias value="Expires"/>
363  <x:anchor-alias value="Last-Modified"/>
364  <x:anchor-alias value="header-field"/>
365  <x:anchor-alias value="partial-URI"/>
366  <x:anchor-alias value="qvalue"/>
367<t>
368  The ABNF rules below are defined in other parts:
369</t>
370<figure><!--Part1--><artwork type="abnf2616">
371  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
372  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
373  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
374  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
375  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
376</artwork></figure>
377<figure><!--Part4--><artwork type="abnf2616">
378  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
379</artwork></figure>
380<figure><!--Part5--><artwork type="abnf2616">
381  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
382</artwork></figure>
383<figure><!--Part6--><artwork type="abnf2616">
384  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
385</artwork></figure>
386</section>
387
388</section>
389
390</section>
391
392<section title="Protocol Parameters" anchor="protocol.parameters">
393
394<section title="Character Sets" anchor="character.sets">
395<t>
396   HTTP uses the same definition of the term "character set" as that
397   described for MIME:
398</t>
399<t>
400   The term "character set" is used in this document to refer to a
401   method used with one or more tables to convert a sequence of octets
402   into a sequence of characters. Note that unconditional conversion in
403   the other direction is not required, in that not all characters may
404   be available in a given character set and a character set may provide
405   more than one sequence of octets to represent a particular character.
406   This definition is intended to allow various kinds of character
407   encoding, from simple single-table mappings such as US-ASCII to
408   complex table switching methods such as those that use ISO-2022's
409   techniques. However, the definition associated with a MIME character
410   set name &MUST; fully specify the mapping to be performed from octets
411   to characters. In particular, use of external profiling information
412   to determine the exact mapping is not permitted.
413</t>
414<x:note>
415  <t>
416    <x:h>Note:</x:h> This use of the term "character set" is more commonly
417    referred to as a "character encoding." However, since HTTP and
418    MIME share the same registry, it is important that the terminology
419    also be shared.
420  </t>
421</x:note>
422<t anchor="rule.charset">
423  <x:anchor-alias value="charset"/>
424   HTTP character sets are identified by case-insensitive tokens. The
425   complete set of tokens is defined by the IANA Character Set registry
426   (<eref target="http://www.iana.org/assignments/character-sets"/>).
427</t>
428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
429  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
430</artwork></figure>
431<t>
432   Although HTTP allows an arbitrary token to be used as a charset
433   value, any token that has a predefined value within the IANA
434   Character Set registry &MUST; represent the character set defined
435   by that registry. Applications &SHOULD; limit their use of character
436   sets to those defined by the IANA registry.
437</t>
438<t>
439   HTTP uses charset in two contexts: within an Accept-Charset request
440   header (in which the charset value is an unquoted token) and as the
441   value of a parameter in a Content-Type header (within a request or
442   response), in which case the parameter value of the charset parameter
443   may be quoted.
444</t>
445<t>
446   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
447   <xref target="RFC2277"/>.
448</t>
449
450<section title="Missing Charset" anchor="missing.charset">
451<t>
452   Some HTTP/1.0 software has interpreted a Content-Type header without
453   charset parameter incorrectly to mean "recipient should guess."
454   Senders wishing to defeat this behavior &MAY; include a charset
455   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
456   it is known that it will not confuse the recipient.
457</t>
458<t>
459   Unfortunately, some older HTTP/1.0 clients did not deal properly with
460   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
461   charset label provided by the sender; and those user agents that have
462   a provision to "guess" a charset &MUST; use the charset from the
463   content-type field if they support that charset, rather than the
464   recipient's preference, when initially displaying a document. See
465   <xref target="canonicalization.and.text.defaults"/>.
466</t>
467</section>
468</section>
469
470<section title="Content Codings" anchor="content.codings">
471  <x:anchor-alias value="content-coding"/>
472<t>
473   Content coding values indicate an encoding transformation that has
474   been or can be applied to an entity. Content codings are primarily
475   used to allow a document to be compressed or otherwise usefully
476   transformed without losing the identity of its underlying media type
477   and without loss of information. Frequently, the entity is stored in
478   coded form, transmitted directly, and only decoded by the recipient.
479</t>
480<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
481  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
482</artwork></figure>
483<t>
484   All content-coding values are case-insensitive. HTTP/1.1 uses
485   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
486   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
487   describes the content-coding, what is more important is that it
488   indicates what decoding mechanism will be required to remove the
489   encoding.
490</t>
491<t>
492   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
493  <list>
494    <t>
495      See &compress-coding;.
496    </t>
497  </list>
498</t>
499<t>
500   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
501  <list>
502    <t>
503      See &deflate-coding;.
504    </t>
505  </list>
506</t>
507<t>
508   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
509  <list>
510    <t>
511      See &gzip-coding;.
512    </t>
513  </list>
514</t>
515<t>
516   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
517  <list><t>
518        The default (identity) encoding; the use of no transformation
519        whatsoever. This content-coding is used only in the Accept-Encoding
520        header, and &SHOULD-NOT;  be used in the Content-Encoding
521        header.
522  </t></list>
523</t>
524
525<section title="Content Coding Registry" anchor="content.coding.registry">
526<t>
527   The HTTP Content Coding Registry defines the name space for the content
528   coding names.
529</t>
530<t>
531   Registrations &MUST; include the following fields:
532   <list style="symbols">
533     <t>Name</t>
534     <t>Description</t>
535     <t>Pointer to specification text</t>
536   </list>
537</t>
538<t>
539   Names of content codings &MUST-NOT; overlap with names of transfer codings
540   (&transfer-codings;), unless the encoding transformation is identical (as it
541   is the case for the compression codings defined in
542   &compression-codings;).
543</t>
544<t>
545   Values to be added to this name space require expert review and a specification
546   (see "Expert Review" and "Specification Required" in
547   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
548   conform to the purpose of content coding defined in this section.
549</t>
550<t>
551   The registry itself is maintained at
552   <eref target="http://www.iana.org/assignments/http-parameters"/>.
553</t>
554</section>
555
556</section>
557
558<section title="Media Types" anchor="media.types">
559  <x:anchor-alias value="media-type"/>
560  <x:anchor-alias value="type"/>
561  <x:anchor-alias value="subtype"/>
562<t>
563   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
564   and Accept (<xref target="header.accept"/>) header fields in order to provide
565   open and extensible data typing and type negotiation.
566</t>
567<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"/>
568  <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> )
569  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
570  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
571</artwork></figure>
572<t anchor="rule.parameter">
573  <x:anchor-alias value="attribute"/>
574  <x:anchor-alias value="parameter"/>
575  <x:anchor-alias value="value"/>
576   Parameters &MAY; follow the type/subtype in the form of attribute/value
577   pairs.
578</t>
579<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"/>
580  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
581  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
582  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
583</artwork></figure>
584<t>
585   The type, subtype, and parameter attribute names are case-insensitive.
586   Parameter values might or might not be case-sensitive, depending on the
587   semantics of the parameter name.  The presence or absence of a parameter might
588   be significant to the processing of a media-type, depending on its
589   definition within the media type registry.
590</t>
591<t>
592   A parameter value that matches the <x:ref>token</x:ref> production may be
593   transmitted as either a token or within a quoted-string. The quoted and
594   unquoted values are equivalent.
595</t>
596<t>
597   Note that some older HTTP applications do not recognize media type
598   parameters. When sending data to older HTTP applications,
599   implementations &SHOULD; only use media type parameters when they are
600   required by that type/subtype definition.
601</t>
602<t>
603   Media-type values are registered with the Internet Assigned Number
604   Authority (IANA). The media type registration process is
605   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
606   discouraged.
607</t>
608
609<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
610<t>
611   Internet media types are registered with a canonical form. An
612   entity-body transferred via HTTP messages &MUST; be represented in the
613   appropriate canonical form prior to its transmission except for
614   "text" types, as defined in the next paragraph.
615</t>
616<t>
617   When in canonical form, media subtypes of the "text" type use CRLF as
618   the text line break. HTTP relaxes this requirement and allows the
619   transport of text media with plain CR or LF alone representing a line
620   break when it is done consistently for an entire entity-body. HTTP
621   applications &MUST; accept CRLF, bare CR, and bare LF as being
622   representative of a line break in text media received via HTTP. In
623   addition, if the text is represented in a character set that does not
624   use octets 13 and 10 for CR and LF respectively, as is the case for
625   some multi-byte character sets, HTTP allows the use of whatever octet
626   sequences are defined by that character set to represent the
627   equivalent of CR and LF for line breaks. This flexibility regarding
628   line breaks applies only to text media in the entity-body; a bare CR
629   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
630   structures (such as header fields and multipart boundaries).
631</t>
632<t>
633   If an entity-body is encoded with a content-coding, the underlying
634   data &MUST; be in a form defined above prior to being encoded.
635</t>
636<t>
637   The "charset" parameter is used with some media types to define the
638   character set (<xref target="character.sets"/>) of the data. When no explicit charset
639   parameter is provided by the sender, media subtypes of the "text"
640   type are defined to have a default charset value of "ISO-8859-1" when
641   received via HTTP. Data in character sets other than "ISO-8859-1" or
642   its subsets &MUST; be labeled with an appropriate charset value. See
643   <xref target="missing.charset"/> for compatibility problems.
644</t>
645</section>
646
647<section title="Multipart Types" anchor="multipart.types">
648<t>
649   MIME provides for a number of "multipart" types -- encapsulations of
650   one or more entities within a single message-body. All multipart
651   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
652   and &MUST; include a boundary parameter as part of the media type
653   value. The message body is itself a protocol element and &MUST;
654   therefore use only CRLF to represent line breaks between body-parts.
655   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
656   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
657   original multipart contains an epilogue). These restrictions exist in
658   order to preserve the self-delimiting nature of a multipart message-body,
659   wherein the "end" of the message-body is indicated by the
660   ending multipart boundary.
661</t>
662<t>
663   In general, HTTP treats a multipart message-body no differently than
664   any other media type: strictly as payload. The one exception is the
665   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
666   (Partial Content) response.
667   <!-- jre: re-insert removed text pointing to caching? -->
668   In all
669   other cases, an HTTP user agent &SHOULD; follow the same or similar
670   behavior as a MIME user agent would upon receipt of a multipart type.
671   The MIME header fields within each body-part of a multipart message-body
672   do not have any significance to HTTP beyond that defined by
673   their MIME semantics.
674</t>
675<t>
676   In general, an HTTP user agent &SHOULD; follow the same or similar
677   behavior as a MIME user agent would upon receipt of a multipart type.
678   If an application receives an unrecognized multipart subtype, the
679   application &MUST; treat it as being equivalent to "multipart/mixed".
680</t>
681<x:note>
682  <t>
683    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
684    for carrying form data suitable for processing via the POST
685    request method, as described in <xref target="RFC2388"/>.
686  </t>
687</x:note>
688</section>
689</section>
690
691<section title="Language Tags" anchor="language.tags">
692  <x:anchor-alias value="language-tag"/>
693<t>
694   A language tag, as defined in <xref target="RFC5646"/>, identifies a
695   natural language spoken, written, or otherwise conveyed by human beings for
696   communication of information to other human beings. Computer languages are
697   explicitly excluded. HTTP uses language tags within the Accept-Language and
698   Content-Language fields.
699</t>
700<t>
701   In summary, a language tag is composed of one or more parts: A primary
702   language subtag followed by a possibly empty series of subtags:
703</t>
704<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
705  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
706</artwork></figure>
707<t>
708   White space is not allowed within the tag and all tags are case-insensitive.
709   The name space of language subtags is administered by the IANA (see
710   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
711</t>
712<figure>
713  <preamble>Example tags include:</preamble>
714<artwork type="example">
715  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
716</artwork>
717</figure>
718<t>
719   See <xref target="RFC5646"/> for further information.
720</t>
721</section>
722</section>
723
724<section title="Entity" anchor="entity">
725<t>
726   Request and Response messages &MAY; transfer an entity if not otherwise
727   restricted by the request method or response status code. An entity
728   consists of entity-header fields and an entity-body, although some
729   responses will only include the entity-headers.
730</t>
731<t>
732   In this section, both sender and recipient refer to either the client
733   or the server, depending on who sends and who receives the entity.
734</t>
735
736<section title="Entity Header Fields" anchor="entity.header.fields">
737  <x:anchor-alias value="entity-header"/>
738  <x:anchor-alias value="extension-header"/>
739<t>
740   Entity-header fields define metainformation about the entity-body or,
741   if no body is present, about the resource identified by the request.
742</t>
743<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
744  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
745                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
746                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
747                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
748                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
749                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
750                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
751                 / <x:ref>Expires</x:ref>                  ; &header-expires;
752                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
753                 / <x:ref>extension-header</x:ref>
754 
755  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
756</artwork></figure>
757<t>
758   The extension-header mechanism allows additional entity-header fields
759   to be defined without changing the protocol, but these fields cannot
760   be assumed to be recognizable by the recipient. Unrecognized header
761   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
762   transparent proxies.
763</t>
764</section>
765
766<section title="Entity Body" anchor="entity.body">
767  <x:anchor-alias value="entity-body"/>
768<t>
769   The entity-body (if any) sent with an HTTP request or response is in
770   a format and encoding defined by the entity-header fields.
771</t>
772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
773  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
774</artwork></figure>
775<t>
776   An entity-body is only present in a message when a message-body is
777   present, as described in &message-body;. The entity-body is obtained
778   from the message-body by decoding any Transfer-Encoding that might
779   have been applied to ensure safe and proper transfer of the message.
780</t>
781
782<section title="Type" anchor="type">
783<t>
784   When an entity-body is included with a message, the data type of that
785   body is determined via the header fields Content-Type and Content-Encoding.
786   These define a two-layer, ordered encoding model:
787</t>
788<figure><artwork type="example">
789  entity-body := Content-Encoding( Content-Type( data ) )
790</artwork></figure>
791<t>
792   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
793   message containing an entity-body &SHOULD; include a Content-Type header
794   field defining the media type of that body, unless that information is
795   unknown.  If the Content-Type header field is not present, it indicates that
796   the sender does not know the media type of the data; recipients &MAY;
797   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
798   or examine the content to determine its type.
799</t>
800<t>
801   Content-Encoding may be used to indicate any additional content
802   codings applied to the data, usually for the purpose of data
803   compression, that are a property of the requested resource.  There is
804   no default encoding.
805</t>
806</section>
807   
808<section title="Entity Length" anchor="entity.length">
809<t>
810   The entity-length of a message is the length of the message-body
811   before any transfer-codings have been applied. &message-length; defines
812   how the transfer-length of a message-body is determined.
813</t>
814</section>
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" -- 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 may not be appropriate. Conversely,
853   when the number of representations to choose from is very large,
854   agent-driven negotiation may 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 may 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 entity-body of the initial response, with each
940   representation identified by its own URI. Selection from among the
941   representations may 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<t>
976   For entity-header fields, both sender and recipient refer to either the
977   client or the server, depending on who sends and who receives the entity.
978</t>
979
980<section title="Accept" anchor="header.accept">
981  <iref primary="true" item="Accept header" x:for-anchor=""/>
982  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
983  <x:anchor-alias value="Accept"/>
984  <x:anchor-alias value="Accept-v"/>
985  <x:anchor-alias value="accept-ext"/>
986  <x:anchor-alias value="accept-params"/>
987  <x:anchor-alias value="media-range"/>
988<t>
989   The "Accept" request-header field can be used by user agents to specify
990   response media types that are acceptable. Accept headers can be used to
991   indicate that the request is specifically limited to a small set of desired
992   types, as in the case of a request for an in-line image.
993</t>
994<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"/>
995  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
996  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
997 
998  <x:ref>media-range</x:ref>    = ( "*/*"
999                   / ( <x:ref>type</x:ref> "/" "*" )
1000                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
1001                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
1002  <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> )
1003  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
1004                   [ "=" <x:ref>word</x:ref> ]
1005</artwork></figure>
1006<t>
1007   The asterisk "*" character is used to group media types into ranges,
1008   with "*/*" indicating all media types and "type/*" indicating all
1009   subtypes of that type. The media-range &MAY; include media type
1010   parameters that are applicable to that range.
1011</t>
1012<t>
1013   Each media-range &MAY; be followed by one or more accept-params,
1014   beginning with the "q" parameter for indicating a relative quality
1015   factor. The first "q" parameter (if any) separates the media-range
1016   parameter(s) from the accept-params. Quality factors allow the user
1017   or user agent to indicate the relative degree of preference for that
1018   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1019   default value is q=1.
1020</t>
1021<x:note>
1022  <t>
1023    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1024    parameters from Accept extension parameters is due to historical
1025    practice. Although this prevents any media type parameter named
1026    "q" from being used with a media range, such an event is believed
1027    to be unlikely given the lack of any "q" parameters in the IANA
1028    media type registry and the rare usage of any media type
1029    parameters in Accept. Future media types are discouraged from
1030    registering any parameter named "q".
1031  </t>
1032</x:note>
1033<t>
1034   The example
1035</t>
1036<figure><artwork type="example">
1037  Accept: audio/*; q=0.2, audio/basic
1038</artwork></figure>
1039<t>
1040   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1041   type if it is the best available after an 80% mark-down in quality."
1042</t>
1043<t>
1044   If no Accept header field is present, then it is assumed that the
1045   client accepts all media types. If an Accept header field is present,
1046   and if the server cannot send a response which is acceptable
1047   according to the combined Accept field value, then the server &SHOULD;
1048   send a 406 (Not Acceptable) response.
1049</t>
1050<t>
1051   A more elaborate example is
1052</t>
1053<figure><artwork type="example">
1054  Accept: text/plain; q=0.5, text/html,
1055          text/x-dvi; q=0.8, text/x-c
1056</artwork></figure>
1057<t>
1058   Verbally, this would be interpreted as "text/html and text/x-c are
1059   the preferred media types, but if they do not exist, then send the
1060   text/x-dvi entity, and if that does not exist, send the text/plain
1061   entity."
1062</t>
1063<t>
1064   Media ranges can be overridden by more specific media ranges or
1065   specific media types. If more than one media range applies to a given
1066   type, the most specific reference has precedence. For example,
1067</t>
1068<figure><artwork type="example">
1069  Accept: text/*, text/html, text/html;level=1, */*
1070</artwork></figure>
1071<t>
1072   have the following precedence:
1073   <list style="numbers">
1074    <t>text/html;level=1</t>
1075    <t>text/html</t>
1076    <t>text/*</t>
1077    <t>*/*</t>
1078   </list>
1079</t>
1080<t>
1081   The media type quality factor associated with a given type is
1082   determined by finding the media range with the highest precedence
1083   which matches that type. For example,
1084</t>
1085<figure><artwork type="example">
1086  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1087          text/html;level=2;q=0.4, */*;q=0.5
1088</artwork></figure>
1089<t>
1090   would cause the following values to be associated:
1091</t>
1092<texttable align="left">
1093  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1094  <c>text/html;level=1</c>    <c>1</c>
1095  <c>text/html</c>            <c>0.7</c>
1096  <c>text/plain</c>           <c>0.3</c>
1097  <c>image/jpeg</c>           <c>0.5</c>
1098  <c>text/html;level=2</c>    <c>0.4</c>
1099  <c>text/html;level=3</c>    <c>0.7</c>
1100</texttable>
1101<t>
1102      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1103      values for certain media ranges. However, unless the user agent is
1104      a closed system which cannot interact with other rendering agents,
1105      this default set ought to be configurable by the user.
1106</t>
1107</section>
1108
1109<section title="Accept-Charset" anchor="header.accept-charset">
1110  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1111  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1112  <x:anchor-alias value="Accept-Charset"/>
1113  <x:anchor-alias value="Accept-Charset-v"/>
1114<t>
1115   The "Accept-Charset" request-header field can be used by user agents to
1116   indicate what response character sets are acceptable. This field allows
1117   clients capable of understanding more comprehensive or special-purpose
1118   character sets to signal that capability to a server which is capable of
1119   representing documents in those character sets.
1120</t>
1121<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1122  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1123          <x:ref>Accept-Charset-v</x:ref>
1124  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1125                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1126</artwork></figure>
1127<t>
1128   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1129   be given an associated quality value which represents the user's
1130   preference for that charset. The default value is q=1. An example is
1131</t>
1132<figure><artwork type="example">
1133  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1134</artwork></figure>
1135<t>
1136   The special value "*", if present in the Accept-Charset field,
1137   matches every character set (including ISO-8859-1) which is not
1138   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1139   in an Accept-Charset field, then all character sets not explicitly
1140   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1141   a quality value of 1 if not explicitly mentioned.
1142</t>
1143<t>
1144   If no Accept-Charset header is present, the default is that any
1145   character set is acceptable. If an Accept-Charset header is present,
1146   and if the server cannot send a response which is acceptable
1147   according to the Accept-Charset header, then the server &SHOULD; send
1148   an error response with the 406 (Not Acceptable) status code, though
1149   the sending of an unacceptable response is also allowed.
1150</t>
1151</section>
1152
1153<section title="Accept-Encoding" anchor="header.accept-encoding">
1154  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1155  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1156  <x:anchor-alias value="Accept-Encoding"/>
1157  <x:anchor-alias value="Accept-Encoding-v"/>
1158  <x:anchor-alias value="codings"/>
1159<t>
1160   The "Accept-Encoding" request-header field can be used by user agents to
1161   indicate what response content-codings (<xref target="content.codings"/>)
1162   are acceptable in the response.
1163</t>
1164<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"/>
1165  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1166                     <x:ref>Accept-Encoding-v</x:ref>
1167  <x:ref>Accept-Encoding-v</x:ref>  =
1168                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1169  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1170</artwork></figure>
1171<t>
1172   Each codings value &MAY; be given an associated quality value which
1173   represents the preference for that encoding. The default value is q=1.
1174</t>
1175<t>
1176   Examples of its use are:
1177</t>
1178<figure><artwork type="example">
1179  Accept-Encoding: compress, gzip
1180  Accept-Encoding:
1181  Accept-Encoding: *
1182  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1183  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1184</artwork></figure>
1185<t>
1186   A server tests whether a content-coding is acceptable, according to
1187   an Accept-Encoding field, using these rules:
1188  <list style="numbers">
1189      <t>If the content-coding is one of the content-codings listed in
1190         the Accept-Encoding field, then it is acceptable, unless it is
1191         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1192         qvalue of 0 means "not acceptable.")</t>
1193
1194      <t>The special "*" symbol in an Accept-Encoding field matches any
1195         available content-coding not explicitly listed in the header
1196         field.</t>
1197
1198      <t>If multiple content-codings are acceptable, then the acceptable
1199         content-coding with the highest non-zero qvalue is preferred.</t>
1200
1201      <t>The "identity" content-coding is always acceptable, unless
1202         specifically refused because the Accept-Encoding field includes
1203         "identity;q=0", or because the field includes "*;q=0" and does
1204         not explicitly include the "identity" content-coding. If the
1205         Accept-Encoding field-value is empty, then only the "identity"
1206         encoding is acceptable.</t>
1207  </list>
1208</t>
1209<t>
1210   If an Accept-Encoding field is present in a request, and if the
1211   server cannot send a response which is acceptable according to the
1212   Accept-Encoding header, then the server &SHOULD; send an error response
1213   with the 406 (Not Acceptable) status code.
1214</t>
1215<t>
1216   If no Accept-Encoding field is present in a request, the server &MAY;
1217   assume that the client will accept any content coding. In this case,
1218   if "identity" is one of the available content-codings, then the
1219   server &SHOULD; use the "identity" content-coding, unless it has
1220   additional information that a different content-coding is meaningful
1221   to the client.
1222</t>
1223<x:note>
1224  <t>
1225    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1226    and if the "identity" content-coding is unavailable, then
1227    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1228    "gzip" and "compress") are preferred; some older clients
1229    improperly display messages sent with other content-codings.  The
1230    server might also make this decision based on information about
1231    the particular user-agent or client.
1232  </t>
1233</x:note>
1234<x:note>
1235  <t>
1236    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1237    associated with content-codings. This means that qvalues will not
1238    work and are not permitted with x-gzip or x-compress.
1239  </t>
1240</x:note>
1241</section>
1242
1243<section title="Accept-Language" anchor="header.accept-language">
1244  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1245  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1246  <x:anchor-alias value="Accept-Language"/>
1247  <x:anchor-alias value="Accept-Language-v"/>
1248  <x:anchor-alias value="language-range"/>
1249<t>
1250   The "Accept-Language" request-header field can be used by user agents to
1251   indicate the set of natural languages that are preferred in the response.
1252   Language tags are defined in <xref target="language.tags"/>.
1253</t>
1254<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"/>
1255  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1256                    <x:ref>Accept-Language-v</x:ref>
1257  <x:ref>Accept-Language-v</x:ref> =
1258                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1259  <x:ref>language-range</x:ref>    =
1260            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1261</artwork></figure>
1262<t>
1263   Each language-range can be given an associated quality value which
1264   represents an estimate of the user's preference for the languages
1265   specified by that range. The quality value defaults to "q=1". For
1266   example,
1267</t>
1268<figure><artwork type="example">
1269  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1270</artwork></figure>
1271<t>
1272   would mean: "I prefer Danish, but will accept British English and
1273   other types of English."
1274   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1275</t>
1276<t>
1277   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1278   several matching schemes. Implementations can offer the most appropriate
1279   matching scheme for their requirements.
1280</t>
1281<x:note>
1282  <t>
1283    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1284    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1285    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1286  </t>
1287</x:note>
1288<t>
1289   It might be contrary to the privacy expectations of the user to send
1290   an Accept-Language header with the complete linguistic preferences of
1291   the user in every request. For a discussion of this issue, see
1292   <xref target="privacy.issues.connected.to.accept.headers"/>.
1293</t>
1294<t>
1295   As intelligibility is highly dependent on the individual user, it is
1296   recommended that client applications make the choice of linguistic
1297   preference available to the user. If the choice is not made
1298   available, then the Accept-Language header field &MUST-NOT; be given in
1299   the request.
1300</t>
1301<x:note>
1302  <t>
1303    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1304    the user, we remind implementors of  the fact that users are not
1305    familiar with the details of language matching as described above,
1306    and should provide appropriate guidance. As an example, users
1307    might assume that on selecting "en-gb", they will be served any
1308    kind of English document if British English is not available. A
1309    user agent might suggest in such a case to add "en" to get the
1310    best matching behavior.
1311  </t>
1312</x:note>
1313</section>
1314
1315<section title="Content-Encoding" anchor="header.content-encoding">
1316  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1317  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1318  <x:anchor-alias value="Content-Encoding"/>
1319  <x:anchor-alias value="Content-Encoding-v"/>
1320<t>
1321   The "Content-Encoding" entity-header field indicates what content-codings
1322   have been applied to the entity-body, and thus what decoding mechanisms
1323   must be applied in order to obtain the media-type referenced by the
1324   Content-Type header field. Content-Encoding is primarily used to allow a
1325   document to be compressed without losing the identity of its underlying
1326   media type.
1327</t>
1328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1329  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1330  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1331</artwork></figure>
1332<t>
1333   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1334</t>
1335<figure><artwork type="example">
1336  Content-Encoding: gzip
1337</artwork></figure>
1338<t>
1339   The content-coding is a characteristic of the entity identified by
1340   the request-target. Typically, the entity-body is stored with this
1341   encoding and is only decoded before rendering or analogous usage.
1342   However, a non-transparent proxy &MAY; modify the content-coding if the
1343   new coding is known to be acceptable to the recipient, unless the
1344   "no-transform" cache-control directive is present in the message.
1345</t>
1346<t>
1347   If the content-coding of an entity is not "identity", then the
1348   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1349   that lists the non-identity content-coding(s) used.
1350</t>
1351<t>
1352   If the content-coding of an entity in a request message is not
1353   acceptable to the origin server, the server &SHOULD; respond with a
1354   status code of 415 (Unsupported Media Type).
1355</t>
1356<t>
1357   If multiple encodings have been applied to an entity, the content
1358   codings &MUST; be listed in the order in which they were applied.
1359   Additional information about the encoding parameters &MAY; be provided
1360   by other entity-header fields not defined by this specification.
1361</t>
1362</section>
1363
1364<section title="Content-Language" anchor="header.content-language">
1365  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1366  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1367  <x:anchor-alias value="Content-Language"/>
1368  <x:anchor-alias value="Content-Language-v"/>
1369<t>
1370   The "Content-Language" entity-header field describes the natural
1371   language(s) of the intended audience for the entity. Note that this might
1372   not be equivalent to all the languages used within the entity-body.
1373</t>
1374<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1375  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1376  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1377</artwork></figure>
1378<t>
1379   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1380   Content-Language is to allow a user to identify and differentiate
1381   entities according to the user's own preferred language. Thus, if the
1382   body content is intended only for a Danish-literate audience, the
1383   appropriate field is
1384</t>
1385<figure><artwork type="example">
1386  Content-Language: da
1387</artwork></figure>
1388<t>
1389   If no Content-Language is specified, the default is that the content
1390   is intended for all language audiences. This might mean that the
1391   sender does not consider it to be specific to any natural language,
1392   or that the sender does not know for which language it is intended.
1393</t>
1394<t>
1395   Multiple languages &MAY; be listed for content that is intended for
1396   multiple audiences. For example, a rendition of the "Treaty of
1397   Waitangi," presented simultaneously in the original Maori and English
1398   versions, would call for
1399</t>
1400<figure><artwork type="example">
1401  Content-Language: mi, en
1402</artwork></figure>
1403<t>
1404   However, just because multiple languages are present within an entity
1405   does not mean that it is intended for multiple linguistic audiences.
1406   An example would be a beginner's language primer, such as "A First
1407   Lesson in Latin," which is clearly intended to be used by an
1408   English-literate audience. In this case, the Content-Language would
1409   properly only include "en".
1410</t>
1411<t>
1412   Content-Language &MAY; be applied to any media type -- it is not
1413   limited to textual documents.
1414</t>
1415</section>
1416
1417<section title="Content-Location" anchor="header.content-location">
1418  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1419  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1420  <x:anchor-alias value="Content-Location"/>
1421  <x:anchor-alias value="Content-Location-v"/>
1422<t>
1423   The "Content-Location" entity-header field is used to supply a URI for the
1424   entity in the message when it is accessible from a location separate from
1425   the requested resource's URI.
1426</t>
1427<t>
1428   A server &SHOULD; provide a Content-Location for the variant corresponding
1429   to the response entity, especially in the case where a resource has multiple
1430   entities associated with it, and those entities actually have separate
1431   locations by which they might be individually accessed, the server &SHOULD;
1432   provide a Content-Location for the particular variant which is returned.
1433</t>
1434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1435  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1436                    <x:ref>Content-Location-v</x:ref>
1437  <x:ref>Content-Location-v</x:ref> =
1438                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1439</artwork></figure>
1440<t>
1441   The Content-Location value is not a replacement for the original
1442   requested URI; it is only a statement of the location of the resource
1443   corresponding to this particular entity at the time of the request.
1444   Future requests &MAY; specify the Content-Location URI as the request-target
1445   if the desire is to identify the source of that particular
1446   entity.
1447</t>
1448<t>
1449   &response-representation; describes how clients may process the Content-Location header field.
1450</t>
1451<t>
1452   A cache cannot assume that an entity with a Content-Location
1453   different from the URI used to retrieve it can be used to respond to
1454   later requests on that Content-Location URI. However, the Content-Location
1455   can be used to differentiate between multiple entities
1456   retrieved from a single requested resource, as described in &caching-neg-resp;.
1457</t>
1458<t>
1459   If the Content-Location is a relative URI, the relative URI is
1460   interpreted relative to the request-target.
1461</t>
1462<t>
1463   The meaning of the Content-Location header in requests is
1464   undefined; servers are free to ignore it in those cases.
1465</t>
1466</section>
1467
1468<section title="Content-MD5" anchor="header.content-md5">
1469  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1470  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1471  <x:anchor-alias value="Content-MD5"/>
1472  <x:anchor-alias value="Content-MD5-v"/>
1473<t>
1474   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1475   an MD5 digest of the entity-body that provides an end-to-end message
1476   integrity check (MIC) of the entity-body. Note that a MIC is good for
1477   detecting accidental modification of the entity-body in transit, but is not
1478   proof against malicious attacks.
1479</t>
1480<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1481  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1482  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1483</artwork></figure>
1484<t>
1485   The Content-MD5 header field &MAY; be generated by an origin server or
1486   client to function as an integrity check of the entity-body. Only
1487   origin servers or clients &MAY; generate the Content-MD5 header field;
1488   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1489   value as an end-to-end integrity check. Any recipient of the entity-body,
1490   including gateways and proxies, &MAY; check that the digest value
1491   in this header field matches that of the entity-body as received.
1492</t>
1493<t>
1494   The MD5 digest is computed based on the content of the entity-body,
1495   including any content-coding that has been applied, but not including
1496   any transfer-encoding applied to the message-body. If the message is
1497   received with a transfer-encoding, that encoding &MUST; be removed
1498   prior to checking the Content-MD5 value against the received entity.
1499</t>
1500<t>
1501   This has the result that the digest is computed on the octets of the
1502   entity-body exactly as, and in the order that, they would be sent if
1503   no transfer-encoding were being applied.
1504</t>
1505<t>
1506   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1507   composite media-types (e.g., multipart/* and message/rfc822), but
1508   this does not change how the digest is computed as defined in the
1509   preceding paragraph.
1510</t>
1511<t>
1512   There are several consequences of this. The entity-body for composite
1513   types &MAY; contain many body-parts, each with its own MIME and HTTP
1514   headers (including Content-MD5, Content-Transfer-Encoding, and
1515   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1516   or Content-Encoding header, it is assumed that the content
1517   of the body-part has had the encoding applied, and the body-part is
1518   included in the Content-MD5 digest as is -- i.e., after the
1519   application. The Transfer-Encoding header field is not allowed within
1520   body-parts.
1521</t>
1522<t>
1523   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1524   computing or checking the digest: the line break convention used in
1525   the text actually transmitted &MUST; be left unaltered when computing
1526   the digest.
1527</t>
1528<x:note>
1529  <t>
1530    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1531    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1532    in which the application of Content-MD5 to HTTP entity-bodies
1533    differs from its application to MIME entity-bodies. One is that
1534    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1535    does use Transfer-Encoding and Content-Encoding. Another is that
1536    HTTP more frequently uses binary content types than MIME, so it is
1537    worth noting that, in such cases, the byte order used to compute
1538    the digest is the transmission byte order defined for the type.
1539    Lastly, HTTP allows transmission of text types with any of several
1540    line break conventions and not just the canonical form using CRLF.
1541  </t>
1542</x:note>
1543</section>
1544
1545<section title="Content-Type" anchor="header.content-type">
1546  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1547  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1548  <x:anchor-alias value="Content-Type"/>
1549  <x:anchor-alias value="Content-Type-v"/>
1550<t>
1551   The "Content-Type" entity-header field indicates the media type of the
1552   entity-body. In the case of responses to the HEAD method, the media type is
1553   that which would have been sent had the request been a GET.
1554</t>
1555<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1556  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1557  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1558</artwork></figure>
1559<t>
1560   Media types are defined in <xref target="media.types"/>. An example of the field is
1561</t>
1562<figure><artwork type="example">
1563  Content-Type: text/html; charset=ISO-8859-4
1564</artwork></figure>
1565<t>
1566   Further discussion of methods for identifying the media type of an
1567   entity is provided in <xref target="type"/>.
1568</t>
1569</section>
1570
1571</section>
1572
1573<section title="IANA Considerations" anchor="IANA.considerations">
1574<section title="Message Header Registration" anchor="message.header.registration">
1575<t>
1576   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1577   with the permanent registrations below (see <xref target="RFC3864"/>):
1578</t>
1579<?BEGININC p3-payload.iana-headers ?>
1580<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1581<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1582   <ttcol>Header Field Name</ttcol>
1583   <ttcol>Protocol</ttcol>
1584   <ttcol>Status</ttcol>
1585   <ttcol>Reference</ttcol>
1586
1587   <c>Accept</c>
1588   <c>http</c>
1589   <c>standard</c>
1590   <c>
1591      <xref target="header.accept"/>
1592   </c>
1593   <c>Accept-Charset</c>
1594   <c>http</c>
1595   <c>standard</c>
1596   <c>
1597      <xref target="header.accept-charset"/>
1598   </c>
1599   <c>Accept-Encoding</c>
1600   <c>http</c>
1601   <c>standard</c>
1602   <c>
1603      <xref target="header.accept-encoding"/>
1604   </c>
1605   <c>Accept-Language</c>
1606   <c>http</c>
1607   <c>standard</c>
1608   <c>
1609      <xref target="header.accept-language"/>
1610   </c>
1611   <c>Content-Disposition</c>
1612   <c>http</c>
1613   <c/>
1614   <c>
1615      <xref target="content-disposition"/>
1616   </c>
1617   <c>Content-Encoding</c>
1618   <c>http</c>
1619   <c>standard</c>
1620   <c>
1621      <xref target="header.content-encoding"/>
1622   </c>
1623   <c>Content-Language</c>
1624   <c>http</c>
1625   <c>standard</c>
1626   <c>
1627      <xref target="header.content-language"/>
1628   </c>
1629   <c>Content-Location</c>
1630   <c>http</c>
1631   <c>standard</c>
1632   <c>
1633      <xref target="header.content-location"/>
1634   </c>
1635   <c>Content-MD5</c>
1636   <c>http</c>
1637   <c>standard</c>
1638   <c>
1639      <xref target="header.content-md5"/>
1640   </c>
1641   <c>Content-Type</c>
1642   <c>http</c>
1643   <c>standard</c>
1644   <c>
1645      <xref target="header.content-type"/>
1646   </c>
1647   <c>MIME-Version</c>
1648   <c>http</c>
1649   <c/>
1650   <c>
1651      <xref target="mime-version"/>
1652   </c>
1653</texttable>
1654<!--(END)-->
1655<?ENDINC p3-payload.iana-headers ?>
1656<t>
1657   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1658</t>
1659</section>
1660
1661<section title="Content Coding Registry" anchor="content.coding.registration">
1662<t>
1663   The registration procedure for HTTP Content Codings is now defined
1664   by <xref target="content.coding.registry"/> of this document.
1665</t>
1666<t>
1667   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1668   should be updated with the registration below:
1669</t>
1670<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1671   <ttcol>Name</ttcol>
1672   <ttcol>Description</ttcol>
1673   <ttcol>Reference</ttcol>
1674   <c>compress</c>
1675   <c>UNIX "compress" program method</c>
1676   <c>
1677      &compress-coding;
1678   </c>
1679   <c>deflate</c>
1680   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1681   the "zlib" data format (<xref target="RFC1950"/>)
1682   </c>
1683   <c>
1684      &deflate-coding;
1685   </c>
1686   <c>gzip</c>
1687   <c>Same as GNU zip <xref target="RFC1952"/></c>
1688   <c>
1689      &gzip-coding;
1690   </c>
1691   <c>identity</c>
1692   <c>No transformation</c>
1693   <c>
1694      <xref target="content.codings"/>
1695   </c>
1696</texttable>
1697</section>
1698
1699</section>
1700
1701<section title="Security Considerations" anchor="security.considerations">
1702<t>
1703   This section is meant to inform application developers, information
1704   providers, and users of the security limitations in HTTP/1.1 as
1705   described by this document. The discussion does not include
1706   definitive solutions to the problems revealed, though it does make
1707   some suggestions for reducing security risks.
1708</t>
1709
1710<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1711<t>
1712   Accept request-headers can reveal information about the user to all
1713   servers which are accessed. The Accept-Language header in particular
1714   can reveal information the user would consider to be of a private
1715   nature, because the understanding of particular languages is often
1716   strongly correlated to the membership of a particular ethnic group.
1717   User agents which offer the option to configure the contents of an
1718   Accept-Language header to be sent in every request are strongly
1719   encouraged to let the configuration process include a message which
1720   makes the user aware of the loss of privacy involved.
1721</t>
1722<t>
1723   An approach that limits the loss of privacy would be for a user agent
1724   to omit the sending of Accept-Language headers by default, and to ask
1725   the user whether or not to start sending Accept-Language headers to a
1726   server if it detects, by looking for any Vary response-header fields
1727   generated by the server, that such sending could improve the quality
1728   of service.
1729</t>
1730<t>
1731   Elaborate user-customized accept header fields sent in every request,
1732   in particular if these include quality values, can be used by servers
1733   as relatively reliable and long-lived user identifiers. Such user
1734   identifiers would allow content providers to do click-trail tracking,
1735   and would allow collaborating content providers to match cross-server
1736   click-trails or form submissions of individual users. Note that for
1737   many users not behind a proxy, the network address of the host
1738   running the user agent will also serve as a long-lived user
1739   identifier. In environments where proxies are used to enhance
1740   privacy, user agents ought to be conservative in offering accept
1741   header configuration options to end users. As an extreme privacy
1742   measure, proxies could filter the accept headers in relayed requests.
1743   General purpose user agents which provide a high degree of header
1744   configurability &SHOULD; warn users about the loss of privacy which can
1745   be involved.
1746</t>
1747</section>
1748
1749<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1750<t>
1751   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1752   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1753   serious security considerations. Content-Disposition is not part of
1754   the HTTP standard, but since it is widely implemented, we are
1755   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1756   for details.
1757</t>
1758</section>
1759
1760</section>
1761
1762<section title="Acknowledgments" anchor="ack">
1763</section>
1764</middle>
1765<back>
1766
1767<references title="Normative References">
1768
1769<reference anchor="ISO-8859-1">
1770  <front>
1771    <title>
1772     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1773    </title>
1774    <author>
1775      <organization>International Organization for Standardization</organization>
1776    </author>
1777    <date year="1998"/>
1778  </front>
1779  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1780</reference>
1781
1782<reference anchor="Part1">
1783  <front>
1784    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1785    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1786      <organization abbrev="Day Software">Day Software</organization>
1787      <address><email>fielding@gbiv.com</email></address>
1788    </author>
1789    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1790      <organization>One Laptop per Child</organization>
1791      <address><email>jg@laptop.org</email></address>
1792    </author>
1793    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1794      <organization abbrev="HP">Hewlett-Packard Company</organization>
1795      <address><email>JeffMogul@acm.org</email></address>
1796    </author>
1797    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1798      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1799      <address><email>henrikn@microsoft.com</email></address>
1800    </author>
1801    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1802      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1803      <address><email>LMM@acm.org</email></address>
1804    </author>
1805    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1806      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1807      <address><email>paulle@microsoft.com</email></address>
1808    </author>
1809    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1810      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1811      <address><email>timbl@w3.org</email></address>
1812    </author>
1813    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1814      <organization abbrev="W3C">World Wide Web Consortium</organization>
1815      <address><email>ylafon@w3.org</email></address>
1816    </author>
1817    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1818      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1819      <address><email>julian.reschke@greenbytes.de</email></address>
1820    </author>
1821    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1822  </front>
1823  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1824  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1825</reference>
1826
1827<reference anchor="Part2">
1828  <front>
1829    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1830    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1831      <organization abbrev="Day Software">Day Software</organization>
1832      <address><email>fielding@gbiv.com</email></address>
1833    </author>
1834    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1835      <organization>One Laptop per Child</organization>
1836      <address><email>jg@laptop.org</email></address>
1837    </author>
1838    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1839      <organization abbrev="HP">Hewlett-Packard Company</organization>
1840      <address><email>JeffMogul@acm.org</email></address>
1841    </author>
1842    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1843      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1844      <address><email>henrikn@microsoft.com</email></address>
1845    </author>
1846    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1847      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1848      <address><email>LMM@acm.org</email></address>
1849    </author>
1850    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1851      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1852      <address><email>paulle@microsoft.com</email></address>
1853    </author>
1854    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1855      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1856      <address><email>timbl@w3.org</email></address>
1857    </author>
1858    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1859      <organization abbrev="W3C">World Wide Web Consortium</organization>
1860      <address><email>ylafon@w3.org</email></address>
1861    </author>
1862    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1863      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1864      <address><email>julian.reschke@greenbytes.de</email></address>
1865    </author>
1866    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1867  </front>
1868  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1869  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1870</reference>
1871
1872<reference anchor="Part4">
1873  <front>
1874    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1875    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1876      <organization abbrev="Day Software">Day Software</organization>
1877      <address><email>fielding@gbiv.com</email></address>
1878    </author>
1879    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1880      <organization>One Laptop per Child</organization>
1881      <address><email>jg@laptop.org</email></address>
1882    </author>
1883    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1884      <organization abbrev="HP">Hewlett-Packard Company</organization>
1885      <address><email>JeffMogul@acm.org</email></address>
1886    </author>
1887    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1888      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1889      <address><email>henrikn@microsoft.com</email></address>
1890    </author>
1891    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1892      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1893      <address><email>LMM@acm.org</email></address>
1894    </author>
1895    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1896      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1897      <address><email>paulle@microsoft.com</email></address>
1898    </author>
1899    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1900      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1901      <address><email>timbl@w3.org</email></address>
1902    </author>
1903    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1904      <organization abbrev="W3C">World Wide Web Consortium</organization>
1905      <address><email>ylafon@w3.org</email></address>
1906    </author>
1907    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1908      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1909      <address><email>julian.reschke@greenbytes.de</email></address>
1910    </author>
1911    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1912  </front>
1913  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1914  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1915</reference>
1916
1917<reference anchor="Part5">
1918  <front>
1919    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1920    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1921      <organization abbrev="Day Software">Day Software</organization>
1922      <address><email>fielding@gbiv.com</email></address>
1923    </author>
1924    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1925      <organization>One Laptop per Child</organization>
1926      <address><email>jg@laptop.org</email></address>
1927    </author>
1928    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1929      <organization abbrev="HP">Hewlett-Packard Company</organization>
1930      <address><email>JeffMogul@acm.org</email></address>
1931    </author>
1932    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1933      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1934      <address><email>henrikn@microsoft.com</email></address>
1935    </author>
1936    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1937      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1938      <address><email>LMM@acm.org</email></address>
1939    </author>
1940    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1941      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1942      <address><email>paulle@microsoft.com</email></address>
1943    </author>
1944    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1945      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1946      <address><email>timbl@w3.org</email></address>
1947    </author>
1948    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1949      <organization abbrev="W3C">World Wide Web Consortium</organization>
1950      <address><email>ylafon@w3.org</email></address>
1951    </author>
1952    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1953      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1954      <address><email>julian.reschke@greenbytes.de</email></address>
1955    </author>
1956    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1957  </front>
1958  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1959  <x:source href="p5-range.xml" basename="p5-range"/>
1960</reference>
1961
1962<reference anchor="Part6">
1963  <front>
1964    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1965    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1966      <organization abbrev="Day Software">Day Software</organization>
1967      <address><email>fielding@gbiv.com</email></address>
1968    </author>
1969    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1970      <organization>One Laptop per Child</organization>
1971      <address><email>jg@laptop.org</email></address>
1972    </author>
1973    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1974      <organization abbrev="HP">Hewlett-Packard Company</organization>
1975      <address><email>JeffMogul@acm.org</email></address>
1976    </author>
1977    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1978      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1979      <address><email>henrikn@microsoft.com</email></address>
1980    </author>
1981    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1982      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1983      <address><email>LMM@acm.org</email></address>
1984    </author>
1985    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1986      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1987      <address><email>paulle@microsoft.com</email></address>
1988    </author>
1989    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1990      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1991      <address><email>timbl@w3.org</email></address>
1992    </author>
1993    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1994      <organization abbrev="W3C">World Wide Web Consortium</organization>
1995      <address><email>ylafon@w3.org</email></address>
1996    </author>
1997    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1998      <address><email>mnot@mnot.net</email></address>
1999    </author>
2000    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2001      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2002      <address><email>julian.reschke@greenbytes.de</email></address>
2003    </author>
2004    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2005  </front>
2006  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2007  <x:source href="p6-cache.xml" basename="p6-cache"/>
2008</reference>
2009
2010<reference anchor="RFC1864">
2011  <front>
2012    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2013    <author initials="J." surname="Myers" fullname="John G. Myers">
2014      <organization>Carnegie Mellon University</organization>
2015      <address><email>jgm+@cmu.edu</email></address>
2016    </author>
2017    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2018      <organization>Dover Beach Consulting, Inc.</organization>
2019      <address><email>mrose@dbc.mtview.ca.us</email></address>
2020    </author>
2021    <date month="October" year="1995"/>
2022  </front>
2023  <seriesInfo name="RFC" value="1864"/>
2024</reference>
2025
2026<reference anchor="RFC1950">
2027  <front>
2028    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2029    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2030      <organization>Aladdin Enterprises</organization>
2031      <address><email>ghost@aladdin.com</email></address>
2032    </author>
2033    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2034    <date month="May" year="1996"/>
2035  </front>
2036  <seriesInfo name="RFC" value="1950"/>
2037  <annotation>
2038    RFC 1950 is an Informational RFC, thus it may be less stable than
2039    this specification. On the other hand, this downward reference was
2040    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2041    therefore it is unlikely to cause problems in practice. See also
2042    <xref target="BCP97"/>.
2043  </annotation>
2044</reference>
2045
2046<reference anchor="RFC1951">
2047  <front>
2048    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2049    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2050      <organization>Aladdin Enterprises</organization>
2051      <address><email>ghost@aladdin.com</email></address>
2052    </author>
2053    <date month="May" year="1996"/>
2054  </front>
2055  <seriesInfo name="RFC" value="1951"/>
2056  <annotation>
2057    RFC 1951 is an Informational RFC, thus it may be less stable than
2058    this specification. On the other hand, this downward reference was
2059    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2060    therefore it is unlikely to cause problems in practice. See also
2061    <xref target="BCP97"/>.
2062  </annotation>
2063</reference>
2064
2065<reference anchor="RFC1952">
2066  <front>
2067    <title>GZIP file format specification version 4.3</title>
2068    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2069      <organization>Aladdin Enterprises</organization>
2070      <address><email>ghost@aladdin.com</email></address>
2071    </author>
2072    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2073      <address><email>gzip@prep.ai.mit.edu</email></address>
2074    </author>
2075    <author initials="M." surname="Adler" fullname="Mark Adler">
2076      <address><email>madler@alumni.caltech.edu</email></address>
2077    </author>
2078    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2079      <address><email>ghost@aladdin.com</email></address>
2080    </author>
2081    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2082      <address><email>randeg@alumni.rpi.edu</email></address>
2083    </author>
2084    <date month="May" year="1996"/>
2085  </front>
2086  <seriesInfo name="RFC" value="1952"/>
2087  <annotation>
2088    RFC 1952 is an Informational RFC, thus it may be less stable than
2089    this specification. On the other hand, this downward reference was
2090    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2091    therefore it is unlikely to cause problems in practice. See also
2092    <xref target="BCP97"/>.
2093  </annotation>
2094</reference>
2095
2096<reference anchor="RFC2045">
2097  <front>
2098    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2099    <author initials="N." surname="Freed" fullname="Ned Freed">
2100      <organization>Innosoft International, Inc.</organization>
2101      <address><email>ned@innosoft.com</email></address>
2102    </author>
2103    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2104      <organization>First Virtual Holdings</organization>
2105      <address><email>nsb@nsb.fv.com</email></address>
2106    </author>
2107    <date month="November" year="1996"/>
2108  </front>
2109  <seriesInfo name="RFC" value="2045"/>
2110</reference>
2111
2112<reference anchor="RFC2046">
2113  <front>
2114    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2115    <author initials="N." surname="Freed" fullname="Ned Freed">
2116      <organization>Innosoft International, Inc.</organization>
2117      <address><email>ned@innosoft.com</email></address>
2118    </author>
2119    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2120      <organization>First Virtual Holdings</organization>
2121      <address><email>nsb@nsb.fv.com</email></address>
2122    </author>
2123    <date month="November" year="1996"/>
2124  </front>
2125  <seriesInfo name="RFC" value="2046"/>
2126</reference>
2127
2128<reference anchor="RFC2119">
2129  <front>
2130    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2131    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2132      <organization>Harvard University</organization>
2133      <address><email>sob@harvard.edu</email></address>
2134    </author>
2135    <date month="March" year="1997"/>
2136  </front>
2137  <seriesInfo name="BCP" value="14"/>
2138  <seriesInfo name="RFC" value="2119"/>
2139</reference>
2140
2141<reference anchor='RFC4647'>
2142  <front>
2143    <title>Matching of Language Tags</title>
2144    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2145      <organization>Yahoo! Inc.</organization>
2146      <address><email>addison@inter-locale.com</email></address>
2147    </author>
2148    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2149      <organization>Google</organization>
2150      <address><email>mark.davis@macchiato.com</email></address>
2151    </author>
2152    <date year='2006' month='September' />
2153  </front>
2154  <seriesInfo name='BCP' value='47' />
2155  <seriesInfo name='RFC' value='4647' />
2156</reference>
2157
2158<reference anchor="RFC5234">
2159  <front>
2160    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2161    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2162      <organization>Brandenburg InternetWorking</organization>
2163      <address>
2164        <email>dcrocker@bbiw.net</email>
2165      </address> 
2166    </author>
2167    <author initials="P." surname="Overell" fullname="Paul Overell">
2168      <organization>THUS plc.</organization>
2169      <address>
2170        <email>paul.overell@thus.net</email>
2171      </address>
2172    </author>
2173    <date month="January" year="2008"/>
2174  </front>
2175  <seriesInfo name="STD" value="68"/>
2176  <seriesInfo name="RFC" value="5234"/>
2177</reference>
2178
2179<reference anchor='RFC5646'>
2180  <front>
2181    <title>Tags for Identifying Languages</title>
2182    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2183      <organization>Lab126</organization>
2184      <address><email>addison@inter-locale.com</email></address>
2185    </author>
2186    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2187      <organization>Google</organization>
2188      <address><email>mark.davis@google.com</email></address>
2189    </author>
2190    <date month='September' year='2009' />
2191  </front>
2192  <seriesInfo name='BCP' value='47' />
2193  <seriesInfo name='RFC' value='5646' />
2194</reference>
2195
2196</references>
2197
2198<references title="Informative References">
2199
2200<reference anchor="RFC1945">
2201  <front>
2202    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2203    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2204      <organization>MIT, Laboratory for Computer Science</organization>
2205      <address><email>timbl@w3.org</email></address>
2206    </author>
2207    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2208      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2209      <address><email>fielding@ics.uci.edu</email></address>
2210    </author>
2211    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2212      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2213      <address><email>frystyk@w3.org</email></address>
2214    </author>
2215    <date month="May" year="1996"/>
2216  </front>
2217  <seriesInfo name="RFC" value="1945"/>
2218</reference>
2219
2220<reference anchor="RFC2049">
2221  <front>
2222    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2223    <author initials="N." surname="Freed" fullname="Ned Freed">
2224      <organization>Innosoft International, Inc.</organization>
2225      <address><email>ned@innosoft.com</email></address>
2226    </author>
2227    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2228      <organization>First Virtual Holdings</organization>
2229      <address><email>nsb@nsb.fv.com</email></address>
2230    </author>
2231    <date month="November" year="1996"/>
2232  </front>
2233  <seriesInfo name="RFC" value="2049"/>
2234</reference>
2235
2236<reference anchor="RFC2068">
2237  <front>
2238    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2239    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2240      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2241      <address><email>fielding@ics.uci.edu</email></address>
2242    </author>
2243    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2244      <organization>MIT Laboratory for Computer Science</organization>
2245      <address><email>jg@w3.org</email></address>
2246    </author>
2247    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2248      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2249      <address><email>mogul@wrl.dec.com</email></address>
2250    </author>
2251    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2252      <organization>MIT Laboratory for Computer Science</organization>
2253      <address><email>frystyk@w3.org</email></address>
2254    </author>
2255    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2256      <organization>MIT Laboratory for Computer Science</organization>
2257      <address><email>timbl@w3.org</email></address>
2258    </author>
2259    <date month="January" year="1997"/>
2260  </front>
2261  <seriesInfo name="RFC" value="2068"/>
2262</reference>
2263
2264<reference anchor="RFC2076">
2265  <front>
2266    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2267    <author initials="J." surname="Palme" fullname="Jacob Palme">
2268      <organization>Stockholm University/KTH</organization>
2269      <address><email>jpalme@dsv.su.se</email></address>
2270    </author>
2271    <date month="February" year="1997"/>
2272  </front>
2273  <seriesInfo name="RFC" value="2076"/>
2274</reference>
2275
2276<reference anchor="RFC2183">
2277  <front>
2278    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2279    <author initials="R." surname="Troost" fullname="Rens Troost">
2280      <organization>New Century Systems</organization>
2281      <address><email>rens@century.com</email></address>
2282    </author>
2283    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2284      <organization>QUALCOMM Incorporated</organization>
2285      <address><email>sdorner@qualcomm.com</email></address>
2286    </author>
2287    <author initials="K." surname="Moore" fullname="Keith Moore">
2288      <organization>Department of Computer Science</organization>
2289      <address><email>moore@cs.utk.edu</email></address>
2290    </author>
2291    <date month="August" year="1997"/>
2292  </front>
2293  <seriesInfo name="RFC" value="2183"/>
2294</reference>
2295
2296<reference anchor="RFC2277">
2297  <front>
2298    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2299    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2300      <organization>UNINETT</organization>
2301      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2302    </author>
2303    <date month="January" year="1998"/>
2304  </front>
2305  <seriesInfo name="BCP" value="18"/>
2306  <seriesInfo name="RFC" value="2277"/>
2307</reference>
2308
2309<reference anchor='RFC2295'>
2310  <front>
2311    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2312    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2313      <organization>Technische Universiteit Eindhoven</organization>
2314      <address>
2315        <email>koen@win.tue.nl</email>
2316      </address>
2317    </author>
2318    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2319      <organization>Hewlett-Packard Company</organization>
2320      <address>
2321        <email>mutz@hpl.hp.com</email>
2322      </address>
2323    </author>
2324    <date year='1998' month='March'/>
2325  </front>
2326  <seriesInfo name='RFC' value='2295'/>
2327</reference>
2328
2329<reference anchor="RFC2388">
2330  <front>
2331    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2332    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2333      <organization>Xerox Palo Alto Research Center</organization>
2334      <address><email>masinter@parc.xerox.com</email></address>
2335    </author>
2336    <date year="1998" month="August"/>
2337  </front>
2338  <seriesInfo name="RFC" value="2388"/>
2339</reference>
2340
2341<reference anchor="RFC2557">
2342  <front>
2343    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2344    <author initials="F." surname="Palme" fullname="Jacob Palme">
2345      <organization>Stockholm University and KTH</organization>
2346      <address><email>jpalme@dsv.su.se</email></address>
2347    </author>
2348    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2349      <organization>Microsoft Corporation</organization>
2350      <address><email>alexhop@microsoft.com</email></address>
2351    </author>
2352    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2353      <organization>Lotus Development Corporation</organization>
2354      <address><email>Shelness@lotus.com</email></address>
2355    </author>
2356    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2357      <address><email>stef@nma.com</email></address>
2358    </author>
2359    <date year="1999" month="March"/>
2360  </front>
2361  <seriesInfo name="RFC" value="2557"/>
2362</reference>
2363
2364<reference anchor="RFC2616">
2365  <front>
2366    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2367    <author initials="R." surname="Fielding" fullname="R. Fielding">
2368      <organization>University of California, Irvine</organization>
2369      <address><email>fielding@ics.uci.edu</email></address>
2370    </author>
2371    <author initials="J." surname="Gettys" fullname="J. Gettys">
2372      <organization>W3C</organization>
2373      <address><email>jg@w3.org</email></address>
2374    </author>
2375    <author initials="J." surname="Mogul" fullname="J. Mogul">
2376      <organization>Compaq Computer Corporation</organization>
2377      <address><email>mogul@wrl.dec.com</email></address>
2378    </author>
2379    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2380      <organization>MIT Laboratory for Computer Science</organization>
2381      <address><email>frystyk@w3.org</email></address>
2382    </author>
2383    <author initials="L." surname="Masinter" fullname="L. Masinter">
2384      <organization>Xerox Corporation</organization>
2385      <address><email>masinter@parc.xerox.com</email></address>
2386    </author>
2387    <author initials="P." surname="Leach" fullname="P. Leach">
2388      <organization>Microsoft Corporation</organization>
2389      <address><email>paulle@microsoft.com</email></address>
2390    </author>
2391    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2392      <organization>W3C</organization>
2393      <address><email>timbl@w3.org</email></address>
2394    </author>
2395    <date month="June" year="1999"/>
2396  </front>
2397  <seriesInfo name="RFC" value="2616"/>
2398</reference>
2399
2400<reference anchor="RFC3629">
2401  <front>
2402    <title>UTF-8, a transformation format of ISO 10646</title>
2403    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2404      <organization>Alis Technologies</organization>
2405      <address><email>fyergeau@alis.com</email></address>
2406    </author>
2407    <date month="November" year="2003"/>
2408  </front>
2409  <seriesInfo name="RFC" value="3629"/>
2410  <seriesInfo name="STD" value="63"/>
2411</reference>
2412
2413<reference anchor='RFC3864'>
2414  <front>
2415    <title>Registration Procedures for Message Header Fields</title>
2416    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2417      <organization>Nine by Nine</organization>
2418      <address><email>GK-IETF@ninebynine.org</email></address>
2419    </author>
2420    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2421      <organization>BEA Systems</organization>
2422      <address><email>mnot@pobox.com</email></address>
2423    </author>
2424    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2425      <organization>HP Labs</organization>
2426      <address><email>JeffMogul@acm.org</email></address>
2427    </author>
2428    <date year='2004' month='September' />
2429  </front>
2430  <seriesInfo name='BCP' value='90' />
2431  <seriesInfo name='RFC' value='3864' />
2432</reference>
2433
2434<reference anchor="RFC4288">
2435  <front>
2436    <title>Media Type Specifications and Registration Procedures</title>
2437    <author initials="N." surname="Freed" fullname="N. Freed">
2438      <organization>Sun Microsystems</organization>
2439      <address>
2440        <email>ned.freed@mrochek.com</email>
2441      </address>
2442    </author>
2443    <author initials="J." surname="Klensin" fullname="J. Klensin">
2444      <address>
2445        <email>klensin+ietf@jck.com</email>
2446      </address>
2447    </author>
2448    <date year="2005" month="December"/>
2449  </front>
2450  <seriesInfo name="BCP" value="13"/>
2451  <seriesInfo name="RFC" value="4288"/>
2452</reference>
2453
2454<reference anchor='RFC5226'>
2455  <front>
2456    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2457    <author initials='T.' surname='Narten' fullname='T. Narten'>
2458      <organization>IBM</organization>
2459      <address><email>narten@us.ibm.com</email></address>
2460    </author>
2461    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2462      <organization>Google</organization>
2463      <address><email>Harald@Alvestrand.no</email></address>
2464    </author>
2465    <date year='2008' month='May' />
2466  </front>
2467  <seriesInfo name='BCP' value='26' />
2468  <seriesInfo name='RFC' value='5226' />
2469</reference>
2470
2471<reference anchor="RFC5322">
2472  <front>
2473    <title>Internet Message Format</title>
2474    <author initials="P." surname="Resnick" fullname="P. Resnick">
2475      <organization>Qualcomm Incorporated</organization>
2476    </author>
2477    <date year="2008" month="October"/>
2478  </front> 
2479  <seriesInfo name="RFC" value="5322"/>
2480</reference>
2481
2482<reference anchor='BCP97'>
2483  <front>
2484    <title>Handling Normative References to Standards-Track Documents</title>
2485    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2486      <address>
2487        <email>klensin+ietf@jck.com</email>
2488      </address>
2489    </author>
2490    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2491      <organization>MIT</organization>
2492      <address>
2493        <email>hartmans-ietf@mit.edu</email>
2494      </address>
2495    </author>
2496    <date year='2007' month='June' />
2497  </front>
2498  <seriesInfo name='BCP' value='97' />
2499  <seriesInfo name='RFC' value='4897' />
2500</reference>
2501
2502
2503</references>
2504
2505<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2506<t>
2507   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
2508   allow entities to be transmitted in an open variety of
2509   representations and with extensible mechanisms. However, RFC 2045
2510   discusses mail, and HTTP has a few features that are different from
2511   those described in RFC 2045. These differences were carefully chosen
2512   to optimize performance over binary connections, to allow greater
2513   freedom in the use of new media types, to make date comparisons
2514   easier, and to acknowledge the practice of some early HTTP servers
2515   and clients.
2516</t>
2517<t>
2518   This appendix describes specific areas where HTTP differs from RFC
2519   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2520   aware of these differences and provide the appropriate conversions
2521   where necessary. Proxies and gateways from MIME environments to HTTP
2522   also need to be aware of the differences because some conversions
2523   might be required.
2524</t>
2525
2526<section title="MIME-Version" anchor="mime-version">
2527  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2528  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2529  <x:anchor-alias value="MIME-Version"/>
2530  <x:anchor-alias value="MIME-Version-v"/>
2531<t>
2532   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2533   include a single MIME-Version general-header field to indicate what
2534   version of the MIME protocol was used to construct the message. Use
2535   of the MIME-Version header field indicates that the message is in
2536   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2537   Proxies/gateways are responsible for ensuring full compliance (where
2538   possible) when exporting HTTP messages to strict MIME environments.
2539</t>
2540<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2541  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2542  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2543</artwork></figure>
2544<t>
2545   MIME version "1.0" is the default for use in HTTP/1.1. However,
2546   HTTP/1.1 message parsing and semantics are defined by this document
2547   and not the MIME specification.
2548</t>
2549</section>
2550
2551<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2552<t>
2553   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2554   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2555   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2556   allowed for subtypes of the "text" media type when transmitted over
2557   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2558   line breaks as CRLF and forbids the use of CR or LF outside of line
2559   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2560   line break within text content when a message is transmitted over
2561   HTTP.
2562</t>
2563<t>
2564   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2565   environment &SHOULD; translate all line breaks within the text media
2566   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2567   canonical form of CRLF. Note, however, that this might be complicated
2568   by the presence of a Content-Encoding and by the fact that HTTP
2569   allows the use of some character sets which do not use octets 13 and
2570   10 to represent CR and LF, as is the case for some multi-byte
2571   character sets.
2572</t>
2573<t>
2574   Implementors should note that conversion will break any cryptographic
2575   checksums applied to the original content unless the original content
2576   is already in canonical form. Therefore, the canonical form is
2577   recommended for any content that uses such checksums in HTTP.
2578</t>
2579</section>
2580
2581
2582<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2583<t>
2584   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2585   simplify the process of date comparison. Proxies and gateways from
2586   other protocols &SHOULD; ensure that any Date header field present in a
2587   message conforms to one of the HTTP/1.1 formats and rewrite the date
2588   if necessary.
2589</t>
2590</section>
2591
2592<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2593<t>
2594   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2595   Content-Encoding header field. Since this acts as a modifier on the
2596   media type, proxies and gateways from HTTP to MIME-compliant
2597   protocols &MUST; either change the value of the Content-Type header
2598   field or decode the entity-body before forwarding the message. (Some
2599   experimental applications of Content-Type for Internet mail have used
2600   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2601   a function equivalent to Content-Encoding. However, this parameter is
2602   not part of RFC 2045).
2603</t>
2604</section>
2605
2606<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2607<t>
2608   HTTP does not use the Content-Transfer-Encoding field of RFC
2609   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2610   remove any Content-Transfer-Encoding
2611   prior to delivering the response message to an HTTP client.
2612</t>
2613<t>
2614   Proxies and gateways from HTTP to MIME-compliant protocols are
2615   responsible for ensuring that the message is in the correct format
2616   and encoding for safe transport on that protocol, where "safe
2617   transport" is defined by the limitations of the protocol being used.
2618   Such a proxy or gateway &SHOULD; label the data with an appropriate
2619   Content-Transfer-Encoding if doing so will improve the likelihood of
2620   safe transport over the destination protocol.
2621</t>
2622</section>
2623
2624<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2625<t>
2626   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2627   Proxies/gateways &MUST; remove any transfer-coding prior to
2628   forwarding a message via a MIME-compliant protocol.
2629</t>
2630</section>
2631
2632<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2633<t>
2634   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2635   need to be aware of MIME line length limitations. Since HTTP does not
2636   have this limitation, HTTP does not fold long lines. MHTML messages
2637   being transported by HTTP follow all conventions of MHTML, including
2638   line length limitations and folding, canonicalization, etc., since
2639   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2640   does not interpret the content or any MIME header lines that might be
2641   contained therein.
2642</t>
2643</section>
2644</section>
2645
2646<section title="Additional Features" anchor="additional.features">
2647<t>
2648   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2649   existing HTTP implementations, but not consistently and correctly
2650   across most HTTP/1.1 applications. Implementors are advised to be
2651   aware of these features, but cannot rely upon their presence in, or
2652   interoperability with, other HTTP/1.1 applications. Some of these
2653   describe proposed experimental features, and some describe features
2654   that experimental deployment found lacking that are now addressed in
2655   the base HTTP/1.1 specification.
2656</t>
2657<t>
2658   A number of other headers, such as Content-Disposition and Title,
2659   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2660</t>
2661
2662<section title="Content-Disposition" anchor="content-disposition">
2663<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2664<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2665  <x:anchor-alias value="content-disposition"/>
2666  <x:anchor-alias value="content-disposition-v"/>
2667  <x:anchor-alias value="disposition-type"/>
2668  <x:anchor-alias value="disposition-parm"/>
2669  <x:anchor-alias value="disp-extension-parm"/>
2670  <x:anchor-alias value="disp-extension-token"/>
2671  <x:anchor-alias value="filename-parm"/>
2672<t>
2673   The "Content-Disposition" response-header field has been proposed as a
2674   means for the origin server to suggest a default filename if the user
2675   requests that the content is saved to a file. This usage is derived
2676   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2677</t>
2678<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2679  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2680                        <x:ref>content-disposition-v</x:ref>
2681  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2682                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2683  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2684  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2685  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2686  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2687  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" <x:ref>word</x:ref>
2688</artwork></figure>
2689<t>
2690   An example is
2691</t>
2692<figure><artwork type="example">
2693  Content-Disposition: attachment; filename="fname.ext"
2694</artwork></figure>
2695<t>
2696   The receiving user agent &SHOULD-NOT;  respect any directory path
2697   information present in the filename-parm parameter, which is the only
2698   parameter believed to apply to HTTP implementations at this time. The
2699   filename &SHOULD; be treated as a terminal component only.
2700</t>
2701<t>
2702   If this header is used in a response with the application/octet-stream
2703   content-type, the implied suggestion is that the user agent
2704   should not display the response, but directly enter a "save response
2705   as..." dialog.
2706</t>
2707<t>
2708   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2709</t>
2710</section>
2711</section>
2712
2713<section title="Compatibility with Previous Versions" anchor="compatibility">
2714<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2715<t>
2716   Transfer-coding and message lengths all interact in ways that
2717   required fixing exactly when chunked encoding is used (to allow for
2718   transfer encoding that may not be self delimiting); it was important
2719   to straighten out exactly how message lengths are computed.
2720   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2721   <xref target="Part5"/> and <xref target="Part6"/>).
2722</t>
2723<t>
2724   Charset wildcarding is introduced to avoid explosion of character set
2725   names in accept headers. (<xref target="header.accept-charset"/>)
2726</t>
2727<t>
2728   Content-Base was deleted from the specification: it was not
2729   implemented widely, and there is no simple, safe way to introduce it
2730   without a robust extension mechanism. In addition, it is used in a
2731   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2732</t>
2733<t>
2734   A content-coding of "identity" was introduced, to solve problems
2735   discovered in caching. (<xref target="content.codings"/>)
2736</t>
2737<t>
2738   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2739   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2740   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2741</t>
2742</section>
2743
2744<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2745<t>
2746  Clarify contexts that charset is used in.
2747  (<xref target="character.sets"/>)
2748</t>
2749<t>
2750  Remove base URI setting semantics for Content-Location due to poor
2751  implementation support, which was caused by too many broken servers emitting
2752  bogus Content-Location headers, and also the potentially undesirable effect
2753  of potentially breaking relative links in content-negotiated resources.
2754  (<xref target="header.content-location"/>)
2755</t>
2756<t>
2757  Remove reference to non-existant identity transfer-coding value tokens.
2758  (<xref target="no.content-transfer-encoding"/>)
2759</t>
2760</section>
2761
2762</section>
2763
2764<?BEGININC p3-payload.abnf-appendix ?>
2765<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2766<figure>
2767<artwork type="abnf" name="p3-payload.parsed-abnf">
2768<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2769<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2770<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2771 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2772 qvalue ] ] )
2773<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2774<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2775 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2776<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2777<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2778 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2779 ] )
2780<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2781 OWS media-range [ accept-params ] ] ) ]
2782
2783<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2784<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2785 content-coding ] )
2786<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2787<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2788 language-tag ] )
2789<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2790<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2791<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2792<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2793<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2794<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2795<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2796<x:ref>Content-Type-v</x:ref> = media-type
2797
2798<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2799
2800<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2801
2802<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2803<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2804
2805<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2806
2807<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2808<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2809<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2810<x:ref>attribute</x:ref> = token
2811
2812<x:ref>charset</x:ref> = token
2813<x:ref>codings</x:ref> = ( content-coding / "*" )
2814<x:ref>content-coding</x:ref> = token
2815<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2816 content-disposition-v
2817<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2818 disposition-parm )
2819
2820<x:ref>disp-extension-parm</x:ref> = token "=" word
2821<x:ref>disp-extension-token</x:ref> = token
2822<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2823<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2824
2825<x:ref>entity-body</x:ref> = *OCTET
2826<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2827 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2828 Expires / Last-Modified / extension-header
2829<x:ref>extension-header</x:ref> = header-field
2830
2831<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2832
2833<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2834
2835<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2836<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2837
2838<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2839 ";" OWS parameter )
2840<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2841
2842<x:ref>parameter</x:ref> = attribute "=" value
2843<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2844
2845<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2846<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2847
2848<x:ref>subtype</x:ref> = token
2849
2850<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2851<x:ref>type</x:ref> = token
2852
2853<x:ref>value</x:ref> = word
2854
2855<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2856</artwork>
2857</figure>
2858<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2859; Accept defined but not used
2860; Accept-Charset defined but not used
2861; Accept-Encoding defined but not used
2862; Accept-Language defined but not used
2863; MIME-Version defined but not used
2864; content-disposition defined but not used
2865; entity-body defined but not used
2866; entity-header defined but not used
2867</artwork></figure></section>
2868<?ENDINC p3-payload.abnf-appendix ?>
2869
2870<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2871
2872<section title="Since RFC2616">
2873<t>
2874  Extracted relevant partitions from <xref target="RFC2616"/>.
2875</t>
2876</section>
2877
2878<section title="Since draft-ietf-httpbis-p3-payload-00">
2879<t>
2880  Closed issues:
2881  <list style="symbols"> 
2882    <t>
2883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2884      "Media Type Registrations"
2885      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2886    </t>
2887    <t>
2888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2889      "Clarification regarding quoting of charset values"
2890      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2891    </t>
2892    <t>
2893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2894      "Remove 'identity' token references"
2895      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2896    </t>
2897    <t>
2898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2899      "Accept-Encoding BNF"
2900    </t>
2901    <t>
2902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2903      "Normative and Informative references"
2904    </t>
2905    <t>
2906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2907      "RFC1700 references"
2908    </t>
2909    <t>
2910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2911      "Updating to RFC4288"
2912    </t>
2913    <t>
2914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2915      "Informative references"
2916    </t>
2917    <t>
2918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2919      "ISO-8859-1 Reference"
2920    </t>
2921    <t>
2922      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2923      "Encoding References Normative"
2924    </t>
2925    <t>
2926      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2927      "Normative up-to-date references"
2928    </t>
2929  </list>
2930</t>
2931</section>
2932
2933<section title="Since draft-ietf-httpbis-p3-payload-01">
2934<t>
2935  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2936  <list style="symbols"> 
2937    <t>
2938      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2939    </t>
2940  </list>
2941</t>
2942</section>
2943
2944<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2945<t>
2946  Closed issues:
2947  <list style="symbols"> 
2948    <t>
2949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2950      "Quoting Charsets"
2951    </t>
2952    <t>
2953      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2954      "Classification for Allow header"
2955    </t>
2956    <t>
2957      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2958      "missing default for qvalue in description of Accept-Encoding"
2959    </t>
2960  </list>
2961</t>
2962<t>
2963  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2964  <list style="symbols"> 
2965    <t>
2966      Reference RFC 3984, and update header registrations for headers defined
2967      in this document.
2968    </t>
2969  </list>
2970</t>
2971</section>
2972
2973<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2974<t>
2975  Closed issues:
2976  <list style="symbols"> 
2977    <t>
2978      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2979      "Quoting Charsets"
2980    </t>
2981    <t>
2982      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2983      "language tag matching (Accept-Language) vs RFC4647"
2984    </t>
2985    <t>
2986      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2987      "RFC 1806 has been replaced by RFC2183"
2988    </t>
2989  </list>
2990</t>
2991<t>
2992  Other changes:
2993  <list style="symbols"> 
2994    <t>
2995      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2996      "Encoding References Normative" -- rephrase the annotation and reference
2997      <xref target="BCP97"/>.
2998    </t>
2999  </list>
3000</t>
3001 </section>
3002
3003<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
3004<t>
3005  Closed issues:
3006  <list style="symbols"> 
3007    <t>
3008      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3009      "RFC 2822 is updated by RFC 5322"
3010    </t>
3011  </list>
3012</t>
3013<t>
3014  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3015  <list style="symbols"> 
3016    <t>
3017      Use "/" instead of "|" for alternatives.
3018    </t>
3019    <t>
3020      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3021      whitespace ("OWS") and required whitespace ("RWS").
3022    </t>
3023    <t>
3024      Rewrite ABNFs to spell out whitespace rules, factor out
3025      header value format definitions.
3026    </t>
3027  </list>
3028</t>
3029</section>
3030
3031<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3032<t>
3033  Closed issues:
3034  <list style="symbols"> 
3035    <t>
3036      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3037      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3038    </t>
3039  </list>
3040</t>
3041<t>
3042  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3043  <list style="symbols"> 
3044    <t>
3045      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3046    </t>
3047  </list>
3048</t>
3049<t>
3050  Other changes:
3051  <list style="symbols"> 
3052    <t>
3053      Move definition of quality values into Part 1.
3054    </t>
3055  </list>
3056</t>
3057</section>
3058
3059<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3060<t>
3061  Closed issues:
3062  <list style="symbols"> 
3063    <t>
3064      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3065      "Content-Location isn't special"
3066    </t>
3067    <t>
3068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3069      "Content Sniffing"
3070    </t>
3071  </list>
3072</t>
3073</section>
3074
3075<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3076<t>
3077  Closed issues:
3078  <list style="symbols"> 
3079    <t>
3080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3081      "Updated reference for language tags"
3082    </t>
3083    <t>
3084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3085      "Clarify rules for determining what entities a response carries"
3086    </t>
3087    <t>
3088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3089      "Content-Location base-setting problems"
3090    </t>
3091    <t>
3092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3093      "Content Sniffing"
3094    </t>
3095    <t>
3096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3097      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3098    </t>
3099    <t>
3100      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3101      "move definitions of gzip/deflate/compress to part 1"
3102    </t>
3103  </list>
3104</t>
3105<t>
3106  Partly resolved issues:
3107  <list style="symbols"> 
3108    <t>
3109      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3110      "update IANA requirements wrt Transfer-Coding values" (add the
3111      IANA Considerations subsection)
3112    </t>
3113    <t>
3114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3115      "update IANA requirements wrt Content-Coding values" (add the
3116      IANA Considerations subsection)
3117    </t>
3118  </list>
3119</t>
3120</section>
3121
3122<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3123<t>
3124  Closed issues:
3125  <list style="symbols"> 
3126    <t>
3127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3128      "Content Negotiation for media types"
3129    </t>
3130    <t>
3131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3132      "Accept-Language: which RFC4647 filtering?"
3133    </t>
3134  </list>
3135</t>
3136</section>
3137
3138<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3139<t>
3140  Closed issues:
3141  <list style="symbols"> 
3142    <t>
3143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3144      "IANA registry for content/transfer encodings"
3145    </t>
3146    <t>
3147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3148      "use of term "word" when talking about header structure"
3149    </t>
3150  </list>
3151</t>
3152</section>
3153
3154</section>
3155
3156</back>
3157</rfc>
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