source: draft-ietf-httpbis/latest/p3-payload.xml @ 376

Last change on this file since 376 was 376, checked in by julian.reschke@…, 11 years ago

fix width problems in ABNF (related to #36)

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File size: 120.4 KB
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[29]1<?xml version="1.0" encoding="utf-8"?>
[101]2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
[8]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>">
[29]14  <!ENTITY ID-VERSION "latest">
[331]15  <!ENTITY ID-MONTH "November">
[124]16  <!ENTITY ID-YEAR "2008">
[205]17  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[115]19  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[31]20  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[115]26  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[31]27  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[206]29  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[31]30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[374]31  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
[8]32]>
33<?rfc toc="yes" ?>
[29]34<?rfc symrefs="yes" ?>
35<?rfc sortrefs="yes" ?>
[8]36<?rfc compact="yes"?>
37<?rfc subcompact="no" ?>
38<?rfc linkmailto="no" ?>
39<?rfc editing="no" ?>
[203]40<?rfc comments="yes"?>
41<?rfc inline="yes"?>
[8]42<?rfc-ext allow-markup-in-artwork="yes" ?>
43<?rfc-ext include-references-in-index="yes" ?>
[308]44<rfc obsoletes="2616" category="std" x:maturity-level="draft"
[29]45     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
[153]46     xmlns:x='http://purl.org/net/xml2rfc/ext'>
[8]47<front>
48
[120]49  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
[8]50
[29]51  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
52    <organization abbrev="Day Software">Day Software</organization>
[8]53    <address>
54      <postal>
[29]55        <street>23 Corporate Plaza DR, Suite 280</street>
56        <city>Newport Beach</city>
[8]57        <region>CA</region>
[29]58        <code>92660</code>
59        <country>USA</country>
[8]60      </postal>
[29]61      <phone>+1-949-706-5300</phone>
62      <facsimile>+1-949-706-5305</facsimile>
63      <email>fielding@gbiv.com</email>
64      <uri>http://roy.gbiv.com/</uri>
[8]65    </address>
66  </author>
67
[29]68  <author initials="J." surname="Gettys" fullname="Jim Gettys">
69    <organization>One Laptop per Child</organization>
[8]70    <address>
71      <postal>
[29]72        <street>21 Oak Knoll Road</street>
73        <city>Carlisle</city>
[8]74        <region>MA</region>
[29]75        <code>01741</code>
76        <country>USA</country>
[8]77      </postal>
[29]78      <email>jg@laptop.org</email>
79      <uri>http://www.laptop.org/</uri>
[8]80    </address>
81  </author>
82 
83  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]84    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]85    <address>
86      <postal>
[29]87        <street>HP Labs, Large Scale Systems Group</street>
88        <street>1501 Page Mill Road, MS 1177</street>
[8]89        <city>Palo Alto</city>
90        <region>CA</region>
[29]91        <code>94304</code>
92        <country>USA</country>
[8]93      </postal>
[29]94      <email>JeffMogul@acm.org</email>
[8]95    </address>
96  </author>
97
98  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]100    <address>
101      <postal>
[29]102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106        <country>USA</country>
[8]107      </postal>
[29]108      <email>henrikn@microsoft.com</email>
[8]109    </address>
110  </author>
111
112  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[29]113    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
[8]114    <address>
115      <postal>
[29]116        <street>345 Park Ave</street>
117        <city>San Jose</city>
[8]118        <region>CA</region>
[29]119        <code>95110</code>
120        <country>USA</country>
[8]121      </postal>
[29]122      <email>LMM@acm.org</email>
123      <uri>http://larry.masinter.net/</uri>
[8]124    </address>
125  </author>
126 
127  <author initials="P." surname="Leach" fullname="Paul J. Leach">
128    <organization abbrev="Microsoft">Microsoft Corporation</organization>
129    <address>
130      <postal>
131        <street>1 Microsoft Way</street>
132        <city>Redmond</city>
133        <region>WA</region>
134        <code>98052</code>
135      </postal>
136      <email>paulle@microsoft.com</email>
137    </address>
138  </author>
139   
140  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
141    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
142    <address>
143      <postal>
[34]144        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
145        <street>The Stata Center, Building 32</street>
146        <street>32 Vassar Street</street>
[8]147        <city>Cambridge</city>
148        <region>MA</region>
149        <code>02139</code>
[29]150        <country>USA</country>
[8]151      </postal>
152      <email>timbl@w3.org</email>
[34]153      <uri>http://www.w3.org/People/Berners-Lee/</uri>
[8]154    </address>
155  </author>
156
[95]157  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]158    <organization abbrev="W3C">World Wide Web Consortium</organization>
159    <address>
160      <postal>
161        <street>W3C / ERCIM</street>
162        <street>2004, rte des Lucioles</street>
163        <city>Sophia-Antipolis</city>
164        <region>AM</region>
165        <code>06902</code>
166        <country>France</country>
167      </postal>
168      <email>ylafon@w3.org</email>
169      <uri>http://www.raubacapeu.net/people/yves/</uri>
170    </address>
171  </author>
172
[95]173  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
174    <organization abbrev="greenbytes">greenbytes GmbH</organization>
175    <address>
176      <postal>
177        <street>Hafenweg 16</street>
178        <city>Muenster</city><region>NW</region><code>48155</code>
179        <country>Germany</country>
180      </postal>
181      <phone>+49 251 2807760</phone>   
182      <facsimile>+49 251 2807761</facsimile>   
183      <email>julian.reschke@greenbytes.de</email>       
184      <uri>http://greenbytes.de/tech/webdav/</uri>     
185    </address>
186  </author>
187
[31]188  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[8]189
190<abstract>
191<t>
192   The Hypertext Transfer Protocol (HTTP) is an application-level
193   protocol for distributed, collaborative, hypermedia information
[29]194   systems. HTTP has been in use by the World Wide Web global information
[35]195   initiative since 1990. This document is Part 3 of the seven-part specification
[29]196   that defines the protocol referred to as "HTTP/1.1" and, taken together,
[42]197   obsoletes RFC 2616.  Part 3 defines HTTP message content,
[29]198   metadata, and content negotiation.
[8]199</t>
200</abstract>
[36]201
202<note title="Editorial Note (To be removed by RFC Editor)">
203  <t>
204    Discussion of this draft should take place on the HTTPBIS working group
205    mailing list (ietf-http-wg@w3.org). The current issues list is
[324]206    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
[36]207    and related documents (including fancy diffs) can be found at
[324]208    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
[36]209  </t>
[153]210  <t>
[345]211    The changes in this draft are summarized in <xref target="changes.since.04"/>.
[153]212  </t>
[36]213</note>
[8]214</front>
215<middle>
216<section title="Introduction" anchor="introduction">
217<t>
[163]218   This document defines HTTP/1.1 message payloads (a.k.a., content), the
[161]219   associated metadata header fields that define how the payload is intended
220   to be interpreted by a recipient, the request header fields that
221   may influence content selection, and the various selection algorithms
222   that are collectively referred to as HTTP content negotiation.
[8]223</t>
[161]224<t>
225   This document is currently disorganized in order to minimize the changes
226   between drafts and enable reviewers to see the smaller errata changes.
227   The next draft will reorganize the sections to better reflect the content.
228   In particular, the sections on entities will be renamed payload and moved
229   to the first half of the document, while the sections on content negotiation
230   and associated request header fields will be moved to the second half.  The
231   current mess reflects how widely dispersed these topics and associated
232   requirements had become in <xref target="RFC2616"/>.
233</t>
[96]234
235<section title="Requirements" anchor="intro.requirements">
236<t>
237   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
238   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
239   document are to be interpreted as described in <xref target="RFC2119"/>.
240</t>
241<t>
242   An implementation is not compliant if it fails to satisfy one or more
243   of the &MUST; or &REQUIRED; level requirements for the protocols it
244   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
245   level and all the &SHOULD; level requirements for its protocols is said
246   to be "unconditionally compliant"; one that satisfies all the &MUST;
247   level requirements but not all the &SHOULD; level requirements for its
248   protocols is said to be "conditionally compliant."
249</t>
[8]250</section>
[96]251</section>
[8]252
[205]253<section title="Notational Conventions and Generic Grammar" anchor="notation">
[229]254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="DIGIT"/>
256  <x:anchor-alias value="OCTET"/>
257  <x:anchor-alias value="quoted-string"/>
258  <x:anchor-alias value="token"/>
[357]259  <x:anchor-alias value="OWS"/>
[205]260<t>
261  This specification uses the ABNF syntax defined in &notation-abnf; and
262  the core rules defined in &basic-rules;:
263  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
264  <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>.</cref>
265</t>
266<figure><artwork type="abnf2616">
[229]267  <x:ref>ALPHA</x:ref>          = &lt;ALPHA, defined in &basic-rules;&gt;
268  <x:ref>DIGIT</x:ref>          = &lt;DIGIT, defined in &basic-rules;&gt;
269  <x:ref>OCTET</x:ref>          = &lt;OCTET, defined in &basic-rules;&gt;
[205]270</artwork></figure>
271<figure><artwork type="abnf2616">
[229]272  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
273  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
[357]274  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
[205]275</artwork></figure>
[207]276<t anchor="abnf.dependencies">
[374]277  <x:anchor-alias value="absolute-URI"/>
[229]278  <x:anchor-alias value="Allow"/>
279  <x:anchor-alias value="Content-Length"/>
280  <x:anchor-alias value="Content-Range"/>
281  <x:anchor-alias value="Expires"/>
282  <x:anchor-alias value="Last-Modified"/>
283  <x:anchor-alias value="message-header"/>
284  <x:anchor-alias value="relativeURI"/>
[206]285  The ABNF rules below are defined in other parts:
286</t>
[207]287<figure><!--Part1--><artwork type="abnf2616">
[374]288  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[229]289  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
[374]290  <x:ref>relativeURI</x:ref>    = &lt;relativeURI, defined in &uri;&gt;
[229]291  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
[207]292</artwork></figure>
293<figure><!--Part4--><artwork type="abnf2616">
[229]294  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
[207]295</artwork></figure>
296<figure><!--Part5--><artwork type="abnf2616">
[229]297  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
[207]298</artwork></figure>
299<figure><!--Part6--><artwork type="abnf2616">
[229]300  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
[206]301</artwork></figure>
[205]302</section>
303
[8]304<section title="Protocol Parameters" anchor="protocol.parameters">
305
306<section title="Character Sets" anchor="character.sets">
307<t>
308   HTTP uses the same definition of the term "character set" as that
309   described for MIME:
310</t>
311<t>
312   The term "character set" is used in this document to refer to a
313   method used with one or more tables to convert a sequence of octets
314   into a sequence of characters. Note that unconditional conversion in
315   the other direction is not required, in that not all characters may
316   be available in a given character set and a character set may provide
317   more than one sequence of octets to represent a particular character.
318   This definition is intended to allow various kinds of character
319   encoding, from simple single-table mappings such as US-ASCII to
320   complex table switching methods such as those that use ISO-2022's
321   techniques. However, the definition associated with a MIME character
322   set name &MUST; fully specify the mapping to be performed from octets
323   to characters. In particular, use of external profiling information
324   to determine the exact mapping is not permitted.
325</t>
326<t><list><t>
327      <x:h>Note:</x:h> This use of the term "character set" is more commonly
328      referred to as a "character encoding." However, since HTTP and
329      MIME share the same registry, it is important that the terminology
330      also be shared.
331</t></list></t>
[229]332<t anchor="rule.charset">
333  <x:anchor-alias value="charset"/>
[8]334   HTTP character sets are identified by case-insensitive tokens. The
335   complete set of tokens is defined by the IANA Character Set registry
[91]336   (<eref target="http://www.iana.org/assignments/character-sets"/>).
[8]337</t>
338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]339  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
[8]340</artwork></figure>
341<t>
342   Although HTTP allows an arbitrary token to be used as a charset
343   value, any token that has a predefined value within the IANA
[91]344   Character Set registry &MUST; represent the character set defined
[8]345   by that registry. Applications &SHOULD; limit their use of character
346   sets to those defined by the IANA registry.
347</t>
348<t>
[81]349   HTTP uses charset in two contexts: within an Accept-Charset request
350   header (in which the charset value is an unquoted token) and as the
[115]351   value of a parameter in a Content-Type header (within a request or
[81]352   response), in which case the parameter value of the charset parameter
353   may be quoted.
354</t>
355<t>
[129]356   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
[8]357   <xref target="RFC2277"/>.
358</t>
[211]359
360<section title="Missing Charset" anchor="missing.charset">
361<t>
362   Some HTTP/1.0 software has interpreted a Content-Type header without
363   charset parameter incorrectly to mean "recipient should guess."
364   Senders wishing to defeat this behavior &MAY; include a charset
365   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
366   it is known that it will not confuse the recipient.
367</t>
368<t>
369   Unfortunately, some older HTTP/1.0 clients did not deal properly with
370   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
371   charset label provided by the sender; and those user agents that have
372   a provision to "guess" a charset &MUST; use the charset from the
373   content-type field if they support that charset, rather than the
374   recipient's preference, when initially displaying a document. See
375   <xref target="canonicalization.and.text.defaults"/>.
376</t>
[8]377</section>
[211]378</section>
[8]379
380<section title="Content Codings" anchor="content.codings">
[229]381  <x:anchor-alias value="content-coding"/>
[8]382<t>
383   Content coding values indicate an encoding transformation that has
384   been or can be applied to an entity. Content codings are primarily
385   used to allow a document to be compressed or otherwise usefully
386   transformed without losing the identity of its underlying media type
387   and without loss of information. Frequently, the entity is stored in
388   coded form, transmitted directly, and only decoded by the recipient.
389</t>
390<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]391  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
[8]392</artwork></figure>
393<t>
394   All content-coding values are case-insensitive. HTTP/1.1 uses
395   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
396   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
397   describes the content-coding, what is more important is that it
398   indicates what decoding mechanism will be required to remove the
399   encoding.
400</t>
401<t>
402   The Internet Assigned Numbers Authority (IANA) acts as a registry for
403   content-coding value tokens. Initially, the registry contains the
404   following tokens:
405</t>
406<t>
407   gzip<iref item="gzip"/>
408  <list>
409    <t>
410        An encoding format produced by the file compression program
[97]411        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
[8]412        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
413    </t>
414  </list>
415</t>
416<t>
417   compress<iref item="compress"/>
418  <list><t>
419        The encoding format produced by the common UNIX file compression
420        program "compress". This format is an adaptive Lempel-Ziv-Welch
421        coding (LZW).
422</t><t>
423        Use of program names for the identification of encoding formats
424        is not desirable and is discouraged for future encodings. Their
425        use here is representative of historical practice, not good
426        design. For compatibility with previous implementations of HTTP,
427        applications &SHOULD; consider "x-gzip" and "x-compress" to be
428        equivalent to "gzip" and "compress" respectively.
429  </t></list>
430</t>
431<t>
432   deflate<iref item="deflate"/>
433  <list><t>
[97]434        The "zlib" format defined in <xref target="RFC1950"/> in combination with
435        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
[8]436  </t></list>
437</t>
438<t>
439   identity<iref item="identity"/>
440  <list><t>
441        The default (identity) encoding; the use of no transformation
442        whatsoever. This content-coding is used only in the Accept-Encoding
443        header, and &SHOULD-NOT;  be used in the Content-Encoding
444        header.
445  </t></list>
446</t>
447<t>
448   New content-coding value tokens &SHOULD; be registered; to allow
449   interoperability between clients and servers, specifications of the
450   content coding algorithms needed to implement a new value &SHOULD; be
451   publicly available and adequate for independent implementation, and
452   conform to the purpose of content coding defined in this section.
453</t>
454</section>
455
456<section title="Media Types" anchor="media.types">
[229]457  <x:anchor-alias value="media-type"/>
458  <x:anchor-alias value="type"/>
459  <x:anchor-alias value="subtype"/>
[8]460<t>
[152]461   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]462   and Accept (<xref target="header.accept"/>) header fields in order to provide
463   open and extensible data typing and type negotiation.
464</t>
465<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"/>
[357]466  <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> )
467  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
468  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[8]469</artwork></figure>
[229]470<t anchor="rule.parameter">
471  <x:anchor-alias value="attribute"/>
472  <x:anchor-alias value="parameter"/>
473  <x:anchor-alias value="value"/>
[8]474   Parameters &MAY; follow the type/subtype in the form of attribute/value
[29]475   pairs.
[8]476</t>
[29]477<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"/>
[250]478  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
479  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[334]480  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
[29]481</artwork></figure>
[8]482<t>
483   The type, subtype, and parameter attribute names are case-insensitive.
[370]484   Parameter values might or might not be case-sensitive, depending on the
485   semantics of the parameter name.  The presence or absence of a parameter might
[8]486   be significant to the processing of a media-type, depending on its
487   definition within the media type registry.
488</t>
489<t>
[297]490   A parameter value that matches the <x:ref>token</x:ref> production may be
491   transmitted as either a token or within a quoted-string. The quoted and
492   unquoted values are equivalent.
[251]493</t>
494<t>
[8]495   Note that some older HTTP applications do not recognize media type
496   parameters. When sending data to older HTTP applications,
497   implementations &SHOULD; only use media type parameters when they are
498   required by that type/subtype definition.
499</t>
500<t>
501   Media-type values are registered with the Internet Assigned Number
[91]502   Authority (IANA). The media type registration process is
[115]503   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]504   discouraged.
505</t>
506
507<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
508<t>
509   Internet media types are registered with a canonical form. An
510   entity-body transferred via HTTP messages &MUST; be represented in the
511   appropriate canonical form prior to its transmission except for
512   "text" types, as defined in the next paragraph.
513</t>
514<t>
515   When in canonical form, media subtypes of the "text" type use CRLF as
516   the text line break. HTTP relaxes this requirement and allows the
517   transport of text media with plain CR or LF alone representing a line
518   break when it is done consistently for an entire entity-body. HTTP
519   applications &MUST; accept CRLF, bare CR, and bare LF as being
520   representative of a line break in text media received via HTTP. In
521   addition, if the text is represented in a character set that does not
522   use octets 13 and 10 for CR and LF respectively, as is the case for
523   some multi-byte character sets, HTTP allows the use of whatever octet
524   sequences are defined by that character set to represent the
525   equivalent of CR and LF for line breaks. This flexibility regarding
526   line breaks applies only to text media in the entity-body; a bare CR
527   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
528   structures (such as header fields and multipart boundaries).
529</t>
530<t>
531   If an entity-body is encoded with a content-coding, the underlying
532   data &MUST; be in a form defined above prior to being encoded.
533</t>
534<t>
[211]535   The "charset" parameter is used with some media types to define the
536   character set (<xref target="character.sets"/>) of the data. When no explicit charset
537   parameter is provided by the sender, media subtypes of the "text"
538   type are defined to have a default charset value of "ISO-8859-1" when
539   received via HTTP. Data in character sets other than "ISO-8859-1" or
540   its subsets &MUST; be labeled with an appropriate charset value. See
541   <xref target="missing.charset"/> for compatibility problems.
[8]542</t>
543</section>
544
545<section title="Multipart Types" anchor="multipart.types">
546<t>
547   MIME provides for a number of "multipart" types -- encapsulations of
548   one or more entities within a single message-body. All multipart
[97]549   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
550   and &MUST; include a boundary parameter as part of the media type
[8]551   value. The message body is itself a protocol element and &MUST;
552   therefore use only CRLF to represent line breaks between body-parts.
553   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
554   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
555   original multipart contains an epilogue). These restrictions exist in
556   order to preserve the self-delimiting nature of a multipart message-body,
557   wherein the "end" of the message-body is indicated by the
558   ending multipart boundary.
559</t>
560<t>
561   In general, HTTP treats a multipart message-body no differently than
562   any other media type: strictly as payload. The one exception is the
[29]563   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
[97]564   (Partial Content) response.
565   <!-- jre: re-insert removed text pointing to caching? -->
566   In all
[8]567   other cases, an HTTP user agent &SHOULD; follow the same or similar
568   behavior as a MIME user agent would upon receipt of a multipart type.
569   The MIME header fields within each body-part of a multipart message-body
570   do not have any significance to HTTP beyond that defined by
571   their MIME semantics.
572</t>
573<t>
574   In general, an HTTP user agent &SHOULD; follow the same or similar
575   behavior as a MIME user agent would upon receipt of a multipart type.
576   If an application receives an unrecognized multipart subtype, the
577   application &MUST; treat it as being equivalent to "multipart/mixed".
578</t>
579<t><list><t>
580      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
581      for carrying form data suitable for processing via the POST
[129]582      request method, as described in <xref target="RFC2388"/>.
[8]583</t></list></t>
584</section>
585</section>
586
587<section title="Quality Values" anchor="quality.values">
[229]588  <x:anchor-alias value="qvalue"/>
[8]589<t>
590   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
591   numbers to indicate the relative importance ("weight") of various
592   negotiable parameters.  A weight is normalized to a real number in
593   the range 0 through 1, where 0 is the minimum and 1 the maximum
594   value. If a parameter has a quality value of 0, then content with
595   this parameter is `not acceptable' for the client. HTTP/1.1
596   applications &MUST-NOT; generate more than three digits after the
597   decimal point. User configuration of these values &SHOULD; also be
598   limited in this fashion.
599</t>
600<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
[229]601  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
[334]602                 / ( "1" [ "." 0*3("0") ] )
[8]603</artwork></figure>
604<t>
605   "Quality values" is a misnomer, since these values merely represent
606   relative degradation in desired quality.
607</t>
608</section>
609
610<section title="Language Tags" anchor="language.tags">
[229]611  <x:anchor-alias value="language-tag"/>
612  <x:anchor-alias value="primary-tag"/>
613  <x:anchor-alias value="subtag"/>
[8]614<t>
615   A language tag identifies a natural language spoken, written, or
616   otherwise conveyed by human beings for communication of information
617   to other human beings. Computer languages are explicitly excluded.
618   HTTP uses language tags within the Accept-Language and Content-Language
619   fields.
620</t>
621<t>
622   The syntax and registry of HTTP language tags is the same as that
[97]623   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
[8]624   or more parts: A primary language tag and a possibly empty series of
625   subtags:
626</t>
627<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
[229]628  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
629  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
630  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
[8]631</artwork></figure>
632<t>
633   White space is not allowed within the tag and all tags are case-insensitive.
634   The name space of language tags is administered by the
635   IANA. Example tags include:
636</t>
637<figure><artwork type="example">
638    en, en-US, en-cockney, i-cherokee, x-pig-latin
639</artwork></figure>
640<t>
641   where any two-letter primary-tag is an ISO-639 language abbreviation
642   and any two-letter initial subtag is an ISO-3166 country code. (The
643   last three tags above are not registered tags; all but the last are
644   examples of tags which could be registered in future.)
645</t>
646</section>
647</section>
648
649<section title="Entity" anchor="entity">
650<t>
651   Request and Response messages &MAY; transfer an entity if not otherwise
652   restricted by the request method or response status code. An entity
653   consists of entity-header fields and an entity-body, although some
654   responses will only include the entity-headers.
655</t>
656<t>
657   In this section, both sender and recipient refer to either the client
658   or the server, depending on who sends and who receives the entity.
659</t>
660
661<section title="Entity Header Fields" anchor="entity.header.fields">
[229]662  <x:anchor-alias value="entity-header"/>
663  <x:anchor-alias value="extension-header"/>
[8]664<t>
665   Entity-header fields define metainformation about the entity-body or,
666   if no body is present, about the resource identified by the request.
667</t>
668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
[232]669  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
[334]670                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
671                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
672                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
673                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
674                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
675                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
676                 / <x:ref>Expires</x:ref>                  ; &header-expires;
677                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
678                 / <x:ref>extension-header</x:ref>
[135]679 
[229]680  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
[8]681</artwork></figure>
682<t>
683   The extension-header mechanism allows additional entity-header fields
684   to be defined without changing the protocol, but these fields cannot
685   be assumed to be recognizable by the recipient. Unrecognized header
686   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
687   transparent proxies.
688</t>
689</section>
690
691<section title="Entity Body" anchor="entity.body">
[229]692  <x:anchor-alias value="entity-body"/>
[8]693<t>
694   The entity-body (if any) sent with an HTTP request or response is in
695   a format and encoding defined by the entity-header fields.
696</t>
697<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
[229]698  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
[8]699</artwork></figure>
700<t>
701   An entity-body is only present in a message when a message-body is
[29]702   present, as described in &message-body;. The entity-body is obtained
[8]703   from the message-body by decoding any Transfer-Encoding that might
704   have been applied to ensure safe and proper transfer of the message.
705</t>
706
707<section title="Type" anchor="type">
708<t>
709   When an entity-body is included with a message, the data type of that
710   body is determined via the header fields Content-Type and Content-Encoding.
711   These define a two-layer, ordered encoding model:
712</t>
713<figure><artwork type="example">
714    entity-body := Content-Encoding( Content-Type( data ) )
715</artwork></figure>
716<t>
717   Content-Type specifies the media type of the underlying data.
718   Content-Encoding may be used to indicate any additional content
719   codings applied to the data, usually for the purpose of data
720   compression, that are a property of the requested resource. There is
721   no default encoding.
722</t>
723<t>
724   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
725   Content-Type header field defining the media type of that body. If
726   and only if the media type is not given by a Content-Type field, the
727   recipient &MAY; attempt to guess the media type via inspection of its
728   content and/or the name extension(s) of the URI used to identify the
729   resource. If the media type remains unknown, the recipient &SHOULD;
730   treat it as type "application/octet-stream".
731</t>
732</section>
733   
734<section title="Entity Length" anchor="entity.length">
735<t>
736   The entity-length of a message is the length of the message-body
[29]737   before any transfer-codings have been applied. &message-length; defines
[8]738   how the transfer-length of a message-body is determined.
739</t>
740</section>
741</section>
742</section>
743
744<section title="Content Negotiation" anchor="content.negotiation">
745<t>
746   Most HTTP responses include an entity which contains information for
747   interpretation by a human user. Naturally, it is desirable to supply
748   the user with the "best available" entity corresponding to the
749   request. Unfortunately for servers and caches, not all users have the
750   same preferences for what is "best," and not all user agents are
751   equally capable of rendering all entity types. For that reason, HTTP
752   has provisions for several mechanisms for "content negotiation" --
753   the process of selecting the best representation for a given response
754   when there are multiple representations available.
755  <list><t>
756      <x:h>Note:</x:h> This is not called "format negotiation" because the
757      alternate representations may be of the same media type, but use
758      different capabilities of that type, be in different languages,
759      etc.
760  </t></list>
761</t>
762<t>
763   Any response containing an entity-body &MAY; be subject to negotiation,
764   including error responses.
765</t>
766<t>
767   There are two kinds of content negotiation which are possible in
768   HTTP: server-driven and agent-driven negotiation. These two kinds of
769   negotiation are orthogonal and thus may be used separately or in
770   combination. One method of combination, referred to as transparent
771   negotiation, occurs when a cache uses the agent-driven negotiation
772   information provided by the origin server in order to provide
773   server-driven negotiation for subsequent requests.
774</t>
775
776<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
777<t>
778   If the selection of the best representation for a response is made by
779   an algorithm located at the server, it is called server-driven
780   negotiation. Selection is based on the available representations of
781   the response (the dimensions over which it can vary; e.g. language,
782   content-coding, etc.) and the contents of particular header fields in
783   the request message or on other information pertaining to the request
784   (such as the network address of the client).
785</t>
786<t>
787   Server-driven negotiation is advantageous when the algorithm for
788   selecting from among the available representations is difficult to
789   describe to the user agent, or when the server desires to send its
790   "best guess" to the client along with the first response (hoping to
791   avoid the round-trip delay of a subsequent request if the "best
792   guess" is good enough for the user). In order to improve the server's
793   guess, the user agent &MAY; include request header fields (Accept,
794   Accept-Language, Accept-Encoding, etc.) which describe its
795   preferences for such a response.
796</t>
797<t>
798   Server-driven negotiation has disadvantages:
799  <list style="numbers">
800    <t>
801         It is impossible for the server to accurately determine what
802         might be "best" for any given user, since that would require
803         complete knowledge of both the capabilities of the user agent
804         and the intended use for the response (e.g., does the user want
805         to view it on screen or print it on paper?).
806    </t>
807    <t>
808         Having the user agent describe its capabilities in every
809         request can be both very inefficient (given that only a small
810         percentage of responses have multiple representations) and a
811         potential violation of the user's privacy.
812    </t>
813    <t>
814         It complicates the implementation of an origin server and the
815         algorithms for generating responses to a request.
816    </t>
817    <t>
818         It may limit a public cache's ability to use the same response
819         for multiple user's requests.
820    </t>
821  </list>
822</t>
823<t>
824   HTTP/1.1 includes the following request-header fields for enabling
825   server-driven negotiation through description of user agent
826   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
827   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[29]828   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
[8]829   origin server is not limited to these dimensions and &MAY; vary the
830   response based on any aspect of the request, including information
831   outside the request-header fields or within extension header fields
832   not defined by this specification.
833</t>
834<t>
[115]835   The Vary header field (&header-vary;) can be used to express the parameters the
[8]836   server uses to select a representation that is subject to server-driven
[29]837   negotiation.
[8]838</t>
839</section>
840
841<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
842<t>
843   With agent-driven negotiation, selection of the best representation
844   for a response is performed by the user agent after receiving an
845   initial response from the origin server. Selection is based on a list
846   of the available representations of the response included within the
847   header fields or entity-body of the initial response, with each
848   representation identified by its own URI. Selection from among the
849   representations may be performed automatically (if the user agent is
850   capable of doing so) or manually by the user selecting from a
851   generated (possibly hypertext) menu.
852</t>
853<t>
854   Agent-driven negotiation is advantageous when the response would vary
855   over commonly-used dimensions (such as type, language, or encoding),
856   when the origin server is unable to determine a user agent's
857   capabilities from examining the request, and generally when public
858   caches are used to distribute server load and reduce network usage.
859</t>
860<t>
861   Agent-driven negotiation suffers from the disadvantage of needing a
862   second request to obtain the best alternate representation. This
863   second request is only efficient when caching is used. In addition,
864   this specification does not define any mechanism for supporting
865   automatic selection, though it also does not prevent any such
866   mechanism from being developed as an extension and used within
867   HTTP/1.1.
868</t>
869<t>
870   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
871   status codes for enabling agent-driven negotiation when the server is
872   unwilling or unable to provide a varying response using server-driven
873   negotiation.
874</t>
875</section>
876
877<section title="Transparent Negotiation" anchor="transparent.negotiation">
878<t>
879   Transparent negotiation is a combination of both server-driven and
880   agent-driven negotiation. When a cache is supplied with a form of the
881   list of available representations of the response (as in agent-driven
882   negotiation) and the dimensions of variance are completely understood
883   by the cache, then the cache becomes capable of performing server-driven
884   negotiation on behalf of the origin server for subsequent
885   requests on that resource.
886</t>
887<t>
888   Transparent negotiation has the advantage of distributing the
889   negotiation work that would otherwise be required of the origin
890   server and also removing the second request delay of agent-driven
891   negotiation when the cache is able to correctly guess the right
892   response.
893</t>
894<t>
895   This specification does not define any mechanism for transparent
896   negotiation, though it also does not prevent any such mechanism from
897   being developed as an extension that could be used within HTTP/1.1.
898</t>
899</section>
900</section>
[117]901
[8]902<section title="Header Field Definitions" anchor="header.fields">
903<t>
[117]904   This section defines the syntax and semantics of HTTP/1.1 header fields
905   related to the payload of messages.
[8]906</t>
[117]907<t>
908   For entity-header fields, both sender and recipient refer to either the
909   client or the server, depending on who sends and who receives the entity.
910</t>
911
[8]912<section title="Accept" anchor="header.accept">
913  <iref primary="true" item="Accept header" x:for-anchor=""/>
914  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
[229]915  <x:anchor-alias value="Accept"/>
[357]916  <x:anchor-alias value="Accept-v"/>
[370]917  <x:anchor-alias value="accept-ext"/>
[229]918  <x:anchor-alias value="accept-params"/>
919  <x:anchor-alias value="media-range"/>
[8]920<t>
[357]921   The request-header field "Accept" can be used to specify certain media
[8]922   types which are acceptable for the response. Accept headers can be
923   used to indicate that the request is specifically limited to a small
924   set of desired types, as in the case of a request for an in-line
925   image.
926</t>
[370]927<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"/>
[366]928  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
[357]929  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[135]930 
[229]931  <x:ref>media-range</x:ref>    = ( "*/*"
[334]932                   / ( <x:ref>type</x:ref> "/" "*" )
933                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]934                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
935  <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> )
[376]936  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
937                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
[8]938</artwork></figure>
939<t>
940   The asterisk "*" character is used to group media types into ranges,
941   with "*/*" indicating all media types and "type/*" indicating all
942   subtypes of that type. The media-range &MAY; include media type
943   parameters that are applicable to that range.
944</t>
945<t>
946   Each media-range &MAY; be followed by one or more accept-params,
947   beginning with the "q" parameter for indicating a relative quality
948   factor. The first "q" parameter (if any) separates the media-range
949   parameter(s) from the accept-params. Quality factors allow the user
950   or user agent to indicate the relative degree of preference for that
951   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
952   default value is q=1.
953  <list><t>
954      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
955      parameters from Accept extension parameters is due to historical
956      practice. Although this prevents any media type parameter named
957      "q" from being used with a media range, such an event is believed
958      to be unlikely given the lack of any "q" parameters in the IANA
959      media type registry and the rare usage of any media type
960      parameters in Accept. Future media types are discouraged from
961      registering any parameter named "q".
962  </t></list>
963</t>
964<t>
965   The example
966</t>
967<figure><artwork type="example">
[357]968  Accept: audio/*; q=0.2, audio/basic
[8]969</artwork></figure>
970<t>
971   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
972   type if it is the best available after an 80% mark-down in quality."
973</t>
974<t>
975   If no Accept header field is present, then it is assumed that the
976   client accepts all media types. If an Accept header field is present,
977   and if the server cannot send a response which is acceptable
978   according to the combined Accept field value, then the server &SHOULD;
[137]979   send a 406 (Not Acceptable) response.
[8]980</t>
981<t>
982   A more elaborate example is
983</t>
984<figure><artwork type="example">
[357]985  Accept: text/plain; q=0.5, text/html,
986          text/x-dvi; q=0.8, text/x-c
[8]987</artwork></figure>
988<t>
989   Verbally, this would be interpreted as "text/html and text/x-c are
990   the preferred media types, but if they do not exist, then send the
991   text/x-dvi entity, and if that does not exist, send the text/plain
992   entity."
993</t>
994<t>
995   Media ranges can be overridden by more specific media ranges or
996   specific media types. If more than one media range applies to a given
997   type, the most specific reference has precedence. For example,
998</t>
999<figure><artwork type="example">
[357]1000  Accept: text/*, text/html, text/html;level=1, */*
[8]1001</artwork></figure>
1002<t>
1003   have the following precedence:
1004</t>
1005<figure><artwork type="example">
1006    1) text/html;level=1
1007    2) text/html
1008    3) text/*
1009    4) */*
1010</artwork></figure>
1011<t>
1012   The media type quality factor associated with a given type is
1013   determined by finding the media range with the highest precedence
1014   which matches that type. For example,
1015</t>
1016<figure><artwork type="example">
[357]1017  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1018          text/html;level=2;q=0.4, */*;q=0.5
[8]1019</artwork></figure>
1020<t>
1021   would cause the following values to be associated:
1022</t>
1023<figure><artwork type="example">
1024    text/html;level=1         = 1
1025    text/html                 = 0.7
1026    text/plain                = 0.3
1027    image/jpeg                = 0.5
1028    text/html;level=2         = 0.4
1029    text/html;level=3         = 0.7
1030</artwork></figure>
1031<t>
1032      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1033      values for certain media ranges. However, unless the user agent is
1034      a closed system which cannot interact with other rendering agents,
1035      this default set ought to be configurable by the user.
1036</t>
1037</section>
1038
1039<section title="Accept-Charset" anchor="header.accept-charset">
1040  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1041  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
[229]1042  <x:anchor-alias value="Accept-Charset"/>
[357]1043  <x:anchor-alias value="Accept-Charset-v"/>
[8]1044<t>
[357]1045   The request-header field "Accept-Charset" can be used to indicate what
[8]1046   character sets are acceptable for the response. This field allows
1047   clients capable of understanding more comprehensive or special-purpose
1048   character sets to signal that capability to a server which is
1049   capable of representing documents in those character sets.
1050</t>
[357]1051<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
[366]1052  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
[357]1053          <x:ref>Accept-Charset-v</x:ref>
[376]1054  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1055                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[8]1056</artwork></figure>
1057<t>
1058   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1059   be given an associated quality value which represents the user's
1060   preference for that charset. The default value is q=1. An example is
1061</t>
1062<figure><artwork type="example">
[357]1063  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
[8]1064</artwork></figure>
1065<t>
1066   The special value "*", if present in the Accept-Charset field,
1067   matches every character set (including ISO-8859-1) which is not
1068   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1069   in an Accept-Charset field, then all character sets not explicitly
1070   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1071   a quality value of 1 if not explicitly mentioned.
1072</t>
1073<t>
1074   If no Accept-Charset header is present, the default is that any
1075   character set is acceptable. If an Accept-Charset header is present,
1076   and if the server cannot send a response which is acceptable
1077   according to the Accept-Charset header, then the server &SHOULD; send
[137]1078   an error response with the 406 (Not Acceptable) status code, though
[8]1079   the sending of an unacceptable response is also allowed.
1080</t>
1081</section>
1082
1083<section title="Accept-Encoding" anchor="header.accept-encoding">
1084  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1085  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1086  <x:anchor-alias value="Accept-Encoding"/>
[357]1087  <x:anchor-alias value="Accept-Encoding-v"/>
[229]1088  <x:anchor-alias value="codings"/>
[8]1089<t>
[357]1090   The request-header field "Accept-Encoding" is similar to Accept, but
[8]1091   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1092   the response.
1093</t>
[357]1094<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"/>
[366]1095  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
[357]1096                     <x:ref>Accept-Encoding-v</x:ref>
1097  <x:ref>Accept-Encoding-v</x:ref>  =
[370]1098                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1099  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
[8]1100</artwork></figure>
1101<t>
[248]1102   Each codings value &MAY; be given an associated quality value which
1103   represents the preference for that encoding. The default value is q=1.
1104</t>
1105<t>
[8]1106   Examples of its use are:
1107</t>
1108<figure><artwork type="example">
[357]1109  Accept-Encoding: compress, gzip
1110  Accept-Encoding:
1111  Accept-Encoding: *
1112  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1113  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
[8]1114</artwork></figure>
1115<t>
1116   A server tests whether a content-coding is acceptable, according to
1117   an Accept-Encoding field, using these rules:
1118  <list style="numbers">
1119      <t>If the content-coding is one of the content-codings listed in
1120         the Accept-Encoding field, then it is acceptable, unless it is
1121         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1122         qvalue of 0 means "not acceptable.")</t>
1123
1124      <t>The special "*" symbol in an Accept-Encoding field matches any
1125         available content-coding not explicitly listed in the header
1126         field.</t>
1127
1128      <t>If multiple content-codings are acceptable, then the acceptable
1129         content-coding with the highest non-zero qvalue is preferred.</t>
1130
1131      <t>The "identity" content-coding is always acceptable, unless
1132         specifically refused because the Accept-Encoding field includes
1133         "identity;q=0", or because the field includes "*;q=0" and does
1134         not explicitly include the "identity" content-coding. If the
1135         Accept-Encoding field-value is empty, then only the "identity"
1136         encoding is acceptable.</t>
1137  </list>
1138</t>
1139<t>
1140   If an Accept-Encoding field is present in a request, and if the
1141   server cannot send a response which is acceptable according to the
1142   Accept-Encoding header, then the server &SHOULD; send an error response
1143   with the 406 (Not Acceptable) status code.
1144</t>
1145<t>
1146   If no Accept-Encoding field is present in a request, the server &MAY;
1147   assume that the client will accept any content coding. In this case,
1148   if "identity" is one of the available content-codings, then the
1149   server &SHOULD; use the "identity" content-coding, unless it has
1150   additional information that a different content-coding is meaningful
1151   to the client.
1152  <list><t>
1153      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1154      and if the "identity" content-coding is unavailable, then
1155      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1156      "gzip" and "compress") are preferred; some older clients
1157      improperly display messages sent with other content-codings.  The
1158      server might also make this decision based on information about
1159      the particular user-agent or client.
1160    </t><t>
1161      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1162      associated with content-codings. This means that qvalues will not
1163      work and are not permitted with x-gzip or x-compress.
1164    </t></list>
1165</t>
1166</section>
1167
1168<section title="Accept-Language" anchor="header.accept-language">
1169  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1170  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
[229]1171  <x:anchor-alias value="Accept-Language"/>
[357]1172  <x:anchor-alias value="Accept-Language-v"/>
[229]1173  <x:anchor-alias value="language-range"/>
[8]1174<t>
[357]1175   The request-header field "Accept-Language" is similar to Accept, but
[8]1176   restricts the set of natural languages that are preferred as a
1177   response to the request. Language tags are defined in <xref target="language.tags"/>.
1178</t>
[357]1179<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"/>
[366]1180  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
[357]1181                    <x:ref>Accept-Language-v</x:ref>
1182  <x:ref>Accept-Language-v</x:ref> =
[370]1183                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1184  <x:ref>language-range</x:ref>    =
[303]1185            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[8]1186</artwork></figure>
1187<t>
[303]1188   Each language-range can be given an associated quality value which
[8]1189   represents an estimate of the user's preference for the languages
1190   specified by that range. The quality value defaults to "q=1". For
1191   example,
1192</t>
1193<figure><artwork type="example">
[357]1194  Accept-Language: da, en-gb;q=0.8, en;q=0.7
[8]1195</artwork></figure>
1196<t>
1197   would mean: "I prefer Danish, but will accept British English and
[303]1198   other types of English."
1199</t>
1200<t>
1201   For matching, the "Basic Filtering" matching scheme, defined in
1202   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1203</t>
1204<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1205  <t>
1206     A language range matches a
1207     particular language tag if, in a case-insensitive comparison, it
1208     exactly equals the tag, or if it exactly equals a prefix of the tag
1209     such that the first character following the prefix is "-".
1210  </t>
1211</x:blockquote> 
1212<t>
[8]1213   The special range "*", if present in the Accept-Language field,
1214   matches every tag not matched by any other range present in the
1215   Accept-Language field.
1216  <list><t>
1217      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1218      language tags are assigned to languages in such a way that it is
1219      always true that if a user understands a language with a certain
1220      tag, then this user will also understand all languages with tags
1221      for which this tag is a prefix. The prefix rule simply allows the
1222      use of prefix tags if this is the case.
1223  </t></list>
1224</t>
1225<t>
1226   The language quality factor assigned to a language-tag by the
1227   Accept-Language field is the quality value of the longest language-range
1228   in the field that matches the language-tag. If no language-range
1229   in the field matches the tag, the language quality factor
1230   assigned is 0. If no Accept-Language header is present in the
1231   request, the server
1232   &SHOULD; assume that all languages are equally acceptable. If an
1233   Accept-Language header is present, then all languages which are
1234   assigned a quality factor greater than 0 are acceptable.
1235</t>
1236<t>
1237   It might be contrary to the privacy expectations of the user to send
1238   an Accept-Language header with the complete linguistic preferences of
1239   the user in every request. For a discussion of this issue, see
1240   <xref target="privacy.issues.connected.to.accept.headers"/>.
1241</t>
1242<t>
1243   As intelligibility is highly dependent on the individual user, it is
1244   recommended that client applications make the choice of linguistic
1245   preference available to the user. If the choice is not made
1246   available, then the Accept-Language header field &MUST-NOT; be given in
1247   the request.
1248  <list><t>
1249      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1250      the user, we remind implementors of  the fact that users are not
1251      familiar with the details of language matching as described above,
1252      and should provide appropriate guidance. As an example, users
1253      might assume that on selecting "en-gb", they will be served any
1254      kind of English document if British English is not available. A
1255      user agent might suggest in such a case to add "en" to get the
1256      best matching behavior.
1257  </t></list>
1258</t>
1259</section>
1260
1261<section title="Content-Encoding" anchor="header.content-encoding">
1262  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1263  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
[229]1264  <x:anchor-alias value="Content-Encoding"/>
[357]1265  <x:anchor-alias value="Content-Encoding-v"/>
[8]1266<t>
[357]1267   The entity-header field "Content-Encoding" is used as a modifier to the
[8]1268   media-type. When present, its value indicates what additional content
1269   codings have been applied to the entity-body, and thus what decoding
1270   mechanisms must be applied in order to obtain the media-type
1271   referenced by the Content-Type header field. Content-Encoding is
1272   primarily used to allow a document to be compressed without losing
1273   the identity of its underlying media type.
1274</t>
[357]1275<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
[366]1276  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
[357]1277  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
[8]1278</artwork></figure>
1279<t>
1280   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1281</t>
1282<figure><artwork type="example">
[357]1283  Content-Encoding: gzip
[8]1284</artwork></figure>
1285<t>
1286   The content-coding is a characteristic of the entity identified by
1287   the Request-URI. Typically, the entity-body is stored with this
1288   encoding and is only decoded before rendering or analogous usage.
1289   However, a non-transparent proxy &MAY; modify the content-coding if the
1290   new coding is known to be acceptable to the recipient, unless the
1291   "no-transform" cache-control directive is present in the message.
1292</t>
1293<t>
1294   If the content-coding of an entity is not "identity", then the
1295   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1296   that lists the non-identity content-coding(s) used.
1297</t>
1298<t>
1299   If the content-coding of an entity in a request message is not
1300   acceptable to the origin server, the server &SHOULD; respond with a
1301   status code of 415 (Unsupported Media Type).
1302</t>
1303<t>
1304   If multiple encodings have been applied to an entity, the content
1305   codings &MUST; be listed in the order in which they were applied.
1306   Additional information about the encoding parameters &MAY; be provided
1307   by other entity-header fields not defined by this specification.
1308</t>
1309</section>
1310
1311<section title="Content-Language" anchor="header.content-language">
1312  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1313  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
[229]1314  <x:anchor-alias value="Content-Language"/>
[357]1315  <x:anchor-alias value="Content-Language-v"/>
[8]1316<t>
[357]1317   The entity-header field "Content-Language" describes the natural
[8]1318   language(s) of the intended audience for the enclosed entity. Note
1319   that this might not be equivalent to all the languages used within
1320   the entity-body.
1321</t>
[357]1322<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
[366]1323  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
[357]1324  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
[8]1325</artwork></figure>
1326<t>
1327   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1328   Content-Language is to allow a user to identify and differentiate
1329   entities according to the user's own preferred language. Thus, if the
1330   body content is intended only for a Danish-literate audience, the
1331   appropriate field is
1332</t>
1333<figure><artwork type="example">
[357]1334  Content-Language: da
[8]1335</artwork></figure>
1336<t>
1337   If no Content-Language is specified, the default is that the content
1338   is intended for all language audiences. This might mean that the
1339   sender does not consider it to be specific to any natural language,
1340   or that the sender does not know for which language it is intended.
1341</t>
1342<t>
1343   Multiple languages &MAY; be listed for content that is intended for
1344   multiple audiences. For example, a rendition of the "Treaty of
1345   Waitangi," presented simultaneously in the original Maori and English
1346   versions, would call for
1347</t>
1348<figure><artwork type="example">
[357]1349  Content-Language: mi, en
[8]1350</artwork></figure>
1351<t>
1352   However, just because multiple languages are present within an entity
1353   does not mean that it is intended for multiple linguistic audiences.
1354   An example would be a beginner's language primer, such as "A First
1355   Lesson in Latin," which is clearly intended to be used by an
1356   English-literate audience. In this case, the Content-Language would
1357   properly only include "en".
1358</t>
1359<t>
1360   Content-Language &MAY; be applied to any media type -- it is not
1361   limited to textual documents.
1362</t>
1363</section>
1364
1365<section title="Content-Location" anchor="header.content-location">
1366  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1367  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
[229]1368  <x:anchor-alias value="Content-Location"/>
[357]1369  <x:anchor-alias value="Content-Location-v"/>
[8]1370<t>
[357]1371   The entity-header field "Content-Location" &MAY; be used to supply the
[8]1372   resource location for the entity enclosed in the message when that
1373   entity is accessible from a location separate from the requested
1374   resource's URI. A server &SHOULD; provide a Content-Location for the
1375   variant corresponding to the response entity; especially in the case
1376   where a resource has multiple entities associated with it, and those
1377   entities actually have separate locations by which they might be
1378   individually accessed, the server &SHOULD; provide a Content-Location
1379   for the particular variant which is returned.
1380</t>
[357]1381<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
[366]1382  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
[357]1383                    <x:ref>Content-Location-v</x:ref>
1384  <x:ref>Content-Location-v</x:ref> =
[374]1385                    <x:ref>absolute-URI</x:ref> / <x:ref>relativeURI</x:ref>
[8]1386</artwork></figure>
1387<t>
1388   The value of Content-Location also defines the base URI for the
1389   entity.
1390</t>
1391<t>
1392   The Content-Location value is not a replacement for the original
1393   requested URI; it is only a statement of the location of the resource
1394   corresponding to this particular entity at the time of the request.
1395   Future requests &MAY; specify the Content-Location URI as the request-URI
1396   if the desire is to identify the source of that particular
1397   entity.
1398</t>
1399<t>
1400   A cache cannot assume that an entity with a Content-Location
1401   different from the URI used to retrieve it can be used to respond to
1402   later requests on that Content-Location URI. However, the Content-Location
1403   can be used to differentiate between multiple entities
[115]1404   retrieved from a single requested resource, as described in &caching-neg-resp;.
[8]1405</t>
1406<t>
1407   If the Content-Location is a relative URI, the relative URI is
1408   interpreted relative to the Request-URI.
1409</t>
1410<t>
1411   The meaning of the Content-Location header in PUT or POST requests is
1412   undefined; servers are free to ignore it in those cases.
1413</t>
1414</section>
1415
1416<section title="Content-MD5" anchor="header.content-md5">
1417  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1418  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
[229]1419  <x:anchor-alias value="Content-MD5"/>
[357]1420  <x:anchor-alias value="Content-MD5-v"/>
[8]1421<t>
[357]1422   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
[8]1423   an MD5 digest of the entity-body for the purpose of providing an
1424   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1425   MIC is good for detecting accidental modification of the entity-body
1426   in transit, but is not proof against malicious attacks.)
1427</t>
[357]1428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
[366]1429  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
[357]1430  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
[8]1431</artwork></figure>
1432<t>
1433   The Content-MD5 header field &MAY; be generated by an origin server or
1434   client to function as an integrity check of the entity-body. Only
1435   origin servers or clients &MAY; generate the Content-MD5 header field;
1436   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1437   value as an end-to-end integrity check. Any recipient of the entity-body,
1438   including gateways and proxies, &MAY; check that the digest value
1439   in this header field matches that of the entity-body as received.
1440</t>
1441<t>
1442   The MD5 digest is computed based on the content of the entity-body,
1443   including any content-coding that has been applied, but not including
1444   any transfer-encoding applied to the message-body. If the message is
1445   received with a transfer-encoding, that encoding &MUST; be removed
1446   prior to checking the Content-MD5 value against the received entity.
1447</t>
1448<t>
1449   This has the result that the digest is computed on the octets of the
1450   entity-body exactly as, and in the order that, they would be sent if
1451   no transfer-encoding were being applied.
1452</t>
1453<t>
1454   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1455   composite media-types (e.g., multipart/* and message/rfc822), but
1456   this does not change how the digest is computed as defined in the
1457   preceding paragraph.
1458</t>
1459<t>
1460   There are several consequences of this. The entity-body for composite
1461   types &MAY; contain many body-parts, each with its own MIME and HTTP
1462   headers (including Content-MD5, Content-Transfer-Encoding, and
1463   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1464   or Content-Encoding header, it is assumed that the content
1465   of the body-part has had the encoding applied, and the body-part is
1466   included in the Content-MD5 digest as is -- i.e., after the
1467   application. The Transfer-Encoding header field is not allowed within
1468   body-parts.
1469</t>
1470<t>
1471   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1472   computing or checking the digest: the line break convention used in
1473   the text actually transmitted &MUST; be left unaltered when computing
1474   the digest.
1475  <list><t>
1476      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1477      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1478      in which the application of Content-MD5 to HTTP entity-bodies
1479      differs from its application to MIME entity-bodies. One is that
1480      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1481      does use Transfer-Encoding and Content-Encoding. Another is that
1482      HTTP more frequently uses binary content types than MIME, so it is
1483      worth noting that, in such cases, the byte order used to compute
1484      the digest is the transmission byte order defined for the type.
1485      Lastly, HTTP allows transmission of text types with any of several
1486      line break conventions and not just the canonical form using CRLF.
1487  </t></list>
1488</t>
1489</section>
1490
1491<section title="Content-Type" anchor="header.content-type">
1492  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1493  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
[229]1494  <x:anchor-alias value="Content-Type"/>
[357]1495  <x:anchor-alias value="Content-Type-v"/>
[8]1496<t>
[357]1497   The entity-header field "Content-Type" indicates the media type of the
[8]1498   entity-body sent to the recipient or, in the case of the HEAD method,
1499   the media type that would have been sent had the request been a GET.
1500</t>
[357]1501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
[366]1502  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
[357]1503  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
[8]1504</artwork></figure>
1505<t>
1506   Media types are defined in <xref target="media.types"/>. An example of the field is
1507</t>
1508<figure><artwork type="example">
[357]1509  Content-Type: text/html; charset=ISO-8859-4
[8]1510</artwork></figure>
1511<t>
1512   Further discussion of methods for identifying the media type of an
1513   entity is provided in <xref target="type"/>.
1514</t>
1515</section>
1516
1517</section>
1518
[29]1519<section title="IANA Considerations" anchor="IANA.considerations">
[253]1520<section title="Message Header Registration" anchor="message.header.registration">
[290]1521<t>
1522   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1523   with the permanent registrations below (see <xref target="RFC3864"/>):
1524</t>
[253]1525<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1526<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1527   <ttcol>Header Field Name</ttcol>
1528   <ttcol>Protocol</ttcol>
1529   <ttcol>Status</ttcol>
1530   <ttcol>Reference</ttcol>
1531
1532   <c>Accept</c>
1533   <c>http</c>
1534   <c>standard</c>
1535   <c>
1536      <xref target="header.accept"/>
1537   </c>
1538   <c>Accept-Charset</c>
1539   <c>http</c>
1540   <c>standard</c>
1541   <c>
1542      <xref target="header.accept-charset"/>
1543   </c>
1544   <c>Accept-Encoding</c>
1545   <c>http</c>
1546   <c>standard</c>
1547   <c>
1548      <xref target="header.accept-encoding"/>
1549   </c>
1550   <c>Accept-Language</c>
1551   <c>http</c>
1552   <c>standard</c>
1553   <c>
1554      <xref target="header.accept-language"/>
1555   </c>
1556   <c>Content-Disposition</c>
1557   <c>http</c>
[291]1558   <c/>
[253]1559   <c>
1560      <xref target="content-disposition"/>
1561   </c>
1562   <c>Content-Encoding</c>
1563   <c>http</c>
1564   <c>standard</c>
1565   <c>
1566      <xref target="header.content-encoding"/>
1567   </c>
1568   <c>Content-Language</c>
1569   <c>http</c>
1570   <c>standard</c>
1571   <c>
1572      <xref target="header.content-language"/>
1573   </c>
1574   <c>Content-Location</c>
1575   <c>http</c>
1576   <c>standard</c>
1577   <c>
1578      <xref target="header.content-location"/>
1579   </c>
1580   <c>Content-MD5</c>
1581   <c>http</c>
1582   <c>standard</c>
1583   <c>
1584      <xref target="header.content-md5"/>
1585   </c>
1586   <c>Content-Type</c>
1587   <c>http</c>
1588   <c>standard</c>
1589   <c>
1590      <xref target="header.content-type"/>
1591   </c>
[291]1592   <c>MIME-Version</c>
1593   <c>http</c>
1594   <c/>
1595   <c>
1596      <xref target="mime-version"/>
1597   </c>
[253]1598</texttable>
[290]1599<!--(END)-->
[253]1600<t>
[290]1601   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1602</t>
[8]1603</section>
[253]1604</section>
[8]1605
1606<section title="Security Considerations" anchor="security.considerations">
1607<t>
1608   This section is meant to inform application developers, information
1609   providers, and users of the security limitations in HTTP/1.1 as
1610   described by this document. The discussion does not include
1611   definitive solutions to the problems revealed, though it does make
1612   some suggestions for reducing security risks.
1613</t>
1614
1615<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1616<t>
1617   Accept request-headers can reveal information about the user to all
1618   servers which are accessed. The Accept-Language header in particular
1619   can reveal information the user would consider to be of a private
1620   nature, because the understanding of particular languages is often
1621   strongly correlated to the membership of a particular ethnic group.
1622   User agents which offer the option to configure the contents of an
1623   Accept-Language header to be sent in every request are strongly
1624   encouraged to let the configuration process include a message which
1625   makes the user aware of the loss of privacy involved.
1626</t>
1627<t>
1628   An approach that limits the loss of privacy would be for a user agent
1629   to omit the sending of Accept-Language headers by default, and to ask
1630   the user whether or not to start sending Accept-Language headers to a
1631   server if it detects, by looking for any Vary response-header fields
1632   generated by the server, that such sending could improve the quality
1633   of service.
1634</t>
1635<t>
1636   Elaborate user-customized accept header fields sent in every request,
1637   in particular if these include quality values, can be used by servers
1638   as relatively reliable and long-lived user identifiers. Such user
1639   identifiers would allow content providers to do click-trail tracking,
1640   and would allow collaborating content providers to match cross-server
1641   click-trails or form submissions of individual users. Note that for
1642   many users not behind a proxy, the network address of the host
1643   running the user agent will also serve as a long-lived user
1644   identifier. In environments where proxies are used to enhance
1645   privacy, user agents ought to be conservative in offering accept
1646   header configuration options to end users. As an extreme privacy
1647   measure, proxies could filter the accept headers in relayed requests.
1648   General purpose user agents which provide a high degree of header
1649   configurability &SHOULD; warn users about the loss of privacy which can
1650   be involved.
1651</t>
1652</section>
1653
1654<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1655<t>
[269]1656   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
[8]1657   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1658   serious security considerations. Content-Disposition is not part of
1659   the HTTP standard, but since it is widely implemented, we are
[269]1660   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1661   for details.
[8]1662</t>
1663</section>
1664
1665</section>
1666
1667<section title="Acknowledgments" anchor="ack">
1668</section>
1669</middle>
1670<back>
1671
[119]1672<references title="Normative References">
1673
[121]1674<reference anchor="ISO-8859-1">
1675  <front>
1676    <title>
1677     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1678    </title>
1679    <author>
1680      <organization>International Organization for Standardization</organization>
1681    </author>
1682    <date year="1998"/>
1683  </front>
1684  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1685</reference>
1686
[31]1687<reference anchor="Part1">
[119]1688  <front>
1689    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1690    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1691      <organization abbrev="Day Software">Day Software</organization>
1692      <address><email>fielding@gbiv.com</email></address>
1693    </author>
1694    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1695      <organization>One Laptop per Child</organization>
1696      <address><email>jg@laptop.org</email></address>
1697    </author>
1698    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1699      <organization abbrev="HP">Hewlett-Packard Company</organization>
1700      <address><email>JeffMogul@acm.org</email></address>
1701    </author>
1702    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1703      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1704      <address><email>henrikn@microsoft.com</email></address>
1705    </author>
1706    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1707      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1708      <address><email>LMM@acm.org</email></address>
1709    </author>
1710    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1711      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1712      <address><email>paulle@microsoft.com</email></address>
1713    </author>
1714    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1715      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1716      <address><email>timbl@w3.org</email></address>
1717    </author>
1718    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1719      <organization abbrev="W3C">World Wide Web Consortium</organization>
1720      <address><email>ylafon@w3.org</email></address>
1721    </author>
1722    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1723      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1724      <address><email>julian.reschke@greenbytes.de</email></address>
1725    </author>
1726    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1727  </front>
1728  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1729  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
[31]1730</reference>
1731
1732<reference anchor="Part2">
[119]1733  <front>
1734    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1735    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1736      <organization abbrev="Day Software">Day Software</organization>
1737      <address><email>fielding@gbiv.com</email></address>
1738    </author>
1739    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1740      <organization>One Laptop per Child</organization>
1741      <address><email>jg@laptop.org</email></address>
1742    </author>
1743    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1744      <organization abbrev="HP">Hewlett-Packard Company</organization>
1745      <address><email>JeffMogul@acm.org</email></address>
1746    </author>
1747    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1748      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1749      <address><email>henrikn@microsoft.com</email></address>
1750    </author>
1751    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1752      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1753      <address><email>LMM@acm.org</email></address>
1754    </author>
1755    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1756      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1757      <address><email>paulle@microsoft.com</email></address>
1758    </author>
1759    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1760      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1761      <address><email>timbl@w3.org</email></address>
1762    </author>
1763    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1764      <organization abbrev="W3C">World Wide Web Consortium</organization>
1765      <address><email>ylafon@w3.org</email></address>
1766    </author>
1767    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1768      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1769      <address><email>julian.reschke@greenbytes.de</email></address>
1770    </author>
1771    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1772  </front>
1773  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1774  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
[31]1775</reference>
1776
1777<reference anchor="Part4">
[119]1778  <front>
1779    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1780    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1781      <organization abbrev="Day Software">Day Software</organization>
1782      <address><email>fielding@gbiv.com</email></address>
1783    </author>
1784    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1785      <organization>One Laptop per Child</organization>
1786      <address><email>jg@laptop.org</email></address>
1787    </author>
1788    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1789      <organization abbrev="HP">Hewlett-Packard Company</organization>
1790      <address><email>JeffMogul@acm.org</email></address>
1791    </author>
1792    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1793      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1794      <address><email>henrikn@microsoft.com</email></address>
1795    </author>
1796    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1797      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1798      <address><email>LMM@acm.org</email></address>
1799    </author>
1800    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1801      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1802      <address><email>paulle@microsoft.com</email></address>
1803    </author>
1804    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1805      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1806      <address><email>timbl@w3.org</email></address>
1807    </author>
1808    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1809      <organization abbrev="W3C">World Wide Web Consortium</organization>
1810      <address><email>ylafon@w3.org</email></address>
1811    </author>
1812    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1813      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1814      <address><email>julian.reschke@greenbytes.de</email></address>
1815    </author>
1816    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1817  </front>
1818  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1819  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
[31]1820</reference>
1821
1822<reference anchor="Part5">
[119]1823  <front>
1824    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1825    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1826      <organization abbrev="Day Software">Day Software</organization>
1827      <address><email>fielding@gbiv.com</email></address>
1828    </author>
1829    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1830      <organization>One Laptop per Child</organization>
1831      <address><email>jg@laptop.org</email></address>
1832    </author>
1833    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1834      <organization abbrev="HP">Hewlett-Packard Company</organization>
1835      <address><email>JeffMogul@acm.org</email></address>
1836    </author>
1837    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1838      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1839      <address><email>henrikn@microsoft.com</email></address>
1840    </author>
1841    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1842      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1843      <address><email>LMM@acm.org</email></address>
1844    </author>
1845    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1846      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1847      <address><email>paulle@microsoft.com</email></address>
1848    </author>
1849    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1850      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1851      <address><email>timbl@w3.org</email></address>
1852    </author>
1853    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1854      <organization abbrev="W3C">World Wide Web Consortium</organization>
1855      <address><email>ylafon@w3.org</email></address>
1856    </author>
1857    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1858      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1859      <address><email>julian.reschke@greenbytes.de</email></address>
1860    </author>
1861    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1862  </front>
1863  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1864  <x:source href="p5-range.xml" basename="p5-range"/>
[31]1865</reference>
1866
1867<reference anchor="Part6">
[119]1868  <front>
1869    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1870    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1871      <organization abbrev="Day Software">Day Software</organization>
1872      <address><email>fielding@gbiv.com</email></address>
1873    </author>
1874    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1875      <organization>One Laptop per Child</organization>
1876      <address><email>jg@laptop.org</email></address>
1877    </author>
1878    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1879      <organization abbrev="HP">Hewlett-Packard Company</organization>
1880      <address><email>JeffMogul@acm.org</email></address>
1881    </author>
1882    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1883      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1884      <address><email>henrikn@microsoft.com</email></address>
1885    </author>
1886    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1887      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1888      <address><email>LMM@acm.org</email></address>
1889    </author>
1890    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1891      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1892      <address><email>paulle@microsoft.com</email></address>
1893    </author>
1894    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1895      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1896      <address><email>timbl@w3.org</email></address>
1897    </author>
1898    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1899      <organization abbrev="W3C">World Wide Web Consortium</organization>
1900      <address><email>ylafon@w3.org</email></address>
1901    </author>
1902    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1903      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1904      <address><email>julian.reschke@greenbytes.de</email></address>
1905    </author>
1906    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1907  </front>
1908  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1909  <x:source href="p6-cache.xml" basename="p6-cache"/>
[31]1910</reference>
1911
[132]1912<reference anchor="RFC1766">
1913  <front>
1914    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1915    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1916      <organization>UNINETT</organization>
1917      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1918    </author>
1919    <date month="March" year="1995"/>
1920  </front>
1921  <seriesInfo name="RFC" value="1766"/>
1922</reference>
1923
[131]1924<reference anchor="RFC1864">
1925  <front>
1926    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1927    <author initials="J." surname="Myers" fullname="John G. Myers">
1928      <organization>Carnegie Mellon University</organization>
1929      <address><email>jgm+@cmu.edu</email></address>
1930    </author>
1931    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1932      <organization>Dover Beach Consulting, Inc.</organization>
1933      <address><email>mrose@dbc.mtview.ca.us</email></address>
1934    </author>
1935    <date month="October" year="1995"/>
1936  </front>
1937  <seriesInfo name="RFC" value="1864"/>
1938</reference>
1939
[122]1940<reference anchor="RFC1950">
1941  <front>
1942    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1943    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1944      <organization>Aladdin Enterprises</organization>
1945      <address><email>ghost@aladdin.com</email></address>
1946    </author>
1947    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1948      <organization/>
1949    </author>
1950    <date month="May" year="1996"/>
1951  </front>
1952  <seriesInfo name="RFC" value="1950"/>
1953  <annotation>
[277]1954    RFC 1950 is an Informational RFC, thus it may be less stable than
[122]1955    this specification. On the other hand, this downward reference was
[277]1956    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1957    therefore it is unlikely to cause problems in practice. See also
1958    <xref target="BCP97"/>.
[122]1959  </annotation>
1960</reference>
1961
1962<reference anchor="RFC1951">
1963  <front>
1964    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1965    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1966      <organization>Aladdin Enterprises</organization>
1967      <address><email>ghost@aladdin.com</email></address>
1968    </author>
1969    <date month="May" year="1996"/>
1970  </front>
1971  <seriesInfo name="RFC" value="1951"/>
1972  <annotation>
[277]1973    RFC 1951 is an Informational RFC, thus it may be less stable than
[122]1974    this specification. On the other hand, this downward reference was
[277]1975    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1976    therefore it is unlikely to cause problems in practice. See also
1977    <xref target="BCP97"/>.
[122]1978  </annotation>
1979</reference>
1980
1981<reference anchor="RFC1952">
1982  <front>
1983    <title>GZIP file format specification version 4.3</title>
1984    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1985      <organization>Aladdin Enterprises</organization>
1986      <address><email>ghost@aladdin.com</email></address>
1987    </author>
1988    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1989      <organization/>
1990      <address><email>gzip@prep.ai.mit.edu</email></address>
1991    </author>
1992    <author initials="M." surname="Adler" fullname="Mark Adler">
1993      <organization/>
1994      <address><email>madler@alumni.caltech.edu</email></address>
1995    </author>
1996    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1997      <organization/>
1998      <address><email>ghost@aladdin.com</email></address>
1999    </author>
2000    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2001      <organization/>
2002      <address><email>randeg@alumni.rpi.edu</email></address>
2003    </author>
2004    <date month="May" year="1996"/>
2005  </front>
2006  <seriesInfo name="RFC" value="1952"/>
2007  <annotation>
[277]2008    RFC 1952 is an Informational RFC, thus it may be less stable than
[122]2009    this specification. On the other hand, this downward reference was
[277]2010    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2011    therefore it is unlikely to cause problems in practice. See also
2012    <xref target="BCP97"/>.
[122]2013  </annotation>
2014</reference>
2015
[131]2016<reference anchor="RFC2045">
2017  <front>
2018    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2019    <author initials="N." surname="Freed" fullname="Ned Freed">
2020      <organization>Innosoft International, Inc.</organization>
2021      <address><email>ned@innosoft.com</email></address>
2022    </author>
2023    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2024      <organization>First Virtual Holdings</organization>
2025      <address><email>nsb@nsb.fv.com</email></address>
2026    </author>
2027    <date month="November" year="1996"/>
2028  </front>
2029  <seriesInfo name="RFC" value="2045"/>
2030</reference>
2031
2032<reference anchor="RFC2046">
2033  <front>
2034    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2035    <author initials="N." surname="Freed" fullname="Ned Freed">
2036      <organization>Innosoft International, Inc.</organization>
2037      <address><email>ned@innosoft.com</email></address>
2038    </author>
2039    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2040      <organization>First Virtual Holdings</organization>
2041      <address><email>nsb@nsb.fv.com</email></address>
2042    </author>
2043    <date month="November" year="1996"/>
2044  </front>
2045  <seriesInfo name="RFC" value="2046"/>
2046</reference>
2047
[119]2048<reference anchor="RFC2119">
2049  <front>
2050    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2051    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2052      <organization>Harvard University</organization>
2053      <address><email>sob@harvard.edu</email></address>
2054    </author>
2055    <date month="March" year="1997"/>
2056  </front>
2057  <seriesInfo name="BCP" value="14"/>
2058  <seriesInfo name="RFC" value="2119"/>
[36]2059</reference>
2060
[303]2061<reference anchor='RFC4647'>
2062  <front>
2063    <title>Matching of Language Tags</title>
2064    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2065      <organization>Yahoo! Inc.</organization>
2066      <address><email>addison@inter-locale.com</email></address>
2067    </author>
2068    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2069      <organization>Google</organization>
2070      <address><email>mark.davis@macchiato.com</email></address>
2071    </author>
2072    <date year='2006' month='September' />
2073  </front>
2074  <seriesInfo name='BCP' value='47' />
2075  <seriesInfo name='RFC' value='4647' />
2076</reference>
2077
[119]2078</references>
2079
2080<references title="Informative References">
2081
[129]2082<reference anchor="RFC1945">
2083  <front>
2084    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2085    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2086      <organization>MIT, Laboratory for Computer Science</organization>
2087      <address><email>timbl@w3.org</email></address>
2088    </author>
2089    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2090      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2091      <address><email>fielding@ics.uci.edu</email></address>
2092    </author>
2093    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2094      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2095      <address><email>frystyk@w3.org</email></address>
2096    </author>
2097    <date month="May" year="1996"/>
2098  </front>
2099  <seriesInfo name="RFC" value="1945"/>
2100</reference>
2101
2102<reference anchor="RFC2049">
2103  <front>
2104    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2105    <author initials="N." surname="Freed" fullname="Ned Freed">
2106      <organization>Innosoft International, Inc.</organization>
2107      <address><email>ned@innosoft.com</email></address>
2108    </author>
2109    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2110      <organization>First Virtual Holdings</organization>
2111      <address><email>nsb@nsb.fv.com</email></address>
2112    </author>
2113    <date month="November" year="1996"/>
2114  </front>
2115  <seriesInfo name="RFC" value="2049"/>
2116</reference>
2117
[133]2118<reference anchor="RFC2068">
2119  <front>
2120    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2121    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2122      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2123      <address><email>fielding@ics.uci.edu</email></address>
2124    </author>
2125    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2126      <organization>MIT Laboratory for Computer Science</organization>
2127      <address><email>jg@w3.org</email></address>
2128    </author>
2129    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2130      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2131      <address><email>mogul@wrl.dec.com</email></address>
2132    </author>
2133    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2134      <organization>MIT Laboratory for Computer Science</organization>
2135      <address><email>frystyk@w3.org</email></address>
2136    </author>
2137    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2138      <organization>MIT Laboratory for Computer Science</organization>
2139      <address><email>timbl@w3.org</email></address>
2140    </author>
2141    <date month="January" year="1997"/>
2142  </front>
2143  <seriesInfo name="RFC" value="2068"/>
2144</reference>
2145
[129]2146<reference anchor="RFC2076">
2147  <front>
2148    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2149    <author initials="J." surname="Palme" fullname="Jacob Palme">
2150      <organization>Stockholm University/KTH</organization>
2151      <address><email>jpalme@dsv.su.se</email></address>
2152    </author>
2153    <date month="February" year="1997"/>
2154  </front>
2155  <seriesInfo name="RFC" value="2076"/>
2156</reference>
2157
2158<reference anchor="RFC2183">
2159  <front>
2160    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2161    <author initials="R." surname="Troost" fullname="Rens Troost">
2162      <organization>New Century Systems</organization>
2163      <address><email>rens@century.com</email></address>
2164    </author>
2165    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2166      <organization>QUALCOMM Incorporated</organization>
2167      <address><email>sdorner@qualcomm.com</email></address>
2168    </author>
2169    <author initials="K." surname="Moore" fullname="Keith Moore">
2170      <organization>Department of Computer Science</organization>
2171      <address><email>moore@cs.utk.edu</email></address>
2172    </author>
2173    <date month="August" year="1997"/>
2174  </front>
2175  <seriesInfo name="RFC" value="2183"/>
2176</reference>
2177
2178<reference anchor="RFC2277">
2179  <front>
2180    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2181    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2182      <organization>UNINETT</organization>
2183      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2184    </author>
2185    <date month="January" year="1998"/>
2186  </front>
2187  <seriesInfo name="BCP" value="18"/>
2188  <seriesInfo name="RFC" value="2277"/>
2189</reference>
2190
2191<reference anchor="RFC2388">
2192  <front>
2193    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2194    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2195      <organization>Xerox Palo Alto Research Center</organization>
2196      <address><email>masinter@parc.xerox.com</email></address>
2197    </author>
2198    <date year="1998" month="August"/>
2199  </front>
2200  <seriesInfo name="RFC" value="2388"/>
2201</reference>
2202
2203<reference anchor="RFC2557">
2204  <front>
2205    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2206    <author initials="F." surname="Palme" fullname="Jacob Palme">
2207      <organization>Stockholm University and KTH</organization>
2208      <address><email>jpalme@dsv.su.se</email></address>
2209    </author>
2210    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2211      <organization>Microsoft Corporation</organization>
2212      <address><email>alexhop@microsoft.com</email></address>
2213    </author>
2214    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2215      <organization>Lotus Development Corporation</organization>
2216      <address><email>Shelness@lotus.com</email></address>
2217    </author>
2218    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2219      <organization/>
2220      <address><email>stef@nma.com</email></address>
2221    </author>
2222    <date year="1999" month="March"/>
2223  </front>
2224  <seriesInfo name="RFC" value="2557"/>
2225</reference>
2226
[119]2227<reference anchor="RFC2616">
2228  <front>
2229    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2230    <author initials="R." surname="Fielding" fullname="R. Fielding">
2231      <organization>University of California, Irvine</organization>
2232      <address><email>fielding@ics.uci.edu</email></address>
2233    </author>
2234    <author initials="J." surname="Gettys" fullname="J. Gettys">
2235      <organization>W3C</organization>
2236      <address><email>jg@w3.org</email></address>
2237    </author>
2238    <author initials="J." surname="Mogul" fullname="J. Mogul">
2239      <organization>Compaq Computer Corporation</organization>
2240      <address><email>mogul@wrl.dec.com</email></address>
2241    </author>
2242    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2243      <organization>MIT Laboratory for Computer Science</organization>
2244      <address><email>frystyk@w3.org</email></address>
2245    </author>
2246    <author initials="L." surname="Masinter" fullname="L. Masinter">
2247      <organization>Xerox Corporation</organization>
2248      <address><email>masinter@parc.xerox.com</email></address>
2249    </author>
2250    <author initials="P." surname="Leach" fullname="P. Leach">
2251      <organization>Microsoft Corporation</organization>
2252      <address><email>paulle@microsoft.com</email></address>
2253    </author>
2254    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2255      <organization>W3C</organization>
2256      <address><email>timbl@w3.org</email></address>
2257    </author>
2258    <date month="June" year="1999"/>
2259  </front>
2260  <seriesInfo name="RFC" value="2616"/>
[129]2261</reference>
[119]2262
[129]2263<reference anchor="RFC3629">
2264  <front>
2265    <title>UTF-8, a transformation format of ISO 10646</title>
2266    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2267      <organization>Alis Technologies</organization>
2268      <address><email>fyergeau@alis.com</email></address>
2269    </author>
2270    <date month="November" year="2003"/>
2271  </front>
2272  <seriesInfo name="RFC" value="3629"/>
2273  <seriesInfo name="STD" value="63"/>
2274</reference>
2275
[253]2276<reference anchor='RFC3864'>
2277  <front>
2278    <title>Registration Procedures for Message Header Fields</title>
2279    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2280      <organization>Nine by Nine</organization>
2281      <address><email>GK-IETF@ninebynine.org</email></address>
2282    </author>
2283    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2284      <organization>BEA Systems</organization>
2285      <address><email>mnot@pobox.com</email></address>
2286    </author>
2287    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2288      <organization>HP Labs</organization>
2289      <address><email>JeffMogul@acm.org</email></address>
2290    </author>
2291    <date year='2004' month='September' />
2292  </front>
2293  <seriesInfo name='BCP' value='90' />
2294  <seriesInfo name='RFC' value='3864' />
2295</reference>
2296
[200]2297<reference anchor="RFC4288">
2298  <front>
2299    <title>Media Type Specifications and Registration Procedures</title>
2300    <author initials="N." surname="Freed" fullname="N. Freed">
2301      <organization>Sun Microsystems</organization>
2302      <address>
2303        <email>ned.freed@mrochek.com</email>
2304      </address>
2305    </author>
2306    <author initials="J." surname="Klensin" fullname="J. Klensin">
2307      <organization/>
2308      <address>
2309        <email>klensin+ietf@jck.com</email>
2310      </address>
2311    </author>
2312    <date year="2005" month="December"/>
2313  </front>
2314  <seriesInfo name="BCP" value="13"/>
2315  <seriesInfo name="RFC" value="4288"/>
2316</reference>
2317
[327]2318<reference anchor="RFC5322">
2319  <front>
2320    <title>Internet Message Format</title>
2321    <author initials="P." surname="Resnick" fullname="P. Resnick">
2322      <organization>Qualcomm Incorporated</organization>
2323    </author>
2324    <date year="2008" month="October"/>
2325  </front> 
2326  <seriesInfo name="RFC" value="5322"/>
2327</reference>
2328
[277]2329<reference anchor='BCP97'>
2330  <front>
2331    <title>Handling Normative References to Standards-Track Documents</title>
2332    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2333      <organization />
2334      <address>
2335        <email>klensin+ietf@jck.com</email>
2336      </address>
2337    </author>
2338    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2339      <organization>MIT</organization>
2340      <address>
2341        <email>hartmans-ietf@mit.edu</email>
2342      </address>
2343    </author>
2344    <date year='2007' month='June' />
2345  </front>
2346  <seriesInfo name='BCP' value='97' />
2347  <seriesInfo name='RFC' value='4897' />
2348</reference>
2349
2350
[119]2351</references>
2352
[8]2353<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2354<t>
[327]2355   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
[8]2356   allow entities to be transmitted in an open variety of
2357   representations and with extensible mechanisms. However, RFC 2045
2358   discusses mail, and HTTP has a few features that are different from
2359   those described in RFC 2045. These differences were carefully chosen
2360   to optimize performance over binary connections, to allow greater
2361   freedom in the use of new media types, to make date comparisons
2362   easier, and to acknowledge the practice of some early HTTP servers
2363   and clients.
2364</t>
2365<t>
2366   This appendix describes specific areas where HTTP differs from RFC
2367   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2368   aware of these differences and provide the appropriate conversions
2369   where necessary. Proxies and gateways from MIME environments to HTTP
2370   also need to be aware of the differences because some conversions
2371   might be required.
2372</t>
[229]2373
[8]2374<section title="MIME-Version" anchor="mime-version">
[291]2375  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2376  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
[229]2377  <x:anchor-alias value="MIME-Version"/>
[357]2378  <x:anchor-alias value="MIME-Version-v"/>
[8]2379<t>
2380   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2381   include a single MIME-Version general-header field to indicate what
2382   version of the MIME protocol was used to construct the message. Use
2383   of the MIME-Version header field indicates that the message is in
[115]2384   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2385   Proxies/gateways are responsible for ensuring full compliance (where
2386   possible) when exporting HTTP messages to strict MIME environments.
2387</t>
[357]2388<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
[366]2389  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
[357]2390  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
[8]2391</artwork></figure>
2392<t>
2393   MIME version "1.0" is the default for use in HTTP/1.1. However,
2394   HTTP/1.1 message parsing and semantics are defined by this document
2395   and not the MIME specification.
2396</t>
2397</section>
2398
2399<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2400<t>
[97]2401   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
[115]2402   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2403   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2404   allowed for subtypes of the "text" media type when transmitted over
[97]2405   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2406   line breaks as CRLF and forbids the use of CR or LF outside of line
2407   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2408   line break within text content when a message is transmitted over
2409   HTTP.
2410</t>
2411<t>
2412   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2413   environment &SHOULD; translate all line breaks within the text media
2414   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2415   canonical form of CRLF. Note, however, that this might be complicated
2416   by the presence of a Content-Encoding and by the fact that HTTP
2417   allows the use of some character sets which do not use octets 13 and
2418   10 to represent CR and LF, as is the case for some multi-byte
2419   character sets.
2420</t>
2421<t>
2422   Implementors should note that conversion will break any cryptographic
2423   checksums applied to the original content unless the original content
2424   is already in canonical form. Therefore, the canonical form is
2425   recommended for any content that uses such checksums in HTTP.
2426</t>
2427</section>
2428
2429<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2430<t>
2431   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2432   Content-Encoding header field. Since this acts as a modifier on the
2433   media type, proxies and gateways from HTTP to MIME-compliant
2434   protocols &MUST; either change the value of the Content-Type header
2435   field or decode the entity-body before forwarding the message. (Some
2436   experimental applications of Content-Type for Internet mail have used
2437   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2438   a function equivalent to Content-Encoding. However, this parameter is
2439   not part of RFC 2045).
2440</t>
2441</section>
2442
2443<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2444<t>
[85]2445   HTTP does not use the Content-Transfer-Encoding field of RFC
[8]2446   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2447   remove any Content-Transfer-Encoding
[8]2448   prior to delivering the response message to an HTTP client.
2449</t>
2450<t>
2451   Proxies and gateways from HTTP to MIME-compliant protocols are
2452   responsible for ensuring that the message is in the correct format
2453   and encoding for safe transport on that protocol, where "safe
2454   transport" is defined by the limitations of the protocol being used.
2455   Such a proxy or gateway &SHOULD; label the data with an appropriate
2456   Content-Transfer-Encoding if doing so will improve the likelihood of
2457   safe transport over the destination protocol.
2458</t>
2459</section>
2460
2461<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2462<t>
[29]2463   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2464   Proxies/gateways &MUST; remove any transfer-coding prior to
2465   forwarding a message via a MIME-compliant protocol.
2466</t>
2467</section>
2468
2469<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2470<t>
[129]2471   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2472   need to be aware of MIME line length limitations. Since HTTP does not
2473   have this limitation, HTTP does not fold long lines. MHTML messages
2474   being transported by HTTP follow all conventions of MHTML, including
2475   line length limitations and folding, canonicalization, etc., since
2476   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2477   does not interpret the content or any MIME header lines that might be
2478   contained therein.
2479</t>
2480</section>
2481</section>
2482
2483<section title="Additional Features" anchor="additional.features">
2484<t>
[97]2485   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2486   existing HTTP implementations, but not consistently and correctly
2487   across most HTTP/1.1 applications. Implementors are advised to be
2488   aware of these features, but cannot rely upon their presence in, or
2489   interoperability with, other HTTP/1.1 applications. Some of these
2490   describe proposed experimental features, and some describe features
2491   that experimental deployment found lacking that are now addressed in
2492   the base HTTP/1.1 specification.
2493</t>
2494<t>
2495   A number of other headers, such as Content-Disposition and Title,
[97]2496   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
[8]2497</t>
2498
2499<section title="Content-Disposition" anchor="content-disposition">
2500<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2501<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
[229]2502  <x:anchor-alias value="content-disposition"/>
[357]2503  <x:anchor-alias value="content-disposition-v"/>
[229]2504  <x:anchor-alias value="disposition-type"/>
2505  <x:anchor-alias value="disposition-parm"/>
2506  <x:anchor-alias value="disp-extension-parm"/>
2507  <x:anchor-alias value="disp-extension-token"/>
2508  <x:anchor-alias value="filename-parm"/>
[8]2509<t>
2510   The Content-Disposition response-header field has been proposed as a
2511   means for the origin server to suggest a default filename if the user
2512   requests that the content is saved to a file. This usage is derived
[269]2513   from the definition of Content-Disposition in <xref target="RFC2183"/>.
[8]2514</t>
[357]2515<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"/>
[366]2516  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
[357]2517                        <x:ref>content-disposition-v</x:ref>
[376]2518  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2519                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
[334]2520  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2521  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
[229]2522  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2523  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
[334]2524  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
[8]2525</artwork></figure>
2526<t>
2527   An example is
2528</t>
2529<figure><artwork type="example">
[357]2530   Content-Disposition: attachment; filename="fname.ext"
[8]2531</artwork></figure>
2532<t>
2533   The receiving user agent &SHOULD-NOT;  respect any directory path
2534   information present in the filename-parm parameter, which is the only
2535   parameter believed to apply to HTTP implementations at this time. The
2536   filename &SHOULD; be treated as a terminal component only.
2537</t>
2538<t>
2539   If this header is used in a response with the application/octet-stream
2540   content-type, the implied suggestion is that the user agent
2541   should not display the response, but directly enter a `save response
2542   as...' dialog.
2543</t>
2544<t>
2545   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2546</t>
2547</section>
2548</section>
2549
[99]2550<section title="Compatibility with Previous Versions" anchor="compatibility">
[8]2551<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2552<t>
[138]2553   Transfer-coding and message lengths all interact in ways that
2554   required fixing exactly when chunked encoding is used (to allow for
2555   transfer encoding that may not be self delimiting); it was important
2556   to straighten out exactly how message lengths are computed.
2557   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2558   <xref target="Part5"/> and <xref target="Part6"/>).
2559</t>
2560<t>
[29]2561   Charset wildcarding is introduced to avoid explosion of character set
2562   names in accept headers. (<xref target="header.accept-charset"/>)
[8]2563</t>
2564<t>
2565   Content-Base was deleted from the specification: it was not
2566   implemented widely, and there is no simple, safe way to introduce it
2567   without a robust extension mechanism. In addition, it is used in a
[129]2568   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
[8]2569</t>
2570<t>
2571   A content-coding of "identity" was introduced, to solve problems
2572   discovered in caching. (<xref target="content.codings"/>)
2573</t>
2574<t>
2575   Quality Values of zero should indicate that "I don't want something"
2576   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2577</t>
2578<t>
2579   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
2580   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
[268]2581   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
[8]2582</t>
2583</section>
[99]2584
2585<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
[102]2586<t>
2587  Clarify contexts that charset is used in.
2588  (<xref target="character.sets"/>)
2589</t>
[104]2590<t>
2591  Remove reference to non-existant identity transfer-coding value tokens.
2592  (<xref target="no.content-transfer-encoding"/>)
2593</t>
[99]2594</section>
2595
2596</section>
2597
[252]2598<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
[115]2599
2600<section title="Since RFC2616">
2601<t>
2602  Extracted relevant partitions from <xref target="RFC2616"/>.
2603</t>
2604</section>
2605
2606<section title="Since draft-ietf-httpbis-p3-payload-00">
2607<t>
[116]2608  Closed issues:
2609  <list style="symbols"> 
2610    <t>
[324]2611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
[116]2612      "Media Type Registrations"
2613      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2614    </t>
2615    <t>
[324]2616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
[116]2617      "Clarification regarding quoting of charset values"
2618      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2619    </t>
2620    <t>
[324]2621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
[116]2622      "Remove 'identity' token references"
2623      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2624    </t>
2625    <t>
[324]2626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
[126]2627      "Accept-Encoding BNF"
2628    </t>
2629    <t>
[324]2630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
[152]2631      "Normative and Informative references"
2632    </t>
2633    <t>
[324]2634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
[116]2635      "RFC1700 references"
2636    </t>
[122]2637    <t>
[324]2638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
[200]2639      "Updating to RFC4288"
2640    </t>
2641    <t>
[324]2642      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
[129]2643      "Informative references"
2644    </t>
2645    <t>
[324]2646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
[123]2647      "ISO-8859-1 Reference"
2648    </t>
2649    <t>
[324]2650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
[122]2651      "Encoding References Normative"
2652    </t>
[131]2653    <t>
[324]2654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
[131]2655      "Normative up-to-date references"
2656    </t>
[116]2657  </list>
[115]2658</t>
2659</section>
2660
[170]2661<section title="Since draft-ietf-httpbis-p3-payload-01">
2662<t>
[324]2663  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
[205]2664  <list style="symbols"> 
2665    <t>
2666      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2667    </t>
2668  </list>
[170]2669</t>
[115]2670</section>
2671
[252]2672<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[228]2673<t>
[232]2674  Closed issues:
2675  <list style="symbols"> 
2676    <t>
[324]2677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
[251]2678      "Quoting Charsets"
2679    </t>
2680    <t>
[324]2681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
[232]2682      "Classification for Allow header"
2683    </t>
[248]2684    <t>
[324]2685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
[248]2686      "missing default for qvalue in description of Accept-Encoding"
2687    </t>
[232]2688  </list>
[228]2689</t>
[253]2690<t>
[324]2691  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
[253]2692  <list style="symbols"> 
2693    <t>
2694      Reference RFC 3984, and update header registrations for headers defined
2695      in this document.
2696    </t>
2697  </list>
2698</t>
[170]2699</section>
2700
[267]2701<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2702<t>
[269]2703  Closed issues:
2704  <list style="symbols"> 
2705    <t>
[297]2706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2707      "Quoting Charsets"
2708    </t>
2709    <t>
[303]2710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2711      "language tag matching (Accept-Language) vs RFC4647"
2712    </t>
2713    <t>
[277]2714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
[269]2715      "RFC 1806 has been replaced by RFC2183"
2716    </t>
2717  </list>
[267]2718</t>
[277]2719<t>
2720  Other changes:
2721  <list style="symbols"> 
2722    <t>
2723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2724      "Encoding References Normative" -- rephrase the annotation and reference
2725      <xref target="BCP97"/>.
2726    </t>
2727  </list>
2728</t>
[269]2729 </section>
[228]2730
[323]2731<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2732<t>
[327]2733  Closed issues:
2734  <list style="symbols"> 
2735    <t>
2736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2737      "RFC 2822 is updated by RFC 5322"
2738    </t>
2739  </list>
[323]2740</t>
[334]2741<t>
2742  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2743  <list style="symbols"> 
2744    <t>
2745      Use "/" instead of "|" for alternatives.
2746    </t>
[357]2747    <t>
2748      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2749      whitespace ("OWS") and required whitespace ("RWS").
2750    </t>
2751    <t>
2752      Rewrite ABNFs to spell out whitespace rules, factor out
2753      header value format definitions.
2754    </t>
[334]2755  </list>
2756</t>
2757</section>
[323]2758
[267]2759</section>
2760
[8]2761</back>
2762</rfc>
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