source: draft-ietf-httpbis/latest/p3-payload.xml @ 689

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38]>
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
52     xmlns:x='http://purl.org/net/xml2rfc/ext'>
53<front>
54
55  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
56
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email>fielding@gbiv.com</email>
70      <uri>http://roy.gbiv.com/</uri>
71    </address>
72  </author>
73
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email>jg@laptop.org</email>
85      <uri>http://www.laptop.org/</uri>
86    </address>
87  </author>
88 
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email>JeffMogul@acm.org</email>
101    </address>
102  </author>
103
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email>henrikn@microsoft.com</email>
115    </address>
116  </author>
117
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email>LMM@acm.org</email>
129      <uri>http://larry.masinter.net/</uri>
130    </address>
131  </author>
132 
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email>paulle@microsoft.com</email>
143    </address>
144  </author>
145   
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email>timbl@w3.org</email>
159      <uri>http://www.w3.org/People/Berners-Lee/</uri>
160    </address>
161  </author>
162
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email>ylafon@w3.org</email>
175      <uri>http://www.raubacapeu.net/people/yves/</uri>
176    </address>
177  </author>
178
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email>julian.reschke@greenbytes.de</email>
190      <uri>http://greenbytes.de/tech/webdav/</uri>
191    </address>
192  </author>
193
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
196
197<abstract>
198<t>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypermedia information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 3 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 3 defines HTTP message content,
205   metadata, and content negotiation.
206</t>
207</abstract>
208
209<note title="Editorial Note (To be removed by RFC Editor)">
210  <t>
211    Discussion of this draft should take place on the HTTPBIS working group
212    mailing list (ietf-http-wg@w3.org). The current issues list is
213    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
214    and related documents (including fancy diffs) can be found at
215    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
216  </t>
217  <t>
218    The changes in this draft are summarized in <xref target="changes.since.07"/>.
219  </t>
220</note>
221</front>
222<middle>
223<section title="Introduction" anchor="introduction">
224<t>
225   This document defines HTTP/1.1 message payloads (a.k.a., content), the
226   associated metadata header fields that define how the payload is intended
227   to be interpreted by a recipient, the request header fields that
228   may influence content selection, and the various selection algorithms
229   that are collectively referred to as HTTP content negotiation.
230</t>
231<t>
232   This document is currently disorganized in order to minimize the changes
233   between drafts and enable reviewers to see the smaller errata changes.
234   The next draft will reorganize the sections to better reflect the content.
235   In particular, the sections on entities will be renamed payload and moved
236   to the first half of the document, while the sections on content negotiation
237   and associated request header fields will be moved to the second half.  The
238   current mess reflects how widely dispersed these topics and associated
239   requirements had become in <xref target="RFC2616"/>.
240</t>
241
242<section title="Terminology" anchor="terminology">
243<t>
244   This specification uses a number of terms to refer to the roles
245   played by participants in, and objects of, the HTTP communication.
246</t>
247<t>
248  <iref item="content negotiation"/>
249  <x:dfn>content negotiation</x:dfn>
250  <list>
251    <t>
252      The mechanism for selecting the appropriate representation when
253      servicing a request. The representation of entities in any response
254      can be negotiated (including error responses).
255    </t>
256  </list>
257</t>
258<t>
259  <iref item="entity"/>
260  <x:dfn>entity</x:dfn>
261  <list>
262    <t>
263      The information transferred as the payload of a request or
264      response. An entity consists of metadata in the form of
265      entity-header fields and content in the form of an entity-body.
266    </t>
267  </list>
268</t>
269<t>
270  <iref item="representation"/>
271  <x:dfn>representation</x:dfn>
272  <list>
273    <t>
274      An entity included with a response that is subject to content
275      negotiation. There may exist multiple
276      representations associated with a particular response status.
277    </t>
278  </list>
279</t>
280<t>
281  <iref item="variant"/>
282  <x:dfn>variant</x:dfn>
283  <list>
284    <t>
285      A resource may have one, or more than one, representation(s)
286      associated with it at any given instant. Each of these
287      representations is termed a `variant'.  Use of the term `variant'
288      does not necessarily imply that the resource is subject to content
289      negotiation.
290    </t>
291  </list>
292</t>
293</section>
294
295<section title="Requirements" anchor="intro.requirements">
296<t>
297   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
298   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
299   document are to be interpreted as described in <xref target="RFC2119"/>.
300</t>
301<t>
302   An implementation is not compliant if it fails to satisfy one or more
303   of the &MUST; or &REQUIRED; level requirements for the protocols it
304   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
305   level and all the &SHOULD; level requirements for its protocols is said
306   to be "unconditionally compliant"; one that satisfies all the &MUST;
307   level requirements but not all the &SHOULD; level requirements for its
308   protocols is said to be "conditionally compliant."
309</t>
310</section>
311
312<section title="Syntax Notation" anchor="notation">
313  <x:anchor-alias value="ALPHA"/>
314  <x:anchor-alias value="CR"/>
315  <x:anchor-alias value="DIGIT"/>
316  <x:anchor-alias value="LF"/>
317  <x:anchor-alias value="OCTET"/>
318  <x:anchor-alias value="VCHAR"/>
319  <x:anchor-alias value="WSP"/>
320<t>
321  This specification uses the ABNF syntax defined in &notation; (which
322  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
323  <xref target="collected.abnf"/> shows the collected ABNF, with the list
324  rule expanded.
325</t>
326<t>
327  The following core rules are included by
328  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
329  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
330  DIGIT (decimal 0-9), DQUOTE (double quote),
331  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
332  OCTET (any 8-bit sequence of data), SP (space),
333  VCHAR (any visible USASCII character),
334  and WSP (whitespace).
335</t>
336
337<section title="Core Rules" anchor="core.rules">
338  <x:anchor-alias value="quoted-string"/>
339  <x:anchor-alias value="token"/>
340  <x:anchor-alias value="OWS"/>
341<t>
342  The core rules below are defined in &basic-rules;:
343</t>
344<figure><artwork type="abnf2616">
345  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
346  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
347  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
348</artwork></figure>
349</section>
350
351<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
352  <x:anchor-alias value="absolute-URI"/>
353  <x:anchor-alias value="Allow"/>
354  <x:anchor-alias value="Content-Length"/>
355  <x:anchor-alias value="Content-Range"/>
356  <x:anchor-alias value="Expires"/>
357  <x:anchor-alias value="Last-Modified"/>
358  <x:anchor-alias value="header-field"/>
359  <x:anchor-alias value="partial-URI"/>
360  <x:anchor-alias value="qvalue"/>
361<t>
362  The ABNF rules below are defined in other parts:
363</t>
364<figure><!--Part1--><artwork type="abnf2616">
365  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
366  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
367  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
368  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
369  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
370</artwork></figure>
371<figure><!--Part4--><artwork type="abnf2616">
372  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
373</artwork></figure>
374<figure><!--Part5--><artwork type="abnf2616">
375  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
376</artwork></figure>
377<figure><!--Part6--><artwork type="abnf2616">
378  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
379</artwork></figure>
380</section>
381
382</section>
383
384</section>
385
386<section title="Protocol Parameters" anchor="protocol.parameters">
387
388<section title="Character Sets" anchor="character.sets">
389<t>
390   HTTP uses the same definition of the term "character set" as that
391   described for MIME:
392</t>
393<t>
394   The term "character set" is used in this document to refer to a
395   method used with one or more tables to convert a sequence of octets
396   into a sequence of characters. Note that unconditional conversion in
397   the other direction is not required, in that not all characters may
398   be available in a given character set and a character set may provide
399   more than one sequence of octets to represent a particular character.
400   This definition is intended to allow various kinds of character
401   encoding, from simple single-table mappings such as US-ASCII to
402   complex table switching methods such as those that use ISO-2022's
403   techniques. However, the definition associated with a MIME character
404   set name &MUST; fully specify the mapping to be performed from octets
405   to characters. In particular, use of external profiling information
406   to determine the exact mapping is not permitted.
407</t>
408<x:note>
409  <t>
410    <x:h>Note:</x:h> This use of the term "character set" is more commonly
411    referred to as a "character encoding." However, since HTTP and
412    MIME share the same registry, it is important that the terminology
413    also be shared.
414  </t>
415</x:note>
416<t anchor="rule.charset">
417  <x:anchor-alias value="charset"/>
418   HTTP character sets are identified by case-insensitive tokens. The
419   complete set of tokens is defined by the IANA Character Set registry
420   (<eref target="http://www.iana.org/assignments/character-sets"/>).
421</t>
422<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
423  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
424</artwork></figure>
425<t>
426   Although HTTP allows an arbitrary token to be used as a charset
427   value, any token that has a predefined value within the IANA
428   Character Set registry &MUST; represent the character set defined
429   by that registry. Applications &SHOULD; limit their use of character
430   sets to those defined by the IANA registry.
431</t>
432<t>
433   HTTP uses charset in two contexts: within an Accept-Charset request
434   header (in which the charset value is an unquoted token) and as the
435   value of a parameter in a Content-Type header (within a request or
436   response), in which case the parameter value of the charset parameter
437   may be quoted.
438</t>
439<t>
440   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
441   <xref target="RFC2277"/>.
442</t>
443
444<section title="Missing Charset" anchor="missing.charset">
445<t>
446   Some HTTP/1.0 software has interpreted a Content-Type header without
447   charset parameter incorrectly to mean "recipient should guess."
448   Senders wishing to defeat this behavior &MAY; include a charset
449   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
450   it is known that it will not confuse the recipient.
451</t>
452<t>
453   Unfortunately, some older HTTP/1.0 clients did not deal properly with
454   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
455   charset label provided by the sender; and those user agents that have
456   a provision to "guess" a charset &MUST; use the charset from the
457   content-type field if they support that charset, rather than the
458   recipient's preference, when initially displaying a document. See
459   <xref target="canonicalization.and.text.defaults"/>.
460</t>
461</section>
462</section>
463
464<section title="Content Codings" anchor="content.codings">
465  <x:anchor-alias value="content-coding"/>
466<t>
467   Content coding values indicate an encoding transformation that has
468   been or can be applied to an entity. Content codings are primarily
469   used to allow a document to be compressed or otherwise usefully
470   transformed without losing the identity of its underlying media type
471   and without loss of information. Frequently, the entity is stored in
472   coded form, transmitted directly, and only decoded by the recipient.
473</t>
474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
475  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
476</artwork></figure>
477<t>
478   All content-coding values are case-insensitive. HTTP/1.1 uses
479   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
480   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
481   describes the content-coding, what is more important is that it
482   indicates what decoding mechanism will be required to remove the
483   encoding.
484</t>
485<t>
486   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
487  <list>
488    <t>
489      See &compress-coding;.
490    </t>
491  </list>
492</t>
493<t>
494   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
495  <list>
496    <t>
497      See &deflate-coding;.
498    </t>
499  </list>
500</t>
501<t>
502   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
503  <list>
504    <t>
505      See &gzip-coding;.
506    </t>
507  </list>
508</t>
509<t>
510   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
511  <list><t>
512        The default (identity) encoding; the use of no transformation
513        whatsoever. This content-coding is used only in the Accept-Encoding
514        header, and &SHOULD-NOT;  be used in the Content-Encoding
515        header.
516  </t></list>
517</t>
518
519<section title="Content Coding Registry" anchor="content.coding.registry">
520<t>
521   The HTTP Content Coding Registry defines the name space for the content
522   coding names.
523</t>
524<t>
525   Registrations &MUST; include the following fields:
526   <list style="symbols">
527     <t>Name</t>
528     <t>Description</t>
529     <t>Pointer to specification text</t>
530   </list>
531</t>
532<t>
533   Values to be added to this name space require expert review and a specification
534   (see "Expert Review" and "Specification Required" in
535   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
536   conform to the purpose of content coding defined in this section.
537</t>
538<t>
539   The registry itself is maintained at
540   <eref target="http://www.iana.org/assignments/http-parameters"/>.
541</t>
542</section>
543
544</section>
545
546<section title="Media Types" anchor="media.types">
547  <x:anchor-alias value="media-type"/>
548  <x:anchor-alias value="type"/>
549  <x:anchor-alias value="subtype"/>
550<t>
551   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
552   and Accept (<xref target="header.accept"/>) header fields in order to provide
553   open and extensible data typing and type negotiation.
554</t>
555<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"/>
556  <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> )
557  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
558  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
559</artwork></figure>
560<t anchor="rule.parameter">
561  <x:anchor-alias value="attribute"/>
562  <x:anchor-alias value="parameter"/>
563  <x:anchor-alias value="value"/>
564   Parameters &MAY; follow the type/subtype in the form of attribute/value
565   pairs.
566</t>
567<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"/>
568  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
569  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
570  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
571</artwork></figure>
572<t>
573   The type, subtype, and parameter attribute names are case-insensitive.
574   Parameter values might or might not be case-sensitive, depending on the
575   semantics of the parameter name.  The presence or absence of a parameter might
576   be significant to the processing of a media-type, depending on its
577   definition within the media type registry.
578</t>
579<t>
580   A parameter value that matches the <x:ref>token</x:ref> production may be
581   transmitted as either a token or within a quoted-string. The quoted and
582   unquoted values are equivalent.
583</t>
584<t>
585   Note that some older HTTP applications do not recognize media type
586   parameters. When sending data to older HTTP applications,
587   implementations &SHOULD; only use media type parameters when they are
588   required by that type/subtype definition.
589</t>
590<t>
591   Media-type values are registered with the Internet Assigned Number
592   Authority (IANA). The media type registration process is
593   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
594   discouraged.
595</t>
596
597<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
598<t>
599   Internet media types are registered with a canonical form. An
600   entity-body transferred via HTTP messages &MUST; be represented in the
601   appropriate canonical form prior to its transmission except for
602   "text" types, as defined in the next paragraph.
603</t>
604<t>
605   When in canonical form, media subtypes of the "text" type use CRLF as
606   the text line break. HTTP relaxes this requirement and allows the
607   transport of text media with plain CR or LF alone representing a line
608   break when it is done consistently for an entire entity-body. HTTP
609   applications &MUST; accept CRLF, bare CR, and bare LF as being
610   representative of a line break in text media received via HTTP. In
611   addition, if the text is represented in a character set that does not
612   use octets 13 and 10 for CR and LF respectively, as is the case for
613   some multi-byte character sets, HTTP allows the use of whatever octet
614   sequences are defined by that character set to represent the
615   equivalent of CR and LF for line breaks. This flexibility regarding
616   line breaks applies only to text media in the entity-body; a bare CR
617   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
618   structures (such as header fields and multipart boundaries).
619</t>
620<t>
621   If an entity-body is encoded with a content-coding, the underlying
622   data &MUST; be in a form defined above prior to being encoded.
623</t>
624<t>
625   The "charset" parameter is used with some media types to define the
626   character set (<xref target="character.sets"/>) of the data. When no explicit charset
627   parameter is provided by the sender, media subtypes of the "text"
628   type are defined to have a default charset value of "ISO-8859-1" when
629   received via HTTP. Data in character sets other than "ISO-8859-1" or
630   its subsets &MUST; be labeled with an appropriate charset value. See
631   <xref target="missing.charset"/> for compatibility problems.
632</t>
633</section>
634
635<section title="Multipart Types" anchor="multipart.types">
636<t>
637   MIME provides for a number of "multipart" types -- encapsulations of
638   one or more entities within a single message-body. All multipart
639   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
640   and &MUST; include a boundary parameter as part of the media type
641   value. The message body is itself a protocol element and &MUST;
642   therefore use only CRLF to represent line breaks between body-parts.
643   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
644   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
645   original multipart contains an epilogue). These restrictions exist in
646   order to preserve the self-delimiting nature of a multipart message-body,
647   wherein the "end" of the message-body is indicated by the
648   ending multipart boundary.
649</t>
650<t>
651   In general, HTTP treats a multipart message-body no differently than
652   any other media type: strictly as payload. The one exception is the
653   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
654   (Partial Content) response.
655   <!-- jre: re-insert removed text pointing to caching? -->
656   In all
657   other cases, an HTTP user agent &SHOULD; follow the same or similar
658   behavior as a MIME user agent would upon receipt of a multipart type.
659   The MIME header fields within each body-part of a multipart message-body
660   do not have any significance to HTTP beyond that defined by
661   their MIME semantics.
662</t>
663<t>
664   In general, an HTTP user agent &SHOULD; follow the same or similar
665   behavior as a MIME user agent would upon receipt of a multipart type.
666   If an application receives an unrecognized multipart subtype, the
667   application &MUST; treat it as being equivalent to "multipart/mixed".
668</t>
669<x:note>
670  <t>
671    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
672    for carrying form data suitable for processing via the POST
673    request method, as described in <xref target="RFC2388"/>.
674  </t>
675</x:note>
676</section>
677</section>
678
679<section title="Language Tags" anchor="language.tags">
680  <x:anchor-alias value="language-tag"/>
681<t>
682   A language tag, as defined in <xref target="RFC4646bis"/>, identifies a
683   natural language spoken, written, or otherwise conveyed by human beings for
684   communication of information to other human beings. Computer languages are
685   explicitly excluded. HTTP uses language tags within the Accept-Language and
686   Content-Language fields.
687</t>
688<t>
689   In summary, a language tag is composed of one or more parts: A primary
690   language subtag followed by a possibly empty series of subtags:
691</t>
692<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
693  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC4646bis" x:sec="2.1"/>&gt;
694</artwork></figure>
695<t>
696   White space is not allowed within the tag and all tags are case-insensitive.
697   The name space of language subtags is administered by the IANA (see
698   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
699</t>
700<figure>
701  <preamble>Example tags include:</preamble>
702<artwork type="example">
703  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
704</artwork>
705</figure>
706<t>
707   See <xref target="RFC4646bis"/> for further information.
708</t>
709</section>
710</section>
711
712<section title="Entity" anchor="entity">
713<t>
714   Request and Response messages &MAY; transfer an entity if not otherwise
715   restricted by the request method or response status code. An entity
716   consists of entity-header fields and an entity-body, although some
717   responses will only include the entity-headers.
718</t>
719<t>
720   In this section, both sender and recipient refer to either the client
721   or the server, depending on who sends and who receives the entity.
722</t>
723
724<section title="Entity Header Fields" anchor="entity.header.fields">
725  <x:anchor-alias value="entity-header"/>
726  <x:anchor-alias value="extension-header"/>
727<t>
728   Entity-header fields define metainformation about the entity-body or,
729   if no body is present, about the resource identified by the request.
730</t>
731<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
732  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
733                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
734                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
735                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
736                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
737                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
738                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
739                 / <x:ref>Expires</x:ref>                  ; &header-expires;
740                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
741                 / <x:ref>extension-header</x:ref>
742 
743  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
744</artwork></figure>
745<t>
746   The extension-header mechanism allows additional entity-header fields
747   to be defined without changing the protocol, but these fields cannot
748   be assumed to be recognizable by the recipient. Unrecognized header
749   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
750   transparent proxies.
751</t>
752</section>
753
754<section title="Entity Body" anchor="entity.body">
755  <x:anchor-alias value="entity-body"/>
756<t>
757   The entity-body (if any) sent with an HTTP request or response is in
758   a format and encoding defined by the entity-header fields.
759</t>
760<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
761  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
762</artwork></figure>
763<t>
764   An entity-body is only present in a message when a message-body is
765   present, as described in &message-body;. The entity-body is obtained
766   from the message-body by decoding any Transfer-Encoding that might
767   have been applied to ensure safe and proper transfer of the message.
768</t>
769
770<section title="Type" anchor="type">
771<t>
772   When an entity-body is included with a message, the data type of that
773   body is determined via the header fields Content-Type and Content-Encoding.
774   These define a two-layer, ordered encoding model:
775</t>
776<figure><artwork type="example">
777  entity-body := Content-Encoding( Content-Type( data ) )
778</artwork></figure>
779<t>
780   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
781   message containing an entity-body &SHOULD; include a Content-Type header
782   field defining the media type of that body, unless that information is
783   unknown.  If the Content-Type header field is not present, it indicates that
784   the sender does not know the media type of the data; recipients &MAY;
785   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
786   or examine the content to determine its type.
787</t>
788<t>
789   Content-Encoding may be used to indicate any additional content
790   codings applied to the data, usually for the purpose of data
791   compression, that are a property of the requested resource.  There is
792   no default encoding.
793</t>
794</section>
795   
796<section title="Entity Length" anchor="entity.length">
797<t>
798   The entity-length of a message is the length of the message-body
799   before any transfer-codings have been applied. &message-length; defines
800   how the transfer-length of a message-body is determined.
801</t>
802</section>
803</section>
804</section>
805
806<section title="Content Negotiation" anchor="content.negotiation">
807<t>
808   Most HTTP responses include an entity which contains information for
809   interpretation by a human user. Naturally, it is desirable to supply
810   the user with the "best available" entity corresponding to the
811   request. Unfortunately for servers and caches, not all users have the
812   same preferences for what is "best," and not all user agents are
813   equally capable of rendering all entity types. For that reason, HTTP
814   has provisions for several mechanisms for "content negotiation" --
815   the process of selecting the best representation for a given response
816   when there are multiple representations available.
817</t>
818<x:note>
819  <t>
820    <x:h>Note:</x:h> This is not called "format negotiation" because the
821    alternate representations may be of the same media type, but use
822    different capabilities of that type, be in different languages,
823    etc.
824  </t>
825</x:note>
826<t>
827   Any response containing an entity-body &MAY; be subject to negotiation,
828   including error responses.
829</t>
830<t>
831   There are two kinds of content negotiation which are possible in
832   HTTP: server-driven and agent-driven negotiation. These two kinds of
833   negotiation are orthogonal and thus may be used separately or in
834   combination. One method of combination, referred to as transparent
835   negotiation, occurs when a cache uses the agent-driven negotiation
836   information provided by the origin server in order to provide
837   server-driven negotiation for subsequent requests.
838</t>
839
840<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
841<t>
842   If the selection of the best representation for a response is made by
843   an algorithm located at the server, it is called server-driven
844   negotiation. Selection is based on the available representations of
845   the response (the dimensions over which it can vary; e.g. language,
846   content-coding, etc.) and the contents of particular header fields in
847   the request message or on other information pertaining to the request
848   (such as the network address of the client).
849</t>
850<t>
851   Server-driven negotiation is advantageous when the algorithm for
852   selecting from among the available representations is difficult to
853   describe to the user agent, or when the server desires to send its
854   "best guess" to the client along with the first response (hoping to
855   avoid the round-trip delay of a subsequent request if the "best
856   guess" is good enough for the user). In order to improve the server's
857   guess, the user agent &MAY; include request header fields (Accept,
858   Accept-Language, Accept-Encoding, etc.) which describe its
859   preferences for such a response.
860</t>
861<t>
862   Server-driven negotiation has disadvantages:
863  <list style="numbers">
864    <t>
865         It is impossible for the server to accurately determine what
866         might be "best" for any given user, since that would require
867         complete knowledge of both the capabilities of the user agent
868         and the intended use for the response (e.g., does the user want
869         to view it on screen or print it on paper?).
870    </t>
871    <t>
872         Having the user agent describe its capabilities in every
873         request can be both very inefficient (given that only a small
874         percentage of responses have multiple representations) and a
875         potential violation of the user's privacy.
876    </t>
877    <t>
878         It complicates the implementation of an origin server and the
879         algorithms for generating responses to a request.
880    </t>
881    <t>
882         It may limit a public cache's ability to use the same response
883         for multiple user's requests.
884    </t>
885  </list>
886</t>
887<t>
888   HTTP/1.1 includes the following request-header fields for enabling
889   server-driven negotiation through description of user agent
890   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
891   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
892   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
893   origin server is not limited to these dimensions and &MAY; vary the
894   response based on any aspect of the request, including information
895   outside the request-header fields or within extension header fields
896   not defined by this specification.
897</t>
898<t>
899   The Vary header field (&header-vary;) can be used to express the parameters the
900   server uses to select a representation that is subject to server-driven
901   negotiation.
902</t>
903</section>
904
905<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
906<t>
907   With agent-driven negotiation, selection of the best representation
908   for a response is performed by the user agent after receiving an
909   initial response from the origin server. Selection is based on a list
910   of the available representations of the response included within the
911   header fields or entity-body of the initial response, with each
912   representation identified by its own URI. Selection from among the
913   representations may be performed automatically (if the user agent is
914   capable of doing so) or manually by the user selecting from a
915   generated (possibly hypertext) menu.
916</t>
917<t>
918   Agent-driven negotiation is advantageous when the response would vary
919   over commonly-used dimensions (such as type, language, or encoding),
920   when the origin server is unable to determine a user agent's
921   capabilities from examining the request, and generally when public
922   caches are used to distribute server load and reduce network usage.
923</t>
924<t>
925   Agent-driven negotiation suffers from the disadvantage of needing a
926   second request to obtain the best alternate representation. This
927   second request is only efficient when caching is used. In addition,
928   this specification does not define any mechanism for supporting
929   automatic selection, though it also does not prevent any such
930   mechanism from being developed as an extension and used within
931   HTTP/1.1.
932</t>
933<t>
934   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
935   status codes for enabling agent-driven negotiation when the server is
936   unwilling or unable to provide a varying response using server-driven
937   negotiation.
938</t>
939</section>
940
941<section title="Transparent Negotiation" anchor="transparent.negotiation">
942<t>
943   Transparent negotiation is a combination of both server-driven and
944   agent-driven negotiation. When a cache is supplied with a form of the
945   list of available representations of the response (as in agent-driven
946   negotiation) and the dimensions of variance are completely understood
947   by the cache, then the cache becomes capable of performing server-driven
948   negotiation on behalf of the origin server for subsequent
949   requests on that resource.
950</t>
951<t>
952   Transparent negotiation has the advantage of distributing the
953   negotiation work that would otherwise be required of the origin
954   server and also removing the second request delay of agent-driven
955   negotiation when the cache is able to correctly guess the right
956   response.
957</t>
958<t>
959   This specification does not define any mechanism for transparent
960   negotiation, though it also does not prevent any such mechanism from
961   being developed as an extension that could be used within HTTP/1.1.
962</t>
963</section>
964</section>
965
966<section title="Header Field Definitions" anchor="header.fields">
967<t>
968   This section defines the syntax and semantics of HTTP/1.1 header fields
969   related to the payload of messages.
970</t>
971<t>
972   For entity-header fields, both sender and recipient refer to either the
973   client or the server, depending on who sends and who receives the entity.
974</t>
975
976<section title="Accept" anchor="header.accept">
977  <iref primary="true" item="Accept header" x:for-anchor=""/>
978  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
979  <x:anchor-alias value="Accept"/>
980  <x:anchor-alias value="Accept-v"/>
981  <x:anchor-alias value="accept-ext"/>
982  <x:anchor-alias value="accept-params"/>
983  <x:anchor-alias value="media-range"/>
984<t>
985   The request-header field "Accept" can be used to specify certain media
986   types which are acceptable for the response. Accept headers can be
987   used to indicate that the request is specifically limited to a small
988   set of desired types, as in the case of a request for an in-line
989   image.
990</t>
991<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"/>
992  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
993  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
994 
995  <x:ref>media-range</x:ref>    = ( "*/*"
996                   / ( <x:ref>type</x:ref> "/" "*" )
997                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
998                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
999  <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> )
1000  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
1001                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
1002</artwork></figure>
1003<t>
1004   The asterisk "*" character is used to group media types into ranges,
1005   with "*/*" indicating all media types and "type/*" indicating all
1006   subtypes of that type. The media-range &MAY; include media type
1007   parameters that are applicable to that range.
1008</t>
1009<t>
1010   Each media-range &MAY; be followed by one or more accept-params,
1011   beginning with the "q" parameter for indicating a relative quality
1012   factor. The first "q" parameter (if any) separates the media-range
1013   parameter(s) from the accept-params. Quality factors allow the user
1014   or user agent to indicate the relative degree of preference for that
1015   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1016   default value is q=1.
1017</t>
1018<x:note>
1019  <t>
1020    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1021    parameters from Accept extension parameters is due to historical
1022    practice. Although this prevents any media type parameter named
1023    "q" from being used with a media range, such an event is believed
1024    to be unlikely given the lack of any "q" parameters in the IANA
1025    media type registry and the rare usage of any media type
1026    parameters in Accept. Future media types are discouraged from
1027    registering any parameter named "q".
1028  </t>
1029</x:note>
1030<t>
1031   The example
1032</t>
1033<figure><artwork type="example">
1034  Accept: audio/*; q=0.2, audio/basic
1035</artwork></figure>
1036<t>
1037   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1038   type if it is the best available after an 80% mark-down in quality."
1039</t>
1040<t>
1041   If no Accept header field is present, then it is assumed that the
1042   client accepts all media types. If an Accept header field is present,
1043   and if the server cannot send a response which is acceptable
1044   according to the combined Accept field value, then the server &SHOULD;
1045   send a 406 (Not Acceptable) response.
1046</t>
1047<t>
1048   A more elaborate example is
1049</t>
1050<figure><artwork type="example">
1051  Accept: text/plain; q=0.5, text/html,
1052          text/x-dvi; q=0.8, text/x-c
1053</artwork></figure>
1054<t>
1055   Verbally, this would be interpreted as "text/html and text/x-c are
1056   the preferred media types, but if they do not exist, then send the
1057   text/x-dvi entity, and if that does not exist, send the text/plain
1058   entity."
1059</t>
1060<t>
1061   Media ranges can be overridden by more specific media ranges or
1062   specific media types. If more than one media range applies to a given
1063   type, the most specific reference has precedence. For example,
1064</t>
1065<figure><artwork type="example">
1066  Accept: text/*, text/html, text/html;level=1, */*
1067</artwork></figure>
1068<t>
1069   have the following precedence:
1070   <list style="numbers">
1071    <t>text/html;level=1</t>
1072    <t>text/html</t>
1073    <t>text/*</t>
1074    <t>*/*</t>
1075   </list>
1076</t>
1077<t>
1078   The media type quality factor associated with a given type is
1079   determined by finding the media range with the highest precedence
1080   which matches that type. For example,
1081</t>
1082<figure><artwork type="example">
1083  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1084          text/html;level=2;q=0.4, */*;q=0.5
1085</artwork></figure>
1086<t>
1087   would cause the following values to be associated:
1088</t>
1089<texttable align="left">
1090  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1091  <c>text/html;level=1</c>    <c>1</c>
1092  <c>text/html</c>            <c>0.7</c>
1093  <c>text/plain</c>           <c>0.3</c>
1094  <c>image/jpeg</c>           <c>0.5</c>
1095  <c>text/html;level=2</c>    <c>0.4</c>
1096  <c>text/html;level=3</c>    <c>0.7</c>
1097</texttable>
1098<t>
1099      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1100      values for certain media ranges. However, unless the user agent is
1101      a closed system which cannot interact with other rendering agents,
1102      this default set ought to be configurable by the user.
1103</t>
1104</section>
1105
1106<section title="Accept-Charset" anchor="header.accept-charset">
1107  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1108  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1109  <x:anchor-alias value="Accept-Charset"/>
1110  <x:anchor-alias value="Accept-Charset-v"/>
1111<t>
1112   The request-header field "Accept-Charset" can be used to indicate what
1113   character sets are acceptable for the response. This field allows
1114   clients capable of understanding more comprehensive or special-purpose
1115   character sets to signal that capability to a server which is
1116   capable of representing documents in those character sets.
1117</t>
1118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1119  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1120          <x:ref>Accept-Charset-v</x:ref>
1121  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1122                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1123</artwork></figure>
1124<t>
1125   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1126   be given an associated quality value which represents the user's
1127   preference for that charset. The default value is q=1. An example is
1128</t>
1129<figure><artwork type="example">
1130  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1131</artwork></figure>
1132<t>
1133   The special value "*", if present in the Accept-Charset field,
1134   matches every character set (including ISO-8859-1) which is not
1135   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1136   in an Accept-Charset field, then all character sets not explicitly
1137   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1138   a quality value of 1 if not explicitly mentioned.
1139</t>
1140<t>
1141   If no Accept-Charset header is present, the default is that any
1142   character set is acceptable. If an Accept-Charset header is present,
1143   and if the server cannot send a response which is acceptable
1144   according to the Accept-Charset header, then the server &SHOULD; send
1145   an error response with the 406 (Not Acceptable) status code, though
1146   the sending of an unacceptable response is also allowed.
1147</t>
1148</section>
1149
1150<section title="Accept-Encoding" anchor="header.accept-encoding">
1151  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1152  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1153  <x:anchor-alias value="Accept-Encoding"/>
1154  <x:anchor-alias value="Accept-Encoding-v"/>
1155  <x:anchor-alias value="codings"/>
1156<t>
1157   The request-header field "Accept-Encoding" is similar to Accept, but
1158   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1159   the response.
1160</t>
1161<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"/>
1162  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1163                     <x:ref>Accept-Encoding-v</x:ref>
1164  <x:ref>Accept-Encoding-v</x:ref>  =
1165                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1166  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1167</artwork></figure>
1168<t>
1169   Each codings value &MAY; be given an associated quality value which
1170   represents the preference for that encoding. The default value is q=1.
1171</t>
1172<t>
1173   Examples of its use are:
1174</t>
1175<figure><artwork type="example">
1176  Accept-Encoding: compress, gzip
1177  Accept-Encoding:
1178  Accept-Encoding: *
1179  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1180  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1181</artwork></figure>
1182<t>
1183   A server tests whether a content-coding is acceptable, according to
1184   an Accept-Encoding field, using these rules:
1185  <list style="numbers">
1186      <t>If the content-coding is one of the content-codings listed in
1187         the Accept-Encoding field, then it is acceptable, unless it is
1188         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1189         qvalue of 0 means "not acceptable.")</t>
1190
1191      <t>The special "*" symbol in an Accept-Encoding field matches any
1192         available content-coding not explicitly listed in the header
1193         field.</t>
1194
1195      <t>If multiple content-codings are acceptable, then the acceptable
1196         content-coding with the highest non-zero qvalue is preferred.</t>
1197
1198      <t>The "identity" content-coding is always acceptable, unless
1199         specifically refused because the Accept-Encoding field includes
1200         "identity;q=0", or because the field includes "*;q=0" and does
1201         not explicitly include the "identity" content-coding. If the
1202         Accept-Encoding field-value is empty, then only the "identity"
1203         encoding is acceptable.</t>
1204  </list>
1205</t>
1206<t>
1207   If an Accept-Encoding field is present in a request, and if the
1208   server cannot send a response which is acceptable according to the
1209   Accept-Encoding header, then the server &SHOULD; send an error response
1210   with the 406 (Not Acceptable) status code.
1211</t>
1212<t>
1213   If no Accept-Encoding field is present in a request, the server &MAY;
1214   assume that the client will accept any content coding. In this case,
1215   if "identity" is one of the available content-codings, then the
1216   server &SHOULD; use the "identity" content-coding, unless it has
1217   additional information that a different content-coding is meaningful
1218   to the client.
1219</t>
1220<x:note>
1221  <t>
1222    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1223    and if the "identity" content-coding is unavailable, then
1224    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1225    "gzip" and "compress") are preferred; some older clients
1226    improperly display messages sent with other content-codings.  The
1227    server might also make this decision based on information about
1228    the particular user-agent or client.
1229  </t>
1230</x:note>
1231<x:note>
1232  <t>
1233    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1234    associated with content-codings. This means that qvalues will not
1235    work and are not permitted with x-gzip or x-compress.
1236  </t>
1237</x:note>
1238</section>
1239
1240<section title="Accept-Language" anchor="header.accept-language">
1241  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1242  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1243  <x:anchor-alias value="Accept-Language"/>
1244  <x:anchor-alias value="Accept-Language-v"/>
1245  <x:anchor-alias value="language-range"/>
1246<t>
1247   The request-header field "Accept-Language" is similar to Accept, but
1248   restricts the set of natural languages that are preferred as a
1249   response to the request. Language tags are defined in <xref target="language.tags"/>.
1250</t>
1251<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"/>
1252  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1253                    <x:ref>Accept-Language-v</x:ref>
1254  <x:ref>Accept-Language-v</x:ref> =
1255                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1256  <x:ref>language-range</x:ref>    =
1257            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1258</artwork></figure>
1259<t>
1260   Each language-range can be given an associated quality value which
1261   represents an estimate of the user's preference for the languages
1262   specified by that range. The quality value defaults to "q=1". For
1263   example,
1264</t>
1265<figure><artwork type="example">
1266  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1267</artwork></figure>
1268<t>
1269   would mean: "I prefer Danish, but will accept British English and
1270   other types of English."
1271</t>
1272<t>
1273   For matching, the "Basic Filtering" matching scheme, defined in
1274   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1275</t>
1276<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1277  <t>
1278     A language range matches a
1279     particular language tag if, in a case-insensitive comparison, it
1280     exactly equals the tag, or if it exactly equals a prefix of the tag
1281     such that the first character following the prefix is "-".
1282  </t>
1283</x:blockquote> 
1284<t>
1285   The special range "*", if present in the Accept-Language field,
1286   matches every tag not matched by any other range present in the
1287   Accept-Language field.
1288</t>
1289<x:note>
1290  <t>
1291    <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1292    language tags are assigned to languages in such a way that it is
1293    always true that if a user understands a language with a certain
1294    tag, then this user will also understand all languages with tags
1295    for which this tag is a prefix. The prefix rule simply allows the
1296    use of prefix tags if this is the case.
1297  </t>
1298</x:note>
1299<t>
1300   The language quality factor assigned to a language-tag by the
1301   Accept-Language field is the quality value of the longest language-range
1302   in the field that matches the language-tag. If no language-range
1303   in the field matches the tag, the language quality factor
1304   assigned is 0. If no Accept-Language header is present in the
1305   request, the server
1306   &SHOULD; assume that all languages are equally acceptable. If an
1307   Accept-Language header is present, then all languages which are
1308   assigned a quality factor greater than 0 are acceptable.
1309</t>
1310<t>
1311   It might be contrary to the privacy expectations of the user to send
1312   an Accept-Language header with the complete linguistic preferences of
1313   the user in every request. For a discussion of this issue, see
1314   <xref target="privacy.issues.connected.to.accept.headers"/>.
1315</t>
1316<t>
1317   As intelligibility is highly dependent on the individual user, it is
1318   recommended that client applications make the choice of linguistic
1319   preference available to the user. If the choice is not made
1320   available, then the Accept-Language header field &MUST-NOT; be given in
1321   the request.
1322</t>
1323<x:note>
1324  <t>
1325    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1326    the user, we remind implementors of  the fact that users are not
1327    familiar with the details of language matching as described above,
1328    and should provide appropriate guidance. As an example, users
1329    might assume that on selecting "en-gb", they will be served any
1330    kind of English document if British English is not available. A
1331    user agent might suggest in such a case to add "en" to get the
1332    best matching behavior.
1333  </t>
1334</x:note>
1335</section>
1336
1337<section title="Content-Encoding" anchor="header.content-encoding">
1338  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1339  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1340  <x:anchor-alias value="Content-Encoding"/>
1341  <x:anchor-alias value="Content-Encoding-v"/>
1342<t>
1343   The entity-header field "Content-Encoding" is used as a modifier to the
1344   media-type. When present, its value indicates what additional content
1345   codings have been applied to the entity-body, and thus what decoding
1346   mechanisms must be applied in order to obtain the media-type
1347   referenced by the Content-Type header field. Content-Encoding is
1348   primarily used to allow a document to be compressed without losing
1349   the identity of its underlying media type.
1350</t>
1351<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1352  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1353  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1354</artwork></figure>
1355<t>
1356   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1357</t>
1358<figure><artwork type="example">
1359  Content-Encoding: gzip
1360</artwork></figure>
1361<t>
1362   The content-coding is a characteristic of the entity identified by
1363   the request-target. Typically, the entity-body is stored with this
1364   encoding and is only decoded before rendering or analogous usage.
1365   However, a non-transparent proxy &MAY; modify the content-coding if the
1366   new coding is known to be acceptable to the recipient, unless the
1367   "no-transform" cache-control directive is present in the message.
1368</t>
1369<t>
1370   If the content-coding of an entity is not "identity", then the
1371   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1372   that lists the non-identity content-coding(s) used.
1373</t>
1374<t>
1375   If the content-coding of an entity in a request message is not
1376   acceptable to the origin server, the server &SHOULD; respond with a
1377   status code of 415 (Unsupported Media Type).
1378</t>
1379<t>
1380   If multiple encodings have been applied to an entity, the content
1381   codings &MUST; be listed in the order in which they were applied.
1382   Additional information about the encoding parameters &MAY; be provided
1383   by other entity-header fields not defined by this specification.
1384</t>
1385</section>
1386
1387<section title="Content-Language" anchor="header.content-language">
1388  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1389  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1390  <x:anchor-alias value="Content-Language"/>
1391  <x:anchor-alias value="Content-Language-v"/>
1392<t>
1393   The entity-header field "Content-Language" describes the natural
1394   language(s) of the intended audience for the enclosed entity. Note
1395   that this might not be equivalent to all the languages used within
1396   the entity-body.
1397</t>
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1399  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1400  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1401</artwork></figure>
1402<t>
1403   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1404   Content-Language is to allow a user to identify and differentiate
1405   entities according to the user's own preferred language. Thus, if the
1406   body content is intended only for a Danish-literate audience, the
1407   appropriate field is
1408</t>
1409<figure><artwork type="example">
1410  Content-Language: da
1411</artwork></figure>
1412<t>
1413   If no Content-Language is specified, the default is that the content
1414   is intended for all language audiences. This might mean that the
1415   sender does not consider it to be specific to any natural language,
1416   or that the sender does not know for which language it is intended.
1417</t>
1418<t>
1419   Multiple languages &MAY; be listed for content that is intended for
1420   multiple audiences. For example, a rendition of the "Treaty of
1421   Waitangi," presented simultaneously in the original Maori and English
1422   versions, would call for
1423</t>
1424<figure><artwork type="example">
1425  Content-Language: mi, en
1426</artwork></figure>
1427<t>
1428   However, just because multiple languages are present within an entity
1429   does not mean that it is intended for multiple linguistic audiences.
1430   An example would be a beginner's language primer, such as "A First
1431   Lesson in Latin," which is clearly intended to be used by an
1432   English-literate audience. In this case, the Content-Language would
1433   properly only include "en".
1434</t>
1435<t>
1436   Content-Language &MAY; be applied to any media type -- it is not
1437   limited to textual documents.
1438</t>
1439</section>
1440
1441<section title="Content-Location" anchor="header.content-location">
1442  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1443  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1444  <x:anchor-alias value="Content-Location"/>
1445  <x:anchor-alias value="Content-Location-v"/>
1446<t>
1447   The entity-header field "Content-Location" &MAY; be used to supply the
1448   resource location for the entity enclosed in the message when that
1449   entity is accessible from a location separate from the requested
1450   resource's URI. A server &SHOULD; provide a Content-Location for the
1451   variant corresponding to the response entity; especially in the case
1452   where a resource has multiple entities associated with it, and those
1453   entities actually have separate locations by which they might be
1454   individually accessed, the server &SHOULD; provide a Content-Location
1455   for the particular variant which is returned.
1456</t>
1457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1458  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1459                    <x:ref>Content-Location-v</x:ref>
1460  <x:ref>Content-Location-v</x:ref> =
1461                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1462</artwork></figure>
1463<t>
1464   The value of Content-Location also defines the base URI for the
1465   entity.
1466</t>
1467<t>
1468   The Content-Location value is not a replacement for the original
1469   requested URI; it is only a statement of the location of the resource
1470   corresponding to this particular entity at the time of the request.
1471   Future requests &MAY; specify the Content-Location URI as the request-target
1472   if the desire is to identify the source of that particular
1473   entity.
1474</t>
1475<t>
1476   A cache cannot assume that an entity with a Content-Location
1477   different from the URI used to retrieve it can be used to respond to
1478   later requests on that Content-Location URI. However, the Content-Location
1479   can be used to differentiate between multiple entities
1480   retrieved from a single requested resource, as described in &caching-neg-resp;.
1481</t>
1482<t>
1483   If the Content-Location is a relative URI, the relative URI is
1484   interpreted relative to the request-target.
1485</t>
1486<t>
1487   The meaning of the Content-Location header in requests is
1488   undefined; servers are free to ignore it in those cases.
1489</t>
1490</section>
1491
1492<section title="Content-MD5" anchor="header.content-md5">
1493  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1494  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1495  <x:anchor-alias value="Content-MD5"/>
1496  <x:anchor-alias value="Content-MD5-v"/>
1497<t>
1498   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1499   an MD5 digest of the entity-body for the purpose of providing an
1500   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1501   MIC is good for detecting accidental modification of the entity-body
1502   in transit, but is not proof against malicious attacks.)
1503</t>
1504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1505  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1506  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1507</artwork></figure>
1508<t>
1509   The Content-MD5 header field &MAY; be generated by an origin server or
1510   client to function as an integrity check of the entity-body. Only
1511   origin servers or clients &MAY; generate the Content-MD5 header field;
1512   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1513   value as an end-to-end integrity check. Any recipient of the entity-body,
1514   including gateways and proxies, &MAY; check that the digest value
1515   in this header field matches that of the entity-body as received.
1516</t>
1517<t>
1518   The MD5 digest is computed based on the content of the entity-body,
1519   including any content-coding that has been applied, but not including
1520   any transfer-encoding applied to the message-body. If the message is
1521   received with a transfer-encoding, that encoding &MUST; be removed
1522   prior to checking the Content-MD5 value against the received entity.
1523</t>
1524<t>
1525   This has the result that the digest is computed on the octets of the
1526   entity-body exactly as, and in the order that, they would be sent if
1527   no transfer-encoding were being applied.
1528</t>
1529<t>
1530   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1531   composite media-types (e.g., multipart/* and message/rfc822), but
1532   this does not change how the digest is computed as defined in the
1533   preceding paragraph.
1534</t>
1535<t>
1536   There are several consequences of this. The entity-body for composite
1537   types &MAY; contain many body-parts, each with its own MIME and HTTP
1538   headers (including Content-MD5, Content-Transfer-Encoding, and
1539   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1540   or Content-Encoding header, it is assumed that the content
1541   of the body-part has had the encoding applied, and the body-part is
1542   included in the Content-MD5 digest as is -- i.e., after the
1543   application. The Transfer-Encoding header field is not allowed within
1544   body-parts.
1545</t>
1546<t>
1547   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1548   computing or checking the digest: the line break convention used in
1549   the text actually transmitted &MUST; be left unaltered when computing
1550   the digest.
1551</t>
1552<x:note>
1553  <t>
1554    <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1555    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1556    in which the application of Content-MD5 to HTTP entity-bodies
1557    differs from its application to MIME entity-bodies. One is that
1558    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1559    does use Transfer-Encoding and Content-Encoding. Another is that
1560    HTTP more frequently uses binary content types than MIME, so it is
1561    worth noting that, in such cases, the byte order used to compute
1562    the digest is the transmission byte order defined for the type.
1563    Lastly, HTTP allows transmission of text types with any of several
1564    line break conventions and not just the canonical form using CRLF.
1565  </t>
1566</x:note>
1567</section>
1568
1569<section title="Content-Type" anchor="header.content-type">
1570  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1571  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1572  <x:anchor-alias value="Content-Type"/>
1573  <x:anchor-alias value="Content-Type-v"/>
1574<t>
1575   The entity-header field "Content-Type" indicates the media type of the
1576   entity-body sent to the recipient or, in the case of the HEAD method,
1577   the media type that would have been sent had the request been a GET.
1578</t>
1579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1580  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1581  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1582</artwork></figure>
1583<t>
1584   Media types are defined in <xref target="media.types"/>. An example of the field is
1585</t>
1586<figure><artwork type="example">
1587  Content-Type: text/html; charset=ISO-8859-4
1588</artwork></figure>
1589<t>
1590   Further discussion of methods for identifying the media type of an
1591   entity is provided in <xref target="type"/>.
1592</t>
1593</section>
1594
1595</section>
1596
1597<section title="IANA Considerations" anchor="IANA.considerations">
1598<section title="Message Header Registration" anchor="message.header.registration">
1599<t>
1600   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1601   with the permanent registrations below (see <xref target="RFC3864"/>):
1602</t>
1603<?BEGININC p3-payload.iana-headers ?>
1604<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1605<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1606   <ttcol>Header Field Name</ttcol>
1607   <ttcol>Protocol</ttcol>
1608   <ttcol>Status</ttcol>
1609   <ttcol>Reference</ttcol>
1610
1611   <c>Accept</c>
1612   <c>http</c>
1613   <c>standard</c>
1614   <c>
1615      <xref target="header.accept"/>
1616   </c>
1617   <c>Accept-Charset</c>
1618   <c>http</c>
1619   <c>standard</c>
1620   <c>
1621      <xref target="header.accept-charset"/>
1622   </c>
1623   <c>Accept-Encoding</c>
1624   <c>http</c>
1625   <c>standard</c>
1626   <c>
1627      <xref target="header.accept-encoding"/>
1628   </c>
1629   <c>Accept-Language</c>
1630   <c>http</c>
1631   <c>standard</c>
1632   <c>
1633      <xref target="header.accept-language"/>
1634   </c>
1635   <c>Content-Disposition</c>
1636   <c>http</c>
1637   <c/>
1638   <c>
1639      <xref target="content-disposition"/>
1640   </c>
1641   <c>Content-Encoding</c>
1642   <c>http</c>
1643   <c>standard</c>
1644   <c>
1645      <xref target="header.content-encoding"/>
1646   </c>
1647   <c>Content-Language</c>
1648   <c>http</c>
1649   <c>standard</c>
1650   <c>
1651      <xref target="header.content-language"/>
1652   </c>
1653   <c>Content-Location</c>
1654   <c>http</c>
1655   <c>standard</c>
1656   <c>
1657      <xref target="header.content-location"/>
1658   </c>
1659   <c>Content-MD5</c>
1660   <c>http</c>
1661   <c>standard</c>
1662   <c>
1663      <xref target="header.content-md5"/>
1664   </c>
1665   <c>Content-Type</c>
1666   <c>http</c>
1667   <c>standard</c>
1668   <c>
1669      <xref target="header.content-type"/>
1670   </c>
1671   <c>MIME-Version</c>
1672   <c>http</c>
1673   <c/>
1674   <c>
1675      <xref target="mime-version"/>
1676   </c>
1677</texttable>
1678<!--(END)-->
1679<?ENDINC p3-payload.iana-headers ?>
1680<t>
1681   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1682</t>
1683</section>
1684
1685<section title="Content Coding Registry" anchor="content.coding.registration">
1686<t>
1687   The registration procedure for HTTP Content Codings is now defined
1688   by <xref target="content.coding.registry"/> of this document.
1689</t>
1690<t>
1691   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1692   should be updated with the registration below:
1693</t>
1694<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1695   <ttcol>Name</ttcol>
1696   <ttcol>Description</ttcol>
1697   <ttcol>Reference</ttcol>
1698   <c>compress</c>
1699   <c>UNIX "compress" program method</c>
1700   <c>
1701      &compress-coding;
1702   </c>
1703   <c>deflate</c>
1704   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
1705   <c>
1706      &deflate-coding;
1707   </c>
1708   <c>gzip</c>
1709   <c>Same as GNU zip <xref target="RFC1952"/></c>
1710   <c>
1711      &gzip-coding;
1712   </c>
1713   <c>identity</c>
1714   <c>No transformation</c>
1715   <c>
1716      <xref target="content.codings"/>
1717   </c>
1718</texttable>
1719</section>
1720
1721</section>
1722
1723<section title="Security Considerations" anchor="security.considerations">
1724<t>
1725   This section is meant to inform application developers, information
1726   providers, and users of the security limitations in HTTP/1.1 as
1727   described by this document. The discussion does not include
1728   definitive solutions to the problems revealed, though it does make
1729   some suggestions for reducing security risks.
1730</t>
1731
1732<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1733<t>
1734   Accept request-headers can reveal information about the user to all
1735   servers which are accessed. The Accept-Language header in particular
1736   can reveal information the user would consider to be of a private
1737   nature, because the understanding of particular languages is often
1738   strongly correlated to the membership of a particular ethnic group.
1739   User agents which offer the option to configure the contents of an
1740   Accept-Language header to be sent in every request are strongly
1741   encouraged to let the configuration process include a message which
1742   makes the user aware of the loss of privacy involved.
1743</t>
1744<t>
1745   An approach that limits the loss of privacy would be for a user agent
1746   to omit the sending of Accept-Language headers by default, and to ask
1747   the user whether or not to start sending Accept-Language headers to a
1748   server if it detects, by looking for any Vary response-header fields
1749   generated by the server, that such sending could improve the quality
1750   of service.
1751</t>
1752<t>
1753   Elaborate user-customized accept header fields sent in every request,
1754   in particular if these include quality values, can be used by servers
1755   as relatively reliable and long-lived user identifiers. Such user
1756   identifiers would allow content providers to do click-trail tracking,
1757   and would allow collaborating content providers to match cross-server
1758   click-trails or form submissions of individual users. Note that for
1759   many users not behind a proxy, the network address of the host
1760   running the user agent will also serve as a long-lived user
1761   identifier. In environments where proxies are used to enhance
1762   privacy, user agents ought to be conservative in offering accept
1763   header configuration options to end users. As an extreme privacy
1764   measure, proxies could filter the accept headers in relayed requests.
1765   General purpose user agents which provide a high degree of header
1766   configurability &SHOULD; warn users about the loss of privacy which can
1767   be involved.
1768</t>
1769</section>
1770
1771<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1772<t>
1773   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1774   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1775   serious security considerations. Content-Disposition is not part of
1776   the HTTP standard, but since it is widely implemented, we are
1777   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1778   for details.
1779</t>
1780</section>
1781
1782</section>
1783
1784<section title="Acknowledgments" anchor="ack">
1785</section>
1786</middle>
1787<back>
1788
1789<references title="Normative References">
1790
1791<reference anchor="ISO-8859-1">
1792  <front>
1793    <title>
1794     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1795    </title>
1796    <author>
1797      <organization>International Organization for Standardization</organization>
1798    </author>
1799    <date year="1998"/>
1800  </front>
1801  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1802</reference>
1803
1804<reference anchor="Part1">
1805  <front>
1806    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1807    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1808      <organization abbrev="Day Software">Day Software</organization>
1809      <address><email>fielding@gbiv.com</email></address>
1810    </author>
1811    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1812      <organization>One Laptop per Child</organization>
1813      <address><email>jg@laptop.org</email></address>
1814    </author>
1815    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1816      <organization abbrev="HP">Hewlett-Packard Company</organization>
1817      <address><email>JeffMogul@acm.org</email></address>
1818    </author>
1819    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1820      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1821      <address><email>henrikn@microsoft.com</email></address>
1822    </author>
1823    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1824      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1825      <address><email>LMM@acm.org</email></address>
1826    </author>
1827    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1828      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1829      <address><email>paulle@microsoft.com</email></address>
1830    </author>
1831    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1832      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1833      <address><email>timbl@w3.org</email></address>
1834    </author>
1835    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1836      <organization abbrev="W3C">World Wide Web Consortium</organization>
1837      <address><email>ylafon@w3.org</email></address>
1838    </author>
1839    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1840      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1841      <address><email>julian.reschke@greenbytes.de</email></address>
1842    </author>
1843    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1844  </front>
1845  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1846  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1847</reference>
1848
1849<reference anchor="Part2">
1850  <front>
1851    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1852    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1853      <organization abbrev="Day Software">Day Software</organization>
1854      <address><email>fielding@gbiv.com</email></address>
1855    </author>
1856    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1857      <organization>One Laptop per Child</organization>
1858      <address><email>jg@laptop.org</email></address>
1859    </author>
1860    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1861      <organization abbrev="HP">Hewlett-Packard Company</organization>
1862      <address><email>JeffMogul@acm.org</email></address>
1863    </author>
1864    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1865      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1866      <address><email>henrikn@microsoft.com</email></address>
1867    </author>
1868    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1869      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1870      <address><email>LMM@acm.org</email></address>
1871    </author>
1872    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1873      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1874      <address><email>paulle@microsoft.com</email></address>
1875    </author>
1876    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1877      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1878      <address><email>timbl@w3.org</email></address>
1879    </author>
1880    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1881      <organization abbrev="W3C">World Wide Web Consortium</organization>
1882      <address><email>ylafon@w3.org</email></address>
1883    </author>
1884    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1885      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1886      <address><email>julian.reschke@greenbytes.de</email></address>
1887    </author>
1888    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1889  </front>
1890  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1891  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1892</reference>
1893
1894<reference anchor="Part4">
1895  <front>
1896    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1897    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1898      <organization abbrev="Day Software">Day Software</organization>
1899      <address><email>fielding@gbiv.com</email></address>
1900    </author>
1901    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1902      <organization>One Laptop per Child</organization>
1903      <address><email>jg@laptop.org</email></address>
1904    </author>
1905    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1906      <organization abbrev="HP">Hewlett-Packard Company</organization>
1907      <address><email>JeffMogul@acm.org</email></address>
1908    </author>
1909    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1910      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1911      <address><email>henrikn@microsoft.com</email></address>
1912    </author>
1913    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1914      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1915      <address><email>LMM@acm.org</email></address>
1916    </author>
1917    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1918      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1919      <address><email>paulle@microsoft.com</email></address>
1920    </author>
1921    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1922      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1923      <address><email>timbl@w3.org</email></address>
1924    </author>
1925    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1926      <organization abbrev="W3C">World Wide Web Consortium</organization>
1927      <address><email>ylafon@w3.org</email></address>
1928    </author>
1929    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1930      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1931      <address><email>julian.reschke@greenbytes.de</email></address>
1932    </author>
1933    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1934  </front>
1935  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1936  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1937</reference>
1938
1939<reference anchor="Part5">
1940  <front>
1941    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1942    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1943      <organization abbrev="Day Software">Day Software</organization>
1944      <address><email>fielding@gbiv.com</email></address>
1945    </author>
1946    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1947      <organization>One Laptop per Child</organization>
1948      <address><email>jg@laptop.org</email></address>
1949    </author>
1950    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1951      <organization abbrev="HP">Hewlett-Packard Company</organization>
1952      <address><email>JeffMogul@acm.org</email></address>
1953    </author>
1954    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1955      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1956      <address><email>henrikn@microsoft.com</email></address>
1957    </author>
1958    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1959      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1960      <address><email>LMM@acm.org</email></address>
1961    </author>
1962    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1963      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1964      <address><email>paulle@microsoft.com</email></address>
1965    </author>
1966    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1967      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1968      <address><email>timbl@w3.org</email></address>
1969    </author>
1970    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1971      <organization abbrev="W3C">World Wide Web Consortium</organization>
1972      <address><email>ylafon@w3.org</email></address>
1973    </author>
1974    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1975      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1976      <address><email>julian.reschke@greenbytes.de</email></address>
1977    </author>
1978    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1979  </front>
1980  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1981  <x:source href="p5-range.xml" basename="p5-range"/>
1982</reference>
1983
1984<reference anchor="Part6">
1985  <front>
1986    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1987    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1988      <organization abbrev="Day Software">Day Software</organization>
1989      <address><email>fielding@gbiv.com</email></address>
1990    </author>
1991    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1992      <organization>One Laptop per Child</organization>
1993      <address><email>jg@laptop.org</email></address>
1994    </author>
1995    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1996      <organization abbrev="HP">Hewlett-Packard Company</organization>
1997      <address><email>JeffMogul@acm.org</email></address>
1998    </author>
1999    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2000      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2001      <address><email>henrikn@microsoft.com</email></address>
2002    </author>
2003    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2004      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2005      <address><email>LMM@acm.org</email></address>
2006    </author>
2007    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2008      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2009      <address><email>paulle@microsoft.com</email></address>
2010    </author>
2011    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2012      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2013      <address><email>timbl@w3.org</email></address>
2014    </author>
2015    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2016      <organization abbrev="W3C">World Wide Web Consortium</organization>
2017      <address><email>ylafon@w3.org</email></address>
2018    </author>
2019    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2020      <organization />
2021      <address><email>mnot@mnot.net</email></address>
2022    </author>
2023    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2024      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2025      <address><email>julian.reschke@greenbytes.de</email></address>
2026    </author>
2027    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2028  </front>
2029  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2030  <x:source href="p6-cache.xml" basename="p6-cache"/>
2031</reference>
2032
2033<reference anchor="RFC1864">
2034  <front>
2035    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2036    <author initials="J." surname="Myers" fullname="John G. Myers">
2037      <organization>Carnegie Mellon University</organization>
2038      <address><email>jgm+@cmu.edu</email></address>
2039    </author>
2040    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2041      <organization>Dover Beach Consulting, Inc.</organization>
2042      <address><email>mrose@dbc.mtview.ca.us</email></address>
2043    </author>
2044    <date month="October" year="1995"/>
2045  </front>
2046  <seriesInfo name="RFC" value="1864"/>
2047</reference>
2048
2049<reference anchor="RFC1950">
2050  <front>
2051    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2052    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2053      <organization>Aladdin Enterprises</organization>
2054      <address><email>ghost@aladdin.com</email></address>
2055    </author>
2056    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2057      <organization/>
2058    </author>
2059    <date month="May" year="1996"/>
2060  </front>
2061  <seriesInfo name="RFC" value="1950"/>
2062  <annotation>
2063    RFC 1950 is an Informational RFC, thus it may be less stable than
2064    this specification. On the other hand, this downward reference was
2065    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2066    therefore it is unlikely to cause problems in practice. See also
2067    <xref target="BCP97"/>.
2068  </annotation>
2069</reference>
2070
2071<reference anchor="RFC1952">
2072  <front>
2073    <title>GZIP file format specification version 4.3</title>
2074    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2075      <organization>Aladdin Enterprises</organization>
2076      <address><email>ghost@aladdin.com</email></address>
2077    </author>
2078    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2079      <organization/>
2080      <address><email>gzip@prep.ai.mit.edu</email></address>
2081    </author>
2082    <author initials="M." surname="Adler" fullname="Mark Adler">
2083      <organization/>
2084      <address><email>madler@alumni.caltech.edu</email></address>
2085    </author>
2086    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2087      <organization/>
2088      <address><email>ghost@aladdin.com</email></address>
2089    </author>
2090    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2091      <organization/>
2092      <address><email>randeg@alumni.rpi.edu</email></address>
2093    </author>
2094    <date month="May" year="1996"/>
2095  </front>
2096  <seriesInfo name="RFC" value="1952"/>
2097  <annotation>
2098    RFC 1952 is an Informational RFC, thus it may be less stable than
2099    this specification. On the other hand, this downward reference was
2100    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2101    therefore it is unlikely to cause problems in practice. See also
2102    <xref target="BCP97"/>.
2103  </annotation>
2104</reference>
2105
2106<reference anchor="RFC2045">
2107  <front>
2108    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2109    <author initials="N." surname="Freed" fullname="Ned Freed">
2110      <organization>Innosoft International, Inc.</organization>
2111      <address><email>ned@innosoft.com</email></address>
2112    </author>
2113    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2114      <organization>First Virtual Holdings</organization>
2115      <address><email>nsb@nsb.fv.com</email></address>
2116    </author>
2117    <date month="November" year="1996"/>
2118  </front>
2119  <seriesInfo name="RFC" value="2045"/>
2120</reference>
2121
2122<reference anchor="RFC2046">
2123  <front>
2124    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2125    <author initials="N." surname="Freed" fullname="Ned Freed">
2126      <organization>Innosoft International, Inc.</organization>
2127      <address><email>ned@innosoft.com</email></address>
2128    </author>
2129    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2130      <organization>First Virtual Holdings</organization>
2131      <address><email>nsb@nsb.fv.com</email></address>
2132    </author>
2133    <date month="November" year="1996"/>
2134  </front>
2135  <seriesInfo name="RFC" value="2046"/>
2136</reference>
2137
2138<reference anchor="RFC2119">
2139  <front>
2140    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2141    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2142      <organization>Harvard University</organization>
2143      <address><email>sob@harvard.edu</email></address>
2144    </author>
2145    <date month="March" year="1997"/>
2146  </front>
2147  <seriesInfo name="BCP" value="14"/>
2148  <seriesInfo name="RFC" value="2119"/>
2149</reference>
2150
2151<reference anchor='RFC4647'>
2152  <front>
2153    <title>Matching of Language Tags</title>
2154    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2155      <organization>Yahoo! Inc.</organization>
2156      <address><email>addison@inter-locale.com</email></address>
2157    </author>
2158    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2159      <organization>Google</organization>
2160      <address><email>mark.davis@macchiato.com</email></address>
2161    </author>
2162    <date year='2006' month='September' />
2163  </front>
2164  <seriesInfo name='BCP' value='47' />
2165  <seriesInfo name='RFC' value='4647' />
2166</reference>
2167
2168<reference anchor="RFC5234">
2169  <front>
2170    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2171    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2172      <organization>Brandenburg InternetWorking</organization>
2173      <address>
2174      <postal>
2175      <street>675 Spruce Dr.</street>
2176      <city>Sunnyvale</city>
2177      <region>CA</region>
2178      <code>94086</code>
2179      <country>US</country></postal>
2180      <phone>+1.408.246.8253</phone>
2181      <email>dcrocker@bbiw.net</email></address> 
2182    </author>
2183    <author initials="P." surname="Overell" fullname="Paul Overell">
2184      <organization>THUS plc.</organization>
2185      <address>
2186      <postal>
2187      <street>1/2 Berkeley Square</street>
2188      <street>99 Berkely Street</street>
2189      <city>Glasgow</city>
2190      <code>G3 7HR</code>
2191      <country>UK</country></postal>
2192      <email>paul.overell@thus.net</email></address>
2193    </author>
2194    <date month="January" year="2008"/>
2195  </front>
2196  <seriesInfo name="STD" value="68"/>
2197  <seriesInfo name="RFC" value="5234"/>
2198</reference>
2199
2200<reference anchor='RFC4646bis'>
2201  <front>
2202    <title>Tags for Identifying Languages</title>
2203    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2204      <organization>Lab126</organization>
2205      <address><email>addison@inter-locale.com</email></address>
2206    </author>
2207    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2208      <organization>Google</organization>
2209      <address><email>mark.davis@google.com</email></address>
2210    </author>
2211    <date month='June' day='11' year='2009' />
2212  </front>
2213  <seriesInfo name='Internet-Draft' value='draft-ietf-ltru-4646bis-23' />
2214</reference>
2215
2216</references>
2217
2218<references title="Informative References">
2219
2220<reference anchor="RFC1945">
2221  <front>
2222    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2223    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2224      <organization>MIT, Laboratory for Computer Science</organization>
2225      <address><email>timbl@w3.org</email></address>
2226    </author>
2227    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2228      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2229      <address><email>fielding@ics.uci.edu</email></address>
2230    </author>
2231    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2232      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2233      <address><email>frystyk@w3.org</email></address>
2234    </author>
2235    <date month="May" year="1996"/>
2236  </front>
2237  <seriesInfo name="RFC" value="1945"/>
2238</reference>
2239
2240<reference anchor="RFC2049">
2241  <front>
2242    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2243    <author initials="N." surname="Freed" fullname="Ned Freed">
2244      <organization>Innosoft International, Inc.</organization>
2245      <address><email>ned@innosoft.com</email></address>
2246    </author>
2247    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2248      <organization>First Virtual Holdings</organization>
2249      <address><email>nsb@nsb.fv.com</email></address>
2250    </author>
2251    <date month="November" year="1996"/>
2252  </front>
2253  <seriesInfo name="RFC" value="2049"/>
2254</reference>
2255
2256<reference anchor="RFC2068">
2257  <front>
2258    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2259    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2260      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2261      <address><email>fielding@ics.uci.edu</email></address>
2262    </author>
2263    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2264      <organization>MIT Laboratory for Computer Science</organization>
2265      <address><email>jg@w3.org</email></address>
2266    </author>
2267    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2268      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2269      <address><email>mogul@wrl.dec.com</email></address>
2270    </author>
2271    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2272      <organization>MIT Laboratory for Computer Science</organization>
2273      <address><email>frystyk@w3.org</email></address>
2274    </author>
2275    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2276      <organization>MIT Laboratory for Computer Science</organization>
2277      <address><email>timbl@w3.org</email></address>
2278    </author>
2279    <date month="January" year="1997"/>
2280  </front>
2281  <seriesInfo name="RFC" value="2068"/>
2282</reference>
2283
2284<reference anchor="RFC2076">
2285  <front>
2286    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2287    <author initials="J." surname="Palme" fullname="Jacob Palme">
2288      <organization>Stockholm University/KTH</organization>
2289      <address><email>jpalme@dsv.su.se</email></address>
2290    </author>
2291    <date month="February" year="1997"/>
2292  </front>
2293  <seriesInfo name="RFC" value="2076"/>
2294</reference>
2295
2296<reference anchor="RFC2183">
2297  <front>
2298    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2299    <author initials="R." surname="Troost" fullname="Rens Troost">
2300      <organization>New Century Systems</organization>
2301      <address><email>rens@century.com</email></address>
2302    </author>
2303    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2304      <organization>QUALCOMM Incorporated</organization>
2305      <address><email>sdorner@qualcomm.com</email></address>
2306    </author>
2307    <author initials="K." surname="Moore" fullname="Keith Moore">
2308      <organization>Department of Computer Science</organization>
2309      <address><email>moore@cs.utk.edu</email></address>
2310    </author>
2311    <date month="August" year="1997"/>
2312  </front>
2313  <seriesInfo name="RFC" value="2183"/>
2314</reference>
2315
2316<reference anchor="RFC2277">
2317  <front>
2318    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2319    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2320      <organization>UNINETT</organization>
2321      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2322    </author>
2323    <date month="January" year="1998"/>
2324  </front>
2325  <seriesInfo name="BCP" value="18"/>
2326  <seriesInfo name="RFC" value="2277"/>
2327</reference>
2328
2329<reference anchor="RFC2388">
2330  <front>
2331    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2332    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2333      <organization>Xerox Palo Alto Research Center</organization>
2334      <address><email>masinter@parc.xerox.com</email></address>
2335    </author>
2336    <date year="1998" month="August"/>
2337  </front>
2338  <seriesInfo name="RFC" value="2388"/>
2339</reference>
2340
2341<reference anchor="RFC2557">
2342  <front>
2343    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2344    <author initials="F." surname="Palme" fullname="Jacob Palme">
2345      <organization>Stockholm University and KTH</organization>
2346      <address><email>jpalme@dsv.su.se</email></address>
2347    </author>
2348    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2349      <organization>Microsoft Corporation</organization>
2350      <address><email>alexhop@microsoft.com</email></address>
2351    </author>
2352    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2353      <organization>Lotus Development Corporation</organization>
2354      <address><email>Shelness@lotus.com</email></address>
2355    </author>
2356    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2357      <organization/>
2358      <address><email>stef@nma.com</email></address>
2359    </author>
2360    <date year="1999" month="March"/>
2361  </front>
2362  <seriesInfo name="RFC" value="2557"/>
2363</reference>
2364
2365<reference anchor="RFC2616">
2366  <front>
2367    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2368    <author initials="R." surname="Fielding" fullname="R. Fielding">
2369      <organization>University of California, Irvine</organization>
2370      <address><email>fielding@ics.uci.edu</email></address>
2371    </author>
2372    <author initials="J." surname="Gettys" fullname="J. Gettys">
2373      <organization>W3C</organization>
2374      <address><email>jg@w3.org</email></address>
2375    </author>
2376    <author initials="J." surname="Mogul" fullname="J. Mogul">
2377      <organization>Compaq Computer Corporation</organization>
2378      <address><email>mogul@wrl.dec.com</email></address>
2379    </author>
2380    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2381      <organization>MIT Laboratory for Computer Science</organization>
2382      <address><email>frystyk@w3.org</email></address>
2383    </author>
2384    <author initials="L." surname="Masinter" fullname="L. Masinter">
2385      <organization>Xerox Corporation</organization>
2386      <address><email>masinter@parc.xerox.com</email></address>
2387    </author>
2388    <author initials="P." surname="Leach" fullname="P. Leach">
2389      <organization>Microsoft Corporation</organization>
2390      <address><email>paulle@microsoft.com</email></address>
2391    </author>
2392    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2393      <organization>W3C</organization>
2394      <address><email>timbl@w3.org</email></address>
2395    </author>
2396    <date month="June" year="1999"/>
2397  </front>
2398  <seriesInfo name="RFC" value="2616"/>
2399</reference>
2400
2401<reference anchor="RFC3629">
2402  <front>
2403    <title>UTF-8, a transformation format of ISO 10646</title>
2404    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2405      <organization>Alis Technologies</organization>
2406      <address><email>fyergeau@alis.com</email></address>
2407    </author>
2408    <date month="November" year="2003"/>
2409  </front>
2410  <seriesInfo name="RFC" value="3629"/>
2411  <seriesInfo name="STD" value="63"/>
2412</reference>
2413
2414<reference anchor='RFC3864'>
2415  <front>
2416    <title>Registration Procedures for Message Header Fields</title>
2417    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2418      <organization>Nine by Nine</organization>
2419      <address><email>GK-IETF@ninebynine.org</email></address>
2420    </author>
2421    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2422      <organization>BEA Systems</organization>
2423      <address><email>mnot@pobox.com</email></address>
2424    </author>
2425    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2426      <organization>HP Labs</organization>
2427      <address><email>JeffMogul@acm.org</email></address>
2428    </author>
2429    <date year='2004' month='September' />
2430  </front>
2431  <seriesInfo name='BCP' value='90' />
2432  <seriesInfo name='RFC' value='3864' />
2433</reference>
2434
2435<reference anchor="RFC4288">
2436  <front>
2437    <title>Media Type Specifications and Registration Procedures</title>
2438    <author initials="N." surname="Freed" fullname="N. Freed">
2439      <organization>Sun Microsystems</organization>
2440      <address>
2441        <email>ned.freed@mrochek.com</email>
2442      </address>
2443    </author>
2444    <author initials="J." surname="Klensin" fullname="J. Klensin">
2445      <organization/>
2446      <address>
2447        <email>klensin+ietf@jck.com</email>
2448      </address>
2449    </author>
2450    <date year="2005" month="December"/>
2451  </front>
2452  <seriesInfo name="BCP" value="13"/>
2453  <seriesInfo name="RFC" value="4288"/>
2454</reference>
2455
2456<reference anchor='RFC5226'>
2457  <front>
2458    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2459    <author initials='T.' surname='Narten' fullname='T. Narten'>
2460      <organization>IBM</organization>
2461      <address><email>narten@us.ibm.com</email></address>
2462    </author>
2463    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2464      <organization>Google</organization>
2465      <address><email>Harald@Alvestrand.no</email></address>
2466    </author>
2467    <date year='2008' month='May' />
2468  </front>
2469  <seriesInfo name='BCP' value='26' />
2470  <seriesInfo name='RFC' value='5226' />
2471</reference>
2472
2473<reference anchor="RFC5322">
2474  <front>
2475    <title>Internet Message Format</title>
2476    <author initials="P." surname="Resnick" fullname="P. Resnick">
2477      <organization>Qualcomm Incorporated</organization>
2478    </author>
2479    <date year="2008" month="October"/>
2480  </front> 
2481  <seriesInfo name="RFC" value="5322"/>
2482</reference>
2483
2484<reference anchor='BCP97'>
2485  <front>
2486    <title>Handling Normative References to Standards-Track Documents</title>
2487    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2488      <organization />
2489      <address>
2490        <email>klensin+ietf@jck.com</email>
2491      </address>
2492    </author>
2493    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2494      <organization>MIT</organization>
2495      <address>
2496        <email>hartmans-ietf@mit.edu</email>
2497      </address>
2498    </author>
2499    <date year='2007' month='June' />
2500  </front>
2501  <seriesInfo name='BCP' value='97' />
2502  <seriesInfo name='RFC' value='4897' />
2503</reference>
2504
2505
2506</references>
2507
2508<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2509<t>
2510   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
2511   allow entities to be transmitted in an open variety of
2512   representations and with extensible mechanisms. However, RFC 2045
2513   discusses mail, and HTTP has a few features that are different from
2514   those described in RFC 2045. These differences were carefully chosen
2515   to optimize performance over binary connections, to allow greater
2516   freedom in the use of new media types, to make date comparisons
2517   easier, and to acknowledge the practice of some early HTTP servers
2518   and clients.
2519</t>
2520<t>
2521   This appendix describes specific areas where HTTP differs from RFC
2522   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2523   aware of these differences and provide the appropriate conversions
2524   where necessary. Proxies and gateways from MIME environments to HTTP
2525   also need to be aware of the differences because some conversions
2526   might be required.
2527</t>
2528
2529<section title="MIME-Version" anchor="mime-version">
2530  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2531  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2532  <x:anchor-alias value="MIME-Version"/>
2533  <x:anchor-alias value="MIME-Version-v"/>
2534<t>
2535   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2536   include a single MIME-Version general-header field to indicate what
2537   version of the MIME protocol was used to construct the message. Use
2538   of the MIME-Version header field indicates that the message is in
2539   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2540   Proxies/gateways are responsible for ensuring full compliance (where
2541   possible) when exporting HTTP messages to strict MIME environments.
2542</t>
2543<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2544  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2545  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2546</artwork></figure>
2547<t>
2548   MIME version "1.0" is the default for use in HTTP/1.1. However,
2549   HTTP/1.1 message parsing and semantics are defined by this document
2550   and not the MIME specification.
2551</t>
2552</section>
2553
2554<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2555<t>
2556   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2557   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2558   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2559   allowed for subtypes of the "text" media type when transmitted over
2560   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2561   line breaks as CRLF and forbids the use of CR or LF outside of line
2562   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2563   line break within text content when a message is transmitted over
2564   HTTP.
2565</t>
2566<t>
2567   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2568   environment &SHOULD; translate all line breaks within the text media
2569   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2570   canonical form of CRLF. Note, however, that this might be complicated
2571   by the presence of a Content-Encoding and by the fact that HTTP
2572   allows the use of some character sets which do not use octets 13 and
2573   10 to represent CR and LF, as is the case for some multi-byte
2574   character sets.
2575</t>
2576<t>
2577   Implementors should note that conversion will break any cryptographic
2578   checksums applied to the original content unless the original content
2579   is already in canonical form. Therefore, the canonical form is
2580   recommended for any content that uses such checksums in HTTP.
2581</t>
2582</section>
2583
2584
2585<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2586<t>
2587   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2588   simplify the process of date comparison. Proxies and gateways from
2589   other protocols &SHOULD; ensure that any Date header field present in a
2590   message conforms to one of the HTTP/1.1 formats and rewrite the date
2591   if necessary.
2592</t>
2593</section>
2594
2595<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2596<t>
2597   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2598   Content-Encoding header field. Since this acts as a modifier on the
2599   media type, proxies and gateways from HTTP to MIME-compliant
2600   protocols &MUST; either change the value of the Content-Type header
2601   field or decode the entity-body before forwarding the message. (Some
2602   experimental applications of Content-Type for Internet mail have used
2603   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2604   a function equivalent to Content-Encoding. However, this parameter is
2605   not part of RFC 2045).
2606</t>
2607</section>
2608
2609<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2610<t>
2611   HTTP does not use the Content-Transfer-Encoding field of RFC
2612   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2613   remove any Content-Transfer-Encoding
2614   prior to delivering the response message to an HTTP client.
2615</t>
2616<t>
2617   Proxies and gateways from HTTP to MIME-compliant protocols are
2618   responsible for ensuring that the message is in the correct format
2619   and encoding for safe transport on that protocol, where "safe
2620   transport" is defined by the limitations of the protocol being used.
2621   Such a proxy or gateway &SHOULD; label the data with an appropriate
2622   Content-Transfer-Encoding if doing so will improve the likelihood of
2623   safe transport over the destination protocol.
2624</t>
2625</section>
2626
2627<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2628<t>
2629   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2630   Proxies/gateways &MUST; remove any transfer-coding prior to
2631   forwarding a message via a MIME-compliant protocol.
2632</t>
2633</section>
2634
2635<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2636<t>
2637   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2638   need to be aware of MIME line length limitations. Since HTTP does not
2639   have this limitation, HTTP does not fold long lines. MHTML messages
2640   being transported by HTTP follow all conventions of MHTML, including
2641   line length limitations and folding, canonicalization, etc., since
2642   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2643   does not interpret the content or any MIME header lines that might be
2644   contained therein.
2645</t>
2646</section>
2647</section>
2648
2649<section title="Additional Features" anchor="additional.features">
2650<t>
2651   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2652   existing HTTP implementations, but not consistently and correctly
2653   across most HTTP/1.1 applications. Implementors are advised to be
2654   aware of these features, but cannot rely upon their presence in, or
2655   interoperability with, other HTTP/1.1 applications. Some of these
2656   describe proposed experimental features, and some describe features
2657   that experimental deployment found lacking that are now addressed in
2658   the base HTTP/1.1 specification.
2659</t>
2660<t>
2661   A number of other headers, such as Content-Disposition and Title,
2662   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2663</t>
2664
2665<section title="Content-Disposition" anchor="content-disposition">
2666<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2667<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2668  <x:anchor-alias value="content-disposition"/>
2669  <x:anchor-alias value="content-disposition-v"/>
2670  <x:anchor-alias value="disposition-type"/>
2671  <x:anchor-alias value="disposition-parm"/>
2672  <x:anchor-alias value="disp-extension-parm"/>
2673  <x:anchor-alias value="disp-extension-token"/>
2674  <x:anchor-alias value="filename-parm"/>
2675<t>
2676   The Content-Disposition response-header field has been proposed as a
2677   means for the origin server to suggest a default filename if the user
2678   requests that the content is saved to a file. This usage is derived
2679   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2680</t>
2681<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"/>
2682  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2683                        <x:ref>content-disposition-v</x:ref>
2684  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2685                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2686  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2687  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2688  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2689  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2690  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2691</artwork></figure>
2692<t>
2693   An example is
2694</t>
2695<figure><artwork type="example">
2696  Content-Disposition: attachment; filename="fname.ext"
2697</artwork></figure>
2698<t>
2699   The receiving user agent &SHOULD-NOT;  respect any directory path
2700   information present in the filename-parm parameter, which is the only
2701   parameter believed to apply to HTTP implementations at this time. The
2702   filename &SHOULD; be treated as a terminal component only.
2703</t>
2704<t>
2705   If this header is used in a response with the application/octet-stream
2706   content-type, the implied suggestion is that the user agent
2707   should not display the response, but directly enter a `save response
2708   as...' dialog.
2709</t>
2710<t>
2711   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2712</t>
2713</section>
2714</section>
2715
2716<section title="Compatibility with Previous Versions" anchor="compatibility">
2717<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2718<t>
2719   Transfer-coding and message lengths all interact in ways that
2720   required fixing exactly when chunked encoding is used (to allow for
2721   transfer encoding that may not be self delimiting); it was important
2722   to straighten out exactly how message lengths are computed.
2723   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2724   <xref target="Part5"/> and <xref target="Part6"/>).
2725</t>
2726<t>
2727   Charset wildcarding is introduced to avoid explosion of character set
2728   names in accept headers. (<xref target="header.accept-charset"/>)
2729</t>
2730<t>
2731   Content-Base was deleted from the specification: it was not
2732   implemented widely, and there is no simple, safe way to introduce it
2733   without a robust extension mechanism. In addition, it is used in a
2734   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2735</t>
2736<t>
2737   A content-coding of "identity" was introduced, to solve problems
2738   discovered in caching. (<xref target="content.codings"/>)
2739</t>
2740<t>
2741   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
2742   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
2743   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2744</t>
2745</section>
2746
2747<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2748<t>
2749  Clarify contexts that charset is used in.
2750  (<xref target="character.sets"/>)
2751</t>
2752<t>
2753  Remove reference to non-existant identity transfer-coding value tokens.
2754  (<xref target="no.content-transfer-encoding"/>)
2755</t>
2756</section>
2757
2758</section>
2759
2760<?BEGININC p3-payload.abnf-appendix ?>
2761<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2762<figure>
2763<artwork type="abnf" name="p3-payload.parsed-abnf">
2764<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2765<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2766<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2767 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2768 qvalue ] ] )
2769<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2770<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2771 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2772<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2773<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2774 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2775 ] )
2776<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2777 OWS media-range [ accept-params ] ] ) ]
2778
2779<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2780<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2781 content-coding ] )
2782<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2783<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2784 language-tag ] )
2785<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2786<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2787<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2788<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2789<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2790<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2791<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2792<x:ref>Content-Type-v</x:ref> = media-type
2793
2794<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2795
2796<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2797
2798<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2799<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2800
2801<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2802
2803<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2804<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2805<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2806<x:ref>attribute</x:ref> = token
2807
2808<x:ref>charset</x:ref> = token
2809<x:ref>codings</x:ref> = ( content-coding / "*" )
2810<x:ref>content-coding</x:ref> = token
2811<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2812 content-disposition-v
2813<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2814 disposition-parm )
2815
2816<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2817<x:ref>disp-extension-token</x:ref> = token
2818<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2819<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2820
2821<x:ref>entity-body</x:ref> = *OCTET
2822<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2823 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2824 Expires / Last-Modified / extension-header
2825<x:ref>extension-header</x:ref> = header-field
2826
2827<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2828
2829<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2830
2831<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2832<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC4646bis], Section 2.1&gt;
2833
2834<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2835 ";" OWS parameter )
2836<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2837
2838<x:ref>parameter</x:ref> = attribute "=" value
2839<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2840
2841<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2842<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2843
2844<x:ref>subtype</x:ref> = token
2845
2846<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2847<x:ref>type</x:ref> = token
2848
2849<x:ref>value</x:ref> = token / quoted-string
2850</artwork>
2851</figure>
2852<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2853; Accept defined but not used
2854; Accept-Charset defined but not used
2855; Accept-Encoding defined but not used
2856; Accept-Language defined but not used
2857; MIME-Version defined but not used
2858; content-disposition defined but not used
2859; entity-body defined but not used
2860; entity-header defined but not used
2861</artwork></figure></section>
2862<?ENDINC p3-payload.abnf-appendix ?>
2863
2864<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2865
2866<section title="Since RFC2616">
2867<t>
2868  Extracted relevant partitions from <xref target="RFC2616"/>.
2869</t>
2870</section>
2871
2872<section title="Since draft-ietf-httpbis-p3-payload-00">
2873<t>
2874  Closed issues:
2875  <list style="symbols"> 
2876    <t>
2877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2878      "Media Type Registrations"
2879      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2880    </t>
2881    <t>
2882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2883      "Clarification regarding quoting of charset values"
2884      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2885    </t>
2886    <t>
2887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2888      "Remove 'identity' token references"
2889      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2890    </t>
2891    <t>
2892      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2893      "Accept-Encoding BNF"
2894    </t>
2895    <t>
2896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2897      "Normative and Informative references"
2898    </t>
2899    <t>
2900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2901      "RFC1700 references"
2902    </t>
2903    <t>
2904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2905      "Updating to RFC4288"
2906    </t>
2907    <t>
2908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2909      "Informative references"
2910    </t>
2911    <t>
2912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2913      "ISO-8859-1 Reference"
2914    </t>
2915    <t>
2916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2917      "Encoding References Normative"
2918    </t>
2919    <t>
2920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2921      "Normative up-to-date references"
2922    </t>
2923  </list>
2924</t>
2925</section>
2926
2927<section title="Since draft-ietf-httpbis-p3-payload-01">
2928<t>
2929  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2930  <list style="symbols"> 
2931    <t>
2932      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2933    </t>
2934  </list>
2935</t>
2936</section>
2937
2938<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2939<t>
2940  Closed issues:
2941  <list style="symbols"> 
2942    <t>
2943      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2944      "Quoting Charsets"
2945    </t>
2946    <t>
2947      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2948      "Classification for Allow header"
2949    </t>
2950    <t>
2951      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2952      "missing default for qvalue in description of Accept-Encoding"
2953    </t>
2954  </list>
2955</t>
2956<t>
2957  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2958  <list style="symbols"> 
2959    <t>
2960      Reference RFC 3984, and update header registrations for headers defined
2961      in this document.
2962    </t>
2963  </list>
2964</t>
2965</section>
2966
2967<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2968<t>
2969  Closed issues:
2970  <list style="symbols"> 
2971    <t>
2972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2973      "Quoting Charsets"
2974    </t>
2975    <t>
2976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2977      "language tag matching (Accept-Language) vs RFC4647"
2978    </t>
2979    <t>
2980      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2981      "RFC 1806 has been replaced by RFC2183"
2982    </t>
2983  </list>
2984</t>
2985<t>
2986  Other changes:
2987  <list style="symbols"> 
2988    <t>
2989      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2990      "Encoding References Normative" -- rephrase the annotation and reference
2991      <xref target="BCP97"/>.
2992    </t>
2993  </list>
2994</t>
2995 </section>
2996
2997<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2998<t>
2999  Closed issues:
3000  <list style="symbols"> 
3001    <t>
3002      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3003      "RFC 2822 is updated by RFC 5322"
3004    </t>
3005  </list>
3006</t>
3007<t>
3008  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3009  <list style="symbols"> 
3010    <t>
3011      Use "/" instead of "|" for alternatives.
3012    </t>
3013    <t>
3014      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3015      whitespace ("OWS") and required whitespace ("RWS").
3016    </t>
3017    <t>
3018      Rewrite ABNFs to spell out whitespace rules, factor out
3019      header value format definitions.
3020    </t>
3021  </list>
3022</t>
3023</section>
3024
3025<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3026<t>
3027  Closed issues:
3028  <list style="symbols"> 
3029    <t>
3030      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3031      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3032    </t>
3033  </list>
3034</t>
3035<t>
3036  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3037  <list style="symbols"> 
3038    <t>
3039      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3040    </t>
3041  </list>
3042</t>
3043<t>
3044  Other changes:
3045  <list style="symbols"> 
3046    <t>
3047      Move definition of quality values into Part 1.
3048    </t>
3049  </list>
3050</t>
3051</section>
3052
3053<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3054<t>
3055  Closed issues:
3056  <list style="symbols"> 
3057    <t>
3058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3059      "Content-Location isn't special"
3060    </t>
3061    <t>
3062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3063      "Content Sniffing"
3064    </t>
3065  </list>
3066</t>
3067</section>
3068
3069<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3070<t>
3071  Closed issues:
3072  <list style="symbols"> 
3073    <t>
3074      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3075      "Updated reference for language tags"
3076    </t>
3077    <t>
3078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3079      "Content Sniffing"
3080    </t>
3081    <t>
3082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3083      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3084    </t>
3085    <t>
3086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3087      "move definitions of gzip/deflate/compress to part 1"
3088    </t>
3089  </list>
3090</t>
3091<t>
3092  Partly resolved issues:
3093  <list style="symbols"> 
3094    <t>
3095      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3096      "update IANA requirements wrt Transfer-Coding values" (add the
3097      IANA Considerations subsection)
3098    </t>
3099    <t>
3100      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3101      "update IANA requirements wrt Content-Coding values" (add the
3102      IANA Considerations subsection)
3103    </t>
3104  </list>
3105</t>
3106</section>
3107
3108</section>
3109
3110</back>
3111</rfc>
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