source: draft-ietf-httpbis/latest/p3-payload.xml @ 806

Last change on this file since 806 was 806, checked in by julian.reschke@…, 10 years ago

"deflate": make the IANA entry more consistent with the actual description (related to #73)

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File size: 131.7 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "April">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY 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  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="2616" category="std" x:maturity-level="draft"
53     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
54     xmlns:x='http://purl.org/net/xml2rfc/ext'>
55<front>
56
57  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
58
59  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
60    <organization abbrev="Day Software">Day Software</organization>
61    <address>
62      <postal>
63        <street>23 Corporate Plaza DR, Suite 280</street>
64        <city>Newport Beach</city>
65        <region>CA</region>
66        <code>92660</code>
67        <country>USA</country>
68      </postal>
69      <phone>+1-949-706-5300</phone>
70      <facsimile>+1-949-706-5305</facsimile>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization>One Laptop per Child</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@laptop.org</email>
87      <uri>http://www.laptop.org/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 3 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 3 defines HTTP message content,
207   metadata, and content negotiation.
208</t>
209</abstract>
210
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (ietf-http-wg@w3.org). The current issues list is
215    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
216    and related documents (including fancy diffs) can be found at
217    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.09"/>.
221  </t>
222</note>
223</front>
224<middle>
225<section title="Introduction" anchor="introduction">
226<t>
227   This document defines HTTP/1.1 message payloads (a.k.a., content), the
228   associated metadata header fields that define how the payload is intended
229   to be interpreted by a recipient, the request header fields that
230   may influence content selection, and the various selection algorithms
231   that are collectively referred to as HTTP content negotiation.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   The next draft will reorganize the sections to better reflect the content.
237   In particular, the sections on entities will be renamed payload and moved
238   to the first half of the document, while the sections on content negotiation
239   and associated request header fields will be moved to the second half.  The
240   current mess reflects how widely dispersed these topics and associated
241   requirements had become in <xref target="RFC2616"/>.
242</t>
243
244<section title="Terminology" anchor="terminology">
245<t>
246   This specification uses a number of terms to refer to the roles
247   played by participants in, and objects of, the HTTP communication.
248</t>
249<t>
250  <iref item="content negotiation"/>
251  <x:dfn>content negotiation</x:dfn>
252  <list>
253    <t>
254      The mechanism for selecting the appropriate representation when
255      servicing a request. The representation of entities in any response
256      can be negotiated (including error responses).
257    </t>
258  </list>
259</t>
260<t>
261  <iref item="entity"/>
262  <x:dfn>entity</x:dfn>
263  <list>
264    <t>
265      The information transferred as the payload of a request or
266      response. An entity consists of metadata in the form of
267      entity-header fields and content in the form of an entity-body.
268    </t>
269  </list>
270</t>
271<t>
272  <iref item="representation"/>
273  <x:dfn>representation</x:dfn>
274  <list>
275    <t>
276      An entity included with a response that is subject to content
277      negotiation. There may exist multiple
278      representations associated with a particular response status.
279    </t>
280  </list>
281</t>
282<t>
283  <iref item="variant"/>
284  <x:dfn>variant</x:dfn>
285  <list>
286    <t>
287      A resource may have one, or more than one, representation(s)
288      associated with it at any given instant. Each of these
289      representations is termed a "variant".  Use of the term "variant"
290      does not necessarily imply that the resource is subject to content
291      negotiation.
292    </t>
293  </list>
294</t>
295</section>
296
297<section title="Requirements" anchor="intro.requirements">
298<t>
299   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
300   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
301   document are to be interpreted as described in <xref target="RFC2119"/>.
302</t>
303<t>
304   An implementation is not compliant if it fails to satisfy one or more
305   of the &MUST; or &REQUIRED; level requirements for the protocols it
306   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
307   level and all the &SHOULD; level requirements for its protocols is said
308   to be "unconditionally compliant"; one that satisfies all the &MUST;
309   level requirements but not all the &SHOULD; level requirements for its
310   protocols is said to be "conditionally compliant."
311</t>
312</section>
313
314<section title="Syntax Notation" anchor="notation">
315  <x:anchor-alias value="ALPHA"/>
316  <x:anchor-alias value="CR"/>
317  <x:anchor-alias value="DIGIT"/>
318  <x:anchor-alias value="LF"/>
319  <x:anchor-alias value="OCTET"/>
320  <x:anchor-alias value="VCHAR"/>
321  <x:anchor-alias value="WSP"/>
322<t>
323  This specification uses the ABNF syntax defined in &notation; (which
324  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
325  <xref target="collected.abnf"/> shows the collected ABNF, with the list
326  rule expanded.
327</t>
328<t>
329  The following core rules are included by
330  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
331  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
332  DIGIT (decimal 0-9), DQUOTE (double quote),
333  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
334  OCTET (any 8-bit sequence of data), SP (space),
335  VCHAR (any visible USASCII character),
336  and WSP (whitespace).
337</t>
338
339<section title="Core Rules" anchor="core.rules">
340  <x:anchor-alias value="quoted-string"/>
341  <x:anchor-alias value="token"/>
342  <x:anchor-alias value="OWS"/>
343<t>
344  The core rules below are defined in &basic-rules;:
345</t>
346<figure><artwork type="abnf2616">
347  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
348  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
349  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
350</artwork></figure>
351</section>
352
353<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
354  <x:anchor-alias value="absolute-URI"/>
355  <x:anchor-alias value="Allow"/>
356  <x:anchor-alias value="Content-Length"/>
357  <x:anchor-alias value="Content-Range"/>
358  <x:anchor-alias value="Expires"/>
359  <x:anchor-alias value="Last-Modified"/>
360  <x:anchor-alias value="header-field"/>
361  <x:anchor-alias value="partial-URI"/>
362  <x:anchor-alias value="qvalue"/>
363<t>
364  The ABNF rules below are defined in other parts:
365</t>
366<figure><!--Part1--><artwork type="abnf2616">
367  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
368  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
369  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
370  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
371  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
372</artwork></figure>
373<figure><!--Part4--><artwork type="abnf2616">
374  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
375</artwork></figure>
376<figure><!--Part5--><artwork type="abnf2616">
377  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
378</artwork></figure>
379<figure><!--Part6--><artwork type="abnf2616">
380  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
381</artwork></figure>
382</section>
383
384</section>
385
386</section>
387
388<section title="Protocol Parameters" anchor="protocol.parameters">
389
390<section title="Character Sets" anchor="character.sets">
391<t>
392   HTTP uses the same definition of the term "character set" as that
393   described for MIME:
394</t>
395<t>
396   The term "character set" is used in this document to refer to a
397   method used with one or more tables to convert a sequence of octets
398   into a sequence of characters. Note that unconditional conversion in
399   the other direction is not required, in that not all characters may
400   be available in a given character set and a character set may provide
401   more than one sequence of octets to represent a particular character.
402   This definition is intended to allow various kinds of character
403   encoding, from simple single-table mappings such as US-ASCII to
404   complex table switching methods such as those that use ISO-2022's
405   techniques. However, the definition associated with a MIME character
406   set name &MUST; fully specify the mapping to be performed from octets
407   to characters. In particular, use of external profiling information
408   to determine the exact mapping is not permitted.
409</t>
410<x:note>
411  <t>
412    <x:h>Note:</x:h> This use of the term "character set" is more commonly
413    referred to as a "character encoding." However, since HTTP and
414    MIME share the same registry, it is important that the terminology
415    also be shared.
416  </t>
417</x:note>
418<t anchor="rule.charset">
419  <x:anchor-alias value="charset"/>
420   HTTP character sets are identified by case-insensitive tokens. The
421   complete set of tokens is defined by the IANA Character Set registry
422   (<eref target="http://www.iana.org/assignments/character-sets"/>).
423</t>
424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
425  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
426</artwork></figure>
427<t>
428   Although HTTP allows an arbitrary token to be used as a charset
429   value, any token that has a predefined value within the IANA
430   Character Set registry &MUST; represent the character set defined
431   by that registry. Applications &SHOULD; limit their use of character
432   sets to those defined by the IANA registry.
433</t>
434<t>
435   HTTP uses charset in two contexts: within an Accept-Charset request
436   header (in which the charset value is an unquoted token) and as the
437   value of a parameter in a Content-Type header (within a request or
438   response), in which case the parameter value of the charset parameter
439   may be quoted.
440</t>
441<t>
442   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
443   <xref target="RFC2277"/>.
444</t>
445
446<section title="Missing Charset" anchor="missing.charset">
447<t>
448   Some HTTP/1.0 software has interpreted a Content-Type header without
449   charset parameter incorrectly to mean "recipient should guess."
450   Senders wishing to defeat this behavior &MAY; include a charset
451   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
452   it is known that it will not confuse the recipient.
453</t>
454<t>
455   Unfortunately, some older HTTP/1.0 clients did not deal properly with
456   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
457   charset label provided by the sender; and those user agents that have
458   a provision to "guess" a charset &MUST; use the charset from the
459   content-type field if they support that charset, rather than the
460   recipient's preference, when initially displaying a document. See
461   <xref target="canonicalization.and.text.defaults"/>.
462</t>
463</section>
464</section>
465
466<section title="Content Codings" anchor="content.codings">
467  <x:anchor-alias value="content-coding"/>
468<t>
469   Content coding values indicate an encoding transformation that has
470   been or can be applied to an entity. Content codings are primarily
471   used to allow a document to be compressed or otherwise usefully
472   transformed without losing the identity of its underlying media type
473   and without loss of information. Frequently, the entity is stored in
474   coded form, transmitted directly, and only decoded by the recipient.
475</t>
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
477  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
478</artwork></figure>
479<t>
480   All content-coding values are case-insensitive. HTTP/1.1 uses
481   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
482   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
483   describes the content-coding, what is more important is that it
484   indicates what decoding mechanism will be required to remove the
485   encoding.
486</t>
487<t>
488   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
489  <list>
490    <t>
491      See &compress-coding;.
492    </t>
493  </list>
494</t>
495<t>
496   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
497  <list>
498    <t>
499      See &deflate-coding;.
500    </t>
501  </list>
502</t>
503<t>
504   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
505  <list>
506    <t>
507      See &gzip-coding;.
508    </t>
509  </list>
510</t>
511<t>
512   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
513  <list><t>
514        The default (identity) encoding; the use of no transformation
515        whatsoever. This content-coding is used only in the Accept-Encoding
516        header, and &SHOULD-NOT;  be used in the Content-Encoding
517        header.
518  </t></list>
519</t>
520
521<section title="Content Coding Registry" anchor="content.coding.registry">
522<t>
523   The HTTP Content Coding Registry defines the name space for the content
524   coding names.
525</t>
526<t>
527   Registrations &MUST; include the following fields:
528   <list style="symbols">
529     <t>Name</t>
530     <t>Description</t>
531     <t>Pointer to specification text</t>
532   </list>
533</t>
534<t>
535   Values to be added to this name space require expert review and a specification
536   (see "Expert Review" and "Specification Required" in
537   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
538   conform to the purpose of content coding defined in this section.
539</t>
540<t>
541   The registry itself is maintained at
542   <eref target="http://www.iana.org/assignments/http-parameters"/>.
543</t>
544</section>
545
546</section>
547
548<section title="Media Types" anchor="media.types">
549  <x:anchor-alias value="media-type"/>
550  <x:anchor-alias value="type"/>
551  <x:anchor-alias value="subtype"/>
552<t>
553   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
554   and Accept (<xref target="header.accept"/>) header fields in order to provide
555   open and extensible data typing and type negotiation.
556</t>
557<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"/>
558  <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> )
559  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
560  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
561</artwork></figure>
562<t anchor="rule.parameter">
563  <x:anchor-alias value="attribute"/>
564  <x:anchor-alias value="parameter"/>
565  <x:anchor-alias value="value"/>
566   Parameters &MAY; follow the type/subtype in the form of attribute/value
567   pairs.
568</t>
569<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"/>
570  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
571  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
572  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
573</artwork></figure>
574<t>
575   The type, subtype, and parameter attribute names are case-insensitive.
576   Parameter values might or might not be case-sensitive, depending on the
577   semantics of the parameter name.  The presence or absence of a parameter might
578   be significant to the processing of a media-type, depending on its
579   definition within the media type registry.
580</t>
581<t>
582   A parameter value that matches the <x:ref>token</x:ref> production may be
583   transmitted as either a token or within a quoted-string. The quoted and
584   unquoted values are equivalent.
585</t>
586<t>
587   Note that some older HTTP applications do not recognize media type
588   parameters. When sending data to older HTTP applications,
589   implementations &SHOULD; only use media type parameters when they are
590   required by that type/subtype definition.
591</t>
592<t>
593   Media-type values are registered with the Internet Assigned Number
594   Authority (IANA). The media type registration process is
595   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
596   discouraged.
597</t>
598
599<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
600<t>
601   Internet media types are registered with a canonical form. An
602   entity-body transferred via HTTP messages &MUST; be represented in the
603   appropriate canonical form prior to its transmission except for
604   "text" types, as defined in the next paragraph.
605</t>
606<t>
607   When in canonical form, media subtypes of the "text" type use CRLF as
608   the text line break. HTTP relaxes this requirement and allows the
609   transport of text media with plain CR or LF alone representing a line
610   break when it is done consistently for an entire entity-body. HTTP
611   applications &MUST; accept CRLF, bare CR, and bare LF as being
612   representative of a line break in text media received via HTTP. In
613   addition, if the text is represented in a character set that does not
614   use octets 13 and 10 for CR and LF respectively, as is the case for
615   some multi-byte character sets, HTTP allows the use of whatever octet
616   sequences are defined by that character set to represent the
617   equivalent of CR and LF for line breaks. This flexibility regarding
618   line breaks applies only to text media in the entity-body; a bare CR
619   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
620   structures (such as header fields and multipart boundaries).
621</t>
622<t>
623   If an entity-body is encoded with a content-coding, the underlying
624   data &MUST; be in a form defined above prior to being encoded.
625</t>
626<t>
627   The "charset" parameter is used with some media types to define the
628   character set (<xref target="character.sets"/>) of the data. When no explicit charset
629   parameter is provided by the sender, media subtypes of the "text"
630   type are defined to have a default charset value of "ISO-8859-1" when
631   received via HTTP. Data in character sets other than "ISO-8859-1" or
632   its subsets &MUST; be labeled with an appropriate charset value. See
633   <xref target="missing.charset"/> for compatibility problems.
634</t>
635</section>
636
637<section title="Multipart Types" anchor="multipart.types">
638<t>
639   MIME provides for a number of "multipart" types -- encapsulations of
640   one or more entities within a single message-body. All multipart
641   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
642   and &MUST; include a boundary parameter as part of the media type
643   value. The message body is itself a protocol element and &MUST;
644   therefore use only CRLF to represent line breaks between body-parts.
645   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
646   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
647   original multipart contains an epilogue). These restrictions exist in
648   order to preserve the self-delimiting nature of a multipart message-body,
649   wherein the "end" of the message-body is indicated by the
650   ending multipart boundary.
651</t>
652<t>
653   In general, HTTP treats a multipart message-body no differently than
654   any other media type: strictly as payload. The one exception is the
655   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
656   (Partial Content) response.
657   <!-- jre: re-insert removed text pointing to caching? -->
658   In all
659   other cases, an HTTP user agent &SHOULD; follow the same or similar
660   behavior as a MIME user agent would upon receipt of a multipart type.
661   The MIME header fields within each body-part of a multipart message-body
662   do not have any significance to HTTP beyond that defined by
663   their MIME semantics.
664</t>
665<t>
666   In general, an HTTP user agent &SHOULD; follow the same or similar
667   behavior as a MIME user agent would upon receipt of a multipart type.
668   If an application receives an unrecognized multipart subtype, the
669   application &MUST; treat it as being equivalent to "multipart/mixed".
670</t>
671<x:note>
672  <t>
673    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
674    for carrying form data suitable for processing via the POST
675    request method, as described in <xref target="RFC2388"/>.
676  </t>
677</x:note>
678</section>
679</section>
680
681<section title="Language Tags" anchor="language.tags">
682  <x:anchor-alias value="language-tag"/>
683<t>
684   A language tag, as defined in <xref target="RFC5646"/>, identifies a
685   natural language spoken, written, or otherwise conveyed by human beings for
686   communication of information to other human beings. Computer languages are
687   explicitly excluded. HTTP uses language tags within the Accept-Language and
688   Content-Language fields.
689</t>
690<t>
691   In summary, a language tag is composed of one or more parts: A primary
692   language subtag followed by a possibly empty series of subtags:
693</t>
694<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
695  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
696</artwork></figure>
697<t>
698   White space is not allowed within the tag and all tags are case-insensitive.
699   The name space of language subtags is administered by the IANA (see
700   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
701</t>
702<figure>
703  <preamble>Example tags include:</preamble>
704<artwork type="example">
705  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
706</artwork>
707</figure>
708<t>
709   See <xref target="RFC5646"/> for further information.
710</t>
711</section>
712</section>
713
714<section title="Entity" anchor="entity">
715<t>
716   Request and Response messages &MAY; transfer an entity if not otherwise
717   restricted by the request method or response status code. An entity
718   consists of entity-header fields and an entity-body, although some
719   responses will only include the entity-headers.
720</t>
721<t>
722   In this section, both sender and recipient refer to either the client
723   or the server, depending on who sends and who receives the entity.
724</t>
725
726<section title="Entity Header Fields" anchor="entity.header.fields">
727  <x:anchor-alias value="entity-header"/>
728  <x:anchor-alias value="extension-header"/>
729<t>
730   Entity-header fields define metainformation about the entity-body or,
731   if no body is present, about the resource identified by the request.
732</t>
733<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
734  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
735                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
736                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
737                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
738                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
739                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
740                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
741                 / <x:ref>Expires</x:ref>                  ; &header-expires;
742                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
743                 / <x:ref>extension-header</x:ref>
744 
745  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
746</artwork></figure>
747<t>
748   The extension-header mechanism allows additional entity-header fields
749   to be defined without changing the protocol, but these fields cannot
750   be assumed to be recognizable by the recipient. Unrecognized header
751   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
752   transparent proxies.
753</t>
754</section>
755
756<section title="Entity Body" anchor="entity.body">
757  <x:anchor-alias value="entity-body"/>
758<t>
759   The entity-body (if any) sent with an HTTP request or response is in
760   a format and encoding defined by the entity-header fields.
761</t>
762<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
763  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
764</artwork></figure>
765<t>
766   An entity-body is only present in a message when a message-body is
767   present, as described in &message-body;. The entity-body is obtained
768   from the message-body by decoding any Transfer-Encoding that might
769   have been applied to ensure safe and proper transfer of the message.
770</t>
771
772<section title="Type" anchor="type">
773<t>
774   When an entity-body is included with a message, the data type of that
775   body is determined via the header fields Content-Type and Content-Encoding.
776   These define a two-layer, ordered encoding model:
777</t>
778<figure><artwork type="example">
779  entity-body := Content-Encoding( Content-Type( data ) )
780</artwork></figure>
781<t>
782   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
783   message containing an entity-body &SHOULD; include a Content-Type header
784   field defining the media type of that body, unless that information is
785   unknown.  If the Content-Type header field is not present, it indicates that
786   the sender does not know the media type of the data; recipients &MAY;
787   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
788   or examine the content to determine its type.
789</t>
790<t>
791   Content-Encoding may be used to indicate any additional content
792   codings applied to the data, usually for the purpose of data
793   compression, that are a property of the requested resource.  There is
794   no default encoding.
795</t>
796</section>
797   
798<section title="Entity Length" anchor="entity.length">
799<t>
800   The entity-length of a message is the length of the message-body
801   before any transfer-codings have been applied. &message-length; defines
802   how the transfer-length of a message-body is determined.
803</t>
804</section>
805</section>
806</section>
807
808<section title="Content Negotiation" anchor="content.negotiation">
809<t>
810   HTTP responses include a representation which contains information for
811   interpretation, whether by a human user or for further processing.
812   Often, the server has different ways of representing the
813   same information; for example, in different formats, languages,
814   or using different character encodings.
815</t>
816<t>
817   HTTP clients and their users might have different or variable
818   capabilities, characteristics or preferences which would influence
819   which representation, among those available from the server,
820   would be best for the server to deliver. For this reason, HTTP
821   provides mechanisms for "content negotiation" -- a process of
822   allowing selection of a representation of a given resource,
823   when more than one is available.
824</t>
825<t>
826   This specification defines two patterns of content negotiation;
827   "server-driven", where the server selects the representation based
828   upon the client's stated preferences, and "agent-driven" negotiation,
829   where the server provides a list of representations for the client to
830   choose from, based upon their metadata. In addition,  there are
831   other patterns: some applications use an "active content" pattern,
832   where the server returns active content which runs on the client
833   and, based on client available parameters, selects additional
834   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
835   has also been proposed.
836</t>
837<t>
838   These patterns are all widely used, and have trade-offs in applicability
839   and practicality. In particular, when the number of preferences or
840   capabilities to be expressed by a client are large (such as when many
841   different formats are supported by a user-agent), server-driven
842   negotiation becomes unwieldy, and may not be appropriate. Conversely,
843   when the number of representations to choose from is very large,
844   agent-driven negotiation may not be appropriate.
845</t>
846<t>
847   Note that in all cases, the supplier of representations has the
848   responsibility for determining which representations might be
849   considered to be the "same information".
850</t>
851
852<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
853<t>
854   If the selection of the best representation for a response is made by
855   an algorithm located at the server, it is called server-driven
856   negotiation. Selection is based on the available representations of
857   the response (the dimensions over which it can vary; e.g., language,
858   content-coding, etc.) and the contents of particular header fields in
859   the request message or on other information pertaining to the request
860   (such as the network address of the client).
861</t>
862<t>
863   Server-driven negotiation is advantageous when the algorithm for
864   selecting from among the available representations is difficult to
865   describe to the user agent, or when the server desires to send its
866   "best guess" to the client along with the first response (hoping to
867   avoid the round-trip delay of a subsequent request if the "best
868   guess" is good enough for the user). In order to improve the server's
869   guess, the user agent &MAY; include request header fields (Accept,
870   Accept-Language, Accept-Encoding, etc.) which describe its
871   preferences for such a response.
872</t>
873<t>
874   Server-driven negotiation has disadvantages:
875  <list style="numbers">
876    <t>
877         It is impossible for the server to accurately determine what
878         might be "best" for any given user, since that would require
879         complete knowledge of both the capabilities of the user agent
880         and the intended use for the response (e.g., does the user want
881         to view it on screen or print it on paper?).
882    </t>
883    <t>
884         Having the user agent describe its capabilities in every
885         request can be both very inefficient (given that only a small
886         percentage of responses have multiple representations) and a
887         potential violation of the user's privacy.
888    </t>
889    <t>
890         It complicates the implementation of an origin server and the
891         algorithms for generating responses to a request.
892    </t>
893    <t>
894         It may limit a public cache's ability to use the same response
895         for multiple user's requests.
896    </t>
897  </list>
898</t>
899<t>
900   HTTP/1.1 includes the following request-header fields for enabling
901   server-driven negotiation through description of user agent
902   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
903   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
904   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
905   However, an origin server is not limited to these dimensions and &MAY; vary
906   the response based on any aspect of the request, including information
907   outside the request-header fields or within extension header fields
908   not defined by this specification.
909</t>
910<x:note>
911  <t>
912    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
913    because new clients might not be recognized.
914  </t>
915</x:note>
916<t>
917   The Vary header field (&header-vary;) can be used to express the parameters the
918   server uses to select a representation that is subject to server-driven
919   negotiation.
920</t>
921</section>
922
923<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
924<t>
925   With agent-driven negotiation, selection of the best representation
926   for a response is performed by the user agent after receiving an
927   initial response from the origin server. Selection is based on a list
928   of the available representations of the response included within the
929   header fields or entity-body of the initial response, with each
930   representation identified by its own URI. Selection from among the
931   representations may be performed automatically (if the user agent is
932   capable of doing so) or manually by the user selecting from a
933   generated (possibly hypertext) menu.
934</t>
935<t>
936   Agent-driven negotiation is advantageous when the response would vary
937   over commonly-used dimensions (such as type, language, or encoding),
938   when the origin server is unable to determine a user agent's
939   capabilities from examining the request, and generally when public
940   caches are used to distribute server load and reduce network usage.
941</t>
942<t>
943   Agent-driven negotiation suffers from the disadvantage of needing a
944   second request to obtain the best alternate representation. This
945   second request is only efficient when caching is used. In addition,
946   this specification does not define any mechanism for supporting
947   automatic selection, though it also does not prevent any such
948   mechanism from being developed as an extension and used within
949   HTTP/1.1.
950</t>
951<t>
952   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
953   status codes for enabling agent-driven negotiation when the server is
954   unwilling or unable to provide a varying response using server-driven
955   negotiation.
956</t>
957</section>
958</section>
959
960<section title="Header Field Definitions" anchor="header.fields">
961<t>
962   This section defines the syntax and semantics of HTTP/1.1 header fields
963   related to the payload of messages.
964</t>
965<t>
966   For entity-header fields, both sender and recipient refer to either the
967   client or the server, depending on who sends and who receives the entity.
968</t>
969
970<section title="Accept" anchor="header.accept">
971  <iref primary="true" item="Accept header" x:for-anchor=""/>
972  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
973  <x:anchor-alias value="Accept"/>
974  <x:anchor-alias value="Accept-v"/>
975  <x:anchor-alias value="accept-ext"/>
976  <x:anchor-alias value="accept-params"/>
977  <x:anchor-alias value="media-range"/>
978<t>
979   The "Accept" request-header field can be used by user agents to specify
980   response media types that are acceptable. Accept headers can be used to
981   indicate that the request is specifically limited to a small set of desired
982   types, as in the case of a request for an in-line image.
983</t>
984<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"/>
985  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
986  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
987 
988  <x:ref>media-range</x:ref>    = ( "*/*"
989                   / ( <x:ref>type</x:ref> "/" "*" )
990                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
991                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
992  <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> )
993  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
994                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
995</artwork></figure>
996<t>
997   The asterisk "*" character is used to group media types into ranges,
998   with "*/*" indicating all media types and "type/*" indicating all
999   subtypes of that type. The media-range &MAY; include media type
1000   parameters that are applicable to that range.
1001</t>
1002<t>
1003   Each media-range &MAY; be followed by one or more accept-params,
1004   beginning with the "q" parameter for indicating a relative quality
1005   factor. The first "q" parameter (if any) separates the media-range
1006   parameter(s) from the accept-params. Quality factors allow the user
1007   or user agent to indicate the relative degree of preference for that
1008   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1009   default value is q=1.
1010</t>
1011<x:note>
1012  <t>
1013    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1014    parameters from Accept extension parameters is due to historical
1015    practice. Although this prevents any media type parameter named
1016    "q" from being used with a media range, such an event is believed
1017    to be unlikely given the lack of any "q" parameters in the IANA
1018    media type registry and the rare usage of any media type
1019    parameters in Accept. Future media types are discouraged from
1020    registering any parameter named "q".
1021  </t>
1022</x:note>
1023<t>
1024   The example
1025</t>
1026<figure><artwork type="example">
1027  Accept: audio/*; q=0.2, audio/basic
1028</artwork></figure>
1029<t>
1030   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1031   type if it is the best available after an 80% mark-down in quality."
1032</t>
1033<t>
1034   If no Accept header field is present, then it is assumed that the
1035   client accepts all media types. If an Accept header field is present,
1036   and if the server cannot send a response which is acceptable
1037   according to the combined Accept field value, then the server &SHOULD;
1038   send a 406 (Not Acceptable) response.
1039</t>
1040<t>
1041   A more elaborate example is
1042</t>
1043<figure><artwork type="example">
1044  Accept: text/plain; q=0.5, text/html,
1045          text/x-dvi; q=0.8, text/x-c
1046</artwork></figure>
1047<t>
1048   Verbally, this would be interpreted as "text/html and text/x-c are
1049   the preferred media types, but if they do not exist, then send the
1050   text/x-dvi entity, and if that does not exist, send the text/plain
1051   entity."
1052</t>
1053<t>
1054   Media ranges can be overridden by more specific media ranges or
1055   specific media types. If more than one media range applies to a given
1056   type, the most specific reference has precedence. For example,
1057</t>
1058<figure><artwork type="example">
1059  Accept: text/*, text/html, text/html;level=1, */*
1060</artwork></figure>
1061<t>
1062   have the following precedence:
1063   <list style="numbers">
1064    <t>text/html;level=1</t>
1065    <t>text/html</t>
1066    <t>text/*</t>
1067    <t>*/*</t>
1068   </list>
1069</t>
1070<t>
1071   The media type quality factor associated with a given type is
1072   determined by finding the media range with the highest precedence
1073   which matches that type. For example,
1074</t>
1075<figure><artwork type="example">
1076  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1077          text/html;level=2;q=0.4, */*;q=0.5
1078</artwork></figure>
1079<t>
1080   would cause the following values to be associated:
1081</t>
1082<texttable align="left">
1083  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1084  <c>text/html;level=1</c>    <c>1</c>
1085  <c>text/html</c>            <c>0.7</c>
1086  <c>text/plain</c>           <c>0.3</c>
1087  <c>image/jpeg</c>           <c>0.5</c>
1088  <c>text/html;level=2</c>    <c>0.4</c>
1089  <c>text/html;level=3</c>    <c>0.7</c>
1090</texttable>
1091<t>
1092      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1093      values for certain media ranges. However, unless the user agent is
1094      a closed system which cannot interact with other rendering agents,
1095      this default set ought to be configurable by the user.
1096</t>
1097</section>
1098
1099<section title="Accept-Charset" anchor="header.accept-charset">
1100  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1101  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1102  <x:anchor-alias value="Accept-Charset"/>
1103  <x:anchor-alias value="Accept-Charset-v"/>
1104<t>
1105   The "Accept-Charset" request-header field can be used by user agents to
1106   indicate what response character sets are acceptable. This field allows
1107   clients capable of understanding more comprehensive or special-purpose
1108   character sets to signal that capability to a server which is capable of
1109   representing documents in those character sets.
1110</t>
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1112  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1113          <x:ref>Accept-Charset-v</x:ref>
1114  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1115                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1116</artwork></figure>
1117<t>
1118   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1119   be given an associated quality value which represents the user's
1120   preference for that charset. The default value is q=1. An example is
1121</t>
1122<figure><artwork type="example">
1123  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1124</artwork></figure>
1125<t>
1126   The special value "*", if present in the Accept-Charset field,
1127   matches every character set (including ISO-8859-1) which is not
1128   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1129   in an Accept-Charset field, then all character sets not explicitly
1130   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1131   a quality value of 1 if not explicitly mentioned.
1132</t>
1133<t>
1134   If no Accept-Charset header is present, the default is that any
1135   character set is acceptable. If an Accept-Charset header is present,
1136   and if the server cannot send a response which is acceptable
1137   according to the Accept-Charset header, then the server &SHOULD; send
1138   an error response with the 406 (Not Acceptable) status code, though
1139   the sending of an unacceptable response is also allowed.
1140</t>
1141</section>
1142
1143<section title="Accept-Encoding" anchor="header.accept-encoding">
1144  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1145  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1146  <x:anchor-alias value="Accept-Encoding"/>
1147  <x:anchor-alias value="Accept-Encoding-v"/>
1148  <x:anchor-alias value="codings"/>
1149<t>
1150   The "Accept-Encoding" request-header field can be used by user agents to
1151   indicate what response content-codings (<xref target="content.codings"/>)
1152   are acceptable in the response.
1153</t>
1154<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"/>
1155  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1156                     <x:ref>Accept-Encoding-v</x:ref>
1157  <x:ref>Accept-Encoding-v</x:ref>  =
1158                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1159  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1160</artwork></figure>
1161<t>
1162   Each codings value &MAY; be given an associated quality value which
1163   represents the preference for that encoding. The default value is q=1.
1164</t>
1165<t>
1166   Examples of its use are:
1167</t>
1168<figure><artwork type="example">
1169  Accept-Encoding: compress, gzip
1170  Accept-Encoding:
1171  Accept-Encoding: *
1172  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1173  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1174</artwork></figure>
1175<t>
1176   A server tests whether a content-coding is acceptable, according to
1177   an Accept-Encoding field, using these rules:
1178  <list style="numbers">
1179      <t>If the content-coding is one of the content-codings listed in
1180         the Accept-Encoding field, then it is acceptable, unless it is
1181         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1182         qvalue of 0 means "not acceptable.")</t>
1183
1184      <t>The special "*" symbol in an Accept-Encoding field matches any
1185         available content-coding not explicitly listed in the header
1186         field.</t>
1187
1188      <t>If multiple content-codings are acceptable, then the acceptable
1189         content-coding with the highest non-zero qvalue is preferred.</t>
1190
1191      <t>The "identity" content-coding is always acceptable, unless
1192         specifically refused because the Accept-Encoding field includes
1193         "identity;q=0", or because the field includes "*;q=0" and does
1194         not explicitly include the "identity" content-coding. If the
1195         Accept-Encoding field-value is empty, then only the "identity"
1196         encoding is acceptable.</t>
1197  </list>
1198</t>
1199<t>
1200   If an Accept-Encoding field is present in a request, and if the
1201   server cannot send a response which is acceptable according to the
1202   Accept-Encoding header, then the server &SHOULD; send an error response
1203   with the 406 (Not Acceptable) status code.
1204</t>
1205<t>
1206   If no Accept-Encoding field is present in a request, the server &MAY;
1207   assume that the client will accept any content coding. In this case,
1208   if "identity" is one of the available content-codings, then the
1209   server &SHOULD; use the "identity" content-coding, unless it has
1210   additional information that a different content-coding is meaningful
1211   to the client.
1212</t>
1213<x:note>
1214  <t>
1215    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1216    and if the "identity" content-coding is unavailable, then
1217    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1218    "gzip" and "compress") are preferred; some older clients
1219    improperly display messages sent with other content-codings.  The
1220    server might also make this decision based on information about
1221    the particular user-agent or client.
1222  </t>
1223</x:note>
1224<x:note>
1225  <t>
1226    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1227    associated with content-codings. This means that qvalues will not
1228    work and are not permitted with x-gzip or x-compress.
1229  </t>
1230</x:note>
1231</section>
1232
1233<section title="Accept-Language" anchor="header.accept-language">
1234  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1235  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1236  <x:anchor-alias value="Accept-Language"/>
1237  <x:anchor-alias value="Accept-Language-v"/>
1238  <x:anchor-alias value="language-range"/>
1239<t>
1240   The "Accept-Language" request-header field can be used by user agents to
1241   indicate the set of natural languages that are preferred in the response.
1242   Language tags are defined in <xref target="language.tags"/>.
1243</t>
1244<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"/>
1245  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1246                    <x:ref>Accept-Language-v</x:ref>
1247  <x:ref>Accept-Language-v</x:ref> =
1248                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1249  <x:ref>language-range</x:ref>    =
1250            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1251</artwork></figure>
1252<t>
1253   Each language-range can be given an associated quality value which
1254   represents an estimate of the user's preference for the languages
1255   specified by that range. The quality value defaults to "q=1". For
1256   example,
1257</t>
1258<figure><artwork type="example">
1259  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1260</artwork></figure>
1261<t>
1262   would mean: "I prefer Danish, but will accept British English and
1263   other types of English."
1264   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1265</t>
1266<t>
1267   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1268   several matching schemes. Implementations can offer the most appropriate
1269   matching scheme for their requirements.
1270</t>
1271<x:note>
1272  <t>
1273    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1274    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1275    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1276  </t>
1277</x:note>
1278<t>
1279   It might be contrary to the privacy expectations of the user to send
1280   an Accept-Language header with the complete linguistic preferences of
1281   the user in every request. For a discussion of this issue, see
1282   <xref target="privacy.issues.connected.to.accept.headers"/>.
1283</t>
1284<t>
1285   As intelligibility is highly dependent on the individual user, it is
1286   recommended that client applications make the choice of linguistic
1287   preference available to the user. If the choice is not made
1288   available, then the Accept-Language header field &MUST-NOT; be given in
1289   the request.
1290</t>
1291<x:note>
1292  <t>
1293    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1294    the user, we remind implementors of  the fact that users are not
1295    familiar with the details of language matching as described above,
1296    and should provide appropriate guidance. As an example, users
1297    might assume that on selecting "en-gb", they will be served any
1298    kind of English document if British English is not available. A
1299    user agent might suggest in such a case to add "en" to get the
1300    best matching behavior.
1301  </t>
1302</x:note>
1303</section>
1304
1305<section title="Content-Encoding" anchor="header.content-encoding">
1306  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1307  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1308  <x:anchor-alias value="Content-Encoding"/>
1309  <x:anchor-alias value="Content-Encoding-v"/>
1310<t>
1311   The "Content-Encoding" entity-header field indicates what content-codings
1312   have been applied to the entity-body, and thus what decoding mechanisms
1313   must be applied in order to obtain the media-type referenced by the
1314   Content-Type header field. Content-Encoding is primarily used to allow a
1315   document to be compressed without losing the identity of its underlying
1316   media type.
1317</t>
1318<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1319  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1320  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1321</artwork></figure>
1322<t>
1323   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1324</t>
1325<figure><artwork type="example">
1326  Content-Encoding: gzip
1327</artwork></figure>
1328<t>
1329   The content-coding is a characteristic of the entity identified by
1330   the request-target. Typically, the entity-body is stored with this
1331   encoding and is only decoded before rendering or analogous usage.
1332   However, a non-transparent proxy &MAY; modify the content-coding if the
1333   new coding is known to be acceptable to the recipient, unless the
1334   "no-transform" cache-control directive is present in the message.
1335</t>
1336<t>
1337   If the content-coding of an entity is not "identity", then the
1338   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1339   that lists the non-identity content-coding(s) used.
1340</t>
1341<t>
1342   If the content-coding of an entity in a request message is not
1343   acceptable to the origin server, the server &SHOULD; respond with a
1344   status code of 415 (Unsupported Media Type).
1345</t>
1346<t>
1347   If multiple encodings have been applied to an entity, the content
1348   codings &MUST; be listed in the order in which they were applied.
1349   Additional information about the encoding parameters &MAY; be provided
1350   by other entity-header fields not defined by this specification.
1351</t>
1352</section>
1353
1354<section title="Content-Language" anchor="header.content-language">
1355  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1356  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1357  <x:anchor-alias value="Content-Language"/>
1358  <x:anchor-alias value="Content-Language-v"/>
1359<t>
1360   The "Content-Language" entity-header field describes the natural
1361   language(s) of the intended audience for the entity. Note that this might
1362   not be equivalent to all the languages used within the entity-body.
1363</t>
1364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1365  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1366  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1367</artwork></figure>
1368<t>
1369   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1370   Content-Language is to allow a user to identify and differentiate
1371   entities according to the user's own preferred language. Thus, if the
1372   body content is intended only for a Danish-literate audience, the
1373   appropriate field is
1374</t>
1375<figure><artwork type="example">
1376  Content-Language: da
1377</artwork></figure>
1378<t>
1379   If no Content-Language is specified, the default is that the content
1380   is intended for all language audiences. This might mean that the
1381   sender does not consider it to be specific to any natural language,
1382   or that the sender does not know for which language it is intended.
1383</t>
1384<t>
1385   Multiple languages &MAY; be listed for content that is intended for
1386   multiple audiences. For example, a rendition of the "Treaty of
1387   Waitangi," presented simultaneously in the original Maori and English
1388   versions, would call for
1389</t>
1390<figure><artwork type="example">
1391  Content-Language: mi, en
1392</artwork></figure>
1393<t>
1394   However, just because multiple languages are present within an entity
1395   does not mean that it is intended for multiple linguistic audiences.
1396   An example would be a beginner's language primer, such as "A First
1397   Lesson in Latin," which is clearly intended to be used by an
1398   English-literate audience. In this case, the Content-Language would
1399   properly only include "en".
1400</t>
1401<t>
1402   Content-Language &MAY; be applied to any media type -- it is not
1403   limited to textual documents.
1404</t>
1405</section>
1406
1407<section title="Content-Location" anchor="header.content-location">
1408  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1409  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1410  <x:anchor-alias value="Content-Location"/>
1411  <x:anchor-alias value="Content-Location-v"/>
1412<t>
1413   The "Content-Location" entity-header field is used to supply a URI for the
1414   entity in the message when it is accessible from a location separate from
1415   the requested resource's URI.
1416</t>
1417<t>
1418   A server &SHOULD; provide a Content-Location for the variant corresponding
1419   to the response entity, especially in the case where a resource has multiple
1420   entities associated with it, and those entities actually have separate
1421   locations by which they might be individually accessed, the server &SHOULD;
1422   provide a Content-Location for the particular variant which is returned.
1423</t>
1424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1425  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1426                    <x:ref>Content-Location-v</x:ref>
1427  <x:ref>Content-Location-v</x:ref> =
1428                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1429</artwork></figure>
1430<t>
1431   The Content-Location value is not a replacement for the original
1432   requested URI; it is only a statement of the location of the resource
1433   corresponding to this particular entity at the time of the request.
1434   Future requests &MAY; specify the Content-Location URI as the request-target
1435   if the desire is to identify the source of that particular
1436   entity.
1437</t>
1438<t>
1439   &response-representation; describes how clients may process the Content-Location header field.
1440</t>
1441<t>
1442   A cache cannot assume that an entity with a Content-Location
1443   different from the URI used to retrieve it can be used to respond to
1444   later requests on that Content-Location URI. However, the Content-Location
1445   can be used to differentiate between multiple entities
1446   retrieved from a single requested resource, as described in &caching-neg-resp;.
1447</t>
1448<t>
1449   If the Content-Location is a relative URI, the relative URI is
1450   interpreted relative to the request-target.
1451</t>
1452<t>
1453   The meaning of the Content-Location header in requests is
1454   undefined; servers are free to ignore it in those cases.
1455</t>
1456</section>
1457
1458<section title="Content-MD5" anchor="header.content-md5">
1459  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1460  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1461  <x:anchor-alias value="Content-MD5"/>
1462  <x:anchor-alias value="Content-MD5-v"/>
1463<t>
1464   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1465   an MD5 digest of the entity-body that provides an end-to-end message
1466   integrity check (MIC) of the entity-body. Note that a MIC is good for
1467   detecting accidental modification of the entity-body in transit, but is not
1468   proof against malicious attacks.
1469</t>
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1471  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1472  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1473</artwork></figure>
1474<t>
1475   The Content-MD5 header field &MAY; be generated by an origin server or
1476   client to function as an integrity check of the entity-body. Only
1477   origin servers or clients &MAY; generate the Content-MD5 header field;
1478   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1479   value as an end-to-end integrity check. Any recipient of the entity-body,
1480   including gateways and proxies, &MAY; check that the digest value
1481   in this header field matches that of the entity-body as received.
1482</t>
1483<t>
1484   The MD5 digest is computed based on the content of the entity-body,
1485   including any content-coding that has been applied, but not including
1486   any transfer-encoding applied to the message-body. If the message is
1487   received with a transfer-encoding, that encoding &MUST; be removed
1488   prior to checking the Content-MD5 value against the received entity.
1489</t>
1490<t>
1491   This has the result that the digest is computed on the octets of the
1492   entity-body exactly as, and in the order that, they would be sent if
1493   no transfer-encoding were being applied.
1494</t>
1495<t>
1496   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1497   composite media-types (e.g., multipart/* and message/rfc822), but
1498   this does not change how the digest is computed as defined in the
1499   preceding paragraph.
1500</t>
1501<t>
1502   There are several consequences of this. The entity-body for composite
1503   types &MAY; contain many body-parts, each with its own MIME and HTTP
1504   headers (including Content-MD5, Content-Transfer-Encoding, and
1505   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1506   or Content-Encoding header, it is assumed that the content
1507   of the body-part has had the encoding applied, and the body-part is
1508   included in the Content-MD5 digest as is -- i.e., after the
1509   application. The Transfer-Encoding header field is not allowed within
1510   body-parts.
1511</t>
1512<t>
1513   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1514   computing or checking the digest: the line break convention used in
1515   the text actually transmitted &MUST; be left unaltered when computing
1516   the digest.
1517</t>
1518<x:note>
1519  <t>
1520    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1521    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1522    in which the application of Content-MD5 to HTTP entity-bodies
1523    differs from its application to MIME entity-bodies. One is that
1524    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1525    does use Transfer-Encoding and Content-Encoding. Another is that
1526    HTTP more frequently uses binary content types than MIME, so it is
1527    worth noting that, in such cases, the byte order used to compute
1528    the digest is the transmission byte order defined for the type.
1529    Lastly, HTTP allows transmission of text types with any of several
1530    line break conventions and not just the canonical form using CRLF.
1531  </t>
1532</x:note>
1533</section>
1534
1535<section title="Content-Type" anchor="header.content-type">
1536  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1537  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1538  <x:anchor-alias value="Content-Type"/>
1539  <x:anchor-alias value="Content-Type-v"/>
1540<t>
1541   The "Content-Type" entity-header field indicates the media type of the
1542   entity-body. In the case of responses to the HEAD method, the media type is
1543   that which would have been sent had the request been a GET.
1544</t>
1545<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1546  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1547  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1548</artwork></figure>
1549<t>
1550   Media types are defined in <xref target="media.types"/>. An example of the field is
1551</t>
1552<figure><artwork type="example">
1553  Content-Type: text/html; charset=ISO-8859-4
1554</artwork></figure>
1555<t>
1556   Further discussion of methods for identifying the media type of an
1557   entity is provided in <xref target="type"/>.
1558</t>
1559</section>
1560
1561</section>
1562
1563<section title="IANA Considerations" anchor="IANA.considerations">
1564<section title="Message Header Registration" anchor="message.header.registration">
1565<t>
1566   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1567   with the permanent registrations below (see <xref target="RFC3864"/>):
1568</t>
1569<?BEGININC p3-payload.iana-headers ?>
1570<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1571<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1572   <ttcol>Header Field Name</ttcol>
1573   <ttcol>Protocol</ttcol>
1574   <ttcol>Status</ttcol>
1575   <ttcol>Reference</ttcol>
1576
1577   <c>Accept</c>
1578   <c>http</c>
1579   <c>standard</c>
1580   <c>
1581      <xref target="header.accept"/>
1582   </c>
1583   <c>Accept-Charset</c>
1584   <c>http</c>
1585   <c>standard</c>
1586   <c>
1587      <xref target="header.accept-charset"/>
1588   </c>
1589   <c>Accept-Encoding</c>
1590   <c>http</c>
1591   <c>standard</c>
1592   <c>
1593      <xref target="header.accept-encoding"/>
1594   </c>
1595   <c>Accept-Language</c>
1596   <c>http</c>
1597   <c>standard</c>
1598   <c>
1599      <xref target="header.accept-language"/>
1600   </c>
1601   <c>Content-Disposition</c>
1602   <c>http</c>
1603   <c/>
1604   <c>
1605      <xref target="content-disposition"/>
1606   </c>
1607   <c>Content-Encoding</c>
1608   <c>http</c>
1609   <c>standard</c>
1610   <c>
1611      <xref target="header.content-encoding"/>
1612   </c>
1613   <c>Content-Language</c>
1614   <c>http</c>
1615   <c>standard</c>
1616   <c>
1617      <xref target="header.content-language"/>
1618   </c>
1619   <c>Content-Location</c>
1620   <c>http</c>
1621   <c>standard</c>
1622   <c>
1623      <xref target="header.content-location"/>
1624   </c>
1625   <c>Content-MD5</c>
1626   <c>http</c>
1627   <c>standard</c>
1628   <c>
1629      <xref target="header.content-md5"/>
1630   </c>
1631   <c>Content-Type</c>
1632   <c>http</c>
1633   <c>standard</c>
1634   <c>
1635      <xref target="header.content-type"/>
1636   </c>
1637   <c>MIME-Version</c>
1638   <c>http</c>
1639   <c/>
1640   <c>
1641      <xref target="mime-version"/>
1642   </c>
1643</texttable>
1644<!--(END)-->
1645<?ENDINC p3-payload.iana-headers ?>
1646<t>
1647   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1648</t>
1649</section>
1650
1651<section title="Content Coding Registry" anchor="content.coding.registration">
1652<t>
1653   The registration procedure for HTTP Content Codings is now defined
1654   by <xref target="content.coding.registry"/> of this document.
1655</t>
1656<t>
1657   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1658   should be updated with the registration below:
1659</t>
1660<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1661   <ttcol>Name</ttcol>
1662   <ttcol>Description</ttcol>
1663   <ttcol>Reference</ttcol>
1664   <c>compress</c>
1665   <c>UNIX "compress" program method</c>
1666   <c>
1667      &compress-coding;
1668   </c>
1669   <c>deflate</c>
1670   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1671   the "zlib" data format (<xref target="RFC1950"/>)
1672   </c>
1673   <c>
1674      &deflate-coding;
1675   </c>
1676   <c>gzip</c>
1677   <c>Same as GNU zip <xref target="RFC1952"/></c>
1678   <c>
1679      &gzip-coding;
1680   </c>
1681   <c>identity</c>
1682   <c>No transformation</c>
1683   <c>
1684      <xref target="content.codings"/>
1685   </c>
1686</texttable>
1687</section>
1688
1689</section>
1690
1691<section title="Security Considerations" anchor="security.considerations">
1692<t>
1693   This section is meant to inform application developers, information
1694   providers, and users of the security limitations in HTTP/1.1 as
1695   described by this document. The discussion does not include
1696   definitive solutions to the problems revealed, though it does make
1697   some suggestions for reducing security risks.
1698</t>
1699
1700<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1701<t>
1702   Accept request-headers can reveal information about the user to all
1703   servers which are accessed. The Accept-Language header in particular
1704   can reveal information the user would consider to be of a private
1705   nature, because the understanding of particular languages is often
1706   strongly correlated to the membership of a particular ethnic group.
1707   User agents which offer the option to configure the contents of an
1708   Accept-Language header to be sent in every request are strongly
1709   encouraged to let the configuration process include a message which
1710   makes the user aware of the loss of privacy involved.
1711</t>
1712<t>
1713   An approach that limits the loss of privacy would be for a user agent
1714   to omit the sending of Accept-Language headers by default, and to ask
1715   the user whether or not to start sending Accept-Language headers to a
1716   server if it detects, by looking for any Vary response-header fields
1717   generated by the server, that such sending could improve the quality
1718   of service.
1719</t>
1720<t>
1721   Elaborate user-customized accept header fields sent in every request,
1722   in particular if these include quality values, can be used by servers
1723   as relatively reliable and long-lived user identifiers. Such user
1724   identifiers would allow content providers to do click-trail tracking,
1725   and would allow collaborating content providers to match cross-server
1726   click-trails or form submissions of individual users. Note that for
1727   many users not behind a proxy, the network address of the host
1728   running the user agent will also serve as a long-lived user
1729   identifier. In environments where proxies are used to enhance
1730   privacy, user agents ought to be conservative in offering accept
1731   header configuration options to end users. As an extreme privacy
1732   measure, proxies could filter the accept headers in relayed requests.
1733   General purpose user agents which provide a high degree of header
1734   configurability &SHOULD; warn users about the loss of privacy which can
1735   be involved.
1736</t>
1737</section>
1738
1739<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1740<t>
1741   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1742   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1743   serious security considerations. Content-Disposition is not part of
1744   the HTTP standard, but since it is widely implemented, we are
1745   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1746   for details.
1747</t>
1748</section>
1749
1750</section>
1751
1752<section title="Acknowledgments" anchor="ack">
1753</section>
1754</middle>
1755<back>
1756
1757<references title="Normative References">
1758
1759<reference anchor="ISO-8859-1">
1760  <front>
1761    <title>
1762     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1763    </title>
1764    <author>
1765      <organization>International Organization for Standardization</organization>
1766    </author>
1767    <date year="1998"/>
1768  </front>
1769  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1770</reference>
1771
1772<reference anchor="Part1">
1773  <front>
1774    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1775    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1776      <organization abbrev="Day Software">Day Software</organization>
1777      <address><email>fielding@gbiv.com</email></address>
1778    </author>
1779    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1780      <organization>One Laptop per Child</organization>
1781      <address><email>jg@laptop.org</email></address>
1782    </author>
1783    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1784      <organization abbrev="HP">Hewlett-Packard Company</organization>
1785      <address><email>JeffMogul@acm.org</email></address>
1786    </author>
1787    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1788      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1789      <address><email>henrikn@microsoft.com</email></address>
1790    </author>
1791    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1792      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1793      <address><email>LMM@acm.org</email></address>
1794    </author>
1795    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1796      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1797      <address><email>paulle@microsoft.com</email></address>
1798    </author>
1799    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1800      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1801      <address><email>timbl@w3.org</email></address>
1802    </author>
1803    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1804      <organization abbrev="W3C">World Wide Web Consortium</organization>
1805      <address><email>ylafon@w3.org</email></address>
1806    </author>
1807    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1808      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1809      <address><email>julian.reschke@greenbytes.de</email></address>
1810    </author>
1811    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1812  </front>
1813  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1814  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1815</reference>
1816
1817<reference anchor="Part2">
1818  <front>
1819    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1820    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1821      <organization abbrev="Day Software">Day Software</organization>
1822      <address><email>fielding@gbiv.com</email></address>
1823    </author>
1824    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1825      <organization>One Laptop per Child</organization>
1826      <address><email>jg@laptop.org</email></address>
1827    </author>
1828    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1829      <organization abbrev="HP">Hewlett-Packard Company</organization>
1830      <address><email>JeffMogul@acm.org</email></address>
1831    </author>
1832    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1833      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1834      <address><email>henrikn@microsoft.com</email></address>
1835    </author>
1836    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1837      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1838      <address><email>LMM@acm.org</email></address>
1839    </author>
1840    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1841      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1842      <address><email>paulle@microsoft.com</email></address>
1843    </author>
1844    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1845      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1846      <address><email>timbl@w3.org</email></address>
1847    </author>
1848    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1849      <organization abbrev="W3C">World Wide Web Consortium</organization>
1850      <address><email>ylafon@w3.org</email></address>
1851    </author>
1852    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1853      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1854      <address><email>julian.reschke@greenbytes.de</email></address>
1855    </author>
1856    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1857  </front>
1858  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1859  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1860</reference>
1861
1862<reference anchor="Part4">
1863  <front>
1864    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1865    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1866      <organization abbrev="Day Software">Day Software</organization>
1867      <address><email>fielding@gbiv.com</email></address>
1868    </author>
1869    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1870      <organization>One Laptop per Child</organization>
1871      <address><email>jg@laptop.org</email></address>
1872    </author>
1873    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1874      <organization abbrev="HP">Hewlett-Packard Company</organization>
1875      <address><email>JeffMogul@acm.org</email></address>
1876    </author>
1877    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1878      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1879      <address><email>henrikn@microsoft.com</email></address>
1880    </author>
1881    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1882      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1883      <address><email>LMM@acm.org</email></address>
1884    </author>
1885    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1886      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1887      <address><email>paulle@microsoft.com</email></address>
1888    </author>
1889    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1890      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1891      <address><email>timbl@w3.org</email></address>
1892    </author>
1893    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1894      <organization abbrev="W3C">World Wide Web Consortium</organization>
1895      <address><email>ylafon@w3.org</email></address>
1896    </author>
1897    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1898      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1899      <address><email>julian.reschke@greenbytes.de</email></address>
1900    </author>
1901    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1902  </front>
1903  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1904  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1905</reference>
1906
1907<reference anchor="Part5">
1908  <front>
1909    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1910    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1911      <organization abbrev="Day Software">Day Software</organization>
1912      <address><email>fielding@gbiv.com</email></address>
1913    </author>
1914    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1915      <organization>One Laptop per Child</organization>
1916      <address><email>jg@laptop.org</email></address>
1917    </author>
1918    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1919      <organization abbrev="HP">Hewlett-Packard Company</organization>
1920      <address><email>JeffMogul@acm.org</email></address>
1921    </author>
1922    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1923      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1924      <address><email>henrikn@microsoft.com</email></address>
1925    </author>
1926    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1927      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1928      <address><email>LMM@acm.org</email></address>
1929    </author>
1930    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1931      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1932      <address><email>paulle@microsoft.com</email></address>
1933    </author>
1934    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1935      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1936      <address><email>timbl@w3.org</email></address>
1937    </author>
1938    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1939      <organization abbrev="W3C">World Wide Web Consortium</organization>
1940      <address><email>ylafon@w3.org</email></address>
1941    </author>
1942    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1943      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1944      <address><email>julian.reschke@greenbytes.de</email></address>
1945    </author>
1946    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1947  </front>
1948  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1949  <x:source href="p5-range.xml" basename="p5-range"/>
1950</reference>
1951
1952<reference anchor="Part6">
1953  <front>
1954    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1955    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1956      <organization abbrev="Day Software">Day Software</organization>
1957      <address><email>fielding@gbiv.com</email></address>
1958    </author>
1959    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1960      <organization>One Laptop per Child</organization>
1961      <address><email>jg@laptop.org</email></address>
1962    </author>
1963    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1964      <organization abbrev="HP">Hewlett-Packard Company</organization>
1965      <address><email>JeffMogul@acm.org</email></address>
1966    </author>
1967    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1968      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1969      <address><email>henrikn@microsoft.com</email></address>
1970    </author>
1971    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1972      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1973      <address><email>LMM@acm.org</email></address>
1974    </author>
1975    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1976      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1977      <address><email>paulle@microsoft.com</email></address>
1978    </author>
1979    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1980      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1981      <address><email>timbl@w3.org</email></address>
1982    </author>
1983    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1984      <organization abbrev="W3C">World Wide Web Consortium</organization>
1985      <address><email>ylafon@w3.org</email></address>
1986    </author>
1987    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1988      <address><email>mnot@mnot.net</email></address>
1989    </author>
1990    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1991      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1992      <address><email>julian.reschke@greenbytes.de</email></address>
1993    </author>
1994    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1995  </front>
1996  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1997  <x:source href="p6-cache.xml" basename="p6-cache"/>
1998</reference>
1999
2000<reference anchor="RFC1864">
2001  <front>
2002    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2003    <author initials="J." surname="Myers" fullname="John G. Myers">
2004      <organization>Carnegie Mellon University</organization>
2005      <address><email>jgm+@cmu.edu</email></address>
2006    </author>
2007    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2008      <organization>Dover Beach Consulting, Inc.</organization>
2009      <address><email>mrose@dbc.mtview.ca.us</email></address>
2010    </author>
2011    <date month="October" year="1995"/>
2012  </front>
2013  <seriesInfo name="RFC" value="1864"/>
2014</reference>
2015
2016<reference anchor="RFC1950">
2017  <front>
2018    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2019    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2020      <organization>Aladdin Enterprises</organization>
2021      <address><email>ghost@aladdin.com</email></address>
2022    </author>
2023    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2024    <date month="May" year="1996"/>
2025  </front>
2026  <seriesInfo name="RFC" value="1950"/>
2027  <annotation>
2028    RFC 1950 is an Informational RFC, thus it may be less stable than
2029    this specification. On the other hand, this downward reference was
2030    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2031    therefore it is unlikely to cause problems in practice. See also
2032    <xref target="BCP97"/>.
2033  </annotation>
2034</reference>
2035
2036<reference anchor="RFC1951">
2037  <front>
2038    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2039    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2040      <organization>Aladdin Enterprises</organization>
2041      <address><email>ghost@aladdin.com</email></address>
2042    </author>
2043    <date month="May" year="1996"/>
2044  </front>
2045  <seriesInfo name="RFC" value="1951"/>
2046  <annotation>
2047    RFC 1951 is an Informational RFC, thus it may be less stable than
2048    this specification. On the other hand, this downward reference was
2049    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2050    therefore it is unlikely to cause problems in practice. See also
2051    <xref target="BCP97"/>.
2052  </annotation>
2053</reference>
2054
2055<reference anchor="RFC1952">
2056  <front>
2057    <title>GZIP file format specification version 4.3</title>
2058    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2059      <organization>Aladdin Enterprises</organization>
2060      <address><email>ghost@aladdin.com</email></address>
2061    </author>
2062    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2063      <address><email>gzip@prep.ai.mit.edu</email></address>
2064    </author>
2065    <author initials="M." surname="Adler" fullname="Mark Adler">
2066      <address><email>madler@alumni.caltech.edu</email></address>
2067    </author>
2068    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2069      <address><email>ghost@aladdin.com</email></address>
2070    </author>
2071    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2072      <address><email>randeg@alumni.rpi.edu</email></address>
2073    </author>
2074    <date month="May" year="1996"/>
2075  </front>
2076  <seriesInfo name="RFC" value="1952"/>
2077  <annotation>
2078    RFC 1952 is an Informational RFC, thus it may be less stable than
2079    this specification. On the other hand, this downward reference was
2080    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2081    therefore it is unlikely to cause problems in practice. See also
2082    <xref target="BCP97"/>.
2083  </annotation>
2084</reference>
2085
2086<reference anchor="RFC2045">
2087  <front>
2088    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2089    <author initials="N." surname="Freed" fullname="Ned Freed">
2090      <organization>Innosoft International, Inc.</organization>
2091      <address><email>ned@innosoft.com</email></address>
2092    </author>
2093    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2094      <organization>First Virtual Holdings</organization>
2095      <address><email>nsb@nsb.fv.com</email></address>
2096    </author>
2097    <date month="November" year="1996"/>
2098  </front>
2099  <seriesInfo name="RFC" value="2045"/>
2100</reference>
2101
2102<reference anchor="RFC2046">
2103  <front>
2104    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2105    <author initials="N." surname="Freed" fullname="Ned Freed">
2106      <organization>Innosoft International, Inc.</organization>
2107      <address><email>ned@innosoft.com</email></address>
2108    </author>
2109    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2110      <organization>First Virtual Holdings</organization>
2111      <address><email>nsb@nsb.fv.com</email></address>
2112    </author>
2113    <date month="November" year="1996"/>
2114  </front>
2115  <seriesInfo name="RFC" value="2046"/>
2116</reference>
2117
2118<reference anchor="RFC2119">
2119  <front>
2120    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2121    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2122      <organization>Harvard University</organization>
2123      <address><email>sob@harvard.edu</email></address>
2124    </author>
2125    <date month="March" year="1997"/>
2126  </front>
2127  <seriesInfo name="BCP" value="14"/>
2128  <seriesInfo name="RFC" value="2119"/>
2129</reference>
2130
2131<reference anchor='RFC4647'>
2132  <front>
2133    <title>Matching of Language Tags</title>
2134    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2135      <organization>Yahoo! Inc.</organization>
2136      <address><email>addison@inter-locale.com</email></address>
2137    </author>
2138    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2139      <organization>Google</organization>
2140      <address><email>mark.davis@macchiato.com</email></address>
2141    </author>
2142    <date year='2006' month='September' />
2143  </front>
2144  <seriesInfo name='BCP' value='47' />
2145  <seriesInfo name='RFC' value='4647' />
2146</reference>
2147
2148<reference anchor="RFC5234">
2149  <front>
2150    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2151    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2152      <organization>Brandenburg InternetWorking</organization>
2153      <address>
2154        <email>dcrocker@bbiw.net</email>
2155      </address> 
2156    </author>
2157    <author initials="P." surname="Overell" fullname="Paul Overell">
2158      <organization>THUS plc.</organization>
2159      <address>
2160        <email>paul.overell@thus.net</email>
2161      </address>
2162    </author>
2163    <date month="January" year="2008"/>
2164  </front>
2165  <seriesInfo name="STD" value="68"/>
2166  <seriesInfo name="RFC" value="5234"/>
2167</reference>
2168
2169<reference anchor='RFC5646'>
2170  <front>
2171    <title>Tags for Identifying Languages</title>
2172    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2173      <organization>Lab126</organization>
2174      <address><email>addison@inter-locale.com</email></address>
2175    </author>
2176    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2177      <organization>Google</organization>
2178      <address><email>mark.davis@google.com</email></address>
2179    </author>
2180    <date month='September' year='2009' />
2181  </front>
2182  <seriesInfo name='BCP' value='47' />
2183  <seriesInfo name='RFC' value='5646' />
2184</reference>
2185
2186</references>
2187
2188<references title="Informative References">
2189
2190<reference anchor="RFC1945">
2191  <front>
2192    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2193    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2194      <organization>MIT, Laboratory for Computer Science</organization>
2195      <address><email>timbl@w3.org</email></address>
2196    </author>
2197    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2198      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2199      <address><email>fielding@ics.uci.edu</email></address>
2200    </author>
2201    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2202      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2203      <address><email>frystyk@w3.org</email></address>
2204    </author>
2205    <date month="May" year="1996"/>
2206  </front>
2207  <seriesInfo name="RFC" value="1945"/>
2208</reference>
2209
2210<reference anchor="RFC2049">
2211  <front>
2212    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2213    <author initials="N." surname="Freed" fullname="Ned Freed">
2214      <organization>Innosoft International, Inc.</organization>
2215      <address><email>ned@innosoft.com</email></address>
2216    </author>
2217    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2218      <organization>First Virtual Holdings</organization>
2219      <address><email>nsb@nsb.fv.com</email></address>
2220    </author>
2221    <date month="November" year="1996"/>
2222  </front>
2223  <seriesInfo name="RFC" value="2049"/>
2224</reference>
2225
2226<reference anchor="RFC2068">
2227  <front>
2228    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2229    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2230      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2231      <address><email>fielding@ics.uci.edu</email></address>
2232    </author>
2233    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2234      <organization>MIT Laboratory for Computer Science</organization>
2235      <address><email>jg@w3.org</email></address>
2236    </author>
2237    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2238      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2239      <address><email>mogul@wrl.dec.com</email></address>
2240    </author>
2241    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2242      <organization>MIT Laboratory for Computer Science</organization>
2243      <address><email>frystyk@w3.org</email></address>
2244    </author>
2245    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2246      <organization>MIT Laboratory for Computer Science</organization>
2247      <address><email>timbl@w3.org</email></address>
2248    </author>
2249    <date month="January" year="1997"/>
2250  </front>
2251  <seriesInfo name="RFC" value="2068"/>
2252</reference>
2253
2254<reference anchor="RFC2076">
2255  <front>
2256    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2257    <author initials="J." surname="Palme" fullname="Jacob Palme">
2258      <organization>Stockholm University/KTH</organization>
2259      <address><email>jpalme@dsv.su.se</email></address>
2260    </author>
2261    <date month="February" year="1997"/>
2262  </front>
2263  <seriesInfo name="RFC" value="2076"/>
2264</reference>
2265
2266<reference anchor="RFC2183">
2267  <front>
2268    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2269    <author initials="R." surname="Troost" fullname="Rens Troost">
2270      <organization>New Century Systems</organization>
2271      <address><email>rens@century.com</email></address>
2272    </author>
2273    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2274      <organization>QUALCOMM Incorporated</organization>
2275      <address><email>sdorner@qualcomm.com</email></address>
2276    </author>
2277    <author initials="K." surname="Moore" fullname="Keith Moore">
2278      <organization>Department of Computer Science</organization>
2279      <address><email>moore@cs.utk.edu</email></address>
2280    </author>
2281    <date month="August" year="1997"/>
2282  </front>
2283  <seriesInfo name="RFC" value="2183"/>
2284</reference>
2285
2286<reference anchor="RFC2277">
2287  <front>
2288    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2289    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2290      <organization>UNINETT</organization>
2291      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2292    </author>
2293    <date month="January" year="1998"/>
2294  </front>
2295  <seriesInfo name="BCP" value="18"/>
2296  <seriesInfo name="RFC" value="2277"/>
2297</reference>
2298
2299<reference anchor='RFC2295'>
2300  <front>
2301    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2302    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2303      <organization>Technische Universiteit Eindhoven</organization>
2304      <address>
2305        <email>koen@win.tue.nl</email>
2306      </address>
2307    </author>
2308    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2309      <organization>Hewlett-Packard Company</organization>
2310      <address>
2311        <email>mutz@hpl.hp.com</email>
2312      </address>
2313    </author>
2314    <date year='1998' month='March'/>
2315  </front>
2316  <seriesInfo name='RFC' value='2295'/>
2317</reference>
2318
2319<reference anchor="RFC2388">
2320  <front>
2321    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2322    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2323      <organization>Xerox Palo Alto Research Center</organization>
2324      <address><email>masinter@parc.xerox.com</email></address>
2325    </author>
2326    <date year="1998" month="August"/>
2327  </front>
2328  <seriesInfo name="RFC" value="2388"/>
2329</reference>
2330
2331<reference anchor="RFC2557">
2332  <front>
2333    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2334    <author initials="F." surname="Palme" fullname="Jacob Palme">
2335      <organization>Stockholm University and KTH</organization>
2336      <address><email>jpalme@dsv.su.se</email></address>
2337    </author>
2338    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2339      <organization>Microsoft Corporation</organization>
2340      <address><email>alexhop@microsoft.com</email></address>
2341    </author>
2342    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2343      <organization>Lotus Development Corporation</organization>
2344      <address><email>Shelness@lotus.com</email></address>
2345    </author>
2346    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2347      <address><email>stef@nma.com</email></address>
2348    </author>
2349    <date year="1999" month="March"/>
2350  </front>
2351  <seriesInfo name="RFC" value="2557"/>
2352</reference>
2353
2354<reference anchor="RFC2616">
2355  <front>
2356    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2357    <author initials="R." surname="Fielding" fullname="R. Fielding">
2358      <organization>University of California, Irvine</organization>
2359      <address><email>fielding@ics.uci.edu</email></address>
2360    </author>
2361    <author initials="J." surname="Gettys" fullname="J. Gettys">
2362      <organization>W3C</organization>
2363      <address><email>jg@w3.org</email></address>
2364    </author>
2365    <author initials="J." surname="Mogul" fullname="J. Mogul">
2366      <organization>Compaq Computer Corporation</organization>
2367      <address><email>mogul@wrl.dec.com</email></address>
2368    </author>
2369    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2370      <organization>MIT Laboratory for Computer Science</organization>
2371      <address><email>frystyk@w3.org</email></address>
2372    </author>
2373    <author initials="L." surname="Masinter" fullname="L. Masinter">
2374      <organization>Xerox Corporation</organization>
2375      <address><email>masinter@parc.xerox.com</email></address>
2376    </author>
2377    <author initials="P." surname="Leach" fullname="P. Leach">
2378      <organization>Microsoft Corporation</organization>
2379      <address><email>paulle@microsoft.com</email></address>
2380    </author>
2381    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2382      <organization>W3C</organization>
2383      <address><email>timbl@w3.org</email></address>
2384    </author>
2385    <date month="June" year="1999"/>
2386  </front>
2387  <seriesInfo name="RFC" value="2616"/>
2388</reference>
2389
2390<reference anchor="RFC3629">
2391  <front>
2392    <title>UTF-8, a transformation format of ISO 10646</title>
2393    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2394      <organization>Alis Technologies</organization>
2395      <address><email>fyergeau@alis.com</email></address>
2396    </author>
2397    <date month="November" year="2003"/>
2398  </front>
2399  <seriesInfo name="RFC" value="3629"/>
2400  <seriesInfo name="STD" value="63"/>
2401</reference>
2402
2403<reference anchor='RFC3864'>
2404  <front>
2405    <title>Registration Procedures for Message Header Fields</title>
2406    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2407      <organization>Nine by Nine</organization>
2408      <address><email>GK-IETF@ninebynine.org</email></address>
2409    </author>
2410    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2411      <organization>BEA Systems</organization>
2412      <address><email>mnot@pobox.com</email></address>
2413    </author>
2414    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2415      <organization>HP Labs</organization>
2416      <address><email>JeffMogul@acm.org</email></address>
2417    </author>
2418    <date year='2004' month='September' />
2419  </front>
2420  <seriesInfo name='BCP' value='90' />
2421  <seriesInfo name='RFC' value='3864' />
2422</reference>
2423
2424<reference anchor="RFC4288">
2425  <front>
2426    <title>Media Type Specifications and Registration Procedures</title>
2427    <author initials="N." surname="Freed" fullname="N. Freed">
2428      <organization>Sun Microsystems</organization>
2429      <address>
2430        <email>ned.freed@mrochek.com</email>
2431      </address>
2432    </author>
2433    <author initials="J." surname="Klensin" fullname="J. Klensin">
2434      <address>
2435        <email>klensin+ietf@jck.com</email>
2436      </address>
2437    </author>
2438    <date year="2005" month="December"/>
2439  </front>
2440  <seriesInfo name="BCP" value="13"/>
2441  <seriesInfo name="RFC" value="4288"/>
2442</reference>
2443
2444<reference anchor='RFC5226'>
2445  <front>
2446    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2447    <author initials='T.' surname='Narten' fullname='T. Narten'>
2448      <organization>IBM</organization>
2449      <address><email>narten@us.ibm.com</email></address>
2450    </author>
2451    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2452      <organization>Google</organization>
2453      <address><email>Harald@Alvestrand.no</email></address>
2454    </author>
2455    <date year='2008' month='May' />
2456  </front>
2457  <seriesInfo name='BCP' value='26' />
2458  <seriesInfo name='RFC' value='5226' />
2459</reference>
2460
2461<reference anchor="RFC5322">
2462  <front>
2463    <title>Internet Message Format</title>
2464    <author initials="P." surname="Resnick" fullname="P. Resnick">
2465      <organization>Qualcomm Incorporated</organization>
2466    </author>
2467    <date year="2008" month="October"/>
2468  </front> 
2469  <seriesInfo name="RFC" value="5322"/>
2470</reference>
2471
2472<reference anchor='BCP97'>
2473  <front>
2474    <title>Handling Normative References to Standards-Track Documents</title>
2475    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2476      <address>
2477        <email>klensin+ietf@jck.com</email>
2478      </address>
2479    </author>
2480    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2481      <organization>MIT</organization>
2482      <address>
2483        <email>hartmans-ietf@mit.edu</email>
2484      </address>
2485    </author>
2486    <date year='2007' month='June' />
2487  </front>
2488  <seriesInfo name='BCP' value='97' />
2489  <seriesInfo name='RFC' value='4897' />
2490</reference>
2491
2492
2493</references>
2494
2495<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2496<t>
2497   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
2498   allow entities to be transmitted in an open variety of
2499   representations and with extensible mechanisms. However, RFC 2045
2500   discusses mail, and HTTP has a few features that are different from
2501   those described in RFC 2045. These differences were carefully chosen
2502   to optimize performance over binary connections, to allow greater
2503   freedom in the use of new media types, to make date comparisons
2504   easier, and to acknowledge the practice of some early HTTP servers
2505   and clients.
2506</t>
2507<t>
2508   This appendix describes specific areas where HTTP differs from RFC
2509   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2510   aware of these differences and provide the appropriate conversions
2511   where necessary. Proxies and gateways from MIME environments to HTTP
2512   also need to be aware of the differences because some conversions
2513   might be required.
2514</t>
2515
2516<section title="MIME-Version" anchor="mime-version">
2517  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2518  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2519  <x:anchor-alias value="MIME-Version"/>
2520  <x:anchor-alias value="MIME-Version-v"/>
2521<t>
2522   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2523   include a single MIME-Version general-header field to indicate what
2524   version of the MIME protocol was used to construct the message. Use
2525   of the MIME-Version header field indicates that the message is in
2526   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2527   Proxies/gateways are responsible for ensuring full compliance (where
2528   possible) when exporting HTTP messages to strict MIME environments.
2529</t>
2530<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2531  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2532  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2533</artwork></figure>
2534<t>
2535   MIME version "1.0" is the default for use in HTTP/1.1. However,
2536   HTTP/1.1 message parsing and semantics are defined by this document
2537   and not the MIME specification.
2538</t>
2539</section>
2540
2541<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2542<t>
2543   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2544   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2545   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2546   allowed for subtypes of the "text" media type when transmitted over
2547   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2548   line breaks as CRLF and forbids the use of CR or LF outside of line
2549   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2550   line break within text content when a message is transmitted over
2551   HTTP.
2552</t>
2553<t>
2554   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2555   environment &SHOULD; translate all line breaks within the text media
2556   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2557   canonical form of CRLF. Note, however, that this might be complicated
2558   by the presence of a Content-Encoding and by the fact that HTTP
2559   allows the use of some character sets which do not use octets 13 and
2560   10 to represent CR and LF, as is the case for some multi-byte
2561   character sets.
2562</t>
2563<t>
2564   Implementors should note that conversion will break any cryptographic
2565   checksums applied to the original content unless the original content
2566   is already in canonical form. Therefore, the canonical form is
2567   recommended for any content that uses such checksums in HTTP.
2568</t>
2569</section>
2570
2571
2572<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2573<t>
2574   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2575   simplify the process of date comparison. Proxies and gateways from
2576   other protocols &SHOULD; ensure that any Date header field present in a
2577   message conforms to one of the HTTP/1.1 formats and rewrite the date
2578   if necessary.
2579</t>
2580</section>
2581
2582<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2583<t>
2584   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2585   Content-Encoding header field. Since this acts as a modifier on the
2586   media type, proxies and gateways from HTTP to MIME-compliant
2587   protocols &MUST; either change the value of the Content-Type header
2588   field or decode the entity-body before forwarding the message. (Some
2589   experimental applications of Content-Type for Internet mail have used
2590   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2591   a function equivalent to Content-Encoding. However, this parameter is
2592   not part of RFC 2045).
2593</t>
2594</section>
2595
2596<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2597<t>
2598   HTTP does not use the Content-Transfer-Encoding field of RFC
2599   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2600   remove any Content-Transfer-Encoding
2601   prior to delivering the response message to an HTTP client.
2602</t>
2603<t>
2604   Proxies and gateways from HTTP to MIME-compliant protocols are
2605   responsible for ensuring that the message is in the correct format
2606   and encoding for safe transport on that protocol, where "safe
2607   transport" is defined by the limitations of the protocol being used.
2608   Such a proxy or gateway &SHOULD; label the data with an appropriate
2609   Content-Transfer-Encoding if doing so will improve the likelihood of
2610   safe transport over the destination protocol.
2611</t>
2612</section>
2613
2614<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2615<t>
2616   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2617   Proxies/gateways &MUST; remove any transfer-coding prior to
2618   forwarding a message via a MIME-compliant protocol.
2619</t>
2620</section>
2621
2622<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2623<t>
2624   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2625   need to be aware of MIME line length limitations. Since HTTP does not
2626   have this limitation, HTTP does not fold long lines. MHTML messages
2627   being transported by HTTP follow all conventions of MHTML, including
2628   line length limitations and folding, canonicalization, etc., since
2629   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2630   does not interpret the content or any MIME header lines that might be
2631   contained therein.
2632</t>
2633</section>
2634</section>
2635
2636<section title="Additional Features" anchor="additional.features">
2637<t>
2638   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2639   existing HTTP implementations, but not consistently and correctly
2640   across most HTTP/1.1 applications. Implementors are advised to be
2641   aware of these features, but cannot rely upon their presence in, or
2642   interoperability with, other HTTP/1.1 applications. Some of these
2643   describe proposed experimental features, and some describe features
2644   that experimental deployment found lacking that are now addressed in
2645   the base HTTP/1.1 specification.
2646</t>
2647<t>
2648   A number of other headers, such as Content-Disposition and Title,
2649   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2650</t>
2651
2652<section title="Content-Disposition" anchor="content-disposition">
2653<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2654<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2655  <x:anchor-alias value="content-disposition"/>
2656  <x:anchor-alias value="content-disposition-v"/>
2657  <x:anchor-alias value="disposition-type"/>
2658  <x:anchor-alias value="disposition-parm"/>
2659  <x:anchor-alias value="disp-extension-parm"/>
2660  <x:anchor-alias value="disp-extension-token"/>
2661  <x:anchor-alias value="filename-parm"/>
2662<t>
2663   The "Content-Disposition" response-header field has been proposed as a
2664   means for the origin server to suggest a default filename if the user
2665   requests that the content is saved to a file. This usage is derived
2666   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2667</t>
2668<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"/>
2669  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2670                        <x:ref>content-disposition-v</x:ref>
2671  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2672                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2673  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2674  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2675  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2676  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2677  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2678</artwork></figure>
2679<t>
2680   An example is
2681</t>
2682<figure><artwork type="example">
2683  Content-Disposition: attachment; filename="fname.ext"
2684</artwork></figure>
2685<t>
2686   The receiving user agent &SHOULD-NOT;  respect any directory path
2687   information present in the filename-parm parameter, which is the only
2688   parameter believed to apply to HTTP implementations at this time. The
2689   filename &SHOULD; be treated as a terminal component only.
2690</t>
2691<t>
2692   If this header is used in a response with the application/octet-stream
2693   content-type, the implied suggestion is that the user agent
2694   should not display the response, but directly enter a "save response
2695   as..." dialog.
2696</t>
2697<t>
2698   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2699</t>
2700</section>
2701</section>
2702
2703<section title="Compatibility with Previous Versions" anchor="compatibility">
2704<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2705<t>
2706   Transfer-coding and message lengths all interact in ways that
2707   required fixing exactly when chunked encoding is used (to allow for
2708   transfer encoding that may not be self delimiting); it was important
2709   to straighten out exactly how message lengths are computed.
2710   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2711   <xref target="Part5"/> and <xref target="Part6"/>).
2712</t>
2713<t>
2714   Charset wildcarding is introduced to avoid explosion of character set
2715   names in accept headers. (<xref target="header.accept-charset"/>)
2716</t>
2717<t>
2718   Content-Base was deleted from the specification: it was not
2719   implemented widely, and there is no simple, safe way to introduce it
2720   without a robust extension mechanism. In addition, it is used in a
2721   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2722</t>
2723<t>
2724   A content-coding of "identity" was introduced, to solve problems
2725   discovered in caching. (<xref target="content.codings"/>)
2726</t>
2727<t>
2728   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
2729   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
2730   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2731</t>
2732</section>
2733
2734<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2735<t>
2736  Clarify contexts that charset is used in.
2737  (<xref target="character.sets"/>)
2738</t>
2739<t>
2740  Remove base URI setting semantics for Content-Location due to poor
2741  implementation support, which was caused by too many broken servers emitting
2742  bogus Content-Location headers, and also the potentially undesirable effect
2743  of potentially breaking relative links in content-negotiated resources.
2744  (<xref target="header.content-location"/>)
2745</t>
2746<t>
2747  Remove reference to non-existant identity transfer-coding value tokens.
2748  (<xref target="no.content-transfer-encoding"/>)
2749</t>
2750</section>
2751
2752</section>
2753
2754<?BEGININC p3-payload.abnf-appendix ?>
2755<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2756<figure>
2757<artwork type="abnf" name="p3-payload.parsed-abnf">
2758<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2759<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2760<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2761 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2762 qvalue ] ] )
2763<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2764<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2765 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2766<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2767<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2768 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2769 ] )
2770<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2771 OWS media-range [ accept-params ] ] ) ]
2772
2773<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2774<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2775 content-coding ] )
2776<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2777<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2778 language-tag ] )
2779<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2780<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2781<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2782<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2783<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2784<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2785<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2786<x:ref>Content-Type-v</x:ref> = media-type
2787
2788<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2789
2790<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2791
2792<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2793<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2794
2795<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2796
2797<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2798<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2799<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2800<x:ref>attribute</x:ref> = token
2801
2802<x:ref>charset</x:ref> = token
2803<x:ref>codings</x:ref> = ( content-coding / "*" )
2804<x:ref>content-coding</x:ref> = token
2805<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2806 content-disposition-v
2807<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2808 disposition-parm )
2809
2810<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2811<x:ref>disp-extension-token</x:ref> = token
2812<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2813<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2814
2815<x:ref>entity-body</x:ref> = *OCTET
2816<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2817 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2818 Expires / Last-Modified / extension-header
2819<x:ref>extension-header</x:ref> = header-field
2820
2821<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2822
2823<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2824
2825<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2826<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2827
2828<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2829 ";" OWS parameter )
2830<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2831
2832<x:ref>parameter</x:ref> = attribute "=" value
2833<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2834
2835<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2836<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2837
2838<x:ref>subtype</x:ref> = token
2839
2840<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2841<x:ref>type</x:ref> = token
2842
2843<x:ref>value</x:ref> = token / quoted-string
2844</artwork>
2845</figure>
2846<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2847; Accept defined but not used
2848; Accept-Charset defined but not used
2849; Accept-Encoding defined but not used
2850; Accept-Language defined but not used
2851; MIME-Version defined but not used
2852; content-disposition defined but not used
2853; entity-body defined but not used
2854; entity-header defined but not used
2855</artwork></figure></section>
2856<?ENDINC p3-payload.abnf-appendix ?>
2857
2858<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2859
2860<section title="Since RFC2616">
2861<t>
2862  Extracted relevant partitions from <xref target="RFC2616"/>.
2863</t>
2864</section>
2865
2866<section title="Since draft-ietf-httpbis-p3-payload-00">
2867<t>
2868  Closed issues:
2869  <list style="symbols"> 
2870    <t>
2871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2872      "Media Type Registrations"
2873      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2874    </t>
2875    <t>
2876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2877      "Clarification regarding quoting of charset values"
2878      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2879    </t>
2880    <t>
2881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2882      "Remove 'identity' token references"
2883      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2884    </t>
2885    <t>
2886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2887      "Accept-Encoding BNF"
2888    </t>
2889    <t>
2890      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2891      "Normative and Informative references"
2892    </t>
2893    <t>
2894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2895      "RFC1700 references"
2896    </t>
2897    <t>
2898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2899      "Updating to RFC4288"
2900    </t>
2901    <t>
2902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2903      "Informative references"
2904    </t>
2905    <t>
2906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2907      "ISO-8859-1 Reference"
2908    </t>
2909    <t>
2910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2911      "Encoding References Normative"
2912    </t>
2913    <t>
2914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2915      "Normative up-to-date references"
2916    </t>
2917  </list>
2918</t>
2919</section>
2920
2921<section title="Since draft-ietf-httpbis-p3-payload-01">
2922<t>
2923  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2924  <list style="symbols"> 
2925    <t>
2926      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2927    </t>
2928  </list>
2929</t>
2930</section>
2931
2932<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2933<t>
2934  Closed issues:
2935  <list style="symbols"> 
2936    <t>
2937      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2938      "Quoting Charsets"
2939    </t>
2940    <t>
2941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2942      "Classification for Allow header"
2943    </t>
2944    <t>
2945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2946      "missing default for qvalue in description of Accept-Encoding"
2947    </t>
2948  </list>
2949</t>
2950<t>
2951  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2952  <list style="symbols"> 
2953    <t>
2954      Reference RFC 3984, and update header registrations for headers defined
2955      in this document.
2956    </t>
2957  </list>
2958</t>
2959</section>
2960
2961<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2962<t>
2963  Closed issues:
2964  <list style="symbols"> 
2965    <t>
2966      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2967      "Quoting Charsets"
2968    </t>
2969    <t>
2970      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2971      "language tag matching (Accept-Language) vs RFC4647"
2972    </t>
2973    <t>
2974      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2975      "RFC 1806 has been replaced by RFC2183"
2976    </t>
2977  </list>
2978</t>
2979<t>
2980  Other changes:
2981  <list style="symbols"> 
2982    <t>
2983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2984      "Encoding References Normative" -- rephrase the annotation and reference
2985      <xref target="BCP97"/>.
2986    </t>
2987  </list>
2988</t>
2989 </section>
2990
2991<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2992<t>
2993  Closed issues:
2994  <list style="symbols"> 
2995    <t>
2996      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2997      "RFC 2822 is updated by RFC 5322"
2998    </t>
2999  </list>
3000</t>
3001<t>
3002  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3003  <list style="symbols"> 
3004    <t>
3005      Use "/" instead of "|" for alternatives.
3006    </t>
3007    <t>
3008      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3009      whitespace ("OWS") and required whitespace ("RWS").
3010    </t>
3011    <t>
3012      Rewrite ABNFs to spell out whitespace rules, factor out
3013      header value format definitions.
3014    </t>
3015  </list>
3016</t>
3017</section>
3018
3019<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3020<t>
3021  Closed issues:
3022  <list style="symbols"> 
3023    <t>
3024      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3025      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3026    </t>
3027  </list>
3028</t>
3029<t>
3030  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3031  <list style="symbols"> 
3032    <t>
3033      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3034    </t>
3035  </list>
3036</t>
3037<t>
3038  Other changes:
3039  <list style="symbols"> 
3040    <t>
3041      Move definition of quality values into Part 1.
3042    </t>
3043  </list>
3044</t>
3045</section>
3046
3047<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3048<t>
3049  Closed issues:
3050  <list style="symbols"> 
3051    <t>
3052      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3053      "Content-Location isn't special"
3054    </t>
3055    <t>
3056      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3057      "Content Sniffing"
3058    </t>
3059  </list>
3060</t>
3061</section>
3062
3063<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3064<t>
3065  Closed issues:
3066  <list style="symbols"> 
3067    <t>
3068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3069      "Updated reference for language tags"
3070    </t>
3071    <t>
3072      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3073      "Clarify rules for determining what entities a response carries"
3074    </t>
3075    <t>
3076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3077      "Content-Location base-setting problems"
3078    </t>
3079    <t>
3080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3081      "Content Sniffing"
3082    </t>
3083    <t>
3084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3085      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3086    </t>
3087    <t>
3088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3089      "move definitions of gzip/deflate/compress to part 1"
3090    </t>
3091  </list>
3092</t>
3093<t>
3094  Partly resolved issues:
3095  <list style="symbols"> 
3096    <t>
3097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3098      "update IANA requirements wrt Transfer-Coding values" (add the
3099      IANA Considerations subsection)
3100    </t>
3101    <t>
3102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3103      "update IANA requirements wrt Content-Coding values" (add the
3104      IANA Considerations subsection)
3105    </t>
3106  </list>
3107</t>
3108</section>
3109
3110<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3111<t>
3112  Closed issues:
3113  <list style="symbols"> 
3114    <t>
3115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3116      "Content Negotiation for media types"
3117    </t>
3118    <t>
3119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3120      "Accept-Language: which RFC4647 filtering?"
3121    </t>
3122  </list>
3123</t>
3124</section>
3125
3126<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3127<t>
3128  None yet.
3129</t>
3130</section>
3131
3132</section>
3133
3134</back>
3135</rfc>
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