source: draft-ietf-httpbis/latest/p3-payload.xml @ 741

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Update to latest version of xml2rfc and rfc2629.xslt, bump document dates

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