source: draft-ietf-httpbis/latest/p3-payload.xml @ 763

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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 "February">
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   HTTP responses include a representation which contains information for
810   interpretation, whether by a human user or for further processing.
811   Often, the server has different ways of representing the
812   same information; for example, in different formats, languages,
813   or using different character encodings.
814</t>
815<t>
816   HTTP clients and their users might have different or variable
817   capabilities, characteristics or preferences which would influence
818   which representation, among those available from the server,
819   would be best for the server to deliver. For this reason, HTTP
820   provides mechanisms for "content negotiation" -- a process of
821   allowing selection of a representation of a given resource,
822   when more than one is available.
823</t>
824<t>
825   This specification defines two patterns of content negotiation;
826   "server-driven", where the server selects the representation based
827   upon the client's stated preferences, and "agent-driven" negotiation,
828   where the server provides a list of representations for the client to
829   choose from, based upon their metadata. In addition,  there are
830   other patterns: some applications use an "active content" pattern,
831   where the server returns active content which runs on the client
832   and, based on client available parameters, selects additional
833   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
834   has also been proposed.
835</t>
836<t>
837   These patterns are all widely used, and have trade-offs in applicability
838   and practicality. In particular, when the number of preferences or
839   capabilities to be expressed by a client are large (such as when many
840   different formats are supported by a user-agent), server-driven
841   negotiation becomes unwieldy, and may not be appropriate. Conversely,
842   when the number of representations to choose from is very large,
843   agent-driven negotiation may not be appropriate.
844</t>
845<t>
846   Note that in all cases, the supplier of representations has the
847   responsibility for determining which representations might be
848   considered to be the "same information".
849</t>
850
851<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
852<t>
853   If the selection of the best representation for a response is made by
854   an algorithm located at the server, it is called server-driven
855   negotiation. Selection is based on the available representations of
856   the response (the dimensions over which it can vary; e.g., language,
857   content-coding, etc.) and the contents of particular header fields in
858   the request message or on other information pertaining to the request
859   (such as the network address of the client).
860</t>
861<t>
862   Server-driven negotiation is advantageous when the algorithm for
863   selecting from among the available representations is difficult to
864   describe to the user agent, or when the server desires to send its
865   "best guess" to the client along with the first response (hoping to
866   avoid the round-trip delay of a subsequent request if the "best
867   guess" is good enough for the user). In order to improve the server's
868   guess, the user agent &MAY; include request header fields (Accept,
869   Accept-Language, Accept-Encoding, etc.) which describe its
870   preferences for such a response.
871</t>
872<t>
873   Server-driven negotiation has disadvantages:
874  <list style="numbers">
875    <t>
876         It is impossible for the server to accurately determine what
877         might be "best" for any given user, since that would require
878         complete knowledge of both the capabilities of the user agent
879         and the intended use for the response (e.g., does the user want
880         to view it on screen or print it on paper?).
881    </t>
882    <t>
883         Having the user agent describe its capabilities in every
884         request can be both very inefficient (given that only a small
885         percentage of responses have multiple representations) and a
886         potential violation of the user's privacy.
887    </t>
888    <t>
889         It complicates the implementation of an origin server and the
890         algorithms for generating responses to a request.
891    </t>
892    <t>
893         It may limit a public cache's ability to use the same response
894         for multiple user's requests.
895    </t>
896  </list>
897</t>
898<t>
899   HTTP/1.1 includes the following request-header fields for enabling
900   server-driven negotiation through description of user agent
901   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
902   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
903   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
904   However, an origin server is not limited to these dimensions and &MAY; vary
905   the response based on any aspect of the request, including information
906   outside the request-header fields or within extension header fields
907   not defined by this specification.
908</t>
909<x:note>
910  <t>
911    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
912    because new clients might not be recognized.
913  </t>
914</x:note>
915<t>
916   The Vary header field (&header-vary;) can be used to express the parameters the
917   server uses to select a representation that is subject to server-driven
918   negotiation.
919</t>
920</section>
921
922<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
923<t>
924   With agent-driven negotiation, selection of the best representation
925   for a response is performed by the user agent after receiving an
926   initial response from the origin server. Selection is based on a list
927   of the available representations of the response included within the
928   header fields or entity-body of the initial response, with each
929   representation identified by its own URI. Selection from among the
930   representations may be performed automatically (if the user agent is
931   capable of doing so) or manually by the user selecting from a
932   generated (possibly hypertext) menu.
933</t>
934<t>
935   Agent-driven negotiation is advantageous when the response would vary
936   over commonly-used dimensions (such as type, language, or encoding),
937   when the origin server is unable to determine a user agent's
938   capabilities from examining the request, and generally when public
939   caches are used to distribute server load and reduce network usage.
940</t>
941<t>
942   Agent-driven negotiation suffers from the disadvantage of needing a
943   second request to obtain the best alternate representation. This
944   second request is only efficient when caching is used. In addition,
945   this specification does not define any mechanism for supporting
946   automatic selection, though it also does not prevent any such
947   mechanism from being developed as an extension and used within
948   HTTP/1.1.
949</t>
950<t>
951   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
952   status codes for enabling agent-driven negotiation when the server is
953   unwilling or unable to provide a varying response using server-driven
954   negotiation.
955</t>
956</section>
957</section>
958
959<section title="Header Field Definitions" anchor="header.fields">
960<t>
961   This section defines the syntax and semantics of HTTP/1.1 header fields
962   related to the payload of messages.
963</t>
964<t>
965   For entity-header fields, both sender and recipient refer to either the
966   client or the server, depending on who sends and who receives the entity.
967</t>
968
969<section title="Accept" anchor="header.accept">
970  <iref primary="true" item="Accept header" x:for-anchor=""/>
971  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
972  <x:anchor-alias value="Accept"/>
973  <x:anchor-alias value="Accept-v"/>
974  <x:anchor-alias value="accept-ext"/>
975  <x:anchor-alias value="accept-params"/>
976  <x:anchor-alias value="media-range"/>
977<t>
978   The "Accept" request-header field can be used by user agents to specify
979   response media types that are acceptable. Accept headers can be used to
980   indicate that the request is specifically limited to a small set of desired
981   types, as in the case of a request for an in-line image.
982</t>
983<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"/>
984  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
985  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
986 
987  <x:ref>media-range</x:ref>    = ( "*/*"
988                   / ( <x:ref>type</x:ref> "/" "*" )
989                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
990                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
991  <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> )
992  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
993                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
994</artwork></figure>
995<t>
996   The asterisk "*" character is used to group media types into ranges,
997   with "*/*" indicating all media types and "type/*" indicating all
998   subtypes of that type. The media-range &MAY; include media type
999   parameters that are applicable to that range.
1000</t>
1001<t>
1002   Each media-range &MAY; be followed by one or more accept-params,
1003   beginning with the "q" parameter for indicating a relative quality
1004   factor. The first "q" parameter (if any) separates the media-range
1005   parameter(s) from the accept-params. Quality factors allow the user
1006   or user agent to indicate the relative degree of preference for that
1007   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1008   default value is q=1.
1009</t>
1010<x:note>
1011  <t>
1012    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1013    parameters from Accept extension parameters is due to historical
1014    practice. Although this prevents any media type parameter named
1015    "q" from being used with a media range, such an event is believed
1016    to be unlikely given the lack of any "q" parameters in the IANA
1017    media type registry and the rare usage of any media type
1018    parameters in Accept. Future media types are discouraged from
1019    registering any parameter named "q".
1020  </t>
1021</x:note>
1022<t>
1023   The example
1024</t>
1025<figure><artwork type="example">
1026  Accept: audio/*; q=0.2, audio/basic
1027</artwork></figure>
1028<t>
1029   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1030   type if it is the best available after an 80% mark-down in quality."
1031</t>
1032<t>
1033   If no Accept header field is present, then it is assumed that the
1034   client accepts all media types. If an Accept header field is present,
1035   and if the server cannot send a response which is acceptable
1036   according to the combined Accept field value, then the server &SHOULD;
1037   send a 406 (Not Acceptable) response.
1038</t>
1039<t>
1040   A more elaborate example is
1041</t>
1042<figure><artwork type="example">
1043  Accept: text/plain; q=0.5, text/html,
1044          text/x-dvi; q=0.8, text/x-c
1045</artwork></figure>
1046<t>
1047   Verbally, this would be interpreted as "text/html and text/x-c are
1048   the preferred media types, but if they do not exist, then send the
1049   text/x-dvi entity, and if that does not exist, send the text/plain
1050   entity."
1051</t>
1052<t>
1053   Media ranges can be overridden by more specific media ranges or
1054   specific media types. If more than one media range applies to a given
1055   type, the most specific reference has precedence. For example,
1056</t>
1057<figure><artwork type="example">
1058  Accept: text/*, text/html, text/html;level=1, */*
1059</artwork></figure>
1060<t>
1061   have the following precedence:
1062   <list style="numbers">
1063    <t>text/html;level=1</t>
1064    <t>text/html</t>
1065    <t>text/*</t>
1066    <t>*/*</t>
1067   </list>
1068</t>
1069<t>
1070   The media type quality factor associated with a given type is
1071   determined by finding the media range with the highest precedence
1072   which matches that type. For example,
1073</t>
1074<figure><artwork type="example">
1075  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1076          text/html;level=2;q=0.4, */*;q=0.5
1077</artwork></figure>
1078<t>
1079   would cause the following values to be associated:
1080</t>
1081<texttable align="left">
1082  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1083  <c>text/html;level=1</c>    <c>1</c>
1084  <c>text/html</c>            <c>0.7</c>
1085  <c>text/plain</c>           <c>0.3</c>
1086  <c>image/jpeg</c>           <c>0.5</c>
1087  <c>text/html;level=2</c>    <c>0.4</c>
1088  <c>text/html;level=3</c>    <c>0.7</c>
1089</texttable>
1090<t>
1091      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1092      values for certain media ranges. However, unless the user agent is
1093      a closed system which cannot interact with other rendering agents,
1094      this default set ought to be configurable by the user.
1095</t>
1096</section>
1097
1098<section title="Accept-Charset" anchor="header.accept-charset">
1099  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1100  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1101  <x:anchor-alias value="Accept-Charset"/>
1102  <x:anchor-alias value="Accept-Charset-v"/>
1103<t>
1104   The "Accept-Charset" request-header field can be used by user agents to
1105   indicate what response character sets are acceptable. This field allows
1106   clients capable of understanding more comprehensive or special-purpose
1107   character sets to signal that capability to a server which is capable of
1108   representing documents in those character sets.
1109</t>
1110<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1111  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1112          <x:ref>Accept-Charset-v</x:ref>
1113  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1114                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1115</artwork></figure>
1116<t>
1117   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1118   be given an associated quality value which represents the user's
1119   preference for that charset. The default value is q=1. An example is
1120</t>
1121<figure><artwork type="example">
1122  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1123</artwork></figure>
1124<t>
1125   The special value "*", if present in the Accept-Charset field,
1126   matches every character set (including ISO-8859-1) which is not
1127   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1128   in an Accept-Charset field, then all character sets not explicitly
1129   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1130   a quality value of 1 if not explicitly mentioned.
1131</t>
1132<t>
1133   If no Accept-Charset header is present, the default is that any
1134   character set is acceptable. If an Accept-Charset header is present,
1135   and if the server cannot send a response which is acceptable
1136   according to the Accept-Charset header, then the server &SHOULD; send
1137   an error response with the 406 (Not Acceptable) status code, though
1138   the sending of an unacceptable response is also allowed.
1139</t>
1140</section>
1141
1142<section title="Accept-Encoding" anchor="header.accept-encoding">
1143  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1144  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1145  <x:anchor-alias value="Accept-Encoding"/>
1146  <x:anchor-alias value="Accept-Encoding-v"/>
1147  <x:anchor-alias value="codings"/>
1148<t>
1149   The "Accept-Encoding" request-header field can be used by user agents to
1150   indicate what response content-codings (<xref target="content.codings"/>)
1151   are acceptable in the response.
1152</t>
1153<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"/>
1154  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1155                     <x:ref>Accept-Encoding-v</x:ref>
1156  <x:ref>Accept-Encoding-v</x:ref>  =
1157                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1158  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1159</artwork></figure>
1160<t>
1161   Each codings value &MAY; be given an associated quality value which
1162   represents the preference for that encoding. The default value is q=1.
1163</t>
1164<t>
1165   Examples of its use are:
1166</t>
1167<figure><artwork type="example">
1168  Accept-Encoding: compress, gzip
1169  Accept-Encoding:
1170  Accept-Encoding: *
1171  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1172  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1173</artwork></figure>
1174<t>
1175   A server tests whether a content-coding is acceptable, according to
1176   an Accept-Encoding field, using these rules:
1177  <list style="numbers">
1178      <t>If the content-coding is one of the content-codings listed in
1179         the Accept-Encoding field, then it is acceptable, unless it is
1180         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1181         qvalue of 0 means "not acceptable.")</t>
1182
1183      <t>The special "*" symbol in an Accept-Encoding field matches any
1184         available content-coding not explicitly listed in the header
1185         field.</t>
1186
1187      <t>If multiple content-codings are acceptable, then the acceptable
1188         content-coding with the highest non-zero qvalue is preferred.</t>
1189
1190      <t>The "identity" content-coding is always acceptable, unless
1191         specifically refused because the Accept-Encoding field includes
1192         "identity;q=0", or because the field includes "*;q=0" and does
1193         not explicitly include the "identity" content-coding. If the
1194         Accept-Encoding field-value is empty, then only the "identity"
1195         encoding is acceptable.</t>
1196  </list>
1197</t>
1198<t>
1199   If an Accept-Encoding field is present in a request, and if the
1200   server cannot send a response which is acceptable according to the
1201   Accept-Encoding header, then the server &SHOULD; send an error response
1202   with the 406 (Not Acceptable) status code.
1203</t>
1204<t>
1205   If no Accept-Encoding field is present in a request, the server &MAY;
1206   assume that the client will accept any content coding. In this case,
1207   if "identity" is one of the available content-codings, then the
1208   server &SHOULD; use the "identity" content-coding, unless it has
1209   additional information that a different content-coding is meaningful
1210   to the client.
1211</t>
1212<x:note>
1213  <t>
1214    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1215    and if the "identity" content-coding is unavailable, then
1216    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1217    "gzip" and "compress") are preferred; some older clients
1218    improperly display messages sent with other content-codings.  The
1219    server might also make this decision based on information about
1220    the particular user-agent or client.
1221  </t>
1222</x:note>
1223<x:note>
1224  <t>
1225    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1226    associated with content-codings. This means that qvalues will not
1227    work and are not permitted with x-gzip or x-compress.
1228  </t>
1229</x:note>
1230</section>
1231
1232<section title="Accept-Language" anchor="header.accept-language">
1233  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1234  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1235  <x:anchor-alias value="Accept-Language"/>
1236  <x:anchor-alias value="Accept-Language-v"/>
1237  <x:anchor-alias value="language-range"/>
1238<t>
1239   The "Accept-Language" request-header field can be used by user agents to
1240   indicate the set of natural languages that are preferred in the response.
1241   Language tags are defined in <xref target="language.tags"/>.
1242</t>
1243<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"/>
1244  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1245                    <x:ref>Accept-Language-v</x:ref>
1246  <x:ref>Accept-Language-v</x:ref> =
1247                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1248  <x:ref>language-range</x:ref>    =
1249            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1250</artwork></figure>
1251<t>
1252   Each language-range can be given an associated quality value which
1253   represents an estimate of the user's preference for the languages
1254   specified by that range. The quality value defaults to "q=1". For
1255   example,
1256</t>
1257<figure><artwork type="example">
1258  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1259</artwork></figure>
1260<t>
1261   would mean: "I prefer Danish, but will accept British English and
1262   other types of English."
1263   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1264</t>
1265<t>
1266   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1267   several matching schemes. Implementations can offer the most appropriate
1268   matching scheme for their requirements.
1269</t>
1270<x:note>
1271  <t>
1272    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1273    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1274    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1275  </t>
1276</x:note>
1277<t>
1278   It might be contrary to the privacy expectations of the user to send
1279   an Accept-Language header with the complete linguistic preferences of
1280   the user in every request. For a discussion of this issue, see
1281   <xref target="privacy.issues.connected.to.accept.headers"/>.
1282</t>
1283<t>
1284   As intelligibility is highly dependent on the individual user, it is
1285   recommended that client applications make the choice of linguistic
1286   preference available to the user. If the choice is not made
1287   available, then the Accept-Language header field &MUST-NOT; be given in
1288   the request.
1289</t>
1290<x:note>
1291  <t>
1292    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1293    the user, we remind implementors of  the fact that users are not
1294    familiar with the details of language matching as described above,
1295    and should provide appropriate guidance. As an example, users
1296    might assume that on selecting "en-gb", they will be served any
1297    kind of English document if British English is not available. A
1298    user agent might suggest in such a case to add "en" to get the
1299    best matching behavior.
1300  </t>
1301</x:note>
1302</section>
1303
1304<section title="Content-Encoding" anchor="header.content-encoding">
1305  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1306  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1307  <x:anchor-alias value="Content-Encoding"/>
1308  <x:anchor-alias value="Content-Encoding-v"/>
1309<t>
1310   The "Content-Encoding" entity-header field indicates what content-codings
1311   have been applied to the entity-body, and thus what decoding mechanisms
1312   must be applied in order to obtain the media-type referenced by the
1313   Content-Type header field. Content-Encoding is primarily used to allow a
1314   document to be compressed without losing the identity of its underlying
1315   media type.
1316</t>
1317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1318  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1319  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1320</artwork></figure>
1321<t>
1322   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1323</t>
1324<figure><artwork type="example">
1325  Content-Encoding: gzip
1326</artwork></figure>
1327<t>
1328   The content-coding is a characteristic of the entity identified by
1329   the request-target. Typically, the entity-body is stored with this
1330   encoding and is only decoded before rendering or analogous usage.
1331   However, a non-transparent proxy &MAY; modify the content-coding if the
1332   new coding is known to be acceptable to the recipient, unless the
1333   "no-transform" cache-control directive is present in the message.
1334</t>
1335<t>
1336   If the content-coding of an entity is not "identity", then the
1337   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1338   that lists the non-identity content-coding(s) used.
1339</t>
1340<t>
1341   If the content-coding of an entity in a request message is not
1342   acceptable to the origin server, the server &SHOULD; respond with a
1343   status code of 415 (Unsupported Media Type).
1344</t>
1345<t>
1346   If multiple encodings have been applied to an entity, the content
1347   codings &MUST; be listed in the order in which they were applied.
1348   Additional information about the encoding parameters &MAY; be provided
1349   by other entity-header fields not defined by this specification.
1350</t>
1351</section>
1352
1353<section title="Content-Language" anchor="header.content-language">
1354  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1355  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1356  <x:anchor-alias value="Content-Language"/>
1357  <x:anchor-alias value="Content-Language-v"/>
1358<t>
1359   The "Content-Language" entity-header field describes the natural
1360   language(s) of the intended audience for the entity. Note that this might
1361   not be equivalent to all the languages used within the entity-body.
1362</t>
1363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1364  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1365  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1366</artwork></figure>
1367<t>
1368   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1369   Content-Language is to allow a user to identify and differentiate
1370   entities according to the user's own preferred language. Thus, if the
1371   body content is intended only for a Danish-literate audience, the
1372   appropriate field is
1373</t>
1374<figure><artwork type="example">
1375  Content-Language: da
1376</artwork></figure>
1377<t>
1378   If no Content-Language is specified, the default is that the content
1379   is intended for all language audiences. This might mean that the
1380   sender does not consider it to be specific to any natural language,
1381   or that the sender does not know for which language it is intended.
1382</t>
1383<t>
1384   Multiple languages &MAY; be listed for content that is intended for
1385   multiple audiences. For example, a rendition of the "Treaty of
1386   Waitangi," presented simultaneously in the original Maori and English
1387   versions, would call for
1388</t>
1389<figure><artwork type="example">
1390  Content-Language: mi, en
1391</artwork></figure>
1392<t>
1393   However, just because multiple languages are present within an entity
1394   does not mean that it is intended for multiple linguistic audiences.
1395   An example would be a beginner's language primer, such as "A First
1396   Lesson in Latin," which is clearly intended to be used by an
1397   English-literate audience. In this case, the Content-Language would
1398   properly only include "en".
1399</t>
1400<t>
1401   Content-Language &MAY; be applied to any media type -- it is not
1402   limited to textual documents.
1403</t>
1404</section>
1405
1406<section title="Content-Location" anchor="header.content-location">
1407  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1408  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1409  <x:anchor-alias value="Content-Location"/>
1410  <x:anchor-alias value="Content-Location-v"/>
1411<t>
1412   The "Content-Location" entity-header field is used to supply a URI for the
1413   entity in the message when it is accessible from a location separate from
1414   the requested resource's URI.
1415</t>
1416<t>
1417   A server &SHOULD; provide a Content-Location for the variant corresponding
1418   to the response entity, especially in the case where a resource has multiple
1419   entities associated with it, and those entities actually have separate
1420   locations by which they might be individually accessed, the server &SHOULD;
1421   provide a Content-Location for the particular variant which is returned.
1422</t>
1423<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1424  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1425                    <x:ref>Content-Location-v</x:ref>
1426  <x:ref>Content-Location-v</x:ref> =
1427                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1428</artwork></figure>
1429<t>
1430   The Content-Location value is not a replacement for the original
1431   requested URI; it is only a statement of the location of the resource
1432   corresponding to this particular entity at the time of the request.
1433   Future requests &MAY; specify the Content-Location URI as the request-target
1434   if the desire is to identify the source of that particular
1435   entity.
1436</t>
1437<t>
1438   &response-representation; describes how clients may process the Content-Location header field.
1439</t>
1440<t>
1441   A cache cannot assume that an entity with a Content-Location
1442   different from the URI used to retrieve it can be used to respond to
1443   later requests on that Content-Location URI. However, the Content-Location
1444   can be used to differentiate between multiple entities
1445   retrieved from a single requested resource, as described in &caching-neg-resp;.
1446</t>
1447<t>
1448   If the Content-Location is a relative URI, the relative URI is
1449   interpreted relative to the request-target.
1450</t>
1451<t>
1452   The meaning of the Content-Location header in requests is
1453   undefined; servers are free to ignore it in those cases.
1454</t>
1455</section>
1456
1457<section title="Content-MD5" anchor="header.content-md5">
1458  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1459  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1460  <x:anchor-alias value="Content-MD5"/>
1461  <x:anchor-alias value="Content-MD5-v"/>
1462<t>
1463   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1464   an MD5 digest of the entity-body that provides an end-to-end message
1465   integrity check (MIC) of the entity-body. Note that a MIC is good for
1466   detecting accidental modification of the entity-body in transit, but is not
1467   proof against malicious attacks.
1468</t>
1469<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1470  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1471  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1472</artwork></figure>
1473<t>
1474   The Content-MD5 header field &MAY; be generated by an origin server or
1475   client to function as an integrity check of the entity-body. Only
1476   origin servers or clients &MAY; generate the Content-MD5 header field;
1477   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1478   value as an end-to-end integrity check. Any recipient of the entity-body,
1479   including gateways and proxies, &MAY; check that the digest value
1480   in this header field matches that of the entity-body as received.
1481</t>
1482<t>
1483   The MD5 digest is computed based on the content of the entity-body,
1484   including any content-coding that has been applied, but not including
1485   any transfer-encoding applied to the message-body. If the message is
1486   received with a transfer-encoding, that encoding &MUST; be removed
1487   prior to checking the Content-MD5 value against the received entity.
1488</t>
1489<t>
1490   This has the result that the digest is computed on the octets of the
1491   entity-body exactly as, and in the order that, they would be sent if
1492   no transfer-encoding were being applied.
1493</t>
1494<t>
1495   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1496   composite media-types (e.g., multipart/* and message/rfc822), but
1497   this does not change how the digest is computed as defined in the
1498   preceding paragraph.
1499</t>
1500<t>
1501   There are several consequences of this. The entity-body for composite
1502   types &MAY; contain many body-parts, each with its own MIME and HTTP
1503   headers (including Content-MD5, Content-Transfer-Encoding, and
1504   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1505   or Content-Encoding header, it is assumed that the content
1506   of the body-part has had the encoding applied, and the body-part is
1507   included in the Content-MD5 digest as is -- i.e., after the
1508   application. The Transfer-Encoding header field is not allowed within
1509   body-parts.
1510</t>
1511<t>
1512   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1513   computing or checking the digest: the line break convention used in
1514   the text actually transmitted &MUST; be left unaltered when computing
1515   the digest.
1516</t>
1517<x:note>
1518  <t>
1519    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1520    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1521    in which the application of Content-MD5 to HTTP entity-bodies
1522    differs from its application to MIME entity-bodies. One is that
1523    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1524    does use Transfer-Encoding and Content-Encoding. Another is that
1525    HTTP more frequently uses binary content types than MIME, so it is
1526    worth noting that, in such cases, the byte order used to compute
1527    the digest is the transmission byte order defined for the type.
1528    Lastly, HTTP allows transmission of text types with any of several
1529    line break conventions and not just the canonical form using CRLF.
1530  </t>
1531</x:note>
1532</section>
1533
1534<section title="Content-Type" anchor="header.content-type">
1535  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1536  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1537  <x:anchor-alias value="Content-Type"/>
1538  <x:anchor-alias value="Content-Type-v"/>
1539<t>
1540   The "Content-Type" entity-header field indicates the media type of the
1541   entity-body. In the case of responses to the HEAD method, the media type is
1542   that which would have been sent had the request been a GET.
1543</t>
1544<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1545  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1546  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1547</artwork></figure>
1548<t>
1549   Media types are defined in <xref target="media.types"/>. An example of the field is
1550</t>
1551<figure><artwork type="example">
1552  Content-Type: text/html; charset=ISO-8859-4
1553</artwork></figure>
1554<t>
1555   Further discussion of methods for identifying the media type of an
1556   entity is provided in <xref target="type"/>.
1557</t>
1558</section>
1559
1560</section>
1561
1562<section title="IANA Considerations" anchor="IANA.considerations">
1563<section title="Message Header Registration" anchor="message.header.registration">
1564<t>
1565   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1566   with the permanent registrations below (see <xref target="RFC3864"/>):
1567</t>
1568<?BEGININC p3-payload.iana-headers ?>
1569<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1570<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1571   <ttcol>Header Field Name</ttcol>
1572   <ttcol>Protocol</ttcol>
1573   <ttcol>Status</ttcol>
1574   <ttcol>Reference</ttcol>
1575
1576   <c>Accept</c>
1577   <c>http</c>
1578   <c>standard</c>
1579   <c>
1580      <xref target="header.accept"/>
1581   </c>
1582   <c>Accept-Charset</c>
1583   <c>http</c>
1584   <c>standard</c>
1585   <c>
1586      <xref target="header.accept-charset"/>
1587   </c>
1588   <c>Accept-Encoding</c>
1589   <c>http</c>
1590   <c>standard</c>
1591   <c>
1592      <xref target="header.accept-encoding"/>
1593   </c>
1594   <c>Accept-Language</c>
1595   <c>http</c>
1596   <c>standard</c>
1597   <c>
1598      <xref target="header.accept-language"/>
1599   </c>
1600   <c>Content-Disposition</c>
1601   <c>http</c>
1602   <c/>
1603   <c>
1604      <xref target="content-disposition"/>
1605   </c>
1606   <c>Content-Encoding</c>
1607   <c>http</c>
1608   <c>standard</c>
1609   <c>
1610      <xref target="header.content-encoding"/>
1611   </c>
1612   <c>Content-Language</c>
1613   <c>http</c>
1614   <c>standard</c>
1615   <c>
1616      <xref target="header.content-language"/>
1617   </c>
1618   <c>Content-Location</c>
1619   <c>http</c>
1620   <c>standard</c>
1621   <c>
1622      <xref target="header.content-location"/>
1623   </c>
1624   <c>Content-MD5</c>
1625   <c>http</c>
1626   <c>standard</c>
1627   <c>
1628      <xref target="header.content-md5"/>
1629   </c>
1630   <c>Content-Type</c>
1631   <c>http</c>
1632   <c>standard</c>
1633   <c>
1634      <xref target="header.content-type"/>
1635   </c>
1636   <c>MIME-Version</c>
1637   <c>http</c>
1638   <c/>
1639   <c>
1640      <xref target="mime-version"/>
1641   </c>
1642</texttable>
1643<!--(END)-->
1644<?ENDINC p3-payload.iana-headers ?>
1645<t>
1646   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1647</t>
1648</section>
1649
1650<section title="Content Coding Registry" anchor="content.coding.registration">
1651<t>
1652   The registration procedure for HTTP Content Codings is now defined
1653   by <xref target="content.coding.registry"/> of this document.
1654</t>
1655<t>
1656   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1657   should be updated with the registration below:
1658</t>
1659<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1660   <ttcol>Name</ttcol>
1661   <ttcol>Description</ttcol>
1662   <ttcol>Reference</ttcol>
1663   <c>compress</c>
1664   <c>UNIX "compress" program method</c>
1665   <c>
1666      &compress-coding;
1667   </c>
1668   <c>deflate</c>
1669   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
1670   <c>
1671      &deflate-coding;
1672   </c>
1673   <c>gzip</c>
1674   <c>Same as GNU zip <xref target="RFC1952"/></c>
1675   <c>
1676      &gzip-coding;
1677   </c>
1678   <c>identity</c>
1679   <c>No transformation</c>
1680   <c>
1681      <xref target="content.codings"/>
1682   </c>
1683</texttable>
1684</section>
1685
1686</section>
1687
1688<section title="Security Considerations" anchor="security.considerations">
1689<t>
1690   This section is meant to inform application developers, information
1691   providers, and users of the security limitations in HTTP/1.1 as
1692   described by this document. The discussion does not include
1693   definitive solutions to the problems revealed, though it does make
1694   some suggestions for reducing security risks.
1695</t>
1696
1697<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1698<t>
1699   Accept request-headers can reveal information about the user to all
1700   servers which are accessed. The Accept-Language header in particular
1701   can reveal information the user would consider to be of a private
1702   nature, because the understanding of particular languages is often
1703   strongly correlated to the membership of a particular ethnic group.
1704   User agents which offer the option to configure the contents of an
1705   Accept-Language header to be sent in every request are strongly
1706   encouraged to let the configuration process include a message which
1707   makes the user aware of the loss of privacy involved.
1708</t>
1709<t>
1710   An approach that limits the loss of privacy would be for a user agent
1711   to omit the sending of Accept-Language headers by default, and to ask
1712   the user whether or not to start sending Accept-Language headers to a
1713   server if it detects, by looking for any Vary response-header fields
1714   generated by the server, that such sending could improve the quality
1715   of service.
1716</t>
1717<t>
1718   Elaborate user-customized accept header fields sent in every request,
1719   in particular if these include quality values, can be used by servers
1720   as relatively reliable and long-lived user identifiers. Such user
1721   identifiers would allow content providers to do click-trail tracking,
1722   and would allow collaborating content providers to match cross-server
1723   click-trails or form submissions of individual users. Note that for
1724   many users not behind a proxy, the network address of the host
1725   running the user agent will also serve as a long-lived user
1726   identifier. In environments where proxies are used to enhance
1727   privacy, user agents ought to be conservative in offering accept
1728   header configuration options to end users. As an extreme privacy
1729   measure, proxies could filter the accept headers in relayed requests.
1730   General purpose user agents which provide a high degree of header
1731   configurability &SHOULD; warn users about the loss of privacy which can
1732   be involved.
1733</t>
1734</section>
1735
1736<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1737<t>
1738   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1739   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1740   serious security considerations. Content-Disposition is not part of
1741   the HTTP standard, but since it is widely implemented, we are
1742   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1743   for details.
1744</t>
1745</section>
1746
1747</section>
1748
1749<section title="Acknowledgments" anchor="ack">
1750</section>
1751</middle>
1752<back>
1753
1754<references title="Normative References">
1755
1756<reference anchor="ISO-8859-1">
1757  <front>
1758    <title>
1759     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1760    </title>
1761    <author>
1762      <organization>International Organization for Standardization</organization>
1763    </author>
1764    <date year="1998"/>
1765  </front>
1766  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1767</reference>
1768
1769<reference anchor="Part1">
1770  <front>
1771    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1772    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1773      <organization abbrev="Day Software">Day Software</organization>
1774      <address><email>fielding@gbiv.com</email></address>
1775    </author>
1776    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1777      <organization>One Laptop per Child</organization>
1778      <address><email>jg@laptop.org</email></address>
1779    </author>
1780    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1781      <organization abbrev="HP">Hewlett-Packard Company</organization>
1782      <address><email>JeffMogul@acm.org</email></address>
1783    </author>
1784    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1785      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1786      <address><email>henrikn@microsoft.com</email></address>
1787    </author>
1788    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1789      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1790      <address><email>LMM@acm.org</email></address>
1791    </author>
1792    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1793      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1794      <address><email>paulle@microsoft.com</email></address>
1795    </author>
1796    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1797      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1798      <address><email>timbl@w3.org</email></address>
1799    </author>
1800    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1801      <organization abbrev="W3C">World Wide Web Consortium</organization>
1802      <address><email>ylafon@w3.org</email></address>
1803    </author>
1804    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1805      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1806      <address><email>julian.reschke@greenbytes.de</email></address>
1807    </author>
1808    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1809  </front>
1810  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1811  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1812</reference>
1813
1814<reference anchor="Part2">
1815  <front>
1816    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1817    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1818      <organization abbrev="Day Software">Day Software</organization>
1819      <address><email>fielding@gbiv.com</email></address>
1820    </author>
1821    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1822      <organization>One Laptop per Child</organization>
1823      <address><email>jg@laptop.org</email></address>
1824    </author>
1825    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1826      <organization abbrev="HP">Hewlett-Packard Company</organization>
1827      <address><email>JeffMogul@acm.org</email></address>
1828    </author>
1829    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1830      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1831      <address><email>henrikn@microsoft.com</email></address>
1832    </author>
1833    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1834      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1835      <address><email>LMM@acm.org</email></address>
1836    </author>
1837    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1838      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1839      <address><email>paulle@microsoft.com</email></address>
1840    </author>
1841    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1842      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1843      <address><email>timbl@w3.org</email></address>
1844    </author>
1845    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1846      <organization abbrev="W3C">World Wide Web Consortium</organization>
1847      <address><email>ylafon@w3.org</email></address>
1848    </author>
1849    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1850      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1851      <address><email>julian.reschke@greenbytes.de</email></address>
1852    </author>
1853    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1854  </front>
1855  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1856  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1857</reference>
1858
1859<reference anchor="Part4">
1860  <front>
1861    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1862    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1863      <organization abbrev="Day Software">Day Software</organization>
1864      <address><email>fielding@gbiv.com</email></address>
1865    </author>
1866    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1867      <organization>One Laptop per Child</organization>
1868      <address><email>jg@laptop.org</email></address>
1869    </author>
1870    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1871      <organization abbrev="HP">Hewlett-Packard Company</organization>
1872      <address><email>JeffMogul@acm.org</email></address>
1873    </author>
1874    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1875      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1876      <address><email>henrikn@microsoft.com</email></address>
1877    </author>
1878    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1879      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1880      <address><email>LMM@acm.org</email></address>
1881    </author>
1882    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1883      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1884      <address><email>paulle@microsoft.com</email></address>
1885    </author>
1886    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1887      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1888      <address><email>timbl@w3.org</email></address>
1889    </author>
1890    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1891      <organization abbrev="W3C">World Wide Web Consortium</organization>
1892      <address><email>ylafon@w3.org</email></address>
1893    </author>
1894    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1895      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1896      <address><email>julian.reschke@greenbytes.de</email></address>
1897    </author>
1898    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1899  </front>
1900  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1901  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1902</reference>
1903
1904<reference anchor="Part5">
1905  <front>
1906    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1907    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1908      <organization abbrev="Day Software">Day Software</organization>
1909      <address><email>fielding@gbiv.com</email></address>
1910    </author>
1911    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1912      <organization>One Laptop per Child</organization>
1913      <address><email>jg@laptop.org</email></address>
1914    </author>
1915    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1916      <organization abbrev="HP">Hewlett-Packard Company</organization>
1917      <address><email>JeffMogul@acm.org</email></address>
1918    </author>
1919    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1920      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1921      <address><email>henrikn@microsoft.com</email></address>
1922    </author>
1923    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1924      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1925      <address><email>LMM@acm.org</email></address>
1926    </author>
1927    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1928      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1929      <address><email>paulle@microsoft.com</email></address>
1930    </author>
1931    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1932      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1933      <address><email>timbl@w3.org</email></address>
1934    </author>
1935    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1936      <organization abbrev="W3C">World Wide Web Consortium</organization>
1937      <address><email>ylafon@w3.org</email></address>
1938    </author>
1939    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1940      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1941      <address><email>julian.reschke@greenbytes.de</email></address>
1942    </author>
1943    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1944  </front>
1945  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1946  <x:source href="p5-range.xml" basename="p5-range"/>
1947</reference>
1948
1949<reference anchor="Part6">
1950  <front>
1951    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1952    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1953      <organization abbrev="Day Software">Day Software</organization>
1954      <address><email>fielding@gbiv.com</email></address>
1955    </author>
1956    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1957      <organization>One Laptop per Child</organization>
1958      <address><email>jg@laptop.org</email></address>
1959    </author>
1960    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1961      <organization abbrev="HP">Hewlett-Packard Company</organization>
1962      <address><email>JeffMogul@acm.org</email></address>
1963    </author>
1964    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1965      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1966      <address><email>henrikn@microsoft.com</email></address>
1967    </author>
1968    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1969      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1970      <address><email>LMM@acm.org</email></address>
1971    </author>
1972    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1973      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1974      <address><email>paulle@microsoft.com</email></address>
1975    </author>
1976    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1977      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1978      <address><email>timbl@w3.org</email></address>
1979    </author>
1980    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1981      <organization abbrev="W3C">World Wide Web Consortium</organization>
1982      <address><email>ylafon@w3.org</email></address>
1983    </author>
1984    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1985      <address><email>mnot@mnot.net</email></address>
1986    </author>
1987    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1988      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1989      <address><email>julian.reschke@greenbytes.de</email></address>
1990    </author>
1991    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1992  </front>
1993  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1994  <x:source href="p6-cache.xml" basename="p6-cache"/>
1995</reference>
1996
1997<reference anchor="RFC1864">
1998  <front>
1999    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2000    <author initials="J." surname="Myers" fullname="John G. Myers">
2001      <organization>Carnegie Mellon University</organization>
2002      <address><email>jgm+@cmu.edu</email></address>
2003    </author>
2004    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2005      <organization>Dover Beach Consulting, Inc.</organization>
2006      <address><email>mrose@dbc.mtview.ca.us</email></address>
2007    </author>
2008    <date month="October" year="1995"/>
2009  </front>
2010  <seriesInfo name="RFC" value="1864"/>
2011</reference>
2012
2013<reference anchor="RFC1950">
2014  <front>
2015    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2016    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2017      <organization>Aladdin Enterprises</organization>
2018      <address><email>ghost@aladdin.com</email></address>
2019    </author>
2020    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2021    <date month="May" year="1996"/>
2022  </front>
2023  <seriesInfo name="RFC" value="1950"/>
2024  <annotation>
2025    RFC 1950 is an Informational RFC, thus it may be less stable than
2026    this specification. On the other hand, this downward reference was
2027    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2028    therefore it is unlikely to cause problems in practice. See also
2029    <xref target="BCP97"/>.
2030  </annotation>
2031</reference>
2032
2033<reference anchor="RFC1952">
2034  <front>
2035    <title>GZIP file format specification version 4.3</title>
2036    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2037      <organization>Aladdin Enterprises</organization>
2038      <address><email>ghost@aladdin.com</email></address>
2039    </author>
2040    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2041      <address><email>gzip@prep.ai.mit.edu</email></address>
2042    </author>
2043    <author initials="M." surname="Adler" fullname="Mark Adler">
2044      <address><email>madler@alumni.caltech.edu</email></address>
2045    </author>
2046    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2047      <address><email>ghost@aladdin.com</email></address>
2048    </author>
2049    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2050      <address><email>randeg@alumni.rpi.edu</email></address>
2051    </author>
2052    <date month="May" year="1996"/>
2053  </front>
2054  <seriesInfo name="RFC" value="1952"/>
2055  <annotation>
2056    RFC 1952 is an Informational RFC, thus it may be less stable than
2057    this specification. On the other hand, this downward reference was
2058    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2059    therefore it is unlikely to cause problems in practice. See also
2060    <xref target="BCP97"/>.
2061  </annotation>
2062</reference>
2063
2064<reference anchor="RFC2045">
2065  <front>
2066    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2067    <author initials="N." surname="Freed" fullname="Ned Freed">
2068      <organization>Innosoft International, Inc.</organization>
2069      <address><email>ned@innosoft.com</email></address>
2070    </author>
2071    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2072      <organization>First Virtual Holdings</organization>
2073      <address><email>nsb@nsb.fv.com</email></address>
2074    </author>
2075    <date month="November" year="1996"/>
2076  </front>
2077  <seriesInfo name="RFC" value="2045"/>
2078</reference>
2079
2080<reference anchor="RFC2046">
2081  <front>
2082    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2083    <author initials="N." surname="Freed" fullname="Ned Freed">
2084      <organization>Innosoft International, Inc.</organization>
2085      <address><email>ned@innosoft.com</email></address>
2086    </author>
2087    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2088      <organization>First Virtual Holdings</organization>
2089      <address><email>nsb@nsb.fv.com</email></address>
2090    </author>
2091    <date month="November" year="1996"/>
2092  </front>
2093  <seriesInfo name="RFC" value="2046"/>
2094</reference>
2095
2096<reference anchor="RFC2119">
2097  <front>
2098    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2099    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2100      <organization>Harvard University</organization>
2101      <address><email>sob@harvard.edu</email></address>
2102    </author>
2103    <date month="March" year="1997"/>
2104  </front>
2105  <seriesInfo name="BCP" value="14"/>
2106  <seriesInfo name="RFC" value="2119"/>
2107</reference>
2108
2109<reference anchor='RFC4647'>
2110  <front>
2111    <title>Matching of Language Tags</title>
2112    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2113      <organization>Yahoo! Inc.</organization>
2114      <address><email>addison@inter-locale.com</email></address>
2115    </author>
2116    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2117      <organization>Google</organization>
2118      <address><email>mark.davis@macchiato.com</email></address>
2119    </author>
2120    <date year='2006' month='September' />
2121  </front>
2122  <seriesInfo name='BCP' value='47' />
2123  <seriesInfo name='RFC' value='4647' />
2124</reference>
2125
2126<reference anchor="RFC5234">
2127  <front>
2128    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2129    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2130      <organization>Brandenburg InternetWorking</organization>
2131      <address>
2132        <email>dcrocker@bbiw.net</email>
2133      </address> 
2134    </author>
2135    <author initials="P." surname="Overell" fullname="Paul Overell">
2136      <organization>THUS plc.</organization>
2137      <address>
2138        <email>paul.overell@thus.net</email>
2139      </address>
2140    </author>
2141    <date month="January" year="2008"/>
2142  </front>
2143  <seriesInfo name="STD" value="68"/>
2144  <seriesInfo name="RFC" value="5234"/>
2145</reference>
2146
2147<reference anchor='RFC5646'>
2148  <front>
2149    <title>Tags for Identifying Languages</title>
2150    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2151      <organization>Lab126</organization>
2152      <address><email>addison@inter-locale.com</email></address>
2153    </author>
2154    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2155      <organization>Google</organization>
2156      <address><email>mark.davis@google.com</email></address>
2157    </author>
2158    <date month='September' year='2009' />
2159  </front>
2160  <seriesInfo name='BCP' value='47' />
2161  <seriesInfo name='RFC' value='5646' />
2162</reference>
2163
2164</references>
2165
2166<references title="Informative References">
2167
2168<reference anchor="RFC1945">
2169  <front>
2170    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2171    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2172      <organization>MIT, Laboratory for Computer Science</organization>
2173      <address><email>timbl@w3.org</email></address>
2174    </author>
2175    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2176      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2177      <address><email>fielding@ics.uci.edu</email></address>
2178    </author>
2179    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2180      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2181      <address><email>frystyk@w3.org</email></address>
2182    </author>
2183    <date month="May" year="1996"/>
2184  </front>
2185  <seriesInfo name="RFC" value="1945"/>
2186</reference>
2187
2188<reference anchor="RFC2049">
2189  <front>
2190    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2191    <author initials="N." surname="Freed" fullname="Ned Freed">
2192      <organization>Innosoft International, Inc.</organization>
2193      <address><email>ned@innosoft.com</email></address>
2194    </author>
2195    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2196      <organization>First Virtual Holdings</organization>
2197      <address><email>nsb@nsb.fv.com</email></address>
2198    </author>
2199    <date month="November" year="1996"/>
2200  </front>
2201  <seriesInfo name="RFC" value="2049"/>
2202</reference>
2203
2204<reference anchor="RFC2068">
2205  <front>
2206    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2207    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2208      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2209      <address><email>fielding@ics.uci.edu</email></address>
2210    </author>
2211    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2212      <organization>MIT Laboratory for Computer Science</organization>
2213      <address><email>jg@w3.org</email></address>
2214    </author>
2215    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2216      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2217      <address><email>mogul@wrl.dec.com</email></address>
2218    </author>
2219    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2220      <organization>MIT Laboratory for Computer Science</organization>
2221      <address><email>frystyk@w3.org</email></address>
2222    </author>
2223    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2224      <organization>MIT Laboratory for Computer Science</organization>
2225      <address><email>timbl@w3.org</email></address>
2226    </author>
2227    <date month="January" year="1997"/>
2228  </front>
2229  <seriesInfo name="RFC" value="2068"/>
2230</reference>
2231
2232<reference anchor="RFC2076">
2233  <front>
2234    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2235    <author initials="J." surname="Palme" fullname="Jacob Palme">
2236      <organization>Stockholm University/KTH</organization>
2237      <address><email>jpalme@dsv.su.se</email></address>
2238    </author>
2239    <date month="February" year="1997"/>
2240  </front>
2241  <seriesInfo name="RFC" value="2076"/>
2242</reference>
2243
2244<reference anchor="RFC2183">
2245  <front>
2246    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2247    <author initials="R." surname="Troost" fullname="Rens Troost">
2248      <organization>New Century Systems</organization>
2249      <address><email>rens@century.com</email></address>
2250    </author>
2251    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2252      <organization>QUALCOMM Incorporated</organization>
2253      <address><email>sdorner@qualcomm.com</email></address>
2254    </author>
2255    <author initials="K." surname="Moore" fullname="Keith Moore">
2256      <organization>Department of Computer Science</organization>
2257      <address><email>moore@cs.utk.edu</email></address>
2258    </author>
2259    <date month="August" year="1997"/>
2260  </front>
2261  <seriesInfo name="RFC" value="2183"/>
2262</reference>
2263
2264<reference anchor="RFC2277">
2265  <front>
2266    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2267    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2268      <organization>UNINETT</organization>
2269      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2270    </author>
2271    <date month="January" year="1998"/>
2272  </front>
2273  <seriesInfo name="BCP" value="18"/>
2274  <seriesInfo name="RFC" value="2277"/>
2275</reference>
2276
2277<reference anchor='RFC2295'>
2278  <front>
2279    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2280    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2281      <organization>Technische Universiteit Eindhoven</organization>
2282      <address>
2283        <email>koen@win.tue.nl</email>
2284      </address>
2285    </author>
2286    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2287      <organization>Hewlett-Packard Company</organization>
2288      <address>
2289        <email>mutz@hpl.hp.com</email>
2290      </address>
2291    </author>
2292    <date year='1998' month='March'/>
2293  </front>
2294  <seriesInfo name='RFC' value='2295'/>
2295</reference>
2296
2297<reference anchor="RFC2388">
2298  <front>
2299    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2300    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2301      <organization>Xerox Palo Alto Research Center</organization>
2302      <address><email>masinter@parc.xerox.com</email></address>
2303    </author>
2304    <date year="1998" month="August"/>
2305  </front>
2306  <seriesInfo name="RFC" value="2388"/>
2307</reference>
2308
2309<reference anchor="RFC2557">
2310  <front>
2311    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2312    <author initials="F." surname="Palme" fullname="Jacob Palme">
2313      <organization>Stockholm University and KTH</organization>
2314      <address><email>jpalme@dsv.su.se</email></address>
2315    </author>
2316    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2317      <organization>Microsoft Corporation</organization>
2318      <address><email>alexhop@microsoft.com</email></address>
2319    </author>
2320    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2321      <organization>Lotus Development Corporation</organization>
2322      <address><email>Shelness@lotus.com</email></address>
2323    </author>
2324    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2325      <address><email>stef@nma.com</email></address>
2326    </author>
2327    <date year="1999" month="March"/>
2328  </front>
2329  <seriesInfo name="RFC" value="2557"/>
2330</reference>
2331
2332<reference anchor="RFC2616">
2333  <front>
2334    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2335    <author initials="R." surname="Fielding" fullname="R. Fielding">
2336      <organization>University of California, Irvine</organization>
2337      <address><email>fielding@ics.uci.edu</email></address>
2338    </author>
2339    <author initials="J." surname="Gettys" fullname="J. Gettys">
2340      <organization>W3C</organization>
2341      <address><email>jg@w3.org</email></address>
2342    </author>
2343    <author initials="J." surname="Mogul" fullname="J. Mogul">
2344      <organization>Compaq Computer Corporation</organization>
2345      <address><email>mogul@wrl.dec.com</email></address>
2346    </author>
2347    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2348      <organization>MIT Laboratory for Computer Science</organization>
2349      <address><email>frystyk@w3.org</email></address>
2350    </author>
2351    <author initials="L." surname="Masinter" fullname="L. Masinter">
2352      <organization>Xerox Corporation</organization>
2353      <address><email>masinter@parc.xerox.com</email></address>
2354    </author>
2355    <author initials="P." surname="Leach" fullname="P. Leach">
2356      <organization>Microsoft Corporation</organization>
2357      <address><email>paulle@microsoft.com</email></address>
2358    </author>
2359    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2360      <organization>W3C</organization>
2361      <address><email>timbl@w3.org</email></address>
2362    </author>
2363    <date month="June" year="1999"/>
2364  </front>
2365  <seriesInfo name="RFC" value="2616"/>
2366</reference>
2367
2368<reference anchor="RFC3629">
2369  <front>
2370    <title>UTF-8, a transformation format of ISO 10646</title>
2371    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2372      <organization>Alis Technologies</organization>
2373      <address><email>fyergeau@alis.com</email></address>
2374    </author>
2375    <date month="November" year="2003"/>
2376  </front>
2377  <seriesInfo name="RFC" value="3629"/>
2378  <seriesInfo name="STD" value="63"/>
2379</reference>
2380
2381<reference anchor='RFC3864'>
2382  <front>
2383    <title>Registration Procedures for Message Header Fields</title>
2384    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2385      <organization>Nine by Nine</organization>
2386      <address><email>GK-IETF@ninebynine.org</email></address>
2387    </author>
2388    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2389      <organization>BEA Systems</organization>
2390      <address><email>mnot@pobox.com</email></address>
2391    </author>
2392    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2393      <organization>HP Labs</organization>
2394      <address><email>JeffMogul@acm.org</email></address>
2395    </author>
2396    <date year='2004' month='September' />
2397  </front>
2398  <seriesInfo name='BCP' value='90' />
2399  <seriesInfo name='RFC' value='3864' />
2400</reference>
2401
2402<reference anchor="RFC4288">
2403  <front>
2404    <title>Media Type Specifications and Registration Procedures</title>
2405    <author initials="N." surname="Freed" fullname="N. Freed">
2406      <organization>Sun Microsystems</organization>
2407      <address>
2408        <email>ned.freed@mrochek.com</email>
2409      </address>
2410    </author>
2411    <author initials="J." surname="Klensin" fullname="J. Klensin">
2412      <address>
2413        <email>klensin+ietf@jck.com</email>
2414      </address>
2415    </author>
2416    <date year="2005" month="December"/>
2417  </front>
2418  <seriesInfo name="BCP" value="13"/>
2419  <seriesInfo name="RFC" value="4288"/>
2420</reference>
2421
2422<reference anchor='RFC5226'>
2423  <front>
2424    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2425    <author initials='T.' surname='Narten' fullname='T. Narten'>
2426      <organization>IBM</organization>
2427      <address><email>narten@us.ibm.com</email></address>
2428    </author>
2429    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2430      <organization>Google</organization>
2431      <address><email>Harald@Alvestrand.no</email></address>
2432    </author>
2433    <date year='2008' month='May' />
2434  </front>
2435  <seriesInfo name='BCP' value='26' />
2436  <seriesInfo name='RFC' value='5226' />
2437</reference>
2438
2439<reference anchor="RFC5322">
2440  <front>
2441    <title>Internet Message Format</title>
2442    <author initials="P." surname="Resnick" fullname="P. Resnick">
2443      <organization>Qualcomm Incorporated</organization>
2444    </author>
2445    <date year="2008" month="October"/>
2446  </front> 
2447  <seriesInfo name="RFC" value="5322"/>
2448</reference>
2449
2450<reference anchor='BCP97'>
2451  <front>
2452    <title>Handling Normative References to Standards-Track Documents</title>
2453    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2454      <address>
2455        <email>klensin+ietf@jck.com</email>
2456      </address>
2457    </author>
2458    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2459      <organization>MIT</organization>
2460      <address>
2461        <email>hartmans-ietf@mit.edu</email>
2462      </address>
2463    </author>
2464    <date year='2007' month='June' />
2465  </front>
2466  <seriesInfo name='BCP' value='97' />
2467  <seriesInfo name='RFC' value='4897' />
2468</reference>
2469
2470
2471</references>
2472
2473<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2474<t>
2475   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
2476   allow entities to be transmitted in an open variety of
2477   representations and with extensible mechanisms. However, RFC 2045
2478   discusses mail, and HTTP has a few features that are different from
2479   those described in RFC 2045. These differences were carefully chosen
2480   to optimize performance over binary connections, to allow greater
2481   freedom in the use of new media types, to make date comparisons
2482   easier, and to acknowledge the practice of some early HTTP servers
2483   and clients.
2484</t>
2485<t>
2486   This appendix describes specific areas where HTTP differs from RFC
2487   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2488   aware of these differences and provide the appropriate conversions
2489   where necessary. Proxies and gateways from MIME environments to HTTP
2490   also need to be aware of the differences because some conversions
2491   might be required.
2492</t>
2493
2494<section title="MIME-Version" anchor="mime-version">
2495  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2496  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2497  <x:anchor-alias value="MIME-Version"/>
2498  <x:anchor-alias value="MIME-Version-v"/>
2499<t>
2500   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2501   include a single MIME-Version general-header field to indicate what
2502   version of the MIME protocol was used to construct the message. Use
2503   of the MIME-Version header field indicates that the message is in
2504   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2505   Proxies/gateways are responsible for ensuring full compliance (where
2506   possible) when exporting HTTP messages to strict MIME environments.
2507</t>
2508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2509  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2510  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2511</artwork></figure>
2512<t>
2513   MIME version "1.0" is the default for use in HTTP/1.1. However,
2514   HTTP/1.1 message parsing and semantics are defined by this document
2515   and not the MIME specification.
2516</t>
2517</section>
2518
2519<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2520<t>
2521   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2522   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2523   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2524   allowed for subtypes of the "text" media type when transmitted over
2525   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2526   line breaks as CRLF and forbids the use of CR or LF outside of line
2527   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2528   line break within text content when a message is transmitted over
2529   HTTP.
2530</t>
2531<t>
2532   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2533   environment &SHOULD; translate all line breaks within the text media
2534   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2535   canonical form of CRLF. Note, however, that this might be complicated
2536   by the presence of a Content-Encoding and by the fact that HTTP
2537   allows the use of some character sets which do not use octets 13 and
2538   10 to represent CR and LF, as is the case for some multi-byte
2539   character sets.
2540</t>
2541<t>
2542   Implementors should note that conversion will break any cryptographic
2543   checksums applied to the original content unless the original content
2544   is already in canonical form. Therefore, the canonical form is
2545   recommended for any content that uses such checksums in HTTP.
2546</t>
2547</section>
2548
2549
2550<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2551<t>
2552   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2553   simplify the process of date comparison. Proxies and gateways from
2554   other protocols &SHOULD; ensure that any Date header field present in a
2555   message conforms to one of the HTTP/1.1 formats and rewrite the date
2556   if necessary.
2557</t>
2558</section>
2559
2560<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2561<t>
2562   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2563   Content-Encoding header field. Since this acts as a modifier on the
2564   media type, proxies and gateways from HTTP to MIME-compliant
2565   protocols &MUST; either change the value of the Content-Type header
2566   field or decode the entity-body before forwarding the message. (Some
2567   experimental applications of Content-Type for Internet mail have used
2568   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2569   a function equivalent to Content-Encoding. However, this parameter is
2570   not part of RFC 2045).
2571</t>
2572</section>
2573
2574<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2575<t>
2576   HTTP does not use the Content-Transfer-Encoding field of RFC
2577   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2578   remove any Content-Transfer-Encoding
2579   prior to delivering the response message to an HTTP client.
2580</t>
2581<t>
2582   Proxies and gateways from HTTP to MIME-compliant protocols are
2583   responsible for ensuring that the message is in the correct format
2584   and encoding for safe transport on that protocol, where "safe
2585   transport" is defined by the limitations of the protocol being used.
2586   Such a proxy or gateway &SHOULD; label the data with an appropriate
2587   Content-Transfer-Encoding if doing so will improve the likelihood of
2588   safe transport over the destination protocol.
2589</t>
2590</section>
2591
2592<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2593<t>
2594   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2595   Proxies/gateways &MUST; remove any transfer-coding prior to
2596   forwarding a message via a MIME-compliant protocol.
2597</t>
2598</section>
2599
2600<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2601<t>
2602   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2603   need to be aware of MIME line length limitations. Since HTTP does not
2604   have this limitation, HTTP does not fold long lines. MHTML messages
2605   being transported by HTTP follow all conventions of MHTML, including
2606   line length limitations and folding, canonicalization, etc., since
2607   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2608   does not interpret the content or any MIME header lines that might be
2609   contained therein.
2610</t>
2611</section>
2612</section>
2613
2614<section title="Additional Features" anchor="additional.features">
2615<t>
2616   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2617   existing HTTP implementations, but not consistently and correctly
2618   across most HTTP/1.1 applications. Implementors are advised to be
2619   aware of these features, but cannot rely upon their presence in, or
2620   interoperability with, other HTTP/1.1 applications. Some of these
2621   describe proposed experimental features, and some describe features
2622   that experimental deployment found lacking that are now addressed in
2623   the base HTTP/1.1 specification.
2624</t>
2625<t>
2626   A number of other headers, such as Content-Disposition and Title,
2627   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2628</t>
2629
2630<section title="Content-Disposition" anchor="content-disposition">
2631<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2632<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2633  <x:anchor-alias value="content-disposition"/>
2634  <x:anchor-alias value="content-disposition-v"/>
2635  <x:anchor-alias value="disposition-type"/>
2636  <x:anchor-alias value="disposition-parm"/>
2637  <x:anchor-alias value="disp-extension-parm"/>
2638  <x:anchor-alias value="disp-extension-token"/>
2639  <x:anchor-alias value="filename-parm"/>
2640<t>
2641   The "Content-Disposition" response-header field has been proposed as a
2642   means for the origin server to suggest a default filename if the user
2643   requests that the content is saved to a file. This usage is derived
2644   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2645</t>
2646<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"/>
2647  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2648                        <x:ref>content-disposition-v</x:ref>
2649  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2650                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2651  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2652  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2653  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2654  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2655  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2656</artwork></figure>
2657<t>
2658   An example is
2659</t>
2660<figure><artwork type="example">
2661  Content-Disposition: attachment; filename="fname.ext"
2662</artwork></figure>
2663<t>
2664   The receiving user agent &SHOULD-NOT;  respect any directory path
2665   information present in the filename-parm parameter, which is the only
2666   parameter believed to apply to HTTP implementations at this time. The
2667   filename &SHOULD; be treated as a terminal component only.
2668</t>
2669<t>
2670   If this header is used in a response with the application/octet-stream
2671   content-type, the implied suggestion is that the user agent
2672   should not display the response, but directly enter a "save response
2673   as..." dialog.
2674</t>
2675<t>
2676   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2677</t>
2678</section>
2679</section>
2680
2681<section title="Compatibility with Previous Versions" anchor="compatibility">
2682<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2683<t>
2684   Transfer-coding and message lengths all interact in ways that
2685   required fixing exactly when chunked encoding is used (to allow for
2686   transfer encoding that may not be self delimiting); it was important
2687   to straighten out exactly how message lengths are computed.
2688   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2689   <xref target="Part5"/> and <xref target="Part6"/>).
2690</t>
2691<t>
2692   Charset wildcarding is introduced to avoid explosion of character set
2693   names in accept headers. (<xref target="header.accept-charset"/>)
2694</t>
2695<t>
2696   Content-Base was deleted from the specification: it was not
2697   implemented widely, and there is no simple, safe way to introduce it
2698   without a robust extension mechanism. In addition, it is used in a
2699   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2700</t>
2701<t>
2702   A content-coding of "identity" was introduced, to solve problems
2703   discovered in caching. (<xref target="content.codings"/>)
2704</t>
2705<t>
2706   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
2707   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
2708   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2709</t>
2710</section>
2711
2712<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2713<t>
2714  Clarify contexts that charset is used in.
2715  (<xref target="character.sets"/>)
2716</t>
2717<t>
2718  Remove base URI setting semantics for Content-Location due to poor
2719  implementation support, which was caused by too many broken servers emitting
2720  bogus Content-Location headers, and also the potentially undesirable effect
2721  of potentially breaking relative links in content-negotiated resources.
2722  (<xref target="header.content-location"/>)
2723</t>
2724<t>
2725  Remove reference to non-existant identity transfer-coding value tokens.
2726  (<xref target="no.content-transfer-encoding"/>)
2727</t>
2728</section>
2729
2730</section>
2731
2732<?BEGININC p3-payload.abnf-appendix ?>
2733<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2734<figure>
2735<artwork type="abnf" name="p3-payload.parsed-abnf">
2736<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2737<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2738<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2739 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2740 qvalue ] ] )
2741<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2742<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2743 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2744<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2745<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2746 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2747 ] )
2748<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2749 OWS media-range [ accept-params ] ] ) ]
2750
2751<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2752<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2753 content-coding ] )
2754<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2755<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2756 language-tag ] )
2757<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2758<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2759<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2760<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2761<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2762<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2763<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2764<x:ref>Content-Type-v</x:ref> = media-type
2765
2766<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2767
2768<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2769
2770<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2771<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2772
2773<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2774
2775<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2776<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2777<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2778<x:ref>attribute</x:ref> = token
2779
2780<x:ref>charset</x:ref> = token
2781<x:ref>codings</x:ref> = ( content-coding / "*" )
2782<x:ref>content-coding</x:ref> = token
2783<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2784 content-disposition-v
2785<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2786 disposition-parm )
2787
2788<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2789<x:ref>disp-extension-token</x:ref> = token
2790<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2791<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2792
2793<x:ref>entity-body</x:ref> = *OCTET
2794<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2795 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2796 Expires / Last-Modified / extension-header
2797<x:ref>extension-header</x:ref> = header-field
2798
2799<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2800
2801<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2802
2803<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2804<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2805
2806<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2807 ";" OWS parameter )
2808<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2809
2810<x:ref>parameter</x:ref> = attribute "=" value
2811<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2812
2813<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2814<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2815
2816<x:ref>subtype</x:ref> = token
2817
2818<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2819<x:ref>type</x:ref> = token
2820
2821<x:ref>value</x:ref> = token / quoted-string
2822</artwork>
2823</figure>
2824<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2825; Accept defined but not used
2826; Accept-Charset defined but not used
2827; Accept-Encoding defined but not used
2828; Accept-Language defined but not used
2829; MIME-Version defined but not used
2830; content-disposition defined but not used
2831; entity-body defined but not used
2832; entity-header defined but not used
2833</artwork></figure></section>
2834<?ENDINC p3-payload.abnf-appendix ?>
2835
2836<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2837
2838<section title="Since RFC2616">
2839<t>
2840  Extracted relevant partitions from <xref target="RFC2616"/>.
2841</t>
2842</section>
2843
2844<section title="Since draft-ietf-httpbis-p3-payload-00">
2845<t>
2846  Closed issues:
2847  <list style="symbols"> 
2848    <t>
2849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2850      "Media Type Registrations"
2851      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2852    </t>
2853    <t>
2854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2855      "Clarification regarding quoting of charset values"
2856      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2857    </t>
2858    <t>
2859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2860      "Remove 'identity' token references"
2861      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2862    </t>
2863    <t>
2864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2865      "Accept-Encoding BNF"
2866    </t>
2867    <t>
2868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2869      "Normative and Informative references"
2870    </t>
2871    <t>
2872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2873      "RFC1700 references"
2874    </t>
2875    <t>
2876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2877      "Updating to RFC4288"
2878    </t>
2879    <t>
2880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2881      "Informative references"
2882    </t>
2883    <t>
2884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2885      "ISO-8859-1 Reference"
2886    </t>
2887    <t>
2888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2889      "Encoding References Normative"
2890    </t>
2891    <t>
2892      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2893      "Normative up-to-date references"
2894    </t>
2895  </list>
2896</t>
2897</section>
2898
2899<section title="Since draft-ietf-httpbis-p3-payload-01">
2900<t>
2901  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2902  <list style="symbols"> 
2903    <t>
2904      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2905    </t>
2906  </list>
2907</t>
2908</section>
2909
2910<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2911<t>
2912  Closed issues:
2913  <list style="symbols"> 
2914    <t>
2915      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2916      "Quoting Charsets"
2917    </t>
2918    <t>
2919      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2920      "Classification for Allow header"
2921    </t>
2922    <t>
2923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2924      "missing default for qvalue in description of Accept-Encoding"
2925    </t>
2926  </list>
2927</t>
2928<t>
2929  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2930  <list style="symbols"> 
2931    <t>
2932      Reference RFC 3984, and update header registrations for headers defined
2933      in this document.
2934    </t>
2935  </list>
2936</t>
2937</section>
2938
2939<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2940<t>
2941  Closed issues:
2942  <list style="symbols"> 
2943    <t>
2944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2945      "Quoting Charsets"
2946    </t>
2947    <t>
2948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2949      "language tag matching (Accept-Language) vs RFC4647"
2950    </t>
2951    <t>
2952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2953      "RFC 1806 has been replaced by RFC2183"
2954    </t>
2955  </list>
2956</t>
2957<t>
2958  Other changes:
2959  <list style="symbols"> 
2960    <t>
2961      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2962      "Encoding References Normative" -- rephrase the annotation and reference
2963      <xref target="BCP97"/>.
2964    </t>
2965  </list>
2966</t>
2967 </section>
2968
2969<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2970<t>
2971  Closed issues:
2972  <list style="symbols"> 
2973    <t>
2974      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2975      "RFC 2822 is updated by RFC 5322"
2976    </t>
2977  </list>
2978</t>
2979<t>
2980  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2981  <list style="symbols"> 
2982    <t>
2983      Use "/" instead of "|" for alternatives.
2984    </t>
2985    <t>
2986      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2987      whitespace ("OWS") and required whitespace ("RWS").
2988    </t>
2989    <t>
2990      Rewrite ABNFs to spell out whitespace rules, factor out
2991      header value format definitions.
2992    </t>
2993  </list>
2994</t>
2995</section>
2996
2997<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2998<t>
2999  Closed issues:
3000  <list style="symbols"> 
3001    <t>
3002      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3003      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3004    </t>
3005  </list>
3006</t>
3007<t>
3008  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3009  <list style="symbols"> 
3010    <t>
3011      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3012    </t>
3013  </list>
3014</t>
3015<t>
3016  Other changes:
3017  <list style="symbols"> 
3018    <t>
3019      Move definition of quality values into Part 1.
3020    </t>
3021  </list>
3022</t>
3023</section>
3024
3025<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3026<t>
3027  Closed issues:
3028  <list style="symbols"> 
3029    <t>
3030      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3031      "Content-Location isn't special"
3032    </t>
3033    <t>
3034      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3035      "Content Sniffing"
3036    </t>
3037  </list>
3038</t>
3039</section>
3040
3041<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3042<t>
3043  Closed issues:
3044  <list style="symbols"> 
3045    <t>
3046      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3047      "Updated reference for language tags"
3048    </t>
3049    <t>
3050      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3051      "Clarify rules for determining what entities a response carries"
3052    </t>
3053    <t>
3054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3055      "Content-Location base-setting problems"
3056    </t>
3057    <t>
3058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3059      "Content Sniffing"
3060    </t>
3061    <t>
3062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3063      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3064    </t>
3065    <t>
3066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3067      "move definitions of gzip/deflate/compress to part 1"
3068    </t>
3069  </list>
3070</t>
3071<t>
3072  Partly resolved issues:
3073  <list style="symbols"> 
3074    <t>
3075      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3076      "update IANA requirements wrt Transfer-Coding values" (add the
3077      IANA Considerations subsection)
3078    </t>
3079    <t>
3080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3081      "update IANA requirements wrt Content-Coding values" (add the
3082      IANA Considerations subsection)
3083    </t>
3084  </list>
3085</t>
3086</section>
3087
3088<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3089<t>
3090  Closed issues:
3091  <list style="symbols"> 
3092    <t>
3093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3094      "Content Negotiation for media types"
3095    </t>
3096    <t>
3097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3098      "Accept-Language: which RFC4647 filtering?"
3099    </t>
3100  </list>
3101</t>
3102</section>
3103
3104</section>
3105
3106</back>
3107</rfc>
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