source: draft-ietf-httpbis/latest/p3-payload.xml @ 1641

Last change on this file since 1641 was 1641, checked in by julian.reschke@…, 8 years ago

Step 3 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 107.7 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture             "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY abnf-extension           "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY acks                     "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY whitespace               "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY field-components         "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-etag              "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY http-date                "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45]>
46<?rfc toc="yes" ?>
47<?rfc symrefs="yes" ?>
48<?rfc sortrefs="yes" ?>
49<?rfc compact="yes"?>
50<?rfc subcompact="no" ?>
51<?rfc linkmailto="no" ?>
52<?rfc editing="no" ?>
53<?rfc comments="yes"?>
54<?rfc inline="yes"?>
55<?rfc rfcedstyle="yes"?>
56<?rfc-ext allow-markup-in-artwork="yes" ?>
57<?rfc-ext include-references-in-index="yes" ?>
58<rfc obsoletes="2616" category="std" x:maturity-level="proposed"
59     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
60     xmlns:x='http://purl.org/net/xml2rfc/ext'>
61<x:link rel="prev" basename="p2-semantics"/>
62<x:link rel="next" basename="p4-conditional"/>
63<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
64<front>
65
66  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
67
68  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
69    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
70    <address>
71      <postal>
72        <street>345 Park Ave</street>
73        <city>San Jose</city>
74        <region>CA</region>
75        <code>95110</code>
76        <country>USA</country>
77      </postal>
78      <email>fielding@gbiv.com</email>
79      <uri>http://roy.gbiv.com/</uri>
80    </address>
81  </author>
82
83  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
84    <organization abbrev="W3C">World Wide Web Consortium</organization>
85    <address>
86      <postal>
87        <street>W3C / ERCIM</street>
88        <street>2004, rte des Lucioles</street>
89        <city>Sophia-Antipolis</city>
90        <region>AM</region>
91        <code>06902</code>
92        <country>France</country>
93      </postal>
94      <email>ylafon@w3.org</email>
95      <uri>http://www.raubacapeu.net/people/yves/</uri>
96    </address>
97  </author>
98
99  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
100    <organization abbrev="greenbytes">greenbytes GmbH</organization>
101    <address>
102      <postal>
103        <street>Hafenweg 16</street>
104        <city>Muenster</city><region>NW</region><code>48155</code>
105        <country>Germany</country>
106      </postal>
107      <phone>+49 251 2807760</phone>
108      <facsimile>+49 251 2807761</facsimile>
109      <email>julian.reschke@greenbytes.de</email>
110      <uri>http://greenbytes.de/tech/webdav/</uri>
111    </address>
112  </author>
113
114  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
115  <workgroup>HTTPbis Working Group</workgroup>
116
117<abstract>
118<t>
119  This part is now obsolete. Please see HTTPbis, Part 2.
120</t>
121</abstract>
122</front>
123<middle>
124<section title="Introduction" anchor="introduction">
125<t>
126  This part is now obsolete. Please see HTTPbis, Part 2.
127</t>
128
129<section title="Syntax Notation" anchor="notation">
130  <x:anchor-alias value="ALPHA"/>
131  <x:anchor-alias value="CR"/>
132  <x:anchor-alias value="DIGIT"/>
133  <x:anchor-alias value="LF"/>
134  <x:anchor-alias value="OCTET"/>
135  <x:anchor-alias value="VCHAR"/>
136<t>
137   This specification uses the Augmented Backus-Naur Form (ABNF) notation
138   of <xref target="RFC5234"/> with the list rule extension defined in
139   &notation;.<!--  <xref target="collected.abnf"/> shows the collected ABNF
140   with the list rule expanded.-->
141</t>
142<t>
143  The following core rules are included by
144  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
145  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
146  DIGIT (decimal 0-9), DQUOTE (double quote),
147  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
148  OCTET (any 8-bit sequence of data), SP (space), and
149  VCHAR (any visible US-ASCII character).
150</t>
151
152<section title="Core Rules" anchor="core.rules">
153  <x:anchor-alias value="token"/>
154  <x:anchor-alias value="word"/>
155  <x:anchor-alias value="OWS"/>
156<t>
157  The core rules below are defined in <xref target="Part1"/>:
158</t>
159<figure><artwork type="abnf2616">
160  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &whitespace;&gt;
161  <x:ref>token</x:ref>          = &lt;token, defined in &field-components;&gt;
162  <x:ref>word</x:ref>           = &lt;word, defined in &field-components;&gt;
163</artwork></figure>
164</section>
165
166<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
167  <x:anchor-alias value="absolute-URI"/>
168  <x:anchor-alias value="partial-URI"/>
169  <x:anchor-alias value="qvalue"/>
170<t>
171  The ABNF rules below are defined in other parts:
172</t>
173<figure><!--Part1--><artwork type="abnf2616">
174  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
175  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
176  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
177</artwork></figure>
178</section>
179
180</section>
181
182</section>
183
184<section title="Protocol Parameters" anchor="protocol.parameters">
185
186<section title="Character Encodings (charset)" anchor="character.sets">
187<t>
188   HTTP uses charset names to indicate the character encoding of a
189   textual representation.
190</t>
191<t anchor="rule.charset">
192  <x:anchor-alias value="charset"/>
193   A character encoding is identified by a case-insensitive token. The
194   complete set of tokens is defined by the IANA Character Set registry
195   (<eref target="http://www.iana.org/assignments/character-sets"/>).
196</t>
197<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
198  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
199</artwork></figure>
200<t>
201   Although HTTP allows an arbitrary token to be used as a charset
202   value, any token that has a predefined value within the IANA
203   Character Set registry &MUST; represent the character encoding defined
204   by that registry. Applications &SHOULD; limit their use of character
205   encodings to those defined within the IANA registry.
206</t>
207<t>
208   HTTP uses charset in two contexts: within an Accept-Charset request
209   header field (in which the charset value is an unquoted token) and as the
210   value of a parameter in a Content-Type header field (within a request or
211   response), in which case the parameter value of the charset parameter
212   can be quoted.
213</t>
214<t>
215   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
216   <xref target="RFC2277"/>.
217</t>
218</section>
219
220<section title="Content Codings" anchor="content.codings">
221  <x:anchor-alias value="content-coding"/>
222<t>
223   Content coding values indicate an encoding transformation that has
224   been or can be applied to a representation. Content codings are primarily
225   used to allow a representation to be compressed or otherwise usefully
226   transformed without losing the identity of its underlying media type
227   and without loss of information. Frequently, the representation is stored in
228   coded form, transmitted directly, and only decoded by the recipient.
229</t>
230<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
231  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
232</artwork></figure>
233<t>
234   All content-coding values are case-insensitive. HTTP/1.1 uses
235   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
236   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
237   describes the content-coding, what is more important is that it
238   indicates what decoding mechanism will be required to remove the
239   encoding.
240</t>
241<t>
242   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
243  <list>
244    <t>
245      See &compress-coding;.
246    </t>
247  </list>
248</t>
249<t>
250   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
251  <list>
252    <t>
253      See &deflate-coding;.
254    </t>
255  </list>
256</t>
257<t>
258   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
259  <list>
260    <t>
261      See &gzip-coding;.
262    </t>
263  </list>
264</t>
265
266<section title="Content Coding Registry" anchor="content.coding.registry">
267<t>
268   The HTTP Content Coding Registry defines the name space for the content
269   coding names.
270</t>
271<t>
272   Registrations &MUST; include the following fields:
273   <list style="symbols">
274     <t>Name</t>
275     <t>Description</t>
276     <t>Pointer to specification text</t>
277   </list>
278</t>
279<t>
280   Names of content codings &MUST-NOT; overlap with names of transfer codings
281   (&transfer-codings;), unless the encoding transformation is identical (as
282   is the case for the compression codings defined in
283   &compression-codings;).
284</t>
285<t>
286   Values to be added to this name space require IETF Review
287   (see <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
288   conform to the purpose of content coding defined in this section.
289</t>
290<t>
291   The registry itself is maintained at
292   <eref target="http://www.iana.org/assignments/http-parameters"/>.
293</t>
294</section>
295
296</section>
297
298<section title="Media Types" anchor="media.types">
299  <x:anchor-alias value="media-type"/>
300  <x:anchor-alias value="type"/>
301  <x:anchor-alias value="subtype"/>
302<t>
303   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
304   and Accept (<xref target="header.accept"/>) header fields in order to provide
305   open and extensible data typing and type negotiation.
306</t>
307<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"/>
308  <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> )
309  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
310  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
311</artwork></figure>
312<t anchor="rule.parameter">
313  <x:anchor-alias value="attribute"/>
314  <x:anchor-alias value="parameter"/>
315  <x:anchor-alias value="value"/>
316   The type/subtype &MAY; be followed by parameters in the form of
317   attribute/value pairs.
318</t>
319<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"/>
320  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
321  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
322  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
323</artwork></figure>
324<t>
325   The type, subtype, and parameter attribute names are case-insensitive.
326   Parameter values might or might not be case-sensitive, depending on the
327   semantics of the parameter name.  The presence or absence of a parameter might
328   be significant to the processing of a media-type, depending on its
329   definition within the media type registry.
330</t>
331<t>
332   A parameter value that matches the <x:ref>token</x:ref> production can be
333   transmitted as either a token or within a quoted-string. The quoted and
334   unquoted values are equivalent.
335</t>
336<t>
337   Note that some older HTTP applications do not recognize media type
338   parameters. When sending data to older HTTP applications,
339   implementations &SHOULD; only use media type parameters when they are
340   required by that type/subtype definition.
341</t>
342<t>
343   Media-type values are registered with the Internet Assigned Number
344   Authority (IANA). The media type registration process is
345   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
346   discouraged.
347</t>
348
349<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
350<t>
351   Internet media types are registered with a canonical form. A
352   representation transferred via HTTP messages &MUST; be in the
353   appropriate canonical form prior to its transmission except for
354   "text" types, as defined in the next paragraph.
355</t>
356<t>
357   When in canonical form, media subtypes of the "text" type use CRLF as
358   the text line break. HTTP relaxes this requirement and allows the
359   transport of text media with plain CR or LF alone representing a line
360   break when it is done consistently for an entire representation. HTTP
361   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
362   a line break in text media received via HTTP. In
363   addition, if the text is in a character encoding that does not
364   use octets 13 and 10 for CR and LF respectively, as is the case for
365   some multi-byte character encodings, HTTP allows the use of whatever octet
366   sequences are defined by that character encoding to represent the
367   equivalent of CR and LF for line breaks. This flexibility regarding
368   line breaks applies only to text media in the payload body; a bare CR
369   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
370   structures (such as header fields and multipart boundaries).
371</t>
372<t>
373   If a representation is encoded with a content-coding, the underlying
374   data &MUST; be in a form defined above prior to being encoded.
375</t>
376</section>
377
378<section title="Multipart Types" anchor="multipart.types">
379<t>
380   MIME provides for a number of "multipart" types &mdash; encapsulations of
381   one or more representations within a single message body. All multipart
382   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
383   and &MUST; include a boundary parameter as part of the media type
384   value. The message body is itself a protocol element and &MUST;
385   therefore use only CRLF to represent line breaks between body-parts.
386</t>
387<t>
388   In general, HTTP treats a multipart message body no differently than
389   any other media type: strictly as payload.  HTTP does not use the
390   multipart boundary as an indicator of message body length.
391   <!-- jre: re-insert removed text pointing to caching? -->
392   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
393   behavior as a MIME user agent would upon receipt of a multipart type.
394   The MIME header fields within each body-part of a multipart message body
395   do not have any significance to HTTP beyond that defined by
396   their MIME semantics.
397</t>
398<t>
399   If an application receives an unrecognized multipart subtype, the
400   application &MUST; treat it as being equivalent to "multipart/mixed".
401</t>
402<x:note>
403  <t>
404    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
405    for carrying form data suitable for processing via the POST
406    request method, as described in <xref target="RFC2388"/>.
407  </t>
408</x:note>
409</section>
410</section>
411
412<section title="Language Tags" anchor="language.tags">
413  <x:anchor-alias value="language-tag"/>
414<t>
415   A language tag, as defined in <xref target="RFC5646"/>, identifies a
416   natural language spoken, written, or otherwise conveyed by human beings for
417   communication of information to other human beings. Computer languages are
418   explicitly excluded. HTTP uses language tags within the Accept-Language and
419   Content-Language fields.
420</t>
421<t>
422   In summary, a language tag is composed of one or more parts: A primary
423   language subtag followed by a possibly empty series of subtags:
424</t>
425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
426  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
427</artwork></figure>
428<t>
429   White space is not allowed within the tag and all tags are case-insensitive.
430   The name space of language subtags is administered by the IANA (see
431   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
432</t>
433<figure>
434  <preamble>Example tags include:</preamble>
435<artwork type="example">
436  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
437</artwork>
438</figure>
439<t>
440   See <xref target="RFC5646"/> for further information.
441</t>
442</section>
443</section>
444
445<section title="Payload" anchor="payload">
446<t>
447   HTTP messages &MAY; transfer a payload if not otherwise restricted by
448   the request method or response status code.  The payload consists of
449   metadata, in the form of header fields, and data, in the form of the
450   sequence of octets in the message body after any transfer-coding has
451   been decoded.
452</t>
453<iref item="payload"/>
454<t>   
455   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
456   representation of some resource.  We use separate terms for payload
457   and representation because some messages contain only the associated
458   representation's header fields (e.g., responses to HEAD) or only some
459   part(s) of the representation (e.g., the 206 status code).
460</t>
461<section title="Payload Header Fields" anchor="payload.header.fields">
462  <x:anchor-alias value="payload-header"/>
463<t>
464   HTTP header fields that specifically define the payload, rather than the
465   associated representation, are referred to as "payload header fields".
466   The following payload header fields are defined by HTTP/1.1:
467</t>
468<texttable align="left">
469  <ttcol>Header Field Name</ttcol>
470  <ttcol>Defined in...</ttcol>
471
472  <c>Content-Length</c> <c>&header-content-length;</c>
473  <c>Content-Range</c> <c>&header-content-range;</c>
474</texttable>
475</section>
476
477<section title="Payload Body" anchor="payload.body">
478  <x:anchor-alias value="payload-body"/>
479<t>
480   A payload body is only present in a message when a message body is
481   present, as described in &message-body;. The payload body is obtained
482   from the message body by decoding any Transfer-Encoding that might
483   have been applied to ensure safe and proper transfer of the message.
484</t>
485</section>
486</section>
487
488<section title="Representation" anchor="representation">
489<iref item="representation"/>
490<t>
491   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
492   communicated from one party to another.  A resource representation
493   is information that reflects the state of that resource, as observed
494   at some point in the past (e.g., in a response to GET) or to be
495   desired at some point in the future (e.g., in a PUT request).
496</t>
497<t>
498   Most, but not all, representations transferred via HTTP are intended
499   to be a representation of the target resource (the resource identified
500   by the effective request URI).  The precise semantics of a representation
501   are determined by the type of message (request or response), the request
502   method, the response status code, and the representation metadata.
503   For example, the above semantic is true for the representation in any
504   200 (OK) response to GET and for the representation in any PUT request.
505   A 200 response to PUT, in contrast, contains either a representation
506   that describes the successful action or a representation of the target
507   resource, with the latter indicated by a Content-Location header field
508   with the same value as the effective request URI.  Likewise, response
509   messages with an error status code usually contain a representation that
510   describes the error and what next steps are suggested for resolving it.
511</t>
512
513<section title="Representation Header Fields" anchor="representation.header.fields">
514  <x:anchor-alias value="representation-header"/>
515<t>
516   Representation header fields define metadata about the representation data
517   enclosed in the message body or, if no message body is present, about
518   the representation that would have been transferred in a 200 response
519   to a simultaneous GET request with the same effective request URI.
520</t>
521<t>
522   The following header fields are defined as representation metadata:
523</t>
524<texttable align="left">
525  <ttcol>Header Field Name</ttcol>
526  <ttcol>Defined in...</ttcol>
527
528  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
529  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
530  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
531  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
532  <c>Expires</c> <c>&header-expires;</c>
533</texttable>
534<t>
535   Additional header fields define metadata about the selected
536   representation, which might differ from the representation included
537   in the message for responses to some state-changing methods.
538   The following header fields are defined as selected representation
539   metadata:
540</t>
541<texttable align="left">
542  <ttcol>Header Field Name</ttcol>
543  <ttcol>Defined in...</ttcol>
544
545  <c>ETag</c> <c>&header-etag;</c>
546  <c>Last-Modified</c> <c>&header-last-modified;</c>
547</texttable>
548</section>
549
550<section title="Representation Data" anchor="representation.data">
551  <x:anchor-alias value="representation-data"/>
552<t>
553   The representation body associated with an HTTP message is
554   either provided as the payload body of the message or
555   referred to by the message semantics and the effective request
556   URI.  The representation data is in a format and encoding defined by
557   the representation metadata header fields.
558</t>
559<t>
560   The data type of the representation data
561   is determined via the header fields Content-Type and Content-Encoding.
562   These define a two-layer, ordered encoding model:
563</t>
564<figure><artwork type="example">
565  representation-data := Content-Encoding( Content-Type( bits ) )
566</artwork></figure>
567<t>
568   Content-Type specifies the media type of the underlying data, which
569   defines both the data format and how that data &SHOULD; be processed
570   by the recipient (within the scope of the request method semantics).
571   Any HTTP/1.1 message containing a payload body &SHOULD; include a
572   Content-Type header field defining the media type of the associated
573   representation unless that metadata is unknown to the sender.
574   If the Content-Type header field is not present, it indicates that
575   the sender does not know the media type of the representation;
576   recipients &MAY; either assume that the media type is
577   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
578   or examine the content to determine its type.
579</t>
580<t>
581   In practice, resource owners do not always properly configure their origin
582   server to provide the correct Content-Type for a given representation,
583   with the result that some clients will examine a response body's content
584   and override the specified type.
585   Clients that do so risk drawing incorrect conclusions, which might expose
586   additional security risks (e.g., "privilege escalation").  Furthermore,
587   it is impossible to determine the sender's intent by examining the data
588   format: many data formats match multiple media types that differ only in
589   processing semantics.  Implementers are encouraged to provide a means of
590   disabling such "content sniffing" when it is used.
591</t>
592<t>
593   Content-Encoding is used to indicate any additional content
594   codings applied to the data, usually for the purpose of data
595   compression, that are a property of the representation.  If
596   Content-Encoding is not present, then there is no additional
597   encoding beyond that defined by the Content-Type.
598</t>
599</section>
600</section>
601
602<section title="Content Negotiation" anchor="content.negotiation">
603<t>
604   HTTP responses include a representation which contains information for
605   interpretation, whether by a human user or for further processing.
606   Often, the server has different ways of representing the
607   same information; for example, in different formats, languages,
608   or using different character encodings.
609</t>
610<t>
611   HTTP clients and their users might have different or variable
612   capabilities, characteristics or preferences which would influence
613   which representation, among those available from the server,
614   would be best for the server to deliver. For this reason, HTTP
615   provides mechanisms for "content negotiation" &mdash; a process of
616   allowing selection of a representation of a given resource,
617   when more than one is available.
618</t>
619<t>
620   This specification defines two patterns of content negotiation;
621   "server-driven", where the server selects the representation based
622   upon the client's stated preferences, and "agent-driven" negotiation,
623   where the server provides a list of representations for the client to
624   choose from, based upon their metadata. In addition,  there are
625   other patterns: some applications use an "active content" pattern,
626   where the server returns active content which runs on the client
627   and, based on client available parameters, selects additional
628   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
629   has also been proposed.
630</t>
631<t>
632   These patterns are all widely used, and have trade-offs in applicability
633   and practicality. In particular, when the number of preferences or
634   capabilities to be expressed by a client are large (such as when many
635   different formats are supported by a user-agent), server-driven
636   negotiation becomes unwieldy, and might not be appropriate. Conversely,
637   when the number of representations to choose from is very large,
638   agent-driven negotiation might not be appropriate.
639</t>
640<t>
641   Note that in all cases, the supplier of representations has the
642   responsibility for determining which representations might be
643   considered to be the "same information".
644</t>
645
646<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
647<t>
648   If the selection of the best representation for a response is made by
649   an algorithm located at the server, it is called server-driven
650   negotiation. Selection is based on the available representations of
651   the response (the dimensions over which it can vary; e.g., language,
652   content-coding, etc.) and the contents of particular header fields in
653   the request message or on other information pertaining to the request
654   (such as the network address of the client).
655</t>
656<t>
657   Server-driven negotiation is advantageous when the algorithm for
658   selecting from among the available representations is difficult to
659   describe to the user agent, or when the server desires to send its
660   "best guess" to the client along with the first response (hoping to
661   avoid the round-trip delay of a subsequent request if the "best
662   guess" is good enough for the user). In order to improve the server's
663   guess, the user agent &MAY; include request header fields (Accept,
664   Accept-Language, Accept-Encoding, etc.) which describe its
665   preferences for such a response.
666</t>
667<t>
668   Server-driven negotiation has disadvantages:
669  <list style="numbers">
670    <t>
671         It is impossible for the server to accurately determine what
672         might be "best" for any given user, since that would require
673         complete knowledge of both the capabilities of the user agent
674         and the intended use for the response (e.g., does the user want
675         to view it on screen or print it on paper?).
676    </t>
677    <t>
678         Having the user agent describe its capabilities in every
679         request can be both very inefficient (given that only a small
680         percentage of responses have multiple representations) and a
681         potential violation of the user's privacy.
682    </t>
683    <t>
684         It complicates the implementation of an origin server and the
685         algorithms for generating responses to a request.
686    </t>
687    <t>
688         It might limit a public cache's ability to use the same response
689         for multiple user's requests.
690    </t>
691  </list>
692</t>
693<t>
694   Server-driven negotiation allows the user agent to specify its preferences,
695   but it cannot expect responses to always honor them. For example, the origin
696   server might not implement server-driven negotiation, or it might decide that
697   sending a response that doesn't conform to them is better than sending a 406
698   (Not Acceptable) response.
699</t>
700<t>
701   Many of the mechanisms for expressing preferences use quality values to
702   declare relative preference. See &qvalue; for more information.
703</t>
704<t>
705   HTTP/1.1 includes the following header fields for enabling
706   server-driven negotiation through description of user agent
707   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
708   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
709   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
710   However, an origin server is not limited to these dimensions and &MAY; vary
711   the response based on any aspect of the request, including aspects
712   of the connection (e.g., IP address) or information within extension
713   header fields not defined by this specification.
714</t>
715<x:note>
716  <t>
717    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
718    because new clients might not be recognized.
719  </t>
720</x:note>
721<t>
722   The Vary header field (&header-vary;) can be used to express the parameters the
723   server uses to select a representation that is subject to server-driven
724   negotiation.
725</t>
726</section>
727
728<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
729<t>
730   With agent-driven negotiation, selection of the best representation
731   for a response is performed by the user agent after receiving an
732   initial response from the origin server. Selection is based on a list
733   of the available representations of the response included within the
734   header fields or body of the initial response, with each
735   representation identified by its own URI. Selection from among the
736   representations can be performed automatically (if the user agent is
737   capable of doing so) or manually by the user selecting from a
738   generated (possibly hypertext) menu.
739</t>
740<t>
741   Agent-driven negotiation is advantageous when the response would vary
742   over commonly-used dimensions (such as type, language, or encoding),
743   when the origin server is unable to determine a user agent's
744   capabilities from examining the request, and generally when public
745   caches are used to distribute server load and reduce network usage.
746</t>
747<t>
748   Agent-driven negotiation suffers from the disadvantage of needing a
749   second request to obtain the best alternate representation. This
750   second request is only efficient when caching is used. In addition,
751   this specification does not define any mechanism for supporting
752   automatic selection, though it also does not prevent any such
753   mechanism from being developed as an extension and used within
754   HTTP/1.1.
755</t>
756<t>
757   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
758   status codes for enabling agent-driven negotiation when the server is
759   unwilling or unable to provide a varying response using server-driven
760   negotiation.
761</t>
762</section>
763</section>
764
765<section title="Header Field Definitions" anchor="header.field.definitions">
766<t>
767   This section defines the syntax and semantics of HTTP/1.1 header fields
768   related to the payload of messages.
769</t>
770
771<section title="Accept" anchor="header.accept">
772  <iref primary="true" item="Accept header field" x:for-anchor=""/>
773  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
774  <x:anchor-alias value="Accept"/>
775  <x:anchor-alias value="accept-ext"/>
776  <x:anchor-alias value="accept-params"/>
777  <x:anchor-alias value="media-range"/>
778<t>
779   The "Accept" header field can be used by user agents to specify
780   response media types that are acceptable. Accept header fields can be used to
781   indicate that the request is specifically limited to a small set of desired
782   types, as in the case of a request for an in-line image.
783</t>
784<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
785  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
786 
787  <x:ref>media-range</x:ref>    = ( "*/*"
788                   / ( <x:ref>type</x:ref> "/" "*" )
789                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
790                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
791  <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> )
792  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
793</artwork></figure>
794<t>
795   The asterisk "*" character is used to group media types into ranges,
796   with "*/*" indicating all media types and "type/*" indicating all
797   subtypes of that type. The media-range &MAY; include media type
798   parameters that are applicable to that range.
799</t>
800<t>
801   Each media-range &MAY; be followed by one or more accept-params,
802   beginning with the "q" parameter for indicating a relative quality
803   factor. The first "q" parameter (if any) separates the media-range
804   parameter(s) from the accept-params. Quality factors allow the user
805   or user agent to indicate the relative degree of preference for that
806   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
807   default value is q=1.
808</t>
809<x:note>
810  <t>
811    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
812    parameters from Accept extension parameters is due to historical
813    practice. Although this prevents any media type parameter named
814    "q" from being used with a media range, such an event is believed
815    to be unlikely given the lack of any "q" parameters in the IANA
816    media type registry and the rare usage of any media type
817    parameters in Accept. Future media types are discouraged from
818    registering any parameter named "q".
819  </t>
820</x:note>
821<t>
822   The example
823</t>
824<figure><artwork type="example">
825  Accept: audio/*; q=0.2, audio/basic
826</artwork></figure>
827<t>
828   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
829   type if it is the best available after an 80% mark-down in quality".
830</t>
831<t>
832   A request without any Accept header field implies that the user agent
833   will accept any media type in response.
834   If an Accept header field is present in a request and none of the
835   available representations for the response have a media type that is
836   listed as acceptable, the origin server &MAY; either
837   honor the Accept header field by sending a 406 (Not Acceptable) response
838   or disregard the Accept header field by treating the response as if
839   it is not subject to content negotiation.
840</t>
841<t>
842   A more elaborate example is
843</t>
844<figure><artwork type="example">
845  Accept: text/plain; q=0.5, text/html,
846          text/x-dvi; q=0.8, text/x-c
847</artwork></figure>
848<t>
849   Verbally, this would be interpreted as "text/html and text/x-c are
850   the preferred media types, but if they do not exist, then send the
851   text/x-dvi representation, and if that does not exist, send the text/plain
852   representation".
853</t>
854<t>
855   Media ranges can be overridden by more specific media ranges or
856   specific media types. If more than one media range applies to a given
857   type, the most specific reference has precedence. For example,
858</t>
859<figure><artwork type="example">
860  Accept: text/*, text/plain, text/plain;format=flowed, */*
861</artwork></figure>
862<t>
863   have the following precedence:
864   <list style="numbers">
865    <t>text/plain;format=flowed</t>
866    <t>text/plain</t>
867    <t>text/*</t>
868    <t>*/*</t>
869   </list>
870</t>
871<t>
872   The media type quality factor associated with a given type is
873   determined by finding the media range with the highest precedence
874   which matches that type. For example,
875</t>
876<figure><artwork type="example">
877  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
878          text/html;level=2;q=0.4, */*;q=0.5
879</artwork></figure>
880<t>
881   would cause the following values to be associated:
882</t>
883<texttable align="left">
884  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
885  <c>text/html;level=1</c>    <c>1</c>
886  <c>text/html</c>            <c>0.7</c>
887  <c>text/plain</c>           <c>0.3</c>
888  <c>image/jpeg</c>           <c>0.5</c>
889  <c>text/html;level=2</c>    <c>0.4</c>
890  <c>text/html;level=3</c>    <c>0.7</c>
891</texttable>
892<t>
893      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
894      values for certain media ranges. However, unless the user agent is
895      a closed system which cannot interact with other rendering agents,
896      this default set ought to be configurable by the user.
897</t>
898</section>
899
900<section title="Accept-Charset" anchor="header.accept-charset">
901  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
902  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
903  <x:anchor-alias value="Accept-Charset"/>
904<t>
905   The "Accept-Charset" header field can be used by user agents to
906   indicate what character encodings are acceptable in a response
907   payload. This field allows
908   clients capable of understanding more comprehensive or special-purpose
909   character encodings to signal that capability to a server which is capable of
910   representing documents in those character encodings.
911</t>
912<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
913  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
914                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
915</artwork></figure>
916<t>
917   Character encoding values (a.k.a., charsets) are described in
918   <xref target="character.sets"/>. Each charset &MAY; be given an
919   associated quality value which represents the user's preference
920   for that charset. The default value is q=1. An example is
921</t>
922<figure><artwork type="example">
923  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
924</artwork></figure>
925<t>
926   The special value "*", if present in the Accept-Charset field,
927   matches every character encoding which is not mentioned elsewhere in the
928   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
929   all character encodings not explicitly mentioned get a quality value of 0.
930</t>
931<t>
932   A request without any Accept-Charset header field implies that the user
933   agent will accept any character encoding in response.
934   If an Accept-Charset header field is present in a request and none of the
935   available representations for the response have a character encoding that
936   is listed as acceptable, the origin server &MAY; either honor the
937   Accept-Charset header field by sending a 406 (Not Acceptable) response or
938   disregard the Accept-Charset header field by treating the response as if
939   it is not subject to content negotiation.
940</t>
941</section>
942
943<section title="Accept-Encoding" anchor="header.accept-encoding">
944  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
945  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
946  <x:anchor-alias value="Accept-Encoding"/>
947  <x:anchor-alias value="codings"/>
948<t>
949   The "Accept-Encoding" header field can be used by user agents to
950   indicate what response content-codings (<xref target="content.codings"/>)
951   are acceptable in the response.  An "identity" token is used as a synonym
952   for "no encoding" in order to communicate when no encoding is preferred.
953</t>
954<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
955  <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
956  <x:ref>codings</x:ref>          = <x:ref>content-coding</x:ref> / "identity" / "*"
957</artwork></figure>
958<t>
959   Each codings value &MAY; be given an associated quality value which
960   represents the preference for that encoding. The default value is q=1.
961</t>
962<t>
963   For example,
964</t>
965<figure><artwork type="example">
966  Accept-Encoding: compress, gzip
967  Accept-Encoding:
968  Accept-Encoding: *
969  Accept-Encoding: compress;q=0.5, gzip;q=1.0
970  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
971</artwork></figure>
972<t>
973   A server tests whether a content-coding for a given representation is
974   acceptable, according to an Accept-Encoding field, using these rules:
975  <list style="numbers">
976      <t>The special "*" symbol in an Accept-Encoding field matches any
977         available content-coding not explicitly listed in the header
978         field.</t>
979
980      <t>If the representation has no content-coding, then it is acceptable
981         by default unless specifically excluded by the Accept-Encoding field
982         stating either "identity;q=0" or "*;q=0" without a more specific
983         entry for "identity".</t>
984
985      <t>If the representation's content-coding is one of the content-codings
986         listed in the Accept-Encoding field, then it is acceptable unless
987         it is accompanied by a qvalue of 0. (As defined in &qvalue;, a
988         qvalue of 0 means "not acceptable".)</t>
989
990      <t>If multiple content-codings are acceptable, then the acceptable
991         content-coding with the highest non-zero qvalue is preferred.</t>
992  </list>
993</t>
994<t>
995   An Accept-Encoding header field with a combined field-value that is empty
996   implies that the user agent does not want any content-coding in response.
997   If an Accept-Encoding header field is present in a request and none of the
998   available representations for the response have a content-coding that
999   is listed as acceptable, the origin server &SHOULD; send a response
1000   without any content-coding.
1001</t>
1002<t>
1003   A request without an Accept-Encoding header field implies that the user
1004   agent will accept any content-coding in response, but a representation
1005   without content-coding is preferred for compatibility with the widest
1006   variety of user agents.
1007</t>
1008<x:note>
1009  <t>
1010    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1011    associated with content-codings. This means that qvalues will not
1012    work and are not permitted with x-gzip or x-compress.
1013  </t>
1014</x:note>
1015</section>
1016
1017<section title="Accept-Language" anchor="header.accept-language">
1018  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1019  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
1020  <x:anchor-alias value="Accept-Language"/>
1021  <x:anchor-alias value="language-range"/>
1022<t>
1023   The "Accept-Language" header field can be used by user agents to
1024   indicate the set of natural languages that are preferred in the response.
1025   Language tags are defined in <xref target="language.tags"/>.
1026</t>
1027<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1028  <x:ref>Accept-Language</x:ref> =
1029                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1030  <x:ref>language-range</x:ref>  =
1031            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1032</artwork></figure>
1033<t>
1034   Each language-range can be given an associated quality value which
1035   represents an estimate of the user's preference for the languages
1036   specified by that range. The quality value defaults to "q=1". For
1037   example,
1038</t>
1039<figure><artwork type="example">
1040  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1041</artwork></figure>
1042<t>
1043   would mean: "I prefer Danish, but will accept British English and
1044   other types of English".
1045   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1046</t>
1047<t>
1048   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1049   several matching schemes. Implementations can offer the most appropriate
1050   matching scheme for their requirements.
1051</t>
1052<x:note>
1053  <t>
1054    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1055    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1056    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1057  </t>
1058</x:note>
1059<t>
1060   It might be contrary to the privacy expectations of the user to send
1061   an Accept-Language header field with the complete linguistic preferences of
1062   the user in every request. For a discussion of this issue, see
1063   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1064</t>
1065<t>
1066   As intelligibility is highly dependent on the individual user, it is
1067   recommended that client applications make the choice of linguistic
1068   preference available to the user. If the choice is not made
1069   available, then the Accept-Language header field &MUST-NOT; be given in
1070   the request.
1071</t>
1072<x:note>
1073  <t>
1074    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1075    the user, we remind implementors of  the fact that users are not
1076    familiar with the details of language matching as described above,
1077    and ought to be provided appropriate guidance. As an example, users
1078    might assume that on selecting "en-gb", they will be served any
1079    kind of English document if British English is not available. A
1080    user agent might suggest in such a case to add "en" to get the
1081    best matching behavior.
1082  </t>
1083</x:note>
1084</section>
1085
1086<section title="Content-Encoding" anchor="header.content-encoding">
1087  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1088  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1089  <x:anchor-alias value="Content-Encoding"/>
1090<t>
1091   The "Content-Encoding" header field indicates what content-codings
1092   have been applied to the representation beyond those inherent in the media
1093   type, and thus what decoding mechanisms have to be applied in order to obtain
1094   the media-type referenced by the Content-Type header field.
1095   Content-Encoding is primarily used to allow a representation to be
1096   compressed without losing the identity of its underlying media type.
1097</t>
1098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1099  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1100</artwork></figure>
1101<t>
1102   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1103</t>
1104<figure><artwork type="example">
1105  Content-Encoding: gzip
1106</artwork></figure>
1107<t>
1108   The content-coding is a characteristic of the representation.
1109   Typically, the representation body is stored with this
1110   encoding and is only decoded before rendering or analogous usage.
1111   However, a transforming proxy &MAY; modify the content-coding if the
1112   new coding is known to be acceptable to the recipient, unless the
1113   "no-transform" cache-control directive is present in the message.
1114</t>
1115<t>
1116   If the media type includes an inherent encoding, such as a data format
1117   that is always compressed, then that encoding would not be restated as
1118   a Content-Encoding even if it happens to be the same algorithm as one
1119   of the content-codings.  Such a content-coding would only be listed if,
1120   for some bizarre reason, it is applied a second time to form the
1121   representation.  Likewise, an origin server might choose to publish the
1122   same payload data as multiple representations that differ only in whether
1123   the coding is defined as part of Content-Type or Content-Encoding, since
1124   some user agents will behave differently in their handling of each
1125   response (e.g., open a "Save as ..." dialog instead of automatic
1126   decompression and rendering of content).
1127</t>
1128<t>
1129   A representation that has a content-coding applied to it &MUST; include
1130   a Content-Encoding header field (<xref target="header.content-encoding"/>)
1131   that lists the content-coding(s) applied.
1132</t>
1133<t>
1134   If multiple encodings have been applied to a representation, the content
1135   codings &MUST; be listed in the order in which they were applied.
1136   Additional information about the encoding parameters &MAY; be provided
1137   by other header fields not defined by this specification.
1138</t>
1139<t>
1140   If the content-coding of a representation in a request message is not
1141   acceptable to the origin server, the server &SHOULD; respond with a
1142   status code of 415 (Unsupported Media Type).
1143</t>
1144</section>
1145
1146<section title="Content-Language" anchor="header.content-language">
1147  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1148  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1149  <x:anchor-alias value="Content-Language"/>
1150<t>
1151   The "Content-Language" header field describes the natural
1152   language(s) of the intended audience for the representation. Note that this might
1153   not be equivalent to all the languages used within the representation.
1154</t>
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1156  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1157</artwork></figure>
1158<t>
1159   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1160   Content-Language is to allow a user to identify and differentiate
1161   representations according to the user's own preferred language. Thus, if the
1162   body content is intended only for a Danish-literate audience, the
1163   appropriate field is
1164</t>
1165<figure><artwork type="example">
1166  Content-Language: da
1167</artwork></figure>
1168<t>
1169   If no Content-Language is specified, the default is that the content
1170   is intended for all language audiences. This might mean that the
1171   sender does not consider it to be specific to any natural language,
1172   or that the sender does not know for which language it is intended.
1173</t>
1174<t>
1175   Multiple languages &MAY; be listed for content that is intended for
1176   multiple audiences. For example, a rendition of the "Treaty of
1177   Waitangi", presented simultaneously in the original Maori and English
1178   versions, would call for
1179</t>
1180<figure><artwork type="example">
1181  Content-Language: mi, en
1182</artwork></figure>
1183<t>
1184   However, just because multiple languages are present within a representation
1185   does not mean that it is intended for multiple linguistic audiences.
1186   An example would be a beginner's language primer, such as "A First
1187   Lesson in Latin", which is clearly intended to be used by an
1188   English-literate audience. In this case, the Content-Language would
1189   properly only include "en".
1190</t>
1191<t>
1192   Content-Language &MAY; be applied to any media type &mdash; it is not
1193   limited to textual documents.
1194</t>
1195</section>
1196
1197<section title="Content-Location" anchor="header.content-location">
1198  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1199  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1200  <x:anchor-alias value="Content-Location"/>
1201<t>
1202   The "Content-Location" header field supplies a URI that can be used
1203   as a specific identifier for the representation in this message.
1204   In other words, if one were to perform a GET on this URI at the time
1205   of this message's generation, then a 200 response would contain the
1206   same representation that is enclosed as payload in this message.
1207</t>
1208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1209  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1210</artwork></figure>
1211<t>
1212   The Content-Location value is not a replacement for the effective
1213   Request URI (&effective-request-uri;).  It is representation metadata.
1214   It has the same syntax and semantics as the header field of the same name
1215   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1216   However, its appearance in an HTTP message has some special implications
1217   for HTTP recipients.
1218</t>
1219<t>
1220   If Content-Location is included in a response message and its value
1221   is the same as the effective request URI, then the response payload
1222   &SHOULD; be considered a current representation of that resource.
1223   For a GET or HEAD request, this is the same as the default semantics
1224   when no Content-Location is provided by the server.  For a state-changing
1225   request like PUT or POST, it implies that the server's response contains
1226   the new representation of that resource, thereby distinguishing it from
1227   representations that might only report about the action (e.g., "It worked!").
1228   This allows authoring applications to update their local copies without
1229   the need for a subsequent GET request.
1230</t>
1231<t>
1232   If Content-Location is included in a response message and its value
1233   differs from the effective request URI, then the origin server is
1234   informing recipients that this representation has its own, presumably
1235   more specific, identifier.  For a GET or HEAD request, this is an
1236   indication that the effective request URI identifies a resource that
1237   is subject to content negotiation and the selected representation for
1238   this response can also be found at the identified URI.  For other
1239   methods, such a Content-Location indicates that this representation
1240   contains a report on the action's status and the same report is
1241   available (for future access with GET) at the given URI.  For
1242   example, a purchase transaction made via a POST request might
1243   include a receipt document as the payload of the 200 response;
1244   the Content-Location value provides an identifier for retrieving
1245   a copy of that same receipt in the future.
1246</t>
1247<t>
1248   If Content-Location is included in a request message, then it &MAY;
1249   be interpreted by the origin server as an indication of where the
1250   user agent originally obtained the content of the enclosed
1251   representation (prior to any subsequent modification of the content
1252   by that user agent).  In other words, the user agent is providing
1253   the same representation metadata that it received with the original
1254   representation.  However, such interpretation &MUST-NOT; be used to
1255   alter the semantics of the method requested by the client.  For
1256   example, if a client makes a PUT request on a negotiated resource
1257   and the origin server accepts that PUT (without redirection), then the
1258   new set of values for that resource is expected to be consistent with
1259   the one representation supplied in that PUT; the Content-Location
1260   cannot be used as a form of reverse content selection that
1261   identifies only one of the negotiated representations to be updated.
1262   If the user agent had wanted the latter semantics, it would have applied
1263   the PUT directly to the Content-Location URI.
1264</t>
1265<t>
1266   A Content-Location field received in a request message is transitory
1267   information that &SHOULD-NOT; be saved with other representation
1268   metadata for use in later responses.  The Content-Location's value
1269   might be saved for use in other contexts, such as within source links
1270   or other metadata.
1271</t>
1272<t>
1273   A cache cannot assume that a representation with a Content-Location
1274   different from the URI used to retrieve it can be used to respond to
1275   later requests on that Content-Location URI.
1276</t>
1277<t>
1278   If the Content-Location value is a partial URI, the partial URI is
1279   interpreted relative to the effective request URI.
1280</t>
1281</section>
1282
1283<section title="Content-Type" anchor="header.content-type">
1284  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1285  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1286  <x:anchor-alias value="Content-Type"/>
1287<t>
1288   The "Content-Type" header field indicates the media type of the
1289   representation. In the case of responses to the HEAD method, the media type is
1290   that which would have been sent had the request been a GET.
1291</t>
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1293  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1294</artwork></figure>
1295<t>
1296   Media types are defined in <xref target="media.types"/>. An example of the field is
1297</t>
1298<figure><artwork type="example">
1299  Content-Type: text/html; charset=ISO-8859-4
1300</artwork></figure>
1301<t>
1302   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1303</t>
1304</section>
1305
1306</section>
1307
1308<section title="IANA Considerations" anchor="IANA.considerations">
1309
1310<section title="Content Coding Registry" anchor="content.coding.registration">
1311<t>
1312   The registration procedure for HTTP Content Codings is now defined
1313   by <xref target="content.coding.registry"/> of this document.
1314</t>
1315<t>
1316   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1317   shall be updated with the registration below:
1318</t>
1319<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1320   <ttcol>Name</ttcol>
1321   <ttcol>Description</ttcol>
1322   <ttcol>Reference</ttcol>
1323   <c>compress</c>
1324   <c>UNIX "compress" program method</c>
1325   <c>
1326      &compress-coding;
1327   </c>
1328   <c>deflate</c>
1329   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1330   the "zlib" data format (<xref target="RFC1950"/>)
1331   </c>
1332   <c>
1333      &deflate-coding;
1334   </c>
1335   <c>gzip</c>
1336   <c>Same as GNU zip <xref target="RFC1952"/></c>
1337   <c>
1338      &gzip-coding;
1339   </c>
1340   <c>identity</c>
1341   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
1342   <c>
1343      <xref target="header.accept-encoding"/>
1344   </c>
1345</texttable>
1346</section>
1347
1348</section>
1349
1350<section title="Security Considerations" anchor="security.considerations">
1351<t>
1352   This section is meant to inform application developers, information
1353   providers, and users of the security limitations in HTTP/1.1 as
1354   described by this document. The discussion does not include
1355   definitive solutions to the problems revealed, though it does make
1356   some suggestions for reducing security risks.
1357</t>
1358
1359<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1360<t>
1361   Accept header fields can reveal information about the user to all
1362   servers which are accessed. The Accept-Language header field in particular
1363   can reveal information the user would consider to be of a private
1364   nature, because the understanding of particular languages is often
1365   strongly correlated to the membership of a particular ethnic group.
1366   User agents which offer the option to configure the contents of an
1367   Accept-Language header field to be sent in every request are strongly
1368   encouraged to let the configuration process include a message which
1369   makes the user aware of the loss of privacy involved.
1370</t>
1371<t>
1372   An approach that limits the loss of privacy would be for a user agent
1373   to omit the sending of Accept-Language header fields by default, and to ask
1374   the user whether or not to start sending Accept-Language header fields to a
1375   server if it detects, by looking for any Vary header fields
1376   generated by the server, that such sending could improve the quality
1377   of service.
1378</t>
1379<t>
1380   Elaborate user-customized accept header fields sent in every request,
1381   in particular if these include quality values, can be used by servers
1382   as relatively reliable and long-lived user identifiers. Such user
1383   identifiers would allow content providers to do click-trail tracking,
1384   and would allow collaborating content providers to match cross-server
1385   click-trails or form submissions of individual users. Note that for
1386   many users not behind a proxy, the network address of the host
1387   running the user agent will also serve as a long-lived user
1388   identifier. In environments where proxies are used to enhance
1389   privacy, user agents ought to be conservative in offering accept
1390   header configuration options to end users. As an extreme privacy
1391   measure, proxies could filter the accept header fields in relayed requests.
1392   General purpose user agents which provide a high degree of header
1393   configurability &SHOULD; warn users about the loss of privacy which can
1394   be involved.
1395</t>
1396</section>
1397
1398</section>
1399
1400</middle>
1401<back>
1402
1403<references title="Normative References">
1404
1405<reference anchor="Part1">
1406  <front>
1407    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1408    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1409      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1410      <address><email>fielding@gbiv.com</email></address>
1411    </author>
1412    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1413      <organization abbrev="W3C">World Wide Web Consortium</organization>
1414      <address><email>ylafon@w3.org</email></address>
1415    </author>
1416    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1417      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1418      <address><email>julian.reschke@greenbytes.de</email></address>
1419    </author>
1420    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1421  </front>
1422  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1423  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1424</reference>
1425
1426<reference anchor="Part2">
1427  <front>
1428    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1429    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1430      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1431      <address><email>fielding@gbiv.com</email></address>
1432    </author>
1433    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1434      <organization abbrev="W3C">World Wide Web Consortium</organization>
1435      <address><email>ylafon@w3.org</email></address>
1436    </author>
1437    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1438      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1439      <address><email>julian.reschke@greenbytes.de</email></address>
1440    </author>
1441    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1442  </front>
1443  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1444  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1445</reference>
1446
1447<reference anchor="Part4">
1448  <front>
1449    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1450    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1451      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1452      <address><email>fielding@gbiv.com</email></address>
1453    </author>
1454    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1455      <organization abbrev="W3C">World Wide Web Consortium</organization>
1456      <address><email>ylafon@w3.org</email></address>
1457    </author>
1458    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1459      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1460      <address><email>julian.reschke@greenbytes.de</email></address>
1461    </author>
1462    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1463  </front>
1464  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1465  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1466</reference>
1467
1468<reference anchor="Part5">
1469  <front>
1470    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1471    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1472      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1473      <address><email>fielding@gbiv.com</email></address>
1474    </author>
1475    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1476      <organization abbrev="W3C">World Wide Web Consortium</organization>
1477      <address><email>ylafon@w3.org</email></address>
1478    </author>
1479    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1480      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1481      <address><email>julian.reschke@greenbytes.de</email></address>
1482    </author>
1483    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1484  </front>
1485  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1486  <x:source href="p5-range.xml" basename="p5-range"/>
1487</reference>
1488
1489<reference anchor="Part6">
1490  <front>
1491    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1492    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1493      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1494      <address><email>fielding@gbiv.com</email></address>
1495    </author>
1496    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1497      <organization abbrev="W3C">World Wide Web Consortium</organization>
1498      <address><email>ylafon@w3.org</email></address>
1499    </author>
1500    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1501      <organization>Rackspace</organization>
1502      <address><email>mnot@mnot.net</email></address>
1503    </author>
1504    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1505      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1506      <address><email>julian.reschke@greenbytes.de</email></address>
1507    </author>
1508    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1509  </front>
1510  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1511  <x:source href="p6-cache.xml" basename="p6-cache"/>
1512</reference>
1513
1514<reference anchor="RFC1950">
1515  <front>
1516    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1517    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1518      <organization>Aladdin Enterprises</organization>
1519      <address><email>ghost@aladdin.com</email></address>
1520    </author>
1521    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1522    <date month="May" year="1996"/>
1523  </front>
1524  <seriesInfo name="RFC" value="1950"/>
1525  <!--<annotation>
1526    RFC 1950 is an Informational RFC, thus it might be less stable than
1527    this specification. On the other hand, this downward reference was
1528    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1529    therefore it is unlikely to cause problems in practice. See also
1530    <xref target="BCP97"/>.
1531  </annotation>-->
1532</reference>
1533
1534<reference anchor="RFC1951">
1535  <front>
1536    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1537    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1538      <organization>Aladdin Enterprises</organization>
1539      <address><email>ghost@aladdin.com</email></address>
1540    </author>
1541    <date month="May" year="1996"/>
1542  </front>
1543  <seriesInfo name="RFC" value="1951"/>
1544  <!--<annotation>
1545    RFC 1951 is an Informational RFC, thus it might be less stable than
1546    this specification. On the other hand, this downward reference was
1547    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1548    therefore it is unlikely to cause problems in practice. See also
1549    <xref target="BCP97"/>.
1550  </annotation>-->
1551</reference>
1552
1553<reference anchor="RFC1952">
1554  <front>
1555    <title>GZIP file format specification version 4.3</title>
1556    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1557      <organization>Aladdin Enterprises</organization>
1558      <address><email>ghost@aladdin.com</email></address>
1559    </author>
1560    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1561      <address><email>gzip@prep.ai.mit.edu</email></address>
1562    </author>
1563    <author initials="M." surname="Adler" fullname="Mark Adler">
1564      <address><email>madler@alumni.caltech.edu</email></address>
1565    </author>
1566    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1567      <address><email>ghost@aladdin.com</email></address>
1568    </author>
1569    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1570      <address><email>randeg@alumni.rpi.edu</email></address>
1571    </author>
1572    <date month="May" year="1996"/>
1573  </front>
1574  <seriesInfo name="RFC" value="1952"/>
1575  <!--<annotation>
1576    RFC 1952 is an Informational RFC, thus it might be less stable than
1577    this specification. On the other hand, this downward reference was
1578    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1579    therefore it is unlikely to cause problems in practice. See also
1580    <xref target="BCP97"/>.
1581  </annotation>-->
1582</reference>
1583
1584<reference anchor="RFC2045">
1585  <front>
1586    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1587    <author initials="N." surname="Freed" fullname="Ned Freed">
1588      <organization>Innosoft International, Inc.</organization>
1589      <address><email>ned@innosoft.com</email></address>
1590    </author>
1591    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1592      <organization>First Virtual Holdings</organization>
1593      <address><email>nsb@nsb.fv.com</email></address>
1594    </author>
1595    <date month="November" year="1996"/>
1596  </front>
1597  <seriesInfo name="RFC" value="2045"/>
1598</reference>
1599
1600<reference anchor="RFC2046">
1601  <front>
1602    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1603    <author initials="N." surname="Freed" fullname="Ned Freed">
1604      <organization>Innosoft International, Inc.</organization>
1605      <address><email>ned@innosoft.com</email></address>
1606    </author>
1607    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1608      <organization>First Virtual Holdings</organization>
1609      <address><email>nsb@nsb.fv.com</email></address>
1610    </author>
1611    <date month="November" year="1996"/>
1612  </front>
1613  <seriesInfo name="RFC" value="2046"/>
1614</reference>
1615
1616<reference anchor='RFC4647'>
1617  <front>
1618    <title>Matching of Language Tags</title>
1619    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
1620      <organization>Yahoo! Inc.</organization>
1621      <address><email>addison@inter-locale.com</email></address>
1622    </author>
1623    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
1624      <organization>Google</organization>
1625      <address><email>mark.davis@macchiato.com</email></address>
1626    </author>
1627    <date year='2006' month='September' />
1628  </front>
1629  <seriesInfo name='BCP' value='47' />
1630  <seriesInfo name='RFC' value='4647' />
1631</reference>
1632
1633<reference anchor="RFC5234">
1634  <front>
1635    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1636    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1637      <organization>Brandenburg InternetWorking</organization>
1638      <address>
1639        <email>dcrocker@bbiw.net</email>
1640      </address> 
1641    </author>
1642    <author initials="P." surname="Overell" fullname="Paul Overell">
1643      <organization>THUS plc.</organization>
1644      <address>
1645        <email>paul.overell@thus.net</email>
1646      </address>
1647    </author>
1648    <date month="January" year="2008"/>
1649  </front>
1650  <seriesInfo name="STD" value="68"/>
1651  <seriesInfo name="RFC" value="5234"/>
1652</reference>
1653
1654<reference anchor='RFC5646'>
1655  <front>
1656    <title>Tags for Identifying Languages</title>
1657    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
1658      <organization>Lab126</organization>
1659      <address><email>addison@inter-locale.com</email></address>
1660    </author>
1661    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
1662      <organization>Google</organization>
1663      <address><email>mark.davis@google.com</email></address>
1664    </author>
1665    <date month='September' year='2009' />
1666  </front>
1667  <seriesInfo name='BCP' value='47' />
1668  <seriesInfo name='RFC' value='5646' />
1669</reference>
1670
1671</references>
1672
1673<references title="Informative References">
1674
1675<reference anchor="RFC1945">
1676  <front>
1677    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
1678    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1679      <organization>MIT, Laboratory for Computer Science</organization>
1680      <address><email>timbl@w3.org</email></address>
1681    </author>
1682    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
1683      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1684      <address><email>fielding@ics.uci.edu</email></address>
1685    </author>
1686    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1687      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
1688      <address><email>frystyk@w3.org</email></address>
1689    </author>
1690    <date month="May" year="1996"/>
1691  </front>
1692  <seriesInfo name="RFC" value="1945"/>
1693</reference>
1694
1695<reference anchor="RFC2049">
1696  <front>
1697    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
1698    <author initials="N." surname="Freed" fullname="Ned Freed">
1699      <organization>Innosoft International, Inc.</organization>
1700      <address><email>ned@innosoft.com</email></address>
1701    </author>
1702    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1703      <organization>First Virtual Holdings</organization>
1704      <address><email>nsb@nsb.fv.com</email></address>
1705    </author>
1706    <date month="November" year="1996"/>
1707  </front>
1708  <seriesInfo name="RFC" value="2049"/>
1709</reference>
1710
1711<reference anchor="RFC2068">
1712  <front>
1713    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1714    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1715      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1716      <address><email>fielding@ics.uci.edu</email></address>
1717    </author>
1718    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1719      <organization>MIT Laboratory for Computer Science</organization>
1720      <address><email>jg@w3.org</email></address>
1721    </author>
1722    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1723      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1724      <address><email>mogul@wrl.dec.com</email></address>
1725    </author>
1726    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1727      <organization>MIT Laboratory for Computer Science</organization>
1728      <address><email>frystyk@w3.org</email></address>
1729    </author>
1730    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1731      <organization>MIT Laboratory for Computer Science</organization>
1732      <address><email>timbl@w3.org</email></address>
1733    </author>
1734    <date month="January" year="1997"/>
1735  </front>
1736  <seriesInfo name="RFC" value="2068"/>
1737</reference>
1738
1739<reference anchor="RFC2076">
1740  <front>
1741    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
1742    <author initials="J." surname="Palme" fullname="Jacob Palme">
1743      <organization>Stockholm University/KTH</organization>
1744      <address><email>jpalme@dsv.su.se</email></address>
1745    </author>
1746    <date month="February" year="1997"/>
1747  </front>
1748  <seriesInfo name="RFC" value="2076"/>
1749</reference>
1750
1751<reference anchor="RFC2277">
1752  <front>
1753    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
1754    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1755      <organization>UNINETT</organization>
1756      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1757    </author>
1758    <date month="January" year="1998"/>
1759  </front>
1760  <seriesInfo name="BCP" value="18"/>
1761  <seriesInfo name="RFC" value="2277"/>
1762</reference>
1763
1764<reference anchor='RFC2295'>
1765  <front>
1766    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
1767    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
1768      <organization>Technische Universiteit Eindhoven</organization>
1769      <address>
1770        <email>koen@win.tue.nl</email>
1771      </address>
1772    </author>
1773    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
1774      <organization>Hewlett-Packard Company</organization>
1775      <address>
1776        <email>mutz@hpl.hp.com</email>
1777      </address>
1778    </author>
1779    <date year='1998' month='March'/>
1780  </front>
1781  <seriesInfo name='RFC' value='2295'/>
1782</reference>
1783
1784<reference anchor="RFC2388">
1785  <front>
1786    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
1787    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1788      <organization>Xerox Palo Alto Research Center</organization>
1789      <address><email>masinter@parc.xerox.com</email></address>
1790    </author>
1791    <date year="1998" month="August"/>
1792  </front>
1793  <seriesInfo name="RFC" value="2388"/>
1794</reference>
1795
1796<reference anchor="RFC2557">
1797  <front>
1798    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
1799    <author initials="F." surname="Palme" fullname="Jacob Palme">
1800      <organization>Stockholm University and KTH</organization>
1801      <address><email>jpalme@dsv.su.se</email></address>
1802    </author>
1803    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
1804      <organization>Microsoft Corporation</organization>
1805      <address><email>alexhop@microsoft.com</email></address>
1806    </author>
1807    <author initials="N." surname="Shelness" fullname="Nick Shelness">
1808      <organization>Lotus Development Corporation</organization>
1809      <address><email>Shelness@lotus.com</email></address>
1810    </author>
1811    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
1812      <address><email>stef@nma.com</email></address>
1813    </author>
1814    <date year="1999" month="March"/>
1815  </front>
1816  <seriesInfo name="RFC" value="2557"/>
1817</reference>
1818
1819<reference anchor="RFC2616">
1820  <front>
1821    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1822    <author initials="R." surname="Fielding" fullname="R. Fielding">
1823      <organization>University of California, Irvine</organization>
1824      <address><email>fielding@ics.uci.edu</email></address>
1825    </author>
1826    <author initials="J." surname="Gettys" fullname="J. Gettys">
1827      <organization>W3C</organization>
1828      <address><email>jg@w3.org</email></address>
1829    </author>
1830    <author initials="J." surname="Mogul" fullname="J. Mogul">
1831      <organization>Compaq Computer Corporation</organization>
1832      <address><email>mogul@wrl.dec.com</email></address>
1833    </author>
1834    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1835      <organization>MIT Laboratory for Computer Science</organization>
1836      <address><email>frystyk@w3.org</email></address>
1837    </author>
1838    <author initials="L." surname="Masinter" fullname="L. Masinter">
1839      <organization>Xerox Corporation</organization>
1840      <address><email>masinter@parc.xerox.com</email></address>
1841    </author>
1842    <author initials="P." surname="Leach" fullname="P. Leach">
1843      <organization>Microsoft Corporation</organization>
1844      <address><email>paulle@microsoft.com</email></address>
1845    </author>
1846    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1847      <organization>W3C</organization>
1848      <address><email>timbl@w3.org</email></address>
1849    </author>
1850    <date month="June" year="1999"/>
1851  </front>
1852  <seriesInfo name="RFC" value="2616"/>
1853</reference>
1854
1855<reference anchor="RFC3629">
1856  <front>
1857    <title>UTF-8, a transformation format of ISO 10646</title>
1858    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
1859      <organization>Alis Technologies</organization>
1860      <address><email>fyergeau@alis.com</email></address>
1861    </author>
1862    <date month="November" year="2003"/>
1863  </front>
1864  <seriesInfo name="STD" value="63"/>
1865  <seriesInfo name="RFC" value="3629"/>
1866</reference>
1867
1868<reference anchor="RFC4288">
1869  <front>
1870    <title>Media Type Specifications and Registration Procedures</title>
1871    <author initials="N." surname="Freed" fullname="N. Freed">
1872      <organization>Sun Microsystems</organization>
1873      <address>
1874        <email>ned.freed@mrochek.com</email>
1875      </address>
1876    </author>
1877    <author initials="J." surname="Klensin" fullname="J. Klensin">
1878      <address>
1879        <email>klensin+ietf@jck.com</email>
1880      </address>
1881    </author>
1882    <date year="2005" month="December"/>
1883  </front>
1884  <seriesInfo name="BCP" value="13"/>
1885  <seriesInfo name="RFC" value="4288"/>
1886</reference>
1887
1888<reference anchor='RFC5226'>
1889  <front>
1890    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
1891    <author initials='T.' surname='Narten' fullname='T. Narten'>
1892      <organization>IBM</organization>
1893      <address><email>narten@us.ibm.com</email></address>
1894    </author>
1895    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
1896      <organization>Google</organization>
1897      <address><email>Harald@Alvestrand.no</email></address>
1898    </author>
1899    <date year='2008' month='May' />
1900  </front>
1901  <seriesInfo name='BCP' value='26' />
1902  <seriesInfo name='RFC' value='5226' />
1903</reference>
1904
1905<reference anchor="RFC5322">
1906  <front>
1907    <title>Internet Message Format</title>
1908    <author initials="P." surname="Resnick" fullname="P. Resnick">
1909      <organization>Qualcomm Incorporated</organization>
1910    </author>
1911    <date year="2008" month="October"/>
1912  </front> 
1913  <seriesInfo name="RFC" value="5322"/>
1914</reference>
1915
1916<reference anchor="RFC6151">
1917  <front>
1918    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
1919    <author initials="S." surname="Turner" fullname="S. Turner"/>
1920    <author initials="L." surname="Chen" fullname="L. Chen"/>
1921    <date year="2011" month="March" />
1922  </front>
1923  <seriesInfo name="RFC" value="6151" />
1924</reference>
1925
1926<!--<reference anchor='BCP97'>
1927  <front>
1928    <title>Handling Normative References to Standards-Track Documents</title>
1929    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
1930      <address>
1931        <email>klensin+ietf@jck.com</email>
1932      </address>
1933    </author>
1934    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
1935      <organization>MIT</organization>
1936      <address>
1937        <email>hartmans-ietf@mit.edu</email>
1938      </address>
1939    </author>
1940    <date year='2007' month='June' />
1941  </front>
1942  <seriesInfo name='BCP' value='97' />
1943  <seriesInfo name='RFC' value='4897' />
1944</reference>-->
1945
1946<reference anchor="RFC6266">
1947  <front>
1948    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
1949    in the Hypertext Transfer Protocol (HTTP)</title>
1950    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
1951      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1952      <address>
1953        <email>julian.reschke@greenbytes.de</email>
1954      </address>
1955    </author>
1956    <date month="June" year="2011"/>
1957  </front>
1958  <seriesInfo name='RFC' value='6266' />
1959</reference>
1960
1961</references>
1962
1963<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
1964<t>
1965   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
1966   allow a message body to be transmitted in an open variety of
1967   representations and with extensible mechanisms. However, RFC 2045
1968   discusses mail, and HTTP has a few features that are different from
1969   those described in MIME. These differences were carefully chosen
1970   to optimize performance over binary connections, to allow greater
1971   freedom in the use of new media types, to make date comparisons
1972   easier, and to acknowledge the practice of some early HTTP servers
1973   and clients.
1974</t>
1975<t>
1976   This appendix describes specific areas where HTTP differs from MIME.
1977   Proxies and gateways to strict MIME environments &SHOULD; be
1978   aware of these differences and provide the appropriate conversions
1979   where necessary. Proxies and gateways from MIME environments to HTTP
1980   also need to be aware of the differences because some conversions
1981   might be required.
1982</t>
1983
1984<section title="MIME-Version" anchor="mime-version">
1985  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
1986  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
1987  <x:anchor-alias value="MIME-Version"/>
1988<t>
1989   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
1990   include a single MIME-Version header field to indicate what
1991   version of the MIME protocol was used to construct the message. Use
1992   of the MIME-Version header field indicates that the message is in
1993   full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
1994   Proxies/gateways are responsible for ensuring full conformance (where
1995   possible) when exporting HTTP messages to strict MIME environments.
1996</t>
1997<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
1998  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
1999</artwork></figure>
2000<t>
2001   MIME version "1.0" is the default for use in HTTP/1.1. However,
2002   HTTP/1.1 message parsing and semantics are defined by this document
2003   and not the MIME specification.
2004</t>
2005</section>
2006
2007<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2008<t>
2009   MIME requires that an Internet mail body-part be converted to
2010   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2011   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2012   allowed for subtypes of the "text" media type when transmitted over
2013   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2014   line breaks as CRLF and forbids the use of CR or LF outside of line
2015   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2016   line break within text content when a message is transmitted over
2017   HTTP.
2018</t>
2019<t>
2020   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2021   environment &SHOULD; translate all line breaks within the text media
2022   types described in <xref target="canonicalization.and.text.defaults"/>
2023   of this document to the RFC 2049
2024   canonical form of CRLF. Note, however, that this might be complicated
2025   by the presence of a Content-Encoding and by the fact that HTTP
2026   allows the use of some character encodings which do not use octets 13 and
2027   10 to represent CR and LF, respectively, as is the case for some multi-byte
2028   character encodings.
2029</t>
2030<t>
2031   Conversion will break any cryptographic
2032   checksums applied to the original content unless the original content
2033   is already in canonical form. Therefore, the canonical form is
2034   recommended for any content that uses such checksums in HTTP.
2035</t>
2036</section>
2037
2038
2039<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2040<t>
2041   HTTP/1.1 uses a restricted set of date formats (&http-date;) to
2042   simplify the process of date comparison. Proxies and gateways from
2043   other protocols &SHOULD; ensure that any Date header field present in a
2044   message conforms to one of the HTTP/1.1 formats and rewrite the date
2045   if necessary.
2046</t>
2047</section>
2048
2049<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2050<t>
2051   MIME does not include any concept equivalent to HTTP/1.1's
2052   Content-Encoding header field. Since this acts as a modifier on the
2053   media type, proxies and gateways from HTTP to MIME-compliant
2054   protocols &MUST; either change the value of the Content-Type header
2055   field or decode the representation before forwarding the message. (Some
2056   experimental applications of Content-Type for Internet mail have used
2057   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2058   a function equivalent to Content-Encoding. However, this parameter is
2059   not part of the MIME standards).
2060</t>
2061</section>
2062
2063<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2064  <iref item="Content-Transfer-Encoding header field" x:for-anchor=""/>
2065  <iref item="Header Fields" subitem="Content-Transfer-Encoding" x:for-anchor=""/>
2066<t>
2067   HTTP does not use the Content-Transfer-Encoding field of MIME.
2068   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2069   remove any Content-Transfer-Encoding
2070   prior to delivering the response message to an HTTP client.
2071</t>
2072<t>
2073   Proxies and gateways from HTTP to MIME-compliant protocols are
2074   responsible for ensuring that the message is in the correct format
2075   and encoding for safe transport on that protocol, where "safe
2076   transport" is defined by the limitations of the protocol being used.
2077   Such a proxy or gateway &SHOULD; label the data with an appropriate
2078   Content-Transfer-Encoding if doing so will improve the likelihood of
2079   safe transport over the destination protocol.
2080</t>
2081</section>
2082
2083<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2084<t>
2085   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2086   Proxies/gateways &MUST; remove any transfer-coding prior to
2087   forwarding a message via a MIME-compliant protocol.
2088</t>
2089</section>
2090
2091<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2092<t>
2093   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2094   need to be aware of MIME line length limitations. Since HTTP does not
2095   have this limitation, HTTP does not fold long lines. MHTML messages
2096   being transported by HTTP follow all conventions of MHTML, including
2097   line length limitations and folding, canonicalization, etc., since
2098   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2099   does not interpret the content or any MIME header lines that might be
2100   contained therein.
2101</t>
2102</section>
2103</section>
2104
2105<section title="Additional Features" anchor="additional.features">
2106<t>
2107   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2108   existing HTTP implementations, but not consistently and correctly
2109   across most HTTP/1.1 applications. Implementors are advised to be
2110   aware of these features, but cannot rely upon their presence in, or
2111   interoperability with, other HTTP/1.1 applications. Some of these
2112   describe proposed experimental features, and some describe features
2113   that experimental deployment found lacking that are now addressed in
2114   the base HTTP/1.1 specification.
2115</t>
2116<t>
2117   A number of other header fields, such as Content-Disposition and Title,
2118   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2119   and <xref target="RFC2076"/>).
2120</t>
2121</section>
2122
2123<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2124<t>
2125  Clarify contexts that charset is used in.
2126  (<xref target="character.sets"/>)
2127</t>
2128<t>
2129  Registration of Content Codings now requires IETF Review
2130  (<xref target="content.coding.registry"/>)
2131</t>
2132<t>
2133  Remove the default character encoding for text media types; the default
2134  now is whatever the media type definition says.
2135  (<xref target="canonicalization.and.text.defaults"/>)
2136</t>
2137<t>
2138  Change ABNF productions for header fields to only define the field value.
2139  (<xref target="header.field.definitions"/>)
2140</t>
2141<t>
2142  Remove definition of Content-MD5 header field because it was inconsistently
2143  implemented with respect to partial responses, and also because of known
2144  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
2145  (<xref target="header.field.definitions"/>)
2146</t>
2147<t>
2148  Remove ISO-8859-1 special-casing in Accept-Charset.
2149  (<xref target="header.accept-charset"/>)
2150</t>
2151<t>
2152  Remove base URI setting semantics for Content-Location due to poor
2153  implementation support, which was caused by too many broken servers emitting
2154  bogus Content-Location header fields, and also the potentially undesirable effect
2155  of potentially breaking relative links in content-negotiated resources.
2156  (<xref target="header.content-location"/>)
2157</t>
2158<t>
2159  Remove reference to non-existant identity transfer-coding value tokens.
2160  (<xref target="no.content-transfer-encoding"/>)
2161</t>
2162<t>
2163  Remove discussion of Content-Disposition header field, it is now defined
2164  by <xref target="RFC6266"/>.
2165  (<xref target="additional.features"/>)
2166</t>
2167</section>
2168
2169<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2170
2171<section title="Since RFC 2616">
2172<t>
2173  Extracted relevant partitions from <xref target="RFC2616"/>.
2174</t>
2175</section>
2176
2177<section title="Since draft-ietf-httpbis-p3-payload-00">
2178<t>
2179  Closed issues:
2180  <list style="symbols"> 
2181    <t>
2182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2183      "Media Type Registrations"
2184      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2185    </t>
2186    <t>
2187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2188      "Clarification regarding quoting of charset values"
2189      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2190    </t>
2191    <t>
2192      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2193      "Remove 'identity' token references"
2194      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2195    </t>
2196    <t>
2197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2198      "Accept-Encoding BNF"
2199    </t>
2200    <t>
2201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2202      "Normative and Informative references"
2203    </t>
2204    <t>
2205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2206      "RFC1700 references"
2207    </t>
2208    <t>
2209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2210      "Updating to RFC4288"
2211    </t>
2212    <t>
2213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2214      "Informative references"
2215    </t>
2216    <t>
2217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2218      "ISO-8859-1 Reference"
2219    </t>
2220    <t>
2221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2222      "Encoding References Normative"
2223    </t>
2224    <t>
2225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2226      "Normative up-to-date references"
2227    </t>
2228  </list>
2229</t>
2230</section>
2231
2232<section title="Since draft-ietf-httpbis-p3-payload-01">
2233<t>
2234  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2235  <list style="symbols"> 
2236    <t>
2237      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2238    </t>
2239  </list>
2240</t>
2241</section>
2242
2243<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2244<t>
2245  Closed issues:
2246  <list style="symbols"> 
2247    <t>
2248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2249      "Quoting Charsets"
2250    </t>
2251    <t>
2252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2253      "Classification for Allow header"
2254    </t>
2255    <t>
2256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2257      "missing default for qvalue in description of Accept-Encoding"
2258    </t>
2259  </list>
2260</t>
2261<t>
2262  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2263  <list style="symbols"> 
2264    <t>
2265      Reference RFC 3984, and update header field registrations for headers defined
2266      in this document.
2267    </t>
2268  </list>
2269</t>
2270</section>
2271
2272<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2273<t>
2274  Closed issues:
2275  <list style="symbols"> 
2276    <t>
2277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2278      "Quoting Charsets"
2279    </t>
2280    <t>
2281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2282      "language tag matching (Accept-Language) vs RFC4647"
2283    </t>
2284    <t>
2285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2286      "RFC 1806 has been replaced by RFC2183"
2287    </t>
2288  </list>
2289</t>
2290<t>
2291  Other changes:
2292  <list style="symbols"> 
2293    <t>
2294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2295      "Encoding References Normative" &mdash; rephrase the annotation and reference
2296      BCP97.
2297    </t>
2298  </list>
2299</t>
2300 </section>
2301
2302<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2303<t>
2304  Closed issues:
2305  <list style="symbols"> 
2306    <t>
2307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2308      "RFC 2822 is updated by RFC 5322"
2309    </t>
2310  </list>
2311</t>
2312<t>
2313  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2314  <list style="symbols"> 
2315    <t>
2316      Use "/" instead of "|" for alternatives.
2317    </t>
2318    <t>
2319      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2320      whitespace ("OWS") and required whitespace ("RWS").
2321    </t>
2322    <t>
2323      Rewrite ABNFs to spell out whitespace rules, factor out
2324      header field value format definitions.
2325    </t>
2326  </list>
2327</t>
2328</section>
2329
2330<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2331<t>
2332  Closed issues:
2333  <list style="symbols"> 
2334    <t>
2335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2336      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2337    </t>
2338  </list>
2339</t>
2340<t>
2341  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2342  <list style="symbols"> 
2343    <t>
2344      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2345    </t>
2346  </list>
2347</t>
2348<t>
2349  Other changes:
2350  <list style="symbols"> 
2351    <t>
2352      Move definition of quality values into Part 1.
2353    </t>
2354  </list>
2355</t>
2356</section>
2357
2358<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2359<t>
2360  Closed issues:
2361  <list style="symbols"> 
2362    <t>
2363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2364      "Content-Location isn't special"
2365    </t>
2366    <t>
2367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2368      "Content Sniffing"
2369    </t>
2370  </list>
2371</t>
2372</section>
2373
2374<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2375<t>
2376  Closed issues:
2377  <list style="symbols"> 
2378    <t>
2379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2380      "Updated reference for language tags"
2381    </t>
2382    <t>
2383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2384      "Clarify rules for determining what entities a response carries"
2385    </t>
2386    <t>
2387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2388      "Content-Location base-setting problems"
2389    </t>
2390    <t>
2391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2392      "Content Sniffing"
2393    </t>
2394    <t>
2395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2396      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2397    </t>
2398    <t>
2399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2400      "move definitions of gzip/deflate/compress to part 1"
2401    </t>
2402  </list>
2403</t>
2404<t>
2405  Partly resolved issues:
2406  <list style="symbols"> 
2407    <t>
2408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2409      "update IANA requirements wrt Transfer-Coding values" (add the
2410      IANA Considerations subsection)
2411    </t>
2412    <t>
2413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2414      "update IANA requirements wrt Content-Coding values" (add the
2415      IANA Considerations subsection)
2416    </t>
2417  </list>
2418</t>
2419</section>
2420
2421<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2422<t>
2423  Closed issues:
2424  <list style="symbols"> 
2425    <t>
2426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2427      "Content Negotiation for media types"
2428    </t>
2429    <t>
2430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2431      "Accept-Language: which RFC4647 filtering?"
2432    </t>
2433  </list>
2434</t>
2435</section>
2436
2437<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2438<t>
2439  Closed issues:
2440  <list style="symbols"> 
2441    <t>
2442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2443      "MIME-Version not listed in P1, general header fields"
2444    </t>
2445    <t>
2446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2447      "IANA registry for content/transfer encodings"
2448    </t>
2449    <t>
2450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2451      "Content Sniffing"
2452    </t>
2453    <t>
2454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2455      "use of term "word" when talking about header structure"
2456    </t>
2457  </list>
2458</t>
2459<t>
2460  Partly resolved issues:
2461  <list style="symbols"> 
2462    <t>
2463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2464      "Term for the requested resource's URI"
2465    </t>
2466  </list>
2467</t>
2468</section>
2469
2470<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2471<t>
2472  Closed issues:
2473  <list style="symbols"> 
2474    <t>
2475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2476      "Clarify 'Requested Variant'"
2477    </t>
2478    <t>
2479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2480      "Content-Location isn't special"
2481    </t>
2482    <t>
2483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2484      "Delimiting messages with multipart/byteranges"
2485    </t>
2486    <t>
2487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2488      "Clarify entity / representation / variant terminology"
2489    </t>
2490    <t>
2491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2492      "confusing req. language for Content-Location"
2493    </t>
2494    <t>
2495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2496      "Content-Location on 304 responses"
2497    </t>
2498    <t>
2499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2500      "'requested resource' in content-encoding definition"
2501    </t>
2502    <t>
2503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2504      "consider removing the 'changes from 2068' sections"
2505    </t>
2506  </list>
2507</t>
2508<t>
2509  Partly resolved issues:
2510  <list style="symbols"> 
2511    <t>
2512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2513      "Content-MD5 and partial responses"
2514    </t>
2515  </list>
2516</t>
2517</section>
2518
2519<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
2520<t>
2521  Closed issues:
2522  <list style="symbols"> 
2523    <t>
2524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
2525      "Factor out Content-Disposition"
2526    </t>
2527  </list>
2528</t>
2529</section>
2530
2531<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
2532<t>
2533  Closed issues:
2534  <list style="symbols"> 
2535    <t>
2536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
2537      "Header Classification"
2538    </t>
2539    <t>
2540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2541      "untangle ABNFs for header fields"
2542    </t>
2543    <t>
2544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
2545      "potentially misleading MAY in media-type def"
2546    </t>
2547  </list>
2548</t>
2549</section>
2550
2551<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
2552<t>
2553  Closed issues:
2554  <list style="symbols"> 
2555    <t>
2556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
2557      "Default charsets for text media types"
2558    </t>
2559    <t>
2560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2561      "Content-MD5 and partial responses"
2562    </t>
2563    <t>
2564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2565      "untangle ABNFs for header fields"
2566    </t>
2567    <t>
2568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
2569      "confusing undefined parameter in media range example"
2570    </t>
2571  </list>
2572</t>
2573</section>
2574
2575<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
2576<t>
2577  None.
2578</t>
2579</section>
2580
2581<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
2582<t>
2583  Closed issues:
2584  <list style="symbols"> 
2585    <t>
2586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
2587      "Strength of requirements on Accept re: 406"
2588    </t>
2589  </list>
2590</t>
2591</section>
2592
2593<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
2594<t>
2595  Closed issues:
2596  <list style="symbols"> 
2597    <t>
2598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
2599      "Document HTTP's error-handling philosophy"
2600    </t>
2601  </list>
2602</t>
2603</section>
2604
2605<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
2606<t>
2607  Closed issues:
2608  <list style="symbols"> 
2609    <t>
2610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
2611      "intended maturity level vs normative references"
2612    </t>
2613  </list>
2614</t>
2615</section>
2616
2617<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.18">
2618<t>
2619  Closed issues:
2620  <list style="symbols">
2621    <t>
2622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
2623      "is ETag a representation header field?"
2624    </t>
2625    <t>
2626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/338"/>:
2627      "Content-Location doesn't constrain the cardinality of representations"
2628    </t>
2629    <t>
2630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
2631      "make IANA policy definitions consistent"
2632    </t>
2633  </list>
2634</t>
2635</section>
2636
2637<section title="Since draft-ietf-httpbis-p3-payload-19" anchor="changes.since.19">
2638<t>
2639  None yet.
2640</t>
2641</section>
2642
2643</section>
2644
2645</back>
2646</rfc>
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