source: draft-ietf-httpbis/19/draft-ietf-httpbis-p3-payload-19.xml @ 1592

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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2616" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-19">
20
21
22
23<front>
24
25  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
26
27  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
28    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
29    <address>
30      <postal>
31        <street>345 Park Ave</street>
32        <city>San Jose</city>
33        <region>CA</region>
34        <code>95110</code>
35        <country>USA</country>
36      </postal>
37      <email>fielding@gbiv.com</email>
38      <uri>http://roy.gbiv.com/</uri>
39    </address>
40  </author>
41
42  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
43    <organization abbrev="W3C">World Wide Web Consortium</organization>
44    <address>
45      <postal>
46        <street>W3C / ERCIM</street>
47        <street>2004, rte des Lucioles</street>
48        <city>Sophia-Antipolis</city>
49        <region>AM</region>
50        <code>06902</code>
51        <country>France</country>
52      </postal>
53      <email>ylafon@w3.org</email>
54      <uri>http://www.raubacapeu.net/people/yves/</uri>
55    </address>
56  </author>
57
58  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
59    <organization abbrev="greenbytes">greenbytes GmbH</organization>
60    <address>
61      <postal>
62        <street>Hafenweg 16</street>
63        <city>Muenster</city><region>NW</region><code>48155</code>
64        <country>Germany</country>
65      </postal>
66      <phone>+49 251 2807760</phone>
67      <facsimile>+49 251 2807761</facsimile>
68      <email>julian.reschke@greenbytes.de</email>
69      <uri>http://greenbytes.de/tech/webdav/</uri>
70    </address>
71  </author>
72
73  <date month="March" year="2012" day="12"/>
74  <workgroup>HTTPbis Working Group</workgroup>
75
76<abstract>
77<t>
78   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
79   distributed, collaborative, hypertext information systems. HTTP has been in
80   use by the World Wide Web global information initiative since 1990. This
81   document is Part 3 of the seven-part specification that defines the protocol
82   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
83</t>
84<t>
85   Part 3 defines HTTP message content, metadata, and content negotiation.
86</t>
87</abstract>
88
89<note title="Editorial Note (To be removed by RFC Editor)">
90  <t>
91    Discussion of this draft should take place on the HTTPBIS working group
92    mailing list (ietf-http-wg@w3.org), which is archived at
93    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
94  </t>
95  <t>
96    The current issues list is at
97    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
98    documents (including fancy diffs) can be found at
99    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
100  </t>
101  <t>
102    The changes in this draft are summarized in <xref target="changes.since.18"/>.
103  </t>
104</note>
105</front>
106<middle>
107<section title="Introduction" anchor="introduction">
108<t>
109   This document defines HTTP/1.1 message payloads (a.k.a., content), the
110   associated metadata header fields that define how the payload is intended
111   to be interpreted by a recipient, the request header fields that
112   might influence content selection, and the various selection algorithms
113   that are collectively referred to as HTTP content negotiation.
114</t>
115<t>
116   This document is currently disorganized in order to minimize the changes
117   between drafts and enable reviewers to see the smaller errata changes.
118   A future draft will reorganize the sections to better reflect the content.
119   In particular, the sections on entities will be renamed payload and moved
120   to the first half of the document, while the sections on content negotiation
121   and associated request header fields will be moved to the second half.  The
122   current mess reflects how widely dispersed these topics and associated
123   requirements had become in <xref target="RFC2616"/>.
124</t>
125
126<section title="Terminology" anchor="terminology">
127<t>
128   This specification uses a number of terms to refer to the roles
129   played by participants in, and objects of, the HTTP communication.
130</t>
131<t>
132  <iref item="content negotiation"/>
133  <?rfc needLines="4"?>content negotiation
134  <list>
135    <t>
136      The mechanism for selecting the appropriate representation when
137      servicing a request. The representation in any response
138      can be negotiated (including error responses).
139    </t>
140  </list>
141</t>
142<t>
143  <iref primary="true" item="selected representation"/>
144  <?rfc needLines="4"?>selected representation
145  <list>
146    <t>
147      The current representation of the target resource that would have been
148      selected in a successful response if the same request had used the
149      method GET and excluded any conditional request header fields.
150    </t>
151  </list>
152</t>
153</section>
154
155<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
156<t>
157   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
158   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
159   document are to be interpreted as described in <xref target="RFC2119"/>.
160</t>
161<t>
162   This document defines conformance criteria for several roles in HTTP
163   communication, including Senders, Recipients, Clients, Servers, User-Agents,
164   Origin Servers, Intermediaries, Proxies and Gateways. See Section 2 of <xref target="Part1"/>
165   for definitions of these terms.
166</t>
167<t>
168   An implementation is considered conformant if it complies with all of the
169   requirements associated with its role(s). Note that SHOULD-level requirements
170   are relevant here, unless one of the documented exceptions is applicable.
171</t>
172<t>
173   This document also uses ABNF to define valid protocol elements
174   (<xref target="notation"/>). In addition to the prose requirements placed
175   upon them, Senders MUST NOT generate protocol elements that are invalid.
176</t>
177<t>
178   Unless noted otherwise, Recipients MAY take steps to recover a usable
179   protocol element from an invalid construct. However, HTTP does not define
180   specific error handling mechanisms, except in cases where it has direct
181   impact on security. This is because different uses of the protocol require
182   different error handling strategies; for example, a Web browser may wish to
183   transparently recover from a response where the Location header field
184   doesn't parse according to the ABNF, whereby in a systems control protocol
185   using HTTP, this type of error recovery could lead to dangerous consequences.
186</t>
187</section>
188
189<section title="Syntax Notation" anchor="notation">
190 
191 
192 
193 
194 
195 
196<t>
197   This specification uses the Augmented Backus-Naur Form (ABNF) notation
198   of <xref target="RFC5234"/> with the list rule extension defined in
199   Section 1.2 of <xref target="Part1"/><xref target="collected.abnf"/> shows the collected ABNF
200   with the list rule expanded.
201</t>
202<t>
203  The following core rules are included by
204  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
205  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
206  DIGIT (decimal 0-9), DQUOTE (double quote),
207  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
208  OCTET (any 8-bit sequence of data), SP (space), and
209  VCHAR (any visible US-ASCII character).
210</t>
211
212<section title="Core Rules" anchor="core.rules">
213 
214 
215 
216<t>
217  The core rules below are defined in <xref target="Part1"/>:
218</t>
219<figure><artwork type="abnf2616"><![CDATA[
220  OWS            = <OWS, defined in [Part1], Section 3.2.1>
221  token          = <token, defined in [Part1], Section 3.2.4>
222  word           = <word, defined in [Part1], Section 3.2.4>
223]]></artwork></figure>
224</section>
225
226<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
227 
228 
229 
230<t>
231  The ABNF rules below are defined in other parts:
232</t>
233<figure><artwork type="abnf2616"><![CDATA[
234  absolute-URI   = <absolute-URI, defined in [Part1], Section 2.7>
235  partial-URI    = <partial-URI, defined in [Part1], Section 2.7>
236  qvalue         = <qvalue, defined in [Part1], Section 4.3.1>
237]]></artwork></figure>
238</section>
239
240</section>
241
242</section>
243
244<section title="Protocol Parameters" anchor="protocol.parameters">
245
246<section title="Character Encodings (charset)" anchor="character.sets">
247<t>
248   HTTP uses charset names to indicate the character encoding of a
249   textual representation.
250</t>
251<t anchor="rule.charset">
252 
253   A character encoding is identified by a case-insensitive token. The
254   complete set of tokens is defined by the IANA Character Set registry
255   (<eref target="http://www.iana.org/assignments/character-sets"/>).
256</t>
257<figure><iref primary="true" item="Grammar" subitem="charset"/><artwork type="abnf2616"><![CDATA[
258  charset = token
259]]></artwork></figure>
260<t>
261   Although HTTP allows an arbitrary token to be used as a charset
262   value, any token that has a predefined value within the IANA
263   Character Set registry MUST represent the character encoding defined
264   by that registry. Applications SHOULD limit their use of character
265   encodings to those defined within the IANA registry.
266</t>
267<t>
268   HTTP uses charset in two contexts: within an Accept-Charset request
269   header field (in which the charset value is an unquoted token) and as the
270   value of a parameter in a Content-Type header field (within a request or
271   response), in which case the parameter value of the charset parameter
272   can be quoted.
273</t>
274<t>
275   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
276   <xref target="RFC2277"/>.
277</t>
278</section>
279
280<section title="Content Codings" anchor="content.codings">
281 
282<t>
283   Content coding values indicate an encoding transformation that has
284   been or can be applied to a representation. Content codings are primarily
285   used to allow a representation to be compressed or otherwise usefully
286   transformed without losing the identity of its underlying media type
287   and without loss of information. Frequently, the representation is stored in
288   coded form, transmitted directly, and only decoded by the recipient.
289</t>
290<figure><iref primary="true" item="Grammar" subitem="content-coding"/><artwork type="abnf2616"><![CDATA[
291  content-coding   = token
292]]></artwork></figure>
293<t>
294   All content-coding values are case-insensitive. HTTP/1.1 uses
295   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
296   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
297   describes the content-coding, what is more important is that it
298   indicates what decoding mechanism will be required to remove the
299   encoding.
300</t>
301<t>
302   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
303  <list>
304    <t>
305      See Section 4.2.1 of <xref target="Part1"/>.
306    </t>
307  </list>
308</t>
309<t>
310   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
311  <list>
312    <t>
313      See Section 4.2.2 of <xref target="Part1"/>.
314    </t>
315  </list>
316</t>
317<t>
318   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
319  <list>
320    <t>
321      See Section 4.2.3 of <xref target="Part1"/>.
322    </t>
323  </list>
324</t>
325
326<section title="Content Coding Registry" anchor="content.coding.registry">
327<t>
328   The HTTP Content Coding Registry defines the name space for the content
329   coding names.
330</t>
331<t>
332   Registrations MUST include the following fields:
333   <list style="symbols">
334     <t>Name</t>
335     <t>Description</t>
336     <t>Pointer to specification text</t>
337   </list>
338</t>
339<t>
340   Names of content codings MUST NOT overlap with names of transfer codings
341   (Section 4 of <xref target="Part1"/>), unless the encoding transformation is identical (as
342   is the case for the compression codings defined in
343   Section 4.2 of <xref target="Part1"/>).
344</t>
345<t>
346   Values to be added to this name space require IETF Review
347   (see Section 4.1 of <xref target="RFC5226"/>), and MUST
348   conform to the purpose of content coding defined in this section.
349</t>
350<t>
351   The registry itself is maintained at
352   <eref target="http://www.iana.org/assignments/http-parameters"/>.
353</t>
354</section>
355
356</section>
357
358<section title="Media Types" anchor="media.types">
359 
360 
361 
362<t>
363   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
364   and Accept (<xref target="header.accept"/>) header fields in order to provide
365   open and extensible data typing and type negotiation.
366</t>
367<figure><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/><artwork type="abnf2616"><![CDATA[
368  media-type = type "/" subtype *( OWS ";" OWS parameter )
369  type       = token
370  subtype    = token
371]]></artwork></figure>
372<t anchor="rule.parameter">
373 
374 
375 
376   The type/subtype MAY be followed by parameters in the form of
377   attribute/value pairs.
378</t>
379<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
380  parameter      = attribute "=" value
381  attribute      = token
382  value          = word
383]]></artwork></figure>
384<t>
385   The type, subtype, and parameter attribute names are case-insensitive.
386   Parameter values might or might not be case-sensitive, depending on the
387   semantics of the parameter name.  The presence or absence of a parameter might
388   be significant to the processing of a media-type, depending on its
389   definition within the media type registry.
390</t>
391<t>
392   A parameter value that matches the <xref target="core.rules" format="none">token</xref> production can be
393   transmitted as either a token or within a quoted-string. The quoted and
394   unquoted values are equivalent.
395</t>
396<t>
397   Note that some older HTTP applications do not recognize media type
398   parameters. When sending data to older HTTP applications,
399   implementations SHOULD only use media type parameters when they are
400   required by that type/subtype definition.
401</t>
402<t>
403   Media-type values are registered with the Internet Assigned Number
404   Authority (IANA). The media type registration process is
405   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
406   discouraged.
407</t>
408
409<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
410<t>
411   Internet media types are registered with a canonical form. A
412   representation transferred via HTTP messages MUST be in the
413   appropriate canonical form prior to its transmission except for
414   "text" types, as defined in the next paragraph.
415</t>
416<t>
417   When in canonical form, media subtypes of the "text" type use CRLF as
418   the text line break. HTTP relaxes this requirement and allows the
419   transport of text media with plain CR or LF alone representing a line
420   break when it is done consistently for an entire representation. HTTP
421   applications MUST accept CRLF, bare CR, and bare LF as indicating
422   a line break in text media received via HTTP. In
423   addition, if the text is in a character encoding that does not
424   use octets 13 and 10 for CR and LF respectively, as is the case for
425   some multi-byte character encodings, HTTP allows the use of whatever octet
426   sequences are defined by that character encoding to represent the
427   equivalent of CR and LF for line breaks. This flexibility regarding
428   line breaks applies only to text media in the payload body; a bare CR
429   or LF MUST NOT be substituted for CRLF within any of the HTTP control
430   structures (such as header fields and multipart boundaries).
431</t>
432<t>
433   If a representation is encoded with a content-coding, the underlying
434   data MUST be in a form defined above prior to being encoded.
435</t>
436</section>
437
438<section title="Multipart Types" anchor="multipart.types">
439<t>
440   MIME provides for a number of "multipart" types — encapsulations of
441   one or more representations within a single message body. All multipart
442   types share a common syntax, as defined in Section 5.1.1 of <xref target="RFC2046"/>,
443   and MUST include a boundary parameter as part of the media type
444   value. The message body is itself a protocol element and MUST
445   therefore use only CRLF to represent line breaks between body-parts.
446</t>
447<t>
448   In general, HTTP treats a multipart message body no differently than
449   any other media type: strictly as payload.  HTTP does not use the
450   multipart boundary as an indicator of message body length.
451   <!-- jre: re-insert removed text pointing to caching? -->
452   In all other respects, an HTTP user agent SHOULD follow the same or similar
453   behavior as a MIME user agent would upon receipt of a multipart type.
454   The MIME header fields within each body-part of a multipart message body
455   do not have any significance to HTTP beyond that defined by
456   their MIME semantics.
457</t>
458<t>
459   If an application receives an unrecognized multipart subtype, the
460   application MUST treat it as being equivalent to "multipart/mixed".
461</t>
462<t><list>
463  <t>
464    Note: The "multipart/form-data" type has been specifically defined
465    for carrying form data suitable for processing via the POST
466    request method, as described in <xref target="RFC2388"/>.
467  </t>
468</list></t>
469</section>
470</section>
471
472<section title="Language Tags" anchor="language.tags">
473 
474<t>
475   A language tag, as defined in <xref target="RFC5646"/>, identifies a
476   natural language spoken, written, or otherwise conveyed by human beings for
477   communication of information to other human beings. Computer languages are
478   explicitly excluded. HTTP uses language tags within the Accept-Language and
479   Content-Language fields.
480</t>
481<t>
482   In summary, a language tag is composed of one or more parts: A primary
483   language subtag followed by a possibly empty series of subtags:
484</t>
485<figure><iref primary="true" item="Grammar" subitem="language-tag"/><artwork type="abnf2616"><![CDATA[
486  language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
487]]></artwork></figure>
488<t>
489   White space is not allowed within the tag and all tags are case-insensitive.
490   The name space of language subtags is administered by the IANA (see
491   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
492</t>
493<figure>
494  <preamble>Example tags include:</preamble>
495<artwork type="example"><![CDATA[
496  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
497]]></artwork>
498</figure>
499<t>
500   See <xref target="RFC5646"/> for further information.
501</t>
502</section>
503</section>
504
505<section title="Payload" anchor="payload">
506<t>
507   HTTP messages MAY transfer a payload if not otherwise restricted by
508   the request method or response status code.  The payload consists of
509   metadata, in the form of header fields, and data, in the form of the
510   sequence of octets in the message body after any transfer-coding has
511   been decoded.
512</t>
513<iref item="payload"/>
514<t>   
515   A "payload" in HTTP is always a partial or complete
516   representation of some resource.  We use separate terms for payload
517   and representation because some messages contain only the associated
518   representation's header fields (e.g., responses to HEAD) or only some
519   part(s) of the representation (e.g., the 206 status code).
520</t>
521<section title="Payload Header Fields" anchor="payload.header.fields">
522 
523<t>
524   HTTP header fields that specifically define the payload, rather than the
525   associated representation, are referred to as "payload header fields".
526   The following payload header fields are defined by HTTP/1.1:
527</t>
528<texttable align="left">
529  <ttcol>Header Field Name</ttcol>
530  <ttcol>Defined in...</ttcol>
531
532  <c>Content-Length</c> <c>Section 3.3.2 of <xref target="Part1"/></c>
533  <c>Content-Range</c> <c>Section 5.2 of <xref target="Part5"/></c>
534</texttable>
535</section>
536
537<section title="Payload Body" anchor="payload.body">
538 
539<t>
540   A payload body is only present in a message when a message body is
541   present, as described in Section 3.3 of <xref target="Part1"/>. The payload body is obtained
542   from the message body by decoding any Transfer-Encoding that might
543   have been applied to ensure safe and proper transfer of the message.
544</t>
545</section>
546</section>
547
548<section title="Representation" anchor="representation">
549<iref item="representation"/>
550<t>
551   A "representation" is information in a format that can be readily
552   communicated from one party to another.  A resource representation
553   is information that reflects the state of that resource, as observed
554   at some point in the past (e.g., in a response to GET) or to be
555   desired at some point in the future (e.g., in a PUT request).
556</t>
557<t>
558   Most, but not all, representations transferred via HTTP are intended
559   to be a representation of the target resource (the resource identified
560   by the effective request URI).  The precise semantics of a representation
561   are determined by the type of message (request or response), the request
562   method, the response status code, and the representation metadata.
563   For example, the above semantic is true for the representation in any
564   200 (OK) response to GET and for the representation in any PUT request.
565   A 200 response to PUT, in contrast, contains either a representation
566   that describes the successful action or a representation of the target
567   resource, with the latter indicated by a Content-Location header field
568   with the same value as the effective request URI.  Likewise, response
569   messages with an error status code usually contain a representation that
570   describes the error and what next steps are suggested for resolving it.
571</t>
572
573<section title="Representation Header Fields" anchor="representation.header.fields">
574 
575<t>
576   Representation header fields define metadata about the representation data
577   enclosed in the message body or, if no message body is present, about
578   the representation that would have been transferred in a 200 response
579   to a simultaneous GET request with the same effective request URI.
580</t>
581<t>
582   The following header fields are defined as representation metadata:
583</t>
584<texttable align="left">
585  <ttcol>Header Field Name</ttcol>
586  <ttcol>Defined in...</ttcol>
587
588  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
589  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
590  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
591  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
592  <c>Expires</c> <c>Section 3.3 of <xref target="Part6"/></c>
593</texttable>
594<t>
595   Additional header fields define metadata about the selected
596   representation, which might differ from the representation included
597   in the message for responses to some state-changing methods.
598   The following header fields are defined as selected representation
599   metadata:
600</t>
601<texttable align="left">
602  <ttcol>Header Field Name</ttcol>
603  <ttcol>Defined in...</ttcol>
604
605  <c>ETag</c> <c>Section 2.3 of <xref target="Part4"/></c>
606  <c>Last-Modified</c> <c>Section 2.2 of <xref target="Part4"/></c>
607</texttable>
608</section>
609
610<section title="Representation Data" anchor="representation.data">
611 
612<t>
613   The representation body associated with an HTTP message is
614   either provided as the payload body of the message or
615   referred to by the message semantics and the effective request
616   URI.  The representation data is in a format and encoding defined by
617   the representation metadata header fields.
618</t>
619<t>
620   The data type of the representation data
621   is determined via the header fields Content-Type and Content-Encoding.
622   These define a two-layer, ordered encoding model:
623</t>
624<figure><artwork type="example"><![CDATA[
625  representation-data := Content-Encoding( Content-Type( bits ) )
626]]></artwork></figure>
627<t>
628   Content-Type specifies the media type of the underlying data, which
629   defines both the data format and how that data SHOULD be processed
630   by the recipient (within the scope of the request method semantics).
631   Any HTTP/1.1 message containing a payload body SHOULD include a
632   Content-Type header field defining the media type of the associated
633   representation unless that metadata is unknown to the sender.
634   If the Content-Type header field is not present, it indicates that
635   the sender does not know the media type of the representation;
636   recipients MAY either assume that the media type is
637   "application/octet-stream" (<xref target="RFC2046"/>, Section 4.5.1)
638   or examine the content to determine its type.
639</t>
640<t>
641   In practice, resource owners do not always properly configure their origin
642   server to provide the correct Content-Type for a given representation,
643   with the result that some clients will examine a response body's content
644   and override the specified type.
645   Clients that do so risk drawing incorrect conclusions, which might expose
646   additional security risks (e.g., "privilege escalation").  Furthermore,
647   it is impossible to determine the sender's intent by examining the data
648   format: many data formats match multiple media types that differ only in
649   processing semantics.  Implementers are encouraged to provide a means of
650   disabling such "content sniffing" when it is used.
651</t>
652<t>
653   Content-Encoding is used to indicate any additional content
654   codings applied to the data, usually for the purpose of data
655   compression, that are a property of the representation.  If
656   Content-Encoding is not present, then there is no additional
657   encoding beyond that defined by the Content-Type.
658</t>
659</section>
660</section>
661
662<section title="Content Negotiation" anchor="content.negotiation">
663<t>
664   HTTP responses include a representation which contains information for
665   interpretation, whether by a human user or for further processing.
666   Often, the server has different ways of representing the
667   same information; for example, in different formats, languages,
668   or using different character encodings.
669</t>
670<t>
671   HTTP clients and their users might have different or variable
672   capabilities, characteristics or preferences which would influence
673   which representation, among those available from the server,
674   would be best for the server to deliver. For this reason, HTTP
675   provides mechanisms for "content negotiation" — a process of
676   allowing selection of a representation of a given resource,
677   when more than one is available.
678</t>
679<t>
680   This specification defines two patterns of content negotiation;
681   "server-driven", where the server selects the representation based
682   upon the client's stated preferences, and "agent-driven" negotiation,
683   where the server provides a list of representations for the client to
684   choose from, based upon their metadata. In addition,  there are
685   other patterns: some applications use an "active content" pattern,
686   where the server returns active content which runs on the client
687   and, based on client available parameters, selects additional
688   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
689   has also been proposed.
690</t>
691<t>
692   These patterns are all widely used, and have trade-offs in applicability
693   and practicality. In particular, when the number of preferences or
694   capabilities to be expressed by a client are large (such as when many
695   different formats are supported by a user-agent), server-driven
696   negotiation becomes unwieldy, and might not be appropriate. Conversely,
697   when the number of representations to choose from is very large,
698   agent-driven negotiation might not be appropriate.
699</t>
700<t>
701   Note that in all cases, the supplier of representations has the
702   responsibility for determining which representations might be
703   considered to be the "same information".
704</t>
705
706<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
707<t>
708   If the selection of the best representation for a response is made by
709   an algorithm located at the server, it is called server-driven
710   negotiation. Selection is based on the available representations of
711   the response (the dimensions over which it can vary; e.g., language,
712   content-coding, etc.) and the contents of particular header fields in
713   the request message or on other information pertaining to the request
714   (such as the network address of the client).
715</t>
716<t>
717   Server-driven negotiation is advantageous when the algorithm for
718   selecting from among the available representations is difficult to
719   describe to the user agent, or when the server desires to send its
720   "best guess" to the client along with the first response (hoping to
721   avoid the round-trip delay of a subsequent request if the "best
722   guess" is good enough for the user). In order to improve the server's
723   guess, the user agent MAY include request header fields (Accept,
724   Accept-Language, Accept-Encoding, etc.) which describe its
725   preferences for such a response.
726</t>
727<t>
728   Server-driven negotiation has disadvantages:
729  <list style="numbers">
730    <t>
731         It is impossible for the server to accurately determine what
732         might be "best" for any given user, since that would require
733         complete knowledge of both the capabilities of the user agent
734         and the intended use for the response (e.g., does the user want
735         to view it on screen or print it on paper?).
736    </t>
737    <t>
738         Having the user agent describe its capabilities in every
739         request can be both very inefficient (given that only a small
740         percentage of responses have multiple representations) and a
741         potential violation of the user's privacy.
742    </t>
743    <t>
744         It complicates the implementation of an origin server and the
745         algorithms for generating responses to a request.
746    </t>
747    <t>
748         It might limit a public cache's ability to use the same response
749         for multiple user's requests.
750    </t>
751  </list>
752</t>
753<t>
754   Server-driven negotiation allows the user agent to specify its preferences,
755   but it cannot expect responses to always honor them. For example, the origin
756   server might not implement server-driven negotiation, or it might decide that
757   sending a response that doesn't conform to them is better than sending a 406
758   (Not Acceptable) response.
759</t>
760<t>
761   Many of the mechanisms for expressing preferences use quality values to
762   declare relative preference. See Section 4.3.1 of <xref target="Part1"/> for more information.
763</t>
764<t>
765   HTTP/1.1 includes the following header fields for enabling
766   server-driven negotiation through description of user agent
767   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
768   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
769   (<xref target="header.accept-language"/>), and User-Agent (Section 10.10 of <xref target="Part2"/>).
770   However, an origin server is not limited to these dimensions and MAY vary
771   the response based on any aspect of the request, including aspects
772   of the connection (e.g., IP address) or information within extension
773   header fields not defined by this specification.
774</t>
775<t><list>
776  <t>
777    Note: In practice, User-Agent based negotiation is fragile,
778    because new clients might not be recognized.
779  </t>
780</list></t>
781<t>
782   The Vary header field (Section 3.5 of <xref target="Part6"/>) can be used to express the parameters the
783   server uses to select a representation that is subject to server-driven
784   negotiation.
785</t>
786</section>
787
788<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
789<t>
790   With agent-driven negotiation, selection of the best representation
791   for a response is performed by the user agent after receiving an
792   initial response from the origin server. Selection is based on a list
793   of the available representations of the response included within the
794   header fields or body of the initial response, with each
795   representation identified by its own URI. Selection from among the
796   representations can be performed automatically (if the user agent is
797   capable of doing so) or manually by the user selecting from a
798   generated (possibly hypertext) menu.
799</t>
800<t>
801   Agent-driven negotiation is advantageous when the response would vary
802   over commonly-used dimensions (such as type, language, or encoding),
803   when the origin server is unable to determine a user agent's
804   capabilities from examining the request, and generally when public
805   caches are used to distribute server load and reduce network usage.
806</t>
807<t>
808   Agent-driven negotiation suffers from the disadvantage of needing a
809   second request to obtain the best alternate representation. This
810   second request is only efficient when caching is used. In addition,
811   this specification does not define any mechanism for supporting
812   automatic selection, though it also does not prevent any such
813   mechanism from being developed as an extension and used within
814   HTTP/1.1.
815</t>
816<t>
817   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
818   status codes for enabling agent-driven negotiation when the server is
819   unwilling or unable to provide a varying response using server-driven
820   negotiation.
821</t>
822</section>
823</section>
824
825<section title="Header Field Definitions" anchor="header.field.definitions">
826<t>
827   This section defines the syntax and semantics of HTTP/1.1 header fields
828   related to the payload of messages.
829</t>
830
831<section title="Accept" anchor="header.accept">
832  <iref primary="true" item="Accept header field"/>
833  <iref primary="true" item="Header Fields" subitem="Accept"/>
834 
835 
836 
837 
838<t>
839   The "Accept" header field can be used by user agents to specify
840   response media types that are acceptable. Accept header fields can be used to
841   indicate that the request is specifically limited to a small set of desired
842   types, as in the case of a request for an in-line image.
843</t>
844<figure><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"/><artwork type="abnf2616"><![CDATA[
845  Accept = #( media-range [ accept-params ] )
846 
847  media-range    = ( "*/*"
848                   / ( type "/" "*" )
849                   / ( type "/" subtype )
850                   ) *( OWS ";" OWS parameter )
851  accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
852  accept-ext     = OWS ";" OWS token [ "=" word ]
853]]></artwork></figure>
854<t>
855   The asterisk "*" character is used to group media types into ranges,
856   with "*/*" indicating all media types and "type/*" indicating all
857   subtypes of that type. The media-range MAY include media type
858   parameters that are applicable to that range.
859</t>
860<t>
861   Each media-range MAY be followed by one or more accept-params,
862   beginning with the "q" parameter for indicating a relative quality
863   factor. The first "q" parameter (if any) separates the media-range
864   parameter(s) from the accept-params. Quality factors allow the user
865   or user agent to indicate the relative degree of preference for that
866   media-range, using the qvalue scale from 0 to 1 (Section 4.3.1 of <xref target="Part1"/>). The
867   default value is q=1.
868</t>
869<t><list>
870  <t>
871    Note: Use of the "q" parameter name to separate media type
872    parameters from Accept extension parameters is due to historical
873    practice. Although this prevents any media type parameter named
874    "q" from being used with a media range, such an event is believed
875    to be unlikely given the lack of any "q" parameters in the IANA
876    media type registry and the rare usage of any media type
877    parameters in Accept. Future media types are discouraged from
878    registering any parameter named "q".
879  </t>
880</list></t>
881<t>
882   The example
883</t>
884<figure><artwork type="example"><![CDATA[
885  Accept: audio/*; q=0.2, audio/basic
886]]></artwork></figure>
887<t>
888   SHOULD be interpreted as "I prefer audio/basic, but send me any audio
889   type if it is the best available after an 80% mark-down in quality".
890</t>
891<t>
892   A request without any Accept header field implies that the user agent
893   will accept any media type in response.
894   If an Accept header field is present in a request and none of the
895   available representations for the response have a media type that is
896   listed as acceptable, the origin server MAY either
897   honor the Accept header field by sending a 406 (Not Acceptable) response
898   or disregard the Accept header field by treating the response as if
899   it is not subject to content negotiation.
900</t>
901<t>
902   A more elaborate example is
903</t>
904<figure><artwork type="example"><![CDATA[
905  Accept: text/plain; q=0.5, text/html,
906          text/x-dvi; q=0.8, text/x-c
907]]></artwork></figure>
908<t>
909   Verbally, this would be interpreted as "text/html and text/x-c are
910   the preferred media types, but if they do not exist, then send the
911   text/x-dvi representation, and if that does not exist, send the text/plain
912   representation".
913</t>
914<t>
915   Media ranges can be overridden by more specific media ranges or
916   specific media types. If more than one media range applies to a given
917   type, the most specific reference has precedence. For example,
918</t>
919<figure><artwork type="example"><![CDATA[
920  Accept: text/*, text/plain, text/plain;format=flowed, */*
921]]></artwork></figure>
922<t>
923   have the following precedence:
924   <list style="numbers">
925    <t>text/plain;format=flowed</t>
926    <t>text/plain</t>
927    <t>text/*</t>
928    <t>*/*</t>
929   </list>
930</t>
931<t>
932   The media type quality factor associated with a given type is
933   determined by finding the media range with the highest precedence
934   which matches that type. For example,
935</t>
936<figure><artwork type="example"><![CDATA[
937  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
938          text/html;level=2;q=0.4, */*;q=0.5
939]]></artwork></figure>
940<t>
941   would cause the following values to be associated:
942</t>
943<texttable align="left">
944  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
945  <c>text/html;level=1</c>    <c>1</c>
946  <c>text/html</c>            <c>0.7</c>
947  <c>text/plain</c>           <c>0.3</c>
948  <c>image/jpeg</c>           <c>0.5</c>
949  <c>text/html;level=2</c>    <c>0.4</c>
950  <c>text/html;level=3</c>    <c>0.7</c>
951</texttable>
952<t>
953      Note: A user agent might be provided with a default set of quality
954      values for certain media ranges. However, unless the user agent is
955      a closed system which cannot interact with other rendering agents,
956      this default set ought to be configurable by the user.
957</t>
958</section>
959
960<section title="Accept-Charset" anchor="header.accept-charset">
961  <iref primary="true" item="Accept-Charset header field"/>
962  <iref primary="true" item="Header Fields" subitem="Accept-Charset"/>
963 
964<t>
965   The "Accept-Charset" header field can be used by user agents to
966   indicate what character encodings are acceptable in a response
967   payload. This field allows
968   clients capable of understanding more comprehensive or special-purpose
969   character encodings to signal that capability to a server which is capable of
970   representing documents in those character encodings.
971</t>
972<figure><iref primary="true" item="Grammar" subitem="Accept-Charset"/><artwork type="abnf2616"><![CDATA[
973  Accept-Charset = 1#( ( charset / "*" )
974                         [ OWS ";" OWS "q=" qvalue ] )
975]]></artwork></figure>
976<t>
977   Character encoding values (a.k.a., charsets) are described in
978   <xref target="character.sets"/>. Each charset MAY be given an
979   associated quality value which represents the user's preference
980   for that charset. The default value is q=1. An example is
981</t>
982<figure><artwork type="example"><![CDATA[
983  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
984]]></artwork></figure>
985<t>
986   The special value "*", if present in the Accept-Charset field,
987   matches every character encoding which is not mentioned elsewhere in the
988   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
989   all character encodings not explicitly mentioned get a quality value of 0.
990</t>
991<t>
992   A request without any Accept-Charset header field implies that the user
993   agent will accept any character encoding in response.
994   If an Accept-Charset header field is present in a request and none of the
995   available representations for the response have a character encoding that
996   is listed as acceptable, the origin server MAY either honor the
997   Accept-Charset header field by sending a 406 (Not Acceptable) response or
998   disregard the Accept-Charset header field by treating the response as if
999   it is not subject to content negotiation.
1000</t>
1001</section>
1002
1003<section title="Accept-Encoding" anchor="header.accept-encoding">
1004  <iref primary="true" item="Accept-Encoding header field"/>
1005  <iref primary="true" item="Header Fields" subitem="Accept-Encoding"/>
1006 
1007 
1008<t>
1009   The "Accept-Encoding" header field can be used by user agents to
1010   indicate what response content-codings (<xref target="content.codings"/>)
1011   are acceptable in the response.  An "identity" token is used as a synonym
1012   for "no encoding" in order to communicate when no encoding is preferred.
1013</t>
1014<figure><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/><artwork type="abnf2616"><![CDATA[
1015  Accept-Encoding  = #( codings [ OWS ";" OWS "q=" qvalue ] )
1016  codings          = content-coding / "identity" / "*"
1017]]></artwork></figure>
1018<t>
1019   Each codings value MAY be given an associated quality value which
1020   represents the preference for that encoding. The default value is q=1.
1021</t>
1022<t>
1023   For example,
1024</t>
1025<figure><artwork type="example"><![CDATA[
1026  Accept-Encoding: compress, gzip
1027  Accept-Encoding:
1028  Accept-Encoding: *
1029  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1030  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1031]]></artwork></figure>
1032<t>
1033   A server tests whether a content-coding for a given representation is
1034   acceptable, according to an Accept-Encoding field, using these rules:
1035  <list style="numbers">
1036      <t>The special "*" symbol in an Accept-Encoding field matches any
1037         available content-coding not explicitly listed in the header
1038         field.</t>
1039
1040      <t>If the representation has no content-coding, then it is acceptable
1041         by default unless specifically excluded by the Accept-Encoding field
1042         stating either "identity;q=0" or "*;q=0" without a more specific
1043         entry for "identity".</t>
1044
1045      <t>If the representation's content-coding is one of the content-codings
1046         listed in the Accept-Encoding field, then it is acceptable unless
1047         it is accompanied by a qvalue of 0. (As defined in Section 4.3.1 of <xref target="Part1"/>, a
1048         qvalue of 0 means "not acceptable".)</t>
1049
1050      <t>If multiple content-codings are acceptable, then the acceptable
1051         content-coding with the highest non-zero qvalue is preferred.</t>
1052  </list>
1053</t>
1054<t>
1055   An Accept-Encoding header field with a combined field-value that is empty
1056   implies that the user agent does not want any content-coding in response.
1057   If an Accept-Encoding header field is present in a request and none of the
1058   available representations for the response have a content-coding that
1059   is listed as acceptable, the origin server SHOULD send a response
1060   without any content-coding.
1061</t>
1062<t>
1063   A request without an Accept-Encoding header field implies that the user
1064   agent will accept any content-coding in response, but a representation
1065   without content-coding is preferred for compatibility with the widest
1066   variety of user agents.
1067</t>
1068<t><list>
1069  <t>
1070    Note: Most HTTP/1.0 applications do not recognize or obey qvalues
1071    associated with content-codings. This means that qvalues will not
1072    work and are not permitted with x-gzip or x-compress.
1073  </t>
1074</list></t>
1075</section>
1076
1077<section title="Accept-Language" anchor="header.accept-language">
1078  <iref primary="true" item="Accept-Language header field"/>
1079  <iref primary="true" item="Header Fields" subitem="Accept-Language"/>
1080 
1081 
1082<t>
1083   The "Accept-Language" header field can be used by user agents to
1084   indicate the set of natural languages that are preferred in the response.
1085   Language tags are defined in <xref target="language.tags"/>.
1086</t>
1087<figure><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/><artwork type="abnf2616"><![CDATA[
1088  Accept-Language =
1089                    1#( language-range [ OWS ";" OWS "q=" qvalue ] )
1090  language-range  =
1091            <language-range, defined in [RFC4647], Section 2.1>
1092]]></artwork></figure>
1093<t>
1094   Each language-range can be given an associated quality value which
1095   represents an estimate of the user's preference for the languages
1096   specified by that range. The quality value defaults to "q=1". For
1097   example,
1098</t>
1099<figure><artwork type="example"><![CDATA[
1100  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1101]]></artwork></figure>
1102<t>
1103   would mean: "I prefer Danish, but will accept British English and
1104   other types of English".
1105   (see also Section 2.3 of <xref target="RFC4647"/>)
1106</t>
1107<t>
1108   For matching, Section 3 of <xref target="RFC4647"/> defines
1109   several matching schemes. Implementations can offer the most appropriate
1110   matching scheme for their requirements.
1111</t>
1112<t><list>
1113  <t>
1114    Note: The "Basic Filtering" scheme (<xref target="RFC4647"/>, Section 3.3.1) is identical to the matching scheme that was
1115    previously defined in Section 14.4 of <xref target="RFC2616"/>.
1116  </t>
1117</list></t>
1118<t>
1119   It might be contrary to the privacy expectations of the user to send
1120   an Accept-Language header field with the complete linguistic preferences of
1121   the user in every request. For a discussion of this issue, see
1122   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1123</t>
1124<t>
1125   As intelligibility is highly dependent on the individual user, it is
1126   recommended that client applications make the choice of linguistic
1127   preference available to the user. If the choice is not made
1128   available, then the Accept-Language header field MUST NOT be given in
1129   the request.
1130</t>
1131<t><list>
1132  <t>
1133    Note: When making the choice of linguistic preference available to
1134    the user, we remind implementors of  the fact that users are not
1135    familiar with the details of language matching as described above,
1136    and ought to be provided appropriate guidance. As an example, users
1137    might assume that on selecting "en-gb", they will be served any
1138    kind of English document if British English is not available. A
1139    user agent might suggest in such a case to add "en" to get the
1140    best matching behavior.
1141  </t>
1142</list></t>
1143</section>
1144
1145<section title="Content-Encoding" anchor="header.content-encoding">
1146  <iref primary="true" item="Content-Encoding header field"/>
1147  <iref primary="true" item="Header Fields" subitem="Content-Encoding"/>
1148 
1149<t>
1150   The "Content-Encoding" header field indicates what content-codings
1151   have been applied to the representation beyond those inherent in the media
1152   type, and thus what decoding mechanisms must be applied in order to obtain
1153   the media-type referenced by the Content-Type header field.
1154   Content-Encoding is primarily used to allow a representation to be
1155   compressed without losing the identity of its underlying media type.
1156</t>
1157<figure><iref primary="true" item="Grammar" subitem="Content-Encoding"/><artwork type="abnf2616"><![CDATA[
1158  Content-Encoding = 1#content-coding
1159]]></artwork></figure>
1160<t>
1161   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1162</t>
1163<figure><artwork type="example"><![CDATA[
1164  Content-Encoding: gzip
1165]]></artwork></figure>
1166<t>
1167   The content-coding is a characteristic of the representation.
1168   Typically, the representation body is stored with this
1169   encoding and is only decoded before rendering or analogous usage.
1170   However, a transforming proxy MAY modify the content-coding if the
1171   new coding is known to be acceptable to the recipient, unless the
1172   "no-transform" cache-control directive is present in the message.
1173</t>
1174<t>
1175   If the media type includes an inherent encoding, such as a data format
1176   that is always compressed, then that encoding would not be restated as
1177   a Content-Encoding even if it happens to be the same algorithm as one
1178   of the content-codings.  Such a content-coding would only be listed if,
1179   for some bizarre reason, it is applied a second time to form the
1180   representation.  Likewise, an origin server might choose to publish the
1181   same payload data as multiple representations that differ only in whether
1182   the coding is defined as part of Content-Type or Content-Encoding, since
1183   some user agents will behave differently in their handling of each
1184   response (e.g., open a "Save as ..." dialog instead of automatic
1185   decompression and rendering of content).
1186</t>
1187<t>
1188   A representation that has a content-coding applied to it MUST include
1189   a Content-Encoding header field (<xref target="header.content-encoding"/>)
1190   that lists the content-coding(s) applied.
1191</t>
1192<t>
1193   If multiple encodings have been applied to a representation, the content
1194   codings MUST be listed in the order in which they were applied.
1195   Additional information about the encoding parameters MAY be provided
1196   by other header fields not defined by this specification.
1197</t>
1198<t>
1199   If the content-coding of a representation in a request message is not
1200   acceptable to the origin server, the server SHOULD respond with a
1201   status code of 415 (Unsupported Media Type).
1202</t>
1203</section>
1204
1205<section title="Content-Language" anchor="header.content-language">
1206  <iref primary="true" item="Content-Language header field"/>
1207  <iref primary="true" item="Header Fields" subitem="Content-Language"/>
1208 
1209<t>
1210   The "Content-Language" header field describes the natural
1211   language(s) of the intended audience for the representation. Note that this might
1212   not be equivalent to all the languages used within the representation.
1213</t>
1214<figure><iref primary="true" item="Grammar" subitem="Content-Language"/><artwork type="abnf2616"><![CDATA[
1215  Content-Language = 1#language-tag
1216]]></artwork></figure>
1217<t>
1218   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1219   Content-Language is to allow a user to identify and differentiate
1220   representations according to the user's own preferred language. Thus, if the
1221   body content is intended only for a Danish-literate audience, the
1222   appropriate field is
1223</t>
1224<figure><artwork type="example"><![CDATA[
1225  Content-Language: da
1226]]></artwork></figure>
1227<t>
1228   If no Content-Language is specified, the default is that the content
1229   is intended for all language audiences. This might mean that the
1230   sender does not consider it to be specific to any natural language,
1231   or that the sender does not know for which language it is intended.
1232</t>
1233<t>
1234   Multiple languages MAY be listed for content that is intended for
1235   multiple audiences. For example, a rendition of the "Treaty of
1236   Waitangi", presented simultaneously in the original Maori and English
1237   versions, would call for
1238</t>
1239<figure><artwork type="example"><![CDATA[
1240  Content-Language: mi, en
1241]]></artwork></figure>
1242<t>
1243   However, just because multiple languages are present within a representation
1244   does not mean that it is intended for multiple linguistic audiences.
1245   An example would be a beginner's language primer, such as "A First
1246   Lesson in Latin", which is clearly intended to be used by an
1247   English-literate audience. In this case, the Content-Language would
1248   properly only include "en".
1249</t>
1250<t>
1251   Content-Language MAY be applied to any media type — it is not
1252   limited to textual documents.
1253</t>
1254</section>
1255
1256<section title="Content-Location" anchor="header.content-location">
1257  <iref primary="true" item="Content-Location header field"/>
1258  <iref primary="true" item="Header Fields" subitem="Content-Location"/>
1259 
1260<t>
1261   The "Content-Location" header field supplies a URI that can be used
1262   as a specific identifier for the representation in this message.
1263   In other words, if one were to perform a GET on this URI at the time
1264   of this message's generation, then a 200 response would contain the
1265   same representation that is enclosed as payload in this message.
1266</t>
1267<figure><iref primary="true" item="Grammar" subitem="Content-Location"/><artwork type="abnf2616"><![CDATA[
1268  Content-Location = absolute-URI / partial-URI
1269]]></artwork></figure>
1270<t>
1271   The Content-Location value is not a replacement for the effective
1272   Request URI (Section 5.5 of <xref target="Part1"/>).  It is representation metadata.
1273   It has the same syntax and semantics as the header field of the same name
1274   defined for MIME body parts in Section 4 of <xref target="RFC2557"/>.
1275   However, its appearance in an HTTP message has some special implications
1276   for HTTP recipients.
1277</t>
1278<t>
1279   If Content-Location is included in a response message and its value
1280   is the same as the effective request URI, then the response payload
1281   SHOULD be considered the current representation of that resource.
1282   For a GET or HEAD request, this is the same as the default semantics
1283   when no Content-Location is provided by the server.  For a state-changing
1284   request like PUT or POST, it implies that the server's response contains
1285   the new representation of that resource, thereby distinguishing it from
1286   representations that might only report about the action (e.g., "It worked!").
1287   This allows authoring applications to update their local copies without
1288   the need for a subsequent GET request.
1289</t>
1290<t>
1291   If Content-Location is included in a response message and its value
1292   differs from the effective request URI, then the origin server is
1293   informing recipients that this representation has its own, presumably
1294   more specific, identifier.  For a GET or HEAD request, this is an
1295   indication that the effective request URI identifies a resource that
1296   is subject to content negotiation and the selected representation for
1297   this response can also be found at the identified URI.  For other
1298   methods, such a Content-Location indicates that this representation
1299   contains a report on the action's status and the same report is
1300   available (for future access with GET) at the given URI.  For
1301   example, a purchase transaction made via a POST request might
1302   include a receipt document as the payload of the 200 response;
1303   the Content-Location value provides an identifier for retrieving
1304   a copy of that same receipt in the future.
1305</t>
1306<t>
1307   If Content-Location is included in a request message, then it MAY
1308   be interpreted by the origin server as an indication of where the
1309   user agent originally obtained the content of the enclosed
1310   representation (prior to any subsequent modification of the content
1311   by that user agent).  In other words, the user agent is providing
1312   the same representation metadata that it received with the original
1313   representation.  However, such interpretation MUST NOT be used to
1314   alter the semantics of the method requested by the client.  For
1315   example, if a client makes a PUT request on a negotiated resource
1316   and the origin server accepts that PUT (without redirection), then the
1317   new set of values for that resource is expected to be consistent with
1318   the one representation supplied in that PUT; the Content-Location
1319   cannot be used as a form of reverse content selection that
1320   identifies only one of the negotiated representations to be updated.
1321   If the user agent had wanted the latter semantics, it would have applied
1322   the PUT directly to the Content-Location URI.
1323</t>
1324<t>
1325   A Content-Location field received in a request message is transitory
1326   information that SHOULD NOT be saved with other representation
1327   metadata for use in later responses.  The Content-Location's value
1328   might be saved for use in other contexts, such as within source links
1329   or other metadata.
1330</t>
1331<t>
1332   A cache cannot assume that a representation with a Content-Location
1333   different from the URI used to retrieve it can be used to respond to
1334   later requests on that Content-Location URI.
1335</t>
1336<t>
1337   If the Content-Location value is a partial URI, the partial URI is
1338   interpreted relative to the effective request URI.
1339</t>
1340</section>
1341
1342<section title="Content-Type" anchor="header.content-type">
1343  <iref primary="true" item="Content-Type header field"/>
1344  <iref primary="true" item="Header Fields" subitem="Content-Type"/>
1345 
1346<t>
1347   The "Content-Type" header field indicates the media type of the
1348   representation. In the case of responses to the HEAD method, the media type is
1349   that which would have been sent had the request been a GET.
1350</t>
1351<figure><iref primary="true" item="Grammar" subitem="Content-Type"/><artwork type="abnf2616"><![CDATA[
1352  Content-Type = media-type
1353]]></artwork></figure>
1354<t>
1355   Media types are defined in <xref target="media.types"/>. An example of the field is
1356</t>
1357<figure><artwork type="example"><![CDATA[
1358  Content-Type: text/html; charset=ISO-8859-4
1359]]></artwork></figure>
1360<t>
1361   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1362</t>
1363</section>
1364
1365</section>
1366
1367<section title="IANA Considerations" anchor="IANA.considerations">
1368<section title="Header Field Registration" anchor="header.field.registration">
1369<t>
1370   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1371   with the permanent registrations below (see <xref target="RFC3864"/>):
1372</t>
1373
1374<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1375<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1376   <ttcol>Header Field Name</ttcol>
1377   <ttcol>Protocol</ttcol>
1378   <ttcol>Status</ttcol>
1379   <ttcol>Reference</ttcol>
1380
1381   <c>Accept</c>
1382   <c>http</c>
1383   <c>standard</c>
1384   <c>
1385      <xref target="header.accept"/>
1386   </c>
1387   <c>Accept-Charset</c>
1388   <c>http</c>
1389   <c>standard</c>
1390   <c>
1391      <xref target="header.accept-charset"/>
1392   </c>
1393   <c>Accept-Encoding</c>
1394   <c>http</c>
1395   <c>standard</c>
1396   <c>
1397      <xref target="header.accept-encoding"/>
1398   </c>
1399   <c>Accept-Language</c>
1400   <c>http</c>
1401   <c>standard</c>
1402   <c>
1403      <xref target="header.accept-language"/>
1404   </c>
1405   <c>Content-Encoding</c>
1406   <c>http</c>
1407   <c>standard</c>
1408   <c>
1409      <xref target="header.content-encoding"/>
1410   </c>
1411   <c>Content-Language</c>
1412   <c>http</c>
1413   <c>standard</c>
1414   <c>
1415      <xref target="header.content-language"/>
1416   </c>
1417   <c>Content-Location</c>
1418   <c>http</c>
1419   <c>standard</c>
1420   <c>
1421      <xref target="header.content-location"/>
1422   </c>
1423   <c>Content-Type</c>
1424   <c>http</c>
1425   <c>standard</c>
1426   <c>
1427      <xref target="header.content-type"/>
1428   </c>
1429   <c>MIME-Version</c>
1430   <c>http</c>
1431   <c>standard</c>
1432   <c>
1433      <xref target="mime-version"/>
1434   </c>
1435</texttable>
1436<!--(END)-->
1437
1438<t>
1439   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1440</t>
1441</section>
1442
1443<section title="Content Coding Registry" anchor="content.coding.registration">
1444<t>
1445   The registration procedure for HTTP Content Codings is now defined
1446   by <xref target="content.coding.registry"/> of this document.
1447</t>
1448<t>
1449   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1450   shall be updated with the registration below:
1451</t>
1452<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1453   <ttcol>Name</ttcol>
1454   <ttcol>Description</ttcol>
1455   <ttcol>Reference</ttcol>
1456   <c>compress</c>
1457   <c>UNIX "compress" program method</c>
1458   <c>
1459      Section 4.2.1 of <xref target="Part1"/>
1460   </c>
1461   <c>deflate</c>
1462   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1463   the "zlib" data format (<xref target="RFC1950"/>)
1464   </c>
1465   <c>
1466      Section 4.2.2 of <xref target="Part1"/>
1467   </c>
1468   <c>gzip</c>
1469   <c>Same as GNU zip <xref target="RFC1952"/></c>
1470   <c>
1471      Section 4.2.3 of <xref target="Part1"/>
1472   </c>
1473   <c>identity</c>
1474   <c>reserved (synonym for "no encoding" in Accept-Encoding header field)</c>
1475   <c>
1476      <xref target="header.accept-encoding"/>
1477   </c>
1478</texttable>
1479</section>
1480
1481</section>
1482
1483<section title="Security Considerations" anchor="security.considerations">
1484<t>
1485   This section is meant to inform application developers, information
1486   providers, and users of the security limitations in HTTP/1.1 as
1487   described by this document. The discussion does not include
1488   definitive solutions to the problems revealed, though it does make
1489   some suggestions for reducing security risks.
1490</t>
1491
1492<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1493<t>
1494   Accept header fields can reveal information about the user to all
1495   servers which are accessed. The Accept-Language header field in particular
1496   can reveal information the user would consider to be of a private
1497   nature, because the understanding of particular languages is often
1498   strongly correlated to the membership of a particular ethnic group.
1499   User agents which offer the option to configure the contents of an
1500   Accept-Language header field to be sent in every request are strongly
1501   encouraged to let the configuration process include a message which
1502   makes the user aware of the loss of privacy involved.
1503</t>
1504<t>
1505   An approach that limits the loss of privacy would be for a user agent
1506   to omit the sending of Accept-Language header fields by default, and to ask
1507   the user whether or not to start sending Accept-Language header fields to a
1508   server if it detects, by looking for any Vary header fields
1509   generated by the server, that such sending could improve the quality
1510   of service.
1511</t>
1512<t>
1513   Elaborate user-customized accept header fields sent in every request,
1514   in particular if these include quality values, can be used by servers
1515   as relatively reliable and long-lived user identifiers. Such user
1516   identifiers would allow content providers to do click-trail tracking,
1517   and would allow collaborating content providers to match cross-server
1518   click-trails or form submissions of individual users. Note that for
1519   many users not behind a proxy, the network address of the host
1520   running the user agent will also serve as a long-lived user
1521   identifier. In environments where proxies are used to enhance
1522   privacy, user agents ought to be conservative in offering accept
1523   header configuration options to end users. As an extreme privacy
1524   measure, proxies could filter the accept header fields in relayed requests.
1525   General purpose user agents which provide a high degree of header
1526   configurability SHOULD warn users about the loss of privacy which can
1527   be involved.
1528</t>
1529</section>
1530
1531</section>
1532
1533<section title="Acknowledgments" anchor="acks">
1534<t>
1535  See Section 9 of <xref target="Part1"/>.
1536</t>
1537</section>
1538</middle>
1539<back>
1540
1541<references title="Normative References">
1542
1543<reference anchor="Part1">
1544  <front>
1545    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1546    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1547      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1548      <address><email>fielding@gbiv.com</email></address>
1549    </author>
1550    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1551      <organization abbrev="W3C">World Wide Web Consortium</organization>
1552      <address><email>ylafon@w3.org</email></address>
1553    </author>
1554    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1555      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1556      <address><email>julian.reschke@greenbytes.de</email></address>
1557    </author>
1558    <date month="March" year="2012"/>
1559  </front>
1560  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-19"/>
1561 
1562</reference>
1563
1564<reference anchor="Part2">
1565  <front>
1566    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1567    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1568      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1569      <address><email>fielding@gbiv.com</email></address>
1570    </author>
1571    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1572      <organization abbrev="W3C">World Wide Web Consortium</organization>
1573      <address><email>ylafon@w3.org</email></address>
1574    </author>
1575    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1576      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1577      <address><email>julian.reschke@greenbytes.de</email></address>
1578    </author>
1579    <date month="March" year="2012"/>
1580  </front>
1581  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-19"/>
1582 
1583</reference>
1584
1585<reference anchor="Part4">
1586  <front>
1587    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1588    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1589      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1590      <address><email>fielding@gbiv.com</email></address>
1591    </author>
1592    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1593      <organization abbrev="W3C">World Wide Web Consortium</organization>
1594      <address><email>ylafon@w3.org</email></address>
1595    </author>
1596    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1597      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1598      <address><email>julian.reschke@greenbytes.de</email></address>
1599    </author>
1600    <date month="March" year="2012"/>
1601  </front>
1602  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-19"/>
1603 
1604</reference>
1605
1606<reference anchor="Part5">
1607  <front>
1608    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1609    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1610      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1611      <address><email>fielding@gbiv.com</email></address>
1612    </author>
1613    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1614      <organization abbrev="W3C">World Wide Web Consortium</organization>
1615      <address><email>ylafon@w3.org</email></address>
1616    </author>
1617    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1618      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1619      <address><email>julian.reschke@greenbytes.de</email></address>
1620    </author>
1621    <date month="March" year="2012"/>
1622  </front>
1623  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-19"/>
1624 
1625</reference>
1626
1627<reference anchor="Part6">
1628  <front>
1629    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1630    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1631      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1632      <address><email>fielding@gbiv.com</email></address>
1633    </author>
1634    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1635      <organization abbrev="W3C">World Wide Web Consortium</organization>
1636      <address><email>ylafon@w3.org</email></address>
1637    </author>
1638    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1639      <organization>Rackspace</organization>
1640      <address><email>mnot@mnot.net</email></address>
1641    </author>
1642    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1643      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1644      <address><email>julian.reschke@greenbytes.de</email></address>
1645    </author>
1646    <date month="March" year="2012"/>
1647  </front>
1648  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-19"/>
1649 
1650</reference>
1651
1652<reference anchor="RFC1950">
1653  <front>
1654    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1655    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1656      <organization>Aladdin Enterprises</organization>
1657      <address><email>ghost@aladdin.com</email></address>
1658    </author>
1659    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1660    <date month="May" year="1996"/>
1661  </front>
1662  <seriesInfo name="RFC" value="1950"/>
1663  <!--<annotation>
1664    RFC 1950 is an Informational RFC, thus it might be less stable than
1665    this specification. On the other hand, this downward reference was
1666    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1667    therefore it is unlikely to cause problems in practice. See also
1668    <xref target="BCP97"/>.
1669  </annotation>-->
1670</reference>
1671
1672<reference anchor="RFC1951">
1673  <front>
1674    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1675    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1676      <organization>Aladdin Enterprises</organization>
1677      <address><email>ghost@aladdin.com</email></address>
1678    </author>
1679    <date month="May" year="1996"/>
1680  </front>
1681  <seriesInfo name="RFC" value="1951"/>
1682  <!--<annotation>
1683    RFC 1951 is an Informational RFC, thus it might be less stable than
1684    this specification. On the other hand, this downward reference was
1685    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1686    therefore it is unlikely to cause problems in practice. See also
1687    <xref target="BCP97"/>.
1688  </annotation>-->
1689</reference>
1690
1691<reference anchor="RFC1952">
1692  <front>
1693    <title>GZIP file format specification version 4.3</title>
1694    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1695      <organization>Aladdin Enterprises</organization>
1696      <address><email>ghost@aladdin.com</email></address>
1697    </author>
1698    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1699      <address><email>gzip@prep.ai.mit.edu</email></address>
1700    </author>
1701    <author initials="M." surname="Adler" fullname="Mark Adler">
1702      <address><email>madler@alumni.caltech.edu</email></address>
1703    </author>
1704    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1705      <address><email>ghost@aladdin.com</email></address>
1706    </author>
1707    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1708      <address><email>randeg@alumni.rpi.edu</email></address>
1709    </author>
1710    <date month="May" year="1996"/>
1711  </front>
1712  <seriesInfo name="RFC" value="1952"/>
1713  <!--<annotation>
1714    RFC 1952 is an Informational RFC, thus it might be less stable than
1715    this specification. On the other hand, this downward reference was
1716    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
1717    therefore it is unlikely to cause problems in practice. See also
1718    <xref target="BCP97"/>.
1719  </annotation>-->
1720</reference>
1721
1722<reference anchor="RFC2045">
1723  <front>
1724    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1725    <author initials="N." surname="Freed" fullname="Ned Freed">
1726      <organization>Innosoft International, Inc.</organization>
1727      <address><email>ned@innosoft.com</email></address>
1728    </author>
1729    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1730      <organization>First Virtual Holdings</organization>
1731      <address><email>nsb@nsb.fv.com</email></address>
1732    </author>
1733    <date month="November" year="1996"/>
1734  </front>
1735  <seriesInfo name="RFC" value="2045"/>
1736</reference>
1737
1738<reference anchor="RFC2046">
1739  <front>
1740    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1741    <author initials="N." surname="Freed" fullname="Ned Freed">
1742      <organization>Innosoft International, Inc.</organization>
1743      <address><email>ned@innosoft.com</email></address>
1744    </author>
1745    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1746      <organization>First Virtual Holdings</organization>
1747      <address><email>nsb@nsb.fv.com</email></address>
1748    </author>
1749    <date month="November" year="1996"/>
1750  </front>
1751  <seriesInfo name="RFC" value="2046"/>
1752</reference>
1753
1754<reference anchor="RFC2119">
1755  <front>
1756    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1757    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1758      <organization>Harvard University</organization>
1759      <address><email>sob@harvard.edu</email></address>
1760    </author>
1761    <date month="March" year="1997"/>
1762  </front>
1763  <seriesInfo name="BCP" value="14"/>
1764  <seriesInfo name="RFC" value="2119"/>
1765</reference>
1766
1767<reference anchor="RFC4647">
1768  <front>
1769    <title>Matching of Language Tags</title>
1770    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1771      <organization>Yahoo! Inc.</organization>
1772      <address><email>addison@inter-locale.com</email></address>
1773    </author>
1774    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1775      <organization>Google</organization>
1776      <address><email>mark.davis@macchiato.com</email></address>
1777    </author>
1778    <date year="2006" month="September"/>
1779  </front>
1780  <seriesInfo name="BCP" value="47"/>
1781  <seriesInfo name="RFC" value="4647"/>
1782</reference>
1783
1784<reference anchor="RFC5234">
1785  <front>
1786    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1787    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1788      <organization>Brandenburg InternetWorking</organization>
1789      <address>
1790        <email>dcrocker@bbiw.net</email>
1791      </address> 
1792    </author>
1793    <author initials="P." surname="Overell" fullname="Paul Overell">
1794      <organization>THUS plc.</organization>
1795      <address>
1796        <email>paul.overell@thus.net</email>
1797      </address>
1798    </author>
1799    <date month="January" year="2008"/>
1800  </front>
1801  <seriesInfo name="STD" value="68"/>
1802  <seriesInfo name="RFC" value="5234"/>
1803</reference>
1804
1805<reference anchor="RFC5646">
1806  <front>
1807    <title>Tags for Identifying Languages</title>
1808    <author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
1809      <organization>Lab126</organization>
1810      <address><email>addison@inter-locale.com</email></address>
1811    </author>
1812    <author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
1813      <organization>Google</organization>
1814      <address><email>mark.davis@google.com</email></address>
1815    </author>
1816    <date month="September" year="2009"/>
1817  </front>
1818  <seriesInfo name="BCP" value="47"/>
1819  <seriesInfo name="RFC" value="5646"/>
1820</reference>
1821
1822</references>
1823
1824<references title="Informative References">
1825
1826<reference anchor="RFC1945">
1827  <front>
1828    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
1829    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1830      <organization>MIT, Laboratory for Computer Science</organization>
1831      <address><email>timbl@w3.org</email></address>
1832    </author>
1833    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
1834      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1835      <address><email>fielding@ics.uci.edu</email></address>
1836    </author>
1837    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1838      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
1839      <address><email>frystyk@w3.org</email></address>
1840    </author>
1841    <date month="May" year="1996"/>
1842  </front>
1843  <seriesInfo name="RFC" value="1945"/>
1844</reference>
1845
1846<reference anchor="RFC2049">
1847  <front>
1848    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
1849    <author initials="N." surname="Freed" fullname="Ned Freed">
1850      <organization>Innosoft International, Inc.</organization>
1851      <address><email>ned@innosoft.com</email></address>
1852    </author>
1853    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1854      <organization>First Virtual Holdings</organization>
1855      <address><email>nsb@nsb.fv.com</email></address>
1856    </author>
1857    <date month="November" year="1996"/>
1858  </front>
1859  <seriesInfo name="RFC" value="2049"/>
1860</reference>
1861
1862<reference anchor="RFC2068">
1863  <front>
1864    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1865    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1866      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1867      <address><email>fielding@ics.uci.edu</email></address>
1868    </author>
1869    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1870      <organization>MIT Laboratory for Computer Science</organization>
1871      <address><email>jg@w3.org</email></address>
1872    </author>
1873    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1874      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1875      <address><email>mogul@wrl.dec.com</email></address>
1876    </author>
1877    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1878      <organization>MIT Laboratory for Computer Science</organization>
1879      <address><email>frystyk@w3.org</email></address>
1880    </author>
1881    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1882      <organization>MIT Laboratory for Computer Science</organization>
1883      <address><email>timbl@w3.org</email></address>
1884    </author>
1885    <date month="January" year="1997"/>
1886  </front>
1887  <seriesInfo name="RFC" value="2068"/>
1888</reference>
1889
1890<reference anchor="RFC2076">
1891  <front>
1892    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
1893    <author initials="J." surname="Palme" fullname="Jacob Palme">
1894      <organization>Stockholm University/KTH</organization>
1895      <address><email>jpalme@dsv.su.se</email></address>
1896    </author>
1897    <date month="February" year="1997"/>
1898  </front>
1899  <seriesInfo name="RFC" value="2076"/>
1900</reference>
1901
1902<reference anchor="RFC2277">
1903  <front>
1904    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
1905    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1906      <organization>UNINETT</organization>
1907      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1908    </author>
1909    <date month="January" year="1998"/>
1910  </front>
1911  <seriesInfo name="BCP" value="18"/>
1912  <seriesInfo name="RFC" value="2277"/>
1913</reference>
1914
1915<reference anchor="RFC2295">
1916  <front>
1917    <title abbrev="HTTP Content Negotiation">Transparent Content Negotiation in HTTP</title>
1918    <author initials="K." surname="Holtman" fullname="Koen Holtman">
1919      <organization>Technische Universiteit Eindhoven</organization>
1920      <address>
1921        <email>koen@win.tue.nl</email>
1922      </address>
1923    </author>
1924    <author initials="A.H." surname="Mutz" fullname="Andrew H. Mutz">
1925      <organization>Hewlett-Packard Company</organization>
1926      <address>
1927        <email>mutz@hpl.hp.com</email>
1928      </address>
1929    </author>
1930    <date year="1998" month="March"/>
1931  </front>
1932  <seriesInfo name="RFC" value="2295"/>
1933</reference>
1934
1935<reference anchor="RFC2388">
1936  <front>
1937    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
1938    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1939      <organization>Xerox Palo Alto Research Center</organization>
1940      <address><email>masinter@parc.xerox.com</email></address>
1941    </author>
1942    <date year="1998" month="August"/>
1943  </front>
1944  <seriesInfo name="RFC" value="2388"/>
1945</reference>
1946
1947<reference anchor="RFC2557">
1948  <front>
1949    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
1950    <author initials="F." surname="Palme" fullname="Jacob Palme">
1951      <organization>Stockholm University and KTH</organization>
1952      <address><email>jpalme@dsv.su.se</email></address>
1953    </author>
1954    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
1955      <organization>Microsoft Corporation</organization>
1956      <address><email>alexhop@microsoft.com</email></address>
1957    </author>
1958    <author initials="N." surname="Shelness" fullname="Nick Shelness">
1959      <organization>Lotus Development Corporation</organization>
1960      <address><email>Shelness@lotus.com</email></address>
1961    </author>
1962    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
1963      <address><email>stef@nma.com</email></address>
1964    </author>
1965    <date year="1999" month="March"/>
1966  </front>
1967  <seriesInfo name="RFC" value="2557"/>
1968</reference>
1969
1970<reference anchor="RFC2616">
1971  <front>
1972    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1973    <author initials="R." surname="Fielding" fullname="R. Fielding">
1974      <organization>University of California, Irvine</organization>
1975      <address><email>fielding@ics.uci.edu</email></address>
1976    </author>
1977    <author initials="J." surname="Gettys" fullname="J. Gettys">
1978      <organization>W3C</organization>
1979      <address><email>jg@w3.org</email></address>
1980    </author>
1981    <author initials="J." surname="Mogul" fullname="J. Mogul">
1982      <organization>Compaq Computer Corporation</organization>
1983      <address><email>mogul@wrl.dec.com</email></address>
1984    </author>
1985    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1986      <organization>MIT Laboratory for Computer Science</organization>
1987      <address><email>frystyk@w3.org</email></address>
1988    </author>
1989    <author initials="L." surname="Masinter" fullname="L. Masinter">
1990      <organization>Xerox Corporation</organization>
1991      <address><email>masinter@parc.xerox.com</email></address>
1992    </author>
1993    <author initials="P." surname="Leach" fullname="P. Leach">
1994      <organization>Microsoft Corporation</organization>
1995      <address><email>paulle@microsoft.com</email></address>
1996    </author>
1997    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1998      <organization>W3C</organization>
1999      <address><email>timbl@w3.org</email></address>
2000    </author>
2001    <date month="June" year="1999"/>
2002  </front>
2003  <seriesInfo name="RFC" value="2616"/>
2004</reference>
2005
2006<reference anchor="RFC3629">
2007  <front>
2008    <title>UTF-8, a transformation format of ISO 10646</title>
2009    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2010      <organization>Alis Technologies</organization>
2011      <address><email>fyergeau@alis.com</email></address>
2012    </author>
2013    <date month="November" year="2003"/>
2014  </front>
2015  <seriesInfo name="STD" value="63"/>
2016  <seriesInfo name="RFC" value="3629"/>
2017</reference>
2018
2019<reference anchor="RFC3864">
2020  <front>
2021    <title>Registration Procedures for Message Header Fields</title>
2022    <author initials="G." surname="Klyne" fullname="G. Klyne">
2023      <organization>Nine by Nine</organization>
2024      <address><email>GK-IETF@ninebynine.org</email></address>
2025    </author>
2026    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2027      <organization>BEA Systems</organization>
2028      <address><email>mnot@pobox.com</email></address>
2029    </author>
2030    <author initials="J." surname="Mogul" fullname="J. Mogul">
2031      <organization>HP Labs</organization>
2032      <address><email>JeffMogul@acm.org</email></address>
2033    </author>
2034    <date year="2004" month="September"/>
2035  </front>
2036  <seriesInfo name="BCP" value="90"/>
2037  <seriesInfo name="RFC" value="3864"/>
2038</reference>
2039
2040<reference anchor="RFC4288">
2041  <front>
2042    <title>Media Type Specifications and Registration Procedures</title>
2043    <author initials="N." surname="Freed" fullname="N. Freed">
2044      <organization>Sun Microsystems</organization>
2045      <address>
2046        <email>ned.freed@mrochek.com</email>
2047      </address>
2048    </author>
2049    <author initials="J." surname="Klensin" fullname="J. Klensin">
2050      <address>
2051        <email>klensin+ietf@jck.com</email>
2052      </address>
2053    </author>
2054    <date year="2005" month="December"/>
2055  </front>
2056  <seriesInfo name="BCP" value="13"/>
2057  <seriesInfo name="RFC" value="4288"/>
2058</reference>
2059
2060<reference anchor="RFC5226">
2061  <front>
2062    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2063    <author initials="T." surname="Narten" fullname="T. Narten">
2064      <organization>IBM</organization>
2065      <address><email>narten@us.ibm.com</email></address>
2066    </author>
2067    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2068      <organization>Google</organization>
2069      <address><email>Harald@Alvestrand.no</email></address>
2070    </author>
2071    <date year="2008" month="May"/>
2072  </front>
2073  <seriesInfo name="BCP" value="26"/>
2074  <seriesInfo name="RFC" value="5226"/>
2075</reference>
2076
2077<reference anchor="RFC5322">
2078  <front>
2079    <title>Internet Message Format</title>
2080    <author initials="P." surname="Resnick" fullname="P. Resnick">
2081      <organization>Qualcomm Incorporated</organization>
2082    </author>
2083    <date year="2008" month="October"/>
2084  </front> 
2085  <seriesInfo name="RFC" value="5322"/>
2086</reference>
2087
2088<reference anchor="RFC6151">
2089  <front>
2090    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
2091    <author initials="S." surname="Turner" fullname="S. Turner"/>
2092    <author initials="L." surname="Chen" fullname="L. Chen"/>
2093    <date year="2011" month="March"/>
2094  </front>
2095  <seriesInfo name="RFC" value="6151"/>
2096</reference>
2097
2098<!--<reference anchor='BCP97'>
2099  <front>
2100    <title>Handling Normative References to Standards-Track Documents</title>
2101    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2102      <address>
2103        <email>klensin+ietf@jck.com</email>
2104      </address>
2105    </author>
2106    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2107      <organization>MIT</organization>
2108      <address>
2109        <email>hartmans-ietf@mit.edu</email>
2110      </address>
2111    </author>
2112    <date year='2007' month='June' />
2113  </front>
2114  <seriesInfo name='BCP' value='97' />
2115  <seriesInfo name='RFC' value='4897' />
2116</reference>-->
2117
2118<reference anchor="RFC6266">
2119  <front>
2120    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
2121    in the Hypertext Transfer Protocol (HTTP)</title>
2122    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
2123      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2124      <address>
2125        <email>julian.reschke@greenbytes.de</email>
2126      </address>
2127    </author>
2128    <date month="June" year="2011"/>
2129  </front>
2130  <seriesInfo name="RFC" value="6266"/>
2131</reference>
2132
2133</references>
2134
2135<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2136<t>
2137   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
2138   allow a message body to be transmitted in an open variety of
2139   representations and with extensible mechanisms. However, RFC 2045
2140   discusses mail, and HTTP has a few features that are different from
2141   those described in MIME. These differences were carefully chosen
2142   to optimize performance over binary connections, to allow greater
2143   freedom in the use of new media types, to make date comparisons
2144   easier, and to acknowledge the practice of some early HTTP servers
2145   and clients.
2146</t>
2147<t>
2148   This appendix describes specific areas where HTTP differs from MIME.
2149   Proxies and gateways to strict MIME environments SHOULD be
2150   aware of these differences and provide the appropriate conversions
2151   where necessary. Proxies and gateways from MIME environments to HTTP
2152   also need to be aware of the differences because some conversions
2153   might be required.
2154</t>
2155
2156<section title="MIME-Version" anchor="mime-version">
2157  <iref primary="true" item="MIME-Version header field"/>
2158  <iref primary="true" item="Header Fields" subitem="MIME-Version"/>
2159 
2160<t>
2161   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages MAY
2162   include a single MIME-Version header field to indicate what
2163   version of the MIME protocol was used to construct the message. Use
2164   of the MIME-Version header field indicates that the message is in
2165   full conformance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2166   Proxies/gateways are responsible for ensuring full conformance (where
2167   possible) when exporting HTTP messages to strict MIME environments.
2168</t>
2169<figure><iref primary="true" item="Grammar" subitem="MIME-Version"/><artwork type="abnf2616"><![CDATA[
2170  MIME-Version = 1*DIGIT "." 1*DIGIT
2171]]></artwork></figure>
2172<t>
2173   MIME version "1.0" is the default for use in HTTP/1.1. However,
2174   HTTP/1.1 message parsing and semantics are defined by this document
2175   and not the MIME specification.
2176</t>
2177</section>
2178
2179<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2180<t>
2181   MIME requires that an Internet mail body-part be converted to
2182   canonical form prior to being transferred, as described in Section 4 of <xref target="RFC2049"/>.
2183   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2184   allowed for subtypes of the "text" media type when transmitted over
2185   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2186   line breaks as CRLF and forbids the use of CR or LF outside of line
2187   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2188   line break within text content when a message is transmitted over
2189   HTTP.
2190</t>
2191<t>
2192   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2193   environment SHOULD translate all line breaks within the text media
2194   types described in <xref target="canonicalization.and.text.defaults"/>
2195   of this document to the RFC 2049
2196   canonical form of CRLF. Note, however, that this might be complicated
2197   by the presence of a Content-Encoding and by the fact that HTTP
2198   allows the use of some character encodings which do not use octets 13 and
2199   10 to represent CR and LF, respectively, as is the case for some multi-byte
2200   character encodings.
2201</t>
2202<t>
2203   Conversion will break any cryptographic
2204   checksums applied to the original content unless the original content
2205   is already in canonical form. Therefore, the canonical form is
2206   recommended for any content that uses such checksums in HTTP.
2207</t>
2208</section>
2209
2210
2211<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2212<t>
2213   HTTP/1.1 uses a restricted set of date formats (Section 8 of <xref target="Part2"/>) to
2214   simplify the process of date comparison. Proxies and gateways from
2215   other protocols SHOULD ensure that any Date header field present in a
2216   message conforms to one of the HTTP/1.1 formats and rewrite the date
2217   if necessary.
2218</t>
2219</section>
2220
2221<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2222<t>
2223   MIME does not include any concept equivalent to HTTP/1.1's
2224   Content-Encoding header field. Since this acts as a modifier on the
2225   media type, proxies and gateways from HTTP to MIME-compliant
2226   protocols MUST either change the value of the Content-Type header
2227   field or decode the representation before forwarding the message. (Some
2228   experimental applications of Content-Type for Internet mail have used
2229   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2230   a function equivalent to Content-Encoding. However, this parameter is
2231   not part of the MIME standards).
2232</t>
2233</section>
2234
2235<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2236  <iref item="Content-Transfer-Encoding header field"/>
2237  <iref item="Header Fields" subitem="Content-Transfer-Encoding"/>
2238<t>
2239   HTTP does not use the Content-Transfer-Encoding field of MIME.
2240   Proxies and gateways from MIME-compliant protocols to HTTP MUST
2241   remove any Content-Transfer-Encoding
2242   prior to delivering the response message to an HTTP client.
2243</t>
2244<t>
2245   Proxies and gateways from HTTP to MIME-compliant protocols are
2246   responsible for ensuring that the message is in the correct format
2247   and encoding for safe transport on that protocol, where "safe
2248   transport" is defined by the limitations of the protocol being used.
2249   Such a proxy or gateway SHOULD label the data with an appropriate
2250   Content-Transfer-Encoding if doing so will improve the likelihood of
2251   safe transport over the destination protocol.
2252</t>
2253</section>
2254
2255<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2256<t>
2257   HTTP/1.1 introduces the Transfer-Encoding header field (Section 3.3.1 of <xref target="Part1"/>).
2258   Proxies/gateways MUST remove any transfer-coding prior to
2259   forwarding a message via a MIME-compliant protocol.
2260</t>
2261</section>
2262
2263<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2264<t>
2265   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2266   need to be aware of MIME line length limitations. Since HTTP does not
2267   have this limitation, HTTP does not fold long lines. MHTML messages
2268   being transported by HTTP follow all conventions of MHTML, including
2269   line length limitations and folding, canonicalization, etc., since
2270   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2271   does not interpret the content or any MIME header lines that might be
2272   contained therein.
2273</t>
2274</section>
2275</section>
2276
2277<section title="Additional Features" anchor="additional.features">
2278<t>
2279   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2280   existing HTTP implementations, but not consistently and correctly
2281   across most HTTP/1.1 applications. Implementors are advised to be
2282   aware of these features, but cannot rely upon their presence in, or
2283   interoperability with, other HTTP/1.1 applications. Some of these
2284   describe proposed experimental features, and some describe features
2285   that experimental deployment found lacking that are now addressed in
2286   the base HTTP/1.1 specification.
2287</t>
2288<t>
2289   A number of other header fields, such as Content-Disposition and Title,
2290   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2291   and <xref target="RFC2076"/>).
2292</t>
2293</section>
2294
2295<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2296<t>
2297  Clarify contexts that charset is used in.
2298  (<xref target="character.sets"/>)
2299</t>
2300<t>
2301  Registration of Content Codings now requires IETF Review
2302  (<xref target="content.coding.registry"/>)
2303</t>
2304<t>
2305  Remove the default character encoding for text media types; the default
2306  now is whatever the media type definition says.
2307  (<xref target="canonicalization.and.text.defaults"/>)
2308</t>
2309<t>
2310  Change ABNF productions for header fields to only define the field value.
2311  (<xref target="header.field.definitions"/>)
2312</t>
2313<t>
2314  Remove definition of Content-MD5 header field because it was inconsistently
2315  implemented with respect to partial responses, and also because of known
2316  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
2317  (<xref target="header.field.definitions"/>)
2318</t>
2319<t>
2320  Remove ISO-8859-1 special-casing in Accept-Charset.
2321  (<xref target="header.accept-charset"/>)
2322</t>
2323<t>
2324  Remove base URI setting semantics for Content-Location due to poor
2325  implementation support, which was caused by too many broken servers emitting
2326  bogus Content-Location header fields, and also the potentially undesirable effect
2327  of potentially breaking relative links in content-negotiated resources.
2328  (<xref target="header.content-location"/>)
2329</t>
2330<t>
2331  Remove reference to non-existant identity transfer-coding value tokens.
2332  (<xref target="no.content-transfer-encoding"/>)
2333</t>
2334<t>
2335  Remove discussion of Content-Disposition header field, it is now defined
2336  by <xref target="RFC6266"/>.
2337  (<xref target="additional.features"/>)
2338</t>
2339</section>
2340
2341
2342<section title="Collected ABNF" anchor="collected.abnf">
2343<figure>
2344<artwork type="abnf" name="p3-payload.parsed-abnf"><![CDATA[
2345Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2346 OWS media-range [ accept-params ] ] ) ]
2347Accept-Charset = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2348 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2349 qvalue ] ] )
2350Accept-Encoding = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2351 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2352Accept-Language = *( "," OWS ) language-range [ OWS ";" OWS "q="
2353 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2354 ] )
2355
2356Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
2357 content-coding ] )
2358Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
2359 language-tag ] )
2360Content-Location = absolute-URI / partial-URI
2361Content-Type = media-type
2362
2363MIME-Version = 1*DIGIT "." 1*DIGIT
2364
2365OWS = <OWS, defined in [Part1], Section 3.2.1>
2366
2367absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
2368accept-ext = OWS ";" OWS token [ "=" word ]
2369accept-params = OWS ";" OWS "q=" qvalue *accept-ext
2370attribute = token
2371
2372charset = token
2373codings = content-coding / "identity" / "*"
2374content-coding = token
2375
2376language-range = <language-range, defined in [RFC4647], Section 2.1>
2377language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
2378
2379media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2380 ";" OWS parameter )
2381media-type = type "/" subtype *( OWS ";" OWS parameter )
2382
2383parameter = attribute "=" value
2384partial-URI = <partial-URI, defined in [Part1], Section 2.7>
2385
2386qvalue = <qvalue, defined in [Part1], Section 4.3.1>
2387
2388subtype = token
2389
2390token = <token, defined in [Part1], Section 3.2.4>
2391type = token
2392
2393value = word
2394
2395word = <word, defined in [Part1], Section 3.2.4>
2396]]></artwork>
2397</figure>
2398<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2399; Accept defined but not used
2400; Accept-Charset defined but not used
2401; Accept-Encoding defined but not used
2402; Accept-Language defined but not used
2403; Content-Encoding defined but not used
2404; Content-Language defined but not used
2405; Content-Location defined but not used
2406; Content-Type defined but not used
2407; MIME-Version defined but not used
2408]]></artwork></figure></section>
2409
2410
2411<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2412
2413<section title="Since RFC 2616">
2414<t>
2415  Extracted relevant partitions from <xref target="RFC2616"/>.
2416</t>
2417</section>
2418
2419<section title="Since draft-ietf-httpbis-p3-payload-00">
2420<t>
2421  Closed issues:
2422  <list style="symbols"> 
2423    <t>
2424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2425      "Media Type Registrations"
2426      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2427    </t>
2428    <t>
2429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2430      "Clarification regarding quoting of charset values"
2431      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2432    </t>
2433    <t>
2434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2435      "Remove 'identity' token references"
2436      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2437    </t>
2438    <t>
2439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2440      "Accept-Encoding BNF"
2441    </t>
2442    <t>
2443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2444      "Normative and Informative references"
2445    </t>
2446    <t>
2447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2448      "RFC1700 references"
2449    </t>
2450    <t>
2451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2452      "Updating to RFC4288"
2453    </t>
2454    <t>
2455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2456      "Informative references"
2457    </t>
2458    <t>
2459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2460      "ISO-8859-1 Reference"
2461    </t>
2462    <t>
2463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2464      "Encoding References Normative"
2465    </t>
2466    <t>
2467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2468      "Normative up-to-date references"
2469    </t>
2470  </list>
2471</t>
2472</section>
2473
2474<section title="Since draft-ietf-httpbis-p3-payload-01">
2475<t>
2476  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2477  <list style="symbols"> 
2478    <t>
2479      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2480    </t>
2481  </list>
2482</t>
2483</section>
2484
2485<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2486<t>
2487  Closed issues:
2488  <list style="symbols"> 
2489    <t>
2490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2491      "Quoting Charsets"
2492    </t>
2493    <t>
2494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2495      "Classification for Allow header"
2496    </t>
2497    <t>
2498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2499      "missing default for qvalue in description of Accept-Encoding"
2500    </t>
2501  </list>
2502</t>
2503<t>
2504  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2505  <list style="symbols"> 
2506    <t>
2507      Reference RFC 3984, and update header field registrations for headers defined
2508      in this document.
2509    </t>
2510  </list>
2511</t>
2512</section>
2513
2514<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2515<t>
2516  Closed issues:
2517  <list style="symbols"> 
2518    <t>
2519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2520      "Quoting Charsets"
2521    </t>
2522    <t>
2523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2524      "language tag matching (Accept-Language) vs RFC4647"
2525    </t>
2526    <t>
2527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2528      "RFC 1806 has been replaced by RFC2183"
2529    </t>
2530  </list>
2531</t>
2532<t>
2533  Other changes:
2534  <list style="symbols"> 
2535    <t>
2536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2537      "Encoding References Normative" — rephrase the annotation and reference
2538      BCP97.
2539    </t>
2540  </list>
2541</t>
2542 </section>
2543
2544<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2545<t>
2546  Closed issues:
2547  <list style="symbols"> 
2548    <t>
2549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2550      "RFC 2822 is updated by RFC 5322"
2551    </t>
2552  </list>
2553</t>
2554<t>
2555  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2556  <list style="symbols"> 
2557    <t>
2558      Use "/" instead of "|" for alternatives.
2559    </t>
2560    <t>
2561      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2562      whitespace ("OWS") and required whitespace ("RWS").
2563    </t>
2564    <t>
2565      Rewrite ABNFs to spell out whitespace rules, factor out
2566      header field value format definitions.
2567    </t>
2568  </list>
2569</t>
2570</section>
2571
2572<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2573<t>
2574  Closed issues:
2575  <list style="symbols"> 
2576    <t>
2577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2578      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2579    </t>
2580  </list>
2581</t>
2582<t>
2583  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2584  <list style="symbols"> 
2585    <t>
2586      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2587    </t>
2588  </list>
2589</t>
2590<t>
2591  Other changes:
2592  <list style="symbols"> 
2593    <t>
2594      Move definition of quality values into Part 1.
2595    </t>
2596  </list>
2597</t>
2598</section>
2599
2600<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2601<t>
2602  Closed issues:
2603  <list style="symbols"> 
2604    <t>
2605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2606      "Content-Location isn't special"
2607    </t>
2608    <t>
2609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2610      "Content Sniffing"
2611    </t>
2612  </list>
2613</t>
2614</section>
2615
2616<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2617<t>
2618  Closed issues:
2619  <list style="symbols"> 
2620    <t>
2621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2622      "Updated reference for language tags"
2623    </t>
2624    <t>
2625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2626      "Clarify rules for determining what entities a response carries"
2627    </t>
2628    <t>
2629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2630      "Content-Location base-setting problems"
2631    </t>
2632    <t>
2633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2634      "Content Sniffing"
2635    </t>
2636    <t>
2637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2638      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2639    </t>
2640    <t>
2641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2642      "move definitions of gzip/deflate/compress to part 1"
2643    </t>
2644  </list>
2645</t>
2646<t>
2647  Partly resolved issues:
2648  <list style="symbols"> 
2649    <t>
2650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2651      "update IANA requirements wrt Transfer-Coding values" (add the
2652      IANA Considerations subsection)
2653    </t>
2654    <t>
2655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2656      "update IANA requirements wrt Content-Coding values" (add the
2657      IANA Considerations subsection)
2658    </t>
2659  </list>
2660</t>
2661</section>
2662
2663<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2664<t>
2665  Closed issues:
2666  <list style="symbols"> 
2667    <t>
2668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2669      "Content Negotiation for media types"
2670    </t>
2671    <t>
2672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2673      "Accept-Language: which RFC4647 filtering?"
2674    </t>
2675  </list>
2676</t>
2677</section>
2678
2679<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2680<t>
2681  Closed issues:
2682  <list style="symbols"> 
2683    <t>
2684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2685      "MIME-Version not listed in P1, general header fields"
2686    </t>
2687    <t>
2688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2689      "IANA registry for content/transfer encodings"
2690    </t>
2691    <t>
2692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2693      "Content Sniffing"
2694    </t>
2695    <t>
2696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2697      "use of term "word" when talking about header structure"
2698    </t>
2699  </list>
2700</t>
2701<t>
2702  Partly resolved issues:
2703  <list style="symbols"> 
2704    <t>
2705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2706      "Term for the requested resource's URI"
2707    </t>
2708  </list>
2709</t>
2710</section>
2711
2712<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2713<t>
2714  Closed issues:
2715  <list style="symbols"> 
2716    <t>
2717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2718      "Clarify 'Requested Variant'"
2719    </t>
2720    <t>
2721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2722      "Content-Location isn't special"
2723    </t>
2724    <t>
2725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
2726      "Delimiting messages with multipart/byteranges"
2727    </t>
2728    <t>
2729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2730      "Clarify entity / representation / variant terminology"
2731    </t>
2732    <t>
2733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
2734      "confusing req. language for Content-Location"
2735    </t>
2736    <t>
2737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2738      "Content-Location on 304 responses"
2739    </t>
2740    <t>
2741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
2742      "'requested resource' in content-encoding definition"
2743    </t>
2744    <t>
2745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2746      "consider removing the 'changes from 2068' sections"
2747    </t>
2748  </list>
2749</t>
2750<t>
2751  Partly resolved issues:
2752  <list style="symbols"> 
2753    <t>
2754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2755      "Content-MD5 and partial responses"
2756    </t>
2757  </list>
2758</t>
2759</section>
2760
2761<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
2762<t>
2763  Closed issues:
2764  <list style="symbols"> 
2765    <t>
2766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
2767      "Factor out Content-Disposition"
2768    </t>
2769  </list>
2770</t>
2771</section>
2772
2773<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
2774<t>
2775  Closed issues:
2776  <list style="symbols"> 
2777    <t>
2778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
2779      "Header Classification"
2780    </t>
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2783      "untangle ABNFs for header fields"
2784    </t>
2785    <t>
2786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
2787      "potentially misleading MAY in media-type def"
2788    </t>
2789  </list>
2790</t>
2791</section>
2792
2793<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
2794<t>
2795  Closed issues:
2796  <list style="symbols"> 
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/20"/>:
2799      "Default charsets for text media types"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
2803      "Content-MD5 and partial responses"
2804    </t>
2805    <t>
2806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
2807      "untangle ABNFs for header fields"
2808    </t>
2809    <t>
2810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/281"/>:
2811      "confusing undefined parameter in media range example"
2812    </t>
2813  </list>
2814</t>
2815</section>
2816
2817<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
2818<t>
2819  None.
2820</t>
2821</section>
2822
2823<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
2824<t>
2825  Closed issues:
2826  <list style="symbols"> 
2827    <t>
2828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
2829      "Strength of requirements on Accept re: 406"
2830    </t>
2831  </list>
2832</t>
2833</section>
2834
2835<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
2836<t>
2837  Closed issues:
2838  <list style="symbols"> 
2839    <t>
2840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
2841      "Document HTTP's error-handling philosophy"
2842    </t>
2843  </list>
2844</t>
2845</section>
2846
2847<section title="Since draft-ietf-httpbis-p3-payload-17" anchor="changes.since.17">
2848<t>
2849  Closed issues:
2850  <list style="symbols"> 
2851    <t>
2852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
2853      "intended maturity level vs normative references"
2854    </t>
2855  </list>
2856</t>
2857</section>
2858
2859<section title="Since draft-ietf-httpbis-p3-payload-18" anchor="changes.since.18">
2860<t>
2861  Closed issues:
2862  <list style="symbols">
2863    <t>
2864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/330"/>:
2865      "is ETag a representation header field?"
2866    </t>
2867    <t>
2868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
2869      "make IANA policy definitions consistent"
2870    </t>
2871  </list>
2872</t>
2873</section>
2874
2875</section>
2876
2877</back>
2878</rfc>
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