source: draft-ietf-httpbis/latest/p3-payload.xml @ 823

Last change on this file since 823 was 823, checked in by julian.reschke@…, 9 years ago

Introduce term "effective request URI" and use it throughout; may require some more fine-tuning (see #196)

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File size: 132.9 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "May">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42]>
43<?rfc toc="yes" ?>
44<?rfc symrefs="yes" ?>
45<?rfc sortrefs="yes" ?>
46<?rfc compact="yes"?>
47<?rfc subcompact="no" ?>
48<?rfc linkmailto="no" ?>
49<?rfc editing="no" ?>
50<?rfc comments="yes"?>
51<?rfc inline="yes"?>
52<?rfc rfcedstyle="yes"?>
53<?rfc-ext allow-markup-in-artwork="yes" ?>
54<?rfc-ext include-references-in-index="yes" ?>
55<rfc obsoletes="2616" category="std" x:maturity-level="draft"
56     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
57     xmlns:x='http://purl.org/net/xml2rfc/ext'>
58<front>
59
60  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
61
62  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
63    <organization abbrev="Day Software">Day Software</organization>
64    <address>
65      <postal>
66        <street>23 Corporate Plaza DR, Suite 280</street>
67        <city>Newport Beach</city>
68        <region>CA</region>
69        <code>92660</code>
70        <country>USA</country>
71      </postal>
72      <phone>+1-949-706-5300</phone>
73      <facsimile>+1-949-706-5305</facsimile>
74      <email>fielding@gbiv.com</email>
75      <uri>http://roy.gbiv.com/</uri>
76    </address>
77  </author>
78
79  <author initials="J." surname="Gettys" fullname="Jim Gettys">
80    <organization>One Laptop per Child</organization>
81    <address>
82      <postal>
83        <street>21 Oak Knoll Road</street>
84        <city>Carlisle</city>
85        <region>MA</region>
86        <code>01741</code>
87        <country>USA</country>
88      </postal>
89      <email>jg@laptop.org</email>
90      <uri>http://www.laptop.org/</uri>
91    </address>
92  </author>
93 
94  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
95    <organization abbrev="HP">Hewlett-Packard Company</organization>
96    <address>
97      <postal>
98        <street>HP Labs, Large Scale Systems Group</street>
99        <street>1501 Page Mill Road, MS 1177</street>
100        <city>Palo Alto</city>
101        <region>CA</region>
102        <code>94304</code>
103        <country>USA</country>
104      </postal>
105      <email>JeffMogul@acm.org</email>
106    </address>
107  </author>
108
109  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
110    <organization abbrev="Microsoft">Microsoft Corporation</organization>
111    <address>
112      <postal>
113        <street>1 Microsoft Way</street>
114        <city>Redmond</city>
115        <region>WA</region>
116        <code>98052</code>
117        <country>USA</country>
118      </postal>
119      <email>henrikn@microsoft.com</email>
120    </address>
121  </author>
122
123  <author initials="L." surname="Masinter" fullname="Larry Masinter">
124    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
125    <address>
126      <postal>
127        <street>345 Park Ave</street>
128        <city>San Jose</city>
129        <region>CA</region>
130        <code>95110</code>
131        <country>USA</country>
132      </postal>
133      <email>LMM@acm.org</email>
134      <uri>http://larry.masinter.net/</uri>
135    </address>
136  </author>
137 
138  <author initials="P." surname="Leach" fullname="Paul J. Leach">
139    <organization abbrev="Microsoft">Microsoft Corporation</organization>
140    <address>
141      <postal>
142        <street>1 Microsoft Way</street>
143        <city>Redmond</city>
144        <region>WA</region>
145        <code>98052</code>
146      </postal>
147      <email>paulle@microsoft.com</email>
148    </address>
149  </author>
150   
151  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
152    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
153    <address>
154      <postal>
155        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
156        <street>The Stata Center, Building 32</street>
157        <street>32 Vassar Street</street>
158        <city>Cambridge</city>
159        <region>MA</region>
160        <code>02139</code>
161        <country>USA</country>
162      </postal>
163      <email>timbl@w3.org</email>
164      <uri>http://www.w3.org/People/Berners-Lee/</uri>
165    </address>
166  </author>
167
168  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
169    <organization abbrev="W3C">World Wide Web Consortium</organization>
170    <address>
171      <postal>
172        <street>W3C / ERCIM</street>
173        <street>2004, rte des Lucioles</street>
174        <city>Sophia-Antipolis</city>
175        <region>AM</region>
176        <code>06902</code>
177        <country>France</country>
178      </postal>
179      <email>ylafon@w3.org</email>
180      <uri>http://www.raubacapeu.net/people/yves/</uri>
181    </address>
182  </author>
183
184  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
185    <organization abbrev="greenbytes">greenbytes GmbH</organization>
186    <address>
187      <postal>
188        <street>Hafenweg 16</street>
189        <city>Muenster</city><region>NW</region><code>48155</code>
190        <country>Germany</country>
191      </postal>
192      <phone>+49 251 2807760</phone>
193      <facsimile>+49 251 2807761</facsimile>
194      <email>julian.reschke@greenbytes.de</email>
195      <uri>http://greenbytes.de/tech/webdav/</uri>
196    </address>
197  </author>
198
199  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
200  <workgroup>HTTPbis Working Group</workgroup>
201
202<abstract>
203<t>
204   The Hypertext Transfer Protocol (HTTP) is an application-level
205   protocol for distributed, collaborative, hypermedia information
206   systems. HTTP has been in use by the World Wide Web global information
207   initiative since 1990. This document is Part 3 of the seven-part specification
208   that defines the protocol referred to as "HTTP/1.1" and, taken together,
209   obsoletes RFC 2616.  Part 3 defines HTTP message content,
210   metadata, and content negotiation.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.09"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   This document defines HTTP/1.1 message payloads (a.k.a., content), the
231   associated metadata header fields that define how the payload is intended
232   to be interpreted by a recipient, the request header fields that
233   may influence content selection, and the various selection algorithms
234   that are collectively referred to as HTTP content negotiation.
235</t>
236<t>
237   This document is currently disorganized in order to minimize the changes
238   between drafts and enable reviewers to see the smaller errata changes.
239   The next draft will reorganize the sections to better reflect the content.
240   In particular, the sections on entities will be renamed payload and moved
241   to the first half of the document, while the sections on content negotiation
242   and associated request header fields will be moved to the second half.  The
243   current mess reflects how widely dispersed these topics and associated
244   requirements had become in <xref target="RFC2616"/>.
245</t>
246
247<section title="Terminology" anchor="terminology">
248<t>
249   This specification uses a number of terms to refer to the roles
250   played by participants in, and objects of, the HTTP communication.
251</t>
252<t>
253  <iref item="content negotiation"/>
254  <x:dfn>content negotiation</x:dfn>
255  <list>
256    <t>
257      The mechanism for selecting the appropriate representation when
258      servicing a request. The representation of entities in any response
259      can be negotiated (including error responses).
260    </t>
261  </list>
262</t>
263<t>
264  <iref item="entity"/>
265  <x:dfn>entity</x:dfn>
266  <list>
267    <t>
268      The information transferred as the payload of a request or
269      response. An entity consists of metadata in the form of
270      entity-header fields and content in the form of an entity-body.
271    </t>
272  </list>
273</t>
274<t>
275  <iref item="representation"/>
276  <x:dfn>representation</x:dfn>
277  <list>
278    <t>
279      An entity included with a response that is subject to content
280      negotiation. There may exist multiple
281      representations associated with a particular response status.
282    </t>
283  </list>
284</t>
285<t>
286  <iref item="variant"/>
287  <x:dfn>variant</x:dfn>
288  <list>
289    <t>
290      A resource may have one, or more than one, representation(s)
291      associated with it at any given instant. Each of these
292      representations is termed a "variant".  Use of the term "variant"
293      does not necessarily imply that the resource is subject to content
294      negotiation.
295    </t>
296  </list>
297</t>
298</section>
299
300<section title="Requirements" anchor="intro.requirements">
301<t>
302   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
303   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
304   document are to be interpreted as described in <xref target="RFC2119"/>.
305</t>
306<t>
307   An implementation is not compliant if it fails to satisfy one or more
308   of the &MUST; or &REQUIRED; level requirements for the protocols it
309   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
310   level and all the &SHOULD; level requirements for its protocols is said
311   to be "unconditionally compliant"; one that satisfies all the &MUST;
312   level requirements but not all the &SHOULD; level requirements for its
313   protocols is said to be "conditionally compliant."
314</t>
315</section>
316
317<section title="Syntax Notation" anchor="notation">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CR"/>
320  <x:anchor-alias value="DIGIT"/>
321  <x:anchor-alias value="LF"/>
322  <x:anchor-alias value="OCTET"/>
323  <x:anchor-alias value="VCHAR"/>
324  <x:anchor-alias value="WSP"/>
325<t>
326  This specification uses the ABNF syntax defined in &notation; (which
327  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
328  <xref target="collected.abnf"/> shows the collected ABNF, with the list
329  rule expanded.
330</t>
331<t>
332  The following core rules are included by
333  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335  DIGIT (decimal 0-9), DQUOTE (double quote),
336  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337  OCTET (any 8-bit sequence of data), SP (space),
338  VCHAR (any visible USASCII character),
339  and WSP (whitespace).
340</t>
341
342<section title="Core Rules" anchor="core.rules">
343  <x:anchor-alias value="quoted-string"/>
344  <x:anchor-alias value="token"/>
345  <x:anchor-alias value="word"/>
346  <x:anchor-alias value="OWS"/>
347<t>
348  The core rules below are defined in &basic-rules;:
349</t>
350<figure><artwork type="abnf2616">
351  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
352  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
353  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
354  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
355</artwork></figure>
356</section>
357
358<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
359  <x:anchor-alias value="absolute-URI"/>
360  <x:anchor-alias value="Allow"/>
361  <x:anchor-alias value="Content-Length"/>
362  <x:anchor-alias value="Content-Range"/>
363  <x:anchor-alias value="Expires"/>
364  <x:anchor-alias value="Last-Modified"/>
365  <x:anchor-alias value="header-field"/>
366  <x:anchor-alias value="partial-URI"/>
367  <x:anchor-alias value="qvalue"/>
368<t>
369  The ABNF rules below are defined in other parts:
370</t>
371<figure><!--Part1--><artwork type="abnf2616">
372  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
373  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
374  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
375  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
376  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
377</artwork></figure>
378<figure><!--Part4--><artwork type="abnf2616">
379  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
380</artwork></figure>
381<figure><!--Part5--><artwork type="abnf2616">
382  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
383</artwork></figure>
384<figure><!--Part6--><artwork type="abnf2616">
385  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
386</artwork></figure>
387</section>
388
389</section>
390
391</section>
392
393<section title="Protocol Parameters" anchor="protocol.parameters">
394
395<section title="Character Sets" anchor="character.sets">
396<t>
397   HTTP uses the same definition of the term "character set" as that
398   described for MIME:
399</t>
400<t>
401   The term "character set" is used in this document to refer to a
402   method used with one or more tables to convert a sequence of octets
403   into a sequence of characters. Note that unconditional conversion in
404   the other direction is not required, in that not all characters may
405   be available in a given character set and a character set may provide
406   more than one sequence of octets to represent a particular character.
407   This definition is intended to allow various kinds of character
408   encoding, from simple single-table mappings such as US-ASCII to
409   complex table switching methods such as those that use ISO-2022's
410   techniques. However, the definition associated with a MIME character
411   set name &MUST; fully specify the mapping to be performed from octets
412   to characters. In particular, use of external profiling information
413   to determine the exact mapping is not permitted.
414</t>
415<x:note>
416  <t>
417    <x:h>Note:</x:h> This use of the term "character set" is more commonly
418    referred to as a "character encoding." However, since HTTP and
419    MIME share the same registry, it is important that the terminology
420    also be shared.
421  </t>
422</x:note>
423<t anchor="rule.charset">
424  <x:anchor-alias value="charset"/>
425   HTTP character sets are identified by case-insensitive tokens. The
426   complete set of tokens is defined by the IANA Character Set registry
427   (<eref target="http://www.iana.org/assignments/character-sets"/>).
428</t>
429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
430  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
431</artwork></figure>
432<t>
433   Although HTTP allows an arbitrary token to be used as a charset
434   value, any token that has a predefined value within the IANA
435   Character Set registry &MUST; represent the character set defined
436   by that registry. Applications &SHOULD; limit their use of character
437   sets to those defined by the IANA registry.
438</t>
439<t>
440   HTTP uses charset in two contexts: within an Accept-Charset request
441   header (in which the charset value is an unquoted token) and as the
442   value of a parameter in a Content-Type header (within a request or
443   response), in which case the parameter value of the charset parameter
444   may be quoted.
445</t>
446<t>
447   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
448   <xref target="RFC2277"/>.
449</t>
450
451<section title="Missing Charset" anchor="missing.charset">
452<t>
453   Some HTTP/1.0 software has interpreted a Content-Type header without
454   charset parameter incorrectly to mean "recipient should guess."
455   Senders wishing to defeat this behavior &MAY; include a charset
456   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
457   it is known that it will not confuse the recipient.
458</t>
459<t>
460   Unfortunately, some older HTTP/1.0 clients did not deal properly with
461   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
462   charset label provided by the sender; and those user agents that have
463   a provision to "guess" a charset &MUST; use the charset from the
464   content-type field if they support that charset, rather than the
465   recipient's preference, when initially displaying a document. See
466   <xref target="canonicalization.and.text.defaults"/>.
467</t>
468</section>
469</section>
470
471<section title="Content Codings" anchor="content.codings">
472  <x:anchor-alias value="content-coding"/>
473<t>
474   Content coding values indicate an encoding transformation that has
475   been or can be applied to an entity. Content codings are primarily
476   used to allow a document to be compressed or otherwise usefully
477   transformed without losing the identity of its underlying media type
478   and without loss of information. Frequently, the entity is stored in
479   coded form, transmitted directly, and only decoded by the recipient.
480</t>
481<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
482  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
483</artwork></figure>
484<t>
485   All content-coding values are case-insensitive. HTTP/1.1 uses
486   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
487   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
488   describes the content-coding, what is more important is that it
489   indicates what decoding mechanism will be required to remove the
490   encoding.
491</t>
492<t>
493   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
494  <list>
495    <t>
496      See &compress-coding;.
497    </t>
498  </list>
499</t>
500<t>
501   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
502  <list>
503    <t>
504      See &deflate-coding;.
505    </t>
506  </list>
507</t>
508<t>
509   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
510  <list>
511    <t>
512      See &gzip-coding;.
513    </t>
514  </list>
515</t>
516<t>
517   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
518  <list><t>
519        The default (identity) encoding; the use of no transformation
520        whatsoever. This content-coding is used only in the Accept-Encoding
521        header, and &SHOULD-NOT;  be used in the Content-Encoding
522        header.
523  </t></list>
524</t>
525
526<section title="Content Coding Registry" anchor="content.coding.registry">
527<t>
528   The HTTP Content Coding Registry defines the name space for the content
529   coding names.
530</t>
531<t>
532   Registrations &MUST; include the following fields:
533   <list style="symbols">
534     <t>Name</t>
535     <t>Description</t>
536     <t>Pointer to specification text</t>
537   </list>
538</t>
539<t>
540   Names of content codings &MUST-NOT; overlap with names of transfer codings
541   (&transfer-codings;), unless the encoding transformation is identical (as it
542   is the case for the compression codings defined in
543   &compression-codings;).
544</t>
545<t>
546   Values to be added to this name space require expert review and a specification
547   (see "Expert Review" and "Specification Required" in
548   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
549   conform to the purpose of content coding defined in this section.
550</t>
551<t>
552   The registry itself is maintained at
553   <eref target="http://www.iana.org/assignments/http-parameters"/>.
554</t>
555</section>
556
557</section>
558
559<section title="Media Types" anchor="media.types">
560  <x:anchor-alias value="media-type"/>
561  <x:anchor-alias value="type"/>
562  <x:anchor-alias value="subtype"/>
563<t>
564   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
565   and Accept (<xref target="header.accept"/>) header fields in order to provide
566   open and extensible data typing and type negotiation.
567</t>
568<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
569  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
570  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
571  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
572</artwork></figure>
573<t anchor="rule.parameter">
574  <x:anchor-alias value="attribute"/>
575  <x:anchor-alias value="parameter"/>
576  <x:anchor-alias value="value"/>
577   Parameters &MAY; follow the type/subtype in the form of attribute/value
578   pairs.
579</t>
580<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
581  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
582  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
583  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
584</artwork></figure>
585<t>
586   The type, subtype, and parameter attribute names are case-insensitive.
587   Parameter values might or might not be case-sensitive, depending on the
588   semantics of the parameter name.  The presence or absence of a parameter might
589   be significant to the processing of a media-type, depending on its
590   definition within the media type registry.
591</t>
592<t>
593   A parameter value that matches the <x:ref>token</x:ref> production may be
594   transmitted as either a token or within a quoted-string. The quoted and
595   unquoted values are equivalent.
596</t>
597<t>
598   Note that some older HTTP applications do not recognize media type
599   parameters. When sending data to older HTTP applications,
600   implementations &SHOULD; only use media type parameters when they are
601   required by that type/subtype definition.
602</t>
603<t>
604   Media-type values are registered with the Internet Assigned Number
605   Authority (IANA). The media type registration process is
606   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
607   discouraged.
608</t>
609
610<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
611<t>
612   Internet media types are registered with a canonical form. An
613   entity-body transferred via HTTP messages &MUST; be represented in the
614   appropriate canonical form prior to its transmission except for
615   "text" types, as defined in the next paragraph.
616</t>
617<t>
618   When in canonical form, media subtypes of the "text" type use CRLF as
619   the text line break. HTTP relaxes this requirement and allows the
620   transport of text media with plain CR or LF alone representing a line
621   break when it is done consistently for an entire entity-body. HTTP
622   applications &MUST; accept CRLF, bare CR, and bare LF as being
623   representative of a line break in text media received via HTTP. In
624   addition, if the text is represented in a character set that does not
625   use octets 13 and 10 for CR and LF respectively, as is the case for
626   some multi-byte character sets, HTTP allows the use of whatever octet
627   sequences are defined by that character set to represent the
628   equivalent of CR and LF for line breaks. This flexibility regarding
629   line breaks applies only to text media in the entity-body; a bare CR
630   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
631   structures (such as header fields and multipart boundaries).
632</t>
633<t>
634   If an entity-body is encoded with a content-coding, the underlying
635   data &MUST; be in a form defined above prior to being encoded.
636</t>
637<t>
638   The "charset" parameter is used with some media types to define the
639   character set (<xref target="character.sets"/>) of the data. When no explicit charset
640   parameter is provided by the sender, media subtypes of the "text"
641   type are defined to have a default charset value of "ISO-8859-1" when
642   received via HTTP. Data in character sets other than "ISO-8859-1" or
643   its subsets &MUST; be labeled with an appropriate charset value. See
644   <xref target="missing.charset"/> for compatibility problems.
645</t>
646</section>
647
648<section title="Multipart Types" anchor="multipart.types">
649<t>
650   MIME provides for a number of "multipart" types -- encapsulations of
651   one or more entities within a single message-body. All multipart
652   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
653   and &MUST; include a boundary parameter as part of the media type
654   value. The message body is itself a protocol element and &MUST;
655   therefore use only CRLF to represent line breaks between body-parts.
656   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
657   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
658   original multipart contains an epilogue). These restrictions exist in
659   order to preserve the self-delimiting nature of a multipart message-body,
660   wherein the "end" of the message-body is indicated by the
661   ending multipart boundary.
662</t>
663<t>
664   In general, HTTP treats a multipart message-body no differently than
665   any other media type: strictly as payload. The one exception is the
666   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
667   (Partial Content) response.
668   <!-- jre: re-insert removed text pointing to caching? -->
669   In all
670   other cases, an HTTP user agent &SHOULD; follow the same or similar
671   behavior as a MIME user agent would upon receipt of a multipart type.
672   The MIME header fields within each body-part of a multipart message-body
673   do not have any significance to HTTP beyond that defined by
674   their MIME semantics.
675</t>
676<t>
677   In general, an HTTP user agent &SHOULD; follow the same or similar
678   behavior as a MIME user agent would upon receipt of a multipart type.
679   If an application receives an unrecognized multipart subtype, the
680   application &MUST; treat it as being equivalent to "multipart/mixed".
681</t>
682<x:note>
683  <t>
684    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
685    for carrying form data suitable for processing via the POST
686    request method, as described in <xref target="RFC2388"/>.
687  </t>
688</x:note>
689</section>
690</section>
691
692<section title="Language Tags" anchor="language.tags">
693  <x:anchor-alias value="language-tag"/>
694<t>
695   A language tag, as defined in <xref target="RFC5646"/>, identifies a
696   natural language spoken, written, or otherwise conveyed by human beings for
697   communication of information to other human beings. Computer languages are
698   explicitly excluded. HTTP uses language tags within the Accept-Language and
699   Content-Language fields.
700</t>
701<t>
702   In summary, a language tag is composed of one or more parts: A primary
703   language subtag followed by a possibly empty series of subtags:
704</t>
705<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
706  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
707</artwork></figure>
708<t>
709   White space is not allowed within the tag and all tags are case-insensitive.
710   The name space of language subtags is administered by the IANA (see
711   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
712</t>
713<figure>
714  <preamble>Example tags include:</preamble>
715<artwork type="example">
716  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
717</artwork>
718</figure>
719<t>
720   See <xref target="RFC5646"/> for further information.
721</t>
722</section>
723</section>
724
725<section title="Entity" anchor="entity">
726<t>
727   Request and Response messages &MAY; transfer an entity if not otherwise
728   restricted by the request method or response status code. An entity
729   consists of entity-header fields and an entity-body, although some
730   responses will only include the entity-headers.
731</t>
732<t>
733   In this section, both sender and recipient refer to either the client
734   or the server, depending on who sends and who receives the entity.
735</t>
736
737<section title="Entity Header Fields" anchor="entity.header.fields">
738  <x:anchor-alias value="entity-header"/>
739  <x:anchor-alias value="extension-header"/>
740<t>
741   Entity-header fields define metainformation about the entity-body or,
742   if no body is present, about the resource identified by the request.
743</t>
744<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
745  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
746                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
747                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
748                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
749                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
750                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
751                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
752                 / <x:ref>Expires</x:ref>                  ; &header-expires;
753                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
754                 / <x:ref>extension-header</x:ref>
755 
756  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
757</artwork></figure>
758<t>
759   The extension-header mechanism allows additional entity-header fields
760   to be defined without changing the protocol, but these fields cannot
761   be assumed to be recognizable by the recipient. Unrecognized header
762   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
763   transparent proxies.
764</t>
765</section>
766
767<section title="Entity Body" anchor="entity.body">
768  <x:anchor-alias value="entity-body"/>
769<t>
770   The entity-body (if any) sent with an HTTP request or response is in
771   a format and encoding defined by the entity-header fields.
772</t>
773<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
774  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
775</artwork></figure>
776<t>
777   An entity-body is only present in a message when a message-body is
778   present, as described in &message-body;. The entity-body is obtained
779   from the message-body by decoding any Transfer-Encoding that might
780   have been applied to ensure safe and proper transfer of the message.
781</t>
782
783<section title="Type" anchor="type">
784<t>
785   When an entity-body is included with a message, the data type of that
786   body is determined via the header fields Content-Type and Content-Encoding.
787   These define a two-layer, ordered encoding model:
788</t>
789<figure><artwork type="example">
790  entity-body := Content-Encoding( Content-Type( data ) )
791</artwork></figure>
792<t>
793   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
794   message containing an entity-body &SHOULD; include a Content-Type header
795   field defining the media type of that body, unless that information is
796   unknown.  If the Content-Type header field is not present, it indicates that
797   the sender does not know the media type of the data; recipients &MAY;
798   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
799   or examine the content to determine its type.
800</t>
801<t>
802   Content-Encoding may be used to indicate any additional content
803   codings applied to the data, usually for the purpose of data
804   compression, that are a property of the requested resource.  There is
805   no default encoding.
806</t>
807</section>
808   
809<section title="Entity Length" anchor="entity.length">
810<t>
811   The entity-length of a message is the length of the message-body
812   before any transfer-codings have been applied. &message-length; defines
813   how the transfer-length of a message-body is determined.
814</t>
815</section>
816</section>
817</section>
818
819<section title="Content Negotiation" anchor="content.negotiation">
820<t>
821   HTTP responses include a representation which contains information for
822   interpretation, whether by a human user or for further processing.
823   Often, the server has different ways of representing the
824   same information; for example, in different formats, languages,
825   or using different character encodings.
826</t>
827<t>
828   HTTP clients and their users might have different or variable
829   capabilities, characteristics or preferences which would influence
830   which representation, among those available from the server,
831   would be best for the server to deliver. For this reason, HTTP
832   provides mechanisms for "content negotiation" -- a process of
833   allowing selection of a representation of a given resource,
834   when more than one is available.
835</t>
836<t>
837   This specification defines two patterns of content negotiation;
838   "server-driven", where the server selects the representation based
839   upon the client's stated preferences, and "agent-driven" negotiation,
840   where the server provides a list of representations for the client to
841   choose from, based upon their metadata. In addition,  there are
842   other patterns: some applications use an "active content" pattern,
843   where the server returns active content which runs on the client
844   and, based on client available parameters, selects additional
845   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
846   has also been proposed.
847</t>
848<t>
849   These patterns are all widely used, and have trade-offs in applicability
850   and practicality. In particular, when the number of preferences or
851   capabilities to be expressed by a client are large (such as when many
852   different formats are supported by a user-agent), server-driven
853   negotiation becomes unwieldy, and may not be appropriate. Conversely,
854   when the number of representations to choose from is very large,
855   agent-driven negotiation may not be appropriate.
856</t>
857<t>
858   Note that in all cases, the supplier of representations has the
859   responsibility for determining which representations might be
860   considered to be the "same information".
861</t>
862
863<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
864<t>
865   If the selection of the best representation for a response is made by
866   an algorithm located at the server, it is called server-driven
867   negotiation. Selection is based on the available representations of
868   the response (the dimensions over which it can vary; e.g., language,
869   content-coding, etc.) and the contents of particular header fields in
870   the request message or on other information pertaining to the request
871   (such as the network address of the client).
872</t>
873<t>
874   Server-driven negotiation is advantageous when the algorithm for
875   selecting from among the available representations is difficult to
876   describe to the user agent, or when the server desires to send its
877   "best guess" to the client along with the first response (hoping to
878   avoid the round-trip delay of a subsequent request if the "best
879   guess" is good enough for the user). In order to improve the server's
880   guess, the user agent &MAY; include request header fields (Accept,
881   Accept-Language, Accept-Encoding, etc.) which describe its
882   preferences for such a response.
883</t>
884<t>
885   Server-driven negotiation has disadvantages:
886  <list style="numbers">
887    <t>
888         It is impossible for the server to accurately determine what
889         might be "best" for any given user, since that would require
890         complete knowledge of both the capabilities of the user agent
891         and the intended use for the response (e.g., does the user want
892         to view it on screen or print it on paper?).
893    </t>
894    <t>
895         Having the user agent describe its capabilities in every
896         request can be both very inefficient (given that only a small
897         percentage of responses have multiple representations) and a
898         potential violation of the user's privacy.
899    </t>
900    <t>
901         It complicates the implementation of an origin server and the
902         algorithms for generating responses to a request.
903    </t>
904    <t>
905         It may limit a public cache's ability to use the same response
906         for multiple user's requests.
907    </t>
908  </list>
909</t>
910<t>
911   HTTP/1.1 includes the following request-header fields for enabling
912   server-driven negotiation through description of user agent
913   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
914   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
915   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
916   However, an origin server is not limited to these dimensions and &MAY; vary
917   the response based on any aspect of the request, including information
918   outside the request-header fields or within extension header fields
919   not defined by this specification.
920</t>
921<x:note>
922  <t>
923    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
924    because new clients might not be recognized.
925  </t>
926</x:note>
927<t>
928   The Vary header field (&header-vary;) can be used to express the parameters the
929   server uses to select a representation that is subject to server-driven
930   negotiation.
931</t>
932</section>
933
934<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
935<t>
936   With agent-driven negotiation, selection of the best representation
937   for a response is performed by the user agent after receiving an
938   initial response from the origin server. Selection is based on a list
939   of the available representations of the response included within the
940   header fields or entity-body of the initial response, with each
941   representation identified by its own URI. Selection from among the
942   representations may be performed automatically (if the user agent is
943   capable of doing so) or manually by the user selecting from a
944   generated (possibly hypertext) menu.
945</t>
946<t>
947   Agent-driven negotiation is advantageous when the response would vary
948   over commonly-used dimensions (such as type, language, or encoding),
949   when the origin server is unable to determine a user agent's
950   capabilities from examining the request, and generally when public
951   caches are used to distribute server load and reduce network usage.
952</t>
953<t>
954   Agent-driven negotiation suffers from the disadvantage of needing a
955   second request to obtain the best alternate representation. This
956   second request is only efficient when caching is used. In addition,
957   this specification does not define any mechanism for supporting
958   automatic selection, though it also does not prevent any such
959   mechanism from being developed as an extension and used within
960   HTTP/1.1.
961</t>
962<t>
963   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
964   status codes for enabling agent-driven negotiation when the server is
965   unwilling or unable to provide a varying response using server-driven
966   negotiation.
967</t>
968</section>
969</section>
970
971<section title="Header Field Definitions" anchor="header.fields">
972<t>
973   This section defines the syntax and semantics of HTTP/1.1 header fields
974   related to the payload of messages.
975</t>
976<t>
977   For entity-header fields, both sender and recipient refer to either the
978   client or the server, depending on who sends and who receives the entity.
979</t>
980
981<section title="Accept" anchor="header.accept">
982  <iref primary="true" item="Accept header" x:for-anchor=""/>
983  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
984  <x:anchor-alias value="Accept"/>
985  <x:anchor-alias value="Accept-v"/>
986  <x:anchor-alias value="accept-ext"/>
987  <x:anchor-alias value="accept-params"/>
988  <x:anchor-alias value="media-range"/>
989<t>
990   The "Accept" request-header field can be used by user agents to specify
991   response media types that are acceptable. Accept headers can be used to
992   indicate that the request is specifically limited to a small set of desired
993   types, as in the case of a request for an in-line image.
994</t>
995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
996  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
997  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
998 
999  <x:ref>media-range</x:ref>    = ( "*/*"
1000                   / ( <x:ref>type</x:ref> "/" "*" )
1001                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
1002                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
1003  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
1004  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
1005                   [ "=" <x:ref>word</x:ref> ]
1006</artwork></figure>
1007<t>
1008   The asterisk "*" character is used to group media types into ranges,
1009   with "*/*" indicating all media types and "type/*" indicating all
1010   subtypes of that type. The media-range &MAY; include media type
1011   parameters that are applicable to that range.
1012</t>
1013<t>
1014   Each media-range &MAY; be followed by one or more accept-params,
1015   beginning with the "q" parameter for indicating a relative quality
1016   factor. The first "q" parameter (if any) separates the media-range
1017   parameter(s) from the accept-params. Quality factors allow the user
1018   or user agent to indicate the relative degree of preference for that
1019   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1020   default value is q=1.
1021</t>
1022<x:note>
1023  <t>
1024    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1025    parameters from Accept extension parameters is due to historical
1026    practice. Although this prevents any media type parameter named
1027    "q" from being used with a media range, such an event is believed
1028    to be unlikely given the lack of any "q" parameters in the IANA
1029    media type registry and the rare usage of any media type
1030    parameters in Accept. Future media types are discouraged from
1031    registering any parameter named "q".
1032  </t>
1033</x:note>
1034<t>
1035   The example
1036</t>
1037<figure><artwork type="example">
1038  Accept: audio/*; q=0.2, audio/basic
1039</artwork></figure>
1040<t>
1041   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1042   type if it is the best available after an 80% mark-down in quality."
1043</t>
1044<t>
1045   If no Accept header field is present, then it is assumed that the
1046   client accepts all media types. If an Accept header field is present,
1047   and if the server cannot send a response which is acceptable
1048   according to the combined Accept field value, then the server &SHOULD;
1049   send a 406 (Not Acceptable) response.
1050</t>
1051<t>
1052   A more elaborate example is
1053</t>
1054<figure><artwork type="example">
1055  Accept: text/plain; q=0.5, text/html,
1056          text/x-dvi; q=0.8, text/x-c
1057</artwork></figure>
1058<t>
1059   Verbally, this would be interpreted as "text/html and text/x-c are
1060   the preferred media types, but if they do not exist, then send the
1061   text/x-dvi entity, and if that does not exist, send the text/plain
1062   entity."
1063</t>
1064<t>
1065   Media ranges can be overridden by more specific media ranges or
1066   specific media types. If more than one media range applies to a given
1067   type, the most specific reference has precedence. For example,
1068</t>
1069<figure><artwork type="example">
1070  Accept: text/*, text/html, text/html;level=1, */*
1071</artwork></figure>
1072<t>
1073   have the following precedence:
1074   <list style="numbers">
1075    <t>text/html;level=1</t>
1076    <t>text/html</t>
1077    <t>text/*</t>
1078    <t>*/*</t>
1079   </list>
1080</t>
1081<t>
1082   The media type quality factor associated with a given type is
1083   determined by finding the media range with the highest precedence
1084   which matches that type. For example,
1085</t>
1086<figure><artwork type="example">
1087  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1088          text/html;level=2;q=0.4, */*;q=0.5
1089</artwork></figure>
1090<t>
1091   would cause the following values to be associated:
1092</t>
1093<texttable align="left">
1094  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1095  <c>text/html;level=1</c>    <c>1</c>
1096  <c>text/html</c>            <c>0.7</c>
1097  <c>text/plain</c>           <c>0.3</c>
1098  <c>image/jpeg</c>           <c>0.5</c>
1099  <c>text/html;level=2</c>    <c>0.4</c>
1100  <c>text/html;level=3</c>    <c>0.7</c>
1101</texttable>
1102<t>
1103      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1104      values for certain media ranges. However, unless the user agent is
1105      a closed system which cannot interact with other rendering agents,
1106      this default set ought to be configurable by the user.
1107</t>
1108</section>
1109
1110<section title="Accept-Charset" anchor="header.accept-charset">
1111  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1112  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1113  <x:anchor-alias value="Accept-Charset"/>
1114  <x:anchor-alias value="Accept-Charset-v"/>
1115<t>
1116   The "Accept-Charset" request-header field can be used by user agents to
1117   indicate what response character sets are acceptable. This field allows
1118   clients capable of understanding more comprehensive or special-purpose
1119   character sets to signal that capability to a server which is capable of
1120   representing documents in those character sets.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1123  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1124          <x:ref>Accept-Charset-v</x:ref>
1125  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1126                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1127</artwork></figure>
1128<t>
1129   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1130   be given an associated quality value which represents the user's
1131   preference for that charset. The default value is q=1. An example is
1132</t>
1133<figure><artwork type="example">
1134  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1135</artwork></figure>
1136<t>
1137   The special value "*", if present in the Accept-Charset field,
1138   matches every character set (including ISO-8859-1) which is not
1139   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1140   in an Accept-Charset field, then all character sets not explicitly
1141   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1142   a quality value of 1 if not explicitly mentioned.
1143</t>
1144<t>
1145   If no Accept-Charset header is present, the default is that any
1146   character set is acceptable. If an Accept-Charset header is present,
1147   and if the server cannot send a response which is acceptable
1148   according to the Accept-Charset header, then the server &SHOULD; send
1149   an error response with the 406 (Not Acceptable) status code, though
1150   the sending of an unacceptable response is also allowed.
1151</t>
1152</section>
1153
1154<section title="Accept-Encoding" anchor="header.accept-encoding">
1155  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1156  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1157  <x:anchor-alias value="Accept-Encoding"/>
1158  <x:anchor-alias value="Accept-Encoding-v"/>
1159  <x:anchor-alias value="codings"/>
1160<t>
1161   The "Accept-Encoding" request-header field can be used by user agents to
1162   indicate what response content-codings (<xref target="content.codings"/>)
1163   are acceptable in the response.
1164</t>
1165<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1166  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1167                     <x:ref>Accept-Encoding-v</x:ref>
1168  <x:ref>Accept-Encoding-v</x:ref>  =
1169                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1170  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1171</artwork></figure>
1172<t>
1173   Each codings value &MAY; be given an associated quality value which
1174   represents the preference for that encoding. The default value is q=1.
1175</t>
1176<t>
1177   Examples of its use are:
1178</t>
1179<figure><artwork type="example">
1180  Accept-Encoding: compress, gzip
1181  Accept-Encoding:
1182  Accept-Encoding: *
1183  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1184  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1185</artwork></figure>
1186<t>
1187   A server tests whether a content-coding is acceptable, according to
1188   an Accept-Encoding field, using these rules:
1189  <list style="numbers">
1190      <t>If the content-coding is one of the content-codings listed in
1191         the Accept-Encoding field, then it is acceptable, unless it is
1192         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1193         qvalue of 0 means "not acceptable.")</t>
1194
1195      <t>The special "*" symbol in an Accept-Encoding field matches any
1196         available content-coding not explicitly listed in the header
1197         field.</t>
1198
1199      <t>If multiple content-codings are acceptable, then the acceptable
1200         content-coding with the highest non-zero qvalue is preferred.</t>
1201
1202      <t>The "identity" content-coding is always acceptable, unless
1203         specifically refused because the Accept-Encoding field includes
1204         "identity;q=0", or because the field includes "*;q=0" and does
1205         not explicitly include the "identity" content-coding. If the
1206         Accept-Encoding field-value is empty, then only the "identity"
1207         encoding is acceptable.</t>
1208  </list>
1209</t>
1210<t>
1211   If an Accept-Encoding field is present in a request, and if the
1212   server cannot send a response which is acceptable according to the
1213   Accept-Encoding header, then the server &SHOULD; send an error response
1214   with the 406 (Not Acceptable) status code.
1215</t>
1216<t>
1217   If no Accept-Encoding field is present in a request, the server &MAY;
1218   assume that the client will accept any content coding. In this case,
1219   if "identity" is one of the available content-codings, then the
1220   server &SHOULD; use the "identity" content-coding, unless it has
1221   additional information that a different content-coding is meaningful
1222   to the client.
1223</t>
1224<x:note>
1225  <t>
1226    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1227    and if the "identity" content-coding is unavailable, then
1228    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1229    "gzip" and "compress") are preferred; some older clients
1230    improperly display messages sent with other content-codings.  The
1231    server might also make this decision based on information about
1232    the particular user-agent or client.
1233  </t>
1234</x:note>
1235<x:note>
1236  <t>
1237    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1238    associated with content-codings. This means that qvalues will not
1239    work and are not permitted with x-gzip or x-compress.
1240  </t>
1241</x:note>
1242</section>
1243
1244<section title="Accept-Language" anchor="header.accept-language">
1245  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1246  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1247  <x:anchor-alias value="Accept-Language"/>
1248  <x:anchor-alias value="Accept-Language-v"/>
1249  <x:anchor-alias value="language-range"/>
1250<t>
1251   The "Accept-Language" request-header field can be used by user agents to
1252   indicate the set of natural languages that are preferred in the response.
1253   Language tags are defined in <xref target="language.tags"/>.
1254</t>
1255<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1256  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1257                    <x:ref>Accept-Language-v</x:ref>
1258  <x:ref>Accept-Language-v</x:ref> =
1259                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1260  <x:ref>language-range</x:ref>    =
1261            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1262</artwork></figure>
1263<t>
1264   Each language-range can be given an associated quality value which
1265   represents an estimate of the user's preference for the languages
1266   specified by that range. The quality value defaults to "q=1". For
1267   example,
1268</t>
1269<figure><artwork type="example">
1270  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1271</artwork></figure>
1272<t>
1273   would mean: "I prefer Danish, but will accept British English and
1274   other types of English."
1275   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1276</t>
1277<t>
1278   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1279   several matching schemes. Implementations can offer the most appropriate
1280   matching scheme for their requirements.
1281</t>
1282<x:note>
1283  <t>
1284    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1285    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1286    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1287  </t>
1288</x:note>
1289<t>
1290   It might be contrary to the privacy expectations of the user to send
1291   an Accept-Language header with the complete linguistic preferences of
1292   the user in every request. For a discussion of this issue, see
1293   <xref target="privacy.issues.connected.to.accept.headers"/>.
1294</t>
1295<t>
1296   As intelligibility is highly dependent on the individual user, it is
1297   recommended that client applications make the choice of linguistic
1298   preference available to the user. If the choice is not made
1299   available, then the Accept-Language header field &MUST-NOT; be given in
1300   the request.
1301</t>
1302<x:note>
1303  <t>
1304    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1305    the user, we remind implementors of  the fact that users are not
1306    familiar with the details of language matching as described above,
1307    and should provide appropriate guidance. As an example, users
1308    might assume that on selecting "en-gb", they will be served any
1309    kind of English document if British English is not available. A
1310    user agent might suggest in such a case to add "en" to get the
1311    best matching behavior.
1312  </t>
1313</x:note>
1314</section>
1315
1316<section title="Content-Encoding" anchor="header.content-encoding">
1317  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1318  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1319  <x:anchor-alias value="Content-Encoding"/>
1320  <x:anchor-alias value="Content-Encoding-v"/>
1321<t>
1322   The "Content-Encoding" entity-header field indicates what content-codings
1323   have been applied to the entity-body, and thus what decoding mechanisms
1324   must be applied in order to obtain the media-type referenced by the
1325   Content-Type header field. Content-Encoding is primarily used to allow a
1326   document to be compressed without losing the identity of its underlying
1327   media type.
1328</t>
1329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1330  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1331  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1332</artwork></figure>
1333<t>
1334   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1335</t>
1336<figure><artwork type="example">
1337  Content-Encoding: gzip
1338</artwork></figure>
1339<t>
1340   The content-coding is a characteristic of the entity identified by
1341   the Effective Request URI (&effective-request-uri;). Typically, the entity-body is stored with this
1342   encoding and is only decoded before rendering or analogous usage.
1343   However, a non-transparent proxy &MAY; modify the content-coding if the
1344   new coding is known to be acceptable to the recipient, unless the
1345   "no-transform" cache-control directive is present in the message.
1346</t>
1347<t>
1348   If the content-coding of an entity is not "identity", then the
1349   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1350   that lists the non-identity content-coding(s) used.
1351</t>
1352<t>
1353   If the content-coding of an entity in a request message is not
1354   acceptable to the origin server, the server &SHOULD; respond with a
1355   status code of 415 (Unsupported Media Type).
1356</t>
1357<t>
1358   If multiple encodings have been applied to an entity, the content
1359   codings &MUST; be listed in the order in which they were applied.
1360   Additional information about the encoding parameters &MAY; be provided
1361   by other entity-header fields not defined by this specification.
1362</t>
1363</section>
1364
1365<section title="Content-Language" anchor="header.content-language">
1366  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1367  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1368  <x:anchor-alias value="Content-Language"/>
1369  <x:anchor-alias value="Content-Language-v"/>
1370<t>
1371   The "Content-Language" entity-header field describes the natural
1372   language(s) of the intended audience for the entity. Note that this might
1373   not be equivalent to all the languages used within the entity-body.
1374</t>
1375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1376  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1377  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1378</artwork></figure>
1379<t>
1380   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1381   Content-Language is to allow a user to identify and differentiate
1382   entities according to the user's own preferred language. Thus, if the
1383   body content is intended only for a Danish-literate audience, the
1384   appropriate field is
1385</t>
1386<figure><artwork type="example">
1387  Content-Language: da
1388</artwork></figure>
1389<t>
1390   If no Content-Language is specified, the default is that the content
1391   is intended for all language audiences. This might mean that the
1392   sender does not consider it to be specific to any natural language,
1393   or that the sender does not know for which language it is intended.
1394</t>
1395<t>
1396   Multiple languages &MAY; be listed for content that is intended for
1397   multiple audiences. For example, a rendition of the "Treaty of
1398   Waitangi," presented simultaneously in the original Maori and English
1399   versions, would call for
1400</t>
1401<figure><artwork type="example">
1402  Content-Language: mi, en
1403</artwork></figure>
1404<t>
1405   However, just because multiple languages are present within an entity
1406   does not mean that it is intended for multiple linguistic audiences.
1407   An example would be a beginner's language primer, such as "A First
1408   Lesson in Latin," which is clearly intended to be used by an
1409   English-literate audience. In this case, the Content-Language would
1410   properly only include "en".
1411</t>
1412<t>
1413   Content-Language &MAY; be applied to any media type -- it is not
1414   limited to textual documents.
1415</t>
1416</section>
1417
1418<section title="Content-Location" anchor="header.content-location">
1419  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1420  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1421  <x:anchor-alias value="Content-Location"/>
1422  <x:anchor-alias value="Content-Location-v"/>
1423<t>
1424   The "Content-Location" entity-header field is used to supply a URI for the
1425   entity in the message when it is accessible from a location separate from
1426   the requested resource's URI.
1427</t>
1428<t>
1429   A server &SHOULD; provide a Content-Location for the variant corresponding
1430   to the response entity, especially in the case where a resource has multiple
1431   entities associated with it, and those entities actually have separate
1432   locations by which they might be individually accessed, the server &SHOULD;
1433   provide a Content-Location for the particular variant which is returned.
1434</t>
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1436  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1437                    <x:ref>Content-Location-v</x:ref>
1438  <x:ref>Content-Location-v</x:ref> =
1439                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1440</artwork></figure>
1441<t>
1442   The Content-Location value is not a replacement for the Effective
1443   Request URI (&effective-request-uri;); it is only a statement of the location of the resource
1444   corresponding to this particular entity at the time of the request.
1445   Future requests &MAY; may be addressed to the Content-Location URI
1446   if the desire is to identify the source of that particular
1447   entity.
1448</t>
1449<t>
1450   &response-representation; describes how clients may process the Content-Location header field.
1451</t>
1452<t>
1453   A cache cannot assume that an entity with a Content-Location
1454   different from the URI used to retrieve it can be used to respond to
1455   later requests on that Content-Location URI. However, the Content-Location
1456   can be used to differentiate between multiple entities
1457   retrieved from a single requested resource, as described in &caching-neg-resp;.
1458</t>
1459<t>
1460   If the Content-Location is a relative URI, the relative URI is
1461   interpreted relative to the Effective Request URI.
1462</t>
1463<t>
1464   The meaning of the Content-Location header in requests is
1465   undefined; servers are free to ignore it in those cases.
1466</t>
1467</section>
1468
1469<section title="Content-MD5" anchor="header.content-md5">
1470  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1471  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1472  <x:anchor-alias value="Content-MD5"/>
1473  <x:anchor-alias value="Content-MD5-v"/>
1474<t>
1475   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
1476   an MD5 digest of the entity-body that provides an end-to-end message
1477   integrity check (MIC) of the entity-body. Note that a MIC is good for
1478   detecting accidental modification of the entity-body in transit, but is not
1479   proof against malicious attacks.
1480</t>
1481<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1482  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1483  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1484</artwork></figure>
1485<t>
1486   The Content-MD5 header field &MAY; be generated by an origin server or
1487   client to function as an integrity check of the entity-body. Only
1488   origin servers or clients &MAY; generate the Content-MD5 header field;
1489   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1490   value as an end-to-end integrity check. Any recipient of the entity-body,
1491   including gateways and proxies, &MAY; check that the digest value
1492   in this header field matches that of the entity-body as received.
1493</t>
1494<t>
1495   The MD5 digest is computed based on the content of the entity-body,
1496   including any content-coding that has been applied, but not including
1497   any transfer-encoding applied to the message-body. If the message is
1498   received with a transfer-encoding, that encoding &MUST; be removed
1499   prior to checking the Content-MD5 value against the received entity.
1500</t>
1501<t>
1502   This has the result that the digest is computed on the octets of the
1503   entity-body exactly as, and in the order that, they would be sent if
1504   no transfer-encoding were being applied.
1505</t>
1506<t>
1507   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1508   composite media-types (e.g., multipart/* and message/rfc822), but
1509   this does not change how the digest is computed as defined in the
1510   preceding paragraph.
1511</t>
1512<t>
1513   There are several consequences of this. The entity-body for composite
1514   types &MAY; contain many body-parts, each with its own MIME and HTTP
1515   headers (including Content-MD5, Content-Transfer-Encoding, and
1516   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1517   or Content-Encoding header, it is assumed that the content
1518   of the body-part has had the encoding applied, and the body-part is
1519   included in the Content-MD5 digest as is -- i.e., after the
1520   application. The Transfer-Encoding header field is not allowed within
1521   body-parts.
1522</t>
1523<t>
1524   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1525   computing or checking the digest: the line break convention used in
1526   the text actually transmitted &MUST; be left unaltered when computing
1527   the digest.
1528</t>
1529<x:note>
1530  <t>
1531    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1532    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1533    in which the application of Content-MD5 to HTTP entity-bodies
1534    differs from its application to MIME entity-bodies. One is that
1535    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1536    does use Transfer-Encoding and Content-Encoding. Another is that
1537    HTTP more frequently uses binary content types than MIME, so it is
1538    worth noting that, in such cases, the byte order used to compute
1539    the digest is the transmission byte order defined for the type.
1540    Lastly, HTTP allows transmission of text types with any of several
1541    line break conventions and not just the canonical form using CRLF.
1542  </t>
1543</x:note>
1544</section>
1545
1546<section title="Content-Type" anchor="header.content-type">
1547  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1548  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1549  <x:anchor-alias value="Content-Type"/>
1550  <x:anchor-alias value="Content-Type-v"/>
1551<t>
1552   The "Content-Type" entity-header field indicates the media type of the
1553   entity-body. In the case of responses to the HEAD method, the media type is
1554   that which would have been sent had the request been a GET.
1555</t>
1556<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1557  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1558  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1559</artwork></figure>
1560<t>
1561   Media types are defined in <xref target="media.types"/>. An example of the field is
1562</t>
1563<figure><artwork type="example">
1564  Content-Type: text/html; charset=ISO-8859-4
1565</artwork></figure>
1566<t>
1567   Further discussion of methods for identifying the media type of an
1568   entity is provided in <xref target="type"/>.
1569</t>
1570</section>
1571
1572</section>
1573
1574<section title="IANA Considerations" anchor="IANA.considerations">
1575<section title="Message Header Registration" anchor="message.header.registration">
1576<t>
1577   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1578   with the permanent registrations below (see <xref target="RFC3864"/>):
1579</t>
1580<?BEGININC p3-payload.iana-headers ?>
1581<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1582<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1583   <ttcol>Header Field Name</ttcol>
1584   <ttcol>Protocol</ttcol>
1585   <ttcol>Status</ttcol>
1586   <ttcol>Reference</ttcol>
1587
1588   <c>Accept</c>
1589   <c>http</c>
1590   <c>standard</c>
1591   <c>
1592      <xref target="header.accept"/>
1593   </c>
1594   <c>Accept-Charset</c>
1595   <c>http</c>
1596   <c>standard</c>
1597   <c>
1598      <xref target="header.accept-charset"/>
1599   </c>
1600   <c>Accept-Encoding</c>
1601   <c>http</c>
1602   <c>standard</c>
1603   <c>
1604      <xref target="header.accept-encoding"/>
1605   </c>
1606   <c>Accept-Language</c>
1607   <c>http</c>
1608   <c>standard</c>
1609   <c>
1610      <xref target="header.accept-language"/>
1611   </c>
1612   <c>Content-Disposition</c>
1613   <c>http</c>
1614   <c/>
1615   <c>
1616      <xref target="content-disposition"/>
1617   </c>
1618   <c>Content-Encoding</c>
1619   <c>http</c>
1620   <c>standard</c>
1621   <c>
1622      <xref target="header.content-encoding"/>
1623   </c>
1624   <c>Content-Language</c>
1625   <c>http</c>
1626   <c>standard</c>
1627   <c>
1628      <xref target="header.content-language"/>
1629   </c>
1630   <c>Content-Location</c>
1631   <c>http</c>
1632   <c>standard</c>
1633   <c>
1634      <xref target="header.content-location"/>
1635   </c>
1636   <c>Content-MD5</c>
1637   <c>http</c>
1638   <c>standard</c>
1639   <c>
1640      <xref target="header.content-md5"/>
1641   </c>
1642   <c>Content-Type</c>
1643   <c>http</c>
1644   <c>standard</c>
1645   <c>
1646      <xref target="header.content-type"/>
1647   </c>
1648   <c>MIME-Version</c>
1649   <c>http</c>
1650   <c/>
1651   <c>
1652      <xref target="mime-version"/>
1653   </c>
1654</texttable>
1655<!--(END)-->
1656<?ENDINC p3-payload.iana-headers ?>
1657<t>
1658   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1659</t>
1660</section>
1661
1662<section title="Content Coding Registry" anchor="content.coding.registration">
1663<t>
1664   The registration procedure for HTTP Content Codings is now defined
1665   by <xref target="content.coding.registry"/> of this document.
1666</t>
1667<t>
1668   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1669   should be updated with the registration below:
1670</t>
1671<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1672   <ttcol>Name</ttcol>
1673   <ttcol>Description</ttcol>
1674   <ttcol>Reference</ttcol>
1675   <c>compress</c>
1676   <c>UNIX "compress" program method</c>
1677   <c>
1678      &compress-coding;
1679   </c>
1680   <c>deflate</c>
1681   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1682   the "zlib" data format (<xref target="RFC1950"/>)
1683   </c>
1684   <c>
1685      &deflate-coding;
1686   </c>
1687   <c>gzip</c>
1688   <c>Same as GNU zip <xref target="RFC1952"/></c>
1689   <c>
1690      &gzip-coding;
1691   </c>
1692   <c>identity</c>
1693   <c>No transformation</c>
1694   <c>
1695      <xref target="content.codings"/>
1696   </c>
1697</texttable>
1698</section>
1699
1700</section>
1701
1702<section title="Security Considerations" anchor="security.considerations">
1703<t>
1704   This section is meant to inform application developers, information
1705   providers, and users of the security limitations in HTTP/1.1 as
1706   described by this document. The discussion does not include
1707   definitive solutions to the problems revealed, though it does make
1708   some suggestions for reducing security risks.
1709</t>
1710
1711<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1712<t>
1713   Accept request-headers can reveal information about the user to all
1714   servers which are accessed. The Accept-Language header in particular
1715   can reveal information the user would consider to be of a private
1716   nature, because the understanding of particular languages is often
1717   strongly correlated to the membership of a particular ethnic group.
1718   User agents which offer the option to configure the contents of an
1719   Accept-Language header to be sent in every request are strongly
1720   encouraged to let the configuration process include a message which
1721   makes the user aware of the loss of privacy involved.
1722</t>
1723<t>
1724   An approach that limits the loss of privacy would be for a user agent
1725   to omit the sending of Accept-Language headers by default, and to ask
1726   the user whether or not to start sending Accept-Language headers to a
1727   server if it detects, by looking for any Vary response-header fields
1728   generated by the server, that such sending could improve the quality
1729   of service.
1730</t>
1731<t>
1732   Elaborate user-customized accept header fields sent in every request,
1733   in particular if these include quality values, can be used by servers
1734   as relatively reliable and long-lived user identifiers. Such user
1735   identifiers would allow content providers to do click-trail tracking,
1736   and would allow collaborating content providers to match cross-server
1737   click-trails or form submissions of individual users. Note that for
1738   many users not behind a proxy, the network address of the host
1739   running the user agent will also serve as a long-lived user
1740   identifier. In environments where proxies are used to enhance
1741   privacy, user agents ought to be conservative in offering accept
1742   header configuration options to end users. As an extreme privacy
1743   measure, proxies could filter the accept headers in relayed requests.
1744   General purpose user agents which provide a high degree of header
1745   configurability &SHOULD; warn users about the loss of privacy which can
1746   be involved.
1747</t>
1748</section>
1749
1750<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1751<t>
1752   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1753   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1754   serious security considerations. Content-Disposition is not part of
1755   the HTTP standard, but since it is widely implemented, we are
1756   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1757   for details.
1758</t>
1759</section>
1760
1761</section>
1762
1763<section title="Acknowledgments" anchor="ack">
1764</section>
1765</middle>
1766<back>
1767
1768<references title="Normative References">
1769
1770<reference anchor="ISO-8859-1">
1771  <front>
1772    <title>
1773     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1774    </title>
1775    <author>
1776      <organization>International Organization for Standardization</organization>
1777    </author>
1778    <date year="1998"/>
1779  </front>
1780  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1781</reference>
1782
1783<reference anchor="Part1">
1784  <front>
1785    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1786    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1787      <organization abbrev="Day Software">Day Software</organization>
1788      <address><email>fielding@gbiv.com</email></address>
1789    </author>
1790    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1791      <organization>One Laptop per Child</organization>
1792      <address><email>jg@laptop.org</email></address>
1793    </author>
1794    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1795      <organization abbrev="HP">Hewlett-Packard Company</organization>
1796      <address><email>JeffMogul@acm.org</email></address>
1797    </author>
1798    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1799      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1800      <address><email>henrikn@microsoft.com</email></address>
1801    </author>
1802    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1803      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1804      <address><email>LMM@acm.org</email></address>
1805    </author>
1806    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1807      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1808      <address><email>paulle@microsoft.com</email></address>
1809    </author>
1810    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1811      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1812      <address><email>timbl@w3.org</email></address>
1813    </author>
1814    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1815      <organization abbrev="W3C">World Wide Web Consortium</organization>
1816      <address><email>ylafon@w3.org</email></address>
1817    </author>
1818    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1819      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1820      <address><email>julian.reschke@greenbytes.de</email></address>
1821    </author>
1822    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1823  </front>
1824  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1825  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1826</reference>
1827
1828<reference anchor="Part2">
1829  <front>
1830    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1831    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1832      <organization abbrev="Day Software">Day Software</organization>
1833      <address><email>fielding@gbiv.com</email></address>
1834    </author>
1835    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1836      <organization>One Laptop per Child</organization>
1837      <address><email>jg@laptop.org</email></address>
1838    </author>
1839    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1840      <organization abbrev="HP">Hewlett-Packard Company</organization>
1841      <address><email>JeffMogul@acm.org</email></address>
1842    </author>
1843    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1844      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1845      <address><email>henrikn@microsoft.com</email></address>
1846    </author>
1847    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1848      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1849      <address><email>LMM@acm.org</email></address>
1850    </author>
1851    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1852      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1853      <address><email>paulle@microsoft.com</email></address>
1854    </author>
1855    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1856      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1857      <address><email>timbl@w3.org</email></address>
1858    </author>
1859    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1860      <organization abbrev="W3C">World Wide Web Consortium</organization>
1861      <address><email>ylafon@w3.org</email></address>
1862    </author>
1863    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1864      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1865      <address><email>julian.reschke@greenbytes.de</email></address>
1866    </author>
1867    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1868  </front>
1869  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1870  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1871</reference>
1872
1873<reference anchor="Part4">
1874  <front>
1875    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1876    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1877      <organization abbrev="Day Software">Day Software</organization>
1878      <address><email>fielding@gbiv.com</email></address>
1879    </author>
1880    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1881      <organization>One Laptop per Child</organization>
1882      <address><email>jg@laptop.org</email></address>
1883    </author>
1884    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1885      <organization abbrev="HP">Hewlett-Packard Company</organization>
1886      <address><email>JeffMogul@acm.org</email></address>
1887    </author>
1888    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1889      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1890      <address><email>henrikn@microsoft.com</email></address>
1891    </author>
1892    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1893      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1894      <address><email>LMM@acm.org</email></address>
1895    </author>
1896    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1897      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1898      <address><email>paulle@microsoft.com</email></address>
1899    </author>
1900    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1901      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1902      <address><email>timbl@w3.org</email></address>
1903    </author>
1904    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1905      <organization abbrev="W3C">World Wide Web Consortium</organization>
1906      <address><email>ylafon@w3.org</email></address>
1907    </author>
1908    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1909      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1910      <address><email>julian.reschke@greenbytes.de</email></address>
1911    </author>
1912    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1913  </front>
1914  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1915  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1916</reference>
1917
1918<reference anchor="Part5">
1919  <front>
1920    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1921    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1922      <organization abbrev="Day Software">Day Software</organization>
1923      <address><email>fielding@gbiv.com</email></address>
1924    </author>
1925    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1926      <organization>One Laptop per Child</organization>
1927      <address><email>jg@laptop.org</email></address>
1928    </author>
1929    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1930      <organization abbrev="HP">Hewlett-Packard Company</organization>
1931      <address><email>JeffMogul@acm.org</email></address>
1932    </author>
1933    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1934      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1935      <address><email>henrikn@microsoft.com</email></address>
1936    </author>
1937    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1938      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1939      <address><email>LMM@acm.org</email></address>
1940    </author>
1941    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1942      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1943      <address><email>paulle@microsoft.com</email></address>
1944    </author>
1945    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1946      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1947      <address><email>timbl@w3.org</email></address>
1948    </author>
1949    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1950      <organization abbrev="W3C">World Wide Web Consortium</organization>
1951      <address><email>ylafon@w3.org</email></address>
1952    </author>
1953    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1954      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1955      <address><email>julian.reschke@greenbytes.de</email></address>
1956    </author>
1957    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1958  </front>
1959  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1960  <x:source href="p5-range.xml" basename="p5-range"/>
1961</reference>
1962
1963<reference anchor="Part6">
1964  <front>
1965    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1966    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1967      <organization abbrev="Day Software">Day Software</organization>
1968      <address><email>fielding@gbiv.com</email></address>
1969    </author>
1970    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1971      <organization>One Laptop per Child</organization>
1972      <address><email>jg@laptop.org</email></address>
1973    </author>
1974    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1975      <organization abbrev="HP">Hewlett-Packard Company</organization>
1976      <address><email>JeffMogul@acm.org</email></address>
1977    </author>
1978    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1979      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1980      <address><email>henrikn@microsoft.com</email></address>
1981    </author>
1982    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1983      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1984      <address><email>LMM@acm.org</email></address>
1985    </author>
1986    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1987      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1988      <address><email>paulle@microsoft.com</email></address>
1989    </author>
1990    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1991      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1992      <address><email>timbl@w3.org</email></address>
1993    </author>
1994    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1995      <organization abbrev="W3C">World Wide Web Consortium</organization>
1996      <address><email>ylafon@w3.org</email></address>
1997    </author>
1998    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1999      <address><email>mnot@mnot.net</email></address>
2000    </author>
2001    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2002      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2003      <address><email>julian.reschke@greenbytes.de</email></address>
2004    </author>
2005    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2006  </front>
2007  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2008  <x:source href="p6-cache.xml" basename="p6-cache"/>
2009</reference>
2010
2011<reference anchor="RFC1864">
2012  <front>
2013    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2014    <author initials="J." surname="Myers" fullname="John G. Myers">
2015      <organization>Carnegie Mellon University</organization>
2016      <address><email>jgm+@cmu.edu</email></address>
2017    </author>
2018    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2019      <organization>Dover Beach Consulting, Inc.</organization>
2020      <address><email>mrose@dbc.mtview.ca.us</email></address>
2021    </author>
2022    <date month="October" year="1995"/>
2023  </front>
2024  <seriesInfo name="RFC" value="1864"/>
2025</reference>
2026
2027<reference anchor="RFC1950">
2028  <front>
2029    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2030    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2031      <organization>Aladdin Enterprises</organization>
2032      <address><email>ghost@aladdin.com</email></address>
2033    </author>
2034    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
2035    <date month="May" year="1996"/>
2036  </front>
2037  <seriesInfo name="RFC" value="1950"/>
2038  <annotation>
2039    RFC 1950 is an Informational RFC, thus it may be less stable than
2040    this specification. On the other hand, this downward reference was
2041    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2042    therefore it is unlikely to cause problems in practice. See also
2043    <xref target="BCP97"/>.
2044  </annotation>
2045</reference>
2046
2047<reference anchor="RFC1951">
2048  <front>
2049    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2050    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2051      <organization>Aladdin Enterprises</organization>
2052      <address><email>ghost@aladdin.com</email></address>
2053    </author>
2054    <date month="May" year="1996"/>
2055  </front>
2056  <seriesInfo name="RFC" value="1951"/>
2057  <annotation>
2058    RFC 1951 is an Informational RFC, thus it may be less stable than
2059    this specification. On the other hand, this downward reference was
2060    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2061    therefore it is unlikely to cause problems in practice. See also
2062    <xref target="BCP97"/>.
2063  </annotation>
2064</reference>
2065
2066<reference anchor="RFC1952">
2067  <front>
2068    <title>GZIP file format specification version 4.3</title>
2069    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2070      <organization>Aladdin Enterprises</organization>
2071      <address><email>ghost@aladdin.com</email></address>
2072    </author>
2073    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2074      <address><email>gzip@prep.ai.mit.edu</email></address>
2075    </author>
2076    <author initials="M." surname="Adler" fullname="Mark Adler">
2077      <address><email>madler@alumni.caltech.edu</email></address>
2078    </author>
2079    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2080      <address><email>ghost@aladdin.com</email></address>
2081    </author>
2082    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2083      <address><email>randeg@alumni.rpi.edu</email></address>
2084    </author>
2085    <date month="May" year="1996"/>
2086  </front>
2087  <seriesInfo name="RFC" value="1952"/>
2088  <annotation>
2089    RFC 1952 is an Informational RFC, thus it may be less stable than
2090    this specification. On the other hand, this downward reference was
2091    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2092    therefore it is unlikely to cause problems in practice. See also
2093    <xref target="BCP97"/>.
2094  </annotation>
2095</reference>
2096
2097<reference anchor="RFC2045">
2098  <front>
2099    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2100    <author initials="N." surname="Freed" fullname="Ned Freed">
2101      <organization>Innosoft International, Inc.</organization>
2102      <address><email>ned@innosoft.com</email></address>
2103    </author>
2104    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2105      <organization>First Virtual Holdings</organization>
2106      <address><email>nsb@nsb.fv.com</email></address>
2107    </author>
2108    <date month="November" year="1996"/>
2109  </front>
2110  <seriesInfo name="RFC" value="2045"/>
2111</reference>
2112
2113<reference anchor="RFC2046">
2114  <front>
2115    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2116    <author initials="N." surname="Freed" fullname="Ned Freed">
2117      <organization>Innosoft International, Inc.</organization>
2118      <address><email>ned@innosoft.com</email></address>
2119    </author>
2120    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2121      <organization>First Virtual Holdings</organization>
2122      <address><email>nsb@nsb.fv.com</email></address>
2123    </author>
2124    <date month="November" year="1996"/>
2125  </front>
2126  <seriesInfo name="RFC" value="2046"/>
2127</reference>
2128
2129<reference anchor="RFC2119">
2130  <front>
2131    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2132    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2133      <organization>Harvard University</organization>
2134      <address><email>sob@harvard.edu</email></address>
2135    </author>
2136    <date month="March" year="1997"/>
2137  </front>
2138  <seriesInfo name="BCP" value="14"/>
2139  <seriesInfo name="RFC" value="2119"/>
2140</reference>
2141
2142<reference anchor='RFC4647'>
2143  <front>
2144    <title>Matching of Language Tags</title>
2145    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2146      <organization>Yahoo! Inc.</organization>
2147      <address><email>addison@inter-locale.com</email></address>
2148    </author>
2149    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2150      <organization>Google</organization>
2151      <address><email>mark.davis@macchiato.com</email></address>
2152    </author>
2153    <date year='2006' month='September' />
2154  </front>
2155  <seriesInfo name='BCP' value='47' />
2156  <seriesInfo name='RFC' value='4647' />
2157</reference>
2158
2159<reference anchor="RFC5234">
2160  <front>
2161    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2162    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2163      <organization>Brandenburg InternetWorking</organization>
2164      <address>
2165        <email>dcrocker@bbiw.net</email>
2166      </address> 
2167    </author>
2168    <author initials="P." surname="Overell" fullname="Paul Overell">
2169      <organization>THUS plc.</organization>
2170      <address>
2171        <email>paul.overell@thus.net</email>
2172      </address>
2173    </author>
2174    <date month="January" year="2008"/>
2175  </front>
2176  <seriesInfo name="STD" value="68"/>
2177  <seriesInfo name="RFC" value="5234"/>
2178</reference>
2179
2180<reference anchor='RFC5646'>
2181  <front>
2182    <title>Tags for Identifying Languages</title>
2183    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2184      <organization>Lab126</organization>
2185      <address><email>addison@inter-locale.com</email></address>
2186    </author>
2187    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2188      <organization>Google</organization>
2189      <address><email>mark.davis@google.com</email></address>
2190    </author>
2191    <date month='September' year='2009' />
2192  </front>
2193  <seriesInfo name='BCP' value='47' />
2194  <seriesInfo name='RFC' value='5646' />
2195</reference>
2196
2197</references>
2198
2199<references title="Informative References">
2200
2201<reference anchor="RFC1945">
2202  <front>
2203    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2204    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2205      <organization>MIT, Laboratory for Computer Science</organization>
2206      <address><email>timbl@w3.org</email></address>
2207    </author>
2208    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2209      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2210      <address><email>fielding@ics.uci.edu</email></address>
2211    </author>
2212    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2213      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2214      <address><email>frystyk@w3.org</email></address>
2215    </author>
2216    <date month="May" year="1996"/>
2217  </front>
2218  <seriesInfo name="RFC" value="1945"/>
2219</reference>
2220
2221<reference anchor="RFC2049">
2222  <front>
2223    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2224    <author initials="N." surname="Freed" fullname="Ned Freed">
2225      <organization>Innosoft International, Inc.</organization>
2226      <address><email>ned@innosoft.com</email></address>
2227    </author>
2228    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2229      <organization>First Virtual Holdings</organization>
2230      <address><email>nsb@nsb.fv.com</email></address>
2231    </author>
2232    <date month="November" year="1996"/>
2233  </front>
2234  <seriesInfo name="RFC" value="2049"/>
2235</reference>
2236
2237<reference anchor="RFC2068">
2238  <front>
2239    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2240    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2241      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2242      <address><email>fielding@ics.uci.edu</email></address>
2243    </author>
2244    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2245      <organization>MIT Laboratory for Computer Science</organization>
2246      <address><email>jg@w3.org</email></address>
2247    </author>
2248    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2249      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2250      <address><email>mogul@wrl.dec.com</email></address>
2251    </author>
2252    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2253      <organization>MIT Laboratory for Computer Science</organization>
2254      <address><email>frystyk@w3.org</email></address>
2255    </author>
2256    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2257      <organization>MIT Laboratory for Computer Science</organization>
2258      <address><email>timbl@w3.org</email></address>
2259    </author>
2260    <date month="January" year="1997"/>
2261  </front>
2262  <seriesInfo name="RFC" value="2068"/>
2263</reference>
2264
2265<reference anchor="RFC2076">
2266  <front>
2267    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2268    <author initials="J." surname="Palme" fullname="Jacob Palme">
2269      <organization>Stockholm University/KTH</organization>
2270      <address><email>jpalme@dsv.su.se</email></address>
2271    </author>
2272    <date month="February" year="1997"/>
2273  </front>
2274  <seriesInfo name="RFC" value="2076"/>
2275</reference>
2276
2277<reference anchor="RFC2183">
2278  <front>
2279    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2280    <author initials="R." surname="Troost" fullname="Rens Troost">
2281      <organization>New Century Systems</organization>
2282      <address><email>rens@century.com</email></address>
2283    </author>
2284    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2285      <organization>QUALCOMM Incorporated</organization>
2286      <address><email>sdorner@qualcomm.com</email></address>
2287    </author>
2288    <author initials="K." surname="Moore" fullname="Keith Moore">
2289      <organization>Department of Computer Science</organization>
2290      <address><email>moore@cs.utk.edu</email></address>
2291    </author>
2292    <date month="August" year="1997"/>
2293  </front>
2294  <seriesInfo name="RFC" value="2183"/>
2295</reference>
2296
2297<reference anchor="RFC2277">
2298  <front>
2299    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2300    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2301      <organization>UNINETT</organization>
2302      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2303    </author>
2304    <date month="January" year="1998"/>
2305  </front>
2306  <seriesInfo name="BCP" value="18"/>
2307  <seriesInfo name="RFC" value="2277"/>
2308</reference>
2309
2310<reference anchor='RFC2295'>
2311  <front>
2312    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2313    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2314      <organization>Technische Universiteit Eindhoven</organization>
2315      <address>
2316        <email>koen@win.tue.nl</email>
2317      </address>
2318    </author>
2319    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2320      <organization>Hewlett-Packard Company</organization>
2321      <address>
2322        <email>mutz@hpl.hp.com</email>
2323      </address>
2324    </author>
2325    <date year='1998' month='March'/>
2326  </front>
2327  <seriesInfo name='RFC' value='2295'/>
2328</reference>
2329
2330<reference anchor="RFC2388">
2331  <front>
2332    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2333    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2334      <organization>Xerox Palo Alto Research Center</organization>
2335      <address><email>masinter@parc.xerox.com</email></address>
2336    </author>
2337    <date year="1998" month="August"/>
2338  </front>
2339  <seriesInfo name="RFC" value="2388"/>
2340</reference>
2341
2342<reference anchor="RFC2557">
2343  <front>
2344    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2345    <author initials="F." surname="Palme" fullname="Jacob Palme">
2346      <organization>Stockholm University and KTH</organization>
2347      <address><email>jpalme@dsv.su.se</email></address>
2348    </author>
2349    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2350      <organization>Microsoft Corporation</organization>
2351      <address><email>alexhop@microsoft.com</email></address>
2352    </author>
2353    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2354      <organization>Lotus Development Corporation</organization>
2355      <address><email>Shelness@lotus.com</email></address>
2356    </author>
2357    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2358      <address><email>stef@nma.com</email></address>
2359    </author>
2360    <date year="1999" month="March"/>
2361  </front>
2362  <seriesInfo name="RFC" value="2557"/>
2363</reference>
2364
2365<reference anchor="RFC2616">
2366  <front>
2367    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2368    <author initials="R." surname="Fielding" fullname="R. Fielding">
2369      <organization>University of California, Irvine</organization>
2370      <address><email>fielding@ics.uci.edu</email></address>
2371    </author>
2372    <author initials="J." surname="Gettys" fullname="J. Gettys">
2373      <organization>W3C</organization>
2374      <address><email>jg@w3.org</email></address>
2375    </author>
2376    <author initials="J." surname="Mogul" fullname="J. Mogul">
2377      <organization>Compaq Computer Corporation</organization>
2378      <address><email>mogul@wrl.dec.com</email></address>
2379    </author>
2380    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2381      <organization>MIT Laboratory for Computer Science</organization>
2382      <address><email>frystyk@w3.org</email></address>
2383    </author>
2384    <author initials="L." surname="Masinter" fullname="L. Masinter">
2385      <organization>Xerox Corporation</organization>
2386      <address><email>masinter@parc.xerox.com</email></address>
2387    </author>
2388    <author initials="P." surname="Leach" fullname="P. Leach">
2389      <organization>Microsoft Corporation</organization>
2390      <address><email>paulle@microsoft.com</email></address>
2391    </author>
2392    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2393      <organization>W3C</organization>
2394      <address><email>timbl@w3.org</email></address>
2395    </author>
2396    <date month="June" year="1999"/>
2397  </front>
2398  <seriesInfo name="RFC" value="2616"/>
2399</reference>
2400
2401<reference anchor="RFC3629">
2402  <front>
2403    <title>UTF-8, a transformation format of ISO 10646</title>
2404    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2405      <organization>Alis Technologies</organization>
2406      <address><email>fyergeau@alis.com</email></address>
2407    </author>
2408    <date month="November" year="2003"/>
2409  </front>
2410  <seriesInfo name="RFC" value="3629"/>
2411  <seriesInfo name="STD" value="63"/>
2412</reference>
2413
2414<reference anchor='RFC3864'>
2415  <front>
2416    <title>Registration Procedures for Message Header Fields</title>
2417    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2418      <organization>Nine by Nine</organization>
2419      <address><email>GK-IETF@ninebynine.org</email></address>
2420    </author>
2421    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2422      <organization>BEA Systems</organization>
2423      <address><email>mnot@pobox.com</email></address>
2424    </author>
2425    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2426      <organization>HP Labs</organization>
2427      <address><email>JeffMogul@acm.org</email></address>
2428    </author>
2429    <date year='2004' month='September' />
2430  </front>
2431  <seriesInfo name='BCP' value='90' />
2432  <seriesInfo name='RFC' value='3864' />
2433</reference>
2434
2435<reference anchor="RFC4288">
2436  <front>
2437    <title>Media Type Specifications and Registration Procedures</title>
2438    <author initials="N." surname="Freed" fullname="N. Freed">
2439      <organization>Sun Microsystems</organization>
2440      <address>
2441        <email>ned.freed@mrochek.com</email>
2442      </address>
2443    </author>
2444    <author initials="J." surname="Klensin" fullname="J. Klensin">
2445      <address>
2446        <email>klensin+ietf@jck.com</email>
2447      </address>
2448    </author>
2449    <date year="2005" month="December"/>
2450  </front>
2451  <seriesInfo name="BCP" value="13"/>
2452  <seriesInfo name="RFC" value="4288"/>
2453</reference>
2454
2455<reference anchor='RFC5226'>
2456  <front>
2457    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2458    <author initials='T.' surname='Narten' fullname='T. Narten'>
2459      <organization>IBM</organization>
2460      <address><email>narten@us.ibm.com</email></address>
2461    </author>
2462    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2463      <organization>Google</organization>
2464      <address><email>Harald@Alvestrand.no</email></address>
2465    </author>
2466    <date year='2008' month='May' />
2467  </front>
2468  <seriesInfo name='BCP' value='26' />
2469  <seriesInfo name='RFC' value='5226' />
2470</reference>
2471
2472<reference anchor="RFC5322">
2473  <front>
2474    <title>Internet Message Format</title>
2475    <author initials="P." surname="Resnick" fullname="P. Resnick">
2476      <organization>Qualcomm Incorporated</organization>
2477    </author>
2478    <date year="2008" month="October"/>
2479  </front> 
2480  <seriesInfo name="RFC" value="5322"/>
2481</reference>
2482
2483<reference anchor='BCP97'>
2484  <front>
2485    <title>Handling Normative References to Standards-Track Documents</title>
2486    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2487      <address>
2488        <email>klensin+ietf@jck.com</email>
2489      </address>
2490    </author>
2491    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2492      <organization>MIT</organization>
2493      <address>
2494        <email>hartmans-ietf@mit.edu</email>
2495      </address>
2496    </author>
2497    <date year='2007' month='June' />
2498  </front>
2499  <seriesInfo name='BCP' value='97' />
2500  <seriesInfo name='RFC' value='4897' />
2501</reference>
2502
2503
2504</references>
2505
2506<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2507<t>
2508   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
2509   allow entities to be transmitted in an open variety of
2510   representations and with extensible mechanisms. However, RFC 2045
2511   discusses mail, and HTTP has a few features that are different from
2512   those described in RFC 2045. These differences were carefully chosen
2513   to optimize performance over binary connections, to allow greater
2514   freedom in the use of new media types, to make date comparisons
2515   easier, and to acknowledge the practice of some early HTTP servers
2516   and clients.
2517</t>
2518<t>
2519   This appendix describes specific areas where HTTP differs from RFC
2520   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2521   aware of these differences and provide the appropriate conversions
2522   where necessary. Proxies and gateways from MIME environments to HTTP
2523   also need to be aware of the differences because some conversions
2524   might be required.
2525</t>
2526
2527<section title="MIME-Version" anchor="mime-version">
2528  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2529  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2530  <x:anchor-alias value="MIME-Version"/>
2531  <x:anchor-alias value="MIME-Version-v"/>
2532<t>
2533   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2534   include a single MIME-Version general-header field to indicate what
2535   version of the MIME protocol was used to construct the message. Use
2536   of the MIME-Version header field indicates that the message is in
2537   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2538   Proxies/gateways are responsible for ensuring full compliance (where
2539   possible) when exporting HTTP messages to strict MIME environments.
2540</t>
2541<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2542  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2543  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2544</artwork></figure>
2545<t>
2546   MIME version "1.0" is the default for use in HTTP/1.1. However,
2547   HTTP/1.1 message parsing and semantics are defined by this document
2548   and not the MIME specification.
2549</t>
2550</section>
2551
2552<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2553<t>
2554   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2555   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2556   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2557   allowed for subtypes of the "text" media type when transmitted over
2558   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2559   line breaks as CRLF and forbids the use of CR or LF outside of line
2560   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2561   line break within text content when a message is transmitted over
2562   HTTP.
2563</t>
2564<t>
2565   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2566   environment &SHOULD; translate all line breaks within the text media
2567   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2568   canonical form of CRLF. Note, however, that this might be complicated
2569   by the presence of a Content-Encoding and by the fact that HTTP
2570   allows the use of some character sets which do not use octets 13 and
2571   10 to represent CR and LF, as is the case for some multi-byte
2572   character sets.
2573</t>
2574<t>
2575   Implementors should note that conversion will break any cryptographic
2576   checksums applied to the original content unless the original content
2577   is already in canonical form. Therefore, the canonical form is
2578   recommended for any content that uses such checksums in HTTP.
2579</t>
2580</section>
2581
2582
2583<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2584<t>
2585   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2586   simplify the process of date comparison. Proxies and gateways from
2587   other protocols &SHOULD; ensure that any Date header field present in a
2588   message conforms to one of the HTTP/1.1 formats and rewrite the date
2589   if necessary.
2590</t>
2591</section>
2592
2593<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2594<t>
2595   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2596   Content-Encoding header field. Since this acts as a modifier on the
2597   media type, proxies and gateways from HTTP to MIME-compliant
2598   protocols &MUST; either change the value of the Content-Type header
2599   field or decode the entity-body before forwarding the message. (Some
2600   experimental applications of Content-Type for Internet mail have used
2601   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2602   a function equivalent to Content-Encoding. However, this parameter is
2603   not part of RFC 2045).
2604</t>
2605</section>
2606
2607<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2608<t>
2609   HTTP does not use the Content-Transfer-Encoding field of RFC
2610   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2611   remove any Content-Transfer-Encoding
2612   prior to delivering the response message to an HTTP client.
2613</t>
2614<t>
2615   Proxies and gateways from HTTP to MIME-compliant protocols are
2616   responsible for ensuring that the message is in the correct format
2617   and encoding for safe transport on that protocol, where "safe
2618   transport" is defined by the limitations of the protocol being used.
2619   Such a proxy or gateway &SHOULD; label the data with an appropriate
2620   Content-Transfer-Encoding if doing so will improve the likelihood of
2621   safe transport over the destination protocol.
2622</t>
2623</section>
2624
2625<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2626<t>
2627   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2628   Proxies/gateways &MUST; remove any transfer-coding prior to
2629   forwarding a message via a MIME-compliant protocol.
2630</t>
2631</section>
2632
2633<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2634<t>
2635   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2636   need to be aware of MIME line length limitations. Since HTTP does not
2637   have this limitation, HTTP does not fold long lines. MHTML messages
2638   being transported by HTTP follow all conventions of MHTML, including
2639   line length limitations and folding, canonicalization, etc., since
2640   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2641   does not interpret the content or any MIME header lines that might be
2642   contained therein.
2643</t>
2644</section>
2645</section>
2646
2647<section title="Additional Features" anchor="additional.features">
2648<t>
2649   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2650   existing HTTP implementations, but not consistently and correctly
2651   across most HTTP/1.1 applications. Implementors are advised to be
2652   aware of these features, but cannot rely upon their presence in, or
2653   interoperability with, other HTTP/1.1 applications. Some of these
2654   describe proposed experimental features, and some describe features
2655   that experimental deployment found lacking that are now addressed in
2656   the base HTTP/1.1 specification.
2657</t>
2658<t>
2659   A number of other headers, such as Content-Disposition and Title,
2660   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2661</t>
2662
2663<section title="Content-Disposition" anchor="content-disposition">
2664<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2665<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2666  <x:anchor-alias value="content-disposition"/>
2667  <x:anchor-alias value="content-disposition-v"/>
2668  <x:anchor-alias value="disposition-type"/>
2669  <x:anchor-alias value="disposition-parm"/>
2670  <x:anchor-alias value="disp-extension-parm"/>
2671  <x:anchor-alias value="disp-extension-token"/>
2672  <x:anchor-alias value="filename-parm"/>
2673<t>
2674   The "Content-Disposition" response-header field has been proposed as a
2675   means for the origin server to suggest a default filename if the user
2676   requests that the content is saved to a file. This usage is derived
2677   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2678</t>
2679<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2680  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2681                        <x:ref>content-disposition-v</x:ref>
2682  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2683                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2684  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2685  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2686  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2687  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2688  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" <x:ref>word</x:ref>
2689</artwork></figure>
2690<t>
2691   An example is
2692</t>
2693<figure><artwork type="example">
2694  Content-Disposition: attachment; filename="fname.ext"
2695</artwork></figure>
2696<t>
2697   The receiving user agent &SHOULD-NOT;  respect any directory path
2698   information present in the filename-parm parameter, which is the only
2699   parameter believed to apply to HTTP implementations at this time. The
2700   filename &SHOULD; be treated as a terminal component only.
2701</t>
2702<t>
2703   If this header is used in a response with the application/octet-stream
2704   content-type, the implied suggestion is that the user agent
2705   should not display the response, but directly enter a "save response
2706   as..." dialog.
2707</t>
2708<t>
2709   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2710</t>
2711</section>
2712</section>
2713
2714<section title="Compatibility with Previous Versions" anchor="compatibility">
2715<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2716<t>
2717   Transfer-coding and message lengths all interact in ways that
2718   required fixing exactly when chunked encoding is used (to allow for
2719   transfer encoding that may not be self delimiting); it was important
2720   to straighten out exactly how message lengths are computed.
2721   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2722   <xref target="Part5"/> and <xref target="Part6"/>).
2723</t>
2724<t>
2725   Charset wildcarding is introduced to avoid explosion of character set
2726   names in accept headers. (<xref target="header.accept-charset"/>)
2727</t>
2728<t>
2729   Content-Base was deleted from the specification: it was not
2730   implemented widely, and there is no simple, safe way to introduce it
2731   without a robust extension mechanism. In addition, it is used in a
2732   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2733</t>
2734<t>
2735   A content-coding of "identity" was introduced, to solve problems
2736   discovered in caching. (<xref target="content.codings"/>)
2737</t>
2738<t>
2739   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2740   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2741   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2742</t>
2743</section>
2744
2745<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2746<t>
2747  Clarify contexts that charset is used in.
2748  (<xref target="character.sets"/>)
2749</t>
2750<t>
2751  Remove base URI setting semantics for Content-Location due to poor
2752  implementation support, which was caused by too many broken servers emitting
2753  bogus Content-Location headers, and also the potentially undesirable effect
2754  of potentially breaking relative links in content-negotiated resources.
2755  (<xref target="header.content-location"/>)
2756</t>
2757<t>
2758  Remove reference to non-existant identity transfer-coding value tokens.
2759  (<xref target="no.content-transfer-encoding"/>)
2760</t>
2761</section>
2762
2763</section>
2764
2765<?BEGININC p3-payload.abnf-appendix ?>
2766<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2767<figure>
2768<artwork type="abnf" name="p3-payload.parsed-abnf">
2769<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2770<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2771<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2772 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2773 qvalue ] ] )
2774<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2775<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2776 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2777<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2778<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2779 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2780 ] )
2781<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2782 OWS media-range [ accept-params ] ] ) ]
2783
2784<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2785<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2786 content-coding ] )
2787<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2788<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2789 language-tag ] )
2790<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
2791<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2792<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2793<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2794<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2795<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2796<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2797<x:ref>Content-Type-v</x:ref> = media-type
2798
2799<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2800
2801<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2802
2803<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2804<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2805
2806<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2807
2808<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2809<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2810<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2811<x:ref>attribute</x:ref> = token
2812
2813<x:ref>charset</x:ref> = token
2814<x:ref>codings</x:ref> = ( content-coding / "*" )
2815<x:ref>content-coding</x:ref> = token
2816<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2817 content-disposition-v
2818<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2819 disposition-parm )
2820
2821<x:ref>disp-extension-parm</x:ref> = token "=" word
2822<x:ref>disp-extension-token</x:ref> = token
2823<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2824<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2825
2826<x:ref>entity-body</x:ref> = *OCTET
2827<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2828 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2829 Expires / Last-Modified / extension-header
2830<x:ref>extension-header</x:ref> = header-field
2831
2832<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2833
2834<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
2835
2836<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2837<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2838
2839<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2840 ";" OWS parameter )
2841<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2842
2843<x:ref>parameter</x:ref> = attribute "=" value
2844<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2845
2846<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2847<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2848
2849<x:ref>subtype</x:ref> = token
2850
2851<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2852<x:ref>type</x:ref> = token
2853
2854<x:ref>value</x:ref> = word
2855
2856<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2857</artwork>
2858</figure>
2859<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2860; Accept defined but not used
2861; Accept-Charset defined but not used
2862; Accept-Encoding defined but not used
2863; Accept-Language defined but not used
2864; MIME-Version defined but not used
2865; content-disposition defined but not used
2866; entity-body defined but not used
2867; entity-header defined but not used
2868</artwork></figure></section>
2869<?ENDINC p3-payload.abnf-appendix ?>
2870
2871<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2872
2873<section title="Since RFC2616">
2874<t>
2875  Extracted relevant partitions from <xref target="RFC2616"/>.
2876</t>
2877</section>
2878
2879<section title="Since draft-ietf-httpbis-p3-payload-00">
2880<t>
2881  Closed issues:
2882  <list style="symbols"> 
2883    <t>
2884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2885      "Media Type Registrations"
2886      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2887    </t>
2888    <t>
2889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2890      "Clarification regarding quoting of charset values"
2891      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2892    </t>
2893    <t>
2894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2895      "Remove 'identity' token references"
2896      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2897    </t>
2898    <t>
2899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2900      "Accept-Encoding BNF"
2901    </t>
2902    <t>
2903      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2904      "Normative and Informative references"
2905    </t>
2906    <t>
2907      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2908      "RFC1700 references"
2909    </t>
2910    <t>
2911      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2912      "Updating to RFC4288"
2913    </t>
2914    <t>
2915      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2916      "Informative references"
2917    </t>
2918    <t>
2919      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2920      "ISO-8859-1 Reference"
2921    </t>
2922    <t>
2923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2924      "Encoding References Normative"
2925    </t>
2926    <t>
2927      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2928      "Normative up-to-date references"
2929    </t>
2930  </list>
2931</t>
2932</section>
2933
2934<section title="Since draft-ietf-httpbis-p3-payload-01">
2935<t>
2936  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2937  <list style="symbols"> 
2938    <t>
2939      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2940    </t>
2941  </list>
2942</t>
2943</section>
2944
2945<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2946<t>
2947  Closed issues:
2948  <list style="symbols"> 
2949    <t>
2950      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2951      "Quoting Charsets"
2952    </t>
2953    <t>
2954      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2955      "Classification for Allow header"
2956    </t>
2957    <t>
2958      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2959      "missing default for qvalue in description of Accept-Encoding"
2960    </t>
2961  </list>
2962</t>
2963<t>
2964  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2965  <list style="symbols"> 
2966    <t>
2967      Reference RFC 3984, and update header registrations for headers defined
2968      in this document.
2969    </t>
2970  </list>
2971</t>
2972</section>
2973
2974<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2975<t>
2976  Closed issues:
2977  <list style="symbols"> 
2978    <t>
2979      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2980      "Quoting Charsets"
2981    </t>
2982    <t>
2983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2984      "language tag matching (Accept-Language) vs RFC4647"
2985    </t>
2986    <t>
2987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2988      "RFC 1806 has been replaced by RFC2183"
2989    </t>
2990  </list>
2991</t>
2992<t>
2993  Other changes:
2994  <list style="symbols"> 
2995    <t>
2996      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2997      "Encoding References Normative" -- rephrase the annotation and reference
2998      <xref target="BCP97"/>.
2999    </t>
3000  </list>
3001</t>
3002 </section>
3003
3004<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
3005<t>
3006  Closed issues:
3007  <list style="symbols"> 
3008    <t>
3009      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3010      "RFC 2822 is updated by RFC 5322"
3011    </t>
3012  </list>
3013</t>
3014<t>
3015  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3016  <list style="symbols"> 
3017    <t>
3018      Use "/" instead of "|" for alternatives.
3019    </t>
3020    <t>
3021      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3022      whitespace ("OWS") and required whitespace ("RWS").
3023    </t>
3024    <t>
3025      Rewrite ABNFs to spell out whitespace rules, factor out
3026      header value format definitions.
3027    </t>
3028  </list>
3029</t>
3030</section>
3031
3032<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3033<t>
3034  Closed issues:
3035  <list style="symbols"> 
3036    <t>
3037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3038      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3039    </t>
3040  </list>
3041</t>
3042<t>
3043  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3044  <list style="symbols"> 
3045    <t>
3046      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3047    </t>
3048  </list>
3049</t>
3050<t>
3051  Other changes:
3052  <list style="symbols"> 
3053    <t>
3054      Move definition of quality values into Part 1.
3055    </t>
3056  </list>
3057</t>
3058</section>
3059
3060<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3061<t>
3062  Closed issues:
3063  <list style="symbols"> 
3064    <t>
3065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3066      "Content-Location isn't special"
3067    </t>
3068    <t>
3069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3070      "Content Sniffing"
3071    </t>
3072  </list>
3073</t>
3074</section>
3075
3076<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3077<t>
3078  Closed issues:
3079  <list style="symbols"> 
3080    <t>
3081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3082      "Updated reference for language tags"
3083    </t>
3084    <t>
3085      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3086      "Clarify rules for determining what entities a response carries"
3087    </t>
3088    <t>
3089      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
3090      "Content-Location base-setting problems"
3091    </t>
3092    <t>
3093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3094      "Content Sniffing"
3095    </t>
3096    <t>
3097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3098      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3099    </t>
3100    <t>
3101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
3102      "move definitions of gzip/deflate/compress to part 1"
3103    </t>
3104  </list>
3105</t>
3106<t>
3107  Partly resolved issues:
3108  <list style="symbols"> 
3109    <t>
3110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3111      "update IANA requirements wrt Transfer-Coding values" (add the
3112      IANA Considerations subsection)
3113    </t>
3114    <t>
3115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3116      "update IANA requirements wrt Content-Coding values" (add the
3117      IANA Considerations subsection)
3118    </t>
3119  </list>
3120</t>
3121</section>
3122
3123<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
3124<t>
3125  Closed issues:
3126  <list style="symbols"> 
3127    <t>
3128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
3129      "Content Negotiation for media types"
3130    </t>
3131    <t>
3132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
3133      "Accept-Language: which RFC4647 filtering?"
3134    </t>
3135  </list>
3136</t>
3137</section>
3138
3139<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
3140<t>
3141  Closed issues:
3142  <list style="symbols"> 
3143    <t>
3144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
3145      "IANA registry for content/transfer encodings"
3146    </t>
3147    <t>
3148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
3149      "use of term "word" when talking about header structure"
3150    </t>
3151  </list>
3152</t>
3153<t>
3154  Partly resolved issues:
3155  <list style="symbols"> 
3156    <t>
3157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3158      "Term for the requested resource's URI"
3159    </t>
3160  </list>
3161</t>
3162</section>
3163
3164</section>
3165
3166</back>
3167</rfc>
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