source: draft-ietf-httpbis/latest/p3-payload.xml @ 592

Last change on this file since 592 was 592, checked in by julian.reschke@…, 10 years ago

Rephrase "Content-Type" discussion so that it is clear that leaving it out can be better than server-side guessing, and that HTTP itself does not rule out client-side sniffing (related to #155)

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File size: 127.6 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 "June">
16  <!ENTITY ID-YEAR "2009">
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 message-headers          "<xref target='Part1' x:rel='#message.headers' 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]>
36<?rfc toc="yes" ?>
37<?rfc symrefs="yes" ?>
38<?rfc sortrefs="yes" ?>
39<?rfc compact="yes"?>
40<?rfc subcompact="no" ?>
41<?rfc linkmailto="no" ?>
42<?rfc editing="no" ?>
43<?rfc comments="yes"?>
44<?rfc inline="yes"?>
45<?rfc-ext allow-markup-in-artwork="yes" ?>
46<?rfc-ext include-references-in-index="yes" ?>
47<rfc obsoletes="2616" category="std" x:maturity-level="draft"
48     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
49     xmlns:x='http://purl.org/net/xml2rfc/ext'>
50<front>
51
52  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
53
54  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
55    <organization abbrev="Day Software">Day Software</organization>
56    <address>
57      <postal>
58        <street>23 Corporate Plaza DR, Suite 280</street>
59        <city>Newport Beach</city>
60        <region>CA</region>
61        <code>92660</code>
62        <country>USA</country>
63      </postal>
64      <phone>+1-949-706-5300</phone>
65      <facsimile>+1-949-706-5305</facsimile>
66      <email>fielding@gbiv.com</email>
67      <uri>http://roy.gbiv.com/</uri>
68    </address>
69  </author>
70
71  <author initials="J." surname="Gettys" fullname="Jim Gettys">
72    <organization>One Laptop per Child</organization>
73    <address>
74      <postal>
75        <street>21 Oak Knoll Road</street>
76        <city>Carlisle</city>
77        <region>MA</region>
78        <code>01741</code>
79        <country>USA</country>
80      </postal>
81      <email>jg@laptop.org</email>
82      <uri>http://www.laptop.org/</uri>
83    </address>
84  </author>
85 
86  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
87    <organization abbrev="HP">Hewlett-Packard Company</organization>
88    <address>
89      <postal>
90        <street>HP Labs, Large Scale Systems Group</street>
91        <street>1501 Page Mill Road, MS 1177</street>
92        <city>Palo Alto</city>
93        <region>CA</region>
94        <code>94304</code>
95        <country>USA</country>
96      </postal>
97      <email>JeffMogul@acm.org</email>
98    </address>
99  </author>
100
101  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
102    <organization abbrev="Microsoft">Microsoft Corporation</organization>
103    <address>
104      <postal>
105        <street>1 Microsoft Way</street>
106        <city>Redmond</city>
107        <region>WA</region>
108        <code>98052</code>
109        <country>USA</country>
110      </postal>
111      <email>henrikn@microsoft.com</email>
112    </address>
113  </author>
114
115  <author initials="L." surname="Masinter" fullname="Larry Masinter">
116    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
117    <address>
118      <postal>
119        <street>345 Park Ave</street>
120        <city>San Jose</city>
121        <region>CA</region>
122        <code>95110</code>
123        <country>USA</country>
124      </postal>
125      <email>LMM@acm.org</email>
126      <uri>http://larry.masinter.net/</uri>
127    </address>
128  </author>
129 
130  <author initials="P." surname="Leach" fullname="Paul J. Leach">
131    <organization abbrev="Microsoft">Microsoft Corporation</organization>
132    <address>
133      <postal>
134        <street>1 Microsoft Way</street>
135        <city>Redmond</city>
136        <region>WA</region>
137        <code>98052</code>
138      </postal>
139      <email>paulle@microsoft.com</email>
140    </address>
141  </author>
142   
143  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
145    <address>
146      <postal>
147        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
148        <street>The Stata Center, Building 32</street>
149        <street>32 Vassar Street</street>
150        <city>Cambridge</city>
151        <region>MA</region>
152        <code>02139</code>
153        <country>USA</country>
154      </postal>
155      <email>timbl@w3.org</email>
156      <uri>http://www.w3.org/People/Berners-Lee/</uri>
157    </address>
158  </author>
159
160  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
161    <organization abbrev="W3C">World Wide Web Consortium</organization>
162    <address>
163      <postal>
164        <street>W3C / ERCIM</street>
165        <street>2004, rte des Lucioles</street>
166        <city>Sophia-Antipolis</city>
167        <region>AM</region>
168        <code>06902</code>
169        <country>France</country>
170      </postal>
171      <email>ylafon@w3.org</email>
172      <uri>http://www.raubacapeu.net/people/yves/</uri>
173    </address>
174  </author>
175
176  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
177    <organization abbrev="greenbytes">greenbytes GmbH</organization>
178    <address>
179      <postal>
180        <street>Hafenweg 16</street>
181        <city>Muenster</city><region>NW</region><code>48155</code>
182        <country>Germany</country>
183      </postal>
184      <phone>+49 251 2807760</phone>   
185      <facsimile>+49 251 2807761</facsimile>   
186      <email>julian.reschke@greenbytes.de</email>       
187      <uri>http://greenbytes.de/tech/webdav/</uri>     
188    </address>
189  </author>
190
191  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
192  <workgroup>HTTPbis Working Group</workgroup>
193
194<abstract>
195<t>
196   The Hypertext Transfer Protocol (HTTP) is an application-level
197   protocol for distributed, collaborative, hypermedia information
198   systems. HTTP has been in use by the World Wide Web global information
199   initiative since 1990. This document is Part 3 of the seven-part specification
200   that defines the protocol referred to as "HTTP/1.1" and, taken together,
201   obsoletes RFC 2616.  Part 3 defines HTTP message content,
202   metadata, and content negotiation.
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org). The current issues list is
210    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
211    and related documents (including fancy diffs) can be found at
212    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
213  </t>
214  <t>
215    The changes in this draft are summarized in <xref target="changes.since.06"/>.
216  </t>
217</note>
218</front>
219<middle>
220<section title="Introduction" anchor="introduction">
221<t>
222   This document defines HTTP/1.1 message payloads (a.k.a., content), the
223   associated metadata header fields that define how the payload is intended
224   to be interpreted by a recipient, the request header fields that
225   may influence content selection, and the various selection algorithms
226   that are collectively referred to as HTTP content negotiation.
227</t>
228<t>
229   This document is currently disorganized in order to minimize the changes
230   between drafts and enable reviewers to see the smaller errata changes.
231   The next draft will reorganize the sections to better reflect the content.
232   In particular, the sections on entities will be renamed payload and moved
233   to the first half of the document, while the sections on content negotiation
234   and associated request header fields will be moved to the second half.  The
235   current mess reflects how widely dispersed these topics and associated
236   requirements had become in <xref target="RFC2616"/>.
237</t>
238
239<section title="Requirements" anchor="intro.requirements">
240<t>
241   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
242   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
243   document are to be interpreted as described in <xref target="RFC2119"/>.
244</t>
245<t>
246   An implementation is not compliant if it fails to satisfy one or more
247   of the &MUST; or &REQUIRED; level requirements for the protocols it
248   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
249   level and all the &SHOULD; level requirements for its protocols is said
250   to be "unconditionally compliant"; one that satisfies all the &MUST;
251   level requirements but not all the &SHOULD; level requirements for its
252   protocols is said to be "conditionally compliant."
253</t>
254</section>
255
256<section title="Syntax Notation" anchor="notation">
257  <x:anchor-alias value="ALPHA"/>
258  <x:anchor-alias value="CR"/>
259  <x:anchor-alias value="DIGIT"/>
260  <x:anchor-alias value="LF"/>
261  <x:anchor-alias value="OCTET"/>
262  <x:anchor-alias value="VCHAR"/>
263  <x:anchor-alias value="WSP"/>
264<t>
265  This specification uses the ABNF syntax defined in &notation; (which
266  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
267  <xref target="collected.abnf"/> shows the collected ABNF, with the list
268  rule expanded.
269</t>
270<t>
271  The following core rules are included by
272  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
273  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
274  DIGIT (decimal 0-9), DQUOTE (double quote),
275  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
276  OCTET (any 8-bit sequence of data), SP (space),
277  VCHAR (any visible USASCII character),
278  and WSP (whitespace).
279</t>
280
281<section title="Core Rules" anchor="core.rules">
282  <x:anchor-alias value="quoted-string"/>
283  <x:anchor-alias value="token"/>
284  <x:anchor-alias value="OWS"/>
285<t>
286  The core rules below are defined in &basic-rules;:
287</t>
288<figure><artwork type="abnf2616">
289  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
290  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
291  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
292</artwork></figure>
293</section>
294
295<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
296  <x:anchor-alias value="absolute-URI"/>
297  <x:anchor-alias value="Allow"/>
298  <x:anchor-alias value="Content-Length"/>
299  <x:anchor-alias value="Content-Range"/>
300  <x:anchor-alias value="Expires"/>
301  <x:anchor-alias value="Last-Modified"/>
302  <x:anchor-alias value="message-header"/>
303  <x:anchor-alias value="partial-URI"/>
304  <x:anchor-alias value="qvalue"/>
305<t>
306  The ABNF rules below are defined in other parts:
307</t>
308<figure><!--Part1--><artwork type="abnf2616">
309  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
310  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
311  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
312  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
313  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
314</artwork></figure>
315<figure><!--Part4--><artwork type="abnf2616">
316  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
317</artwork></figure>
318<figure><!--Part5--><artwork type="abnf2616">
319  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
320</artwork></figure>
321<figure><!--Part6--><artwork type="abnf2616">
322  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
323</artwork></figure>
324</section>
325
326</section>
327
328</section>
329
330<section title="Protocol Parameters" anchor="protocol.parameters">
331
332<section title="Character Sets" anchor="character.sets">
333<t>
334   HTTP uses the same definition of the term "character set" as that
335   described for MIME:
336</t>
337<t>
338   The term "character set" is used in this document to refer to a
339   method used with one or more tables to convert a sequence of octets
340   into a sequence of characters. Note that unconditional conversion in
341   the other direction is not required, in that not all characters may
342   be available in a given character set and a character set may provide
343   more than one sequence of octets to represent a particular character.
344   This definition is intended to allow various kinds of character
345   encoding, from simple single-table mappings such as US-ASCII to
346   complex table switching methods such as those that use ISO-2022's
347   techniques. However, the definition associated with a MIME character
348   set name &MUST; fully specify the mapping to be performed from octets
349   to characters. In particular, use of external profiling information
350   to determine the exact mapping is not permitted.
351</t>
352<x:note>
353  <t>
354    <x:h>Note:</x:h> This use of the term "character set" is more commonly
355    referred to as a "character encoding." However, since HTTP and
356    MIME share the same registry, it is important that the terminology
357    also be shared.
358  </t>
359</x:note>
360<t anchor="rule.charset">
361  <x:anchor-alias value="charset"/>
362   HTTP character sets are identified by case-insensitive tokens. The
363   complete set of tokens is defined by the IANA Character Set registry
364   (<eref target="http://www.iana.org/assignments/character-sets"/>).
365</t>
366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
367  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
368</artwork></figure>
369<t>
370   Although HTTP allows an arbitrary token to be used as a charset
371   value, any token that has a predefined value within the IANA
372   Character Set registry &MUST; represent the character set defined
373   by that registry. Applications &SHOULD; limit their use of character
374   sets to those defined by the IANA registry.
375</t>
376<t>
377   HTTP uses charset in two contexts: within an Accept-Charset request
378   header (in which the charset value is an unquoted token) and as the
379   value of a parameter in a Content-Type header (within a request or
380   response), in which case the parameter value of the charset parameter
381   may be quoted.
382</t>
383<t>
384   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
385   <xref target="RFC2277"/>.
386</t>
387
388<section title="Missing Charset" anchor="missing.charset">
389<t>
390   Some HTTP/1.0 software has interpreted a Content-Type header without
391   charset parameter incorrectly to mean "recipient should guess."
392   Senders wishing to defeat this behavior &MAY; include a charset
393   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
394   it is known that it will not confuse the recipient.
395</t>
396<t>
397   Unfortunately, some older HTTP/1.0 clients did not deal properly with
398   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
399   charset label provided by the sender; and those user agents that have
400   a provision to "guess" a charset &MUST; use the charset from the
401   content-type field if they support that charset, rather than the
402   recipient's preference, when initially displaying a document. See
403   <xref target="canonicalization.and.text.defaults"/>.
404</t>
405</section>
406</section>
407
408<section title="Content Codings" anchor="content.codings">
409  <x:anchor-alias value="content-coding"/>
410<t>
411   Content coding values indicate an encoding transformation that has
412   been or can be applied to an entity. Content codings are primarily
413   used to allow a document to be compressed or otherwise usefully
414   transformed without losing the identity of its underlying media type
415   and without loss of information. Frequently, the entity is stored in
416   coded form, transmitted directly, and only decoded by the recipient.
417</t>
418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
419  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
420</artwork></figure>
421<t>
422   All content-coding values are case-insensitive. HTTP/1.1 uses
423   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
424   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
425   describes the content-coding, what is more important is that it
426   indicates what decoding mechanism will be required to remove the
427   encoding.
428</t>
429<t>
430   The Internet Assigned Numbers Authority (IANA) acts as a registry for
431   content-coding value tokens. Initially, the registry contains the
432   following tokens:
433</t>
434<t>
435   gzip<iref item="gzip"/>
436  <list>
437    <t>
438        An encoding format produced by the file compression program
439        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
440        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
441    </t>
442  </list>
443</t>
444<t>
445   compress<iref item="compress"/>
446  <list><t>
447        The encoding format produced by the common UNIX file compression
448        program "compress". This format is an adaptive Lempel-Ziv-Welch
449        coding (LZW).
450</t><t>
451        Use of program names for the identification of encoding formats
452        is not desirable and is discouraged for future encodings. Their
453        use here is representative of historical practice, not good
454        design. For compatibility with previous implementations of HTTP,
455        applications &SHOULD; consider "x-gzip" and "x-compress" to be
456        equivalent to "gzip" and "compress" respectively.
457  </t></list>
458</t>
459<t>
460   deflate<iref item="deflate"/>
461  <list><t>
462        The "zlib" format defined in <xref target="RFC1950"/> in combination with
463        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
464  </t></list>
465</t>
466<t>
467   identity<iref item="identity"/>
468  <list><t>
469        The default (identity) encoding; the use of no transformation
470        whatsoever. This content-coding is used only in the Accept-Encoding
471        header, and &SHOULD-NOT;  be used in the Content-Encoding
472        header.
473  </t></list>
474</t>
475<t>
476   New content-coding value tokens &SHOULD; be registered; to allow
477   interoperability between clients and servers, specifications of the
478   content coding algorithms needed to implement a new value &SHOULD; be
479   publicly available and adequate for independent implementation, and
480   conform to the purpose of content coding defined in this section.
481</t>
482</section>
483
484<section title="Media Types" anchor="media.types">
485  <x:anchor-alias value="media-type"/>
486  <x:anchor-alias value="type"/>
487  <x:anchor-alias value="subtype"/>
488<t>
489   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
490   and Accept (<xref target="header.accept"/>) header fields in order to provide
491   open and extensible data typing and type negotiation.
492</t>
493<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"/>
494  <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> )
495  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
496  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
497</artwork></figure>
498<t anchor="rule.parameter">
499  <x:anchor-alias value="attribute"/>
500  <x:anchor-alias value="parameter"/>
501  <x:anchor-alias value="value"/>
502   Parameters &MAY; follow the type/subtype in the form of attribute/value
503   pairs.
504</t>
505<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"/>
506  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
507  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
508  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
509</artwork></figure>
510<t>
511   The type, subtype, and parameter attribute names are case-insensitive.
512   Parameter values might or might not be case-sensitive, depending on the
513   semantics of the parameter name.  The presence or absence of a parameter might
514   be significant to the processing of a media-type, depending on its
515   definition within the media type registry.
516</t>
517<t>
518   A parameter value that matches the <x:ref>token</x:ref> production may be
519   transmitted as either a token or within a quoted-string. The quoted and
520   unquoted values are equivalent.
521</t>
522<t>
523   Note that some older HTTP applications do not recognize media type
524   parameters. When sending data to older HTTP applications,
525   implementations &SHOULD; only use media type parameters when they are
526   required by that type/subtype definition.
527</t>
528<t>
529   Media-type values are registered with the Internet Assigned Number
530   Authority (IANA). The media type registration process is
531   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
532   discouraged.
533</t>
534
535<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
536<t>
537   Internet media types are registered with a canonical form. An
538   entity-body transferred via HTTP messages &MUST; be represented in the
539   appropriate canonical form prior to its transmission except for
540   "text" types, as defined in the next paragraph.
541</t>
542<t>
543   When in canonical form, media subtypes of the "text" type use CRLF as
544   the text line break. HTTP relaxes this requirement and allows the
545   transport of text media with plain CR or LF alone representing a line
546   break when it is done consistently for an entire entity-body. HTTP
547   applications &MUST; accept CRLF, bare CR, and bare LF as being
548   representative of a line break in text media received via HTTP. In
549   addition, if the text is represented in a character set that does not
550   use octets 13 and 10 for CR and LF respectively, as is the case for
551   some multi-byte character sets, HTTP allows the use of whatever octet
552   sequences are defined by that character set to represent the
553   equivalent of CR and LF for line breaks. This flexibility regarding
554   line breaks applies only to text media in the entity-body; a bare CR
555   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
556   structures (such as header fields and multipart boundaries).
557</t>
558<t>
559   If an entity-body is encoded with a content-coding, the underlying
560   data &MUST; be in a form defined above prior to being encoded.
561</t>
562<t>
563   The "charset" parameter is used with some media types to define the
564   character set (<xref target="character.sets"/>) of the data. When no explicit charset
565   parameter is provided by the sender, media subtypes of the "text"
566   type are defined to have a default charset value of "ISO-8859-1" when
567   received via HTTP. Data in character sets other than "ISO-8859-1" or
568   its subsets &MUST; be labeled with an appropriate charset value. See
569   <xref target="missing.charset"/> for compatibility problems.
570</t>
571</section>
572
573<section title="Multipart Types" anchor="multipart.types">
574<t>
575   MIME provides for a number of "multipart" types -- encapsulations of
576   one or more entities within a single message-body. All multipart
577   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
578   and &MUST; include a boundary parameter as part of the media type
579   value. The message body is itself a protocol element and &MUST;
580   therefore use only CRLF to represent line breaks between body-parts.
581   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
582   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
583   original multipart contains an epilogue). These restrictions exist in
584   order to preserve the self-delimiting nature of a multipart message-body,
585   wherein the "end" of the message-body is indicated by the
586   ending multipart boundary.
587</t>
588<t>
589   In general, HTTP treats a multipart message-body no differently than
590   any other media type: strictly as payload. The one exception is the
591   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
592   (Partial Content) response.
593   <!-- jre: re-insert removed text pointing to caching? -->
594   In all
595   other cases, an HTTP user agent &SHOULD; follow the same or similar
596   behavior as a MIME user agent would upon receipt of a multipart type.
597   The MIME header fields within each body-part of a multipart message-body
598   do not have any significance to HTTP beyond that defined by
599   their MIME semantics.
600</t>
601<t>
602   In general, an HTTP user agent &SHOULD; follow the same or similar
603   behavior as a MIME user agent would upon receipt of a multipart type.
604   If an application receives an unrecognized multipart subtype, the
605   application &MUST; treat it as being equivalent to "multipart/mixed".
606</t>
607<x:note>
608  <t>
609    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
610    for carrying form data suitable for processing via the POST
611    request method, as described in <xref target="RFC2388"/>.
612  </t>
613</x:note>
614</section>
615</section>
616
617<section title="Language Tags" anchor="language.tags">
618  <x:anchor-alias value="language-tag"/>
619  <x:anchor-alias value="primary-tag"/>
620  <x:anchor-alias value="subtag"/>
621<t>
622   A language tag identifies a natural language spoken, written, or
623   otherwise conveyed by human beings for communication of information
624   to other human beings. Computer languages are explicitly excluded.
625   HTTP uses language tags within the Accept-Language and Content-Language
626   fields.
627</t>
628<t>
629   The syntax and registry of HTTP language tags is the same as that
630   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
631   or more parts: A primary language tag and a possibly empty series of
632   subtags:
633</t>
634<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
635  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
636  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
637  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
638</artwork></figure>
639<t>
640   White space is not allowed within the tag and all tags are case-insensitive.
641   The name space of language tags is administered by the
642   IANA. Example tags include:
643</t>
644<figure><artwork type="example">
645  en, en-US, en-cockney, i-cherokee, x-pig-latin
646</artwork></figure>
647<t>
648   where any two-letter primary-tag is an ISO-639 language abbreviation
649   and any two-letter initial subtag is an ISO-3166 country code. (The
650   last three tags above are not registered tags; all but the last are
651   examples of tags which could be registered in future.)
652</t>
653</section>
654</section>
655
656<section title="Entity" anchor="entity">
657<t>
658   Request and Response messages &MAY; transfer an entity if not otherwise
659   restricted by the request method or response status code. An entity
660   consists of entity-header fields and an entity-body, although some
661   responses will only include the entity-headers.
662</t>
663<t>
664   In this section, both sender and recipient refer to either the client
665   or the server, depending on who sends and who receives the entity.
666</t>
667
668<section title="Entity Header Fields" anchor="entity.header.fields">
669  <x:anchor-alias value="entity-header"/>
670  <x:anchor-alias value="extension-header"/>
671<t>
672   Entity-header fields define metainformation about the entity-body or,
673   if no body is present, about the resource identified by the request.
674</t>
675<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
676  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
677                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
678                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
679                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
680                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
681                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
682                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
683                 / <x:ref>Expires</x:ref>                  ; &header-expires;
684                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
685                 / <x:ref>extension-header</x:ref>
686 
687  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
688</artwork></figure>
689<t>
690   The extension-header mechanism allows additional entity-header fields
691   to be defined without changing the protocol, but these fields cannot
692   be assumed to be recognizable by the recipient. Unrecognized header
693   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
694   transparent proxies.
695</t>
696</section>
697
698<section title="Entity Body" anchor="entity.body">
699  <x:anchor-alias value="entity-body"/>
700<t>
701   The entity-body (if any) sent with an HTTP request or response is in
702   a format and encoding defined by the entity-header fields.
703</t>
704<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
705  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
706</artwork></figure>
707<t>
708   An entity-body is only present in a message when a message-body is
709   present, as described in &message-body;. The entity-body is obtained
710   from the message-body by decoding any Transfer-Encoding that might
711   have been applied to ensure safe and proper transfer of the message.
712</t>
713
714<section title="Type" anchor="type">
715<t>
716   When an entity-body is included with a message, the data type of that
717   body is determined via the header fields Content-Type and Content-Encoding.
718   These define a two-layer, ordered encoding model:
719</t>
720<figure><artwork type="example">
721  entity-body := Content-Encoding( Content-Type( data ) )
722</artwork></figure>
723<t>
724   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
725   message containing an entity-body &SHOULD; include a Content-Type header
726   field defining the media type of that body, unless that information is
727   unknown.  If the Content-Type header field is not present, it indicates that
728   the sender does not know the media type of the data; recipients &MAY;
729   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
730   or examine the content to determine its type.
731</t>
732<t>
733   Content-Encoding may be used to indicate any additional content
734   codings applied to the data, usually for the purpose of data
735   compression, that are a property of the requested resource.  There is
736   no default encoding.
737</t>
738<t>
739   Note that neither the interpretation of the data type of a message nor
740   the behaviors caused by it are defined by HTTP; this
741   potentially includes examination of the content to override any
742   indicated type ("sniffing")<iref item="Content Type Sniffing"/>.
743</t>
744</section>
745   
746<section title="Entity Length" anchor="entity.length">
747<t>
748   The entity-length of a message is the length of the message-body
749   before any transfer-codings have been applied. &message-length; defines
750   how the transfer-length of a message-body is determined.
751</t>
752</section>
753</section>
754</section>
755
756<section title="Content Negotiation" anchor="content.negotiation">
757<t>
758   Most HTTP responses include an entity which contains information for
759   interpretation by a human user. Naturally, it is desirable to supply
760   the user with the "best available" entity corresponding to the
761   request. Unfortunately for servers and caches, not all users have the
762   same preferences for what is "best," and not all user agents are
763   equally capable of rendering all entity types. For that reason, HTTP
764   has provisions for several mechanisms for "content negotiation" --
765   the process of selecting the best representation for a given response
766   when there are multiple representations available.
767</t>
768<x:note>
769  <t>
770    <x:h>Note:</x:h> This is not called "format negotiation" because the
771    alternate representations may be of the same media type, but use
772    different capabilities of that type, be in different languages,
773    etc.
774  </t>
775</x:note>
776<t>
777   Any response containing an entity-body &MAY; be subject to negotiation,
778   including error responses.
779</t>
780<t>
781   There are two kinds of content negotiation which are possible in
782   HTTP: server-driven and agent-driven negotiation. These two kinds of
783   negotiation are orthogonal and thus may be used separately or in
784   combination. One method of combination, referred to as transparent
785   negotiation, occurs when a cache uses the agent-driven negotiation
786   information provided by the origin server in order to provide
787   server-driven negotiation for subsequent requests.
788</t>
789
790<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
791<t>
792   If the selection of the best representation for a response is made by
793   an algorithm located at the server, it is called server-driven
794   negotiation. Selection is based on the available representations of
795   the response (the dimensions over which it can vary; e.g. language,
796   content-coding, etc.) and the contents of particular header fields in
797   the request message or on other information pertaining to the request
798   (such as the network address of the client).
799</t>
800<t>
801   Server-driven negotiation is advantageous when the algorithm for
802   selecting from among the available representations is difficult to
803   describe to the user agent, or when the server desires to send its
804   "best guess" to the client along with the first response (hoping to
805   avoid the round-trip delay of a subsequent request if the "best
806   guess" is good enough for the user). In order to improve the server's
807   guess, the user agent &MAY; include request header fields (Accept,
808   Accept-Language, Accept-Encoding, etc.) which describe its
809   preferences for such a response.
810</t>
811<t>
812   Server-driven negotiation has disadvantages:
813  <list style="numbers">
814    <t>
815         It is impossible for the server to accurately determine what
816         might be "best" for any given user, since that would require
817         complete knowledge of both the capabilities of the user agent
818         and the intended use for the response (e.g., does the user want
819         to view it on screen or print it on paper?).
820    </t>
821    <t>
822         Having the user agent describe its capabilities in every
823         request can be both very inefficient (given that only a small
824         percentage of responses have multiple representations) and a
825         potential violation of the user's privacy.
826    </t>
827    <t>
828         It complicates the implementation of an origin server and the
829         algorithms for generating responses to a request.
830    </t>
831    <t>
832         It may limit a public cache's ability to use the same response
833         for multiple user's requests.
834    </t>
835  </list>
836</t>
837<t>
838   HTTP/1.1 includes the following request-header fields for enabling
839   server-driven negotiation through description of user agent
840   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
841   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
842   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
843   origin server is not limited to these dimensions and &MAY; vary the
844   response based on any aspect of the request, including information
845   outside the request-header fields or within extension header fields
846   not defined by this specification.
847</t>
848<t>
849   The Vary header field (&header-vary;) can be used to express the parameters the
850   server uses to select a representation that is subject to server-driven
851   negotiation.
852</t>
853</section>
854
855<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
856<t>
857   With agent-driven negotiation, selection of the best representation
858   for a response is performed by the user agent after receiving an
859   initial response from the origin server. Selection is based on a list
860   of the available representations of the response included within the
861   header fields or entity-body of the initial response, with each
862   representation identified by its own URI. Selection from among the
863   representations may be performed automatically (if the user agent is
864   capable of doing so) or manually by the user selecting from a
865   generated (possibly hypertext) menu.
866</t>
867<t>
868   Agent-driven negotiation is advantageous when the response would vary
869   over commonly-used dimensions (such as type, language, or encoding),
870   when the origin server is unable to determine a user agent's
871   capabilities from examining the request, and generally when public
872   caches are used to distribute server load and reduce network usage.
873</t>
874<t>
875   Agent-driven negotiation suffers from the disadvantage of needing a
876   second request to obtain the best alternate representation. This
877   second request is only efficient when caching is used. In addition,
878   this specification does not define any mechanism for supporting
879   automatic selection, though it also does not prevent any such
880   mechanism from being developed as an extension and used within
881   HTTP/1.1.
882</t>
883<t>
884   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
885   status codes for enabling agent-driven negotiation when the server is
886   unwilling or unable to provide a varying response using server-driven
887   negotiation.
888</t>
889</section>
890
891<section title="Transparent Negotiation" anchor="transparent.negotiation">
892<t>
893   Transparent negotiation is a combination of both server-driven and
894   agent-driven negotiation. When a cache is supplied with a form of the
895   list of available representations of the response (as in agent-driven
896   negotiation) and the dimensions of variance are completely understood
897   by the cache, then the cache becomes capable of performing server-driven
898   negotiation on behalf of the origin server for subsequent
899   requests on that resource.
900</t>
901<t>
902   Transparent negotiation has the advantage of distributing the
903   negotiation work that would otherwise be required of the origin
904   server and also removing the second request delay of agent-driven
905   negotiation when the cache is able to correctly guess the right
906   response.
907</t>
908<t>
909   This specification does not define any mechanism for transparent
910   negotiation, though it also does not prevent any such mechanism from
911   being developed as an extension that could be used within HTTP/1.1.
912</t>
913</section>
914</section>
915
916<section title="Header Field Definitions" anchor="header.fields">
917<t>
918   This section defines the syntax and semantics of HTTP/1.1 header fields
919   related to the payload of messages.
920</t>
921<t>
922   For entity-header fields, both sender and recipient refer to either the
923   client or the server, depending on who sends and who receives the entity.
924</t>
925
926<section title="Accept" anchor="header.accept">
927  <iref primary="true" item="Accept header" x:for-anchor=""/>
928  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
929  <x:anchor-alias value="Accept"/>
930  <x:anchor-alias value="Accept-v"/>
931  <x:anchor-alias value="accept-ext"/>
932  <x:anchor-alias value="accept-params"/>
933  <x:anchor-alias value="media-range"/>
934<t>
935   The request-header field "Accept" can be used to specify certain media
936   types which are acceptable for the response. Accept headers can be
937   used to indicate that the request is specifically limited to a small
938   set of desired types, as in the case of a request for an in-line
939   image.
940</t>
941<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"/>
942  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
943  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
944 
945  <x:ref>media-range</x:ref>    = ( "*/*"
946                   / ( <x:ref>type</x:ref> "/" "*" )
947                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
948                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
949  <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> )
950  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
951                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
952</artwork></figure>
953<t>
954   The asterisk "*" character is used to group media types into ranges,
955   with "*/*" indicating all media types and "type/*" indicating all
956   subtypes of that type. The media-range &MAY; include media type
957   parameters that are applicable to that range.
958</t>
959<t>
960   Each media-range &MAY; be followed by one or more accept-params,
961   beginning with the "q" parameter for indicating a relative quality
962   factor. The first "q" parameter (if any) separates the media-range
963   parameter(s) from the accept-params. Quality factors allow the user
964   or user agent to indicate the relative degree of preference for that
965   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
966   default value is q=1.
967</t>
968<x:note>
969  <t>
970    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
971    parameters from Accept extension parameters is due to historical
972    practice. Although this prevents any media type parameter named
973    "q" from being used with a media range, such an event is believed
974    to be unlikely given the lack of any "q" parameters in the IANA
975    media type registry and the rare usage of any media type
976    parameters in Accept. Future media types are discouraged from
977    registering any parameter named "q".
978  </t>
979</x:note>
980<t>
981   The example
982</t>
983<figure><artwork type="example">
984  Accept: audio/*; q=0.2, audio/basic
985</artwork></figure>
986<t>
987   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
988   type if it is the best available after an 80% mark-down in quality."
989</t>
990<t>
991   If no Accept header field is present, then it is assumed that the
992   client accepts all media types. If an Accept header field is present,
993   and if the server cannot send a response which is acceptable
994   according to the combined Accept field value, then the server &SHOULD;
995   send a 406 (Not Acceptable) response.
996</t>
997<t>
998   A more elaborate example is
999</t>
1000<figure><artwork type="example">
1001  Accept: text/plain; q=0.5, text/html,
1002          text/x-dvi; q=0.8, text/x-c
1003</artwork></figure>
1004<t>
1005   Verbally, this would be interpreted as "text/html and text/x-c are
1006   the preferred media types, but if they do not exist, then send the
1007   text/x-dvi entity, and if that does not exist, send the text/plain
1008   entity."
1009</t>
1010<t>
1011   Media ranges can be overridden by more specific media ranges or
1012   specific media types. If more than one media range applies to a given
1013   type, the most specific reference has precedence. For example,
1014</t>
1015<figure><artwork type="example">
1016  Accept: text/*, text/html, text/html;level=1, */*
1017</artwork></figure>
1018<t>
1019   have the following precedence:
1020   <list style="numbers">
1021    <t>text/html;level=1</t>
1022    <t>text/html</t>
1023    <t>text/*</t>
1024    <t>*/*</t>
1025   </list>
1026</t>
1027<t>
1028   The media type quality factor associated with a given type is
1029   determined by finding the media range with the highest precedence
1030   which matches that type. For example,
1031</t>
1032<figure><artwork type="example">
1033  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1034          text/html;level=2;q=0.4, */*;q=0.5
1035</artwork></figure>
1036<t>
1037   would cause the following values to be associated:
1038</t>
1039<texttable align="left">
1040  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1041  <c>text/html;level=1</c>    <c>1</c>
1042  <c>text/html</c>            <c>0.7</c>
1043  <c>text/plain</c>           <c>0.3</c>
1044  <c>image/jpeg</c>           <c>0.5</c>
1045  <c>text/html;level=2</c>    <c>0.4</c>
1046  <c>text/html;level=3</c>    <c>0.7</c>
1047</texttable>
1048<t>
1049      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1050      values for certain media ranges. However, unless the user agent is
1051      a closed system which cannot interact with other rendering agents,
1052      this default set ought to be configurable by the user.
1053</t>
1054</section>
1055
1056<section title="Accept-Charset" anchor="header.accept-charset">
1057  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1058  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1059  <x:anchor-alias value="Accept-Charset"/>
1060  <x:anchor-alias value="Accept-Charset-v"/>
1061<t>
1062   The request-header field "Accept-Charset" can be used to indicate what
1063   character sets are acceptable for the response. This field allows
1064   clients capable of understanding more comprehensive or special-purpose
1065   character sets to signal that capability to a server which is
1066   capable of representing documents in those character sets.
1067</t>
1068<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1069  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1070          <x:ref>Accept-Charset-v</x:ref>
1071  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1072                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1073</artwork></figure>
1074<t>
1075   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1076   be given an associated quality value which represents the user's
1077   preference for that charset. The default value is q=1. An example is
1078</t>
1079<figure><artwork type="example">
1080  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1081</artwork></figure>
1082<t>
1083   The special value "*", if present in the Accept-Charset field,
1084   matches every character set (including ISO-8859-1) which is not
1085   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1086   in an Accept-Charset field, then all character sets not explicitly
1087   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1088   a quality value of 1 if not explicitly mentioned.
1089</t>
1090<t>
1091   If no Accept-Charset header is present, the default is that any
1092   character set is acceptable. If an Accept-Charset header is present,
1093   and if the server cannot send a response which is acceptable
1094   according to the Accept-Charset header, then the server &SHOULD; send
1095   an error response with the 406 (Not Acceptable) status code, though
1096   the sending of an unacceptable response is also allowed.
1097</t>
1098</section>
1099
1100<section title="Accept-Encoding" anchor="header.accept-encoding">
1101  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1102  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1103  <x:anchor-alias value="Accept-Encoding"/>
1104  <x:anchor-alias value="Accept-Encoding-v"/>
1105  <x:anchor-alias value="codings"/>
1106<t>
1107   The request-header field "Accept-Encoding" is similar to Accept, but
1108   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1109   the response.
1110</t>
1111<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"/>
1112  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1113                     <x:ref>Accept-Encoding-v</x:ref>
1114  <x:ref>Accept-Encoding-v</x:ref>  =
1115                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1116  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1117</artwork></figure>
1118<t>
1119   Each codings value &MAY; be given an associated quality value which
1120   represents the preference for that encoding. The default value is q=1.
1121</t>
1122<t>
1123   Examples of its use are:
1124</t>
1125<figure><artwork type="example">
1126  Accept-Encoding: compress, gzip
1127  Accept-Encoding:
1128  Accept-Encoding: *
1129  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1130  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1131</artwork></figure>
1132<t>
1133   A server tests whether a content-coding is acceptable, according to
1134   an Accept-Encoding field, using these rules:
1135  <list style="numbers">
1136      <t>If the content-coding is one of the content-codings listed in
1137         the Accept-Encoding field, then it is acceptable, unless it is
1138         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1139         qvalue of 0 means "not acceptable.")</t>
1140
1141      <t>The special "*" symbol in an Accept-Encoding field matches any
1142         available content-coding not explicitly listed in the header
1143         field.</t>
1144
1145      <t>If multiple content-codings are acceptable, then the acceptable
1146         content-coding with the highest non-zero qvalue is preferred.</t>
1147
1148      <t>The "identity" content-coding is always acceptable, unless
1149         specifically refused because the Accept-Encoding field includes
1150         "identity;q=0", or because the field includes "*;q=0" and does
1151         not explicitly include the "identity" content-coding. If the
1152         Accept-Encoding field-value is empty, then only the "identity"
1153         encoding is acceptable.</t>
1154  </list>
1155</t>
1156<t>
1157   If an Accept-Encoding field is present in a request, and if the
1158   server cannot send a response which is acceptable according to the
1159   Accept-Encoding header, then the server &SHOULD; send an error response
1160   with the 406 (Not Acceptable) status code.
1161</t>
1162<t>
1163   If no Accept-Encoding field is present in a request, the server &MAY;
1164   assume that the client will accept any content coding. In this case,
1165   if "identity" is one of the available content-codings, then the
1166   server &SHOULD; use the "identity" content-coding, unless it has
1167   additional information that a different content-coding is meaningful
1168   to the client.
1169</t>
1170<x:note>
1171  <t>
1172    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1173    and if the "identity" content-coding is unavailable, then
1174    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1175    "gzip" and "compress") are preferred; some older clients
1176    improperly display messages sent with other content-codings.  The
1177    server might also make this decision based on information about
1178    the particular user-agent or client.
1179  </t>
1180</x:note>
1181<x:note>
1182  <t>
1183    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1184    associated with content-codings. This means that qvalues will not
1185    work and are not permitted with x-gzip or x-compress.
1186  </t>
1187</x:note>
1188</section>
1189
1190<section title="Accept-Language" anchor="header.accept-language">
1191  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1192  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1193  <x:anchor-alias value="Accept-Language"/>
1194  <x:anchor-alias value="Accept-Language-v"/>
1195  <x:anchor-alias value="language-range"/>
1196<t>
1197   The request-header field "Accept-Language" is similar to Accept, but
1198   restricts the set of natural languages that are preferred as a
1199   response to the request. Language tags are defined in <xref target="language.tags"/>.
1200</t>
1201<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"/>
1202  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1203                    <x:ref>Accept-Language-v</x:ref>
1204  <x:ref>Accept-Language-v</x:ref> =
1205                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1206  <x:ref>language-range</x:ref>    =
1207            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1208</artwork></figure>
1209<t>
1210   Each language-range can be given an associated quality value which
1211   represents an estimate of the user's preference for the languages
1212   specified by that range. The quality value defaults to "q=1". For
1213   example,
1214</t>
1215<figure><artwork type="example">
1216  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1217</artwork></figure>
1218<t>
1219   would mean: "I prefer Danish, but will accept British English and
1220   other types of English."
1221</t>
1222<t>
1223   For matching, the "Basic Filtering" matching scheme, defined in
1224   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1225</t>
1226<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1227  <t>
1228     A language range matches a
1229     particular language tag if, in a case-insensitive comparison, it
1230     exactly equals the tag, or if it exactly equals a prefix of the tag
1231     such that the first character following the prefix is "-".
1232  </t>
1233</x:blockquote> 
1234<t>
1235   The special range "*", if present in the Accept-Language field,
1236   matches every tag not matched by any other range present in the
1237   Accept-Language field.
1238</t>
1239<x:note>
1240  <t>
1241    <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1242    language tags are assigned to languages in such a way that it is
1243    always true that if a user understands a language with a certain
1244    tag, then this user will also understand all languages with tags
1245    for which this tag is a prefix. The prefix rule simply allows the
1246    use of prefix tags if this is the case.
1247  </t>
1248</x:note>
1249<t>
1250   The language quality factor assigned to a language-tag by the
1251   Accept-Language field is the quality value of the longest language-range
1252   in the field that matches the language-tag. If no language-range
1253   in the field matches the tag, the language quality factor
1254   assigned is 0. If no Accept-Language header is present in the
1255   request, the server
1256   &SHOULD; assume that all languages are equally acceptable. If an
1257   Accept-Language header is present, then all languages which are
1258   assigned a quality factor greater than 0 are acceptable.
1259</t>
1260<t>
1261   It might be contrary to the privacy expectations of the user to send
1262   an Accept-Language header with the complete linguistic preferences of
1263   the user in every request. For a discussion of this issue, see
1264   <xref target="privacy.issues.connected.to.accept.headers"/>.
1265</t>
1266<t>
1267   As intelligibility is highly dependent on the individual user, it is
1268   recommended that client applications make the choice of linguistic
1269   preference available to the user. If the choice is not made
1270   available, then the Accept-Language header field &MUST-NOT; be given in
1271   the request.
1272</t>
1273<x:note>
1274  <t>
1275    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1276    the user, we remind implementors of  the fact that users are not
1277    familiar with the details of language matching as described above,
1278    and should provide appropriate guidance. As an example, users
1279    might assume that on selecting "en-gb", they will be served any
1280    kind of English document if British English is not available. A
1281    user agent might suggest in such a case to add "en" to get the
1282    best matching behavior.
1283  </t>
1284</x:note>
1285</section>
1286
1287<section title="Content-Encoding" anchor="header.content-encoding">
1288  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1289  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1290  <x:anchor-alias value="Content-Encoding"/>
1291  <x:anchor-alias value="Content-Encoding-v"/>
1292<t>
1293   The entity-header field "Content-Encoding" is used as a modifier to the
1294   media-type. When present, its value indicates what additional content
1295   codings have been applied to the entity-body, and thus what decoding
1296   mechanisms must be applied in order to obtain the media-type
1297   referenced by the Content-Type header field. Content-Encoding is
1298   primarily used to allow a document to be compressed without losing
1299   the identity of its underlying media type.
1300</t>
1301<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1302  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1303  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1304</artwork></figure>
1305<t>
1306   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1307</t>
1308<figure><artwork type="example">
1309  Content-Encoding: gzip
1310</artwork></figure>
1311<t>
1312   The content-coding is a characteristic of the entity identified by
1313   the request-target. Typically, the entity-body is stored with this
1314   encoding and is only decoded before rendering or analogous usage.
1315   However, a non-transparent proxy &MAY; modify the content-coding if the
1316   new coding is known to be acceptable to the recipient, unless the
1317   "no-transform" cache-control directive is present in the message.
1318</t>
1319<t>
1320   If the content-coding of an entity is not "identity", then the
1321   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1322   that lists the non-identity content-coding(s) used.
1323</t>
1324<t>
1325   If the content-coding of an entity in a request message is not
1326   acceptable to the origin server, the server &SHOULD; respond with a
1327   status code of 415 (Unsupported Media Type).
1328</t>
1329<t>
1330   If multiple encodings have been applied to an entity, the content
1331   codings &MUST; be listed in the order in which they were applied.
1332   Additional information about the encoding parameters &MAY; be provided
1333   by other entity-header fields not defined by this specification.
1334</t>
1335</section>
1336
1337<section title="Content-Language" anchor="header.content-language">
1338  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1339  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1340  <x:anchor-alias value="Content-Language"/>
1341  <x:anchor-alias value="Content-Language-v"/>
1342<t>
1343   The entity-header field "Content-Language" describes the natural
1344   language(s) of the intended audience for the enclosed entity. Note
1345   that this might not be equivalent to all the languages used within
1346   the entity-body.
1347</t>
1348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1349  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1350  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1351</artwork></figure>
1352<t>
1353   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1354   Content-Language is to allow a user to identify and differentiate
1355   entities according to the user's own preferred language. Thus, if the
1356   body content is intended only for a Danish-literate audience, the
1357   appropriate field is
1358</t>
1359<figure><artwork type="example">
1360  Content-Language: da
1361</artwork></figure>
1362<t>
1363   If no Content-Language is specified, the default is that the content
1364   is intended for all language audiences. This might mean that the
1365   sender does not consider it to be specific to any natural language,
1366   or that the sender does not know for which language it is intended.
1367</t>
1368<t>
1369   Multiple languages &MAY; be listed for content that is intended for
1370   multiple audiences. For example, a rendition of the "Treaty of
1371   Waitangi," presented simultaneously in the original Maori and English
1372   versions, would call for
1373</t>
1374<figure><artwork type="example">
1375  Content-Language: mi, en
1376</artwork></figure>
1377<t>
1378   However, just because multiple languages are present within an entity
1379   does not mean that it is intended for multiple linguistic audiences.
1380   An example would be a beginner's language primer, such as "A First
1381   Lesson in Latin," which is clearly intended to be used by an
1382   English-literate audience. In this case, the Content-Language would
1383   properly only include "en".
1384</t>
1385<t>
1386   Content-Language &MAY; be applied to any media type -- it is not
1387   limited to textual documents.
1388</t>
1389</section>
1390
1391<section title="Content-Location" anchor="header.content-location">
1392  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1393  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1394  <x:anchor-alias value="Content-Location"/>
1395  <x:anchor-alias value="Content-Location-v"/>
1396<t>
1397   The entity-header field "Content-Location" &MAY; be used to supply the
1398   resource location for the entity enclosed in the message when that
1399   entity is accessible from a location separate from the requested
1400   resource's URI. A server &SHOULD; provide a Content-Location for the
1401   variant corresponding to the response entity; especially in the case
1402   where a resource has multiple entities associated with it, and those
1403   entities actually have separate locations by which they might be
1404   individually accessed, the server &SHOULD; provide a Content-Location
1405   for the particular variant which is returned.
1406</t>
1407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1408  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1409                    <x:ref>Content-Location-v</x:ref>
1410  <x:ref>Content-Location-v</x:ref> =
1411                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1412</artwork></figure>
1413<t>
1414   The value of Content-Location also defines the base URI for the
1415   entity.
1416</t>
1417<t>
1418   The Content-Location value is not a replacement for the original
1419   requested URI; it is only a statement of the location of the resource
1420   corresponding to this particular entity at the time of the request.
1421   Future requests &MAY; specify the Content-Location URI as the request-target
1422   if the desire is to identify the source of that particular
1423   entity.
1424</t>
1425<t>
1426   A cache cannot assume that an entity with a Content-Location
1427   different from the URI used to retrieve it can be used to respond to
1428   later requests on that Content-Location URI. However, the Content-Location
1429   can be used to differentiate between multiple entities
1430   retrieved from a single requested resource, as described in &caching-neg-resp;.
1431</t>
1432<t>
1433   If the Content-Location is a relative URI, the relative URI is
1434   interpreted relative to the request-target.
1435</t>
1436<t>
1437   The meaning of the Content-Location header in requests is
1438   undefined; servers are free to ignore it in those cases.
1439</t>
1440</section>
1441
1442<section title="Content-MD5" anchor="header.content-md5">
1443  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1444  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1445  <x:anchor-alias value="Content-MD5"/>
1446  <x:anchor-alias value="Content-MD5-v"/>
1447<t>
1448   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1449   an MD5 digest of the entity-body for the purpose of providing an
1450   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1451   MIC is good for detecting accidental modification of the entity-body
1452   in transit, but is not proof against malicious attacks.)
1453</t>
1454<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1455  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1456  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1457</artwork></figure>
1458<t>
1459   The Content-MD5 header field &MAY; be generated by an origin server or
1460   client to function as an integrity check of the entity-body. Only
1461   origin servers or clients &MAY; generate the Content-MD5 header field;
1462   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1463   value as an end-to-end integrity check. Any recipient of the entity-body,
1464   including gateways and proxies, &MAY; check that the digest value
1465   in this header field matches that of the entity-body as received.
1466</t>
1467<t>
1468   The MD5 digest is computed based on the content of the entity-body,
1469   including any content-coding that has been applied, but not including
1470   any transfer-encoding applied to the message-body. If the message is
1471   received with a transfer-encoding, that encoding &MUST; be removed
1472   prior to checking the Content-MD5 value against the received entity.
1473</t>
1474<t>
1475   This has the result that the digest is computed on the octets of the
1476   entity-body exactly as, and in the order that, they would be sent if
1477   no transfer-encoding were being applied.
1478</t>
1479<t>
1480   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1481   composite media-types (e.g., multipart/* and message/rfc822), but
1482   this does not change how the digest is computed as defined in the
1483   preceding paragraph.
1484</t>
1485<t>
1486   There are several consequences of this. The entity-body for composite
1487   types &MAY; contain many body-parts, each with its own MIME and HTTP
1488   headers (including Content-MD5, Content-Transfer-Encoding, and
1489   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1490   or Content-Encoding header, it is assumed that the content
1491   of the body-part has had the encoding applied, and the body-part is
1492   included in the Content-MD5 digest as is -- i.e., after the
1493   application. The Transfer-Encoding header field is not allowed within
1494   body-parts.
1495</t>
1496<t>
1497   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1498   computing or checking the digest: the line break convention used in
1499   the text actually transmitted &MUST; be left unaltered when computing
1500   the digest.
1501</t>
1502<x:note>
1503  <t>
1504    <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1505    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1506    in which the application of Content-MD5 to HTTP entity-bodies
1507    differs from its application to MIME entity-bodies. One is that
1508    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1509    does use Transfer-Encoding and Content-Encoding. Another is that
1510    HTTP more frequently uses binary content types than MIME, so it is
1511    worth noting that, in such cases, the byte order used to compute
1512    the digest is the transmission byte order defined for the type.
1513    Lastly, HTTP allows transmission of text types with any of several
1514    line break conventions and not just the canonical form using CRLF.
1515  </t>
1516</x:note>
1517</section>
1518
1519<section title="Content-Type" anchor="header.content-type">
1520  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1521  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1522  <x:anchor-alias value="Content-Type"/>
1523  <x:anchor-alias value="Content-Type-v"/>
1524<t>
1525   The entity-header field "Content-Type" indicates the media type of the
1526   entity-body sent to the recipient or, in the case of the HEAD method,
1527   the media type that would have been sent had the request been a GET.
1528</t>
1529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1530  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1531  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1532</artwork></figure>
1533<t>
1534   Media types are defined in <xref target="media.types"/>. An example of the field is
1535</t>
1536<figure><artwork type="example">
1537  Content-Type: text/html; charset=ISO-8859-4
1538</artwork></figure>
1539<t>
1540   Further discussion of methods for identifying the media type of an
1541   entity is provided in <xref target="type"/>.
1542</t>
1543</section>
1544
1545</section>
1546
1547<section title="IANA Considerations" anchor="IANA.considerations">
1548<section title="Message Header Registration" anchor="message.header.registration">
1549<t>
1550   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1551   with the permanent registrations below (see <xref target="RFC3864"/>):
1552</t>
1553<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1554<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1555   <ttcol>Header Field Name</ttcol>
1556   <ttcol>Protocol</ttcol>
1557   <ttcol>Status</ttcol>
1558   <ttcol>Reference</ttcol>
1559
1560   <c>Accept</c>
1561   <c>http</c>
1562   <c>standard</c>
1563   <c>
1564      <xref target="header.accept"/>
1565   </c>
1566   <c>Accept-Charset</c>
1567   <c>http</c>
1568   <c>standard</c>
1569   <c>
1570      <xref target="header.accept-charset"/>
1571   </c>
1572   <c>Accept-Encoding</c>
1573   <c>http</c>
1574   <c>standard</c>
1575   <c>
1576      <xref target="header.accept-encoding"/>
1577   </c>
1578   <c>Accept-Language</c>
1579   <c>http</c>
1580   <c>standard</c>
1581   <c>
1582      <xref target="header.accept-language"/>
1583   </c>
1584   <c>Content-Disposition</c>
1585   <c>http</c>
1586   <c/>
1587   <c>
1588      <xref target="content-disposition"/>
1589   </c>
1590   <c>Content-Encoding</c>
1591   <c>http</c>
1592   <c>standard</c>
1593   <c>
1594      <xref target="header.content-encoding"/>
1595   </c>
1596   <c>Content-Language</c>
1597   <c>http</c>
1598   <c>standard</c>
1599   <c>
1600      <xref target="header.content-language"/>
1601   </c>
1602   <c>Content-Location</c>
1603   <c>http</c>
1604   <c>standard</c>
1605   <c>
1606      <xref target="header.content-location"/>
1607   </c>
1608   <c>Content-MD5</c>
1609   <c>http</c>
1610   <c>standard</c>
1611   <c>
1612      <xref target="header.content-md5"/>
1613   </c>
1614   <c>Content-Type</c>
1615   <c>http</c>
1616   <c>standard</c>
1617   <c>
1618      <xref target="header.content-type"/>
1619   </c>
1620   <c>MIME-Version</c>
1621   <c>http</c>
1622   <c/>
1623   <c>
1624      <xref target="mime-version"/>
1625   </c>
1626</texttable>
1627<!--(END)-->
1628<t>
1629   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1630</t>
1631</section>
1632</section>
1633
1634<section title="Security Considerations" anchor="security.considerations">
1635<t>
1636   This section is meant to inform application developers, information
1637   providers, and users of the security limitations in HTTP/1.1 as
1638   described by this document. The discussion does not include
1639   definitive solutions to the problems revealed, though it does make
1640   some suggestions for reducing security risks.
1641</t>
1642
1643<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1644<t>
1645   Accept request-headers can reveal information about the user to all
1646   servers which are accessed. The Accept-Language header in particular
1647   can reveal information the user would consider to be of a private
1648   nature, because the understanding of particular languages is often
1649   strongly correlated to the membership of a particular ethnic group.
1650   User agents which offer the option to configure the contents of an
1651   Accept-Language header to be sent in every request are strongly
1652   encouraged to let the configuration process include a message which
1653   makes the user aware of the loss of privacy involved.
1654</t>
1655<t>
1656   An approach that limits the loss of privacy would be for a user agent
1657   to omit the sending of Accept-Language headers by default, and to ask
1658   the user whether or not to start sending Accept-Language headers to a
1659   server if it detects, by looking for any Vary response-header fields
1660   generated by the server, that such sending could improve the quality
1661   of service.
1662</t>
1663<t>
1664   Elaborate user-customized accept header fields sent in every request,
1665   in particular if these include quality values, can be used by servers
1666   as relatively reliable and long-lived user identifiers. Such user
1667   identifiers would allow content providers to do click-trail tracking,
1668   and would allow collaborating content providers to match cross-server
1669   click-trails or form submissions of individual users. Note that for
1670   many users not behind a proxy, the network address of the host
1671   running the user agent will also serve as a long-lived user
1672   identifier. In environments where proxies are used to enhance
1673   privacy, user agents ought to be conservative in offering accept
1674   header configuration options to end users. As an extreme privacy
1675   measure, proxies could filter the accept headers in relayed requests.
1676   General purpose user agents which provide a high degree of header
1677   configurability &SHOULD; warn users about the loss of privacy which can
1678   be involved.
1679</t>
1680</section>
1681
1682<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1683<t>
1684   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1685   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1686   serious security considerations. Content-Disposition is not part of
1687   the HTTP standard, but since it is widely implemented, we are
1688   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1689   for details.
1690</t>
1691</section>
1692
1693</section>
1694
1695<section title="Acknowledgments" anchor="ack">
1696</section>
1697</middle>
1698<back>
1699
1700<references title="Normative References">
1701
1702<reference anchor="ISO-8859-1">
1703  <front>
1704    <title>
1705     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1706    </title>
1707    <author>
1708      <organization>International Organization for Standardization</organization>
1709    </author>
1710    <date year="1998"/>
1711  </front>
1712  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1713</reference>
1714
1715<reference anchor="Part1">
1716  <front>
1717    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1718    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1719      <organization abbrev="Day Software">Day Software</organization>
1720      <address><email>fielding@gbiv.com</email></address>
1721    </author>
1722    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1723      <organization>One Laptop per Child</organization>
1724      <address><email>jg@laptop.org</email></address>
1725    </author>
1726    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1727      <organization abbrev="HP">Hewlett-Packard Company</organization>
1728      <address><email>JeffMogul@acm.org</email></address>
1729    </author>
1730    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1731      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1732      <address><email>henrikn@microsoft.com</email></address>
1733    </author>
1734    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1735      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1736      <address><email>LMM@acm.org</email></address>
1737    </author>
1738    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1739      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1740      <address><email>paulle@microsoft.com</email></address>
1741    </author>
1742    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1743      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1744      <address><email>timbl@w3.org</email></address>
1745    </author>
1746    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1747      <organization abbrev="W3C">World Wide Web Consortium</organization>
1748      <address><email>ylafon@w3.org</email></address>
1749    </author>
1750    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1751      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1752      <address><email>julian.reschke@greenbytes.de</email></address>
1753    </author>
1754    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1755  </front>
1756  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1757  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1758</reference>
1759
1760<reference anchor="Part2">
1761  <front>
1762    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1763    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1764      <organization abbrev="Day Software">Day Software</organization>
1765      <address><email>fielding@gbiv.com</email></address>
1766    </author>
1767    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1768      <organization>One Laptop per Child</organization>
1769      <address><email>jg@laptop.org</email></address>
1770    </author>
1771    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1772      <organization abbrev="HP">Hewlett-Packard Company</organization>
1773      <address><email>JeffMogul@acm.org</email></address>
1774    </author>
1775    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1776      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1777      <address><email>henrikn@microsoft.com</email></address>
1778    </author>
1779    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1780      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1781      <address><email>LMM@acm.org</email></address>
1782    </author>
1783    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1784      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1785      <address><email>paulle@microsoft.com</email></address>
1786    </author>
1787    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1788      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1789      <address><email>timbl@w3.org</email></address>
1790    </author>
1791    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1792      <organization abbrev="W3C">World Wide Web Consortium</organization>
1793      <address><email>ylafon@w3.org</email></address>
1794    </author>
1795    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1796      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1797      <address><email>julian.reschke@greenbytes.de</email></address>
1798    </author>
1799    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1800  </front>
1801  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1802  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1803</reference>
1804
1805<reference anchor="Part4">
1806  <front>
1807    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1808    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1809      <organization abbrev="Day Software">Day Software</organization>
1810      <address><email>fielding@gbiv.com</email></address>
1811    </author>
1812    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1813      <organization>One Laptop per Child</organization>
1814      <address><email>jg@laptop.org</email></address>
1815    </author>
1816    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1817      <organization abbrev="HP">Hewlett-Packard Company</organization>
1818      <address><email>JeffMogul@acm.org</email></address>
1819    </author>
1820    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1821      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1822      <address><email>henrikn@microsoft.com</email></address>
1823    </author>
1824    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1825      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1826      <address><email>LMM@acm.org</email></address>
1827    </author>
1828    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1829      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1830      <address><email>paulle@microsoft.com</email></address>
1831    </author>
1832    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1833      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1834      <address><email>timbl@w3.org</email></address>
1835    </author>
1836    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1837      <organization abbrev="W3C">World Wide Web Consortium</organization>
1838      <address><email>ylafon@w3.org</email></address>
1839    </author>
1840    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1841      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1842      <address><email>julian.reschke@greenbytes.de</email></address>
1843    </author>
1844    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1845  </front>
1846  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1847  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1848</reference>
1849
1850<reference anchor="Part5">
1851  <front>
1852    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1853    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1854      <organization abbrev="Day Software">Day Software</organization>
1855      <address><email>fielding@gbiv.com</email></address>
1856    </author>
1857    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1858      <organization>One Laptop per Child</organization>
1859      <address><email>jg@laptop.org</email></address>
1860    </author>
1861    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1862      <organization abbrev="HP">Hewlett-Packard Company</organization>
1863      <address><email>JeffMogul@acm.org</email></address>
1864    </author>
1865    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1866      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1867      <address><email>henrikn@microsoft.com</email></address>
1868    </author>
1869    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1870      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1871      <address><email>LMM@acm.org</email></address>
1872    </author>
1873    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1874      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1875      <address><email>paulle@microsoft.com</email></address>
1876    </author>
1877    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1878      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1879      <address><email>timbl@w3.org</email></address>
1880    </author>
1881    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1882      <organization abbrev="W3C">World Wide Web Consortium</organization>
1883      <address><email>ylafon@w3.org</email></address>
1884    </author>
1885    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1886      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1887      <address><email>julian.reschke@greenbytes.de</email></address>
1888    </author>
1889    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1890  </front>
1891  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1892  <x:source href="p5-range.xml" basename="p5-range"/>
1893</reference>
1894
1895<reference anchor="Part6">
1896  <front>
1897    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1898    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1899      <organization abbrev="Day Software">Day Software</organization>
1900      <address><email>fielding@gbiv.com</email></address>
1901    </author>
1902    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1903      <organization>One Laptop per Child</organization>
1904      <address><email>jg@laptop.org</email></address>
1905    </author>
1906    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1907      <organization abbrev="HP">Hewlett-Packard Company</organization>
1908      <address><email>JeffMogul@acm.org</email></address>
1909    </author>
1910    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1911      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1912      <address><email>henrikn@microsoft.com</email></address>
1913    </author>
1914    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1915      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1916      <address><email>LMM@acm.org</email></address>
1917    </author>
1918    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1919      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1920      <address><email>paulle@microsoft.com</email></address>
1921    </author>
1922    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1923      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1924      <address><email>timbl@w3.org</email></address>
1925    </author>
1926    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1927      <organization abbrev="W3C">World Wide Web Consortium</organization>
1928      <address><email>ylafon@w3.org</email></address>
1929    </author>
1930    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1931      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1932      <address><email>julian.reschke@greenbytes.de</email></address>
1933    </author>
1934    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1935  </front>
1936  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1937  <x:source href="p6-cache.xml" basename="p6-cache"/>
1938</reference>
1939
1940<reference anchor="RFC1766">
1941  <front>
1942    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1943    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1944      <organization>UNINETT</organization>
1945      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1946    </author>
1947    <date month="March" year="1995"/>
1948  </front>
1949  <seriesInfo name="RFC" value="1766"/>
1950</reference>
1951
1952<reference anchor="RFC1864">
1953  <front>
1954    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1955    <author initials="J." surname="Myers" fullname="John G. Myers">
1956      <organization>Carnegie Mellon University</organization>
1957      <address><email>jgm+@cmu.edu</email></address>
1958    </author>
1959    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1960      <organization>Dover Beach Consulting, Inc.</organization>
1961      <address><email>mrose@dbc.mtview.ca.us</email></address>
1962    </author>
1963    <date month="October" year="1995"/>
1964  </front>
1965  <seriesInfo name="RFC" value="1864"/>
1966</reference>
1967
1968<reference anchor="RFC1950">
1969  <front>
1970    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1971    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1972      <organization>Aladdin Enterprises</organization>
1973      <address><email>ghost@aladdin.com</email></address>
1974    </author>
1975    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1976      <organization/>
1977    </author>
1978    <date month="May" year="1996"/>
1979  </front>
1980  <seriesInfo name="RFC" value="1950"/>
1981  <annotation>
1982    RFC 1950 is an Informational RFC, thus it may be less stable than
1983    this specification. On the other hand, this downward reference was
1984    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1985    therefore it is unlikely to cause problems in practice. See also
1986    <xref target="BCP97"/>.
1987  </annotation>
1988</reference>
1989
1990<reference anchor="RFC1951">
1991  <front>
1992    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1993    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1994      <organization>Aladdin Enterprises</organization>
1995      <address><email>ghost@aladdin.com</email></address>
1996    </author>
1997    <date month="May" year="1996"/>
1998  </front>
1999  <seriesInfo name="RFC" value="1951"/>
2000  <annotation>
2001    RFC 1951 is an Informational RFC, thus it may be less stable than
2002    this specification. On the other hand, this downward reference was
2003    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2004    therefore it is unlikely to cause problems in practice. See also
2005    <xref target="BCP97"/>.
2006  </annotation>
2007</reference>
2008
2009<reference anchor="RFC1952">
2010  <front>
2011    <title>GZIP file format specification version 4.3</title>
2012    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2013      <organization>Aladdin Enterprises</organization>
2014      <address><email>ghost@aladdin.com</email></address>
2015    </author>
2016    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2017      <organization/>
2018      <address><email>gzip@prep.ai.mit.edu</email></address>
2019    </author>
2020    <author initials="M." surname="Adler" fullname="Mark Adler">
2021      <organization/>
2022      <address><email>madler@alumni.caltech.edu</email></address>
2023    </author>
2024    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2025      <organization/>
2026      <address><email>ghost@aladdin.com</email></address>
2027    </author>
2028    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2029      <organization/>
2030      <address><email>randeg@alumni.rpi.edu</email></address>
2031    </author>
2032    <date month="May" year="1996"/>
2033  </front>
2034  <seriesInfo name="RFC" value="1952"/>
2035  <annotation>
2036    RFC 1952 is an Informational RFC, thus it may be less stable than
2037    this specification. On the other hand, this downward reference was
2038    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2039    therefore it is unlikely to cause problems in practice. See also
2040    <xref target="BCP97"/>.
2041  </annotation>
2042</reference>
2043
2044<reference anchor="RFC2045">
2045  <front>
2046    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2047    <author initials="N." surname="Freed" fullname="Ned Freed">
2048      <organization>Innosoft International, Inc.</organization>
2049      <address><email>ned@innosoft.com</email></address>
2050    </author>
2051    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2052      <organization>First Virtual Holdings</organization>
2053      <address><email>nsb@nsb.fv.com</email></address>
2054    </author>
2055    <date month="November" year="1996"/>
2056  </front>
2057  <seriesInfo name="RFC" value="2045"/>
2058</reference>
2059
2060<reference anchor="RFC2046">
2061  <front>
2062    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2063    <author initials="N." surname="Freed" fullname="Ned Freed">
2064      <organization>Innosoft International, Inc.</organization>
2065      <address><email>ned@innosoft.com</email></address>
2066    </author>
2067    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2068      <organization>First Virtual Holdings</organization>
2069      <address><email>nsb@nsb.fv.com</email></address>
2070    </author>
2071    <date month="November" year="1996"/>
2072  </front>
2073  <seriesInfo name="RFC" value="2046"/>
2074</reference>
2075
2076<reference anchor="RFC2119">
2077  <front>
2078    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2079    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2080      <organization>Harvard University</organization>
2081      <address><email>sob@harvard.edu</email></address>
2082    </author>
2083    <date month="March" year="1997"/>
2084  </front>
2085  <seriesInfo name="BCP" value="14"/>
2086  <seriesInfo name="RFC" value="2119"/>
2087</reference>
2088
2089<reference anchor='RFC4647'>
2090  <front>
2091    <title>Matching of Language Tags</title>
2092    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2093      <organization>Yahoo! Inc.</organization>
2094      <address><email>addison@inter-locale.com</email></address>
2095    </author>
2096    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2097      <organization>Google</organization>
2098      <address><email>mark.davis@macchiato.com</email></address>
2099    </author>
2100    <date year='2006' month='September' />
2101  </front>
2102  <seriesInfo name='BCP' value='47' />
2103  <seriesInfo name='RFC' value='4647' />
2104</reference>
2105
2106<reference anchor="RFC5234">
2107  <front>
2108    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2109    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2110      <organization>Brandenburg InternetWorking</organization>
2111      <address>
2112      <postal>
2113      <street>675 Spruce Dr.</street>
2114      <city>Sunnyvale</city>
2115      <region>CA</region>
2116      <code>94086</code>
2117      <country>US</country></postal>
2118      <phone>+1.408.246.8253</phone>
2119      <email>dcrocker@bbiw.net</email></address> 
2120    </author>
2121    <author initials="P." surname="Overell" fullname="Paul Overell">
2122      <organization>THUS plc.</organization>
2123      <address>
2124      <postal>
2125      <street>1/2 Berkeley Square</street>
2126      <street>99 Berkely Street</street>
2127      <city>Glasgow</city>
2128      <code>G3 7HR</code>
2129      <country>UK</country></postal>
2130      <email>paul.overell@thus.net</email></address>
2131    </author>
2132    <date month="January" year="2008"/>
2133  </front>
2134  <seriesInfo name="STD" value="68"/>
2135  <seriesInfo name="RFC" value="5234"/>
2136</reference>
2137
2138</references>
2139
2140<references title="Informative References">
2141
2142<reference anchor="RFC1945">
2143  <front>
2144    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2145    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2146      <organization>MIT, Laboratory for Computer Science</organization>
2147      <address><email>timbl@w3.org</email></address>
2148    </author>
2149    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2150      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2151      <address><email>fielding@ics.uci.edu</email></address>
2152    </author>
2153    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2154      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2155      <address><email>frystyk@w3.org</email></address>
2156    </author>
2157    <date month="May" year="1996"/>
2158  </front>
2159  <seriesInfo name="RFC" value="1945"/>
2160</reference>
2161
2162<reference anchor="RFC2049">
2163  <front>
2164    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2165    <author initials="N." surname="Freed" fullname="Ned Freed">
2166      <organization>Innosoft International, Inc.</organization>
2167      <address><email>ned@innosoft.com</email></address>
2168    </author>
2169    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2170      <organization>First Virtual Holdings</organization>
2171      <address><email>nsb@nsb.fv.com</email></address>
2172    </author>
2173    <date month="November" year="1996"/>
2174  </front>
2175  <seriesInfo name="RFC" value="2049"/>
2176</reference>
2177
2178<reference anchor="RFC2068">
2179  <front>
2180    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2181    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2182      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2183      <address><email>fielding@ics.uci.edu</email></address>
2184    </author>
2185    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2186      <organization>MIT Laboratory for Computer Science</organization>
2187      <address><email>jg@w3.org</email></address>
2188    </author>
2189    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2190      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2191      <address><email>mogul@wrl.dec.com</email></address>
2192    </author>
2193    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2194      <organization>MIT Laboratory for Computer Science</organization>
2195      <address><email>frystyk@w3.org</email></address>
2196    </author>
2197    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2198      <organization>MIT Laboratory for Computer Science</organization>
2199      <address><email>timbl@w3.org</email></address>
2200    </author>
2201    <date month="January" year="1997"/>
2202  </front>
2203  <seriesInfo name="RFC" value="2068"/>
2204</reference>
2205
2206<reference anchor="RFC2076">
2207  <front>
2208    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2209    <author initials="J." surname="Palme" fullname="Jacob Palme">
2210      <organization>Stockholm University/KTH</organization>
2211      <address><email>jpalme@dsv.su.se</email></address>
2212    </author>
2213    <date month="February" year="1997"/>
2214  </front>
2215  <seriesInfo name="RFC" value="2076"/>
2216</reference>
2217
2218<reference anchor="RFC2183">
2219  <front>
2220    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2221    <author initials="R." surname="Troost" fullname="Rens Troost">
2222      <organization>New Century Systems</organization>
2223      <address><email>rens@century.com</email></address>
2224    </author>
2225    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2226      <organization>QUALCOMM Incorporated</organization>
2227      <address><email>sdorner@qualcomm.com</email></address>
2228    </author>
2229    <author initials="K." surname="Moore" fullname="Keith Moore">
2230      <organization>Department of Computer Science</organization>
2231      <address><email>moore@cs.utk.edu</email></address>
2232    </author>
2233    <date month="August" year="1997"/>
2234  </front>
2235  <seriesInfo name="RFC" value="2183"/>
2236</reference>
2237
2238<reference anchor="RFC2277">
2239  <front>
2240    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2241    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2242      <organization>UNINETT</organization>
2243      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2244    </author>
2245    <date month="January" year="1998"/>
2246  </front>
2247  <seriesInfo name="BCP" value="18"/>
2248  <seriesInfo name="RFC" value="2277"/>
2249</reference>
2250
2251<reference anchor="RFC2388">
2252  <front>
2253    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2254    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2255      <organization>Xerox Palo Alto Research Center</organization>
2256      <address><email>masinter@parc.xerox.com</email></address>
2257    </author>
2258    <date year="1998" month="August"/>
2259  </front>
2260  <seriesInfo name="RFC" value="2388"/>
2261</reference>
2262
2263<reference anchor="RFC2557">
2264  <front>
2265    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2266    <author initials="F." surname="Palme" fullname="Jacob Palme">
2267      <organization>Stockholm University and KTH</organization>
2268      <address><email>jpalme@dsv.su.se</email></address>
2269    </author>
2270    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2271      <organization>Microsoft Corporation</organization>
2272      <address><email>alexhop@microsoft.com</email></address>
2273    </author>
2274    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2275      <organization>Lotus Development Corporation</organization>
2276      <address><email>Shelness@lotus.com</email></address>
2277    </author>
2278    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2279      <organization/>
2280      <address><email>stef@nma.com</email></address>
2281    </author>
2282    <date year="1999" month="March"/>
2283  </front>
2284  <seriesInfo name="RFC" value="2557"/>
2285</reference>
2286
2287<reference anchor="RFC2616">
2288  <front>
2289    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2290    <author initials="R." surname="Fielding" fullname="R. Fielding">
2291      <organization>University of California, Irvine</organization>
2292      <address><email>fielding@ics.uci.edu</email></address>
2293    </author>
2294    <author initials="J." surname="Gettys" fullname="J. Gettys">
2295      <organization>W3C</organization>
2296      <address><email>jg@w3.org</email></address>
2297    </author>
2298    <author initials="J." surname="Mogul" fullname="J. Mogul">
2299      <organization>Compaq Computer Corporation</organization>
2300      <address><email>mogul@wrl.dec.com</email></address>
2301    </author>
2302    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2303      <organization>MIT Laboratory for Computer Science</organization>
2304      <address><email>frystyk@w3.org</email></address>
2305    </author>
2306    <author initials="L." surname="Masinter" fullname="L. Masinter">
2307      <organization>Xerox Corporation</organization>
2308      <address><email>masinter@parc.xerox.com</email></address>
2309    </author>
2310    <author initials="P." surname="Leach" fullname="P. Leach">
2311      <organization>Microsoft Corporation</organization>
2312      <address><email>paulle@microsoft.com</email></address>
2313    </author>
2314    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2315      <organization>W3C</organization>
2316      <address><email>timbl@w3.org</email></address>
2317    </author>
2318    <date month="June" year="1999"/>
2319  </front>
2320  <seriesInfo name="RFC" value="2616"/>
2321</reference>
2322
2323<reference anchor="RFC3629">
2324  <front>
2325    <title>UTF-8, a transformation format of ISO 10646</title>
2326    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2327      <organization>Alis Technologies</organization>
2328      <address><email>fyergeau@alis.com</email></address>
2329    </author>
2330    <date month="November" year="2003"/>
2331  </front>
2332  <seriesInfo name="RFC" value="3629"/>
2333  <seriesInfo name="STD" value="63"/>
2334</reference>
2335
2336<reference anchor='RFC3864'>
2337  <front>
2338    <title>Registration Procedures for Message Header Fields</title>
2339    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2340      <organization>Nine by Nine</organization>
2341      <address><email>GK-IETF@ninebynine.org</email></address>
2342    </author>
2343    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2344      <organization>BEA Systems</organization>
2345      <address><email>mnot@pobox.com</email></address>
2346    </author>
2347    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2348      <organization>HP Labs</organization>
2349      <address><email>JeffMogul@acm.org</email></address>
2350    </author>
2351    <date year='2004' month='September' />
2352  </front>
2353  <seriesInfo name='BCP' value='90' />
2354  <seriesInfo name='RFC' value='3864' />
2355</reference>
2356
2357<reference anchor="RFC4288">
2358  <front>
2359    <title>Media Type Specifications and Registration Procedures</title>
2360    <author initials="N." surname="Freed" fullname="N. Freed">
2361      <organization>Sun Microsystems</organization>
2362      <address>
2363        <email>ned.freed@mrochek.com</email>
2364      </address>
2365    </author>
2366    <author initials="J." surname="Klensin" fullname="J. Klensin">
2367      <organization/>
2368      <address>
2369        <email>klensin+ietf@jck.com</email>
2370      </address>
2371    </author>
2372    <date year="2005" month="December"/>
2373  </front>
2374  <seriesInfo name="BCP" value="13"/>
2375  <seriesInfo name="RFC" value="4288"/>
2376</reference>
2377
2378<reference anchor="RFC5322">
2379  <front>
2380    <title>Internet Message Format</title>
2381    <author initials="P." surname="Resnick" fullname="P. Resnick">
2382      <organization>Qualcomm Incorporated</organization>
2383    </author>
2384    <date year="2008" month="October"/>
2385  </front> 
2386  <seriesInfo name="RFC" value="5322"/>
2387</reference>
2388
2389<reference anchor='BCP97'>
2390  <front>
2391    <title>Handling Normative References to Standards-Track Documents</title>
2392    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2393      <organization />
2394      <address>
2395        <email>klensin+ietf@jck.com</email>
2396      </address>
2397    </author>
2398    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2399      <organization>MIT</organization>
2400      <address>
2401        <email>hartmans-ietf@mit.edu</email>
2402      </address>
2403    </author>
2404    <date year='2007' month='June' />
2405  </front>
2406  <seriesInfo name='BCP' value='97' />
2407  <seriesInfo name='RFC' value='4897' />
2408</reference>
2409
2410
2411</references>
2412
2413<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2414<t>
2415   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
2416   allow entities to be transmitted in an open variety of
2417   representations and with extensible mechanisms. However, RFC 2045
2418   discusses mail, and HTTP has a few features that are different from
2419   those described in RFC 2045. These differences were carefully chosen
2420   to optimize performance over binary connections, to allow greater
2421   freedom in the use of new media types, to make date comparisons
2422   easier, and to acknowledge the practice of some early HTTP servers
2423   and clients.
2424</t>
2425<t>
2426   This appendix describes specific areas where HTTP differs from RFC
2427   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2428   aware of these differences and provide the appropriate conversions
2429   where necessary. Proxies and gateways from MIME environments to HTTP
2430   also need to be aware of the differences because some conversions
2431   might be required.
2432</t>
2433
2434<section title="MIME-Version" anchor="mime-version">
2435  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2436  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2437  <x:anchor-alias value="MIME-Version"/>
2438  <x:anchor-alias value="MIME-Version-v"/>
2439<t>
2440   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2441   include a single MIME-Version general-header field to indicate what
2442   version of the MIME protocol was used to construct the message. Use
2443   of the MIME-Version header field indicates that the message is in
2444   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2445   Proxies/gateways are responsible for ensuring full compliance (where
2446   possible) when exporting HTTP messages to strict MIME environments.
2447</t>
2448<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2449  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2450  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2451</artwork></figure>
2452<t>
2453   MIME version "1.0" is the default for use in HTTP/1.1. However,
2454   HTTP/1.1 message parsing and semantics are defined by this document
2455   and not the MIME specification.
2456</t>
2457</section>
2458
2459<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2460<t>
2461   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2462   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2463   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2464   allowed for subtypes of the "text" media type when transmitted over
2465   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2466   line breaks as CRLF and forbids the use of CR or LF outside of line
2467   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2468   line break within text content when a message is transmitted over
2469   HTTP.
2470</t>
2471<t>
2472   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2473   environment &SHOULD; translate all line breaks within the text media
2474   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2475   canonical form of CRLF. Note, however, that this might be complicated
2476   by the presence of a Content-Encoding and by the fact that HTTP
2477   allows the use of some character sets which do not use octets 13 and
2478   10 to represent CR and LF, as is the case for some multi-byte
2479   character sets.
2480</t>
2481<t>
2482   Implementors should note that conversion will break any cryptographic
2483   checksums applied to the original content unless the original content
2484   is already in canonical form. Therefore, the canonical form is
2485   recommended for any content that uses such checksums in HTTP.
2486</t>
2487</section>
2488
2489
2490<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2491<t>
2492   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2493   simplify the process of date comparison. Proxies and gateways from
2494   other protocols &SHOULD; ensure that any Date header field present in a
2495   message conforms to one of the HTTP/1.1 formats and rewrite the date
2496   if necessary.
2497</t>
2498</section>
2499
2500<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2501<t>
2502   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2503   Content-Encoding header field. Since this acts as a modifier on the
2504   media type, proxies and gateways from HTTP to MIME-compliant
2505   protocols &MUST; either change the value of the Content-Type header
2506   field or decode the entity-body before forwarding the message. (Some
2507   experimental applications of Content-Type for Internet mail have used
2508   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2509   a function equivalent to Content-Encoding. However, this parameter is
2510   not part of RFC 2045).
2511</t>
2512</section>
2513
2514<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2515<t>
2516   HTTP does not use the Content-Transfer-Encoding field of RFC
2517   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2518   remove any Content-Transfer-Encoding
2519   prior to delivering the response message to an HTTP client.
2520</t>
2521<t>
2522   Proxies and gateways from HTTP to MIME-compliant protocols are
2523   responsible for ensuring that the message is in the correct format
2524   and encoding for safe transport on that protocol, where "safe
2525   transport" is defined by the limitations of the protocol being used.
2526   Such a proxy or gateway &SHOULD; label the data with an appropriate
2527   Content-Transfer-Encoding if doing so will improve the likelihood of
2528   safe transport over the destination protocol.
2529</t>
2530</section>
2531
2532<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2533<t>
2534   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2535   Proxies/gateways &MUST; remove any transfer-coding prior to
2536   forwarding a message via a MIME-compliant protocol.
2537</t>
2538</section>
2539
2540<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2541<t>
2542   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2543   need to be aware of MIME line length limitations. Since HTTP does not
2544   have this limitation, HTTP does not fold long lines. MHTML messages
2545   being transported by HTTP follow all conventions of MHTML, including
2546   line length limitations and folding, canonicalization, etc., since
2547   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2548   does not interpret the content or any MIME header lines that might be
2549   contained therein.
2550</t>
2551</section>
2552</section>
2553
2554<section title="Additional Features" anchor="additional.features">
2555<t>
2556   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2557   existing HTTP implementations, but not consistently and correctly
2558   across most HTTP/1.1 applications. Implementors are advised to be
2559   aware of these features, but cannot rely upon their presence in, or
2560   interoperability with, other HTTP/1.1 applications. Some of these
2561   describe proposed experimental features, and some describe features
2562   that experimental deployment found lacking that are now addressed in
2563   the base HTTP/1.1 specification.
2564</t>
2565<t>
2566   A number of other headers, such as Content-Disposition and Title,
2567   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2568</t>
2569
2570<section title="Content-Disposition" anchor="content-disposition">
2571<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2572<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2573  <x:anchor-alias value="content-disposition"/>
2574  <x:anchor-alias value="content-disposition-v"/>
2575  <x:anchor-alias value="disposition-type"/>
2576  <x:anchor-alias value="disposition-parm"/>
2577  <x:anchor-alias value="disp-extension-parm"/>
2578  <x:anchor-alias value="disp-extension-token"/>
2579  <x:anchor-alias value="filename-parm"/>
2580<t>
2581   The Content-Disposition response-header field has been proposed as a
2582   means for the origin server to suggest a default filename if the user
2583   requests that the content is saved to a file. This usage is derived
2584   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2585</t>
2586<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"/>
2587  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2588                        <x:ref>content-disposition-v</x:ref>
2589  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2590                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2591  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2592  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2593  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2594  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2595  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2596</artwork></figure>
2597<t>
2598   An example is
2599</t>
2600<figure><artwork type="example">
2601  Content-Disposition: attachment; filename="fname.ext"
2602</artwork></figure>
2603<t>
2604   The receiving user agent &SHOULD-NOT;  respect any directory path
2605   information present in the filename-parm parameter, which is the only
2606   parameter believed to apply to HTTP implementations at this time. The
2607   filename &SHOULD; be treated as a terminal component only.
2608</t>
2609<t>
2610   If this header is used in a response with the application/octet-stream
2611   content-type, the implied suggestion is that the user agent
2612   should not display the response, but directly enter a `save response
2613   as...' dialog.
2614</t>
2615<t>
2616   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2617</t>
2618</section>
2619</section>
2620
2621<section title="Compatibility with Previous Versions" anchor="compatibility">
2622<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2623<t>
2624   Transfer-coding and message lengths all interact in ways that
2625   required fixing exactly when chunked encoding is used (to allow for
2626   transfer encoding that may not be self delimiting); it was important
2627   to straighten out exactly how message lengths are computed.
2628   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2629   <xref target="Part5"/> and <xref target="Part6"/>).
2630</t>
2631<t>
2632   Charset wildcarding is introduced to avoid explosion of character set
2633   names in accept headers. (<xref target="header.accept-charset"/>)
2634</t>
2635<t>
2636   Content-Base was deleted from the specification: it was not
2637   implemented widely, and there is no simple, safe way to introduce it
2638   without a robust extension mechanism. In addition, it is used in a
2639   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2640</t>
2641<t>
2642   A content-coding of "identity" was introduced, to solve problems
2643   discovered in caching. (<xref target="content.codings"/>)
2644</t>
2645<t>
2646   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
2647   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
2648   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2649</t>
2650</section>
2651
2652<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2653<t>
2654  Clarify contexts that charset is used in.
2655  (<xref target="character.sets"/>)
2656</t>
2657<t>
2658  Remove reference to non-existant identity transfer-coding value tokens.
2659  (<xref target="no.content-transfer-encoding"/>)
2660</t>
2661</section>
2662
2663</section>
2664
2665<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2666<figure>
2667<artwork type="abnf" name="p3-payload.parsed-abnf">
2668<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2669<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2670<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2671 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2672 qvalue ] ] )
2673<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2674<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2675 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2676<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2677<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2678 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2679 ] )
2680<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2681 OWS media-range [ accept-params ] ] ) ]
2682
2683<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2684<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2685 content-coding ] )
2686<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2687<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2688 language-tag ] )
2689<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 8.2&gt;
2690<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2691<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2692<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2693<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2694<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2695<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2696<x:ref>Content-Type-v</x:ref> = media-type
2697
2698<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2699
2700<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2701
2702<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2703<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2704
2705<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2706
2707<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
2708<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2709<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2710<x:ref>attribute</x:ref> = token
2711
2712<x:ref>charset</x:ref> = token
2713<x:ref>codings</x:ref> = ( content-coding / "*" )
2714<x:ref>content-coding</x:ref> = token
2715<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2716 content-disposition-v
2717<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2718 disposition-parm )
2719
2720<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2721<x:ref>disp-extension-token</x:ref> = token
2722<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2723<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2724
2725<x:ref>entity-body</x:ref> = *OCTET
2726<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2727 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2728 Expires / Last-Modified / extension-header
2729<x:ref>extension-header</x:ref> = message-header
2730
2731<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2732
2733<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2734<x:ref>language-tag</x:ref> = primary-tag *( "-" subtag )
2735
2736<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2737 ";" OWS parameter )
2738<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2739<x:ref>message-header</x:ref> = &lt;message-header, defined in [Part1], Section 4.2&gt;
2740
2741<x:ref>parameter</x:ref> = attribute "=" value
2742<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
2743<x:ref>primary-tag</x:ref> = 1*8ALPHA
2744
2745<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2746<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 3.5&gt;
2747
2748<x:ref>subtag</x:ref> = 1*8ALPHA
2749<x:ref>subtype</x:ref> = token
2750
2751<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2752<x:ref>type</x:ref> = token
2753
2754<x:ref>value</x:ref> = token / quoted-string
2755
2756
2757</artwork>
2758</figure>
2759<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2760; Accept defined but not used
2761; Accept-Charset defined but not used
2762; Accept-Encoding defined but not used
2763; Accept-Language defined but not used
2764; MIME-Version defined but not used
2765; content-disposition defined but not used
2766; entity-body defined but not used
2767; entity-header defined but not used
2768</artwork></figure></section>
2769
2770<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2771
2772<section title="Since RFC2616">
2773<t>
2774  Extracted relevant partitions from <xref target="RFC2616"/>.
2775</t>
2776</section>
2777
2778<section title="Since draft-ietf-httpbis-p3-payload-00">
2779<t>
2780  Closed issues:
2781  <list style="symbols"> 
2782    <t>
2783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2784      "Media Type Registrations"
2785      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2786    </t>
2787    <t>
2788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2789      "Clarification regarding quoting of charset values"
2790      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2791    </t>
2792    <t>
2793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2794      "Remove 'identity' token references"
2795      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2796    </t>
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2799      "Accept-Encoding BNF"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2803      "Normative and Informative references"
2804    </t>
2805    <t>
2806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2807      "RFC1700 references"
2808    </t>
2809    <t>
2810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2811      "Updating to RFC4288"
2812    </t>
2813    <t>
2814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2815      "Informative references"
2816    </t>
2817    <t>
2818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2819      "ISO-8859-1 Reference"
2820    </t>
2821    <t>
2822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2823      "Encoding References Normative"
2824    </t>
2825    <t>
2826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2827      "Normative up-to-date references"
2828    </t>
2829  </list>
2830</t>
2831</section>
2832
2833<section title="Since draft-ietf-httpbis-p3-payload-01">
2834<t>
2835  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2836  <list style="symbols"> 
2837    <t>
2838      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2839    </t>
2840  </list>
2841</t>
2842</section>
2843
2844<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2845<t>
2846  Closed issues:
2847  <list style="symbols"> 
2848    <t>
2849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2850      "Quoting Charsets"
2851    </t>
2852    <t>
2853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2854      "Classification for Allow header"
2855    </t>
2856    <t>
2857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2858      "missing default for qvalue in description of Accept-Encoding"
2859    </t>
2860  </list>
2861</t>
2862<t>
2863  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2864  <list style="symbols"> 
2865    <t>
2866      Reference RFC 3984, and update header registrations for headers defined
2867      in this document.
2868    </t>
2869  </list>
2870</t>
2871</section>
2872
2873<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2874<t>
2875  Closed issues:
2876  <list style="symbols"> 
2877    <t>
2878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2879      "Quoting Charsets"
2880    </t>
2881    <t>
2882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2883      "language tag matching (Accept-Language) vs RFC4647"
2884    </t>
2885    <t>
2886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2887      "RFC 1806 has been replaced by RFC2183"
2888    </t>
2889  </list>
2890</t>
2891<t>
2892  Other changes:
2893  <list style="symbols"> 
2894    <t>
2895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2896      "Encoding References Normative" -- rephrase the annotation and reference
2897      <xref target="BCP97"/>.
2898    </t>
2899  </list>
2900</t>
2901 </section>
2902
2903<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2904<t>
2905  Closed issues:
2906  <list style="symbols"> 
2907    <t>
2908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2909      "RFC 2822 is updated by RFC 5322"
2910    </t>
2911  </list>
2912</t>
2913<t>
2914  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2915  <list style="symbols"> 
2916    <t>
2917      Use "/" instead of "|" for alternatives.
2918    </t>
2919    <t>
2920      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2921      whitespace ("OWS") and required whitespace ("RWS").
2922    </t>
2923    <t>
2924      Rewrite ABNFs to spell out whitespace rules, factor out
2925      header value format definitions.
2926    </t>
2927  </list>
2928</t>
2929</section>
2930
2931<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2932<t>
2933  Closed issues:
2934  <list style="symbols"> 
2935    <t>
2936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2937      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2938    </t>
2939  </list>
2940</t>
2941<t>
2942  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2943  <list style="symbols"> 
2944    <t>
2945      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2946    </t>
2947  </list>
2948</t>
2949<t>
2950  Other changes:
2951  <list style="symbols"> 
2952    <t>
2953      Move definition of quality values into Part 1.
2954    </t>
2955  </list>
2956</t>
2957</section>
2958
2959<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2960<t>
2961  Closed issues:
2962  <list style="symbols"> 
2963    <t>
2964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2965      "Content-Location isn't special"
2966    </t>
2967    <t>
2968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2969      "Content Sniffing"
2970    </t>
2971  </list>
2972</t>
2973</section>
2974
2975</section>
2976
2977</back>
2978</rfc>
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