source: draft-ietf-httpbis/latest/p3-payload.xml @ 867

Last change on this file since 867 was 867, checked in by fielding@…, 9 years ago

(editorial) replace "metainformation" with more common "metadata"

  • Property svn:eol-style set to native
File size: 135.8 KB
[29]1<?xml version="1.0" encoding="utf-8"?>
[101]2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
[8]3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
[29]14  <!ENTITY ID-VERSION "latest">
[832]15  <!ENTITY ID-MONTH "July">
[741]16  <!ENTITY ID-YEAR "2010">
[424]17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x=''/>">
[205]18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
[115]20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
[31]21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
[115]27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
[31]28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
[647]29  <!ENTITY header-fields            "<xref target='Part1' x:rel='#header.fields' xmlns:x=''/>">
[31]30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
[580]31  <!ENTITY full-date                "<xref target='Part1' x:rel='' xmlns:x=''/>">
[457]32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x=''/>">
[374]33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[808]35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x=''/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x=''/>">
[673]37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x=''/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x=''/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x=''/>">
[716]40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x=''/>">
42<?rfc toc="yes" ?>
[29]43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
[8]45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
[203]49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
[799]51<?rfc rfcedstyle="yes"?>
[8]52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
[308]54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
[446]55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
[153]56     xmlns:x=''>
[120]59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
[29]61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Day Software">Day Software</organization>
[8]63    <address>
64      <postal>
[29]65        <street>23 Corporate Plaza DR, Suite 280</street>
66        <city>Newport Beach</city>
[8]67        <region>CA</region>
[29]68        <code>92660</code>
69        <country>USA</country>
[8]70      </postal>
[29]71      <phone>+1-949-706-5300</phone>
72      <facsimile>+1-949-706-5305</facsimile>
73      <email></email>
74      <uri></uri>
[8]75    </address>
76  </author>
[29]78  <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]79    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
[8]80    <address>
81      <postal>
[29]82        <street>21 Oak Knoll Road</street>
83        <city>Carlisle</city>
[8]84        <region>MA</region>
[29]85        <code>01741</code>
86        <country>USA</country>
[8]87      </postal>
[844]88      <email></email>
89      <uri></uri>
[8]90    </address>
91  </author>
93  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]94    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]95    <address>
96      <postal>
[29]97        <street>HP Labs, Large Scale Systems Group</street>
98        <street>1501 Page Mill Road, MS 1177</street>
[8]99        <city>Palo Alto</city>
100        <region>CA</region>
[29]101        <code>94304</code>
102        <country>USA</country>
[8]103      </postal>
[29]104      <email></email>
[8]105    </address>
106  </author>
108  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]109    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]110    <address>
111      <postal>
[29]112        <street>1 Microsoft Way</street>
113        <city>Redmond</city>
114        <region>WA</region>
115        <code>98052</code>
116        <country>USA</country>
[8]117      </postal>
[29]118      <email></email>
[8]119    </address>
120  </author>
122  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[29]123    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
[8]124    <address>
125      <postal>
[29]126        <street>345 Park Ave</street>
127        <city>San Jose</city>
[8]128        <region>CA</region>
[29]129        <code>95110</code>
130        <country>USA</country>
[8]131      </postal>
[29]132      <email></email>
133      <uri></uri>
[8]134    </address>
135  </author>
137  <author initials="P." surname="Leach" fullname="Paul J. Leach">
138    <organization abbrev="Microsoft">Microsoft Corporation</organization>
139    <address>
140      <postal>
141        <street>1 Microsoft Way</street>
142        <city>Redmond</city>
143        <region>WA</region>
144        <code>98052</code>
145      </postal>
146      <email></email>
147    </address>
148  </author>
150  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
151    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
152    <address>
153      <postal>
[34]154        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
155        <street>The Stata Center, Building 32</street>
156        <street>32 Vassar Street</street>
[8]157        <city>Cambridge</city>
158        <region>MA</region>
159        <code>02139</code>
[29]160        <country>USA</country>
[8]161      </postal>
162      <email></email>
[34]163      <uri></uri>
[8]164    </address>
165  </author>
[95]167  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]168    <organization abbrev="W3C">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>W3C / ERCIM</street>
172        <street>2004, rte des Lucioles</street>
173        <city>Sophia-Antipolis</city>
174        <region>AM</region>
175        <code>06902</code>
176        <country>France</country>
177      </postal>
178      <email></email>
179      <uri></uri>
180    </address>
181  </author>
[95]183  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
184    <organization abbrev="greenbytes">greenbytes GmbH</organization>
185    <address>
186      <postal>
187        <street>Hafenweg 16</street>
188        <city>Muenster</city><region>NW</region><code>48155</code>
189        <country>Germany</country>
190      </postal>
[609]191      <phone>+49 251 2807760</phone>
192      <facsimile>+49 251 2807761</facsimile>
193      <email></email>
194      <uri></uri>
[95]195    </address>
196  </author>
[31]198  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[440]199  <workgroup>HTTPbis Working Group</workgroup>
203   The Hypertext Transfer Protocol (HTTP) is an application-level
204   protocol for distributed, collaborative, hypermedia information
[29]205   systems. HTTP has been in use by the World Wide Web global information
[35]206   initiative since 1990. This document is Part 3 of the seven-part specification
[29]207   that defines the protocol referred to as "HTTP/1.1" and, taken together,
[42]208   obsoletes RFC 2616.  Part 3 defines HTTP message content,
[29]209   metadata, and content negotiation.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
[848]217    at <eref target=""/>
[36]218    and related documents (including fancy diffs) can be found at
[324]219    <eref target=""/>.
[36]220  </t>
[153]221  <t>
[841]222    The changes in this draft are summarized in <xref target="changes.since.10"/>.
[153]223  </t>
227<section title="Introduction" anchor="introduction">
[163]229   This document defines HTTP/1.1 message payloads (a.k.a., content), the
[161]230   associated metadata header fields that define how the payload is intended
231   to be interpreted by a recipient, the request header fields that
232   may influence content selection, and the various selection algorithms
233   that are collectively referred to as HTTP content negotiation.
236   This document is currently disorganized in order to minimize the changes
237   between drafts and enable reviewers to see the smaller errata changes.
238   The next draft will reorganize the sections to better reflect the content.
239   In particular, the sections on entities will be renamed payload and moved
240   to the first half of the document, while the sections on content negotiation
241   and associated request header fields will be moved to the second half.  The
242   current mess reflects how widely dispersed these topics and associated
243   requirements had become in <xref target="RFC2616"/>.
[660]246<section title="Terminology" anchor="terminology">
248   This specification uses a number of terms to refer to the roles
249   played by participants in, and objects of, the HTTP communication.
252  <iref item="content negotiation"/>
253  <x:dfn>content negotiation</x:dfn>
254  <list>
255    <t>
256      The mechanism for selecting the appropriate representation when
[856]257      servicing a request. The representation in any response
[660]258      can be negotiated (including error responses).
259    </t>
260  </list>
[856]263  <iref item="payload"/>
264  <x:dfn>payload</x:dfn>
[660]265  <list>
266    <t>
[856]267      The information transferred within a given message is called the
268      payload, consisting  of optional payload metadata and an optional
269      payload body.  The payload in HTTP is always a partial or complete
270      representation of some resource, though which resource is represented
271      is dependent on the type of message (request or response), the
272      request method, and the response status code.
[660]273    </t>
274  </list>
277  <iref item="representation"/>
278  <x:dfn>representation</x:dfn>
279  <list>
280    <t>
[856]281      A representation is information in a format that can be readily
282      communicated from one party to another.  For our purposes, a
283      representation is binary data and its associated metadata.
284      A representation of a resource is information that reflects the
285      state of that resource, as observed at some point in the past
286      or to be desired at some point in the future.
[660]287    </t>
288  </list>
[96]292<section title="Requirements" anchor="intro.requirements">
294   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
295   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
296   document are to be interpreted as described in <xref target="RFC2119"/>.
299   An implementation is not compliant if it fails to satisfy one or more
[847]300   of the "MUST" or "REQUIRED" level requirements for the protocols it
301   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
302   level and all the "SHOULD" level requirements for its protocols is said
303   to be "unconditionally compliant"; one that satisfies all the "MUST"
304   level requirements but not all the "SHOULD" level requirements for its
305   protocols is said to be "conditionally compliant".
[424]309<section title="Syntax Notation" anchor="notation">
[425]310  <x:anchor-alias value="ALPHA"/>
311  <x:anchor-alias value="CR"/>
312  <x:anchor-alias value="DIGIT"/>
313  <x:anchor-alias value="LF"/>
314  <x:anchor-alias value="OCTET"/>
315  <x:anchor-alias value="VCHAR"/>
316  <x:anchor-alias value="WSP"/>
[543]318  This specification uses the ABNF syntax defined in &notation; (which
319  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
320  <xref target="collected.abnf"/> shows the collected ABNF, with the list
321  rule expanded.
[425]324  The following core rules are included by
325  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
326  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
327  DIGIT (decimal 0-9), DQUOTE (double quote),
328  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
329  OCTET (any 8-bit sequence of data), SP (space),
330  VCHAR (any visible USASCII character),
331  and WSP (whitespace).
334<section title="Core Rules" anchor="core.rules">
[229]335  <x:anchor-alias value="quoted-string"/>
336  <x:anchor-alias value="token"/>
[810]337  <x:anchor-alias value="word"/>
[357]338  <x:anchor-alias value="OWS"/>
[424]340  The core rules below are defined in &basic-rules;:
342<figure><artwork type="abnf2616">
[229]343  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
344  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
[810]345  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
[357]346  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
350<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]351  <x:anchor-alias value="absolute-URI"/>
[229]352  <x:anchor-alias value="Allow"/>
353  <x:anchor-alias value="Content-Length"/>
354  <x:anchor-alias value="Content-Range"/>
355  <x:anchor-alias value="Expires"/>
356  <x:anchor-alias value="Last-Modified"/>
[647]357  <x:anchor-alias value="header-field"/>
[391]358  <x:anchor-alias value="partial-URI"/>
[457]359  <x:anchor-alias value="qvalue"/>
[206]361  The ABNF rules below are defined in other parts:
[207]363<figure><!--Part1--><artwork type="abnf2616">
[374]364  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[229]365  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
[647]366  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
[391]367  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
[457]368  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
370<figure><!--Part4--><artwork type="abnf2616">
[229]371  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
373<figure><!--Part5--><artwork type="abnf2616">
[229]374  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
376<figure><!--Part6--><artwork type="abnf2616">
[229]377  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
[8]385<section title="Protocol Parameters" anchor="protocol.parameters">
387<section title="Character Sets" anchor="character.sets">
389   HTTP uses the same definition of the term "character set" as that
390   described for MIME:
393   The term "character set" is used in this document to refer to a
394   method used with one or more tables to convert a sequence of octets
395   into a sequence of characters. Note that unconditional conversion in
396   the other direction is not required, in that not all characters may
397   be available in a given character set and a character set may provide
398   more than one sequence of octets to represent a particular character.
399   This definition is intended to allow various kinds of character
400   encoding, from simple single-table mappings such as US-ASCII to
401   complex table switching methods such as those that use ISO-2022's
402   techniques. However, the definition associated with a MIME character
403   set name &MUST; fully specify the mapping to be performed from octets
404   to characters. In particular, use of external profiling information
405   to determine the exact mapping is not permitted.
408  <t>
409    <x:h>Note:</x:h> This use of the term "character set" is more commonly
410    referred to as a "character encoding." However, since HTTP and
411    MIME share the same registry, it is important that the terminology
412    also be shared.
413  </t>
[229]415<t anchor="rule.charset">
416  <x:anchor-alias value="charset"/>
[8]417   HTTP character sets are identified by case-insensitive tokens. The
418   complete set of tokens is defined by the IANA Character Set registry
[91]419   (<eref target=""/>).
421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]422  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
425   Although HTTP allows an arbitrary token to be used as a charset
426   value, any token that has a predefined value within the IANA
[91]427   Character Set registry &MUST; represent the character set defined
[8]428   by that registry. Applications &SHOULD; limit their use of character
429   sets to those defined by the IANA registry.
[81]432   HTTP uses charset in two contexts: within an Accept-Charset request
433   header (in which the charset value is an unquoted token) and as the
[115]434   value of a parameter in a Content-Type header (within a request or
[81]435   response), in which case the parameter value of the charset parameter
436   may be quoted.
[129]439   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
[8]440   <xref target="RFC2277"/>.
443<section title="Missing Charset" anchor="missing.charset">
445   Some HTTP/1.0 software has interpreted a Content-Type header without
446   charset parameter incorrectly to mean "recipient should guess."
447   Senders wishing to defeat this behavior &MAY; include a charset
448   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
449   it is known that it will not confuse the recipient.
452   Unfortunately, some older HTTP/1.0 clients did not deal properly with
453   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
454   charset label provided by the sender; and those user agents that have
455   a provision to "guess" a charset &MUST; use the charset from the
456   content-type field if they support that charset, rather than the
457   recipient's preference, when initially displaying a document. See
458   <xref target="canonicalization.and.text.defaults"/>.
463<section title="Content Codings" anchor="content.codings">
[229]464  <x:anchor-alias value="content-coding"/>
466   Content coding values indicate an encoding transformation that has
[866]467   been or can be applied to a representation. Content codings are primarily
468   used to allow a representation to be compressed or otherwise usefully
[8]469   transformed without losing the identity of its underlying media type
[866]470   and without loss of information. Frequently, the representation is stored in
[8]471   coded form, transmitted directly, and only decoded by the recipient.
473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]474  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
477   All content-coding values are case-insensitive. HTTP/1.1 uses
478   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
479   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
480   describes the content-coding, what is more important is that it
481   indicates what decoding mechanism will be required to remove the
482   encoding.
[673]485   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
486  <list>
487    <t>
488      See &compress-coding;.
489    </t>
490  </list>
[673]493   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
[8]494  <list>
495    <t>
[673]496      See &deflate-coding;.
[8]497    </t>
498  </list>
[673]501   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
502  <list>
503    <t>
504      See &gzip-coding;.
505    </t>
506  </list>
[673]509   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
[8]510  <list><t>
511        The default (identity) encoding; the use of no transformation
512        whatsoever. This content-coding is used only in the Accept-Encoding
513        header, and &SHOULD-NOT;  be used in the Content-Encoding
514        header.
515  </t></list>
518<section title="Content Coding Registry" anchor="content.coding.registry">
[670]520   The HTTP Content Coding Registry defines the name space for the content
521   coding names.
524   Registrations &MUST; include the following fields:
525   <list style="symbols">
526     <t>Name</t>
527     <t>Description</t>
528     <t>Pointer to specification text</t>
529   </list>
[808]532   Names of content codings &MUST-NOT; overlap with names of transfer codings
533   (&transfer-codings;), unless the encoding transformation is identical (as it
534   is the case for the compression codings defined in
535   &compression-codings;).
[670]538   Values to be added to this name space require expert review and a specification
539   (see "Expert Review" and "Specification Required" in
540   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
[8]541   conform to the purpose of content coding defined in this section.
544   The registry itself is maintained at
545   <eref target=""/>.
[8]551<section title="Media Types" anchor="media.types">
[229]552  <x:anchor-alias value="media-type"/>
553  <x:anchor-alias value="type"/>
554  <x:anchor-alias value="subtype"/>
[152]556   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]557   and Accept (<xref target="header.accept"/>) header fields in order to provide
558   open and extensible data typing and type negotiation.
560<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"/>
[357]561  <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> )
562  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
563  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[229]565<t anchor="rule.parameter">
566  <x:anchor-alias value="attribute"/>
567  <x:anchor-alias value="parameter"/>
568  <x:anchor-alias value="value"/>
[8]569   Parameters &MAY; follow the type/subtype in the form of attribute/value
[29]570   pairs.
[29]572<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"/>
[250]573  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
574  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[810]575  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
578   The type, subtype, and parameter attribute names are case-insensitive.
[370]579   Parameter values might or might not be case-sensitive, depending on the
580   semantics of the parameter name.  The presence or absence of a parameter might
[8]581   be significant to the processing of a media-type, depending on its
582   definition within the media type registry.
[297]585   A parameter value that matches the <x:ref>token</x:ref> production may be
586   transmitted as either a token or within a quoted-string. The quoted and
587   unquoted values are equivalent.
[8]590   Note that some older HTTP applications do not recognize media type
591   parameters. When sending data to older HTTP applications,
592   implementations &SHOULD; only use media type parameters when they are
593   required by that type/subtype definition.
596   Media-type values are registered with the Internet Assigned Number
[91]597   Authority (IANA). The media type registration process is
[115]598   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]599   discouraged.
602<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
604   Internet media types are registered with a canonical form. An
605   entity-body transferred via HTTP messages &MUST; be represented in the
606   appropriate canonical form prior to its transmission except for
607   "text" types, as defined in the next paragraph.
610   When in canonical form, media subtypes of the "text" type use CRLF as
611   the text line break. HTTP relaxes this requirement and allows the
612   transport of text media with plain CR or LF alone representing a line
613   break when it is done consistently for an entire entity-body. HTTP
614   applications &MUST; accept CRLF, bare CR, and bare LF as being
615   representative of a line break in text media received via HTTP. In
616   addition, if the text is represented in a character set that does not
617   use octets 13 and 10 for CR and LF respectively, as is the case for
618   some multi-byte character sets, HTTP allows the use of whatever octet
619   sequences are defined by that character set to represent the
620   equivalent of CR and LF for line breaks. This flexibility regarding
621   line breaks applies only to text media in the entity-body; a bare CR
622   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
623   structures (such as header fields and multipart boundaries).
626   If an entity-body is encoded with a content-coding, the underlying
627   data &MUST; be in a form defined above prior to being encoded.
[211]630   The "charset" parameter is used with some media types to define the
631   character set (<xref target="character.sets"/>) of the data. When no explicit charset
632   parameter is provided by the sender, media subtypes of the "text"
633   type are defined to have a default charset value of "ISO-8859-1" when
634   received via HTTP. Data in character sets other than "ISO-8859-1" or
635   its subsets &MUST; be labeled with an appropriate charset value. See
636   <xref target="missing.charset"/> for compatibility problems.
640<section title="Multipart Types" anchor="multipart.types">
642   MIME provides for a number of "multipart" types -- encapsulations of
643   one or more entities within a single message-body. All multipart
[97]644   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
645   and &MUST; include a boundary parameter as part of the media type
[8]646   value. The message body is itself a protocol element and &MUST;
647   therefore use only CRLF to represent line breaks between body-parts.
650   In general, HTTP treats a multipart message-body no differently than
[852]651   any other media type: strictly as payload.  HTTP does not use the
652   multipart boundary as an indicator of message-body length.
[97]653   <!-- jre: re-insert removed text pointing to caching? -->
[852]654   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
[8]655   behavior as a MIME user agent would upon receipt of a multipart type.
656   The MIME header fields within each body-part of a multipart message-body
657   do not have any significance to HTTP beyond that defined by
658   their MIME semantics.
661   If an application receives an unrecognized multipart subtype, the
662   application &MUST; treat it as being equivalent to "multipart/mixed".
665  <t>
666    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
667    for carrying form data suitable for processing via the POST
668    request method, as described in <xref target="RFC2388"/>.
669  </t>
674<section title="Language Tags" anchor="language.tags">
[229]675  <x:anchor-alias value="language-tag"/>
[690]677   A language tag, as defined in <xref target="RFC5646"/>, identifies a
[613]678   natural language spoken, written, or otherwise conveyed by human beings for
679   communication of information to other human beings. Computer languages are
680   explicitly excluded. HTTP uses language tags within the Accept-Language and
681   Content-Language fields.
[613]684   In summary, a language tag is composed of one or more parts: A primary
685   language subtag followed by a possibly empty series of subtags:
[613]687<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
[690]688  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
691   White space is not allowed within the tag and all tags are case-insensitive.
[613]692   The name space of language subtags is administered by the IANA (see
693   <eref target=""/>).
696  <preamble>Example tags include:</preamble>
697<artwork type="example">
698  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
[690]702   See <xref target="RFC5646"/> for further information.
707<section title="Entity" anchor="entity">
[866]709   Request and Response messages &MAY; transfer a representation if not otherwise
710   restricted by the request method or response status code. A representation
711   consists of entity-header fields and a representation body, although some
[8]712   responses will only include the entity-headers.
715   In this section, both sender and recipient refer to either the client
[866]716   or the server, depending on who sends and who receives the message.
719<section title="Entity Header Fields" anchor="entity.header.fields">
[229]720  <x:anchor-alias value="entity-header"/>
721  <x:anchor-alias value="extension-header"/>
[867]723   Entity-header fields define metadata about the entity-body or,
[8]724   if no body is present, about the resource identified by the request.
726<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
[232]727  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
[334]728                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
729                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
730                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
731                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
732                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
733                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
734                 / <x:ref>Expires</x:ref>                  ; &header-expires;
735                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
736                 / <x:ref>extension-header</x:ref>
[647]738  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
741   The extension-header mechanism allows additional entity-header fields
742   to be defined without changing the protocol, but these fields cannot
743   be assumed to be recognizable by the recipient. Unrecognized header
744   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
745   transparent proxies.
749<section title="Entity Body" anchor="entity.body">
[229]750  <x:anchor-alias value="entity-body"/>
752   The entity-body (if any) sent with an HTTP request or response is in
753   a format and encoding defined by the entity-header fields.
755<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
[229]756  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
759   An entity-body is only present in a message when a message-body is
[29]760   present, as described in &message-body;. The entity-body is obtained
[8]761   from the message-body by decoding any Transfer-Encoding that might
762   have been applied to ensure safe and proper transfer of the message.
765<section title="Type" anchor="type">
767   When an entity-body is included with a message, the data type of that
768   body is determined via the header fields Content-Type and Content-Encoding.
769   These define a two-layer, ordered encoding model:
771<figure><artwork type="example">
[458]772  entity-body := Content-Encoding( Content-Type( data ) )
[592]775   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
776   message containing an entity-body &SHOULD; include a Content-Type header
777   field defining the media type of that body, unless that information is
[831]778   unknown.
781   If the Content-Type header field is not present, it indicates that
[592]782   the sender does not know the media type of the data; recipients &MAY;
783   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
784   or examine the content to determine its type.
[831]787   In practice, currently-deployed servers sometimes provide a Content-Type
788   header which does not correctly convey the intended interpretation of the
789   content sent, with the result that some clients will examine the response
790   body's content and override the specified type.
793   Client that do so risk drawing incorrect conclusions, which may expose
794   additional security risks (e.g., "privilege escalation"). Implementers are
795   encouraged to provide a means of disabling such "content sniffing" when it
796   is used.
[8]799   Content-Encoding may be used to indicate any additional content
800   codings applied to the data, usually for the purpose of data
[592]801   compression, that are a property of the requested resource.  There is
[8]802   no default encoding.
809<section title="Content Negotiation" anchor="content.negotiation">
[745]811   HTTP responses include a representation which contains information for
812   interpretation, whether by a human user or for further processing.
813   Often, the server has different ways of representing the
814   same information; for example, in different formats, languages,
815   or using different character encodings.
[745]818   HTTP clients and their users might have different or variable
819   capabilities, characteristics or preferences which would influence
820   which representation, among those available from the server,
821   would be best for the server to deliver. For this reason, HTTP
822   provides mechanisms for "content negotiation" -- a process of
823   allowing selection of a representation of a given resource,
824   when more than one is available.
[745]827   This specification defines two patterns of content negotiation;
828   "server-driven", where the server selects the representation based
829   upon the client's stated preferences, and "agent-driven" negotiation,
830   where the server provides a list of representations for the client to
831   choose from, based upon their metadata. In addition,  there are
832   other patterns: some applications use an "active content" pattern,
833   where the server returns active content which runs on the client
834   and, based on client available parameters, selects additional
835   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
836   has also been proposed.
839   These patterns are all widely used, and have trade-offs in applicability
840   and practicality. In particular, when the number of preferences or
841   capabilities to be expressed by a client are large (such as when many
842   different formats are supported by a user-agent), server-driven
843   negotiation becomes unwieldy, and may not be appropriate. Conversely,
844   when the number of representations to choose from is very large,
845   agent-driven negotiation may not be appropriate.
848   Note that in all cases, the supplier of representations has the
849   responsibility for determining which representations might be
850   considered to be the "same information".
853<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
855   If the selection of the best representation for a response is made by
856   an algorithm located at the server, it is called server-driven
857   negotiation. Selection is based on the available representations of
[763]858   the response (the dimensions over which it can vary; e.g., language,
[8]859   content-coding, etc.) and the contents of particular header fields in
860   the request message or on other information pertaining to the request
861   (such as the network address of the client).
864   Server-driven negotiation is advantageous when the algorithm for
865   selecting from among the available representations is difficult to
866   describe to the user agent, or when the server desires to send its
867   "best guess" to the client along with the first response (hoping to
868   avoid the round-trip delay of a subsequent request if the "best
869   guess" is good enough for the user). In order to improve the server's
870   guess, the user agent &MAY; include request header fields (Accept,
871   Accept-Language, Accept-Encoding, etc.) which describe its
872   preferences for such a response.
875   Server-driven negotiation has disadvantages:
876  <list style="numbers">
877    <t>
878         It is impossible for the server to accurately determine what
879         might be "best" for any given user, since that would require
880         complete knowledge of both the capabilities of the user agent
881         and the intended use for the response (e.g., does the user want
882         to view it on screen or print it on paper?).
883    </t>
884    <t>
885         Having the user agent describe its capabilities in every
886         request can be both very inefficient (given that only a small
887         percentage of responses have multiple representations) and a
888         potential violation of the user's privacy.
889    </t>
890    <t>
891         It complicates the implementation of an origin server and the
892         algorithms for generating responses to a request.
893    </t>
894    <t>
895         It may limit a public cache's ability to use the same response
896         for multiple user's requests.
897    </t>
898  </list>
901   HTTP/1.1 includes the following request-header fields for enabling
902   server-driven negotiation through description of user agent
903   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
904   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[745]905   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
906   However, an origin server is not limited to these dimensions and &MAY; vary
907   the response based on any aspect of the request, including information
[8]908   outside the request-header fields or within extension header fields
909   not defined by this specification.
912  <t>
913    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
914    because new clients might not be recognized.
915  </t>
[115]918   The Vary header field (&header-vary;) can be used to express the parameters the
[8]919   server uses to select a representation that is subject to server-driven
[29]920   negotiation.
924<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
926   With agent-driven negotiation, selection of the best representation
927   for a response is performed by the user agent after receiving an
928   initial response from the origin server. Selection is based on a list
929   of the available representations of the response included within the
930   header fields or entity-body of the initial response, with each
931   representation identified by its own URI. Selection from among the
932   representations may be performed automatically (if the user agent is
933   capable of doing so) or manually by the user selecting from a
934   generated (possibly hypertext) menu.
937   Agent-driven negotiation is advantageous when the response would vary
938   over commonly-used dimensions (such as type, language, or encoding),
939   when the origin server is unable to determine a user agent's
940   capabilities from examining the request, and generally when public
941   caches are used to distribute server load and reduce network usage.
944   Agent-driven negotiation suffers from the disadvantage of needing a
945   second request to obtain the best alternate representation. This
946   second request is only efficient when caching is used. In addition,
947   this specification does not define any mechanism for supporting
948   automatic selection, though it also does not prevent any such
949   mechanism from being developed as an extension and used within
950   HTTP/1.1.
[745]953   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
[8]954   status codes for enabling agent-driven negotiation when the server is
955   unwilling or unable to provide a varying response using server-driven
956   negotiation.
[8]961<section title="Header Field Definitions" anchor="header.fields">
[117]963   This section defines the syntax and semantics of HTTP/1.1 header fields
964   related to the payload of messages.
967   For entity-header fields, both sender and recipient refer to either the
[866]968   client or the server, depending on who sends and who receives the message.
[8]971<section title="Accept" anchor="header.accept">
972  <iref primary="true" item="Accept header" x:for-anchor=""/>
973  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
[229]974  <x:anchor-alias value="Accept"/>
[357]975  <x:anchor-alias value="Accept-v"/>
[370]976  <x:anchor-alias value="accept-ext"/>
[229]977  <x:anchor-alias value="accept-params"/>
978  <x:anchor-alias value="media-range"/>
[698]980   The "Accept" request-header field can be used by user agents to specify
981   response media types that are acceptable. Accept headers can be used to
982   indicate that the request is specifically limited to a small set of desired
983   types, as in the case of a request for an in-line image.
[370]985<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"/>
[366]986  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
[357]987  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[229]989  <x:ref>media-range</x:ref>    = ( "*/*"
[334]990                   / ( <x:ref>type</x:ref> "/" "*" )
991                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]992                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
993  <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> )
[376]994  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
[810]995                   [ "=" <x:ref>word</x:ref> ]
998   The asterisk "*" character is used to group media types into ranges,
999   with "*/*" indicating all media types and "type/*" indicating all
1000   subtypes of that type. The media-range &MAY; include media type
1001   parameters that are applicable to that range.
1004   Each media-range &MAY; be followed by one or more accept-params,
1005   beginning with the "q" parameter for indicating a relative quality
1006   factor. The first "q" parameter (if any) separates the media-range
1007   parameter(s) from the accept-params. Quality factors allow the user
1008   or user agent to indicate the relative degree of preference for that
[457]1009   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
[8]1010   default value is q=1.
1013  <t>
1014    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1015    parameters from Accept extension parameters is due to historical
1016    practice. Although this prevents any media type parameter named
1017    "q" from being used with a media range, such an event is believed
1018    to be unlikely given the lack of any "q" parameters in the IANA
1019    media type registry and the rare usage of any media type
1020    parameters in Accept. Future media types are discouraged from
1021    registering any parameter named "q".
1022  </t>
1025   The example
1027<figure><artwork type="example">
[357]1028  Accept: audio/*; q=0.2, audio/basic
1031   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1032   type if it is the best available after an 80% mark-down in quality."
1035   If no Accept header field is present, then it is assumed that the
1036   client accepts all media types. If an Accept header field is present,
1037   and if the server cannot send a response which is acceptable
1038   according to the combined Accept field value, then the server &SHOULD;
[137]1039   send a 406 (Not Acceptable) response.
1042   A more elaborate example is
1044<figure><artwork type="example">
[357]1045  Accept: text/plain; q=0.5, text/html,
1046          text/x-dvi; q=0.8, text/x-c
1049   Verbally, this would be interpreted as "text/html and text/x-c are
1050   the preferred media types, but if they do not exist, then send the
[866]1051   text/x-dvi representation, and if that does not exist, send the text/plain
1052   representation."
1055   Media ranges can be overridden by more specific media ranges or
1056   specific media types. If more than one media range applies to a given
1057   type, the most specific reference has precedence. For example,
1059<figure><artwork type="example">
[357]1060  Accept: text/*, text/html, text/html;level=1, */*
1063   have the following precedence:
[459]1064   <list style="numbers">
1065    <t>text/html;level=1</t>
1066    <t>text/html</t>
1067    <t>text/*</t>
1068    <t>*/*</t>
1069   </list>
1072   The media type quality factor associated with a given type is
1073   determined by finding the media range with the highest precedence
1074   which matches that type. For example,
1076<figure><artwork type="example">
[357]1077  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1078          text/html;level=2;q=0.4, */*;q=0.5
1081   would cause the following values to be associated:
[459]1083<texttable align="left">
1084  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1085  <c>text/html;level=1</c>    <c>1</c>
1086  <c>text/html</c>            <c>0.7</c>
1087  <c>text/plain</c>           <c>0.3</c>
1088  <c>image/jpeg</c>           <c>0.5</c>
1089  <c>text/html;level=2</c>    <c>0.4</c>
1090  <c>text/html;level=3</c>    <c>0.7</c>
1093      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1094      values for certain media ranges. However, unless the user agent is
1095      a closed system which cannot interact with other rendering agents,
1096      this default set ought to be configurable by the user.
1100<section title="Accept-Charset" anchor="header.accept-charset">
1101  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1102  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
[229]1103  <x:anchor-alias value="Accept-Charset"/>
[357]1104  <x:anchor-alias value="Accept-Charset-v"/>
[698]1106   The "Accept-Charset" request-header field can be used by user agents to
1107   indicate what response character sets are acceptable. This field allows
[8]1108   clients capable of understanding more comprehensive or special-purpose
[698]1109   character sets to signal that capability to a server which is capable of
1110   representing documents in those character sets.
[357]1112<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
[366]1113  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
[357]1114          <x:ref>Accept-Charset-v</x:ref>
[376]1115  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1116                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1119   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1120   be given an associated quality value which represents the user's
1121   preference for that charset. The default value is q=1. An example is
1123<figure><artwork type="example">
[357]1124  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1127   The special value "*", if present in the Accept-Charset field,
1128   matches every character set (including ISO-8859-1) which is not
1129   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1130   in an Accept-Charset field, then all character sets not explicitly
1131   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1132   a quality value of 1 if not explicitly mentioned.
1135   If no Accept-Charset header is present, the default is that any
1136   character set is acceptable. If an Accept-Charset header is present,
1137   and if the server cannot send a response which is acceptable
1138   according to the Accept-Charset header, then the server &SHOULD; send
[137]1139   an error response with the 406 (Not Acceptable) status code, though
[8]1140   the sending of an unacceptable response is also allowed.
1144<section title="Accept-Encoding" anchor="header.accept-encoding">
1145  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1146  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1147  <x:anchor-alias value="Accept-Encoding"/>
[357]1148  <x:anchor-alias value="Accept-Encoding-v"/>
[229]1149  <x:anchor-alias value="codings"/>
[698]1151   The "Accept-Encoding" request-header field can be used by user agents to
1152   indicate what response content-codings (<xref target="content.codings"/>)
1153   are acceptable in the response.
[357]1155<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"/>
[366]1156  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
[357]1157                     <x:ref>Accept-Encoding-v</x:ref>
1158  <x:ref>Accept-Encoding-v</x:ref>  =
[370]1159                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1160  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
[248]1163   Each codings value &MAY; be given an associated quality value which
1164   represents the preference for that encoding. The default value is q=1.
[8]1167   Examples of its use are:
1169<figure><artwork type="example">
[357]1170  Accept-Encoding: compress, gzip
1171  Accept-Encoding:
1172  Accept-Encoding: *
1173  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1174  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1177   A server tests whether a content-coding is acceptable, according to
1178   an Accept-Encoding field, using these rules:
1179  <list style="numbers">
1180      <t>If the content-coding is one of the content-codings listed in
1181         the Accept-Encoding field, then it is acceptable, unless it is
[457]1182         accompanied by a qvalue of 0. (As defined in &qvalue;, a
[8]1183         qvalue of 0 means "not acceptable.")</t>
1185      <t>The special "*" symbol in an Accept-Encoding field matches any
1186         available content-coding not explicitly listed in the header
1187         field.</t>
1189      <t>If multiple content-codings are acceptable, then the acceptable
1190         content-coding with the highest non-zero qvalue is preferred.</t>
1192      <t>The "identity" content-coding is always acceptable, unless
1193         specifically refused because the Accept-Encoding field includes
1194         "identity;q=0", or because the field includes "*;q=0" and does
1195         not explicitly include the "identity" content-coding. If the
1196         Accept-Encoding field-value is empty, then only the "identity"
1197         encoding is acceptable.</t>
1198  </list>
1201   If an Accept-Encoding field is present in a request, and if the
1202   server cannot send a response which is acceptable according to the
1203   Accept-Encoding header, then the server &SHOULD; send an error response
1204   with the 406 (Not Acceptable) status code.
1207   If no Accept-Encoding field is present in a request, the server &MAY;
1208   assume that the client will accept any content coding. In this case,
1209   if "identity" is one of the available content-codings, then the
1210   server &SHOULD; use the "identity" content-coding, unless it has
1211   additional information that a different content-coding is meaningful
1212   to the client.
1215  <t>
1216    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1217    and if the "identity" content-coding is unavailable, then
1218    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1219    "gzip" and "compress") are preferred; some older clients
1220    improperly display messages sent with other content-codings.  The
1221    server might also make this decision based on information about
1222    the particular user-agent or client.
1223  </t>
1226  <t>
1227    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1228    associated with content-codings. This means that qvalues will not
1229    work and are not permitted with x-gzip or x-compress.
1230  </t>
1234<section title="Accept-Language" anchor="header.accept-language">
1235  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1236  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
[229]1237  <x:anchor-alias value="Accept-Language"/>
[357]1238  <x:anchor-alias value="Accept-Language-v"/>
[229]1239  <x:anchor-alias value="language-range"/>
[698]1241   The "Accept-Language" request-header field can be used by user agents to
1242   indicate the set of natural languages that are preferred in the response.
1243   Language tags are defined in <xref target="language.tags"/>.
[357]1245<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"/>
[366]1246  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
[357]1247                    <x:ref>Accept-Language-v</x:ref>
1248  <x:ref>Accept-Language-v</x:ref> =
[370]1249                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1250  <x:ref>language-range</x:ref>    =
[303]1251            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[303]1254   Each language-range can be given an associated quality value which
[8]1255   represents an estimate of the user's preference for the languages
1256   specified by that range. The quality value defaults to "q=1". For
1257   example,
1259<figure><artwork type="example">
[357]1260  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1263   would mean: "I prefer Danish, but will accept British English and
[303]1264   other types of English."
[724]1265   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
[724]1268   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1269   several matching schemes. Implementations can offer the most appropriate
1270   matching scheme for their requirements.
1273  <t>
[756]1274    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
[724]1275    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1276    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
[563]1277  </t>
1280   It might be contrary to the privacy expectations of the user to send
1281   an Accept-Language header with the complete linguistic preferences of
1282   the user in every request. For a discussion of this issue, see
1283   <xref target=""/>.
1286   As intelligibility is highly dependent on the individual user, it is
1287   recommended that client applications make the choice of linguistic
1288   preference available to the user. If the choice is not made
1289   available, then the Accept-Language header field &MUST-NOT; be given in
1290   the request.
1293  <t>
1294    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1295    the user, we remind implementors of  the fact that users are not
1296    familiar with the details of language matching as described above,
1297    and should provide appropriate guidance. As an example, users
1298    might assume that on selecting "en-gb", they will be served any
1299    kind of English document if British English is not available. A
1300    user agent might suggest in such a case to add "en" to get the
1301    best matching behavior.
1302  </t>
1306<section title="Content-Encoding" anchor="header.content-encoding">
1307  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1308  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
[229]1309  <x:anchor-alias value="Content-Encoding"/>
[357]1310  <x:anchor-alias value="Content-Encoding-v"/>
[698]1312   The "Content-Encoding" entity-header field indicates what content-codings
[866]1313   have been applied to the representation, and thus what decoding mechanisms
[698]1314   must be applied in order to obtain the media-type referenced by the
1315   Content-Type header field. Content-Encoding is primarily used to allow a
[866]1316   representation to be compressed without losing the identity of its underlying
[698]1317   media type.
[357]1319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
[366]1320  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
[357]1321  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1324   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1326<figure><artwork type="example">
[357]1327  Content-Encoding: gzip
[866]1330   The content-coding is a characteristic of the representation.
1331   Typically, the representation body is stored with this
[8]1332   encoding and is only decoded before rendering or analogous usage.
1333   However, a non-transparent proxy &MAY; modify the content-coding if the
1334   new coding is known to be acceptable to the recipient, unless the
1335   "no-transform" cache-control directive is present in the message.
[866]1338   If the content-coding of a representation is not "identity", then the
1339   representation metadata &MUST; include a Content-Encoding header
1340   field (<xref target="header.content-encoding"/>)
[8]1341   that lists the non-identity content-coding(s) used.
1344   If the content-coding of an entity in a request message is not
1345   acceptable to the origin server, the server &SHOULD; respond with a
1346   status code of 415 (Unsupported Media Type).
[866]1349   If multiple encodings have been applied to a representation, the content
[8]1350   codings &MUST; be listed in the order in which they were applied.
1351   Additional information about the encoding parameters &MAY; be provided
[866]1352   by other header fields not defined by this specification.
1356<section title="Content-Language" anchor="header.content-language">
1357  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1358  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
[229]1359  <x:anchor-alias value="Content-Language"/>
[357]1360  <x:anchor-alias value="Content-Language-v"/>
[697]1362   The "Content-Language" entity-header field describes the natural
[866]1363   language(s) of the intended audience for the representation. Note that this might
[698]1364   not be equivalent to all the languages used within the entity-body.
[357]1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
[366]1367  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
[357]1368  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1371   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1372   Content-Language is to allow a user to identify and differentiate
[866]1373   representations according to the user's own preferred language. Thus, if the
[8]1374   body content is intended only for a Danish-literate audience, the
1375   appropriate field is
1377<figure><artwork type="example">
[357]1378  Content-Language: da
1381   If no Content-Language is specified, the default is that the content
1382   is intended for all language audiences. This might mean that the
1383   sender does not consider it to be specific to any natural language,
1384   or that the sender does not know for which language it is intended.
1387   Multiple languages &MAY; be listed for content that is intended for
1388   multiple audiences. For example, a rendition of the "Treaty of
1389   Waitangi," presented simultaneously in the original Maori and English
1390   versions, would call for
1392<figure><artwork type="example">
[357]1393  Content-Language: mi, en
[866]1396   However, just because multiple languages are present within a representation
[8]1397   does not mean that it is intended for multiple linguistic audiences.
1398   An example would be a beginner's language primer, such as "A First
1399   Lesson in Latin," which is clearly intended to be used by an
1400   English-literate audience. In this case, the Content-Language would
1401   properly only include "en".
1404   Content-Language &MAY; be applied to any media type -- it is not
1405   limited to textual documents.
1409<section title="Content-Location" anchor="header.content-location">
1410  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1411  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
[229]1412  <x:anchor-alias value="Content-Location"/>
[357]1413  <x:anchor-alias value="Content-Location-v"/>
[856]1415   The "Content-Location" header field supplies a URI that can be used
1416   as a specific identifier for the representation in this message.
1417   In other words, if one were to perform a GET on this URI at the time
1418   of this message's generation, then a 200 response would contain the
1419   same representation that is enclosed as payload in this message.
[357]1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
[366]1422  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
[357]1423                    <x:ref>Content-Location-v</x:ref>
1424  <x:ref>Content-Location-v</x:ref> =
[391]1425                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
[823]1428   The Content-Location value is not a replacement for the Effective
[856]1429   Request URI (&effective-request-uri;).  It is representation metadata.
1430   It has the same syntax and semantics as the header field of the same name
[858]1431   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
[856]1432   However, its appearance in an HTTP message has some special implications
1433   for HTTP recipients.
[856]1436   If Content-Location is included in a response message and its value
1437   is the same as the Effective Request URI, then the response payload
1438   &SHOULD; be considered the current representation of that resource.
1439   For a GET or HEAD request, this is the same as the default semantics
1440   when no Content-Location is provided by the server.  For a state-changing
1441   method like PUT or POST, it implies that the server's response contains
1442   the new representation of that resource, thereby distinguishing it from
1443   representations that might only report about the action (e.g., "It worked!").
1444   This allows authoring applications to update their local copies without
1445   the need for a subsequent GET request.
[856]1448   If Content-Location is included in a response message and its value
1449   differs from the Effective Request URI, then the origin server is
1450   informing recipients that this representation has its own, presumably
1451   more specific, identifier.  For a GET or HEAD request, this is an
1452   indication that the Effective Request URI identifies a resource that
1453   is subject to content negotiation and the representation selected for
1454   this response can also be found at the identified URI.  For other
1455   methods, such a Content-Location indicates that this representation
1456   contains a report on the action's status and the same report is
1457   available (for future access with GET) at the given URI.  For
1458   example, a purchase transaction made via the POST method may
1459   include a receipt document as the payload of the 200 response;
1460   the Content-Location value provides an identifier for retrieving
1461   a copy of that same receipt in the future.
1464   If Content-Location is included in a request message, then it &MAY;
1465   be interpreted by the origin server as an indication of where the
1466   user agent originally obtained the content of the enclosed
1467   representation (prior to any subsequent modification of the content
1468   by that user agent).  In other words, the user agent is providing
1469   the same representation metadata that it received with the original
1470   representation.  However, such interpretation &MUST-NOT; be used to
1471   alter the semantics of the method requested by the client.  For
1472   example, if a client makes a PUT request on a negotiated resource
1473   and the origin server accepts that PUT (without redirection), then the
1474   new set of values for that resource is expected to be consistent with
1475   the one representation supplied in that PUT; the Content-Location
1476   cannot be used as a form of reverse content selection that
1477   identifies only one of the negotiated representations to be updated.
1478   If the user agent had wanted the latter semantics, it would have applied
1479   the PUT directly to the Content-Location URI.
1482   A Content-Location field received in a request message is transitory
1483   information that &SHOULD-NOT; be saved with other representation
1484   metadata for use in later responses.  The Content-Location's value
1485   might be saved for use in other contexts, such as within source links
1486   or other metadata.
1489   A cache cannot assume that a representation with a Content-Location
[8]1490   different from the URI used to retrieve it can be used to respond to
[856]1491   later requests on that Content-Location URI.
[856]1494   If the Content-Location value is a partial URI, it is
[823]1495   interpreted relative to the Effective Request URI.
1499<section title="Content-MD5" anchor="header.content-md5">
1500  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1501  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
[229]1502  <x:anchor-alias value="Content-MD5"/>
[357]1503  <x:anchor-alias value="Content-MD5-v"/>
[697]1505   The "Content-MD5" entity-header field, as defined in <xref target="RFC1864"/>, is
[699]1506   an MD5 digest of the entity-body that provides an end-to-end message
1507   integrity check (MIC) of the entity-body. Note that a MIC is good for
1508   detecting accidental modification of the entity-body in transit, but is not
1509   proof against malicious attacks.
[357]1511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
[366]1512  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
[357]1513  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1516   The Content-MD5 header field &MAY; be generated by an origin server or
1517   client to function as an integrity check of the entity-body. Only
1518   origin servers or clients &MAY; generate the Content-MD5 header field;
1519   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1520   value as an end-to-end integrity check. Any recipient of the entity-body,
1521   including gateways and proxies, &MAY; check that the digest value
1522   in this header field matches that of the entity-body as received.
1525   The MD5 digest is computed based on the content of the entity-body,
1526   including any content-coding that has been applied, but not including
1527   any transfer-encoding applied to the message-body. If the message is
1528   received with a transfer-encoding, that encoding &MUST; be removed
[866]1529   prior to checking the Content-MD5 value against the received representation.
1532   This has the result that the digest is computed on the octets of the
1533   entity-body exactly as, and in the order that, they would be sent if
1534   no transfer-encoding were being applied.
1537   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1538   composite media-types (e.g., multipart/* and message/rfc822), but
1539   this does not change how the digest is computed as defined in the
1540   preceding paragraph.
1543   There are several consequences of this. The entity-body for composite
1544   types &MAY; contain many body-parts, each with its own MIME and HTTP
1545   headers (including Content-MD5, Content-Transfer-Encoding, and
1546   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1547   or Content-Encoding header, it is assumed that the content
1548   of the body-part has had the encoding applied, and the body-part is
1549   included in the Content-MD5 digest as is -- i.e., after the
1550   application. The Transfer-Encoding header field is not allowed within
1551   body-parts.
1554   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1555   computing or checking the digest: the line break convention used in
1556   the text actually transmitted &MUST; be left unaltered when computing
1557   the digest.
1560  <t>
[756]1561    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
[563]1562    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1563    in which the application of Content-MD5 to HTTP entity-bodies
1564    differs from its application to MIME entity-bodies. One is that
1565    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1566    does use Transfer-Encoding and Content-Encoding. Another is that
1567    HTTP more frequently uses binary content types than MIME, so it is
1568    worth noting that, in such cases, the byte order used to compute
1569    the digest is the transmission byte order defined for the type.
1570    Lastly, HTTP allows transmission of text types with any of several
1571    line break conventions and not just the canonical form using CRLF.
1572  </t>
1576<section title="Content-Type" anchor="header.content-type">
1577  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1578  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
[229]1579  <x:anchor-alias value="Content-Type"/>
[357]1580  <x:anchor-alias value="Content-Type-v"/>
[697]1582   The "Content-Type" entity-header field indicates the media type of the
[698]1583   entity-body. In the case of responses to the HEAD method, the media type is
1584   that which would have been sent had the request been a GET.
[357]1586<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
[366]1587  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
[357]1588  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1591   Media types are defined in <xref target="media.types"/>. An example of the field is
1593<figure><artwork type="example">
[357]1594  Content-Type: text/html; charset=ISO-8859-4
1597   Further discussion of methods for identifying the media type of an
1598   entity is provided in <xref target="type"/>.
[29]1604<section title="IANA Considerations" anchor="IANA.considerations">
[253]1605<section title="Message Header Registration" anchor="message.header.registration">
1607   The Message Header Registry located at <eref target=""/> should be updated
1608   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]1610<?BEGININC p3-payload.iana-headers ?>
[253]1611<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1612<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1613   <ttcol>Header Field Name</ttcol>
1614   <ttcol>Protocol</ttcol>
1615   <ttcol>Status</ttcol>
1616   <ttcol>Reference</ttcol>
1618   <c>Accept</c>
1619   <c>http</c>
1620   <c>standard</c>
1621   <c>
1622      <xref target="header.accept"/>
1623   </c>
1624   <c>Accept-Charset</c>
1625   <c>http</c>
1626   <c>standard</c>
1627   <c>
1628      <xref target="header.accept-charset"/>
1629   </c>
1630   <c>Accept-Encoding</c>
1631   <c>http</c>
1632   <c>standard</c>
1633   <c>
1634      <xref target="header.accept-encoding"/>
1635   </c>
1636   <c>Accept-Language</c>
1637   <c>http</c>
1638   <c>standard</c>
1639   <c>
1640      <xref target="header.accept-language"/>
1641   </c>
1642   <c>Content-Disposition</c>
1643   <c>http</c>
[291]1644   <c/>
[253]1645   <c>
1646      <xref target="content-disposition"/>
1647   </c>
1648   <c>Content-Encoding</c>
1649   <c>http</c>
1650   <c>standard</c>
1651   <c>
1652      <xref target="header.content-encoding"/>
1653   </c>
1654   <c>Content-Language</c>
1655   <c>http</c>
1656   <c>standard</c>
1657   <c>
1658      <xref target="header.content-language"/>
1659   </c>
1660   <c>Content-Location</c>
1661   <c>http</c>
1662   <c>standard</c>
1663   <c>
1664      <xref target="header.content-location"/>
1665   </c>
1666   <c>Content-MD5</c>
1667   <c>http</c>
1668   <c>standard</c>
1669   <c>
1670      <xref target="header.content-md5"/>
1671   </c>
1672   <c>Content-Type</c>
1673   <c>http</c>
1674   <c>standard</c>
1675   <c>
1676      <xref target="header.content-type"/>
1677   </c>
[291]1678   <c>MIME-Version</c>
1679   <c>http</c>
1680   <c/>
1681   <c>
1682      <xref target="mime-version"/>
1683   </c>
[680]1686<?ENDINC p3-payload.iana-headers ?>
[290]1688   The change controller is: "IETF ( - Internet Engineering Task Force".
[668]1692<section title="Content Coding Registry" anchor="content.coding.registration">
1694   The registration procedure for HTTP Content Codings is now defined
[670]1695   by <xref target="content.coding.registry"/> of this document.
1698   The HTTP Content Codings Registry located at <eref target=""/>
[673]1699   should be updated with the registration below:
1701<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
[670]1702   <ttcol>Name</ttcol>
[668]1703   <ttcol>Description</ttcol>
1704   <ttcol>Reference</ttcol>
1705   <c>compress</c>
1706   <c>UNIX "compress" program method</c>
1707   <c>
[673]1708      &compress-coding;
[668]1709   </c>
1710   <c>deflate</c>
[806]1711   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1712   the "zlib" data format (<xref target="RFC1950"/>)
1713   </c>
[668]1714   <c>
[673]1715      &deflate-coding;
[668]1716   </c>
1717   <c>gzip</c>
1718   <c>Same as GNU zip <xref target="RFC1952"/></c>
1719   <c>
[673]1720      &gzip-coding;
[668]1721   </c>
1722   <c>identity</c>
1723   <c>No transformation</c>
1724   <c>
1725      <xref target="content.codings"/>
1726   </c>
[8]1732<section title="Security Considerations" anchor="security.considerations">
1734   This section is meant to inform application developers, information
1735   providers, and users of the security limitations in HTTP/1.1 as
1736   described by this document. The discussion does not include
1737   definitive solutions to the problems revealed, though it does make
1738   some suggestions for reducing security risks.
1741<section title="Privacy Issues Connected to Accept Headers" anchor="">
1743   Accept request-headers can reveal information about the user to all
1744   servers which are accessed. The Accept-Language header in particular
1745   can reveal information the user would consider to be of a private
1746   nature, because the understanding of particular languages is often
1747   strongly correlated to the membership of a particular ethnic group.
1748   User agents which offer the option to configure the contents of an
1749   Accept-Language header to be sent in every request are strongly
1750   encouraged to let the configuration process include a message which
1751   makes the user aware of the loss of privacy involved.
1754   An approach that limits the loss of privacy would be for a user agent
1755   to omit the sending of Accept-Language headers by default, and to ask
1756   the user whether or not to start sending Accept-Language headers to a
1757   server if it detects, by looking for any Vary response-header fields
1758   generated by the server, that such sending could improve the quality
1759   of service.
1762   Elaborate user-customized accept header fields sent in every request,
1763   in particular if these include quality values, can be used by servers
1764   as relatively reliable and long-lived user identifiers. Such user
1765   identifiers would allow content providers to do click-trail tracking,
1766   and would allow collaborating content providers to match cross-server
1767   click-trails or form submissions of individual users. Note that for
1768   many users not behind a proxy, the network address of the host
1769   running the user agent will also serve as a long-lived user
1770   identifier. In environments where proxies are used to enhance
1771   privacy, user agents ought to be conservative in offering accept
1772   header configuration options to end users. As an extreme privacy
1773   measure, proxies could filter the accept headers in relayed requests.
1774   General purpose user agents which provide a high degree of header
1775   configurability &SHOULD; warn users about the loss of privacy which can
1776   be involved.
1780<section title="Content-Disposition Issues" anchor="content-disposition.issues">
[269]1782   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
[8]1783   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1784   serious security considerations. Content-Disposition is not part of
1785   the HTTP standard, but since it is widely implemented, we are
[269]1786   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1787   for details.
1793<section title="Acknowledgments" anchor="ack">
[119]1798<references title="Normative References">
[121]1800<reference anchor="ISO-8859-1">
1801  <front>
1802    <title>
1803     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1804    </title>
1805    <author>
1806      <organization>International Organization for Standardization</organization>
1807    </author>
1808    <date year="1998"/>
1809  </front>
1810  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
[31]1813<reference anchor="Part1">
[119]1814  <front>
1815    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1816    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1817      <organization abbrev="Day Software">Day Software</organization>
1818      <address><email></email></address>
1819    </author>
1820    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1821      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1822      <address><email></email></address>
[119]1823    </author>
1824    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1825      <organization abbrev="HP">Hewlett-Packard Company</organization>
1826      <address><email></email></address>
1827    </author>
1828    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1829      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1830      <address><email></email></address>
1831    </author>
1832    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1833      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1834      <address><email></email></address>
1835    </author>
1836    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1837      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1838      <address><email></email></address>
1839    </author>
1840    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1841      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1842      <address><email></email></address>
1843    </author>
1844    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1845      <organization abbrev="W3C">World Wide Web Consortium</organization>
1846      <address><email></email></address>
1847    </author>
1848    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1849      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1850      <address><email></email></address>
1851    </author>
1852    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1853  </front>
1854  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1855  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1858<reference anchor="Part2">
[119]1859  <front>
1860    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1861    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1862      <organization abbrev="Day Software">Day Software</organization>
1863      <address><email></email></address>
1864    </author>
1865    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1866      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1867      <address><email></email></address>
[119]1868    </author>
1869    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1870      <organization abbrev="HP">Hewlett-Packard Company</organization>
1871      <address><email></email></address>
1872    </author>
1873    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1874      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1875      <address><email></email></address>
1876    </author>
1877    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1878      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1879      <address><email></email></address>
1880    </author>
1881    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1882      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1883      <address><email></email></address>
1884    </author>
1885    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1886      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1887      <address><email></email></address>
1888    </author>
1889    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1890      <organization abbrev="W3C">World Wide Web Consortium</organization>
1891      <address><email></email></address>
1892    </author>
1893    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1894      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1895      <address><email></email></address>
1896    </author>
1897    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1898  </front>
1899  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1900  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1903<reference anchor="Part4">
[119]1904  <front>
1905    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1906    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1907      <organization abbrev="Day Software">Day Software</organization>
1908      <address><email></email></address>
1909    </author>
1910    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1911      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1912      <address><email></email></address>
[119]1913    </author>
1914    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1915      <organization abbrev="HP">Hewlett-Packard Company</organization>
1916      <address><email></email></address>
1917    </author>
1918    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1919      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1920      <address><email></email></address>
1921    </author>
1922    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1923      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1924      <address><email></email></address>
1925    </author>
1926    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1927      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1928      <address><email></email></address>
1929    </author>
1930    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1931      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1932      <address><email></email></address>
1933    </author>
1934    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1935      <organization abbrev="W3C">World Wide Web Consortium</organization>
1936      <address><email></email></address>
1937    </author>
1938    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1939      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1940      <address><email></email></address>
1941    </author>
1942    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1943  </front>
1944  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1945  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1948<reference anchor="Part5">
[119]1949  <front>
1950    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1951    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1952      <organization abbrev="Day Software">Day Software</organization>
1953      <address><email></email></address>
1954    </author>
1955    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1956      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1957      <address><email></email></address>
[119]1958    </author>
1959    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1960      <organization abbrev="HP">Hewlett-Packard Company</organization>
1961      <address><email></email></address>
1962    </author>
1963    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1964      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1965      <address><email></email></address>
1966    </author>
1967    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1968      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1969      <address><email></email></address>
1970    </author>
1971    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1972      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1973      <address><email></email></address>
1974    </author>
1975    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1976      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1977      <address><email></email></address>
1978    </author>
1979    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1980      <organization abbrev="W3C">World Wide Web Consortium</organization>
1981      <address><email></email></address>
1982    </author>
1983    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1984      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1985      <address><email></email></address>
1986    </author>
1987    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1988  </front>
1989  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1990  <x:source href="p5-range.xml" basename="p5-range"/>
1993<reference anchor="Part6">
[119]1994  <front>
1995    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1996    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1997      <organization abbrev="Day Software">Day Software</organization>
1998      <address><email></email></address>
1999    </author>
2000    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]2001      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2002      <address><email></email></address>
[119]2003    </author>
2004    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2005      <organization abbrev="HP">Hewlett-Packard Company</organization>
2006      <address><email></email></address>
2007    </author>
2008    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2009      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2010      <address><email></email></address>
2011    </author>
2012    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2013      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2014      <address><email></email></address>
2015    </author>
2016    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2017      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2018      <address><email></email></address>
2019    </author>
2020    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2021      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2022      <address><email></email></address>
2023    </author>
2024    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2025      <organization abbrev="W3C">World Wide Web Consortium</organization>
2026      <address><email></email></address>
2027    </author>
[601]2028    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2029      <address><email></email></address>
2030    </author>
[119]2031    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2032      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2033      <address><email></email></address>
2034    </author>
2035    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2036  </front>
2037  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2038  <x:source href="p6-cache.xml" basename="p6-cache"/>
[131]2041<reference anchor="RFC1864">
2042  <front>
2043    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2044    <author initials="J." surname="Myers" fullname="John G. Myers">
2045      <organization>Carnegie Mellon University</organization>
2046      <address><email></email></address>
2047    </author>
2048    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2049      <organization>Dover Beach Consulting, Inc.</organization>
2050      <address><email></email></address>
2051    </author>
2052    <date month="October" year="1995"/>
2053  </front>
2054  <seriesInfo name="RFC" value="1864"/>
[122]2057<reference anchor="RFC1950">
2058  <front>
2059    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2060    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2061      <organization>Aladdin Enterprises</organization>
2062      <address><email></email></address>
2063    </author>
[713]2064    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
[122]2065    <date month="May" year="1996"/>
2066  </front>
2067  <seriesInfo name="RFC" value="1950"/>
2068  <annotation>
[277]2069    RFC 1950 is an Informational RFC, thus it may be less stable than
[122]2070    this specification. On the other hand, this downward reference was
[277]2071    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2072    therefore it is unlikely to cause problems in practice. See also
2073    <xref target="BCP97"/>.
[122]2074  </annotation>
[806]2077<reference anchor="RFC1951">
2078  <front>
2079    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2080    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2081      <organization>Aladdin Enterprises</organization>
2082      <address><email></email></address>
2083    </author>
2084    <date month="May" year="1996"/>
2085  </front>
2086  <seriesInfo name="RFC" value="1951"/>
2087  <annotation>
2088    RFC 1951 is an Informational RFC, thus it may be less stable than
2089    this specification. On the other hand, this downward reference was
2090    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2091    therefore it is unlikely to cause problems in practice. See also
2092    <xref target="BCP97"/>.
2093  </annotation>
[122]2096<reference anchor="RFC1952">
2097  <front>
2098    <title>GZIP file format specification version 4.3</title>
2099    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2100      <organization>Aladdin Enterprises</organization>
2101      <address><email></email></address>
2102    </author>
2103    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2104      <address><email></email></address>
2105    </author>
2106    <author initials="M." surname="Adler" fullname="Mark Adler">
2107      <address><email></email></address>
2108    </author>
2109    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2110      <address><email></email></address>
2111    </author>
2112    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2113      <address><email></email></address>
2114    </author>
2115    <date month="May" year="1996"/>
2116  </front>
2117  <seriesInfo name="RFC" value="1952"/>
2118  <annotation>
[277]2119    RFC 1952 is an Informational RFC, thus it may be less stable than
[122]2120    this specification. On the other hand, this downward reference was
[277]2121    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2122    therefore it is unlikely to cause problems in practice. See also
2123    <xref target="BCP97"/>.
[122]2124  </annotation>
[131]2127<reference anchor="RFC2045">
2128  <front>
2129    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2130    <author initials="N." surname="Freed" fullname="Ned Freed">
2131      <organization>Innosoft International, Inc.</organization>
2132      <address><email></email></address>
2133    </author>
2134    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2135      <organization>First Virtual Holdings</organization>
2136      <address><email></email></address>
2137    </author>
2138    <date month="November" year="1996"/>
2139  </front>
2140  <seriesInfo name="RFC" value="2045"/>
2143<reference anchor="RFC2046">
2144  <front>
2145    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2146    <author initials="N." surname="Freed" fullname="Ned Freed">
2147      <organization>Innosoft International, Inc.</organization>
2148      <address><email></email></address>
2149    </author>
2150    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2151      <organization>First Virtual Holdings</organization>
2152      <address><email></email></address>
2153    </author>
2154    <date month="November" year="1996"/>
2155  </front>
2156  <seriesInfo name="RFC" value="2046"/>
[119]2159<reference anchor="RFC2119">
2160  <front>
2161    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2162    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2163      <organization>Harvard University</organization>
2164      <address><email></email></address>
2165    </author>
2166    <date month="March" year="1997"/>
2167  </front>
2168  <seriesInfo name="BCP" value="14"/>
2169  <seriesInfo name="RFC" value="2119"/>
[303]2172<reference anchor='RFC4647'>
2173  <front>
2174    <title>Matching of Language Tags</title>
2175    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2176      <organization>Yahoo! Inc.</organization>
2177      <address><email></email></address>
2178    </author>
2179    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2180      <organization>Google</organization>
2181      <address><email></email></address>
2182    </author>
2183    <date year='2006' month='September' />
2184  </front>
2185  <seriesInfo name='BCP' value='47' />
2186  <seriesInfo name='RFC' value='4647' />
[425]2189<reference anchor="RFC5234">
2190  <front>
2191    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2192    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2193      <organization>Brandenburg InternetWorking</organization>
2194      <address>
[728]2195        <email></email>
2196      </address> 
[425]2197    </author>
2198    <author initials="P." surname="Overell" fullname="Paul Overell">
2199      <organization>THUS plc.</organization>
2200      <address>
[728]2201        <email></email>
2202      </address>
[425]2203    </author>
2204    <date month="January" year="2008"/>
2205  </front>
2206  <seriesInfo name="STD" value="68"/>
2207  <seriesInfo name="RFC" value="5234"/>
[690]2210<reference anchor='RFC5646'>
[613]2211  <front>
2212    <title>Tags for Identifying Languages</title>
2213    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2214      <organization>Lab126</organization>
2215      <address><email></email></address>
2216    </author>
2217    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2218      <organization>Google</organization>
2219      <address><email></email></address>
2220    </author>
[690]2221    <date month='September' year='2009' />
[613]2222  </front>
[690]2223  <seriesInfo name='BCP' value='47' />
2224  <seriesInfo name='RFC' value='5646' />
2229<references title="Informative References">
[129]2231<reference anchor="RFC1945">
2232  <front>
2233    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2234    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2235      <organization>MIT, Laboratory for Computer Science</organization>
2236      <address><email></email></address>
2237    </author>
2238    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2239      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2240      <address><email></email></address>
2241    </author>
2242    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2243      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2244      <address><email></email></address>
2245    </author>
2246    <date month="May" year="1996"/>
2247  </front>
2248  <seriesInfo name="RFC" value="1945"/>
2251<reference anchor="RFC2049">
2252  <front>
2253    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2254    <author initials="N." surname="Freed" fullname="Ned Freed">
2255      <organization>Innosoft International, Inc.</organization>
2256      <address><email></email></address>
2257    </author>
2258    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2259      <organization>First Virtual Holdings</organization>
2260      <address><email></email></address>
2261    </author>
2262    <date month="November" year="1996"/>
2263  </front>
2264  <seriesInfo name="RFC" value="2049"/>
[133]2267<reference anchor="RFC2068">
2268  <front>
2269    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2270    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2271      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2272      <address><email></email></address>
2273    </author>
2274    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2275      <organization>MIT Laboratory for Computer Science</organization>
2276      <address><email></email></address>
2277    </author>
2278    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2279      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2280      <address><email></email></address>
2281    </author>
2282    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2283      <organization>MIT Laboratory for Computer Science</organization>
2284      <address><email></email></address>
2285    </author>
2286    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2287      <organization>MIT Laboratory for Computer Science</organization>
2288      <address><email></email></address>
2289    </author>
2290    <date month="January" year="1997"/>
2291  </front>
2292  <seriesInfo name="RFC" value="2068"/>
[129]2295<reference anchor="RFC2076">
2296  <front>
2297    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2298    <author initials="J." surname="Palme" fullname="Jacob Palme">
2299      <organization>Stockholm University/KTH</organization>
2300      <address><email></email></address>
2301    </author>
2302    <date month="February" year="1997"/>
2303  </front>
2304  <seriesInfo name="RFC" value="2076"/>
2307<reference anchor="RFC2183">
2308  <front>
2309    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2310    <author initials="R." surname="Troost" fullname="Rens Troost">
2311      <organization>New Century Systems</organization>
2312      <address><email></email></address>
2313    </author>
2314    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2315      <organization>QUALCOMM Incorporated</organization>
2316      <address><email></email></address>
2317    </author>
2318    <author initials="K." surname="Moore" fullname="Keith Moore">
2319      <organization>Department of Computer Science</organization>
2320      <address><email></email></address>
2321    </author>
2322    <date month="August" year="1997"/>
2323  </front>
2324  <seriesInfo name="RFC" value="2183"/>
2327<reference anchor="RFC2277">
2328  <front>
2329    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2330    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2331      <organization>UNINETT</organization>
2332      <address><email></email></address>
2333    </author>
2334    <date month="January" year="1998"/>
2335  </front>
2336  <seriesInfo name="BCP" value="18"/>
2337  <seriesInfo name="RFC" value="2277"/>
[745]2340<reference anchor='RFC2295'>
2341  <front>
2342    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2343    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2344      <organization>Technische Universiteit Eindhoven</organization>
2345      <address>
2346        <email></email>
2347      </address>
2348    </author>
2349    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2350      <organization>Hewlett-Packard Company</organization>
2351      <address>
2352        <email></email>
2353      </address>
2354    </author>
2355    <date year='1998' month='March'/>
2356  </front>
2357  <seriesInfo name='RFC' value='2295'/>
[129]2360<reference anchor="RFC2388">
2361  <front>
2362    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2363    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2364      <organization>Xerox Palo Alto Research Center</organization>
2365      <address><email></email></address>
2366    </author>
2367    <date year="1998" month="August"/>
2368  </front>
2369  <seriesInfo name="RFC" value="2388"/>
2372<reference anchor="RFC2557">
2373  <front>
2374    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2375    <author initials="F." surname="Palme" fullname="Jacob Palme">
2376      <organization>Stockholm University and KTH</organization>
2377      <address><email></email></address>
2378    </author>
2379    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2380      <organization>Microsoft Corporation</organization>
2381      <address><email></email></address>
2382    </author>
2383    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2384      <organization>Lotus Development Corporation</organization>
2385      <address><email></email></address>
2386    </author>
2387    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2388      <address><email></email></address>
2389    </author>
2390    <date year="1999" month="March"/>
2391  </front>
2392  <seriesInfo name="RFC" value="2557"/>
[119]2395<reference anchor="RFC2616">
2396  <front>
2397    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2398    <author initials="R." surname="Fielding" fullname="R. Fielding">
2399      <organization>University of California, Irvine</organization>
2400      <address><email></email></address>
2401    </author>
2402    <author initials="J." surname="Gettys" fullname="J. Gettys">
2403      <organization>W3C</organization>
2404      <address><email></email></address>
2405    </author>
2406    <author initials="J." surname="Mogul" fullname="J. Mogul">
2407      <organization>Compaq Computer Corporation</organization>
2408      <address><email></email></address>
2409    </author>
2410    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2411      <organization>MIT Laboratory for Computer Science</organization>
2412      <address><email></email></address>
2413    </author>
2414    <author initials="L." surname="Masinter" fullname="L. Masinter">
2415      <organization>Xerox Corporation</organization>
2416      <address><email></email></address>
2417    </author>
2418    <author initials="P." surname="Leach" fullname="P. Leach">
2419      <organization>Microsoft Corporation</organization>
2420      <address><email></email></address>
2421    </author>
2422    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2423      <organization>W3C</organization>
2424      <address><email></email></address>
2425    </author>
2426    <date month="June" year="1999"/>
2427  </front>
2428  <seriesInfo name="RFC" value="2616"/>
[129]2431<reference anchor="RFC3629">
2432  <front>
2433    <title>UTF-8, a transformation format of ISO 10646</title>
2434    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2435      <organization>Alis Technologies</organization>
2436      <address><email></email></address>
2437    </author>
2438    <date month="November" year="2003"/>
2439  </front>
2440  <seriesInfo name="RFC" value="3629"/>
2441  <seriesInfo name="STD" value="63"/>
[253]2444<reference anchor='RFC3864'>
2445  <front>
2446    <title>Registration Procedures for Message Header Fields</title>
2447    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2448      <organization>Nine by Nine</organization>
2449      <address><email></email></address>
2450    </author>
2451    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2452      <organization>BEA Systems</organization>
2453      <address><email></email></address>
2454    </author>
2455    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2456      <organization>HP Labs</organization>
2457      <address><email></email></address>
2458    </author>
2459    <date year='2004' month='September' />
2460  </front>
2461  <seriesInfo name='BCP' value='90' />
2462  <seriesInfo name='RFC' value='3864' />
[200]2465<reference anchor="RFC4288">
2466  <front>
2467    <title>Media Type Specifications and Registration Procedures</title>
2468    <author initials="N." surname="Freed" fullname="N. Freed">
2469      <organization>Sun Microsystems</organization>
2470      <address>
2471        <email></email>
2472      </address>
2473    </author>
2474    <author initials="J." surname="Klensin" fullname="J. Klensin">
2475      <address>
2476        <email></email>
2477      </address>
2478    </author>
2479    <date year="2005" month="December"/>
2480  </front>
2481  <seriesInfo name="BCP" value="13"/>
2482  <seriesInfo name="RFC" value="4288"/>
[670]2485<reference anchor='RFC5226'>
2486  <front>
2487    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2488    <author initials='T.' surname='Narten' fullname='T. Narten'>
2489      <organization>IBM</organization>
2490      <address><email></email></address>
2491    </author>
2492    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2493      <organization>Google</organization>
2494      <address><email></email></address>
2495    </author>
2496    <date year='2008' month='May' />
2497  </front>
2498  <seriesInfo name='BCP' value='26' />
2499  <seriesInfo name='RFC' value='5226' />
[327]2502<reference anchor="RFC5322">
2503  <front>
2504    <title>Internet Message Format</title>
2505    <author initials="P." surname="Resnick" fullname="P. Resnick">
2506      <organization>Qualcomm Incorporated</organization>
2507    </author>
2508    <date year="2008" month="October"/>
2509  </front> 
2510  <seriesInfo name="RFC" value="5322"/>
[277]2513<reference anchor='BCP97'>
2514  <front>
2515    <title>Handling Normative References to Standards-Track Documents</title>
2516    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2517      <address>
2518        <email></email>
2519      </address>
2520    </author>
2521    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2522      <organization>MIT</organization>
2523      <address>
2524        <email></email>
2525      </address>
2526    </author>
2527    <date year='2007' month='June' />
2528  </front>
2529  <seriesInfo name='BCP' value='97' />
2530  <seriesInfo name='RFC' value='4897' />
[8]2536<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
[327]2538   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
[8]2539   allow entities to be transmitted in an open variety of
2540   representations and with extensible mechanisms. However, RFC 2045
2541   discusses mail, and HTTP has a few features that are different from
2542   those described in RFC 2045. These differences were carefully chosen
2543   to optimize performance over binary connections, to allow greater
2544   freedom in the use of new media types, to make date comparisons
2545   easier, and to acknowledge the practice of some early HTTP servers
2546   and clients.
2549   This appendix describes specific areas where HTTP differs from RFC
2550   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2551   aware of these differences and provide the appropriate conversions
2552   where necessary. Proxies and gateways from MIME environments to HTTP
2553   also need to be aware of the differences because some conversions
2554   might be required.
[8]2557<section title="MIME-Version" anchor="mime-version">
[291]2558  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2559  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
[229]2560  <x:anchor-alias value="MIME-Version"/>
[357]2561  <x:anchor-alias value="MIME-Version-v"/>
2563   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2564   include a single MIME-Version general-header field to indicate what
2565   version of the MIME protocol was used to construct the message. Use
2566   of the MIME-Version header field indicates that the message is in
[115]2567   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2568   Proxies/gateways are responsible for ensuring full compliance (where
2569   possible) when exporting HTTP messages to strict MIME environments.
[357]2571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
[366]2572  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
[357]2573  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2576   MIME version "1.0" is the default for use in HTTP/1.1. However,
2577   HTTP/1.1 message parsing and semantics are defined by this document
2578   and not the MIME specification.
2582<section title="Conversion to Canonical Form" anchor="">
[97]2584   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
[115]2585   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2586   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2587   allowed for subtypes of the "text" media type when transmitted over
[97]2588   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2589   line breaks as CRLF and forbids the use of CR or LF outside of line
2590   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2591   line break within text content when a message is transmitted over
2592   HTTP.
2595   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2596   environment &SHOULD; translate all line breaks within the text media
2597   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2598   canonical form of CRLF. Note, however, that this might be complicated
2599   by the presence of a Content-Encoding and by the fact that HTTP
2600   allows the use of some character sets which do not use octets 13 and
2601   10 to represent CR and LF, as is the case for some multi-byte
2602   character sets.
2605   Implementors should note that conversion will break any cryptographic
2606   checksums applied to the original content unless the original content
2607   is already in canonical form. Therefore, the canonical form is
2608   recommended for any content that uses such checksums in HTTP.
2613<section title="Conversion of Date Formats" anchor="">
2615   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2616   simplify the process of date comparison. Proxies and gateways from
2617   other protocols &SHOULD; ensure that any Date header field present in a
2618   message conforms to one of the HTTP/1.1 formats and rewrite the date
2619   if necessary.
[8]2623<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2625   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2626   Content-Encoding header field. Since this acts as a modifier on the
2627   media type, proxies and gateways from HTTP to MIME-compliant
2628   protocols &MUST; either change the value of the Content-Type header
2629   field or decode the entity-body before forwarding the message. (Some
2630   experimental applications of Content-Type for Internet mail have used
2631   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2632   a function equivalent to Content-Encoding. However, this parameter is
2633   not part of RFC 2045).
2637<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
[85]2639   HTTP does not use the Content-Transfer-Encoding field of RFC
[8]2640   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2641   remove any Content-Transfer-Encoding
[8]2642   prior to delivering the response message to an HTTP client.
2645   Proxies and gateways from HTTP to MIME-compliant protocols are
2646   responsible for ensuring that the message is in the correct format
2647   and encoding for safe transport on that protocol, where "safe
2648   transport" is defined by the limitations of the protocol being used.
2649   Such a proxy or gateway &SHOULD; label the data with an appropriate
2650   Content-Transfer-Encoding if doing so will improve the likelihood of
2651   safe transport over the destination protocol.
2655<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
[29]2657   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2658   Proxies/gateways &MUST; remove any transfer-coding prior to
2659   forwarding a message via a MIME-compliant protocol.
2663<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
[129]2665   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2666   need to be aware of MIME line length limitations. Since HTTP does not
2667   have this limitation, HTTP does not fold long lines. MHTML messages
2668   being transported by HTTP follow all conventions of MHTML, including
2669   line length limitations and folding, canonicalization, etc., since
2670   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2671   does not interpret the content or any MIME header lines that might be
2672   contained therein.
2677<section title="Additional Features" anchor="additional.features">
[97]2679   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2680   existing HTTP implementations, but not consistently and correctly
2681   across most HTTP/1.1 applications. Implementors are advised to be
2682   aware of these features, but cannot rely upon their presence in, or
2683   interoperability with, other HTTP/1.1 applications. Some of these
2684   describe proposed experimental features, and some describe features
2685   that experimental deployment found lacking that are now addressed in
2686   the base HTTP/1.1 specification.
2689   A number of other headers, such as Content-Disposition and Title,
[97]2690   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2693<section title="Content-Disposition" anchor="content-disposition">
2694<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2695<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
[229]2696  <x:anchor-alias value="content-disposition"/>
[357]2697  <x:anchor-alias value="content-disposition-v"/>
[229]2698  <x:anchor-alias value="disposition-type"/>
2699  <x:anchor-alias value="disposition-parm"/>
2700  <x:anchor-alias value="disp-extension-parm"/>
2701  <x:anchor-alias value="disp-extension-token"/>
2702  <x:anchor-alias value="filename-parm"/>
[697]2704   The "Content-Disposition" response-header field has been proposed as a
[8]2705   means for the origin server to suggest a default filename if the user
2706   requests that the content is saved to a file. This usage is derived
[269]2707   from the definition of Content-Disposition in <xref target="RFC2183"/>.
[357]2709<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"/>
[366]2710  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
[357]2711                        <x:ref>content-disposition-v</x:ref>
[376]2712  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2713                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
[334]2714  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2715  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
[229]2716  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2717  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
[810]2718  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" <x:ref>word</x:ref>
2721   An example is
2723<figure><artwork type="example">
[458]2724  Content-Disposition: attachment; filename="fname.ext"
2727   The receiving user agent &SHOULD-NOT;  respect any directory path
2728   information present in the filename-parm parameter, which is the only
2729   parameter believed to apply to HTTP implementations at this time. The
2730   filename &SHOULD; be treated as a terminal component only.
2733   If this header is used in a response with the application/octet-stream
2734   content-type, the implied suggestion is that the user agent
[746]2735   should not display the response, but directly enter a "save response
2736   as..." dialog.
2739   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
[99]2744<section title="Compatibility with Previous Versions" anchor="compatibility">
[8]2745<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
[29]2747   Charset wildcarding is introduced to avoid explosion of character set
2748   names in accept headers. (<xref target="header.accept-charset"/>)
2751   Content-Base was deleted from the specification: it was not
2752   implemented widely, and there is no simple, safe way to introduce it
2753   without a robust extension mechanism. In addition, it is used in a
[129]2754   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2757   A content-coding of "identity" was introduced, to solve problems
2758   discovered in caching. (<xref target="content.codings"/>)
2761   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
2762   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
[268]2763   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2767<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2769  Clarify contexts that charset is used in.
2770  (<xref target="character.sets"/>)
[712]2773  Remove base URI setting semantics for Content-Location due to poor
[714]2774  implementation support, which was caused by too many broken servers emitting
2775  bogus Content-Location headers, and also the potentially undesirable effect
2776  of potentially breaking relative links in content-negotiated resources.
[712]2777  (<xref target="header.content-location"/>)
[104]2780  Remove reference to non-existant identity transfer-coding value tokens.
2781  (<xref target="no.content-transfer-encoding"/>)
[680]2787<?BEGININC p3-payload.abnf-appendix ?>
[427]2788<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
2790<artwork type="abnf" name="p3-payload.parsed-abnf">
2791<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2792<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2793<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[425]2794 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2795 qvalue ] ] )
[427]2796<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2797<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
[425]2798 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
[427]2799<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2800<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[425]2801 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2802 ] )
[427]2803<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
[425]2804 OWS media-range [ accept-params ] ] ) ]
[427]2806<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2807<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
[425]2808 content-coding ] )
[427]2809<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2810<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
[425]2811 language-tag ] )
[678]2812<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
[427]2813<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2814<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2815<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2816<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2817<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2818<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2819<x:ref>Content-Type-v</x:ref> = media-type
[538]2821<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2823<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2825<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2826<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2828<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
[648]2830<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
[810]2831<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
[427]2832<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2833<x:ref>attribute</x:ref> = token
2835<x:ref>charset</x:ref> = token
2836<x:ref>codings</x:ref> = ( content-coding / "*" )
2837<x:ref>content-coding</x:ref> = token
2838<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
[425]2839 content-disposition-v
[427]2840<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
[425]2841 disposition-parm )
[810]2843<x:ref>disp-extension-parm</x:ref> = token "=" word
[427]2844<x:ref>disp-extension-token</x:ref> = token
2845<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2846<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2848<x:ref>entity-body</x:ref> = *OCTET
2849<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
[425]2850 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2851 Expires / Last-Modified / extension-header
[647]2852<x:ref>extension-header</x:ref> = header-field
2854<x:ref>filename-parm</x:ref> = "filename=" quoted-string
[678]2856<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 3.2&gt;
[427]2858<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
[690]2859<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2861<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[425]2862 ";" OWS parameter )
[427]2863<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2865<x:ref>parameter</x:ref> = attribute "=" value
[648]2866<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2868<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
[678]2869<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2871<x:ref>subtype</x:ref> = token
2873<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2874<x:ref>type</x:ref> = token
[810]2876<x:ref>value</x:ref> = word
2878<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
[532]2881<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2882; Accept defined but not used
[425]2883; Accept-Charset defined but not used
2884; Accept-Encoding defined but not used
2885; Accept-Language defined but not used
2886; MIME-Version defined but not used
2887; content-disposition defined but not used
2888; entity-body defined but not used
2889; entity-header defined but not used
[680]2891<?ENDINC p3-payload.abnf-appendix ?>
[252]2893<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2895<section title="Since RFC2616">
2897  Extracted relevant partitions from <xref target="RFC2616"/>.
2901<section title="Since draft-ietf-httpbis-p3-payload-00">
[116]2903  Closed issues:
2904  <list style="symbols"> 
2905    <t>
[324]2906      <eref target=""/>:
[116]2907      "Media Type Registrations"
2908      (<eref target=""/>)
2909    </t>
2910    <t>
[324]2911      <eref target=""/>:
[116]2912      "Clarification regarding quoting of charset values"
2913      (<eref target=""/>)
2914    </t>
2915    <t>
[324]2916      <eref target=""/>:
[116]2917      "Remove 'identity' token references"
2918      (<eref target=""/>)
2919    </t>
2920    <t>
[324]2921      <eref target=""/>:
[126]2922      "Accept-Encoding BNF"
2923    </t>
2924    <t>
[324]2925      <eref target=""/>:
[152]2926      "Normative and Informative references"
2927    </t>
2928    <t>
[324]2929      <eref target=""/>:
[116]2930      "RFC1700 references"
2931    </t>
[122]2932    <t>
[324]2933      <eref target=""/>:
[200]2934      "Updating to RFC4288"
2935    </t>
2936    <t>
[324]2937      <eref target=""/>:
[129]2938      "Informative references"
2939    </t>
2940    <t>
[324]2941      <eref target=""/>:
[123]2942      "ISO-8859-1 Reference"
2943    </t>
2944    <t>
[324]2945      <eref target=""/>:
[122]2946      "Encoding References Normative"
2947    </t>
[131]2948    <t>
[324]2949      <eref target=""/>:
[131]2950      "Normative up-to-date references"
2951    </t>
[116]2952  </list>
[170]2956<section title="Since draft-ietf-httpbis-p3-payload-01">
[324]2958  Ongoing work on ABNF conversion (<eref target=""/>):
[205]2959  <list style="symbols"> 
2960    <t>
2961      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2962    </t>
2963  </list>
[252]2967<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[232]2969  Closed issues:
2970  <list style="symbols"> 
2971    <t>
[324]2972      <eref target=""/>:
[251]2973      "Quoting Charsets"
2974    </t>
2975    <t>
[324]2976      <eref target=""/>:
[232]2977      "Classification for Allow header"
2978    </t>
[248]2979    <t>
[324]2980      <eref target=""/>:
[248]2981      "missing default for qvalue in description of Accept-Encoding"
2982    </t>
[232]2983  </list>
[324]2986  Ongoing work on IANA Message Header Registration (<eref target=""/>):
[253]2987  <list style="symbols"> 
2988    <t>
2989      Reference RFC 3984, and update header registrations for headers defined
2990      in this document.
2991    </t>
2992  </list>
[267]2996<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
[269]2998  Closed issues:
2999  <list style="symbols"> 
3000    <t>
[297]3001      <eref target=""/>:
3002      "Quoting Charsets"
3003    </t>
3004    <t>
[303]3005      <eref target=""/>:
3006      "language tag matching (Accept-Language) vs RFC4647"
3007    </t>
3008    <t>
[277]3009      <eref target=""/>:
[269]3010      "RFC 1806 has been replaced by RFC2183"
3011    </t>
3012  </list>
3015  Other changes:
3016  <list style="symbols"> 
3017    <t>
3018      <eref target=""/>:
3019      "Encoding References Normative" -- rephrase the annotation and reference
3020      <xref target="BCP97"/>.
3021    </t>
3022  </list>
[269]3024 </section>
[323]3026<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
[327]3028  Closed issues:
3029  <list style="symbols"> 
3030    <t>
3031      <eref target=""/>:
3032      "RFC 2822 is updated by RFC 5322"
3033    </t>
3034  </list>
3037  Ongoing work on ABNF conversion (<eref target=""/>):
3038  <list style="symbols"> 
3039    <t>
3040      Use "/" instead of "|" for alternatives.
3041    </t>
[357]3042    <t>
3043      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3044      whitespace ("OWS") and required whitespace ("RWS").
3045    </t>
3046    <t>
3047      Rewrite ABNFs to spell out whitespace rules, factor out
3048      header value format definitions.
3049    </t>
[334]3050  </list>
[382]3054<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
[385]3056  Closed issues:
3057  <list style="symbols"> 
3058    <t>
3059      <eref target=""/>:
3060      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3061    </t>
3062  </list>
[543]3065  Final work on ABNF conversion (<eref target=""/>):
[421]3066  <list style="symbols"> 
3067    <t>
[424]3068      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
[421]3069    </t>
3070  </list>
3073  Other changes:
3074  <list style="symbols"> 
3075    <t>
3076      Move definition of quality values into Part 1.
3077    </t>
3078  </list>
[547]3082<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
[577]3084  Closed issues:
3085  <list style="symbols"> 
3086    <t>
3087      <eref target=""/>:
3088      "Content-Location isn't special"
3089    </t>
[592]3090    <t>
3091      <eref target=""/>:
3092      "Content Sniffing"
3093    </t>
[577]3094  </list>
[604]3098<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
[613]3100  Closed issues:
3101  <list style="symbols"> 
3102    <t>
[670]3103      <eref target=""/>:
[613]3104      "Updated reference for language tags"
3105    </t>
[663]3106    <t>
[716]3107      <eref target=""/>:
3108      "Clarify rules for determining what entities a response carries"
3109    </t>
3110    <t>
[712]3111      <eref target=""/>:
3112      "Content-Location base-setting problems"
3113    </t>
3114    <t>
[663]3115      <eref target=""/>:
3116      "Content Sniffing"
3117    </t>
[670]3118    <t>
3119      <eref target=""/>:
3120      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3121    </t>
[673]3122    <t>
3123      <eref target=""/>:
3124      "move definitions of gzip/deflate/compress to part 1"
3125    </t>
[613]3126  </list>
3129  Partly resolved issues:
3130  <list style="symbols"> 
3131    <t>
3132      <eref target=""/>:
3133      "update IANA requirements wrt Transfer-Coding values" (add the
3134      IANA Considerations subsection)
3135    </t>
[668]3136    <t>
3137      <eref target=""/>:
3138      "update IANA requirements wrt Content-Coding values" (add the
3139      IANA Considerations subsection)
3140    </t>
[667]3141  </list>
[720]3145<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
[724]3147  Closed issues:
3148  <list style="symbols"> 
3149    <t>
[745]3150      <eref target=""/>:
3151      "Content Negotiation for media types"
3152    </t>
3153    <t>
[724]3154      <eref target=""/>:
3155      "Accept-Language: which RFC4647 filtering?"
3156    </t>
3157  </list>
[773]3161<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
[808]3163  Closed issues:
3164  <list style="symbols"> 
3165    <t>
3166      <eref target=""/>:
3167      "IANA registry for content/transfer encodings"
3168    </t>
[810]3169    <t>
[831]3170      <eref target=""/>:
3171      "Content Sniffing"
3172    </t>
3173    <t>
[810]3174      <eref target=""/>:
3175      "use of term "word" when talking about header structure"
3176    </t>
[808]3177  </list>
3180  Partly resolved issues:
3181  <list style="symbols"> 
3182    <t>
3183      <eref target=""/>:
3184      "Term for the requested resource's URI"
3185    </t>
3186  </list>
[841]3190<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
[854]3192  Closed issues:
3193  <list style="symbols"> 
3194    <t>
[858]3195      <eref target=""/>:
3196      "Clarify 'Requested Variant'"
3197    </t>
3198    <t>
3199      <eref target=""/>:
3200      "Content-Location isn't special"
3201    </t>
3202    <t>
[854]3203      <eref target=""/>:
3204      "Delimiting messages with multipart/byteranges"
3205    </t>
[858]3206    <t>
3207      <eref target=""/>:
3208      "Clarify entity / representation / variant terminology"
3209    </t>
3210    <t>
3211      <eref target=""/>:
3212      "confusing req. language for Content-Location"
3213    </t>
3214    <t>
3215      <eref target=""/>:
3216      "Content-Location on 304 responses"
3217    </t>
[854]3218  </list>
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