source: draft-ietf-httpbis/latest/p3-payload.xml @ 357

Last change on this file since 357 was 357, checked in by julian.reschke@…, 14 years ago

Rewrite header ABNFs to spell out whitespace rules, factor out value format definitions. (related to #36)

  • Property svn:eol-style set to native
File size: 120.3 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>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>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
18  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
19  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
20  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
21  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
22  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
23  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
24  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
25  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
26  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
27  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
28  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x=''/>">
29  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x=''/>">
30  <!ENTITY general-syntax           "<xref target='Part1' x:rel='#general.syntax' xmlns:x=''/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
33<?rfc toc="yes" ?>
34<?rfc symrefs="yes" ?>
35<?rfc sortrefs="yes" ?>
36<?rfc compact="yes"?>
37<?rfc subcompact="no" ?>
38<?rfc linkmailto="no" ?>
39<?rfc editing="no" ?>
40<?rfc comments="yes"?>
41<?rfc inline="yes"?>
42<?rfc-ext allow-markup-in-artwork="yes" ?>
43<?rfc-ext include-references-in-index="yes" ?>
44<rfc obsoletes="2616" category="std" x:maturity-level="draft"
45     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
46     xmlns:x=''>
49  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
51  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
52    <organization abbrev="Day Software">Day Software</organization>
53    <address>
54      <postal>
55        <street>23 Corporate Plaza DR, Suite 280</street>
56        <city>Newport Beach</city>
57        <region>CA</region>
58        <code>92660</code>
59        <country>USA</country>
60      </postal>
61      <phone>+1-949-706-5300</phone>
62      <facsimile>+1-949-706-5305</facsimile>
63      <email></email>
64      <uri></uri>
65    </address>
66  </author>
68  <author initials="J." surname="Gettys" fullname="Jim Gettys">
69    <organization>One Laptop per Child</organization>
70    <address>
71      <postal>
72        <street>21 Oak Knoll Road</street>
73        <city>Carlisle</city>
74        <region>MA</region>
75        <code>01741</code>
76        <country>USA</country>
77      </postal>
78      <email></email>
79      <uri></uri>
80    </address>
81  </author>
83  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
84    <organization abbrev="HP">Hewlett-Packard Company</organization>
85    <address>
86      <postal>
87        <street>HP Labs, Large Scale Systems Group</street>
88        <street>1501 Page Mill Road, MS 1177</street>
89        <city>Palo Alto</city>
90        <region>CA</region>
91        <code>94304</code>
92        <country>USA</country>
93      </postal>
94      <email></email>
95    </address>
96  </author>
98  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106        <country>USA</country>
107      </postal>
108      <email></email>
109    </address>
110  </author>
112  <author initials="L." surname="Masinter" fullname="Larry Masinter">
113    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
114    <address>
115      <postal>
116        <street>345 Park Ave</street>
117        <city>San Jose</city>
118        <region>CA</region>
119        <code>95110</code>
120        <country>USA</country>
121      </postal>
122      <email></email>
123      <uri></uri>
124    </address>
125  </author>
127  <author initials="P." surname="Leach" fullname="Paul J. Leach">
128    <organization abbrev="Microsoft">Microsoft Corporation</organization>
129    <address>
130      <postal>
131        <street>1 Microsoft Way</street>
132        <city>Redmond</city>
133        <region>WA</region>
134        <code>98052</code>
135      </postal>
136      <email></email>
137    </address>
138  </author>
140  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
141    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
142    <address>
143      <postal>
144        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
145        <street>The Stata Center, Building 32</street>
146        <street>32 Vassar Street</street>
147        <city>Cambridge</city>
148        <region>MA</region>
149        <code>02139</code>
150        <country>USA</country>
151      </postal>
152      <email></email>
153      <uri></uri>
154    </address>
155  </author>
157  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
158    <organization abbrev="W3C">World Wide Web Consortium</organization>
159    <address>
160      <postal>
161        <street>W3C / ERCIM</street>
162        <street>2004, rte des Lucioles</street>
163        <city>Sophia-Antipolis</city>
164        <region>AM</region>
165        <code>06902</code>
166        <country>France</country>
167      </postal>
168      <email></email>
169      <uri></uri>
170    </address>
171  </author>
173  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
174    <organization abbrev="greenbytes">greenbytes GmbH</organization>
175    <address>
176      <postal>
177        <street>Hafenweg 16</street>
178        <city>Muenster</city><region>NW</region><code>48155</code>
179        <country>Germany</country>
180      </postal>
181      <phone>+49 251 2807760</phone>   
182      <facsimile>+49 251 2807761</facsimile>   
183      <email></email>       
184      <uri></uri>     
185    </address>
186  </author>
188  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
192   The Hypertext Transfer Protocol (HTTP) is an application-level
193   protocol for distributed, collaborative, hypermedia information
194   systems. HTTP has been in use by the World Wide Web global information
195   initiative since 1990. This document is Part 3 of the seven-part specification
196   that defines the protocol referred to as "HTTP/1.1" and, taken together,
197   obsoletes RFC 2616.  Part 3 defines HTTP message content,
198   metadata, and content negotiation.
202<note title="Editorial Note (To be removed by RFC Editor)">
203  <t>
204    Discussion of this draft should take place on the HTTPBIS working group
205    mailing list ( The current issues list is
206    at <eref target=""/>
207    and related documents (including fancy diffs) can be found at
208    <eref target=""/>.
209  </t>
210  <t>
211    The changes in this draft are summarized in <xref target="changes.since.04"/>.
212  </t>
216<section title="Introduction" anchor="introduction">
218   This document defines HTTP/1.1 message payloads (a.k.a., content), the
219   associated metadata header fields that define how the payload is intended
220   to be interpreted by a recipient, the request header fields that
221   may influence content selection, and the various selection algorithms
222   that are collectively referred to as HTTP content negotiation.
225   This document is currently disorganized in order to minimize the changes
226   between drafts and enable reviewers to see the smaller errata changes.
227   The next draft will reorganize the sections to better reflect the content.
228   In particular, the sections on entities will be renamed payload and moved
229   to the first half of the document, while the sections on content negotiation
230   and associated request header fields will be moved to the second half.  The
231   current mess reflects how widely dispersed these topics and associated
232   requirements had become in <xref target="RFC2616"/>.
235<section title="Requirements" anchor="intro.requirements">
237   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
238   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
239   document are to be interpreted as described in <xref target="RFC2119"/>.
242   An implementation is not compliant if it fails to satisfy one or more
243   of the &MUST; or &REQUIRED; level requirements for the protocols it
244   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
245   level and all the &SHOULD; level requirements for its protocols is said
246   to be "unconditionally compliant"; one that satisfies all the &MUST;
247   level requirements but not all the &SHOULD; level requirements for its
248   protocols is said to be "conditionally compliant."
253<section title="Notational Conventions and Generic Grammar" anchor="notation">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="DIGIT"/>
256  <x:anchor-alias value="OCTET"/>
257  <x:anchor-alias value="quoted-string"/>
258  <x:anchor-alias value="token"/>
259  <x:anchor-alias value="BWS"/>
260  <x:anchor-alias value="OWS"/>
261  <x:anchor-alias value="RWS"/>
263  This specification uses the ABNF syntax defined in &notation-abnf; and
264  the core rules defined in &basic-rules;:
265  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
266  <eref target=""/>.</cref>
268<figure><artwork type="abnf2616">
269  <x:ref>ALPHA</x:ref>          = &lt;ALPHA, defined in &basic-rules;&gt;
270  <x:ref>DIGIT</x:ref>          = &lt;DIGIT, defined in &basic-rules;&gt;
271  <x:ref>OCTET</x:ref>          = &lt;OCTET, defined in &basic-rules;&gt;
273<figure><artwork type="abnf2616">
274  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
275  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
276  <x:ref>BWS</x:ref>            = &lt;BWS, defined in &basic-rules;&gt;
277  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
278  <x:ref>RWS</x:ref>            = &lt;RWS, defined in &basic-rules;&gt;
280<t anchor="abnf.dependencies">
281  <x:anchor-alias value="absoluteURI"/>
282  <x:anchor-alias value="Allow"/>
283  <x:anchor-alias value="Content-Length"/>
284  <x:anchor-alias value="Content-Range"/>
285  <x:anchor-alias value="Expires"/>
286  <x:anchor-alias value="Last-Modified"/>
287  <x:anchor-alias value="message-header"/>
288  <x:anchor-alias value="relativeURI"/>
289  The ABNF rules below are defined in other parts:
291<figure><!--Part1--><artwork type="abnf2616">
292  <x:ref>absoluteURI</x:ref>    = &lt;absoluteURI, defined in &general-syntax;&gt;
293  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
294  <x:ref>relativeURI</x:ref>    = &lt;relativeURI, defined in &general-syntax;&gt;
295  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
297<figure><!--Part4--><artwork type="abnf2616">
298  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
300<figure><!--Part5--><artwork type="abnf2616">
301  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
303<figure><!--Part6--><artwork type="abnf2616">
304  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
308<section title="Protocol Parameters" anchor="protocol.parameters">
310<section title="Character Sets" anchor="character.sets">
312   HTTP uses the same definition of the term "character set" as that
313   described for MIME:
316   The term "character set" is used in this document to refer to a
317   method used with one or more tables to convert a sequence of octets
318   into a sequence of characters. Note that unconditional conversion in
319   the other direction is not required, in that not all characters may
320   be available in a given character set and a character set may provide
321   more than one sequence of octets to represent a particular character.
322   This definition is intended to allow various kinds of character
323   encoding, from simple single-table mappings such as US-ASCII to
324   complex table switching methods such as those that use ISO-2022's
325   techniques. However, the definition associated with a MIME character
326   set name &MUST; fully specify the mapping to be performed from octets
327   to characters. In particular, use of external profiling information
328   to determine the exact mapping is not permitted.
331      <x:h>Note:</x:h> This use of the term "character set" is more commonly
332      referred to as a "character encoding." However, since HTTP and
333      MIME share the same registry, it is important that the terminology
334      also be shared.
336<t anchor="rule.charset">
337  <x:anchor-alias value="charset"/>
338   HTTP character sets are identified by case-insensitive tokens. The
339   complete set of tokens is defined by the IANA Character Set registry
340   (<eref target=""/>).
342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
343  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
346   Although HTTP allows an arbitrary token to be used as a charset
347   value, any token that has a predefined value within the IANA
348   Character Set registry &MUST; represent the character set defined
349   by that registry. Applications &SHOULD; limit their use of character
350   sets to those defined by the IANA registry.
353   HTTP uses charset in two contexts: within an Accept-Charset request
354   header (in which the charset value is an unquoted token) and as the
355   value of a parameter in a Content-Type header (within a request or
356   response), in which case the parameter value of the charset parameter
357   may be quoted.
360   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
361   <xref target="RFC2277"/>.
364<section title="Missing Charset" anchor="missing.charset">
366   Some HTTP/1.0 software has interpreted a Content-Type header without
367   charset parameter incorrectly to mean "recipient should guess."
368   Senders wishing to defeat this behavior &MAY; include a charset
369   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
370   it is known that it will not confuse the recipient.
373   Unfortunately, some older HTTP/1.0 clients did not deal properly with
374   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
375   charset label provided by the sender; and those user agents that have
376   a provision to "guess" a charset &MUST; use the charset from the
377   content-type field if they support that charset, rather than the
378   recipient's preference, when initially displaying a document. See
379   <xref target="canonicalization.and.text.defaults"/>.
384<section title="Content Codings" anchor="content.codings">
385  <x:anchor-alias value="content-coding"/>
387   Content coding values indicate an encoding transformation that has
388   been or can be applied to an entity. Content codings are primarily
389   used to allow a document to be compressed or otherwise usefully
390   transformed without losing the identity of its underlying media type
391   and without loss of information. Frequently, the entity is stored in
392   coded form, transmitted directly, and only decoded by the recipient.
394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
395  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
398   All content-coding values are case-insensitive. HTTP/1.1 uses
399   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
400   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
401   describes the content-coding, what is more important is that it
402   indicates what decoding mechanism will be required to remove the
403   encoding.
406   The Internet Assigned Numbers Authority (IANA) acts as a registry for
407   content-coding value tokens. Initially, the registry contains the
408   following tokens:
411   gzip<iref item="gzip"/>
412  <list>
413    <t>
414        An encoding format produced by the file compression program
415        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
416        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
417    </t>
418  </list>
421   compress<iref item="compress"/>
422  <list><t>
423        The encoding format produced by the common UNIX file compression
424        program "compress". This format is an adaptive Lempel-Ziv-Welch
425        coding (LZW).
427        Use of program names for the identification of encoding formats
428        is not desirable and is discouraged for future encodings. Their
429        use here is representative of historical practice, not good
430        design. For compatibility with previous implementations of HTTP,
431        applications &SHOULD; consider "x-gzip" and "x-compress" to be
432        equivalent to "gzip" and "compress" respectively.
433  </t></list>
436   deflate<iref item="deflate"/>
437  <list><t>
438        The "zlib" format defined in <xref target="RFC1950"/> in combination with
439        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
440  </t></list>
443   identity<iref item="identity"/>
444  <list><t>
445        The default (identity) encoding; the use of no transformation
446        whatsoever. This content-coding is used only in the Accept-Encoding
447        header, and &SHOULD-NOT;  be used in the Content-Encoding
448        header.
449  </t></list>
452   New content-coding value tokens &SHOULD; be registered; to allow
453   interoperability between clients and servers, specifications of the
454   content coding algorithms needed to implement a new value &SHOULD; be
455   publicly available and adequate for independent implementation, and
456   conform to the purpose of content coding defined in this section.
460<section title="Media Types" anchor="media.types">
461  <x:anchor-alias value="media-type"/>
462  <x:anchor-alias value="type"/>
463  <x:anchor-alias value="subtype"/>
465   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
466   and Accept (<xref target="header.accept"/>) header fields in order to provide
467   open and extensible data typing and type negotiation.
469<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"/>
470  <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> )
471  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
472  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
474<t anchor="rule.parameter">
475  <x:anchor-alias value="attribute"/>
476  <x:anchor-alias value="parameter"/>
477  <x:anchor-alias value="value"/>
478   Parameters &MAY; follow the type/subtype in the form of attribute/value
479   pairs.
481<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"/>
482  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
483  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
484  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
487   The type, subtype, and parameter attribute names are case-insensitive.
488   Parameter values might or might not be case-sensitive,
489   depending on the semantics of the parameter name. Linear white space
490   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
491   attribute and its value. The presence or absence of a parameter might
492   be significant to the processing of a media-type, depending on its
493   definition within the media type registry.
496   A parameter value that matches the <x:ref>token</x:ref> production may be
497   transmitted as either a token or within a quoted-string. The quoted and
498   unquoted values are equivalent.
501   Note that some older HTTP applications do not recognize media type
502   parameters. When sending data to older HTTP applications,
503   implementations &SHOULD; only use media type parameters when they are
504   required by that type/subtype definition.
507   Media-type values are registered with the Internet Assigned Number
508   Authority (IANA). The media type registration process is
509   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
510   discouraged.
513<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
515   Internet media types are registered with a canonical form. An
516   entity-body transferred via HTTP messages &MUST; be represented in the
517   appropriate canonical form prior to its transmission except for
518   "text" types, as defined in the next paragraph.
521   When in canonical form, media subtypes of the "text" type use CRLF as
522   the text line break. HTTP relaxes this requirement and allows the
523   transport of text media with plain CR or LF alone representing a line
524   break when it is done consistently for an entire entity-body. HTTP
525   applications &MUST; accept CRLF, bare CR, and bare LF as being
526   representative of a line break in text media received via HTTP. In
527   addition, if the text is represented in a character set that does not
528   use octets 13 and 10 for CR and LF respectively, as is the case for
529   some multi-byte character sets, HTTP allows the use of whatever octet
530   sequences are defined by that character set to represent the
531   equivalent of CR and LF for line breaks. This flexibility regarding
532   line breaks applies only to text media in the entity-body; a bare CR
533   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
534   structures (such as header fields and multipart boundaries).
537   If an entity-body is encoded with a content-coding, the underlying
538   data &MUST; be in a form defined above prior to being encoded.
541   The "charset" parameter is used with some media types to define the
542   character set (<xref target="character.sets"/>) of the data. When no explicit charset
543   parameter is provided by the sender, media subtypes of the "text"
544   type are defined to have a default charset value of "ISO-8859-1" when
545   received via HTTP. Data in character sets other than "ISO-8859-1" or
546   its subsets &MUST; be labeled with an appropriate charset value. See
547   <xref target="missing.charset"/> for compatibility problems.
551<section title="Multipart Types" anchor="multipart.types">
553   MIME provides for a number of "multipart" types -- encapsulations of
554   one or more entities within a single message-body. All multipart
555   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
556   and &MUST; include a boundary parameter as part of the media type
557   value. The message body is itself a protocol element and &MUST;
558   therefore use only CRLF to represent line breaks between body-parts.
559   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
560   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
561   original multipart contains an epilogue). These restrictions exist in
562   order to preserve the self-delimiting nature of a multipart message-body,
563   wherein the "end" of the message-body is indicated by the
564   ending multipart boundary.
567   In general, HTTP treats a multipart message-body no differently than
568   any other media type: strictly as payload. The one exception is the
569   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
570   (Partial Content) response.
571   <!-- jre: re-insert removed text pointing to caching? -->
572   In all
573   other cases, an HTTP user agent &SHOULD; follow the same or similar
574   behavior as a MIME user agent would upon receipt of a multipart type.
575   The MIME header fields within each body-part of a multipart message-body
576   do not have any significance to HTTP beyond that defined by
577   their MIME semantics.
580   In general, an HTTP user agent &SHOULD; follow the same or similar
581   behavior as a MIME user agent would upon receipt of a multipart type.
582   If an application receives an unrecognized multipart subtype, the
583   application &MUST; treat it as being equivalent to "multipart/mixed".
586      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
587      for carrying form data suitable for processing via the POST
588      request method, as described in <xref target="RFC2388"/>.
593<section title="Quality Values" anchor="quality.values">
594  <x:anchor-alias value="qvalue"/>
596   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
597   numbers to indicate the relative importance ("weight") of various
598   negotiable parameters.  A weight is normalized to a real number in
599   the range 0 through 1, where 0 is the minimum and 1 the maximum
600   value. If a parameter has a quality value of 0, then content with
601   this parameter is `not acceptable' for the client. HTTP/1.1
602   applications &MUST-NOT; generate more than three digits after the
603   decimal point. User configuration of these values &SHOULD; also be
604   limited in this fashion.
606<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
607  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
608                 / ( "1" [ "." 0*3("0") ] )
611   "Quality values" is a misnomer, since these values merely represent
612   relative degradation in desired quality.
616<section title="Language Tags" anchor="language.tags">
617  <x:anchor-alias value="language-tag"/>
618  <x:anchor-alias value="primary-tag"/>
619  <x:anchor-alias value="subtag"/>
621   A language tag identifies a natural language spoken, written, or
622   otherwise conveyed by human beings for communication of information
623   to other human beings. Computer languages are explicitly excluded.
624   HTTP uses language tags within the Accept-Language and Content-Language
625   fields.
628   The syntax and registry of HTTP language tags is the same as that
629   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
630   or more parts: A primary language tag and a possibly empty series of
631   subtags:
633<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
634  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
635  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
636  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
639   White space is not allowed within the tag and all tags are case-insensitive.
640   The name space of language tags is administered by the
641   IANA. Example tags include:
643<figure><artwork type="example">
644    en, en-US, en-cockney, i-cherokee, x-pig-latin
647   where any two-letter primary-tag is an ISO-639 language abbreviation
648   and any two-letter initial subtag is an ISO-3166 country code. (The
649   last three tags above are not registered tags; all but the last are
650   examples of tags which could be registered in future.)
655<section title="Entity" anchor="entity">
657   Request and Response messages &MAY; transfer an entity if not otherwise
658   restricted by the request method or response status code. An entity
659   consists of entity-header fields and an entity-body, although some
660   responses will only include the entity-headers.
663   In this section, both sender and recipient refer to either the client
664   or the server, depending on who sends and who receives the entity.
667<section title="Entity Header Fields" anchor="entity.header.fields">
668  <x:anchor-alias value="entity-header"/>
669  <x:anchor-alias value="extension-header"/>
671   Entity-header fields define metainformation about the entity-body or,
672   if no body is present, about the resource identified by the request.
674<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
675  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
676                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
677                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
678                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
679                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
680                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
681                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
682                 / <x:ref>Expires</x:ref>                  ; &header-expires;
683                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
684                 / <x:ref>extension-header</x:ref>
686  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
689   The extension-header mechanism allows additional entity-header fields
690   to be defined without changing the protocol, but these fields cannot
691   be assumed to be recognizable by the recipient. Unrecognized header
692   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
693   transparent proxies.
697<section title="Entity Body" anchor="entity.body">
698  <x:anchor-alias value="entity-body"/>
700   The entity-body (if any) sent with an HTTP request or response is in
701   a format and encoding defined by the entity-header fields.
703<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
704  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
707   An entity-body is only present in a message when a message-body is
708   present, as described in &message-body;. The entity-body is obtained
709   from the message-body by decoding any Transfer-Encoding that might
710   have been applied to ensure safe and proper transfer of the message.
713<section title="Type" anchor="type">
715   When an entity-body is included with a message, the data type of that
716   body is determined via the header fields Content-Type and Content-Encoding.
717   These define a two-layer, ordered encoding model:
719<figure><artwork type="example">
720    entity-body := Content-Encoding( Content-Type( data ) )
723   Content-Type specifies the media type of the underlying data.
724   Content-Encoding may be used to indicate any additional content
725   codings applied to the data, usually for the purpose of data
726   compression, that are a property of the requested resource. There is
727   no default encoding.
730   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
731   Content-Type header field defining the media type of that body. If
732   and only if the media type is not given by a Content-Type field, the
733   recipient &MAY; attempt to guess the media type via inspection of its
734   content and/or the name extension(s) of the URI used to identify the
735   resource. If the media type remains unknown, the recipient &SHOULD;
736   treat it as type "application/octet-stream".
740<section title="Entity Length" anchor="entity.length">
742   The entity-length of a message is the length of the message-body
743   before any transfer-codings have been applied. &message-length; defines
744   how the transfer-length of a message-body is determined.
750<section title="Content Negotiation" anchor="content.negotiation">
752   Most HTTP responses include an entity which contains information for
753   interpretation by a human user. Naturally, it is desirable to supply
754   the user with the "best available" entity corresponding to the
755   request. Unfortunately for servers and caches, not all users have the
756   same preferences for what is "best," and not all user agents are
757   equally capable of rendering all entity types. For that reason, HTTP
758   has provisions for several mechanisms for "content negotiation" --
759   the process of selecting the best representation for a given response
760   when there are multiple representations available.
761  <list><t>
762      <x:h>Note:</x:h> This is not called "format negotiation" because the
763      alternate representations may be of the same media type, but use
764      different capabilities of that type, be in different languages,
765      etc.
766  </t></list>
769   Any response containing an entity-body &MAY; be subject to negotiation,
770   including error responses.
773   There are two kinds of content negotiation which are possible in
774   HTTP: server-driven and agent-driven negotiation. These two kinds of
775   negotiation are orthogonal and thus may be used separately or in
776   combination. One method of combination, referred to as transparent
777   negotiation, occurs when a cache uses the agent-driven negotiation
778   information provided by the origin server in order to provide
779   server-driven negotiation for subsequent requests.
782<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
784   If the selection of the best representation for a response is made by
785   an algorithm located at the server, it is called server-driven
786   negotiation. Selection is based on the available representations of
787   the response (the dimensions over which it can vary; e.g. language,
788   content-coding, etc.) and the contents of particular header fields in
789   the request message or on other information pertaining to the request
790   (such as the network address of the client).
793   Server-driven negotiation is advantageous when the algorithm for
794   selecting from among the available representations is difficult to
795   describe to the user agent, or when the server desires to send its
796   "best guess" to the client along with the first response (hoping to
797   avoid the round-trip delay of a subsequent request if the "best
798   guess" is good enough for the user). In order to improve the server's
799   guess, the user agent &MAY; include request header fields (Accept,
800   Accept-Language, Accept-Encoding, etc.) which describe its
801   preferences for such a response.
804   Server-driven negotiation has disadvantages:
805  <list style="numbers">
806    <t>
807         It is impossible for the server to accurately determine what
808         might be "best" for any given user, since that would require
809         complete knowledge of both the capabilities of the user agent
810         and the intended use for the response (e.g., does the user want
811         to view it on screen or print it on paper?).
812    </t>
813    <t>
814         Having the user agent describe its capabilities in every
815         request can be both very inefficient (given that only a small
816         percentage of responses have multiple representations) and a
817         potential violation of the user's privacy.
818    </t>
819    <t>
820         It complicates the implementation of an origin server and the
821         algorithms for generating responses to a request.
822    </t>
823    <t>
824         It may limit a public cache's ability to use the same response
825         for multiple user's requests.
826    </t>
827  </list>
830   HTTP/1.1 includes the following request-header fields for enabling
831   server-driven negotiation through description of user agent
832   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
833   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
834   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
835   origin server is not limited to these dimensions and &MAY; vary the
836   response based on any aspect of the request, including information
837   outside the request-header fields or within extension header fields
838   not defined by this specification.
841   The Vary header field (&header-vary;) can be used to express the parameters the
842   server uses to select a representation that is subject to server-driven
843   negotiation.
847<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
849   With agent-driven negotiation, selection of the best representation
850   for a response is performed by the user agent after receiving an
851   initial response from the origin server. Selection is based on a list
852   of the available representations of the response included within the
853   header fields or entity-body of the initial response, with each
854   representation identified by its own URI. Selection from among the
855   representations may be performed automatically (if the user agent is
856   capable of doing so) or manually by the user selecting from a
857   generated (possibly hypertext) menu.
860   Agent-driven negotiation is advantageous when the response would vary
861   over commonly-used dimensions (such as type, language, or encoding),
862   when the origin server is unable to determine a user agent's
863   capabilities from examining the request, and generally when public
864   caches are used to distribute server load and reduce network usage.
867   Agent-driven negotiation suffers from the disadvantage of needing a
868   second request to obtain the best alternate representation. This
869   second request is only efficient when caching is used. In addition,
870   this specification does not define any mechanism for supporting
871   automatic selection, though it also does not prevent any such
872   mechanism from being developed as an extension and used within
873   HTTP/1.1.
876   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
877   status codes for enabling agent-driven negotiation when the server is
878   unwilling or unable to provide a varying response using server-driven
879   negotiation.
883<section title="Transparent Negotiation" anchor="transparent.negotiation">
885   Transparent negotiation is a combination of both server-driven and
886   agent-driven negotiation. When a cache is supplied with a form of the
887   list of available representations of the response (as in agent-driven
888   negotiation) and the dimensions of variance are completely understood
889   by the cache, then the cache becomes capable of performing server-driven
890   negotiation on behalf of the origin server for subsequent
891   requests on that resource.
894   Transparent negotiation has the advantage of distributing the
895   negotiation work that would otherwise be required of the origin
896   server and also removing the second request delay of agent-driven
897   negotiation when the cache is able to correctly guess the right
898   response.
901   This specification does not define any mechanism for transparent
902   negotiation, though it also does not prevent any such mechanism from
903   being developed as an extension that could be used within HTTP/1.1.
908<section title="Header Field Definitions" anchor="header.fields">
910   This section defines the syntax and semantics of HTTP/1.1 header fields
911   related to the payload of messages.
914   For entity-header fields, both sender and recipient refer to either the
915   client or the server, depending on who sends and who receives the entity.
918<section title="Accept" anchor="header.accept">
919  <iref primary="true" item="Accept header" x:for-anchor=""/>
920  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
921  <x:anchor-alias value="Accept"/>
922  <x:anchor-alias value="Accept-v"/>
923  <x:anchor-alias value="accept-extension"/>
924  <x:anchor-alias value="accept-params"/>
925  <x:anchor-alias value="media-range"/>
927   The request-header field "Accept" can be used to specify certain media
928   types which are acceptable for the response. Accept headers can be
929   used to indicate that the request is specifically limited to a small
930   set of desired types, as in the case of a request for an in-line
931   image.
933<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-extension"/>
934  <x:ref>Accept</x:ref>   = "Accept" BWS ":" OWS <x:ref>Accept-v</x:ref>
935  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
937  <x:ref>media-range</x:ref>    = ( "*/*"
938                   / ( <x:ref>type</x:ref> "/" "*" )
939                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
940                   ) *( ";" <x:ref>parameter</x:ref> )
941  <x:ref>accept-params</x:ref>  = ";" "q" "=" <x:ref>qvalue</x:ref> *( <x:ref>accept-extension</x:ref> )
942  <x:ref>accept-extension</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
945   The asterisk "*" character is used to group media types into ranges,
946   with "*/*" indicating all media types and "type/*" indicating all
947   subtypes of that type. The media-range &MAY; include media type
948   parameters that are applicable to that range.
951   Each media-range &MAY; be followed by one or more accept-params,
952   beginning with the "q" parameter for indicating a relative quality
953   factor. The first "q" parameter (if any) separates the media-range
954   parameter(s) from the accept-params. Quality factors allow the user
955   or user agent to indicate the relative degree of preference for that
956   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
957   default value is q=1.
958  <list><t>
959      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
960      parameters from Accept extension parameters is due to historical
961      practice. Although this prevents any media type parameter named
962      "q" from being used with a media range, such an event is believed
963      to be unlikely given the lack of any "q" parameters in the IANA
964      media type registry and the rare usage of any media type
965      parameters in Accept. Future media types are discouraged from
966      registering any parameter named "q".
967  </t></list>
970   The example
972<figure><artwork type="example">
973  Accept: audio/*; q=0.2, audio/basic
976   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
977   type if it is the best available after an 80% mark-down in quality."
980   If no Accept header field is present, then it is assumed that the
981   client accepts all media types. If an Accept header field is present,
982   and if the server cannot send a response which is acceptable
983   according to the combined Accept field value, then the server &SHOULD;
984   send a 406 (Not Acceptable) response.
987   A more elaborate example is
989<figure><artwork type="example">
990  Accept: text/plain; q=0.5, text/html,
991          text/x-dvi; q=0.8, text/x-c
994   Verbally, this would be interpreted as "text/html and text/x-c are
995   the preferred media types, but if they do not exist, then send the
996   text/x-dvi entity, and if that does not exist, send the text/plain
997   entity."
1000   Media ranges can be overridden by more specific media ranges or
1001   specific media types. If more than one media range applies to a given
1002   type, the most specific reference has precedence. For example,
1004<figure><artwork type="example">
1005  Accept: text/*, text/html, text/html;level=1, */*
1008   have the following precedence:
1010<figure><artwork type="example">
1011    1) text/html;level=1
1012    2) text/html
1013    3) text/*
1014    4) */*
1017   The media type quality factor associated with a given type is
1018   determined by finding the media range with the highest precedence
1019   which matches that type. For example,
1021<figure><artwork type="example">
1022  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1023          text/html;level=2;q=0.4, */*;q=0.5
1026   would cause the following values to be associated:
1028<figure><artwork type="example">
1029    text/html;level=1         = 1
1030    text/html                 = 0.7
1031    text/plain                = 0.3
1032    image/jpeg                = 0.5
1033    text/html;level=2         = 0.4
1034    text/html;level=3         = 0.7
1037      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1038      values for certain media ranges. However, unless the user agent is
1039      a closed system which cannot interact with other rendering agents,
1040      this default set ought to be configurable by the user.
1044<section title="Accept-Charset" anchor="header.accept-charset">
1045  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1046  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1047  <x:anchor-alias value="Accept-Charset"/>
1048  <x:anchor-alias value="Accept-Charset-v"/>
1050   The request-header field "Accept-Charset" can be used to indicate what
1051   character sets are acceptable for the response. This field allows
1052   clients capable of understanding more comprehensive or special-purpose
1053   character sets to signal that capability to a server which is
1054   capable of representing documents in those character sets.
1056<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1057  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" BWS ":" OWS
1058          <x:ref>Accept-Charset-v</x:ref>
1059  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" ) [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1062   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1063   be given an associated quality value which represents the user's
1064   preference for that charset. The default value is q=1. An example is
1066<figure><artwork type="example">
1067  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1070   The special value "*", if present in the Accept-Charset field,
1071   matches every character set (including ISO-8859-1) which is not
1072   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1073   in an Accept-Charset field, then all character sets not explicitly
1074   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1075   a quality value of 1 if not explicitly mentioned.
1078   If no Accept-Charset header is present, the default is that any
1079   character set is acceptable. If an Accept-Charset header is present,
1080   and if the server cannot send a response which is acceptable
1081   according to the Accept-Charset header, then the server &SHOULD; send
1082   an error response with the 406 (Not Acceptable) status code, though
1083   the sending of an unacceptable response is also allowed.
1087<section title="Accept-Encoding" anchor="header.accept-encoding">
1088  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1089  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1090  <x:anchor-alias value="Accept-Encoding"/>
1091  <x:anchor-alias value="Accept-Encoding-v"/>
1092  <x:anchor-alias value="codings"/>
1094   The request-header field "Accept-Encoding" is similar to Accept, but
1095   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1096   the response.
1098<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"/>
1099  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" BWS ":" OWS
1100                     <x:ref>Accept-Encoding-v</x:ref>
1101  <x:ref>Accept-Encoding-v</x:ref>  =
1102                     #( <x:ref>codings</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1103  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1106   Each codings value &MAY; be given an associated quality value which
1107   represents the preference for that encoding. The default value is q=1.
1110   Examples of its use are:
1112<figure><artwork type="example">
1113  Accept-Encoding: compress, gzip
1114  Accept-Encoding:
1115  Accept-Encoding: *
1116  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1117  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1120   A server tests whether a content-coding is acceptable, according to
1121   an Accept-Encoding field, using these rules:
1122  <list style="numbers">
1123      <t>If the content-coding is one of the content-codings listed in
1124         the Accept-Encoding field, then it is acceptable, unless it is
1125         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1126         qvalue of 0 means "not acceptable.")</t>
1128      <t>The special "*" symbol in an Accept-Encoding field matches any
1129         available content-coding not explicitly listed in the header
1130         field.</t>
1132      <t>If multiple content-codings are acceptable, then the acceptable
1133         content-coding with the highest non-zero qvalue is preferred.</t>
1135      <t>The "identity" content-coding is always acceptable, unless
1136         specifically refused because the Accept-Encoding field includes
1137         "identity;q=0", or because the field includes "*;q=0" and does
1138         not explicitly include the "identity" content-coding. If the
1139         Accept-Encoding field-value is empty, then only the "identity"
1140         encoding is acceptable.</t>
1141  </list>
1144   If an Accept-Encoding field is present in a request, and if the
1145   server cannot send a response which is acceptable according to the
1146   Accept-Encoding header, then the server &SHOULD; send an error response
1147   with the 406 (Not Acceptable) status code.
1150   If no Accept-Encoding field is present in a request, the server &MAY;
1151   assume that the client will accept any content coding. In this case,
1152   if "identity" is one of the available content-codings, then the
1153   server &SHOULD; use the "identity" content-coding, unless it has
1154   additional information that a different content-coding is meaningful
1155   to the client.
1156  <list><t>
1157      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1158      and if the "identity" content-coding is unavailable, then
1159      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1160      "gzip" and "compress") are preferred; some older clients
1161      improperly display messages sent with other content-codings.  The
1162      server might also make this decision based on information about
1163      the particular user-agent or client.
1164    </t><t>
1165      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1166      associated with content-codings. This means that qvalues will not
1167      work and are not permitted with x-gzip or x-compress.
1168    </t></list>
1172<section title="Accept-Language" anchor="header.accept-language">
1173  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1174  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1175  <x:anchor-alias value="Accept-Language"/>
1176  <x:anchor-alias value="Accept-Language-v"/>
1177  <x:anchor-alias value="language-range"/>
1179   The request-header field "Accept-Language" is similar to Accept, but
1180   restricts the set of natural languages that are preferred as a
1181   response to the request. Language tags are defined in <xref target="language.tags"/>.
1183<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"/>
1184  <x:ref>Accept-Language</x:ref>   = "Accept-Language" BWS ":" OWS
1185                    <x:ref>Accept-Language-v</x:ref>
1186  <x:ref>Accept-Language-v</x:ref> =
1187                    1#( <x:ref>language-range</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1188  <x:ref>language-range</x:ref>    =
1189            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1192   Each language-range can be given an associated quality value which
1193   represents an estimate of the user's preference for the languages
1194   specified by that range. The quality value defaults to "q=1". For
1195   example,
1197<figure><artwork type="example">
1198  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1201   would mean: "I prefer Danish, but will accept British English and
1202   other types of English."
1205   For matching, the "Basic Filtering" matching scheme, defined in
1206   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1208<x:blockquote cite="">
1209  <t>
1210     A language range matches a
1211     particular language tag if, in a case-insensitive comparison, it
1212     exactly equals the tag, or if it exactly equals a prefix of the tag
1213     such that the first character following the prefix is "-".
1214  </t>
1217   The special range "*", if present in the Accept-Language field,
1218   matches every tag not matched by any other range present in the
1219   Accept-Language field.
1220  <list><t>
1221      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1222      language tags are assigned to languages in such a way that it is
1223      always true that if a user understands a language with a certain
1224      tag, then this user will also understand all languages with tags
1225      for which this tag is a prefix. The prefix rule simply allows the
1226      use of prefix tags if this is the case.
1227  </t></list>
1230   The language quality factor assigned to a language-tag by the
1231   Accept-Language field is the quality value of the longest language-range
1232   in the field that matches the language-tag. If no language-range
1233   in the field matches the tag, the language quality factor
1234   assigned is 0. If no Accept-Language header is present in the
1235   request, the server
1236   &SHOULD; assume that all languages are equally acceptable. If an
1237   Accept-Language header is present, then all languages which are
1238   assigned a quality factor greater than 0 are acceptable.
1241   It might be contrary to the privacy expectations of the user to send
1242   an Accept-Language header with the complete linguistic preferences of
1243   the user in every request. For a discussion of this issue, see
1244   <xref target=""/>.
1247   As intelligibility is highly dependent on the individual user, it is
1248   recommended that client applications make the choice of linguistic
1249   preference available to the user. If the choice is not made
1250   available, then the Accept-Language header field &MUST-NOT; be given in
1251   the request.
1252  <list><t>
1253      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1254      the user, we remind implementors of  the fact that users are not
1255      familiar with the details of language matching as described above,
1256      and should provide appropriate guidance. As an example, users
1257      might assume that on selecting "en-gb", they will be served any
1258      kind of English document if British English is not available. A
1259      user agent might suggest in such a case to add "en" to get the
1260      best matching behavior.
1261  </t></list>
1265<section title="Content-Encoding" anchor="header.content-encoding">
1266  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1267  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1268  <x:anchor-alias value="Content-Encoding"/>
1269  <x:anchor-alias value="Content-Encoding-v"/>
1271   The entity-header field "Content-Encoding" is used as a modifier to the
1272   media-type. When present, its value indicates what additional content
1273   codings have been applied to the entity-body, and thus what decoding
1274   mechanisms must be applied in order to obtain the media-type
1275   referenced by the Content-Type header field. Content-Encoding is
1276   primarily used to allow a document to be compressed without losing
1277   the identity of its underlying media type.
1279<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1280  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" BWS ":" OWS <x:ref>Content-Encoding-v</x:ref>
1281  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1284   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1286<figure><artwork type="example">
1287  Content-Encoding: gzip
1290   The content-coding is a characteristic of the entity identified by
1291   the Request-URI. Typically, the entity-body is stored with this
1292   encoding and is only decoded before rendering or analogous usage.
1293   However, a non-transparent proxy &MAY; modify the content-coding if the
1294   new coding is known to be acceptable to the recipient, unless the
1295   "no-transform" cache-control directive is present in the message.
1298   If the content-coding of an entity is not "identity", then the
1299   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1300   that lists the non-identity content-coding(s) used.
1303   If the content-coding of an entity in a request message is not
1304   acceptable to the origin server, the server &SHOULD; respond with a
1305   status code of 415 (Unsupported Media Type).
1308   If multiple encodings have been applied to an entity, the content
1309   codings &MUST; be listed in the order in which they were applied.
1310   Additional information about the encoding parameters &MAY; be provided
1311   by other entity-header fields not defined by this specification.
1315<section title="Content-Language" anchor="header.content-language">
1316  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1317  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1318  <x:anchor-alias value="Content-Language"/>
1319  <x:anchor-alias value="Content-Language-v"/>
1321   The entity-header field "Content-Language" describes the natural
1322   language(s) of the intended audience for the enclosed entity. Note
1323   that this might not be equivalent to all the languages used within
1324   the entity-body.
1326<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1327  <x:ref>Content-Language</x:ref>   = "Content-Language" BWS ":" OWS <x:ref>Content-Language-v</x:ref>
1328  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1331   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1332   Content-Language is to allow a user to identify and differentiate
1333   entities according to the user's own preferred language. Thus, if the
1334   body content is intended only for a Danish-literate audience, the
1335   appropriate field is
1337<figure><artwork type="example">
1338  Content-Language: da
1341   If no Content-Language is specified, the default is that the content
1342   is intended for all language audiences. This might mean that the
1343   sender does not consider it to be specific to any natural language,
1344   or that the sender does not know for which language it is intended.
1347   Multiple languages &MAY; be listed for content that is intended for
1348   multiple audiences. For example, a rendition of the "Treaty of
1349   Waitangi," presented simultaneously in the original Maori and English
1350   versions, would call for
1352<figure><artwork type="example">
1353  Content-Language: mi, en
1356   However, just because multiple languages are present within an entity
1357   does not mean that it is intended for multiple linguistic audiences.
1358   An example would be a beginner's language primer, such as "A First
1359   Lesson in Latin," which is clearly intended to be used by an
1360   English-literate audience. In this case, the Content-Language would
1361   properly only include "en".
1364   Content-Language &MAY; be applied to any media type -- it is not
1365   limited to textual documents.
1369<section title="Content-Location" anchor="header.content-location">
1370  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1371  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1372  <x:anchor-alias value="Content-Location"/>
1373  <x:anchor-alias value="Content-Location-v"/>
1375   The entity-header field "Content-Location" &MAY; be used to supply the
1376   resource location for the entity enclosed in the message when that
1377   entity is accessible from a location separate from the requested
1378   resource's URI. A server &SHOULD; provide a Content-Location for the
1379   variant corresponding to the response entity; especially in the case
1380   where a resource has multiple entities associated with it, and those
1381   entities actually have separate locations by which they might be
1382   individually accessed, the server &SHOULD; provide a Content-Location
1383   for the particular variant which is returned.
1385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1386  <x:ref>Content-Location</x:ref>   = "Content-Location" BWS ":" OWS
1387                    <x:ref>Content-Location-v</x:ref>
1388  <x:ref>Content-Location-v</x:ref> =
1389                    <x:ref>absoluteURI</x:ref> / <x:ref>relativeURI</x:ref>
1392   The value of Content-Location also defines the base URI for the
1393   entity.
1396   The Content-Location value is not a replacement for the original
1397   requested URI; it is only a statement of the location of the resource
1398   corresponding to this particular entity at the time of the request.
1399   Future requests &MAY; specify the Content-Location URI as the request-URI
1400   if the desire is to identify the source of that particular
1401   entity.
1404   A cache cannot assume that an entity with a Content-Location
1405   different from the URI used to retrieve it can be used to respond to
1406   later requests on that Content-Location URI. However, the Content-Location
1407   can be used to differentiate between multiple entities
1408   retrieved from a single requested resource, as described in &caching-neg-resp;.
1411   If the Content-Location is a relative URI, the relative URI is
1412   interpreted relative to the Request-URI.
1415   The meaning of the Content-Location header in PUT or POST requests is
1416   undefined; servers are free to ignore it in those cases.
1420<section title="Content-MD5" anchor="header.content-md5">
1421  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1422  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1423  <x:anchor-alias value="Content-MD5"/>
1424  <x:anchor-alias value="Content-MD5-v"/>
1426   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1427   an MD5 digest of the entity-body for the purpose of providing an
1428   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1429   MIC is good for detecting accidental modification of the entity-body
1430   in transit, but is not proof against malicious attacks.)
1432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1433  <x:ref>Content-MD5</x:ref>   = "Content-MD5" BWS ":" OWS <x:ref>Content-MD5-v</x:ref>
1434  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1437   The Content-MD5 header field &MAY; be generated by an origin server or
1438   client to function as an integrity check of the entity-body. Only
1439   origin servers or clients &MAY; generate the Content-MD5 header field;
1440   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1441   value as an end-to-end integrity check. Any recipient of the entity-body,
1442   including gateways and proxies, &MAY; check that the digest value
1443   in this header field matches that of the entity-body as received.
1446   The MD5 digest is computed based on the content of the entity-body,
1447   including any content-coding that has been applied, but not including
1448   any transfer-encoding applied to the message-body. If the message is
1449   received with a transfer-encoding, that encoding &MUST; be removed
1450   prior to checking the Content-MD5 value against the received entity.
1453   This has the result that the digest is computed on the octets of the
1454   entity-body exactly as, and in the order that, they would be sent if
1455   no transfer-encoding were being applied.
1458   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1459   composite media-types (e.g., multipart/* and message/rfc822), but
1460   this does not change how the digest is computed as defined in the
1461   preceding paragraph.
1464   There are several consequences of this. The entity-body for composite
1465   types &MAY; contain many body-parts, each with its own MIME and HTTP
1466   headers (including Content-MD5, Content-Transfer-Encoding, and
1467   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1468   or Content-Encoding header, it is assumed that the content
1469   of the body-part has had the encoding applied, and the body-part is
1470   included in the Content-MD5 digest as is -- i.e., after the
1471   application. The Transfer-Encoding header field is not allowed within
1472   body-parts.
1475   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1476   computing or checking the digest: the line break convention used in
1477   the text actually transmitted &MUST; be left unaltered when computing
1478   the digest.
1479  <list><t>
1480      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1481      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1482      in which the application of Content-MD5 to HTTP entity-bodies
1483      differs from its application to MIME entity-bodies. One is that
1484      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1485      does use Transfer-Encoding and Content-Encoding. Another is that
1486      HTTP more frequently uses binary content types than MIME, so it is
1487      worth noting that, in such cases, the byte order used to compute
1488      the digest is the transmission byte order defined for the type.
1489      Lastly, HTTP allows transmission of text types with any of several
1490      line break conventions and not just the canonical form using CRLF.
1491  </t></list>
1495<section title="Content-Type" anchor="header.content-type">
1496  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1497  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1498  <x:anchor-alias value="Content-Type"/>
1499  <x:anchor-alias value="Content-Type-v"/>
1501   The entity-header field "Content-Type" indicates the media type of the
1502   entity-body sent to the recipient or, in the case of the HEAD method,
1503   the media type that would have been sent had the request been a GET.
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1506  <x:ref>Content-Type</x:ref>   = "Content-Type" BWS ":" OWS <x:ref>Content-Type-v</x:ref>
1507  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1510   Media types are defined in <xref target="media.types"/>. An example of the field is
1512<figure><artwork type="example">
1513  Content-Type: text/html; charset=ISO-8859-4
1516   Further discussion of methods for identifying the media type of an
1517   entity is provided in <xref target="type"/>.
1523<section title="IANA Considerations" anchor="IANA.considerations">
1524<section title="Message Header Registration" anchor="message.header.registration">
1526   The Message Header Registry located at <eref target=""/> should be updated
1527   with the permanent registrations below (see <xref target="RFC3864"/>):
1529<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1530<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1531   <ttcol>Header Field Name</ttcol>
1532   <ttcol>Protocol</ttcol>
1533   <ttcol>Status</ttcol>
1534   <ttcol>Reference</ttcol>
1536   <c>Accept</c>
1537   <c>http</c>
1538   <c>standard</c>
1539   <c>
1540      <xref target="header.accept"/>
1541   </c>
1542   <c>Accept-Charset</c>
1543   <c>http</c>
1544   <c>standard</c>
1545   <c>
1546      <xref target="header.accept-charset"/>
1547   </c>
1548   <c>Accept-Encoding</c>
1549   <c>http</c>
1550   <c>standard</c>
1551   <c>
1552      <xref target="header.accept-encoding"/>
1553   </c>
1554   <c>Accept-Language</c>
1555   <c>http</c>
1556   <c>standard</c>
1557   <c>
1558      <xref target="header.accept-language"/>
1559   </c>
1560   <c>Content-Disposition</c>
1561   <c>http</c>
1562   <c/>
1563   <c>
1564      <xref target="content-disposition"/>
1565   </c>
1566   <c>Content-Encoding</c>
1567   <c>http</c>
1568   <c>standard</c>
1569   <c>
1570      <xref target="header.content-encoding"/>
1571   </c>
1572   <c>Content-Language</c>
1573   <c>http</c>
1574   <c>standard</c>
1575   <c>
1576      <xref target="header.content-language"/>
1577   </c>
1578   <c>Content-Location</c>
1579   <c>http</c>
1580   <c>standard</c>
1581   <c>
1582      <xref target="header.content-location"/>
1583   </c>
1584   <c>Content-MD5</c>
1585   <c>http</c>
1586   <c>standard</c>
1587   <c>
1588      <xref target="header.content-md5"/>
1589   </c>
1590   <c>Content-Type</c>
1591   <c>http</c>
1592   <c>standard</c>
1593   <c>
1594      <xref target="header.content-type"/>
1595   </c>
1596   <c>MIME-Version</c>
1597   <c>http</c>
1598   <c/>
1599   <c>
1600      <xref target="mime-version"/>
1601   </c>
1605   The change controller is: "IETF ( - Internet Engineering Task Force".
1610<section title="Security Considerations" anchor="security.considerations">
1612   This section is meant to inform application developers, information
1613   providers, and users of the security limitations in HTTP/1.1 as
1614   described by this document. The discussion does not include
1615   definitive solutions to the problems revealed, though it does make
1616   some suggestions for reducing security risks.
1619<section title="Privacy Issues Connected to Accept Headers" anchor="">
1621   Accept request-headers can reveal information about the user to all
1622   servers which are accessed. The Accept-Language header in particular
1623   can reveal information the user would consider to be of a private
1624   nature, because the understanding of particular languages is often
1625   strongly correlated to the membership of a particular ethnic group.
1626   User agents which offer the option to configure the contents of an
1627   Accept-Language header to be sent in every request are strongly
1628   encouraged to let the configuration process include a message which
1629   makes the user aware of the loss of privacy involved.
1632   An approach that limits the loss of privacy would be for a user agent
1633   to omit the sending of Accept-Language headers by default, and to ask
1634   the user whether or not to start sending Accept-Language headers to a
1635   server if it detects, by looking for any Vary response-header fields
1636   generated by the server, that such sending could improve the quality
1637   of service.
1640   Elaborate user-customized accept header fields sent in every request,
1641   in particular if these include quality values, can be used by servers
1642   as relatively reliable and long-lived user identifiers. Such user
1643   identifiers would allow content providers to do click-trail tracking,
1644   and would allow collaborating content providers to match cross-server
1645   click-trails or form submissions of individual users. Note that for
1646   many users not behind a proxy, the network address of the host
1647   running the user agent will also serve as a long-lived user
1648   identifier. In environments where proxies are used to enhance
1649   privacy, user agents ought to be conservative in offering accept
1650   header configuration options to end users. As an extreme privacy
1651   measure, proxies could filter the accept headers in relayed requests.
1652   General purpose user agents which provide a high degree of header
1653   configurability &SHOULD; warn users about the loss of privacy which can
1654   be involved.
1658<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1660   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1661   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1662   serious security considerations. Content-Disposition is not part of
1663   the HTTP standard, but since it is widely implemented, we are
1664   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1665   for details.
1671<section title="Acknowledgments" anchor="ack">
1676<references title="Normative References">
1678<reference anchor="ISO-8859-1">
1679  <front>
1680    <title>
1681     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1682    </title>
1683    <author>
1684      <organization>International Organization for Standardization</organization>
1685    </author>
1686    <date year="1998"/>
1687  </front>
1688  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1691<reference anchor="Part1">
1692  <front>
1693    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1694    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1695      <organization abbrev="Day Software">Day Software</organization>
1696      <address><email></email></address>
1697    </author>
1698    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1699      <organization>One Laptop per Child</organization>
1700      <address><email></email></address>
1701    </author>
1702    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1703      <organization abbrev="HP">Hewlett-Packard Company</organization>
1704      <address><email></email></address>
1705    </author>
1706    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1707      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1708      <address><email></email></address>
1709    </author>
1710    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1711      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1712      <address><email></email></address>
1713    </author>
1714    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1715      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1716      <address><email></email></address>
1717    </author>
1718    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1719      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1720      <address><email></email></address>
1721    </author>
1722    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1723      <organization abbrev="W3C">World Wide Web Consortium</organization>
1724      <address><email></email></address>
1725    </author>
1726    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1727      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1728      <address><email></email></address>
1729    </author>
1730    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1731  </front>
1732  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1733  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1736<reference anchor="Part2">
1737  <front>
1738    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1739    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1740      <organization abbrev="Day Software">Day Software</organization>
1741      <address><email></email></address>
1742    </author>
1743    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1744      <organization>One Laptop per Child</organization>
1745      <address><email></email></address>
1746    </author>
1747    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1748      <organization abbrev="HP">Hewlett-Packard Company</organization>
1749      <address><email></email></address>
1750    </author>
1751    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1752      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1753      <address><email></email></address>
1754    </author>
1755    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1756      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1757      <address><email></email></address>
1758    </author>
1759    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1760      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1761      <address><email></email></address>
1762    </author>
1763    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1764      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1765      <address><email></email></address>
1766    </author>
1767    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1768      <organization abbrev="W3C">World Wide Web Consortium</organization>
1769      <address><email></email></address>
1770    </author>
1771    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1772      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1773      <address><email></email></address>
1774    </author>
1775    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1776  </front>
1777  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1778  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1781<reference anchor="Part4">
1782  <front>
1783    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1784    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1785      <organization abbrev="Day Software">Day Software</organization>
1786      <address><email></email></address>
1787    </author>
1788    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1789      <organization>One Laptop per Child</organization>
1790      <address><email></email></address>
1791    </author>
1792    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1793      <organization abbrev="HP">Hewlett-Packard Company</organization>
1794      <address><email></email></address>
1795    </author>
1796    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1797      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1798      <address><email></email></address>
1799    </author>
1800    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1801      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1802      <address><email></email></address>
1803    </author>
1804    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1805      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1806      <address><email></email></address>
1807    </author>
1808    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1809      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1810      <address><email></email></address>
1811    </author>
1812    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1813      <organization abbrev="W3C">World Wide Web Consortium</organization>
1814      <address><email></email></address>
1815    </author>
1816    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1817      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1818      <address><email></email></address>
1819    </author>
1820    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1821  </front>
1822  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1823  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1826<reference anchor="Part5">
1827  <front>
1828    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1829    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1830      <organization abbrev="Day Software">Day Software</organization>
1831      <address><email></email></address>
1832    </author>
1833    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1834      <organization>One Laptop per Child</organization>
1835      <address><email></email></address>
1836    </author>
1837    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1838      <organization abbrev="HP">Hewlett-Packard Company</organization>
1839      <address><email></email></address>
1840    </author>
1841    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1842      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1843      <address><email></email></address>
1844    </author>
1845    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1846      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1847      <address><email></email></address>
1848    </author>
1849    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1850      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1851      <address><email></email></address>
1852    </author>
1853    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1854      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1855      <address><email></email></address>
1856    </author>
1857    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1858      <organization abbrev="W3C">World Wide Web Consortium</organization>
1859      <address><email></email></address>
1860    </author>
1861    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1862      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1863      <address><email></email></address>
1864    </author>
1865    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1866  </front>
1867  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1868  <x:source href="p5-range.xml" basename="p5-range"/>
1871<reference anchor="Part6">
1872  <front>
1873    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1874    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1875      <organization abbrev="Day Software">Day Software</organization>
1876      <address><email></email></address>
1877    </author>
1878    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1879      <organization>One Laptop per Child</organization>
1880      <address><email></email></address>
1881    </author>
1882    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1883      <organization abbrev="HP">Hewlett-Packard Company</organization>
1884      <address><email></email></address>
1885    </author>
1886    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1887      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1888      <address><email></email></address>
1889    </author>
1890    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1891      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1892      <address><email></email></address>
1893    </author>
1894    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1895      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1896      <address><email></email></address>
1897    </author>
1898    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1899      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1900      <address><email></email></address>
1901    </author>
1902    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1903      <organization abbrev="W3C">World Wide Web Consortium</organization>
1904      <address><email></email></address>
1905    </author>
1906    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1907      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1908      <address><email></email></address>
1909    </author>
1910    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1911  </front>
1912  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1913  <x:source href="p6-cache.xml" basename="p6-cache"/>
1916<reference anchor="RFC1766">
1917  <front>
1918    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1919    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1920      <organization>UNINETT</organization>
1921      <address><email></email></address>
1922    </author>
1923    <date month="March" year="1995"/>
1924  </front>
1925  <seriesInfo name="RFC" value="1766"/>
1928<reference anchor="RFC1864">
1929  <front>
1930    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1931    <author initials="J." surname="Myers" fullname="John G. Myers">
1932      <organization>Carnegie Mellon University</organization>
1933      <address><email></email></address>
1934    </author>
1935    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1936      <organization>Dover Beach Consulting, Inc.</organization>
1937      <address><email></email></address>
1938    </author>
1939    <date month="October" year="1995"/>
1940  </front>
1941  <seriesInfo name="RFC" value="1864"/>
1944<reference anchor="RFC1950">
1945  <front>
1946    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1947    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1948      <organization>Aladdin Enterprises</organization>
1949      <address><email></email></address>
1950    </author>
1951    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1952      <organization/>
1953    </author>
1954    <date month="May" year="1996"/>
1955  </front>
1956  <seriesInfo name="RFC" value="1950"/>
1957  <annotation>
1958    RFC 1950 is an Informational RFC, thus it may be less stable than
1959    this specification. On the other hand, this downward reference was
1960    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1961    therefore it is unlikely to cause problems in practice. See also
1962    <xref target="BCP97"/>.
1963  </annotation>
1966<reference anchor="RFC1951">
1967  <front>
1968    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1969    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1970      <organization>Aladdin Enterprises</organization>
1971      <address><email></email></address>
1972    </author>
1973    <date month="May" year="1996"/>
1974  </front>
1975  <seriesInfo name="RFC" value="1951"/>
1976  <annotation>
1977    RFC 1951 is an Informational RFC, thus it may be less stable than
1978    this specification. On the other hand, this downward reference was
1979    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1980    therefore it is unlikely to cause problems in practice. See also
1981    <xref target="BCP97"/>.
1982  </annotation>
1985<reference anchor="RFC1952">
1986  <front>
1987    <title>GZIP file format specification version 4.3</title>
1988    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1989      <organization>Aladdin Enterprises</organization>
1990      <address><email></email></address>
1991    </author>
1992    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1993      <organization/>
1994      <address><email></email></address>
1995    </author>
1996    <author initials="M." surname="Adler" fullname="Mark Adler">
1997      <organization/>
1998      <address><email></email></address>
1999    </author>
2000    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2001      <organization/>
2002      <address><email></email></address>
2003    </author>
2004    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2005      <organization/>
2006      <address><email></email></address>
2007    </author>
2008    <date month="May" year="1996"/>
2009  </front>
2010  <seriesInfo name="RFC" value="1952"/>
2011  <annotation>
2012    RFC 1952 is an Informational RFC, thus it may be less stable than
2013    this specification. On the other hand, this downward reference was
2014    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2015    therefore it is unlikely to cause problems in practice. See also
2016    <xref target="BCP97"/>.
2017  </annotation>
2020<reference anchor="RFC2045">
2021  <front>
2022    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2023    <author initials="N." surname="Freed" fullname="Ned Freed">
2024      <organization>Innosoft International, Inc.</organization>
2025      <address><email></email></address>
2026    </author>
2027    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2028      <organization>First Virtual Holdings</organization>
2029      <address><email></email></address>
2030    </author>
2031    <date month="November" year="1996"/>
2032  </front>
2033  <seriesInfo name="RFC" value="2045"/>
2036<reference anchor="RFC2046">
2037  <front>
2038    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2039    <author initials="N." surname="Freed" fullname="Ned Freed">
2040      <organization>Innosoft International, Inc.</organization>
2041      <address><email></email></address>
2042    </author>
2043    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2044      <organization>First Virtual Holdings</organization>
2045      <address><email></email></address>
2046    </author>
2047    <date month="November" year="1996"/>
2048  </front>
2049  <seriesInfo name="RFC" value="2046"/>
2052<reference anchor="RFC2119">
2053  <front>
2054    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2055    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2056      <organization>Harvard University</organization>
2057      <address><email></email></address>
2058    </author>
2059    <date month="March" year="1997"/>
2060  </front>
2061  <seriesInfo name="BCP" value="14"/>
2062  <seriesInfo name="RFC" value="2119"/>
2065<reference anchor='RFC4647'>
2066  <front>
2067    <title>Matching of Language Tags</title>
2068    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2069      <organization>Yahoo! Inc.</organization>
2070      <address><email></email></address>
2071    </author>
2072    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2073      <organization>Google</organization>
2074      <address><email></email></address>
2075    </author>
2076    <date year='2006' month='September' />
2077  </front>
2078  <seriesInfo name='BCP' value='47' />
2079  <seriesInfo name='RFC' value='4647' />
2084<references title="Informative References">
2086<reference anchor="RFC1945">
2087  <front>
2088    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2089    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2090      <organization>MIT, Laboratory for Computer Science</organization>
2091      <address><email></email></address>
2092    </author>
2093    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2094      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2095      <address><email></email></address>
2096    </author>
2097    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2098      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2099      <address><email></email></address>
2100    </author>
2101    <date month="May" year="1996"/>
2102  </front>
2103  <seriesInfo name="RFC" value="1945"/>
2106<reference anchor="RFC2049">
2107  <front>
2108    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2109    <author initials="N." surname="Freed" fullname="Ned Freed">
2110      <organization>Innosoft International, Inc.</organization>
2111      <address><email></email></address>
2112    </author>
2113    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2114      <organization>First Virtual Holdings</organization>
2115      <address><email></email></address>
2116    </author>
2117    <date month="November" year="1996"/>
2118  </front>
2119  <seriesInfo name="RFC" value="2049"/>
2122<reference anchor="RFC2068">
2123  <front>
2124    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2125    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2126      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2127      <address><email></email></address>
2128    </author>
2129    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2130      <organization>MIT Laboratory for Computer Science</organization>
2131      <address><email></email></address>
2132    </author>
2133    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2134      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2135      <address><email></email></address>
2136    </author>
2137    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2138      <organization>MIT Laboratory for Computer Science</organization>
2139      <address><email></email></address>
2140    </author>
2141    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2142      <organization>MIT Laboratory for Computer Science</organization>
2143      <address><email></email></address>
2144    </author>
2145    <date month="January" year="1997"/>
2146  </front>
2147  <seriesInfo name="RFC" value="2068"/>
2150<reference anchor="RFC2076">
2151  <front>
2152    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2153    <author initials="J." surname="Palme" fullname="Jacob Palme">
2154      <organization>Stockholm University/KTH</organization>
2155      <address><email></email></address>
2156    </author>
2157    <date month="February" year="1997"/>
2158  </front>
2159  <seriesInfo name="RFC" value="2076"/>
2162<reference anchor="RFC2183">
2163  <front>
2164    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2165    <author initials="R." surname="Troost" fullname="Rens Troost">
2166      <organization>New Century Systems</organization>
2167      <address><email></email></address>
2168    </author>
2169    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2170      <organization>QUALCOMM Incorporated</organization>
2171      <address><email></email></address>
2172    </author>
2173    <author initials="K." surname="Moore" fullname="Keith Moore">
2174      <organization>Department of Computer Science</organization>
2175      <address><email></email></address>
2176    </author>
2177    <date month="August" year="1997"/>
2178  </front>
2179  <seriesInfo name="RFC" value="2183"/>
2182<reference anchor="RFC2277">
2183  <front>
2184    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2185    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2186      <organization>UNINETT</organization>
2187      <address><email></email></address>
2188    </author>
2189    <date month="January" year="1998"/>
2190  </front>
2191  <seriesInfo name="BCP" value="18"/>
2192  <seriesInfo name="RFC" value="2277"/>
2195<reference anchor="RFC2388">
2196  <front>
2197    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2198    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2199      <organization>Xerox Palo Alto Research Center</organization>
2200      <address><email></email></address>
2201    </author>
2202    <date year="1998" month="August"/>
2203  </front>
2204  <seriesInfo name="RFC" value="2388"/>
2207<reference anchor="RFC2557">
2208  <front>
2209    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2210    <author initials="F." surname="Palme" fullname="Jacob Palme">
2211      <organization>Stockholm University and KTH</organization>
2212      <address><email></email></address>
2213    </author>
2214    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2215      <organization>Microsoft Corporation</organization>
2216      <address><email></email></address>
2217    </author>
2218    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2219      <organization>Lotus Development Corporation</organization>
2220      <address><email></email></address>
2221    </author>
2222    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2223      <organization/>
2224      <address><email></email></address>
2225    </author>
2226    <date year="1999" month="March"/>
2227  </front>
2228  <seriesInfo name="RFC" value="2557"/>
2231<reference anchor="RFC2616">
2232  <front>
2233    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2234    <author initials="R." surname="Fielding" fullname="R. Fielding">
2235      <organization>University of California, Irvine</organization>
2236      <address><email></email></address>
2237    </author>
2238    <author initials="J." surname="Gettys" fullname="J. Gettys">
2239      <organization>W3C</organization>
2240      <address><email></email></address>
2241    </author>
2242    <author initials="J." surname="Mogul" fullname="J. Mogul">
2243      <organization>Compaq Computer Corporation</organization>
2244      <address><email></email></address>
2245    </author>
2246    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2247      <organization>MIT Laboratory for Computer Science</organization>
2248      <address><email></email></address>
2249    </author>
2250    <author initials="L." surname="Masinter" fullname="L. Masinter">
2251      <organization>Xerox Corporation</organization>
2252      <address><email></email></address>
2253    </author>
2254    <author initials="P." surname="Leach" fullname="P. Leach">
2255      <organization>Microsoft Corporation</organization>
2256      <address><email></email></address>
2257    </author>
2258    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2259      <organization>W3C</organization>
2260      <address><email></email></address>
2261    </author>
2262    <date month="June" year="1999"/>
2263  </front>
2264  <seriesInfo name="RFC" value="2616"/>
2267<reference anchor="RFC3629">
2268  <front>
2269    <title>UTF-8, a transformation format of ISO 10646</title>
2270    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2271      <organization>Alis Technologies</organization>
2272      <address><email></email></address>
2273    </author>
2274    <date month="November" year="2003"/>
2275  </front>
2276  <seriesInfo name="RFC" value="3629"/>
2277  <seriesInfo name="STD" value="63"/>
2280<reference anchor='RFC3864'>
2281  <front>
2282    <title>Registration Procedures for Message Header Fields</title>
2283    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2284      <organization>Nine by Nine</organization>
2285      <address><email></email></address>
2286    </author>
2287    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2288      <organization>BEA Systems</organization>
2289      <address><email></email></address>
2290    </author>
2291    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2292      <organization>HP Labs</organization>
2293      <address><email></email></address>
2294    </author>
2295    <date year='2004' month='September' />
2296  </front>
2297  <seriesInfo name='BCP' value='90' />
2298  <seriesInfo name='RFC' value='3864' />
2301<reference anchor="RFC4288">
2302  <front>
2303    <title>Media Type Specifications and Registration Procedures</title>
2304    <author initials="N." surname="Freed" fullname="N. Freed">
2305      <organization>Sun Microsystems</organization>
2306      <address>
2307        <email></email>
2308      </address>
2309    </author>
2310    <author initials="J." surname="Klensin" fullname="J. Klensin">
2311      <organization/>
2312      <address>
2313        <email></email>
2314      </address>
2315    </author>
2316    <date year="2005" month="December"/>
2317  </front>
2318  <seriesInfo name="BCP" value="13"/>
2319  <seriesInfo name="RFC" value="4288"/>
2322<reference anchor="RFC5322">
2323  <front>
2324    <title>Internet Message Format</title>
2325    <author initials="P." surname="Resnick" fullname="P. Resnick">
2326      <organization>Qualcomm Incorporated</organization>
2327    </author>
2328    <date year="2008" month="October"/>
2329  </front>
2330  <seriesInfo name="RFC" value="5322"/>
2333<reference anchor='BCP97'>
2334  <front>
2335    <title>Handling Normative References to Standards-Track Documents</title>
2336    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2337      <organization />
2338      <address>
2339        <email></email>
2340      </address>
2341    </author>
2342    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2343      <organization>MIT</organization>
2344      <address>
2345        <email></email>
2346      </address>
2347    </author>
2348    <date year='2007' month='June' />
2349  </front>
2350  <seriesInfo name='BCP' value='97' />
2351  <seriesInfo name='RFC' value='4897' />
2357<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2359   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
2360   allow entities to be transmitted in an open variety of
2361   representations and with extensible mechanisms. However, RFC 2045
2362   discusses mail, and HTTP has a few features that are different from
2363   those described in RFC 2045. These differences were carefully chosen
2364   to optimize performance over binary connections, to allow greater
2365   freedom in the use of new media types, to make date comparisons
2366   easier, and to acknowledge the practice of some early HTTP servers
2367   and clients.
2370   This appendix describes specific areas where HTTP differs from RFC
2371   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2372   aware of these differences and provide the appropriate conversions
2373   where necessary. Proxies and gateways from MIME environments to HTTP
2374   also need to be aware of the differences because some conversions
2375   might be required.
2378<section title="MIME-Version" anchor="mime-version">
2379  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2380  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2381  <x:anchor-alias value="MIME-Version"/>
2382  <x:anchor-alias value="MIME-Version-v"/>
2384   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2385   include a single MIME-Version general-header field to indicate what
2386   version of the MIME protocol was used to construct the message. Use
2387   of the MIME-Version header field indicates that the message is in
2388   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2389   Proxies/gateways are responsible for ensuring full compliance (where
2390   possible) when exporting HTTP messages to strict MIME environments.
2392<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2393  <x:ref>MIME-Version</x:ref>   = "MIME-Version" BWS ":" OWS <x:ref>MIME-Version-v</x:ref>
2394  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2397   MIME version "1.0" is the default for use in HTTP/1.1. However,
2398   HTTP/1.1 message parsing and semantics are defined by this document
2399   and not the MIME specification.
2403<section title="Conversion to Canonical Form" anchor="">
2405   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2406   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2407   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2408   allowed for subtypes of the "text" media type when transmitted over
2409   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2410   line breaks as CRLF and forbids the use of CR or LF outside of line
2411   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2412   line break within text content when a message is transmitted over
2413   HTTP.
2416   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2417   environment &SHOULD; translate all line breaks within the text media
2418   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2419   canonical form of CRLF. Note, however, that this might be complicated
2420   by the presence of a Content-Encoding and by the fact that HTTP
2421   allows the use of some character sets which do not use octets 13 and
2422   10 to represent CR and LF, as is the case for some multi-byte
2423   character sets.
2426   Implementors should note that conversion will break any cryptographic
2427   checksums applied to the original content unless the original content
2428   is already in canonical form. Therefore, the canonical form is
2429   recommended for any content that uses such checksums in HTTP.
2433<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2435   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2436   Content-Encoding header field. Since this acts as a modifier on the
2437   media type, proxies and gateways from HTTP to MIME-compliant
2438   protocols &MUST; either change the value of the Content-Type header
2439   field or decode the entity-body before forwarding the message. (Some
2440   experimental applications of Content-Type for Internet mail have used
2441   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2442   a function equivalent to Content-Encoding. However, this parameter is
2443   not part of RFC 2045).
2447<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2449   HTTP does not use the Content-Transfer-Encoding field of RFC
2450   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2451   remove any Content-Transfer-Encoding
2452   prior to delivering the response message to an HTTP client.
2455   Proxies and gateways from HTTP to MIME-compliant protocols are
2456   responsible for ensuring that the message is in the correct format
2457   and encoding for safe transport on that protocol, where "safe
2458   transport" is defined by the limitations of the protocol being used.
2459   Such a proxy or gateway &SHOULD; label the data with an appropriate
2460   Content-Transfer-Encoding if doing so will improve the likelihood of
2461   safe transport over the destination protocol.
2465<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2467   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2468   Proxies/gateways &MUST; remove any transfer-coding prior to
2469   forwarding a message via a MIME-compliant protocol.
2473<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2475   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2476   need to be aware of MIME line length limitations. Since HTTP does not
2477   have this limitation, HTTP does not fold long lines. MHTML messages
2478   being transported by HTTP follow all conventions of MHTML, including
2479   line length limitations and folding, canonicalization, etc., since
2480   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2481   does not interpret the content or any MIME header lines that might be
2482   contained therein.
2487<section title="Additional Features" anchor="additional.features">
2489   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2490   existing HTTP implementations, but not consistently and correctly
2491   across most HTTP/1.1 applications. Implementors are advised to be
2492   aware of these features, but cannot rely upon their presence in, or
2493   interoperability with, other HTTP/1.1 applications. Some of these
2494   describe proposed experimental features, and some describe features
2495   that experimental deployment found lacking that are now addressed in
2496   the base HTTP/1.1 specification.
2499   A number of other headers, such as Content-Disposition and Title,
2500   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2503<section title="Content-Disposition" anchor="content-disposition">
2504<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2505<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2506  <x:anchor-alias value="content-disposition"/>
2507  <x:anchor-alias value="content-disposition-v"/>
2508  <x:anchor-alias value="disposition-type"/>
2509  <x:anchor-alias value="disposition-parm"/>
2510  <x:anchor-alias value="disp-extension-parm"/>
2511  <x:anchor-alias value="disp-extension-token"/>
2512  <x:anchor-alias value="filename-parm"/>
2514   The Content-Disposition response-header field has been proposed as a
2515   means for the origin server to suggest a default filename if the user
2516   requests that the content is saved to a file. This usage is derived
2517   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2519<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"/>
2520  <x:ref>content-disposition</x:ref> = "Content-Disposition" BWS ":" OWS
2521                        <x:ref>content-disposition-v</x:ref>
2522  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref> *( ";" <x:ref>disposition-parm</x:ref> )
2523  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2524  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2525  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2526  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2527  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2530   An example is
2532<figure><artwork type="example">
2533   Content-Disposition: attachment; filename="fname.ext"
2536   The receiving user agent &SHOULD-NOT;  respect any directory path
2537   information present in the filename-parm parameter, which is the only
2538   parameter believed to apply to HTTP implementations at this time. The
2539   filename &SHOULD; be treated as a terminal component only.
2542   If this header is used in a response with the application/octet-stream
2543   content-type, the implied suggestion is that the user agent
2544   should not display the response, but directly enter a `save response
2545   as...' dialog.
2548   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2553<section title="Compatibility with Previous Versions" anchor="compatibility">
2554<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2556   Transfer-coding and message lengths all interact in ways that
2557   required fixing exactly when chunked encoding is used (to allow for
2558   transfer encoding that may not be self delimiting); it was important
2559   to straighten out exactly how message lengths are computed.
2560   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2561   <xref target="Part5"/> and <xref target="Part6"/>).
2564   Charset wildcarding is introduced to avoid explosion of character set
2565   names in accept headers. (<xref target="header.accept-charset"/>)
2568   Content-Base was deleted from the specification: it was not
2569   implemented widely, and there is no simple, safe way to introduce it
2570   without a robust extension mechanism. In addition, it is used in a
2571   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2574   A content-coding of "identity" was introduced, to solve problems
2575   discovered in caching. (<xref target="content.codings"/>)
2578   Quality Values of zero should indicate that "I don't want something"
2579   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2582   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
2583   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
2584   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2588<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2590  Clarify contexts that charset is used in.
2591  (<xref target="character.sets"/>)
2594  Remove reference to non-existant identity transfer-coding value tokens.
2595  (<xref target="no.content-transfer-encoding"/>)
2601<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2603<section title="Since RFC2616">
2605  Extracted relevant partitions from <xref target="RFC2616"/>.
2609<section title="Since draft-ietf-httpbis-p3-payload-00">
2611  Closed issues:
2612  <list style="symbols">
2613    <t>
2614      <eref target=""/>:
2615      "Media Type Registrations"
2616      (<eref target=""/>)
2617    </t>
2618    <t>
2619      <eref target=""/>:
2620      "Clarification regarding quoting of charset values"
2621      (<eref target=""/>)
2622    </t>
2623    <t>
2624      <eref target=""/>:
2625      "Remove 'identity' token references"
2626      (<eref target=""/>)
2627    </t>
2628    <t>
2629      <eref target=""/>:
2630      "Accept-Encoding BNF"
2631    </t>
2632    <t>
2633      <eref target=""/>:
2634      "Normative and Informative references"
2635    </t>
2636    <t>
2637      <eref target=""/>:
2638      "RFC1700 references"
2639    </t>
2640    <t>
2641      <eref target=""/>:
2642      "Updating to RFC4288"
2643    </t>
2644    <t>
2645      <eref target=""/>:
2646      "Informative references"
2647    </t>
2648    <t>
2649      <eref target=""/>:
2650      "ISO-8859-1 Reference"
2651    </t>
2652    <t>
2653      <eref target=""/>:
2654      "Encoding References Normative"
2655    </t>
2656    <t>
2657      <eref target=""/>:
2658      "Normative up-to-date references"
2659    </t>
2660  </list>
2664<section title="Since draft-ietf-httpbis-p3-payload-01">
2666  Ongoing work on ABNF conversion (<eref target=""/>):
2667  <list style="symbols">
2668    <t>
2669      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2670    </t>
2671  </list>
2675<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2677  Closed issues:
2678  <list style="symbols">
2679    <t>
2680      <eref target=""/>:
2681      "Quoting Charsets"
2682    </t>
2683    <t>
2684      <eref target=""/>:
2685      "Classification for Allow header"
2686    </t>
2687    <t>
2688      <eref target=""/>:
2689      "missing default for qvalue in description of Accept-Encoding"
2690    </t>
2691  </list>
2694  Ongoing work on IANA Message Header Registration (<eref target=""/>):
2695  <list style="symbols">
2696    <t>
2697      Reference RFC 3984, and update header registrations for headers defined
2698      in this document.
2699    </t>
2700  </list>
2704<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2706  Closed issues:
2707  <list style="symbols">
2708    <t>
2709      <eref target=""/>:
2710      "Quoting Charsets"
2711    </t>
2712    <t>
2713      <eref target=""/>:
2714      "language tag matching (Accept-Language) vs RFC4647"
2715    </t>
2716    <t>
2717      <eref target=""/>:
2718      "RFC 1806 has been replaced by RFC2183"
2719    </t>
2720  </list>
2723  Other changes:
2724  <list style="symbols">
2725    <t>
2726      <eref target=""/>:
2727      "Encoding References Normative" -- rephrase the annotation and reference
2728      <xref target="BCP97"/>.
2729    </t>
2730  </list>
2732 </section>
2734<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2736  Closed issues:
2737  <list style="symbols">
2738    <t>
2739      <eref target=""/>:
2740      "RFC 2822 is updated by RFC 5322"
2741    </t>
2742  </list>
2745  Ongoing work on ABNF conversion (<eref target=""/>):
2746  <list style="symbols">
2747    <t>
2748      Use "/" instead of "|" for alternatives.
2749    </t>
2750    <t>
2751      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2752      whitespace ("OWS") and required whitespace ("RWS").
2753    </t>
2754    <t>
2755      Rewrite ABNFs to spell out whitespace rules, factor out
2756      header value format definitions.
2757    </t>
2758  </list>
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