source: draft-ietf-httpbis/latest/p3-payload.xml @ 35

Last change on this file since 35 was 35, checked in by fielding@…, 12 years ago

Use obsoletes instead of updates and seven-part instead of eight.

  • Property svn:eol-style set to native
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1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY caching                  "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY header-allow             "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27]>
28<?rfc toc="yes" ?>
29<?rfc symrefs="yes" ?>
30<?rfc sortrefs="yes" ?>
31<?rfc compact="yes"?>
32<?rfc subcompact="no" ?>
33<?rfc linkmailto="no" ?>
34<?rfc editing="no" ?>
35<?rfc-ext allow-markup-in-artwork="yes" ?>
36<?rfc-ext include-references-in-index="yes" ?>
37<rfc obsoletes="2068, 2616, 2617" category="std"
38     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
39     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
40<front>
41
42  <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
43
44  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
45    <organization abbrev="Day Software">Day Software</organization>
46    <address>
47      <postal>
48        <street>23 Corporate Plaza DR, Suite 280</street>
49        <city>Newport Beach</city>
50        <region>CA</region>
51        <code>92660</code>
52        <country>USA</country>
53      </postal>
54      <phone>+1-949-706-5300</phone>
55      <facsimile>+1-949-706-5305</facsimile>
56      <email>fielding@gbiv.com</email>
57      <uri>http://roy.gbiv.com/</uri>
58    </address>
59  </author>
60
61  <author initials="J." surname="Gettys" fullname="Jim Gettys">
62    <organization>One Laptop per Child</organization>
63    <address>
64      <postal>
65        <street>21 Oak Knoll Road</street>
66        <city>Carlisle</city>
67        <region>MA</region>
68        <code>01741</code>
69        <country>USA</country>
70      </postal>
71      <email>jg@laptop.org</email>
72      <uri>http://www.laptop.org/</uri>
73    </address>
74  </author>
75 
76  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
77    <organization abbrev="HP">Hewlett-Packard Company</organization>
78    <address>
79      <postal>
80        <street>HP Labs, Large Scale Systems Group</street>
81        <street>1501 Page Mill Road, MS 1177</street>
82        <city>Palo Alto</city>
83        <region>CA</region>
84        <code>94304</code>
85        <country>USA</country>
86      </postal>
87      <email>JeffMogul@acm.org</email>
88    </address>
89  </author>
90
91  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
92    <organization abbrev="Microsoft">Microsoft Corporation</organization>
93    <address>
94      <postal>
95        <street>1 Microsoft Way</street>
96        <city>Redmond</city>
97        <region>WA</region>
98        <code>98052</code>
99        <country>USA</country>
100      </postal>
101      <email>henrikn@microsoft.com</email>
102    </address>
103  </author>
104
105  <author initials="L." surname="Masinter" fullname="Larry Masinter">
106    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
107    <address>
108      <postal>
109        <street>345 Park Ave</street>
110        <city>San Jose</city>
111        <region>CA</region>
112        <code>95110</code>
113        <country>USA</country>
114      </postal>
115      <email>LMM@acm.org</email>
116      <uri>http://larry.masinter.net/</uri>
117    </address>
118  </author>
119 
120  <author initials="P." surname="Leach" fullname="Paul J. Leach">
121    <organization abbrev="Microsoft">Microsoft Corporation</organization>
122    <address>
123      <postal>
124        <street>1 Microsoft Way</street>
125        <city>Redmond</city>
126        <region>WA</region>
127        <code>98052</code>
128      </postal>
129      <email>paulle@microsoft.com</email>
130    </address>
131  </author>
132   
133  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
134    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
135    <address>
136      <postal>
137        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
138        <street>The Stata Center, Building 32</street>
139        <street>32 Vassar Street</street>
140        <city>Cambridge</city>
141        <region>MA</region>
142        <code>02139</code>
143        <country>USA</country>
144      </postal>
145      <email>timbl@w3.org</email>
146      <uri>http://www.w3.org/People/Berners-Lee/</uri>
147    </address>
148  </author>
149
150  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
151
152<abstract>
153<t>
154   The Hypertext Transfer Protocol (HTTP) is an application-level
155   protocol for distributed, collaborative, hypermedia information
156   systems. HTTP has been in use by the World Wide Web global information
157   initiative since 1990. This document is Part 3 of the seven-part specification
158   that defines the protocol referred to as "HTTP/1.1" and, taken together,
159   obsoletes RFC 2616 and RFC 2617.  Part 3 defines HTTP message content,
160   metadata, and content negotiation.
161</t>
162</abstract>
163</front>
164<middle>
165<section title="Introduction" anchor="introduction">
166<t>
167   This document will define aspects of HTTP related to the payload of
168   messages (message content), including metadata and media types, along
169   with HTTP content negotiation.  Right now it only includes the extracted
170   relevant sections of RFC 2616 without edit.
171</t>
172</section>
173
174<section title="Protocol Parameters" anchor="protocol.parameters">
175
176<section title="Character Sets" anchor="character.sets">
177<t>
178   HTTP uses the same definition of the term "character set" as that
179   described for MIME:
180</t>
181<t>
182   The term "character set" is used in this document to refer to a
183   method used with one or more tables to convert a sequence of octets
184   into a sequence of characters. Note that unconditional conversion in
185   the other direction is not required, in that not all characters may
186   be available in a given character set and a character set may provide
187   more than one sequence of octets to represent a particular character.
188   This definition is intended to allow various kinds of character
189   encoding, from simple single-table mappings such as US-ASCII to
190   complex table switching methods such as those that use ISO-2022's
191   techniques. However, the definition associated with a MIME character
192   set name &MUST; fully specify the mapping to be performed from octets
193   to characters. In particular, use of external profiling information
194   to determine the exact mapping is not permitted.
195</t>
196<t><list><t>
197      <x:h>Note:</x:h> This use of the term "character set" is more commonly
198      referred to as a "character encoding." However, since HTTP and
199      MIME share the same registry, it is important that the terminology
200      also be shared.
201</t></list></t>
202<t>
203   HTTP character sets are identified by case-insensitive tokens. The
204   complete set of tokens is defined by the IANA Character Set registry
205   <xref target="RFC1700"/>.
206</t>
207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
208    charset = token
209</artwork></figure>
210<t>
211   Although HTTP allows an arbitrary token to be used as a charset
212   value, any token that has a predefined value within the IANA
213   Character Set registry <xref target="RFC1700"/> &MUST; represent the character set defined
214   by that registry. Applications &SHOULD; limit their use of character
215   sets to those defined by the IANA registry.
216</t>
217<t>
218   Implementors should be aware of IETF character set requirements <xref target="RFC2279"/>
219   <xref target="RFC2277"/>.
220</t>
221
222<section title="Missing Charset" anchor="missing.charset">
223<t>
224   Some HTTP/1.0 software has interpreted a Content-Type header without
225   charset parameter incorrectly to mean "recipient should guess."
226   Senders wishing to defeat this behavior &MAY; include a charset
227   parameter even when the charset is ISO-8859-1 and &SHOULD; do so when
228   it is known that it will not confuse the recipient.
229</t>
230<t>
231   Unfortunately, some older HTTP/1.0 clients did not deal properly with
232   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
233   charset label provided by the sender; and those user agents that have
234   a provision to "guess" a charset &MUST; use the charset from the
235   content-type field if they support that charset, rather than the
236   recipient's preference, when initially displaying a document. See
237   <xref target="canonicalization.and.text.defaults"/>.
238</t>
239</section>
240</section>
241
242<section title="Content Codings" anchor="content.codings">
243<t>
244   Content coding values indicate an encoding transformation that has
245   been or can be applied to an entity. Content codings are primarily
246   used to allow a document to be compressed or otherwise usefully
247   transformed without losing the identity of its underlying media type
248   and without loss of information. Frequently, the entity is stored in
249   coded form, transmitted directly, and only decoded by the recipient.
250</t>
251<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
252    content-coding   = token
253</artwork></figure>
254<t>
255   All content-coding values are case-insensitive. HTTP/1.1 uses
256   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
257   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
258   describes the content-coding, what is more important is that it
259   indicates what decoding mechanism will be required to remove the
260   encoding.
261</t>
262<t>
263   The Internet Assigned Numbers Authority (IANA) acts as a registry for
264   content-coding value tokens. Initially, the registry contains the
265   following tokens:
266</t>
267<t>
268   gzip<iref item="gzip"/>
269  <list>
270    <t>
271        An encoding format produced by the file compression program
272        "gzip" (GNU zip) as described in RFC 1952 <xref target="RFC1952"/>. This format is a
273        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
274    </t>
275  </list>
276</t>
277<t>
278   compress<iref item="compress"/>
279  <list><t>
280        The encoding format produced by the common UNIX file compression
281        program "compress". This format is an adaptive Lempel-Ziv-Welch
282        coding (LZW).
283</t><t>
284        Use of program names for the identification of encoding formats
285        is not desirable and is discouraged for future encodings. Their
286        use here is representative of historical practice, not good
287        design. For compatibility with previous implementations of HTTP,
288        applications &SHOULD; consider "x-gzip" and "x-compress" to be
289        equivalent to "gzip" and "compress" respectively.
290  </t></list>
291</t>
292<t>
293   deflate<iref item="deflate"/>
294  <list><t>
295        The "zlib" format defined in RFC 1950 <xref target="RFC1950"/> in combination with
296        the "deflate" compression mechanism described in RFC 1951 <xref target="RFC1951"/>.
297  </t></list>
298</t>
299<t>
300   identity<iref item="identity"/>
301  <list><t>
302        The default (identity) encoding; the use of no transformation
303        whatsoever. This content-coding is used only in the Accept-Encoding
304        header, and &SHOULD-NOT;  be used in the Content-Encoding
305        header.
306  </t></list>
307</t>
308<t>
309   New content-coding value tokens &SHOULD; be registered; to allow
310   interoperability between clients and servers, specifications of the
311   content coding algorithms needed to implement a new value &SHOULD; be
312   publicly available and adequate for independent implementation, and
313   conform to the purpose of content coding defined in this section.
314</t>
315</section>
316
317<section title="Media Types" anchor="media.types">
318<t>
319   HTTP uses Internet Media Types <xref target="RFC1590"/> in the Content-Type (<xref target="header.content-type"/>)
320   and Accept (<xref target="header.accept"/>) header fields in order to provide
321   open and extensible data typing and type negotiation.
322</t>
323<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"/>
324    media-type     = type "/" subtype *( ";" parameter )
325    type           = token
326    subtype        = token
327</artwork></figure>
328<t>
329   Parameters &MAY; follow the type/subtype in the form of attribute/value
330   pairs.
331</t>
332<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"/>
333    parameter               = attribute "=" value
334    attribute               = token
335    value                   = token | quoted-string
336</artwork></figure>
337<t>
338   The type, subtype, and parameter attribute names are case-insensitive.
339   Parameter values might or might not be case-sensitive,
340   depending on the semantics of the parameter name. Linear white space
341   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
342   attribute and its value. The presence or absence of a parameter might
343   be significant to the processing of a media-type, depending on its
344   definition within the media type registry.
345</t>
346<t>
347   Note that some older HTTP applications do not recognize media type
348   parameters. When sending data to older HTTP applications,
349   implementations &SHOULD; only use media type parameters when they are
350   required by that type/subtype definition.
351</t>
352<t>
353   Media-type values are registered with the Internet Assigned Number
354   Authority (IANA <xref target="RFC1700"/>). The media type registration process is
355   outlined in RFC 1590 <xref target="RFC1590"/>. Use of non-registered media types is
356   discouraged.
357</t>
358
359<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
360<t>
361   Internet media types are registered with a canonical form. An
362   entity-body transferred via HTTP messages &MUST; be represented in the
363   appropriate canonical form prior to its transmission except for
364   "text" types, as defined in the next paragraph.
365</t>
366<t>
367   When in canonical form, media subtypes of the "text" type use CRLF as
368   the text line break. HTTP relaxes this requirement and allows the
369   transport of text media with plain CR or LF alone representing a line
370   break when it is done consistently for an entire entity-body. HTTP
371   applications &MUST; accept CRLF, bare CR, and bare LF as being
372   representative of a line break in text media received via HTTP. In
373   addition, if the text is represented in a character set that does not
374   use octets 13 and 10 for CR and LF respectively, as is the case for
375   some multi-byte character sets, HTTP allows the use of whatever octet
376   sequences are defined by that character set to represent the
377   equivalent of CR and LF for line breaks. This flexibility regarding
378   line breaks applies only to text media in the entity-body; a bare CR
379   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
380   structures (such as header fields and multipart boundaries).
381</t>
382<t>
383   If an entity-body is encoded with a content-coding, the underlying
384   data &MUST; be in a form defined above prior to being encoded.
385</t>
386<t>
387   The "charset" parameter is used with some media types to define the
388   character set (<xref target="character.sets"/>) of the data. When no explicit charset
389   parameter is provided by the sender, media subtypes of the "text"
390   type are defined to have a default charset value of "ISO-8859-1" when
391   received via HTTP. Data in character sets other than "ISO-8859-1" or
392   its subsets &MUST; be labeled with an appropriate charset value. See
393   <xref target="missing.charset"/> for compatibility problems.
394</t>
395</section>
396
397<section title="Multipart Types" anchor="multipart.types">
398<t>
399   MIME provides for a number of "multipart" types -- encapsulations of
400   one or more entities within a single message-body. All multipart
401   types share a common syntax, as defined in section <xref target="RFC2046" x:sec="5.1.1" x:fmt="number"/> of RFC 2046
402   <xref target="RFC2046"/>, and &MUST; include a boundary parameter as part of the media type
403   value. The message body is itself a protocol element and &MUST;
404   therefore use only CRLF to represent line breaks between body-parts.
405   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
406   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
407   original multipart contains an epilogue). These restrictions exist in
408   order to preserve the self-delimiting nature of a multipart message-body,
409   wherein the "end" of the message-body is indicated by the
410   ending multipart boundary.
411</t>
412<t>
413   In general, HTTP treats a multipart message-body no differently than
414   any other media type: strictly as payload. The one exception is the
415   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
416   (Partial Content) response. In all
417   other cases, an HTTP user agent &SHOULD; follow the same or similar
418   behavior as a MIME user agent would upon receipt of a multipart type.
419   The MIME header fields within each body-part of a multipart message-body
420   do not have any significance to HTTP beyond that defined by
421   their MIME semantics.
422</t>
423<t>
424   In general, an HTTP user agent &SHOULD; follow the same or similar
425   behavior as a MIME user agent would upon receipt of a multipart type.
426   If an application receives an unrecognized multipart subtype, the
427   application &MUST; treat it as being equivalent to "multipart/mixed".
428</t>
429<t><list><t>
430      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
431      for carrying form data suitable for processing via the POST
432      request method, as described in RFC 1867 <xref target="RFC1867"/>.
433</t></list></t>
434</section>
435</section>
436
437<section title="Quality Values" anchor="quality.values">
438<t>
439   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
440   numbers to indicate the relative importance ("weight") of various
441   negotiable parameters.  A weight is normalized to a real number in
442   the range 0 through 1, where 0 is the minimum and 1 the maximum
443   value. If a parameter has a quality value of 0, then content with
444   this parameter is `not acceptable' for the client. HTTP/1.1
445   applications &MUST-NOT; generate more than three digits after the
446   decimal point. User configuration of these values &SHOULD; also be
447   limited in this fashion.
448</t>
449<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
450    qvalue         = ( "0" [ "." 0*3DIGIT ] )
451                   | ( "1" [ "." 0*3("0") ] )
452</artwork></figure>
453<t>
454   "Quality values" is a misnomer, since these values merely represent
455   relative degradation in desired quality.
456</t>
457</section>
458
459<section title="Language Tags" anchor="language.tags">
460<t>
461   A language tag identifies a natural language spoken, written, or
462   otherwise conveyed by human beings for communication of information
463   to other human beings. Computer languages are explicitly excluded.
464   HTTP uses language tags within the Accept-Language and Content-Language
465   fields.
466</t>
467<t>
468   The syntax and registry of HTTP language tags is the same as that
469   defined by RFC 1766 <xref target="RFC1766"/>. In summary, a language tag is composed of 1
470   or more parts: A primary language tag and a possibly empty series of
471   subtags:
472</t>
473<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"/>
474     language-tag  = primary-tag *( "-" subtag )
475     primary-tag   = 1*8ALPHA
476     subtag        = 1*8ALPHA
477</artwork></figure>
478<t>
479   White space is not allowed within the tag and all tags are case-insensitive.
480   The name space of language tags is administered by the
481   IANA. Example tags include:
482</t>
483<figure><artwork type="example">
484    en, en-US, en-cockney, i-cherokee, x-pig-latin
485</artwork></figure>
486<t>
487   where any two-letter primary-tag is an ISO-639 language abbreviation
488   and any two-letter initial subtag is an ISO-3166 country code. (The
489   last three tags above are not registered tags; all but the last are
490   examples of tags which could be registered in future.)
491</t>
492</section>
493</section>
494
495<section title="Entity" anchor="entity">
496<t>
497   Request and Response messages &MAY; transfer an entity if not otherwise
498   restricted by the request method or response status code. An entity
499   consists of entity-header fields and an entity-body, although some
500   responses will only include the entity-headers.
501</t>
502<t>
503   In this section, both sender and recipient refer to either the client
504   or the server, depending on who sends and who receives the entity.
505</t>
506
507<section title="Entity Header Fields" anchor="entity.header.fields">
508<t>
509   Entity-header fields define metainformation about the entity-body or,
510   if no body is present, about the resource identified by the request.
511   Some of this metainformation is &OPTIONAL;; some might be &REQUIRED; by
512   portions of this specification.
513</t>
514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
515    entity-header  = Allow                    ; &header-allow;
516                   | Content-Encoding         ; <xref target="header.content-encoding"/>
517                   | Content-Language         ; <xref target="header.content-language"/>
518                   | Content-Length           ; &header-content-length;
519                   | Content-Location         ; <xref target="header.content-location"/>
520                   | Content-MD5              ; <xref target="header.content-md5"/>
521                   | Content-Range            ; &header-content-range;
522                   | Content-Type             ; <xref target="header.content-type"/>
523                   | Expires                  ; &header-expires;
524                   | Last-Modified            ; &header-last-modified;
525                   | extension-header
526
527    extension-header = message-header
528</artwork></figure>
529<t>
530   The extension-header mechanism allows additional entity-header fields
531   to be defined without changing the protocol, but these fields cannot
532   be assumed to be recognizable by the recipient. Unrecognized header
533   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
534   transparent proxies.
535</t>
536</section>
537
538<section title="Entity Body" anchor="entity.body">
539<t>
540   The entity-body (if any) sent with an HTTP request or response is in
541   a format and encoding defined by the entity-header fields.
542</t>
543<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
544    entity-body    = *OCTET
545</artwork></figure>
546<t>
547   An entity-body is only present in a message when a message-body is
548   present, as described in &message-body;. The entity-body is obtained
549   from the message-body by decoding any Transfer-Encoding that might
550   have been applied to ensure safe and proper transfer of the message.
551</t>
552
553<section title="Type" anchor="type">
554<t>
555   When an entity-body is included with a message, the data type of that
556   body is determined via the header fields Content-Type and Content-Encoding.
557   These define a two-layer, ordered encoding model:
558</t>
559<figure><artwork type="example">
560    entity-body := Content-Encoding( Content-Type( data ) )
561</artwork></figure>
562<t>
563   Content-Type specifies the media type of the underlying data.
564   Content-Encoding may be used to indicate any additional content
565   codings applied to the data, usually for the purpose of data
566   compression, that are a property of the requested resource. There is
567   no default encoding.
568</t>
569<t>
570   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
571   Content-Type header field defining the media type of that body. If
572   and only if the media type is not given by a Content-Type field, the
573   recipient &MAY; attempt to guess the media type via inspection of its
574   content and/or the name extension(s) of the URI used to identify the
575   resource. If the media type remains unknown, the recipient &SHOULD;
576   treat it as type "application/octet-stream".
577</t>
578</section>
579   
580<section title="Entity Length" anchor="entity.length">
581<t>
582   The entity-length of a message is the length of the message-body
583   before any transfer-codings have been applied. &message-length; defines
584   how the transfer-length of a message-body is determined.
585</t>
586</section>
587</section>
588</section>
589
590<section title="Content Negotiation" anchor="content.negotiation">
591<t>
592   Most HTTP responses include an entity which contains information for
593   interpretation by a human user. Naturally, it is desirable to supply
594   the user with the "best available" entity corresponding to the
595   request. Unfortunately for servers and caches, not all users have the
596   same preferences for what is "best," and not all user agents are
597   equally capable of rendering all entity types. For that reason, HTTP
598   has provisions for several mechanisms for "content negotiation" --
599   the process of selecting the best representation for a given response
600   when there are multiple representations available.
601  <list><t>
602      <x:h>Note:</x:h> This is not called "format negotiation" because the
603      alternate representations may be of the same media type, but use
604      different capabilities of that type, be in different languages,
605      etc.
606  </t></list>
607</t>
608<t>
609   Any response containing an entity-body &MAY; be subject to negotiation,
610   including error responses.
611</t>
612<t>
613   There are two kinds of content negotiation which are possible in
614   HTTP: server-driven and agent-driven negotiation. These two kinds of
615   negotiation are orthogonal and thus may be used separately or in
616   combination. One method of combination, referred to as transparent
617   negotiation, occurs when a cache uses the agent-driven negotiation
618   information provided by the origin server in order to provide
619   server-driven negotiation for subsequent requests.
620</t>
621
622<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
623<t>
624   If the selection of the best representation for a response is made by
625   an algorithm located at the server, it is called server-driven
626   negotiation. Selection is based on the available representations of
627   the response (the dimensions over which it can vary; e.g. language,
628   content-coding, etc.) and the contents of particular header fields in
629   the request message or on other information pertaining to the request
630   (such as the network address of the client).
631</t>
632<t>
633   Server-driven negotiation is advantageous when the algorithm for
634   selecting from among the available representations is difficult to
635   describe to the user agent, or when the server desires to send its
636   "best guess" to the client along with the first response (hoping to
637   avoid the round-trip delay of a subsequent request if the "best
638   guess" is good enough for the user). In order to improve the server's
639   guess, the user agent &MAY; include request header fields (Accept,
640   Accept-Language, Accept-Encoding, etc.) which describe its
641   preferences for such a response.
642</t>
643<t>
644   Server-driven negotiation has disadvantages:
645  <list style="numbers">
646    <t>
647         It is impossible for the server to accurately determine what
648         might be "best" for any given user, since that would require
649         complete knowledge of both the capabilities of the user agent
650         and the intended use for the response (e.g., does the user want
651         to view it on screen or print it on paper?).
652    </t>
653    <t>
654         Having the user agent describe its capabilities in every
655         request can be both very inefficient (given that only a small
656         percentage of responses have multiple representations) and a
657         potential violation of the user's privacy.
658    </t>
659    <t>
660         It complicates the implementation of an origin server and the
661         algorithms for generating responses to a request.
662    </t>
663    <t>
664         It may limit a public cache's ability to use the same response
665         for multiple user's requests.
666    </t>
667  </list>
668</t>
669<t>
670   HTTP/1.1 includes the following request-header fields for enabling
671   server-driven negotiation through description of user agent
672   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
673   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
674   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
675   origin server is not limited to these dimensions and &MAY; vary the
676   response based on any aspect of the request, including information
677   outside the request-header fields or within extension header fields
678   not defined by this specification.
679</t>
680<t>
681   The Vary header field &caching; can be used to express the parameters the
682   server uses to select a representation that is subject to server-driven
683   negotiation.
684</t>
685</section>
686
687<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
688<t>
689   With agent-driven negotiation, selection of the best representation
690   for a response is performed by the user agent after receiving an
691   initial response from the origin server. Selection is based on a list
692   of the available representations of the response included within the
693   header fields or entity-body of the initial response, with each
694   representation identified by its own URI. Selection from among the
695   representations may be performed automatically (if the user agent is
696   capable of doing so) or manually by the user selecting from a
697   generated (possibly hypertext) menu.
698</t>
699<t>
700   Agent-driven negotiation is advantageous when the response would vary
701   over commonly-used dimensions (such as type, language, or encoding),
702   when the origin server is unable to determine a user agent's
703   capabilities from examining the request, and generally when public
704   caches are used to distribute server load and reduce network usage.
705</t>
706<t>
707   Agent-driven negotiation suffers from the disadvantage of needing a
708   second request to obtain the best alternate representation. This
709   second request is only efficient when caching is used. In addition,
710   this specification does not define any mechanism for supporting
711   automatic selection, though it also does not prevent any such
712   mechanism from being developed as an extension and used within
713   HTTP/1.1.
714</t>
715<t>
716   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
717   status codes for enabling agent-driven negotiation when the server is
718   unwilling or unable to provide a varying response using server-driven
719   negotiation.
720</t>
721</section>
722
723<section title="Transparent Negotiation" anchor="transparent.negotiation">
724<t>
725   Transparent negotiation is a combination of both server-driven and
726   agent-driven negotiation. When a cache is supplied with a form of the
727   list of available representations of the response (as in agent-driven
728   negotiation) and the dimensions of variance are completely understood
729   by the cache, then the cache becomes capable of performing server-driven
730   negotiation on behalf of the origin server for subsequent
731   requests on that resource.
732</t>
733<t>
734   Transparent negotiation has the advantage of distributing the
735   negotiation work that would otherwise be required of the origin
736   server and also removing the second request delay of agent-driven
737   negotiation when the cache is able to correctly guess the right
738   response.
739</t>
740<t>
741   This specification does not define any mechanism for transparent
742   negotiation, though it also does not prevent any such mechanism from
743   being developed as an extension that could be used within HTTP/1.1.
744</t>
745</section>
746</section>
747<section title="Header Field Definitions" anchor="header.fields">
748<t>
749   This section defines the syntax and semantics of all standard
750   HTTP/1.1 header fields. For entity-header fields, both sender and
751   recipient refer to either the client or the server, depending on who
752   sends and who receives the entity.
753</t>
754<section title="Accept" anchor="header.accept">
755  <iref primary="true" item="Accept header" x:for-anchor=""/>
756  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
757<t>
758   The Accept request-header field can be used to specify certain media
759   types which are acceptable for the response. Accept headers can be
760   used to indicate that the request is specifically limited to a small
761   set of desired types, as in the case of a request for an in-line
762   image.
763</t>
764<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-extension"/>
765    Accept         = "Accept" ":"
766                     #( media-range [ accept-params ] )
767
768    media-range    = ( "*/*"
769                     | ( type "/" "*" )
770                     | ( type "/" subtype )
771                     ) *( ";" parameter )
772    accept-params  = ";" "q" "=" qvalue *( accept-extension )
773    accept-extension = ";" token [ "=" ( token | quoted-string ) ]
774</artwork></figure>
775<t>
776   The asterisk "*" character is used to group media types into ranges,
777   with "*/*" indicating all media types and "type/*" indicating all
778   subtypes of that type. The media-range &MAY; include media type
779   parameters that are applicable to that range.
780</t>
781<t>
782   Each media-range &MAY; be followed by one or more accept-params,
783   beginning with the "q" parameter for indicating a relative quality
784   factor. The first "q" parameter (if any) separates the media-range
785   parameter(s) from the accept-params. Quality factors allow the user
786   or user agent to indicate the relative degree of preference for that
787   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
788   default value is q=1.
789  <list><t>
790      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
791      parameters from Accept extension parameters is due to historical
792      practice. Although this prevents any media type parameter named
793      "q" from being used with a media range, such an event is believed
794      to be unlikely given the lack of any "q" parameters in the IANA
795      media type registry and the rare usage of any media type
796      parameters in Accept. Future media types are discouraged from
797      registering any parameter named "q".
798  </t></list>
799</t>
800<t>
801   The example
802</t>
803<figure><artwork type="example">
804    Accept: audio/*; q=0.2, audio/basic
805</artwork></figure>
806<t>
807   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
808   type if it is the best available after an 80% mark-down in quality."
809</t>
810<t>
811   If no Accept header field is present, then it is assumed that the
812   client accepts all media types. If an Accept header field is present,
813   and if the server cannot send a response which is acceptable
814   according to the combined Accept field value, then the server &SHOULD;
815   send a 406 (not acceptable) response.
816</t>
817<t>
818   A more elaborate example is
819</t>
820<figure><artwork type="example">
821    Accept: text/plain; q=0.5, text/html,
822            text/x-dvi; q=0.8, text/x-c
823</artwork></figure>
824<t>
825   Verbally, this would be interpreted as "text/html and text/x-c are
826   the preferred media types, but if they do not exist, then send the
827   text/x-dvi entity, and if that does not exist, send the text/plain
828   entity."
829</t>
830<t>
831   Media ranges can be overridden by more specific media ranges or
832   specific media types. If more than one media range applies to a given
833   type, the most specific reference has precedence. For example,
834</t>
835<figure><artwork type="example">
836    Accept: text/*, text/html, text/html;level=1, */*
837</artwork></figure>
838<t>
839   have the following precedence:
840</t>
841<figure><artwork type="example">
842    1) text/html;level=1
843    2) text/html
844    3) text/*
845    4) */*
846</artwork></figure>
847<t>
848   The media type quality factor associated with a given type is
849   determined by finding the media range with the highest precedence
850   which matches that type. For example,
851</t>
852<figure><artwork type="example">
853    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
854            text/html;level=2;q=0.4, */*;q=0.5
855</artwork></figure>
856<t>
857   would cause the following values to be associated:
858</t>
859<figure><artwork type="example">
860    text/html;level=1         = 1
861    text/html                 = 0.7
862    text/plain                = 0.3
863    image/jpeg                = 0.5
864    text/html;level=2         = 0.4
865    text/html;level=3         = 0.7
866</artwork></figure>
867<t>
868      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
869      values for certain media ranges. However, unless the user agent is
870      a closed system which cannot interact with other rendering agents,
871      this default set ought to be configurable by the user.
872</t>
873</section>
874
875<section title="Accept-Charset" anchor="header.accept-charset">
876  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
877  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
878<t>
879   The Accept-Charset request-header field can be used to indicate what
880   character sets are acceptable for the response. This field allows
881   clients capable of understanding more comprehensive or special-purpose
882   character sets to signal that capability to a server which is
883   capable of representing documents in those character sets.
884</t>
885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
886   Accept-Charset = "Accept-Charset" ":"
887           1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
888</artwork></figure>
889<t>
890   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
891   be given an associated quality value which represents the user's
892   preference for that charset. The default value is q=1. An example is
893</t>
894<figure><artwork type="example">
895   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
896</artwork></figure>
897<t>
898   The special value "*", if present in the Accept-Charset field,
899   matches every character set (including ISO-8859-1) which is not
900   mentioned elsewhere in the Accept-Charset field. If no "*" is present
901   in an Accept-Charset field, then all character sets not explicitly
902   mentioned get a quality value of 0, except for ISO-8859-1, which gets
903   a quality value of 1 if not explicitly mentioned.
904</t>
905<t>
906   If no Accept-Charset header is present, the default is that any
907   character set is acceptable. If an Accept-Charset header is present,
908   and if the server cannot send a response which is acceptable
909   according to the Accept-Charset header, then the server &SHOULD; send
910   an error response with the 406 (not acceptable) status code, though
911   the sending of an unacceptable response is also allowed.
912</t>
913</section>
914
915<section title="Accept-Encoding" anchor="header.accept-encoding">
916  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
917  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
918<t>
919   The Accept-Encoding request-header field is similar to Accept, but
920   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
921   the response.
922</t>
923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
924    Accept-Encoding  = "Accept-Encoding" ":"
925                       1#( codings [ ";" "q" "=" qvalue ] )
926    codings          = ( content-coding | "*" )
927</artwork></figure>
928<t>
929   Examples of its use are:
930</t>
931<figure><artwork type="example">
932    Accept-Encoding: compress, gzip
933    Accept-Encoding:
934    Accept-Encoding: *
935    Accept-Encoding: compress;q=0.5, gzip;q=1.0
936    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
937</artwork></figure>
938<t>
939   A server tests whether a content-coding is acceptable, according to
940   an Accept-Encoding field, using these rules:
941  <list style="numbers">
942      <t>If the content-coding is one of the content-codings listed in
943         the Accept-Encoding field, then it is acceptable, unless it is
944         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
945         qvalue of 0 means "not acceptable.")</t>
946
947      <t>The special "*" symbol in an Accept-Encoding field matches any
948         available content-coding not explicitly listed in the header
949         field.</t>
950
951      <t>If multiple content-codings are acceptable, then the acceptable
952         content-coding with the highest non-zero qvalue is preferred.</t>
953
954      <t>The "identity" content-coding is always acceptable, unless
955         specifically refused because the Accept-Encoding field includes
956         "identity;q=0", or because the field includes "*;q=0" and does
957         not explicitly include the "identity" content-coding. If the
958         Accept-Encoding field-value is empty, then only the "identity"
959         encoding is acceptable.</t>
960  </list>
961</t>
962<t>
963   If an Accept-Encoding field is present in a request, and if the
964   server cannot send a response which is acceptable according to the
965   Accept-Encoding header, then the server &SHOULD; send an error response
966   with the 406 (Not Acceptable) status code.
967</t>
968<t>
969   If no Accept-Encoding field is present in a request, the server &MAY;
970   assume that the client will accept any content coding. In this case,
971   if "identity" is one of the available content-codings, then the
972   server &SHOULD; use the "identity" content-coding, unless it has
973   additional information that a different content-coding is meaningful
974   to the client.
975  <list><t>
976      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
977      and if the "identity" content-coding is unavailable, then
978      content-codings commonly understood by HTTP/1.0 clients (i.e.,
979      "gzip" and "compress") are preferred; some older clients
980      improperly display messages sent with other content-codings.  The
981      server might also make this decision based on information about
982      the particular user-agent or client.
983    </t><t>
984      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
985      associated with content-codings. This means that qvalues will not
986      work and are not permitted with x-gzip or x-compress.
987    </t></list>
988</t>
989</section>
990
991<section title="Accept-Language" anchor="header.accept-language">
992  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
993  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
994<t>
995   The Accept-Language request-header field is similar to Accept, but
996   restricts the set of natural languages that are preferred as a
997   response to the request. Language tags are defined in <xref target="language.tags"/>.
998</t>
999<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1000    Accept-Language = "Accept-Language" ":"
1001                      1#( language-range [ ";" "q" "=" qvalue ] )
1002    language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
1003</artwork></figure>
1004<t>
1005   Each language-range &MAY; be given an associated quality value which
1006   represents an estimate of the user's preference for the languages
1007   specified by that range. The quality value defaults to "q=1". For
1008   example,
1009</t>
1010<figure><artwork type="example">
1011    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1012</artwork></figure>
1013<t>
1014   would mean: "I prefer Danish, but will accept British English and
1015   other types of English." A language-range matches a language-tag if
1016   it exactly equals the tag, or if it exactly equals a prefix of the
1017   tag such that the first tag character following the prefix is "-".
1018   The special range "*", if present in the Accept-Language field,
1019   matches every tag not matched by any other range present in the
1020   Accept-Language field.
1021  <list><t>
1022      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1023      language tags are assigned to languages in such a way that it is
1024      always true that if a user understands a language with a certain
1025      tag, then this user will also understand all languages with tags
1026      for which this tag is a prefix. The prefix rule simply allows the
1027      use of prefix tags if this is the case.
1028  </t></list>
1029</t>
1030<t>
1031   The language quality factor assigned to a language-tag by the
1032   Accept-Language field is the quality value of the longest language-range
1033   in the field that matches the language-tag. If no language-range
1034   in the field matches the tag, the language quality factor
1035   assigned is 0. If no Accept-Language header is present in the
1036   request, the server
1037   &SHOULD; assume that all languages are equally acceptable. If an
1038   Accept-Language header is present, then all languages which are
1039   assigned a quality factor greater than 0 are acceptable.
1040</t>
1041<t>
1042   It might be contrary to the privacy expectations of the user to send
1043   an Accept-Language header with the complete linguistic preferences of
1044   the user in every request. For a discussion of this issue, see
1045   <xref target="privacy.issues.connected.to.accept.headers"/>.
1046</t>
1047<t>
1048   As intelligibility is highly dependent on the individual user, it is
1049   recommended that client applications make the choice of linguistic
1050   preference available to the user. If the choice is not made
1051   available, then the Accept-Language header field &MUST-NOT; be given in
1052   the request.
1053  <list><t>
1054      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1055      the user, we remind implementors of  the fact that users are not
1056      familiar with the details of language matching as described above,
1057      and should provide appropriate guidance. As an example, users
1058      might assume that on selecting "en-gb", they will be served any
1059      kind of English document if British English is not available. A
1060      user agent might suggest in such a case to add "en" to get the
1061      best matching behavior.
1062  </t></list>
1063</t>
1064</section>
1065
1066<section title="Content-Encoding" anchor="header.content-encoding">
1067  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1068  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1069<t>
1070   The Content-Encoding entity-header field is used as a modifier to the
1071   media-type. When present, its value indicates what additional content
1072   codings have been applied to the entity-body, and thus what decoding
1073   mechanisms must be applied in order to obtain the media-type
1074   referenced by the Content-Type header field. Content-Encoding is
1075   primarily used to allow a document to be compressed without losing
1076   the identity of its underlying media type.
1077</t>
1078<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1079    Content-Encoding  = "Content-Encoding" ":" 1#content-coding
1080</artwork></figure>
1081<t>
1082   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1083</t>
1084<figure><artwork type="example">
1085    Content-Encoding: gzip
1086</artwork></figure>
1087<t>
1088   The content-coding is a characteristic of the entity identified by
1089   the Request-URI. Typically, the entity-body is stored with this
1090   encoding and is only decoded before rendering or analogous usage.
1091   However, a non-transparent proxy &MAY; modify the content-coding if the
1092   new coding is known to be acceptable to the recipient, unless the
1093   "no-transform" cache-control directive is present in the message.
1094</t>
1095<t>
1096   If the content-coding of an entity is not "identity", then the
1097   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1098   that lists the non-identity content-coding(s) used.
1099</t>
1100<t>
1101   If the content-coding of an entity in a request message is not
1102   acceptable to the origin server, the server &SHOULD; respond with a
1103   status code of 415 (Unsupported Media Type).
1104</t>
1105<t>
1106   If multiple encodings have been applied to an entity, the content
1107   codings &MUST; be listed in the order in which they were applied.
1108   Additional information about the encoding parameters &MAY; be provided
1109   by other entity-header fields not defined by this specification.
1110</t>
1111</section>
1112
1113<section title="Content-Language" anchor="header.content-language">
1114  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1115  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1116<t>
1117   The Content-Language entity-header field describes the natural
1118   language(s) of the intended audience for the enclosed entity. Note
1119   that this might not be equivalent to all the languages used within
1120   the entity-body.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1123    Content-Language  = "Content-Language" ":" 1#language-tag
1124</artwork></figure>
1125<t>
1126   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1127   Content-Language is to allow a user to identify and differentiate
1128   entities according to the user's own preferred language. Thus, if the
1129   body content is intended only for a Danish-literate audience, the
1130   appropriate field is
1131</t>
1132<figure><artwork type="example">
1133    Content-Language: da
1134</artwork></figure>
1135<t>
1136   If no Content-Language is specified, the default is that the content
1137   is intended for all language audiences. This might mean that the
1138   sender does not consider it to be specific to any natural language,
1139   or that the sender does not know for which language it is intended.
1140</t>
1141<t>
1142   Multiple languages &MAY; be listed for content that is intended for
1143   multiple audiences. For example, a rendition of the "Treaty of
1144   Waitangi," presented simultaneously in the original Maori and English
1145   versions, would call for
1146</t>
1147<figure><artwork type="example">
1148    Content-Language: mi, en
1149</artwork></figure>
1150<t>
1151   However, just because multiple languages are present within an entity
1152   does not mean that it is intended for multiple linguistic audiences.
1153   An example would be a beginner's language primer, such as "A First
1154   Lesson in Latin," which is clearly intended to be used by an
1155   English-literate audience. In this case, the Content-Language would
1156   properly only include "en".
1157</t>
1158<t>
1159   Content-Language &MAY; be applied to any media type -- it is not
1160   limited to textual documents.
1161</t>
1162</section>
1163
1164<section title="Content-Location" anchor="header.content-location">
1165  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1166  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1167<t>
1168   The Content-Location entity-header field &MAY; be used to supply the
1169   resource location for the entity enclosed in the message when that
1170   entity is accessible from a location separate from the requested
1171   resource's URI. A server &SHOULD; provide a Content-Location for the
1172   variant corresponding to the response entity; especially in the case
1173   where a resource has multiple entities associated with it, and those
1174   entities actually have separate locations by which they might be
1175   individually accessed, the server &SHOULD; provide a Content-Location
1176   for the particular variant which is returned.
1177</t>
1178<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1179    Content-Location = "Content-Location" ":"
1180                      ( absoluteURI | relativeURI )
1181</artwork></figure>
1182<t>
1183   The value of Content-Location also defines the base URI for the
1184   entity.
1185</t>
1186<t>
1187   The Content-Location value is not a replacement for the original
1188   requested URI; it is only a statement of the location of the resource
1189   corresponding to this particular entity at the time of the request.
1190   Future requests &MAY; specify the Content-Location URI as the request-URI
1191   if the desire is to identify the source of that particular
1192   entity.
1193</t>
1194<t>
1195   A cache cannot assume that an entity with a Content-Location
1196   different from the URI used to retrieve it can be used to respond to
1197   later requests on that Content-Location URI. However, the Content-Location
1198   can be used to differentiate between multiple entities
1199   retrieved from a single requested resource, as described in &caching;.
1200</t>
1201<t>
1202   If the Content-Location is a relative URI, the relative URI is
1203   interpreted relative to the Request-URI.
1204</t>
1205<t>
1206   The meaning of the Content-Location header in PUT or POST requests is
1207   undefined; servers are free to ignore it in those cases.
1208</t>
1209</section>
1210
1211<section title="Content-MD5" anchor="header.content-md5">
1212  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1213  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1214<t>
1215   The Content-MD5 entity-header field, as defined in RFC 1864 <xref target="RFC1864"/>, is
1216   an MD5 digest of the entity-body for the purpose of providing an
1217   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1218   MIC is good for detecting accidental modification of the entity-body
1219   in transit, but is not proof against malicious attacks.)
1220</t>
1221<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1222     Content-MD5   = "Content-MD5" ":" md5-digest
1223     md5-digest   = &lt;base64 of 128 bit MD5 digest as per RFC 1864&gt;
1224</artwork></figure>
1225<t>
1226   The Content-MD5 header field &MAY; be generated by an origin server or
1227   client to function as an integrity check of the entity-body. Only
1228   origin servers or clients &MAY; generate the Content-MD5 header field;
1229   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1230   value as an end-to-end integrity check. Any recipient of the entity-body,
1231   including gateways and proxies, &MAY; check that the digest value
1232   in this header field matches that of the entity-body as received.
1233</t>
1234<t>
1235   The MD5 digest is computed based on the content of the entity-body,
1236   including any content-coding that has been applied, but not including
1237   any transfer-encoding applied to the message-body. If the message is
1238   received with a transfer-encoding, that encoding &MUST; be removed
1239   prior to checking the Content-MD5 value against the received entity.
1240</t>
1241<t>
1242   This has the result that the digest is computed on the octets of the
1243   entity-body exactly as, and in the order that, they would be sent if
1244   no transfer-encoding were being applied.
1245</t>
1246<t>
1247   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1248   composite media-types (e.g., multipart/* and message/rfc822), but
1249   this does not change how the digest is computed as defined in the
1250   preceding paragraph.
1251</t>
1252<t>
1253   There are several consequences of this. The entity-body for composite
1254   types &MAY; contain many body-parts, each with its own MIME and HTTP
1255   headers (including Content-MD5, Content-Transfer-Encoding, and
1256   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1257   or Content-Encoding header, it is assumed that the content
1258   of the body-part has had the encoding applied, and the body-part is
1259   included in the Content-MD5 digest as is -- i.e., after the
1260   application. The Transfer-Encoding header field is not allowed within
1261   body-parts.
1262</t>
1263<t>
1264   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1265   computing or checking the digest: the line break convention used in
1266   the text actually transmitted &MUST; be left unaltered when computing
1267   the digest.
1268  <list><t>
1269      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1270      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1271      in which the application of Content-MD5 to HTTP entity-bodies
1272      differs from its application to MIME entity-bodies. One is that
1273      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1274      does use Transfer-Encoding and Content-Encoding. Another is that
1275      HTTP more frequently uses binary content types than MIME, so it is
1276      worth noting that, in such cases, the byte order used to compute
1277      the digest is the transmission byte order defined for the type.
1278      Lastly, HTTP allows transmission of text types with any of several
1279      line break conventions and not just the canonical form using CRLF.
1280  </t></list>
1281</t>
1282</section>
1283
1284<section title="Content-Type" anchor="header.content-type">
1285  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1286  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1287<t>
1288   The Content-Type entity-header field indicates the media type of the
1289   entity-body sent to the recipient or, in the case of the HEAD method,
1290   the media type that would have been sent had the request been a GET.
1291</t>
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1293    Content-Type   = "Content-Type" ":" media-type
1294</artwork></figure>
1295<t>
1296   Media types are defined in <xref target="media.types"/>. An example of the field is
1297</t>
1298<figure><artwork type="example">
1299    Content-Type: text/html; charset=ISO-8859-4
1300</artwork></figure>
1301<t>
1302   Further discussion of methods for identifying the media type of an
1303   entity is provided in <xref target="type"/>.
1304</t>
1305</section>
1306
1307</section>
1308
1309<section title="IANA Considerations" anchor="IANA.considerations">
1310<t>
1311   TBD.
1312</t>
1313</section>
1314
1315<section title="Security Considerations" anchor="security.considerations">
1316<t>
1317   This section is meant to inform application developers, information
1318   providers, and users of the security limitations in HTTP/1.1 as
1319   described by this document. The discussion does not include
1320   definitive solutions to the problems revealed, though it does make
1321   some suggestions for reducing security risks.
1322</t>
1323
1324<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1325<t>
1326   Accept request-headers can reveal information about the user to all
1327   servers which are accessed. The Accept-Language header in particular
1328   can reveal information the user would consider to be of a private
1329   nature, because the understanding of particular languages is often
1330   strongly correlated to the membership of a particular ethnic group.
1331   User agents which offer the option to configure the contents of an
1332   Accept-Language header to be sent in every request are strongly
1333   encouraged to let the configuration process include a message which
1334   makes the user aware of the loss of privacy involved.
1335</t>
1336<t>
1337   An approach that limits the loss of privacy would be for a user agent
1338   to omit the sending of Accept-Language headers by default, and to ask
1339   the user whether or not to start sending Accept-Language headers to a
1340   server if it detects, by looking for any Vary response-header fields
1341   generated by the server, that such sending could improve the quality
1342   of service.
1343</t>
1344<t>
1345   Elaborate user-customized accept header fields sent in every request,
1346   in particular if these include quality values, can be used by servers
1347   as relatively reliable and long-lived user identifiers. Such user
1348   identifiers would allow content providers to do click-trail tracking,
1349   and would allow collaborating content providers to match cross-server
1350   click-trails or form submissions of individual users. Note that for
1351   many users not behind a proxy, the network address of the host
1352   running the user agent will also serve as a long-lived user
1353   identifier. In environments where proxies are used to enhance
1354   privacy, user agents ought to be conservative in offering accept
1355   header configuration options to end users. As an extreme privacy
1356   measure, proxies could filter the accept headers in relayed requests.
1357   General purpose user agents which provide a high degree of header
1358   configurability &SHOULD; warn users about the loss of privacy which can
1359   be involved.
1360</t>
1361</section>
1362
1363<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1364<t>
1365   RFC 1806 <xref target="RFC1806"/>, from which the often implemented Content-Disposition
1366   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1367   serious security considerations. Content-Disposition is not part of
1368   the HTTP standard, but since it is widely implemented, we are
1369   documenting its use and risks for implementors. See RFC 2183 <xref target="RFC2183"/>
1370   (which updates RFC 1806) for details.
1371</t>
1372</section>
1373
1374</section>
1375
1376<section title="Acknowledgments" anchor="ack">
1377<t>
1378   Based on an XML translation of RFC 2616 by Julian Reschke.
1379</t>
1380</section>
1381</middle>
1382<back>
1383<references>
1384
1385<reference anchor="Part1">
1386  <front>
1387    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1388 
1389    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1390      <organization abbrev="Day Software">Day Software</organization>
1391      <address>
1392        <email>fielding@gbiv.com</email>
1393      </address>
1394    </author>
1395 
1396    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1397      <organization>One Laptop per Child</organization>
1398      <address>
1399        <email>jg@laptop.org</email>
1400      </address>
1401    </author>
1402   
1403    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1404      <organization abbrev="HP">Hewlett-Packard Company</organization>
1405      <address>
1406        <email>JeffMogul@acm.org</email>
1407      </address>
1408    </author>
1409 
1410    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1411      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1412      <address>
1413        <email>henrikn@microsoft.com</email>
1414      </address>
1415    </author>
1416 
1417    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1418      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1419      <address>
1420        <email>LMM@acm.org</email>
1421      </address>
1422    </author>
1423   
1424    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1425      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1426      <address>
1427        <email>paulle@microsoft.com</email>
1428      </address>
1429    </author>
1430     
1431    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1432      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1433      <address>
1434        <email>timbl@w3.org</email>
1435      </address>
1436    </author>
1437 
1438    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1439  </front>
1440  <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
1441  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1442</reference>
1443
1444<reference anchor="Part2">
1445  <front>
1446    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1447 
1448    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1449      <organization abbrev="Day Software">Day Software</organization>
1450      <address>
1451        <email>fielding@gbiv.com</email>
1452      </address>
1453    </author>
1454 
1455    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1456      <organization>One Laptop per Child</organization>
1457      <address>
1458        <email>jg@laptop.org</email>
1459      </address>
1460    </author>
1461   
1462    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1463      <organization abbrev="HP">Hewlett-Packard Company</organization>
1464      <address>
1465        <email>JeffMogul@acm.org</email>
1466      </address>
1467    </author>
1468 
1469    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1470      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1471      <address>
1472        <email>henrikn@microsoft.com</email>
1473      </address>
1474    </author>
1475 
1476    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1477      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1478      <address>
1479        <email>LMM@acm.org</email>
1480      </address>
1481    </author>
1482   
1483    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1484      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1485      <address>
1486        <email>paulle@microsoft.com</email>
1487      </address>
1488    </author>
1489     
1490    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1491      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1492      <address>
1493        <email>timbl@w3.org</email>
1494      </address>
1495    </author>
1496 
1497    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1498  </front>
1499  <seriesInfo name="Internet-Draft" value="draft-fielding-p2-semantics-&ID-VERSION;"/>
1500  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1501</reference>
1502
1503<reference anchor="Part4">
1504  <front>
1505    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1506 
1507    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1508      <organization abbrev="Day Software">Day Software</organization>
1509      <address>
1510        <email>fielding@gbiv.com</email>
1511      </address>
1512    </author>
1513 
1514    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1515      <organization>One Laptop per Child</organization>
1516      <address>
1517        <email>jg@laptop.org</email>
1518      </address>
1519    </author>
1520   
1521    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1522      <organization abbrev="HP">Hewlett-Packard Company</organization>
1523      <address>
1524        <email>JeffMogul@acm.org</email>
1525      </address>
1526    </author>
1527 
1528    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1529      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1530      <address>
1531        <email>henrikn@microsoft.com</email>
1532      </address>
1533    </author>
1534 
1535    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1536      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1537      <address>
1538        <email>LMM@acm.org</email>
1539      </address>
1540    </author>
1541   
1542    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1543      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1544      <address>
1545        <email>paulle@microsoft.com</email>
1546      </address>
1547    </author>
1548     
1549    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1550      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1551      <address>
1552        <email>timbl@w3.org</email>
1553      </address>
1554    </author>
1555 
1556    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1557  </front>
1558  <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
1559  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1560</reference>
1561
1562<reference anchor="Part5">
1563  <front>
1564    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1565 
1566    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1567      <organization abbrev="Day Software">Day Software</organization>
1568      <address>
1569        <email>fielding@gbiv.com</email>
1570      </address>
1571    </author>
1572 
1573    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1574      <organization>One Laptop per Child</organization>
1575      <address>
1576        <email>jg@laptop.org</email>
1577      </address>
1578    </author>
1579   
1580    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1581      <organization abbrev="HP">Hewlett-Packard Company</organization>
1582      <address>
1583        <email>JeffMogul@acm.org</email>
1584      </address>
1585    </author>
1586 
1587    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1588      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1589      <address>
1590        <email>henrikn@microsoft.com</email>
1591      </address>
1592    </author>
1593 
1594    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1595      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1596      <address>
1597        <email>LMM@acm.org</email>
1598      </address>
1599    </author>
1600   
1601    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1602      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1603      <address>
1604        <email>paulle@microsoft.com</email>
1605      </address>
1606    </author>
1607     
1608    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1609      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1610      <address>
1611        <email>timbl@w3.org</email>
1612      </address>
1613    </author>
1614 
1615    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1616  </front>
1617  <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
1618  <x:source href="p5-range.xml" basename="p5-range"/>
1619</reference>
1620
1621<reference anchor="Part6">
1622  <front>
1623    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1624 
1625    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1626      <organization abbrev="Day Software">Day Software</organization>
1627      <address>
1628        <email>fielding@gbiv.com</email>
1629      </address>
1630    </author>
1631 
1632    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1633      <organization>One Laptop per Child</organization>
1634      <address>
1635        <email>jg@laptop.org</email>
1636      </address>
1637    </author>
1638   
1639    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1640      <organization abbrev="HP">Hewlett-Packard Company</organization>
1641      <address>
1642        <email>JeffMogul@acm.org</email>
1643      </address>
1644    </author>
1645 
1646    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1647      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1648      <address>
1649        <email>henrikn@microsoft.com</email>
1650      </address>
1651    </author>
1652 
1653    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1654      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1655      <address>
1656        <email>LMM@acm.org</email>
1657      </address>
1658    </author>
1659   
1660    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1661      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1662      <address>
1663        <email>paulle@microsoft.com</email>
1664      </address>
1665    </author>
1666     
1667    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1668      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1669      <address>
1670        <email>timbl@w3.org</email>
1671      </address>
1672    </author>
1673 
1674    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1675  </front>
1676  <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
1677  <x:source href="p6-cache.xml" basename="p6-cache"/>
1678</reference>
1679
1680<reference anchor="RFC1766">
1681<front>
1682<title abbrev="Language Tag">Tags for the Identification of Languages</title>
1683<author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1684<organization>UNINETT</organization>
1685<address>
1686<postal>
1687<street>Pb. 6883 Elgeseter</street>
1688<city>Trondheim</city>
1689<region/>
1690<code>N-7002</code>
1691<country>NO</country></postal>
1692<phone>+47 73 597094</phone>
1693<email>Harald.T.Alvestrand@uninett.no</email></address></author>
1694<date month="March" year="1995"/>
1695</front>
1696<seriesInfo name="RFC" value="1766"/>
1697</reference>
1698
1699<reference anchor="RFC2045">
1700<front>
1701<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1702<author initials="N." surname="Freed" fullname="Ned Freed">
1703<organization>Innosoft International, Inc.</organization>
1704<address>
1705<postal>
1706<street>1050 East Garvey Avenue South</street>
1707<city>West Covina</city>
1708<region>CA</region>
1709<code>91790</code>
1710<country>US</country></postal>
1711<phone>+1 818 919 3600</phone>
1712<facsimile>+1 818 919 3614</facsimile>
1713<email>ned@innosoft.com</email></address></author>
1714<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1715<organization>First Virtual Holdings</organization>
1716<address>
1717<postal>
1718<street>25 Washington Avenue</street>
1719<city>Morristown</city>
1720<region>NJ</region>
1721<code>07960</code>
1722<country>US</country></postal>
1723<phone>+1 201 540 8967</phone>
1724<facsimile>+1 201 993 3032</facsimile>
1725<email>nsb@nsb.fv.com</email></address></author>
1726<date month="November" year="1996"/>
1727</front>
1728<seriesInfo name="RFC" value="2045"/>
1729</reference>
1730
1731<reference anchor="RFC822">
1732<front>
1733<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
1734<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
1735<organization>University of Delaware, Dept. of Electrical Engineering</organization>
1736<address>
1737<postal>
1738<street/>
1739<city>Newark</city>
1740<region>DE</region>
1741<code>19711</code>
1742<country>US</country></postal>
1743<email>DCrocker@UDel-Relay</email></address></author>
1744<date month="August" day="13" year="1982"/></front>
1745<seriesInfo name="STD" value="11"/>
1746<seriesInfo name="RFC" value="822"/>
1747</reference>
1748
1749<reference anchor="RFC1867">
1750<front>
1751<title>Form-based File Upload in HTML</title>
1752<author initials="L." surname="Masinter" fullname="Larry Masinter">
1753<organization>Xerox Palo Alto Research Center</organization>
1754<address>
1755<postal>
1756<street>3333 Coyote Hill Road</street>
1757<city>Palo Alto</city>
1758<region>CA</region>
1759<code>94304</code>
1760<country>US</country></postal>
1761<phone>+1 415 812 4365</phone>
1762<facsimile>+1 415 812 4333</facsimile>
1763<email>masinter@parc.xerox.com</email></address></author>
1764<author initials="E." surname="Nebel" fullname="Ernesto Nebel">
1765<organization>XSoft, Xerox Corporation</organization>
1766<address>
1767<postal>
1768<street>10875 Rancho Bernardo Road</street>
1769<street>Suite 200</street>
1770<city>San Diego</city>
1771<region>CA</region>
1772<code>92127-2116</code>
1773<country>US</country></postal>
1774<phone>+1 619 676 7817</phone>
1775<facsimile>+1 619 676 7865</facsimile>
1776<email>nebel@xsoft.sd.xerox.com</email></address></author>
1777<date month="November" year="1995"/>
1778</front>
1779<seriesInfo name="RFC" value="1867"/>
1780</reference>
1781
1782<reference anchor="RFC1590">
1783<front>
1784<title>Media Type Registration Procedure</title>
1785<author initials="J." surname="Postel" fullname="Jon Postel">
1786<organization>USC/Information Sciences Institute</organization>
1787<address>
1788<postal>
1789<street>4676 Admiralty Way</street>
1790<city>Marina del Rey</city>
1791<region>CA</region>
1792<code>90292</code>
1793<country>US</country></postal>
1794<phone>+1 310 822 1511</phone>
1795<facsimile>+1 310 823 6714</facsimile>
1796<email>Postel@ISI.EDU</email></address></author>
1797<date month="November" year="1996"/>
1798</front>
1799<seriesInfo name="RFC" value="1590"/>
1800</reference>
1801
1802<reference anchor="RFC1700">
1803<front>
1804<title abbrev="Assigned Numbers">Assigned Numbers</title>
1805<author initials="J." surname="Reynolds" fullname="Joyce K. Reynolds">
1806<organization>USC/Information Sciences Institute</organization>
1807<address>
1808<postal>
1809<street>4676 Admiralty Way</street>
1810<city>Marina del Rey</city>
1811<region>CA</region>
1812<code>90292-6695</code>
1813<country>US</country></postal>
1814<phone>+1 310 822 1511</phone>
1815<email>jkrey@isi.edu</email></address></author>
1816<author initials="J." surname="Postel" fullname="Jon Postel">
1817<organization>USC/Information Sciences Institute</organization>
1818<address>
1819<postal>
1820<street>4676 Admiralty Way</street>
1821<city>Marina del Rey</city>
1822<region>CA</region>
1823<code>90292-6695</code>
1824<country>US</country></postal>
1825<phone>+1 310 822 1511</phone>
1826<email>postel@isi.edu</email></address></author>
1827<date month="October" year="1994"/>
1828<abstract>
1829<t/></abstract></front>
1830<seriesInfo name="STD" value="2"/>
1831<seriesInfo name="RFC" value="1700"/>
1832</reference>
1833
1834<reference anchor="RFC1864">
1835<front>
1836<title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1837<author initials="J." surname="Myers" fullname="John G. Myers">
1838<organization>Carnegie Mellon University</organization>
1839<address>
1840<phone/>
1841<email>jgm+@cmu.edu</email></address></author>
1842<author initials="M." surname="Rose" fullname="Marshall T. Rose">
1843<organization>Dover Beach Consulting, Inc.</organization>
1844<address>
1845<phone/>
1846<email>mrose@dbc.mtview.ca.us</email></address></author>
1847<date month="October" year="1995"/>
1848</front>
1849<seriesInfo name="RFC" value="1864"/>
1850</reference>
1851
1852
1853<reference anchor="RFC1952">
1854<front>
1855<title>GZIP file format specification version 4.3</title>
1856<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1857<organization>Aladdin Enterprises</organization>
1858<address>
1859<postal>
1860<street>203 Santa Margarita Ave.</street>
1861<city>Menlo Park</city>
1862<region>CA</region>
1863<code>94025</code>
1864<country>US</country></postal>
1865<phone>+1 415 322 0103</phone>
1866<facsimile>+1 415 322 1734</facsimile>
1867<email>ghost@aladdin.com</email></address></author>
1868<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1869<organization/>
1870<address>
1871<postal>
1872<street/>
1873<city/>
1874<region/>
1875<code/>
1876<country/></postal>
1877<phone/>
1878<email>gzip@prep.ai.mit.edu</email></address></author>
1879<author initials="M." surname="Adler" fullname="Mark Adler">
1880<organization/>
1881<address>
1882<postal>
1883<street/>
1884<city/>
1885<region/>
1886<code/>
1887<country/></postal>
1888<phone/>
1889<email>madler@alumni.caltech.edu</email></address></author>
1890<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1891<organization/>
1892<address>
1893<postal>
1894<street/>
1895<city/>
1896<region/>
1897<code/>
1898<country/></postal>
1899<phone/>
1900<email>ghost@aladdin.com</email></address></author>
1901<author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1902<organization/>
1903<address>
1904<postal>
1905<street/>
1906<city/>
1907<region/>
1908<code/>
1909<country/></postal>
1910<phone/>
1911<email>randeg@alumni.rpi.edu</email></address></author>
1912<date month="May" year="1996"/>
1913</front>
1914<seriesInfo name="RFC" value="1952"/>
1915</reference>
1916
1917<reference anchor="RFC1951">
1918<front>
1919<title>DEFLATE Compressed Data Format Specification version 1.3</title>
1920<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1921<organization>Aladdin Enterprises</organization>
1922<address>
1923<postal>
1924<street>203 Santa Margarita Ave.</street>
1925<city>Menlo Park</city>
1926<region>CA</region>
1927<code>94025</code>
1928<country>US</country></postal>
1929<phone>+1 415 322 0103</phone>
1930<facsimile>+1 415 322 1734</facsimile>
1931<email>ghost@aladdin.com</email></address></author>
1932<date month="May" year="1996"/>
1933<abstract>
1934<t>This specification defines a lossless compressed data format that compresses data using a combination of the LZ77 algorithm and Huffman coding, with efficiency comparable to the best currently available general-purpose compression methods.  The data can be produced or consumed, even for an arbitrarily long sequentially presented input data stream, using only an a priori bounded amount of intermediate storage.  The format can be implemented readily in a manner not covered by patents.</t></abstract></front>
1935<seriesInfo name="RFC" value="1951"/>
1936</reference>
1937
1938<reference anchor="RFC1950">
1939<front>
1940<title>ZLIB Compressed Data Format Specification version 3.3</title>
1941<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1942<organization>Aladdin Enterprises</organization>
1943<address>
1944<postal>
1945<street>203 Santa Margarita Ave.</street>
1946<city>Menlo Park</city>
1947<region>CA</region>
1948<code>94025</code>
1949<country>US</country></postal>
1950<phone>+1 415 322 0103</phone>
1951<facsimile>+1 415 322 1734</facsimile>
1952<email>ghost@aladdin.com</email></address></author>
1953<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1954<organization/></author>
1955<date month="May" year="1996"/>
1956<abstract>
1957<t>This specification defines a lossless compressed data format.  The data can be produced or consumed, even for an arbitrarily long sequentially presented input data stream, using only an a priori bounded amount of intermediate storage.  The format presently uses the DEFLATE compression method but can be easily extended to use
1958   other compression methods.  It can be implemented readily in a manner not covered by patents.  This specification also defines the ADLER-32 checksum (an extension and improvement of the Fletcher checksum), used for detection of data corruption, and provides an algorithm for computing it.</t></abstract></front>
1959<seriesInfo name="RFC" value="1950"/>
1960</reference>
1961
1962<reference anchor="RFC2068">
1963<front>
1964<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1965<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1966<organization>University of California, Irvine, Department of Information and Computer Science</organization>
1967<address>
1968<postal>
1969<street/>
1970<city>Irvine</city>
1971<region>CA</region>
1972<code>92717-3425</code>
1973<country>US</country></postal>
1974<facsimile>+1 714 824 4056</facsimile>
1975<email>fielding@ics.uci.edu</email></address></author>
1976<author initials="J." surname="Gettys" fullname="Jim Gettys">
1977<organization>MIT Laboratory for Computer Science</organization>
1978<address>
1979<postal>
1980<street>545 Technology Square</street>
1981<city>Cambridge</city>
1982<region>MA</region>
1983<code>02139</code>
1984<country>US</country></postal>
1985<facsimile>+1 617 258 8682</facsimile>
1986<email>jg@w3.org</email></address></author>
1987<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1988<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1989<address>
1990<postal>
1991<street>250 University Avenue</street>
1992<city>Palo Alto</city>
1993<region>CA</region>
1994<code>94301</code>
1995<country>US</country></postal>
1996<email>mogul@wrl.dec.com</email></address></author>
1997<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1998<organization>MIT Laboratory for Computer Science</organization>
1999<address>
2000<postal>
2001<street>545 Technology Square</street>
2002<city>Cambridge</city>
2003<region>MA</region>
2004<code>02139</code>
2005<country>US</country></postal>
2006<facsimile>+1 617 258 8682</facsimile>
2007<email>frystyk@w3.org</email></address></author>
2008<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2009<organization>MIT Laboratory for Computer Science</organization>
2010<address>
2011<postal>
2012<street>545 Technology Square</street>
2013<city>Cambridge</city>
2014<region>MA</region>
2015<code>02139</code>
2016<country>US</country></postal>
2017<facsimile>+1 617 258 8682</facsimile>
2018<email>timbl@w3.org</email></address></author>
2019<date month="January" year="1997"/>
2020<abstract>
2021<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
2022<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
2023<seriesInfo name="RFC" value="2068"/>
2024</reference>
2025
2026<reference anchor="RFC1806">
2027<front>
2028<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header</title>
2029<author initials="R." surname="Troost" fullname="Rens Troost">
2030<organization>New Century Systems</organization>
2031<address>
2032<postal>
2033<street>324 East 41st Street #804</street>
2034<city>New York</city>
2035<region>NY</region>
2036<code>10017</code>
2037<country>US</country></postal>
2038<phone>+1 212 557 2050</phone>
2039<facsimile>+1 212 557 2049</facsimile>
2040<email>rens@century.com</email></address></author>
2041<author initials="S." surname="Dorner" fullname="Steve Dorner">
2042<organization>QUALCOMM Incorporated</organization>
2043<address>
2044<postal>
2045<street>6455 Lusk Boulevard</street>
2046<city>San Diego</city>
2047<region>CA</region>
2048<code>92121</code>
2049<country>US</country></postal>
2050<email>sdorner@qualcomm.com</email></address></author>
2051<date month="June" year="1995"/>
2052<abstract>
2053<t>This memo provides a mechanism whereby messages conforming to the("MIME") specification can convey presentational information.  It specifies a new "Content-Disposition" header, optional and valid for anyentity ("message" or "body part"). Two values for this header are described in this memo; one for the ordinary linear presentation of the body part, and another to facilitate the use of mail to transfer files. It is expected that more values will be defined in the future, and procedures are defined for extending this set of values.</t>
2054<t>This document is intended as an extension to. As such, the reader is assumed to be familiar with, and. The information presented herein supplements but does not replace that found in those documents.</t></abstract></front>
2055<seriesInfo name="RFC" value="1806"/>
2056</reference>
2057
2058<reference anchor="RFC2076">
2059<front>
2060<title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2061<author initials="J." surname="Palme" fullname="Jacob Palme">
2062<organization>Stockholm University/KTH</organization>
2063<address>
2064<postal>
2065<street>Electrum 230</street>
2066<street>S-164 40 Kista</street>
2067<country>SE</country></postal>
2068<phone>+46 8 161667</phone>
2069<facsimile>+46 8 7830829</facsimile>
2070<email>jpalme@dsv.su.se</email></address></author>
2071<date month="February" year="1997"/>
2072<abstract>
2073<t>This memo contains a table of commonly occurring headers in headings of e-mail messages. The document compiles information from other RFCs such as RFC 822, RFC 1036, RFC 1123, RFC 1327, RFC 1496, RFC 1521, RFC 1766, RFC 1806, RFC 1864 and RFC 1911. A few commonly occurring headers which are not defined in RFCs are also included. For each header, the memo gives a short description and a reference to the RFC in which the header is defined.</t></abstract></front>
2074<seriesInfo name="RFC" value="2076"/>
2075</reference>
2076
2077<reference anchor="RFC2279">
2078<front>
2079<title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
2080<author initials="F." surname="Yergeau" fullname="Francois Yergeau">
2081<organization>Alis Technologies</organization>
2082<address>
2083<postal>
2084<street>100, boul. Alexis-Nihon</street>
2085<street>Suite 600</street>
2086<city>Montreal</city>
2087<region>Quebec</region>
2088<code>H4M 2P2</code>
2089<country>CA</country></postal>
2090<phone>+1 514 747 2547</phone>
2091<facsimile>+1 514 747 2561</facsimile>
2092<email>fyergeau@alis.com</email></address></author>
2093<date month="January" year="1998"/>
2094<abstract>
2095<t>ISO/IEC 10646-1 defines a multi-octet character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. Multi-octet characters, however, are not compatible with many current applications and protocols, and this has led to the development of a few so-called UCS transformation formats (UTF), each with different characteristics.  UTF-8, the object of this memo, has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo updates and replaces RFC 2044, in particular addressing the question of versions of the relevant standards.</t></abstract></front>
2096<seriesInfo name="RFC" value="2279"/>
2097</reference>
2098
2099<reference anchor="RFC2046">
2100<front>
2101<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2102<author initials="N." surname="Freed" fullname="Ned Freed">
2103<organization>Innosoft International, Inc.</organization>
2104<address>
2105<postal>
2106<street>1050 East Garvey Avenue South</street>
2107<city>West Covina</city>
2108<region>CA</region>
2109<code>91790</code>
2110<country>US</country></postal>
2111<phone>+1 818 919 3600</phone>
2112<facsimile>+1 818 919 3614</facsimile>
2113<email>ned@innosoft.com</email></address></author>
2114<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2115<organization>First Virtual Holdings</organization>
2116<address>
2117<postal>
2118<street>25 Washington Avenue</street>
2119<city>Morristown</city>
2120<region>NJ</region>
2121<code>07960</code>
2122<country>US</country></postal>
2123<phone>+1 201 540 8967</phone>
2124<facsimile>+1 201 993 3032</facsimile>
2125<email>nsb@nsb.fv.com</email></address></author>
2126<date month="November" year="1996"/>
2127</front>
2128<seriesInfo name="RFC" value="2046"/>
2129</reference>
2130
2131<reference anchor="RFC2277">
2132<front>
2133<title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2134<author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2135<organization>UNINETT</organization>
2136<address>
2137<postal>
2138<street>P.O.Box 6883 Elgeseter</street>
2139<street>N-7002 TRONDHEIM</street>
2140<country>NORWAY</country></postal>
2141<phone>+47 73 59 70 94</phone>
2142<email>Harald.T.Alvestrand@uninett.no</email></address></author>
2143<date month="January" year="1998"/>
2144<area>Applications</area>
2145<keyword>Internet Engineering Task Force</keyword>
2146<keyword>character encoding</keyword></front>
2147<seriesInfo name="BCP" value="18"/>
2148<seriesInfo name="RFC" value="2277"/>
2149</reference>
2150
2151<reference anchor="RFC2110">
2152<front>
2153<title abbrev="MHTML">MIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2154<author initials="J." surname="Palme" fullname="Jacob Palme">
2155<organization>Stockholm University and KTH</organization>
2156<address>
2157<postal>
2158<street>Electrum 230</street>
2159<street>S-164 40 Kista</street>
2160<country>Sweden</country></postal>
2161<phone>+46-8-16 16 67</phone>
2162<facsimile>+46-8-783 08 29</facsimile>
2163<email>jpalme@dsv.su.se</email></address></author>
2164<author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2165<organization>Microsoft Corporation</organization>
2166<address>
2167<postal>
2168<street>3590 North First Street</street>
2169<street>Suite 300</street>
2170<street>San Jose</street>
2171<street>CA 95134</street>
2172<street>Working group chairman:</street></postal>
2173<email>alexhop@microsoft.com</email></address></author>
2174<date month="March" year="1997"/>
2175<area>Applications</area>
2176<keyword>encapsulate</keyword>
2177<keyword>hypertext markup language</keyword>
2178<keyword>mail</keyword>
2179<keyword>multipurpose internet mail extensions</keyword>
2180</front>
2181<seriesInfo name="RFC" value="2110"/>
2182</reference>
2183
2184<reference anchor="RFC2049">
2185<front>
2186<title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2187<author initials="N." surname="Freed" fullname="Ned Freed">
2188<organization>Innosoft International, Inc.</organization>
2189<address>
2190<postal>
2191<street>1050 East Garvey Avenue South</street>
2192<street>West Covina</street>
2193<street>CA 91790</street>
2194<country>USA</country></postal>
2195<phone>+1 818 919 3600</phone>
2196<facsimile>+1 818 919 3614</facsimile>
2197<email>ned@innosoft.com</email></address></author>
2198<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2199<organization>First Virtual Holdings</organization>
2200<address>
2201<postal>
2202<street>25 Washington Avenue</street>
2203<street>Morristown</street>
2204<street>NJ 07960</street>
2205<country>USA</country></postal>
2206<phone>+1 201 540 8967</phone>
2207<facsimile>+1 201 993 3032</facsimile>
2208<email>nsb@nsb.fv.com</email></address></author>
2209<date month="November" year="1996"/>
2210<area>Applications</area>
2211<keyword>mail</keyword>
2212<keyword>multipurpose internet mail extensions</keyword>
2213</front>
2214<seriesInfo name="RFC" value="2049"/>
2215</reference>
2216
2217<reference anchor="RFC2183">
2218<front>
2219<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2220<author initials="R." surname="Troost" fullname="Rens Troost">
2221<organization>New Century Systems</organization>
2222<address>
2223<postal>
2224<street>324 East 41st Street #804</street>
2225<street>New York</street>
2226<street>NY</street>
2227<street>10017</street>
2228<country>USA</country></postal>
2229<phone>+1 (212) 557-2050</phone>
2230<facsimile>+1 (212) 557-2049</facsimile>
2231<email>rens@century.com</email></address></author>
2232<author initials="S." surname="Dorner" fullname="Steve Dorner">
2233<organization>QUALCOMM Incorporated</organization>
2234<address>
2235<postal>
2236<street>6455 Lusk Boulevard</street>
2237<street>San Diego</street>
2238<street>CA 92121</street>
2239<country>USA</country></postal>
2240<email>sdorner@qualcomm.com</email></address></author>
2241<author initials="K." surname="Moore" fullname="Keith Moore">
2242<organization>Department of Computer Science</organization>
2243<address>
2244<postal>
2245<street>University of Tennessee</street>
2246<street>Knoxville</street>
2247<street>107 Ayres Hall</street>
2248<street>Knoxville TN  37996-1301</street>
2249<country>USA</country></postal>
2250<phone>+1 (423) 974-5067</phone>
2251<facsimile>+1 (423) 974-8296</facsimile>
2252<email>moore@cs.utk.edu</email></address></author>
2253<date month="August" year="1997"/>
2254<area>Applications</area>
2255<keyword>MIME</keyword>
2256<keyword>internet message</keyword>
2257<keyword>multipurpose internet mail extensions</keyword>
2258</front>
2259<seriesInfo name="RFC" value="2183"/>
2260</reference>
2261
2262</references>
2263
2264<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2265<t>
2266   HTTP/1.1 uses many of the constructs defined for Internet Mail (RFC
2267   822 <xref target="RFC822"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2268   allow entities to be transmitted in an open variety of
2269   representations and with extensible mechanisms. However, RFC 2045
2270   discusses mail, and HTTP has a few features that are different from
2271   those described in RFC 2045. These differences were carefully chosen
2272   to optimize performance over binary connections, to allow greater
2273   freedom in the use of new media types, to make date comparisons
2274   easier, and to acknowledge the practice of some early HTTP servers
2275   and clients.
2276</t>
2277<t>
2278   This appendix describes specific areas where HTTP differs from RFC
2279   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2280   aware of these differences and provide the appropriate conversions
2281   where necessary. Proxies and gateways from MIME environments to HTTP
2282   also need to be aware of the differences because some conversions
2283   might be required.
2284</t>
2285<section title="MIME-Version" anchor="mime-version">
2286<t>
2287   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2288   include a single MIME-Version general-header field to indicate what
2289   version of the MIME protocol was used to construct the message. Use
2290   of the MIME-Version header field indicates that the message is in
2291   full compliance with the MIME protocol (as defined in RFC 2045<xref target="RFC2045"/>).
2292   Proxies/gateways are responsible for ensuring full compliance (where
2293   possible) when exporting HTTP messages to strict MIME environments.
2294</t>
2295<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2296    MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
2297</artwork></figure>
2298<t>
2299   MIME version "1.0" is the default for use in HTTP/1.1. However,
2300   HTTP/1.1 message parsing and semantics are defined by this document
2301   and not the MIME specification.
2302</t>
2303</section>
2304
2305<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2306<t>
2307   RFC 2045 <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2308   canonical form prior to being transferred, as described in section <xref target="RFC2049" x:fmt="number" x:sec="4"/>
2309   of RFC 2049 <xref target="RFC2049"/>. <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2310   allowed for subtypes of the "text" media type when transmitted over
2311   HTTP. RFC 2046 requires that content with a type of "text" represent
2312   line breaks as CRLF and forbids the use of CR or LF outside of line
2313   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2314   line break within text content when a message is transmitted over
2315   HTTP.
2316</t>
2317<t>
2318   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2319   environment &SHOULD; translate all line breaks within the text media
2320   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2321   canonical form of CRLF. Note, however, that this might be complicated
2322   by the presence of a Content-Encoding and by the fact that HTTP
2323   allows the use of some character sets which do not use octets 13 and
2324   10 to represent CR and LF, as is the case for some multi-byte
2325   character sets.
2326</t>
2327<t>
2328   Implementors should note that conversion will break any cryptographic
2329   checksums applied to the original content unless the original content
2330   is already in canonical form. Therefore, the canonical form is
2331   recommended for any content that uses such checksums in HTTP.
2332</t>
2333</section>
2334
2335<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2336<t>
2337   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2338   Content-Encoding header field. Since this acts as a modifier on the
2339   media type, proxies and gateways from HTTP to MIME-compliant
2340   protocols &MUST; either change the value of the Content-Type header
2341   field or decode the entity-body before forwarding the message. (Some
2342   experimental applications of Content-Type for Internet mail have used
2343   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2344   a function equivalent to Content-Encoding. However, this parameter is
2345   not part of RFC 2045).
2346</t>
2347</section>
2348
2349<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2350<t>
2351   HTTP does not use the Content-Transfer-Encoding (CTE) field of RFC
2352   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2353   remove any non-identity CTE ("quoted-printable" or "base64") encoding
2354   prior to delivering the response message to an HTTP client.
2355</t>
2356<t>
2357   Proxies and gateways from HTTP to MIME-compliant protocols are
2358   responsible for ensuring that the message is in the correct format
2359   and encoding for safe transport on that protocol, where "safe
2360   transport" is defined by the limitations of the protocol being used.
2361   Such a proxy or gateway &SHOULD; label the data with an appropriate
2362   Content-Transfer-Encoding if doing so will improve the likelihood of
2363   safe transport over the destination protocol.
2364</t>
2365</section>
2366
2367<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2368<t>
2369   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2370   Proxies/gateways &MUST; remove any transfer-coding prior to
2371   forwarding a message via a MIME-compliant protocol.
2372</t>
2373</section>
2374
2375<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2376<t>
2377   HTTP implementations which share code with MHTML <xref target="RFC2110"/> implementations
2378   need to be aware of MIME line length limitations. Since HTTP does not
2379   have this limitation, HTTP does not fold long lines. MHTML messages
2380   being transported by HTTP follow all conventions of MHTML, including
2381   line length limitations and folding, canonicalization, etc., since
2382   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2383   does not interpret the content or any MIME header lines that might be
2384   contained therein.
2385</t>
2386</section>
2387</section>
2388
2389<section title="Additional Features" anchor="additional.features">
2390<t>
2391   RFC 1945 and RFC 2068 document protocol elements used by some
2392   existing HTTP implementations, but not consistently and correctly
2393   across most HTTP/1.1 applications. Implementors are advised to be
2394   aware of these features, but cannot rely upon their presence in, or
2395   interoperability with, other HTTP/1.1 applications. Some of these
2396   describe proposed experimental features, and some describe features
2397   that experimental deployment found lacking that are now addressed in
2398   the base HTTP/1.1 specification.
2399</t>
2400<t>
2401   A number of other headers, such as Content-Disposition and Title,
2402   from SMTP and MIME are also often implemented (see RFC 2076 <xref target="RFC2076"/>).
2403</t>
2404
2405<section title="Content-Disposition" anchor="content-disposition">
2406<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2407<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2408<t>
2409   The Content-Disposition response-header field has been proposed as a
2410   means for the origin server to suggest a default filename if the user
2411   requests that the content is saved to a file. This usage is derived
2412   from the definition of Content-Disposition in RFC 1806 <xref target="RFC1806"/>.
2413</t>
2414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><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"/>
2415     content-disposition = "Content-Disposition" ":"
2416                           disposition-type *( ";" disposition-parm )
2417     disposition-type = "attachment" | disp-extension-token
2418     disposition-parm = filename-parm | disp-extension-parm
2419     filename-parm = "filename" "=" quoted-string
2420     disp-extension-token = token
2421     disp-extension-parm = token "=" ( token | quoted-string )
2422</artwork></figure>
2423<t>
2424   An example is
2425</t>
2426<figure><artwork type="example">
2427     Content-Disposition: attachment; filename="fname.ext"
2428</artwork></figure>
2429<t>
2430   The receiving user agent &SHOULD-NOT;  respect any directory path
2431   information present in the filename-parm parameter, which is the only
2432   parameter believed to apply to HTTP implementations at this time. The
2433   filename &SHOULD; be treated as a terminal component only.
2434</t>
2435<t>
2436   If this header is used in a response with the application/octet-stream
2437   content-type, the implied suggestion is that the user agent
2438   should not display the response, but directly enter a `save response
2439   as...' dialog.
2440</t>
2441<t>
2442   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2443</t>
2444</section>
2445</section>
2446
2447<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2448<t>
2449   Charset wildcarding is introduced to avoid explosion of character set
2450   names in accept headers. (<xref target="header.accept-charset"/>)
2451</t>
2452<t>
2453   Content-Base was deleted from the specification: it was not
2454   implemented widely, and there is no simple, safe way to introduce it
2455   without a robust extension mechanism. In addition, it is used in a
2456   similar, but not identical fashion in MHTML <xref target="RFC2110"/>.
2457</t>
2458<t>
2459   A content-coding of "identity" was introduced, to solve problems
2460   discovered in caching. (<xref target="content.codings"/>)
2461</t>
2462<t>
2463   Quality Values of zero should indicate that "I don't want something"
2464   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2465</t>
2466<t>
2467   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
2468   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
2469   specification, but not commonly implemented. See RFC 2068 <xref target="RFC2068"/>.
2470</t>
2471</section>
2472</back>
2473</rfc>
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