source: draft-ietf-httpbis/latest/p2-semantics.xml @ 228

Last change on this file since 228 was 228, checked in by julian.reschke@…, 14 years ago

Add subsections for changes from -02.

  • Property svn:eol-style set to native
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x=''/>">
18  <!ENTITY payload                    "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY conditional                "<xref target='Part4' xmlns:x=''/>">
20  <!ENTITY range                      "<xref target='Part5' xmlns:x=''/>">
21  <!ENTITY caching                    "<xref target='Part6' xmlns:x=''/>">
22  <!ENTITY auth                       "<xref target='Part7' xmlns:x=''/>">
23  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
24  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
25  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
26  <!ENTITY general-syntax             "<xref target='Part1' x:rel='#general.syntax' xmlns:x=''/>">
27  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
28  <!ENTITY full-date                  "<xref target='Part1' x:rel='' xmlns:x=''/>">
29  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
30  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
31  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
32  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
33  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
34  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
35  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
36  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
37  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
38  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
39  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
40  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
41  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
42  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
43  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
44  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
45  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
46  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
47  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
48  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
49  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
50  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
51  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
52  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
53  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
54  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
55  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
56  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
57  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
58  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
59  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
60  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
61  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
62  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x=''/>">
64<?rfc toc="yes" ?>
65<?rfc symrefs="yes" ?>
66<?rfc sortrefs="yes" ?>
67<?rfc compact="yes"?>
68<?rfc subcompact="no" ?>
69<?rfc linkmailto="no" ?>
70<?rfc editing="no" ?>
71<?rfc comments="yes"?>
72<?rfc inline="yes"?>
73<?rfc-ext allow-markup-in-artwork="yes" ?>
74<?rfc-ext include-references-in-index="yes" ?>
75<rfc obsoletes="2616" category="std"
76     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
77     xmlns:x=''>
80  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
82  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
83    <organization abbrev="Day Software">Day Software</organization>
84    <address>
85      <postal>
86        <street>23 Corporate Plaza DR, Suite 280</street>
87        <city>Newport Beach</city>
88        <region>CA</region>
89        <code>92660</code>
90        <country>USA</country>
91      </postal>
92      <phone>+1-949-706-5300</phone>
93      <facsimile>+1-949-706-5305</facsimile>
94      <email></email>
95      <uri></uri>
96    </address>
97  </author>
99  <author initials="J." surname="Gettys" fullname="Jim Gettys">
100    <organization>One Laptop per Child</organization>
101    <address>
102      <postal>
103        <street>21 Oak Knoll Road</street>
104        <city>Carlisle</city>
105        <region>MA</region>
106        <code>01741</code>
107        <country>USA</country>
108      </postal>
109      <email></email>
110      <uri></uri>
111    </address>
112  </author>
114  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
115    <organization abbrev="HP">Hewlett-Packard Company</organization>
116    <address>
117      <postal>
118        <street>HP Labs, Large Scale Systems Group</street>
119        <street>1501 Page Mill Road, MS 1177</street>
120        <city>Palo Alto</city>
121        <region>CA</region>
122        <code>94304</code>
123        <country>USA</country>
124      </postal>
125      <email></email>
126    </address>
127  </author>
129  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137        <country>USA</country>
138      </postal>
139      <email></email>
140    </address>
141  </author>
143  <author initials="L." surname="Masinter" fullname="Larry Masinter">
144    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
145    <address>
146      <postal>
147        <street>345 Park Ave</street>
148        <city>San Jose</city>
149        <region>CA</region>
150        <code>95110</code>
151        <country>USA</country>
152      </postal>
153      <email></email>
154      <uri></uri>
155    </address>
156  </author>
158  <author initials="P." surname="Leach" fullname="Paul J. Leach">
159    <organization abbrev="Microsoft">Microsoft Corporation</organization>
160    <address>
161      <postal>
162        <street>1 Microsoft Way</street>
163        <city>Redmond</city>
164        <region>WA</region>
165        <code>98052</code>
166      </postal>
167      <email></email>
168    </address>
169  </author>
171  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
172    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
173    <address>
174      <postal>
175        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
176        <street>The Stata Center, Building 32</street>
177        <street>32 Vassar Street</street>
178        <city>Cambridge</city>
179        <region>MA</region>
180        <code>02139</code>
181        <country>USA</country>
182      </postal>
183      <email></email>
184      <uri></uri>
185    </address>
186  </author>
188  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
189    <organization abbrev="W3C">World Wide Web Consortium</organization>
190    <address>
191      <postal>
192        <street>W3C / ERCIM</street>
193        <street>2004, rte des Lucioles</street>
194        <city>Sophia-Antipolis</city>
195        <region>AM</region>
196        <code>06902</code>
197        <country>France</country>
198      </postal>
199      <email></email>
200      <uri></uri>
201    </address>
202  </author>
204  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
205    <organization abbrev="greenbytes">greenbytes GmbH</organization>
206    <address>
207      <postal>
208        <street>Hafenweg 16</street>
209        <city>Muenster</city><region>NW</region><code>48155</code>
210        <country>Germany</country>
211      </postal>
212      <phone>+49 251 2807760</phone>   
213      <facsimile>+49 251 2807761</facsimile>   
214      <email></email>       
215      <uri></uri>     
216    </address>
217  </author>
219  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
223   The Hypertext Transfer Protocol (HTTP) is an application-level
224   protocol for distributed, collaborative, hypermedia information
225   systems. HTTP has been in use by the World Wide Web global information
226   initiative since 1990. This document is Part 2 of the seven-part specification
227   that defines the protocol referred to as "HTTP/1.1" and, taken together,
228   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
229   as expressed by request methods, request-header fields, response status codes,
230   and response-header fields.
234<note title="Editorial Note (To be removed by RFC Editor)">
235  <t>
236    Discussion of this draft should take place on the HTTPBIS working group
237    mailing list ( The current issues list is
238    at <eref target=""/>
239    and related documents (including fancy diffs) can be found at
240    <eref target=""/>.
241  </t>
242  <t>
243    This draft incorporates those issue resolutions that were either
244    collected in the original RFC2616 errata list (<eref target=""/>),
245    or which were agreed upon on the mailing list between October 2006 and
246    November 2007 (as published in "draft-lafon-rfc2616bis-03").
247  </t>
251<section title="Introduction" anchor="introduction">
253   This document defines HTTP/1.1 request and response semantics.  Each HTTP
254   message, as defined in &messaging;, is in the form of either a request or
255   a response.  An HTTP server listens on a connection for HTTP requests and
256   responds to each request, in the order received on that connection, with
257   one or more HTTP response messages.  This document defines the commonly
258   agreed upon semantics of the HTTP uniform interface, the intentions defined
259   by each request method, and the various response messages that might be
260   expected as a result of applying that method for the requested resource.
263   This document is currently disorganized in order to minimize the changes
264   between drafts and enable reviewers to see the smaller errata changes.
265   The next draft will reorganize the sections to better reflect the content.
266   In particular, the sections will be ordered according to the typical
267   processing of an HTTP request message (after message parsing): resource
268   mapping, general header fields, methods, request modifiers, response
269   status, and resource metadata.  The current mess reflects how widely
270   dispersed these topics and associated requirements had become in
271   <xref target="RFC2616"/>.
274<section title="Requirements" anchor="intro.requirements">
276   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
277   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
278   document are to be interpreted as described in <xref target="RFC2119"/>.
281   An implementation is not compliant if it fails to satisfy one or more
282   of the &MUST; or &REQUIRED; level requirements for the protocols it
283   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
284   level and all the &SHOULD; level requirements for its protocols is said
285   to be "unconditionally compliant"; one that satisfies all the &MUST;
286   level requirements but not all the &SHOULD; level requirements for its
287   protocols is said to be "conditionally compliant."
292<section title="Notational Conventions and Generic Grammar" anchor="notation">
294  This specification uses the ABNF syntax defined in &notation-abnf; and
295  the core rules defined in &basic-rules;:
296  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
297  <eref target=""/>.</cref>
299<figure><artwork type="abnf2616">
300  DIGIT         = &lt;DIGIT, defined in &basic-rules;&gt;
302<figure><artwork type="abnf2616">
303  comment       = &lt;comment, defined in &basic-rules;&gt;
304  quoted-string = &lt;quoted-string, defined in &basic-rules;&gt;
305  token         = &lt;token, defined in &basic-rules;&gt;
307<t anchor="abnf.dependencies">
308  The ABNF rules below are defined in other parts:
310<figure><!--Part1--><artwork type="abnf2616">
311  absoluteURI   = &lt;absoluteURI, defined in &general-syntax;&gt;
312  fragment      = &lt;fragment, defined in &general-syntax;&gt;
313  Host          = &lt;Host, defined in &header-host;&gt;
314  HTTP-date     = &lt;HTTP-date, defined in &full-date;&gt;
315  product       = &lt;product, defined in &product-tokens;&gt;
316  relativeURI   = &lt;relativeURI, defined in &general-syntax;&gt;
317  TE            = &lt;TE, defined in &header-te;&gt;
319<figure><!--Part3--><artwork type="abnf2616">
320  Accept        = &lt;Accept, defined in &header-accept;&gt;
321  Accept-Charset =
322             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
323  Accept-Encoding =
324             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
325  Accept-Language =
326             &lt;Accept-Language, defined in &header-accept-language;&gt;
328<figure><!--Part4--><artwork type="abnf2616">
329  ETag          = &lt;ETag, defined in &header-etag;&gt;
330  If-Match      = &lt;If-Match, defined in &header-if-match;&gt;
331  If-Modified-Since =
332             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
333  If-None-Match = &lt;If-None-Match, defined in &header-if-none-match;&gt;
334  If-Unmodified-Since =
335             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
337<figure><!--Part5--><artwork type="abnf2616">
338  Accept-Ranges = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
339  If-Range      = &lt;If-Range, defined in &header-if-range;&gt;
340  Range         = &lt;Range, defined in &header-range;&gt;
342<figure><!--Part6--><artwork type="abnf2616">
343  Age           = &lt;Age, defined in &header-age;&gt;
344  Vary          = &lt;Vary, defined in &header-vary;&gt;
346<figure><artwork type="abnf2616">
347  Authorization = &lt;Authorization, defined in &header-authorization;&gt;
348  Proxy-Authenticate =
349             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
350  Proxy-Authorization =
351             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
352  WWW-Authenticate =
353             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
357<section title="Method" anchor="method">
359   The Method  token indicates the method to be performed on the
360   resource identified by the Request-URI. The method is case-sensitive.
362<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
363  Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
364                 | "GET"                    ; <xref target="GET"/>
365                 | "HEAD"                   ; <xref target="HEAD"/>
366                 | "POST"                   ; <xref target="POST"/>
367                 | "PUT"                    ; <xref target="PUT"/>
368                 | "DELETE"                 ; <xref target="DELETE"/>
369                 | "TRACE"                  ; <xref target="TRACE"/>
370                 | "CONNECT"                ; <xref target="CONNECT"/>
371                 | extension-method
372  extension-method = token
375   The list of methods allowed by a resource can be specified in an
376   Allow header field (<xref target="header.allow"/>). The return code of the response
377   always notifies the client whether a method is currently allowed on a
378   resource, since the set of allowed methods can change dynamically. An
379   origin server &SHOULD; return the status code 405 (Method Not Allowed)
380   if the method is known by the origin server but not allowed for the
381   requested resource, and 501 (Not Implemented) if the method is
382   unrecognized or not implemented by the origin server. The methods GET
383   and HEAD &MUST; be supported by all general-purpose servers. All other
384   methods are &OPTIONAL;; however, if the above methods are implemented,
385   they &MUST; be implemented with the same semantics as those specified
386   in <xref target="method.definitions"/>.
390<section title="Request Header Fields" anchor="request.header.fields">
392   The request-header fields allow the client to pass additional
393   information about the request, and about the client itself, to the
394   server. These fields act as request modifiers, with semantics
395   equivalent to the parameters on a programming language method
396   invocation.
398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
399  request-header = Accept                   ; &header-accept;
400                 | Accept-Charset           ; &header-accept-charset;
401                 | Accept-Encoding          ; &header-accept-encoding;
402                 | Accept-Language          ; &header-accept-language;
403                 | Authorization            ; &header-authorization;
404                 | Expect                   ; <xref target="header.expect"/>
405                 | From                     ; <xref target="header.from"/>
406                 | Host                     ; &header-host;
407                 | If-Match                 ; &header-if-match;
408                 | If-Modified-Since        ; &header-if-modified-since;
409                 | If-None-Match            ; &header-if-none-match;
410                 | If-Range                 ; &header-if-range;
411                 | If-Unmodified-Since      ; &header-if-unmodified-since;
412                 | Max-Forwards             ; <xref target="header.max-forwards"/>
413                 | Proxy-Authorization      ; &header-proxy-authorization;
414                 | Range                    ; &header-range;
415                 | Referer                  ; <xref target="header.referer"/>
416                 | TE                       ; &header-te;
417                 | User-Agent               ; <xref target="header.user-agent"/>
420   Request-header field names can be extended reliably only in
421   combination with a change in the protocol version. However, new or
422   experimental header fields &MAY; be given the semantics of request-header
423   fields if all parties in the communication recognize them to
424   be request-header fields. Unrecognized header fields are treated as
425   entity-header fields.
429<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
431   The Status-Code element is a 3-digit integer result code of the
432   attempt to understand and satisfy the request. The status codes listed
433   below are defined in <xref target=""/>.
434   The Reason-Phrase is intended to give a short
435   textual description of the Status-Code. The Status-Code is intended
436   for use by automata and the Reason-Phrase is intended for the human
437   user. The client is not required to examine or display the Reason-Phrase.
440   The individual values of the numeric status codes defined for
441   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
442   presented below. The reason phrases listed here are only
443   recommendations -- they &MAY; be replaced by local equivalents without
444   affecting the protocol.
446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
447  Status-Code    =
448         "100"  ; <xref target="status.100"/>: Continue
449       | "101"  ; <xref target="status.101"/>: Switching Protocols
450       | "200"  ; <xref target="status.200"/>: OK
451       | "201"  ; <xref target="status.201"/>: Created
452       | "202"  ; <xref target="status.202"/>: Accepted
453       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
454       | "204"  ; <xref target="status.204"/>: No Content
455       | "205"  ; <xref target="status.205"/>: Reset Content
456       | "206"  ; <xref target="status.206"/>: Partial Content
457       | "300"  ; <xref target="status.300"/>: Multiple Choices
458       | "301"  ; <xref target="status.301"/>: Moved Permanently
459       | "302"  ; <xref target="status.302"/>: Found
460       | "303"  ; <xref target="status.303"/>: See Other
461       | "304"  ; <xref target="status.304"/>: Not Modified
462       | "305"  ; <xref target="status.305"/>: Use Proxy
463       | "307"  ; <xref target="status.307"/>: Temporary Redirect
464       | "400"  ; <xref target="status.400"/>: Bad Request
465       | "401"  ; <xref target="status.401"/>: Unauthorized
466       | "402"  ; <xref target="status.402"/>: Payment Required
467       | "403"  ; <xref target="status.403"/>: Forbidden
468       | "404"  ; <xref target="status.404"/>: Not Found
469       | "405"  ; <xref target="status.405"/>: Method Not Allowed
470       | "406"  ; <xref target="status.406"/>: Not Acceptable
471       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
472       | "408"  ; <xref target="status.408"/>: Request Time-out
473       | "409"  ; <xref target="status.409"/>: Conflict
474       | "410"  ; <xref target="status.410"/>: Gone
475       | "411"  ; <xref target="status.411"/>: Length Required
476       | "412"  ; <xref target="status.412"/>: Precondition Failed
477       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
478       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
479       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
480       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
481       | "417"  ; <xref target="status.417"/>: Expectation Failed
482       | "500"  ; <xref target="status.500"/>: Internal Server Error
483       | "501"  ; <xref target="status.501"/>: Not Implemented
484       | "502"  ; <xref target="status.502"/>: Bad Gateway
485       | "503"  ; <xref target="status.503"/>: Service Unavailable
486       | "504"  ; <xref target="status.504"/>: Gateway Time-out
487       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
488       | extension-code
490  extension-code = 3DIGIT
491  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
494   HTTP status codes are extensible. HTTP applications are not required
495   to understand the meaning of all registered status codes, though such
496   understanding is obviously desirable. However, applications &MUST;
497   understand the class of any status code, as indicated by the first
498   digit, and treat any unrecognized response as being equivalent to the
499   x00 status code of that class, with the exception that an
500   unrecognized response &MUST-NOT; be cached. For example, if an
501   unrecognized status code of 431 is received by the client, it can
502   safely assume that there was something wrong with its request and
503   treat the response as if it had received a 400 status code. In such
504   cases, user agents &SHOULD; present to the user the entity returned
505   with the response, since that entity is likely to include human-readable
506   information which will explain the unusual status.
510<section title="Response Header Fields" anchor="response.header.fields">
512   The response-header fields allow the server to pass additional
513   information about the response which cannot be placed in the Status-Line.
514   These header fields give information about the server and about
515   further access to the resource identified by the Request-URI.
517<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
518  response-header = Accept-Ranges           ; &header-accept-ranges;
519                  | Age                     ; &header-age;
520                  | ETag                    ; &header-etag;
521                  | Location                ; <xref target="header.location"/>
522                  | Proxy-Authenticate      ; &header-proxy-authenticate;
523                  | Retry-After             ; <xref target="header.retry-after"/>
524                  | Server                  ; <xref target="header.server"/>
525                  | Vary                    ; &header-vary;
526                  | WWW-Authenticate        ; &header-www-authenticate;
529   Response-header field names can be extended reliably only in
530   combination with a change in the protocol version. However, new or
531   experimental header fields &MAY; be given the semantics of response-header
532   fields if all parties in the communication recognize them to
533   be response-header fields. Unrecognized header fields are treated as
534   entity-header fields.
538<section title="Entity" anchor="entity">
540   Request and Response messages &MAY; transfer an entity if not otherwise
541   restricted by the request method or response status code. An entity
542   consists of entity-header fields and an entity-body, although some
543   responses will only include the entity-headers. HTTP entity-body and
544   entity-header fields are defined in &payload;.
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.
555<section title="Method Definitions" anchor="method.definitions">
557   The set of common methods for HTTP/1.1 is defined below. Although
558   this set can be expanded, additional methods cannot be assumed to
559   share the same semantics for separately extended clients and servers.
562<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
564<section title="Safe Methods" anchor="safe.methods">
566   Implementors should be aware that the software represents the user in
567   their interactions over the Internet, and should be careful to allow
568   the user to be aware of any actions they might take which may have an
569   unexpected significance to themselves or others.
572   In particular, the convention has been established that the GET and
573   HEAD methods &SHOULD-NOT;  have the significance of taking an action
574   other than retrieval. These methods ought to be considered "safe".
575   This allows user agents to represent other methods, such as POST, PUT
576   and DELETE, in a special way, so that the user is made aware of the
577   fact that a possibly unsafe action is being requested.
580   Naturally, it is not possible to ensure that the server does not
581   generate side-effects as a result of performing a GET request; in
582   fact, some dynamic resources consider that a feature. The important
583   distinction here is that the user did not request the side-effects,
584   so therefore cannot be held accountable for them.
588<section title="Idempotent Methods" anchor="idempotent.methods">
590   Methods can also have the property of "idempotence" in that (aside
591   from error or expiration issues) the side-effects of N &gt; 0 identical
592   requests is the same as for a single request. The methods GET, HEAD,
593   PUT and DELETE share this property. Also, the methods OPTIONS and
594   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
597   However, it is possible that a sequence of several requests is non-idempotent,
598   even if all of the methods executed in that sequence are
599   idempotent. (A sequence is idempotent if a single execution of the
600   entire sequence always yields a result that is not changed by a
601   reexecution of all, or part, of that sequence.) For example, a
602   sequence is non-idempotent if its result depends on a value that is
603   later modified in the same sequence.
606   A sequence that never has side effects is idempotent, by definition
607   (provided that no concurrent operations are being executed on the
608   same set of resources).
613<section title="OPTIONS" anchor="OPTIONS">
614  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
615  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
617   The OPTIONS method represents a request for information about the
618   communication options available on the request/response chain
619   identified by the Request-URI. This method allows the client to
620   determine the options and/or requirements associated with a resource,
621   or the capabilities of a server, without implying a resource action
622   or initiating a resource retrieval.
625   Responses to this method are not cacheable.
628   If the OPTIONS request includes an entity-body (as indicated by the
629   presence of Content-Length or Transfer-Encoding), then the media type
630   &MUST; be indicated by a Content-Type field. Although this
631   specification does not define any use for such a body, future
632   extensions to HTTP might use the OPTIONS body to make more detailed
633   queries on the server. A server that does not support such an
634   extension &MAY; discard the request body.
637   If the Request-URI is an asterisk ("*"), the OPTIONS request is
638   intended to apply to the server in general rather than to a specific
639   resource. Since a server's communication options typically depend on
640   the resource, the "*" request is only useful as a "ping" or "no-op"
641   type of method; it does nothing beyond allowing the client to test
642   the capabilities of the server. For example, this can be used to test
643   a proxy for HTTP/1.1 compliance (or lack thereof).
646   If the Request-URI is not an asterisk, the OPTIONS request applies
647   only to the options that are available when communicating with that
648   resource.
651   A 200 response &SHOULD; include any header fields that indicate
652   optional features implemented by the server and applicable to that
653   resource (e.g., Allow), possibly including extensions not defined by
654   this specification. The response body, if any, &SHOULD; also include
655   information about the communication options. The format for such a
656   body is not defined by this specification, but might be defined by
657   future extensions to HTTP. Content negotiation &MAY; be used to select
658   the appropriate response format. If no response body is included, the
659   response &MUST; include a Content-Length field with a field-value of
660   "0".
663   The Max-Forwards request-header field &MAY; be used to target a
664   specific proxy in the request chain. When a proxy receives an OPTIONS
665   request on an absoluteURI for which request forwarding is permitted,
666   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
667   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
668   instead, the proxy &SHOULD; respond with its own communication options.
669   If the Max-Forwards field-value is an integer greater than zero, the
670   proxy &MUST; decrement the field-value when it forwards the request. If
671   no Max-Forwards field is present in the request, then the forwarded
672   request &MUST-NOT; include a Max-Forwards field.
676<section title="GET" anchor="GET">
677  <iref primary="true" item="GET method" x:for-anchor=""/>
678  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
680   The GET method means retrieve whatever information (in the form of an
681   entity) is identified by the Request-URI. If the Request-URI refers
682   to a data-producing process, it is the produced data which shall be
683   returned as the entity in the response and not the source text of the
684   process, unless that text happens to be the output of the process.
687   The semantics of the GET method change to a "conditional GET" if the
688   request message includes an If-Modified-Since, If-Unmodified-Since,
689   If-Match, If-None-Match, or If-Range header field. A conditional GET
690   method requests that the entity be transferred only under the
691   circumstances described by the conditional header field(s). The
692   conditional GET method is intended to reduce unnecessary network
693   usage by allowing cached entities to be refreshed without requiring
694   multiple requests or transferring data already held by the client.
697   The semantics of the GET method change to a "partial GET" if the
698   request message includes a Range header field. A partial GET requests
699   that only part of the entity be transferred, as described in &header-range;.
700   The partial GET method is intended to reduce unnecessary
701   network usage by allowing partially-retrieved entities to be
702   completed without transferring data already held by the client.
705   The response to a GET request is cacheable if and only if it meets
706   the requirements for HTTP caching described in &caching;.
709   See <xref target=""/> for security considerations when used for forms.
713<section title="HEAD" anchor="HEAD">
714  <iref primary="true" item="HEAD method" x:for-anchor=""/>
715  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
717   The HEAD method is identical to GET except that the server &MUST-NOT;
718   return a message-body in the response. The metainformation contained
719   in the HTTP headers in response to a HEAD request &SHOULD; be identical
720   to the information sent in response to a GET request. This method can
721   be used for obtaining metainformation about the entity implied by the
722   request without transferring the entity-body itself. This method is
723   often used for testing hypertext links for validity, accessibility,
724   and recent modification.
727   The response to a HEAD request &MAY; be cacheable in the sense that the
728   information contained in the response &MAY; be used to update a
729   previously cached entity from that resource. If the new field values
730   indicate that the cached entity differs from the current entity (as
731   would be indicated by a change in Content-Length, Content-MD5, ETag
732   or Last-Modified), then the cache &MUST; treat the cache entry as
733   stale.
737<section title="POST" anchor="POST">
738  <iref primary="true" item="POST method" x:for-anchor=""/>
739  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
741   The POST method is used to request that the origin server accept the
742   entity enclosed in the request as data to be processed by the resource
743   identified by the Request-URI in the Request-Line. POST is designed
744   to allow a uniform method to cover the following functions:
745  <list style="symbols">
746    <t>
747      Annotation of existing resources;
748    </t>
749    <t>
750        Posting a message to a bulletin board, newsgroup, mailing list,
751        or similar group of articles;
752    </t>
753    <t>
754        Providing a block of data, such as the result of submitting a
755        form, to a data-handling process;
756    </t>
757    <t>
758        Extending a database through an append operation.
759    </t>
760  </list>
763   The actual function performed by the POST method is determined by the
764   server and is usually dependent on the Request-URI.
767   The action performed by the POST method might not result in a
768   resource that can be identified by a URI. In this case, either 200
769   (OK) or 204 (No Content) is the appropriate response status,
770   depending on whether or not the response includes an entity that
771   describes the result.
774   If a resource has been created on the origin server, the response
775   &SHOULD; be 201 (Created) and contain an entity which describes the
776   status of the request and refers to the new resource, and a Location
777   header (see <xref target="header.location"/>).
780   Responses to this method are not cacheable, unless the response
781   includes appropriate Cache-Control or Expires header fields. However,
782   the 303 (See Other) response can be used to direct the user agent to
783   retrieve a cacheable resource.
787<section title="PUT" anchor="PUT">
788  <iref primary="true" item="PUT method" x:for-anchor=""/>
789  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
791   The PUT method requests that the enclosed entity be stored under the
792   supplied Request-URI. If the Request-URI refers to an already
793   existing resource, the enclosed entity &SHOULD; be considered as a
794   modified version of the one residing on the origin server. If the
795   Request-URI does not point to an existing resource, and that URI is
796   capable of being defined as a new resource by the requesting user
797   agent, the origin server can create the resource with that URI. If a
798   new resource is created at the Request-URI, the origin server &MUST;
799         inform the user agent
800   via the 201 (Created) response. If an existing resource is modified,
801   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
802   to indicate successful completion of the request. If the resource
803   could not be created or modified with the Request-URI, an appropriate
804   error response &SHOULD; be given that reflects the nature of the
805   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
806   (e.g. Content-Range) headers that it does not understand or implement
807   and &MUST; return a 501 (Not Implemented) response in such cases.
810   If the request passes through a cache and the Request-URI identifies
811   one or more currently cached entities, those entries &SHOULD; be
812   treated as stale. Responses to this method are not cacheable.
815   The fundamental difference between the POST and PUT requests is
816   reflected in the different meaning of the Request-URI. The URI in a
817   POST request identifies the resource that will handle the enclosed
818   entity. That resource might be a data-accepting process, a gateway to
819   some other protocol, or a separate entity that accepts annotations.
820   In contrast, the URI in a PUT request identifies the entity enclosed
821   with the request -- the user agent knows what URI is intended and the
822   server &MUST-NOT; attempt to apply the request to some other resource.
823   If the server desires that the request be applied to a different URI,
824   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
825   then make its own decision regarding whether or not to redirect the
826   request.
829   A single resource &MAY; be identified by many different URIs. For
830   example, an article might have a URI for identifying "the current
831   version" which is separate from the URI identifying each particular
832   version. In this case, a PUT request on a general URI might result in
833   several other URIs being defined by the origin server.
836   HTTP/1.1 does not define how a PUT method affects the state of an
837   origin server.
840   Unless otherwise specified for a particular entity-header, the
841   entity-headers in the PUT request &SHOULD; be applied to the resource
842   created or modified by the PUT.
846<section title="DELETE" anchor="DELETE">
847  <iref primary="true" item="DELETE method" x:for-anchor=""/>
848  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
850   The DELETE method requests that the origin server delete the resource
851   identified by the Request-URI. This method &MAY; be overridden by human
852   intervention (or other means) on the origin server. The client cannot
853   be guaranteed that the operation has been carried out, even if the
854   status code returned from the origin server indicates that the action
855   has been completed successfully. However, the server &SHOULD-NOT;
856   indicate success unless, at the time the response is given, it
857   intends to delete the resource or move it to an inaccessible
858   location.
861   A successful response &SHOULD; be 200 (OK) if the response includes an
862   entity describing the status, 202 (Accepted) if the action has not
863   yet been enacted, or 204 (No Content) if the action has been enacted
864   but the response does not include an entity.
867   If the request passes through a cache and the Request-URI identifies
868   one or more currently cached entities, those entries &SHOULD; be
869   treated as stale. Responses to this method are not cacheable.
873<section title="TRACE" anchor="TRACE">
874  <iref primary="true" item="TRACE method" x:for-anchor=""/>
875  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
877   The TRACE method is used to invoke a remote, application-layer loop-back
878   of the request message. The final recipient of the request
879   &SHOULD; reflect the message received back to the client as the
880   entity-body of a 200 (OK) response. The final recipient is either the
881   origin server or the first proxy or gateway to receive a Max-Forwards
882   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
883   &MUST-NOT; include an entity.
886   TRACE allows the client to see what is being received at the other
887   end of the request chain and use that data for testing or diagnostic
888   information. The value of the Via header field (&header-via;) is of
889   particular interest, since it acts as a trace of the request chain.
890   Use of the Max-Forwards header field allows the client to limit the
891   length of the request chain, which is useful for testing a chain of
892   proxies forwarding messages in an infinite loop.
895   If the request is valid, the response &SHOULD; contain the entire
896   request message in the entity-body, with a Content-Type of
897   "message/http". Responses to this method &MUST-NOT; be cached.
901<section title="CONNECT" anchor="CONNECT">
902  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
903  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
905   This specification reserves the method name CONNECT for use with a
906   proxy that can dynamically switch to being a tunnel (e.g. SSL
907   tunneling <xref target="Luo1998"/>).
913<section title="Status Code Definitions" anchor="">
915   Each Status-Code is described below, including a description of which
916   method(s) it can follow and any metainformation required in the
917   response.
920<section title="Informational 1xx" anchor="status.1xx">
922   This class of status code indicates a provisional response,
923   consisting only of the Status-Line and optional headers, and is
924   terminated by an empty line. There are no required headers for this
925   class of status code. Since HTTP/1.0 did not define any 1xx status
926   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
927   except under experimental conditions.
930   A client &MUST; be prepared to accept one or more 1xx status responses
931   prior to a regular response, even if the client does not expect a 100
932   (Continue) status message. Unexpected 1xx status responses &MAY; be
933   ignored by a user agent.
936   Proxies &MUST; forward 1xx responses, unless the connection between the
937   proxy and its client has been closed, or unless the proxy itself
938   requested the generation of the 1xx response. (For example, if a
939   proxy adds a "Expect: 100-continue" field when it forwards a request,
940   then it need not forward the corresponding 100 (Continue)
941   response(s).)
944<section title="100 Continue" anchor="status.100">
945  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
946  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
948   The client &SHOULD; continue with its request. This interim response is
949   used to inform the client that the initial part of the request has
950   been received and has not yet been rejected by the server. The client
951   &SHOULD; continue by sending the remainder of the request or, if the
952   request has already been completed, ignore this response. The server
953   &MUST; send a final response after the request has been completed. See
954   &use100; for detailed discussion of the use and handling of this
955   status code.
959<section title="101 Switching Protocols" anchor="status.101">
960  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
961  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
963   The server understands and is willing to comply with the client's
964   request, via the Upgrade message header field (&header-upgrade;), for a
965   change in the application protocol being used on this connection. The
966   server will switch protocols to those defined by the response's
967   Upgrade header field immediately after the empty line which
968   terminates the 101 response.
971   The protocol &SHOULD; be switched only when it is advantageous to do
972   so. For example, switching to a newer version of HTTP is advantageous
973   over older versions, and switching to a real-time, synchronous
974   protocol might be advantageous when delivering resources that use
975   such features.
980<section title="Successful 2xx" anchor="status.2xx">
982   This class of status code indicates that the client's request was
983   successfully received, understood, and accepted.
986<section title="200 OK" anchor="status.200">
987  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
988  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
990   The request has succeeded. The information returned with the response
991   is dependent on the method used in the request, for example:
992  <list style="hanging">
993    <t hangText="GET">
994          an entity corresponding to the requested resource is sent in
995          the response;
996    </t>
997    <t hangText="HEAD">
998          the entity-header fields corresponding to the requested
999          resource are sent in the response without any message-body;
1000    </t>
1001    <t hangText="POST">
1002      an entity describing or containing the result of the action;
1003    </t>
1004    <t hangText="TRACE">
1005      an entity containing the request message as received by the
1006      end server.
1007    </t>
1008  </list>
1012<section title="201 Created" anchor="status.201">
1013  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1014  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1016   The request has been fulfilled and resulted in a new resource being
1017   created. The newly created resource can be referenced by the URI(s)
1018   returned in the entity of the response, with the most specific URI
1019   for the resource given by a Location header field. The response
1020   &SHOULD; include an entity containing a list of resource
1021   characteristics and location(s) from which the user or user agent can
1022   choose the one most appropriate. The entity format is specified by
1023   the media type given in the Content-Type header field. The origin
1024   server &MUST; create the resource before returning the 201 status code.
1025   If the action cannot be carried out immediately, the server &SHOULD;
1026   respond with 202 (Accepted) response instead.
1029   A 201 response &MAY; contain an ETag response header field indicating
1030   the current value of the entity tag for the requested variant just
1031   created, see &header-etag;.
1035<section title="202 Accepted" anchor="status.202">
1036  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1037  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1039   The request has been accepted for processing, but the processing has
1040   not been completed.  The request might or might not eventually be
1041   acted upon, as it might be disallowed when processing actually takes
1042   place. There is no facility for re-sending a status code from an
1043   asynchronous operation such as this.
1046   The 202 response is intentionally non-committal. Its purpose is to
1047   allow a server to accept a request for some other process (perhaps a
1048   batch-oriented process that is only run once per day) without
1049   requiring that the user agent's connection to the server persist
1050   until the process is completed. The entity returned with this
1051   response &SHOULD; include an indication of the request's current status
1052   and either a pointer to a status monitor or some estimate of when the
1053   user can expect the request to be fulfilled.
1057<section title="203 Non-Authoritative Information" anchor="status.203">
1058  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1059  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1061   The returned metainformation in the entity-header is not the
1062   definitive set as available from the origin server, but is gathered
1063   from a local or a third-party copy. The set presented &MAY; be a subset
1064   or superset of the original version. For example, including local
1065   annotation information about the resource might result in a superset
1066   of the metainformation known by the origin server. Use of this
1067   response code is not required and is only appropriate when the
1068   response would otherwise be 200 (OK).
1072<section title="204 No Content" anchor="status.204">
1073  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1074  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1076   The server has fulfilled the request but does not need to return an
1077   entity-body, and might want to return updated metainformation. The
1078   response &MAY; include new or updated metainformation in the form of
1079   entity-headers, which if present &SHOULD; be associated with the
1080   requested variant.
1083   If the client is a user agent, it &SHOULD-NOT;  change its document view
1084   from that which caused the request to be sent. This response is
1085   primarily intended to allow input for actions to take place without
1086   causing a change to the user agent's active document view, although
1087   any new or updated metainformation &SHOULD; be applied to the document
1088   currently in the user agent's active view.
1091   The 204 response &MUST-NOT; include a message-body, and thus is always
1092   terminated by the first empty line after the header fields.
1096<section title="205 Reset Content" anchor="status.205">
1097  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1098  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1100   The server has fulfilled the request and the user agent &SHOULD; reset
1101   the document view which caused the request to be sent. This response
1102   is primarily intended to allow input for actions to take place via
1103   user input, followed by a clearing of the form in which the input is
1104   given so that the user can easily initiate another input action. The
1105   response &MUST-NOT; include an entity.
1109<section title="206 Partial Content" anchor="status.206">
1110  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1111  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1113   The server has fulfilled the partial GET request for the resource
1114   and the enclosed entity is a partial representation as defined in &range;.
1119<section title="Redirection 3xx" anchor="status.3xx">
1121   This class of status code indicates that further action needs to be
1122   taken by the user agent in order to fulfill the request.  The action
1123   required &MAY; be carried out by the user agent without interaction
1124   with the user if and only if the method used in the second request is
1125   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1126   such loops generate network traffic for each redirection.
1127  <list><t>
1128      <x:h>Note:</x:h> previous versions of this specification recommended a
1129      maximum of five redirections. Content developers should be aware
1130      that there might be clients that implement such a fixed
1131      limitation.
1132  </t></list>
1135<section title="300 Multiple Choices" anchor="status.300">
1136  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1137  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1139   The requested resource corresponds to any one of a set of
1140   representations, each with its own specific location, and agent-driven
1141   negotiation information (&content-negotiation;) is being provided so that
1142   the user (or user agent) can select a preferred representation and
1143   redirect its request to that location.
1146   Unless it was a HEAD request, the response &SHOULD; include an entity
1147   containing a list of resource characteristics and location(s) from
1148   which the user or user agent can choose the one most appropriate. The
1149   entity format is specified by the media type given in the Content-Type
1150   header field. Depending upon the format and the capabilities of
1151   the user agent, selection of the most appropriate choice &MAY; be
1152   performed automatically. However, this specification does not define
1153   any standard for such automatic selection.
1156   If the server has a preferred choice of representation, it &SHOULD;
1157   include the specific URI for that representation in the Location
1158   field; user agents &MAY; use the Location field value for automatic
1159   redirection. This response is cacheable unless indicated otherwise.
1163<section title="301 Moved Permanently" anchor="status.301">
1164  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1165  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1167   The requested resource has been assigned a new permanent URI and any
1168   future references to this resource &SHOULD; use one of the returned
1169   URIs.  Clients with link editing capabilities ought to automatically
1170   re-link references to the Request-URI to one or more of the new
1171   references returned by the server, where possible. This response is
1172   cacheable unless indicated otherwise.
1175   The new permanent URI &SHOULD; be given by the Location field in the
1176   response. Unless the request method was HEAD, the entity of the
1177   response &SHOULD; contain a short hypertext note with a hyperlink to
1178   the new URI(s).
1181   If the 301 status code is received in response to a request method
1182   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1183   then the request &MAY; be automatically redirected by the user agent without
1184   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1185   request unless it can be confirmed by the user, since this might
1186   change the conditions under which the request was issued.
1187  <list><t>
1188      <x:h>Note:</x:h> When automatically redirecting a POST request after
1189      receiving a 301 status code, some existing HTTP/1.0 user agents
1190      will erroneously change it into a GET request.
1191  </t></list>
1195<section title="302 Found" anchor="status.302">
1196  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1197  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1199   The requested resource resides temporarily under a different URI.
1200   Since the redirection might be altered on occasion, the client &SHOULD;
1201   continue to use the Request-URI for future requests.  This response
1202   is only cacheable if indicated by a Cache-Control or Expires header
1203   field.
1206   The temporary URI &SHOULD; be given by the Location field in the
1207   response. Unless the request method was HEAD, the entity of the
1208   response &SHOULD; contain a short hypertext note with a hyperlink to
1209   the new URI(s).
1212   If the 302 status code is received in response to a request method
1213   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1214   then the request &MAY; be automatically redirected by the user agent without
1215   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1216   request unless it can be confirmed by the user, since this might
1217   change the conditions under which the request was issued.
1218  <list><t>
1219      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1220      to change the method on the redirected request.  However, most
1221      existing user agent implementations treat 302 as if it were a 303
1222      response, performing a GET on the Location field-value regardless
1223      of the original request method. The status codes 303 and 307 have
1224      been added for servers that wish to make unambiguously clear which
1225      kind of reaction is expected of the client.
1226  </t></list>
1230<section title="303 See Other" anchor="status.303">
1231  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1234   The response to the request can be found under a different URI and
1235   &SHOULD; be retrieved using a GET method on that resource. This method
1236   exists primarily to allow the output of a POST-activated script to
1237   redirect the user agent to a selected resource. The new URI is not a
1238   substitute reference for the originally requested resource. The 303
1239   response &MUST-NOT; be cached, but the response to the second
1240   (redirected) request might be cacheable.
1243   The different URI &SHOULD; be given by the Location field in the
1244   response. Unless the request method was HEAD, the entity of the
1245   response &SHOULD; contain a short hypertext note with a hyperlink to
1246   the new URI(s).
1247  <list><t>
1248      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1249      status. When interoperability with such clients is a concern, the
1250      302 status code may be used instead, since most user agents react
1251      to a 302 response as described here for 303.
1252  </t></list>
1256<section title="304 Not Modified" anchor="status.304">
1257  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1258  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1260   The response to the request has not been modified since the conditions
1261   indicated by the client's conditional GET request, as defined in &conditional;.
1265<section title="305 Use Proxy" anchor="status.305">
1266  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1267  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1269   The requested resource &MUST; be accessed through the proxy given by
1270   the Location field. The Location field gives the URI of the proxy.
1271   The recipient is expected to repeat this single request via the
1272   proxy. 305 responses &MUST; only be generated by origin servers.
1273  <list><t>
1274      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1275      single request, and to be generated by origin servers only.  Not
1276      observing these limitations has significant security consequences.
1277  </t></list>
1281<section title="306 (Unused)" anchor="status.306">
1282  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1283  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1285   The 306 status code was used in a previous version of the
1286   specification, is no longer used, and the code is reserved.
1290<section title="307 Temporary Redirect" anchor="status.307">
1291  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1292  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1294   The requested resource resides temporarily under a different URI.
1295   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1296   continue to use the Request-URI for future requests.  This response
1297   is only cacheable if indicated by a Cache-Control or Expires header
1298   field.
1301   The temporary URI &SHOULD; be given by the Location field in the
1302   response. Unless the request method was HEAD, the entity of the
1303   response &SHOULD; contain a short hypertext note with a hyperlink to
1304   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1305   understand the 307 status. Therefore, the note &SHOULD; contain the
1306   information necessary for a user to repeat the original request on
1307   the new URI.
1310   If the 307 status code is received in response to a request method
1311   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1312   then the request &MAY; be automatically redirected by the user agent without
1313   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1314   request unless it can be confirmed by the user, since this might
1315   change the conditions under which the request was issued.
1320<section title="Client Error 4xx" anchor="status.4xx">
1322   The 4xx class of status code is intended for cases in which the
1323   client seems to have erred. Except when responding to a HEAD request,
1324   the server &SHOULD; include an entity containing an explanation of the
1325   error situation, and whether it is a temporary or permanent
1326   condition. These status codes are applicable to any request method.
1327   User agents &SHOULD; display any included entity to the user.
1330   If the client is sending data, a server implementation using TCP
1331   &SHOULD; be careful to ensure that the client acknowledges receipt of
1332   the packet(s) containing the response, before the server closes the
1333   input connection. If the client continues sending data to the server
1334   after the close, the server's TCP stack will send a reset packet to
1335   the client, which may erase the client's unacknowledged input buffers
1336   before they can be read and interpreted by the HTTP application.
1339<section title="400 Bad Request" anchor="status.400">
1340  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1341  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1343   The request could not be understood by the server due to malformed
1344   syntax. The client &SHOULD-NOT;  repeat the request without
1345   modifications.
1349<section title="401 Unauthorized" anchor="status.401">
1350  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1351  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1353   The request requires user authentication (see &auth;).
1357<section title="402 Payment Required" anchor="status.402">
1358  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1359  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1361   This code is reserved for future use.
1365<section title="403 Forbidden" anchor="status.403">
1366  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1367  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1369   The server understood the request, but is refusing to fulfill it.
1370   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1371   If the request method was not HEAD and the server wishes to make
1372   public why the request has not been fulfilled, it &SHOULD; describe the
1373   reason for the refusal in the entity.  If the server does not wish to
1374   make this information available to the client, the status code 404
1375   (Not Found) can be used instead.
1379<section title="404 Not Found" anchor="status.404">
1380  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1381  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1383   The server has not found anything matching the Request-URI. No
1384   indication is given of whether the condition is temporary or
1385   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1386   knows, through some internally configurable mechanism, that an old
1387   resource is permanently unavailable and has no forwarding address.
1388   This status code is commonly used when the server does not wish to
1389   reveal exactly why the request has been refused, or when no other
1390   response is applicable.
1394<section title="405 Method Not Allowed" anchor="status.405">
1395  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1396  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1398   The method specified in the Request-Line is not allowed for the
1399   resource identified by the Request-URI. The response &MUST; include an
1400   Allow header containing a list of valid methods for the requested
1401   resource.
1405<section title="406 Not Acceptable" anchor="status.406">
1406  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1407  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1409   The resource identified by the request is only capable of generating
1410   response entities which have content characteristics not acceptable
1411   according to the accept headers sent in the request.
1414   Unless it was a HEAD request, the response &SHOULD; include an entity
1415   containing a list of available entity characteristics and location(s)
1416   from which the user or user agent can choose the one most
1417   appropriate. The entity format is specified by the media type given
1418   in the Content-Type header field. Depending upon the format and the
1419   capabilities of the user agent, selection of the most appropriate
1420   choice &MAY; be performed automatically. However, this specification
1421   does not define any standard for such automatic selection.
1422  <list><t>
1423      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1424      not acceptable according to the accept headers sent in the
1425      request. In some cases, this may even be preferable to sending a
1426      406 response. User agents are encouraged to inspect the headers of
1427      an incoming response to determine if it is acceptable.
1428  </t></list>
1431   If the response could be unacceptable, a user agent &SHOULD;
1432   temporarily stop receipt of more data and query the user for a
1433   decision on further actions.
1437<section title="407 Proxy Authentication Required" anchor="status.407">
1438  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1439  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1441   This code is similar to 401 (Unauthorized), but indicates that the
1442   client must first authenticate itself with the proxy (see &auth;).
1446<section title="408 Request Timeout" anchor="status.408">
1447  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1448  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1450   The client did not produce a request within the time that the server
1451   was prepared to wait. The client &MAY; repeat the request without
1452   modifications at any later time.
1456<section title="409 Conflict" anchor="status.409">
1457  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1458  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1460   The request could not be completed due to a conflict with the current
1461   state of the resource. This code is only allowed in situations where
1462   it is expected that the user might be able to resolve the conflict
1463   and resubmit the request. The response body &SHOULD; include enough
1464   information for the user to recognize the source of the conflict.
1465   Ideally, the response entity would include enough information for the
1466   user or user agent to fix the problem; however, that might not be
1467   possible and is not required.
1470   Conflicts are most likely to occur in response to a PUT request. For
1471   example, if versioning were being used and the entity being PUT
1472   included changes to a resource which conflict with those made by an
1473   earlier (third-party) request, the server might use the 409 response
1474   to indicate that it can't complete the request. In this case, the
1475   response entity would likely contain a list of the differences
1476   between the two versions in a format defined by the response
1477   Content-Type.
1481<section title="410 Gone" anchor="status.410">
1482  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1483  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1485   The requested resource is no longer available at the server and no
1486   forwarding address is known. This condition is expected to be
1487   considered permanent. Clients with link editing capabilities &SHOULD;
1488   delete references to the Request-URI after user approval. If the
1489   server does not know, or has no facility to determine, whether or not
1490   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1491   used instead. This response is cacheable unless indicated otherwise.
1494   The 410 response is primarily intended to assist the task of web
1495   maintenance by notifying the recipient that the resource is
1496   intentionally unavailable and that the server owners desire that
1497   remote links to that resource be removed. Such an event is common for
1498   limited-time, promotional services and for resources belonging to
1499   individuals no longer working at the server's site. It is not
1500   necessary to mark all permanently unavailable resources as "gone" or
1501   to keep the mark for any length of time -- that is left to the
1502   discretion of the server owner.
1506<section title="411 Length Required" anchor="status.411">
1507  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1508  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1510   The server refuses to accept the request without a defined Content-Length.
1511   The client &MAY; repeat the request if it adds a valid
1512   Content-Length header field containing the length of the message-body
1513   in the request message.
1517<section title="412 Precondition Failed" anchor="status.412">
1518  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1521   The precondition given in one or more of the request-header fields
1522   evaluated to false when it was tested on the server, as defined in
1523   &conditional;.
1527<section title="413 Request Entity Too Large" anchor="status.413">
1528  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1529  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1531   The server is refusing to process a request because the request
1532   entity is larger than the server is willing or able to process. The
1533   server &MAY; close the connection to prevent the client from continuing
1534   the request.
1537   If the condition is temporary, the server &SHOULD; include a Retry-After
1538   header field to indicate that it is temporary and after what
1539   time the client &MAY; try again.
1543<section title="414 Request-URI Too Long" anchor="status.414">
1544  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1545  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1547   The server is refusing to service the request because the Request-URI
1548   is longer than the server is willing to interpret. This rare
1549   condition is only likely to occur when a client has improperly
1550   converted a POST request to a GET request with long query
1551   information, when the client has descended into a URI "black hole" of
1552   redirection (e.g., a redirected URI prefix that points to a suffix of
1553   itself), or when the server is under attack by a client attempting to
1554   exploit security holes present in some servers using fixed-length
1555   buffers for reading or manipulating the Request-URI.
1559<section title="415 Unsupported Media Type" anchor="status.415">
1560  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1561  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1563   The server is refusing to service the request because the entity of
1564   the request is in a format not supported by the requested resource
1565   for the requested method.
1569<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1570  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1571  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1573   The request included a Range request-header field (&header-range;) and none of
1574   the range-specifier values in this field overlap the current extent
1575   of the selected resource.
1579<section title="417 Expectation Failed" anchor="status.417">
1580  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1581  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1583   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1584   could not be met by this server, or, if the server is a proxy,
1585   the server has unambiguous evidence that the request could not be met
1586   by the next-hop server.
1591<section title="Server Error 5xx" anchor="status.5xx">
1593   Response status codes beginning with the digit "5" indicate cases in
1594   which the server is aware that it has erred or is incapable of
1595   performing the request. Except when responding to a HEAD request, the
1596   server &SHOULD; include an entity containing an explanation of the
1597   error situation, and whether it is a temporary or permanent
1598   condition. User agents &SHOULD; display any included entity to the
1599   user. These response codes are applicable to any request method.
1602<section title="500 Internal Server Error" anchor="status.500">
1603  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1604  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1606   The server encountered an unexpected condition which prevented it
1607   from fulfilling the request.
1611<section title="501 Not Implemented" anchor="status.501">
1612  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1613  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1615   The server does not support the functionality required to fulfill the
1616   request. This is the appropriate response when the server does not
1617   recognize the request method and is not capable of supporting it for
1618   any resource.
1622<section title="502 Bad Gateway" anchor="status.502">
1623  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1624  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1626   The server, while acting as a gateway or proxy, received an invalid
1627   response from the upstream server it accessed in attempting to
1628   fulfill the request.
1632<section title="503 Service Unavailable" anchor="status.503">
1633  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1634  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1636   The server is currently unable to handle the request due to a
1637   temporary overloading or maintenance of the server. The implication
1638   is that this is a temporary condition which will be alleviated after
1639   some delay. If known, the length of the delay &MAY; be indicated in a
1640   Retry-After header. If no Retry-After is given, the client &SHOULD;
1641   handle the response as it would for a 500 response.
1642  <list><t>
1643      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1644      server must use it when becoming overloaded. Some servers may wish
1645      to simply refuse the connection.
1646  </t></list>
1650<section title="504 Gateway Timeout" anchor="status.504">
1651  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1652  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1654   The server, while acting as a gateway or proxy, did not receive a
1655   timely response from the upstream server specified by the URI (e.g.
1656   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1657   to access in attempting to complete the request.
1658  <list><t>
1659      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1660      return 400 or 500 when DNS lookups time out.
1661  </t></list>
1665<section title="505 HTTP Version Not Supported" anchor="status.505">
1666  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1667  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1669   The server does not support, or refuses to support, the protocol
1670   version that was used in the request message. The server is
1671   indicating that it is unable or unwilling to complete the request
1672   using the same major version as the client, as described in &http-version;,
1673   other than with this error message. The response &SHOULD; contain
1674   an entity describing why that version is not supported and what other
1675   protocols are supported by that server.
1683<section title="Header Field Definitions" anchor="header.fields">
1685   This section defines the syntax and semantics of HTTP/1.1 header fields
1686   related to request and response semantics.
1689   For entity-header fields, both sender and recipient refer to either the
1690   client or the server, depending on who sends and who receives the entity.
1693<section title="Allow" anchor="header.allow">
1694  <iref primary="true" item="Allow header" x:for-anchor=""/>
1695  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1697      The Allow entity-header field lists the set of methods supported
1698      by the resource identified by the Request-URI. The purpose of this
1699      field is strictly to inform the recipient of valid methods
1700      associated with the resource. An Allow header field &MUST; be
1701      present in a 405 (Method Not Allowed) response.
1703<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1704  Allow   = "Allow" ":" #Method
1707      Example of use:
1709<figure><artwork type="example">
1710       Allow: GET, HEAD, PUT
1713      This field cannot prevent a client from trying other methods.
1714      However, the indications given by the Allow header field value
1715      &SHOULD; be followed. The actual set of allowed methods is defined
1716      by the origin server at the time of each request.
1719      The Allow header field &MAY; be provided with a PUT request to
1720      recommend the methods to be supported by the new or modified
1721      resource. The server is not required to support these methods and
1722      &SHOULD; include an Allow header in the response giving the actual
1723      supported methods.
1726      A proxy &MUST-NOT; modify the Allow header field even if it does not
1727      understand all the methods specified, since the user agent might
1728      have other means of communicating with the origin server.
1732<section title="Expect" anchor="header.expect">
1733  <iref primary="true" item="Expect header" x:for-anchor=""/>
1734  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1736   The Expect request-header field is used to indicate that particular
1737   server behaviors are required by the client.
1739<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
1740  Expect       =  "Expect" ":" 1#expectation
1742  expectation  =  "100-continue" | expectation-extension
1743  expectation-extension =  token [ "=" ( token | quoted-string )
1744                           *expect-params ]
1745  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1748   A server that does not understand or is unable to comply with any of
1749   the expectation values in the Expect field of a request &MUST; respond
1750   with appropriate error status. The server &MUST; respond with a 417
1751   (Expectation Failed) status if any of the expectations cannot be met
1752   or, if there are other problems with the request, some other 4xx
1753   status.
1756   This header field is defined with extensible syntax to allow for
1757   future extensions. If a server receives a request containing an
1758   Expect field that includes an expectation-extension that it does not
1759   support, it &MUST; respond with a 417 (Expectation Failed) status.
1762   Comparison of expectation values is case-insensitive for unquoted
1763   tokens (including the 100-continue token), and is case-sensitive for
1764   quoted-string expectation-extensions.
1767   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1768   return a 417 (Expectation Failed) status if it receives a request
1769   with an expectation that it cannot meet. However, the Expect
1770   request-header itself is end-to-end; it &MUST; be forwarded if the
1771   request is forwarded.
1774   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1775   Expect header.
1778   See &use100; for the use of the 100 (Continue) status.
1782<section title="From" anchor="header.from">
1783  <iref primary="true" item="From header" x:for-anchor=""/>
1784  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1786   The From request-header field, if given, &SHOULD; contain an Internet
1787   e-mail address for the human user who controls the requesting user
1788   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1789   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1791<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1792  From    = "From" ":" mailbox
1794  mailbox = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC2822"/>&gt;
1797   An example is:
1799<figure><artwork type="example">
1800    From:
1803   This header field &MAY; be used for logging purposes and as a means for
1804   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1805   be used as an insecure form of access protection. The interpretation
1806   of this field is that the request is being performed on behalf of the
1807   person given, who accepts responsibility for the method performed. In
1808   particular, robot agents &SHOULD; include this header so that the
1809   person responsible for running the robot can be contacted if problems
1810   occur on the receiving end.
1813   The Internet e-mail address in this field &MAY; be separate from the
1814   Internet host which issued the request. For example, when a request
1815   is passed through a proxy the original issuer's address &SHOULD; be
1816   used.
1819   The client &SHOULD-NOT;  send the From header field without the user's
1820   approval, as it might conflict with the user's privacy interests or
1821   their site's security policy. It is strongly recommended that the
1822   user be able to disable, enable, and modify the value of this field
1823   at any time prior to a request.
1827<section title="Location" anchor="header.location">
1828  <iref primary="true" item="Location header" x:for-anchor=""/>
1829  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1831   The Location response-header field is used to redirect the recipient
1832   to a location other than the Request-URI for completion of the
1833   request or identification of a new resource. For 201 (Created)
1834   responses, the Location is that of the new resource which was created
1835   by the request. For 3xx responses, the location &SHOULD; indicate the
1836   server's preferred URI for automatic redirection to the resource. The
1837   field value consists of a single absolute URI.
1839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1840  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1843   An example is:
1845<figure><artwork type="example">
1846    Location:
1849  <list><t>
1850      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1851      from Location in that the Content-Location identifies the original
1852      location of the entity enclosed in the request. It is therefore
1853      possible for a response to contain header fields for both Location
1854      and Content-Location.
1855  </t></list>
1858   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1859   <list style="symbols">
1860      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1861      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1862      <t>With 305 Use Proxy.</t>
1863   </list>
1867<section title="Max-Forwards" anchor="header.max-forwards">
1868  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1869  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1871   The Max-Forwards request-header field provides a mechanism with the
1872   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1873   number of proxies or gateways that can forward the request to the
1874   next inbound server. This can be useful when the client is attempting
1875   to trace a request chain which appears to be failing or looping in
1876   mid-chain.
1878<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1879  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1882   The Max-Forwards value is a decimal integer indicating the remaining
1883   number of times this request message may be forwarded.
1886   Each proxy or gateway recipient of a TRACE or OPTIONS request
1887   containing a Max-Forwards header field &MUST; check and update its
1888   value prior to forwarding the request. If the received value is zero
1889   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1890   respond as the final recipient. If the received Max-Forwards value is
1891   greater than zero, then the forwarded message &MUST; contain an updated
1892   Max-Forwards field with a value decremented by one (1).
1895   The Max-Forwards header field &MAY; be ignored for all other methods
1896   defined by this specification and for any extension methods for which
1897   it is not explicitly referred to as part of that method definition.
1901<section title="Referer" anchor="header.referer">
1902  <iref primary="true" item="Referer header" x:for-anchor=""/>
1903  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1905   The Referer[sic] request-header field allows the client to specify,
1906   for the server's benefit, the address (URI) of the resource from
1907   which the Request-URI was obtained (the "referrer", although the
1908   header field is misspelled.) The Referer request-header allows a
1909   server to generate lists of back-links to resources for interest,
1910   logging, optimized caching, etc. It also allows obsolete or mistyped
1911   links to be traced for maintenance. The Referer field &MUST-NOT; be
1912   sent if the Request-URI was obtained from a source that does not have
1913   its own URI, such as input from the user keyboard.
1915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1916  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1919   Example:
1921<figure><artwork type="example">
1922    Referer:
1925   If the field value is a relative URI, it &SHOULD; be interpreted
1926   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1927   <xref target=""/> for security considerations.
1931<section title="Retry-After" anchor="header.retry-after">
1932  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1933  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1935   The Retry-After response-header field can be used with a 503 (Service
1936   Unavailable) response to indicate how long the service is expected to
1937   be unavailable to the requesting client. This field &MAY; also be used
1938   with any 3xx (Redirection) response to indicate the minimum time the
1939   user-agent is asked wait before issuing the redirected request. The
1940   value of this field can be either an HTTP-date or an integer number
1941   of seconds (in decimal) after the time of the response.
1943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1944  Retry-After   = "Retry-After" ":" ( HTTP-date | delta-seconds )
1947   Time spans are non-negative decimal integers, representing time in
1948   seconds.
1950<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
1951  delta-seconds  = 1*DIGIT
1954   Two examples of its use are
1956<figure><artwork type="example">
1957    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1958    Retry-After: 120
1961   In the latter example, the delay is 2 minutes.
1965<section title="Server" anchor="header.server">
1966  <iref primary="true" item="Server header" x:for-anchor=""/>
1967  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1969   The Server response-header field contains information about the
1970   software used by the origin server to handle the request. The field
1971   can contain multiple product tokens (&product-tokens;) and comments
1972   identifying the server and any significant subproducts. The product
1973   tokens are listed in order of their significance for identifying the
1974   application.
1976<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1977  Server         = "Server" ":" 1*( product | comment )
1980   Example:
1982<figure><artwork type="example">
1983    Server: CERN/3.0 libwww/2.17
1986   If the response is being forwarded through a proxy, the proxy
1987   application &MUST-NOT; modify the Server response-header. Instead, it
1988   &MUST; include a Via field (as described in &header-via;).
1989  <list><t>
1990      <x:h>Note:</x:h> Revealing the specific software version of the server might
1991      allow the server machine to become more vulnerable to attacks
1992      against software that is known to contain security holes. Server
1993      implementors are encouraged to make this field a configurable
1994      option.
1995  </t></list>
1999<section title="User-Agent" anchor="header.user-agent">
2000  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2001  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2003   The User-Agent request-header field contains information about the
2004   user agent originating the request. This is for statistical purposes,
2005   the tracing of protocol violations, and automated recognition of user
2006   agents for the sake of tailoring responses to avoid particular user
2007   agent limitations. User agents &SHOULD; include this field with
2008   requests. The field can contain multiple product tokens (&product-tokens;)
2009   and comments identifying the agent and any subproducts which form a
2010   significant part of the user agent. By convention, the product tokens
2011   are listed in order of their significance for identifying the
2012   application.
2014<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2015  User-Agent     = "User-Agent" ":" 1*( product | comment )
2018   Example:
2020<figure><artwork type="example">
2021    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2027<section title="IANA Considerations" anchor="IANA.considerations">
2029   <cref>TBD.</cref>
2033<section title="Security Considerations" anchor="security.considerations">
2035   This section is meant to inform application developers, information
2036   providers, and users of the security limitations in HTTP/1.1 as
2037   described by this document. The discussion does not include
2038   definitive solutions to the problems revealed, though it does make
2039   some suggestions for reducing security risks.
2042<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2044   Like any generic data transfer protocol, HTTP cannot regulate the
2045   content of the data that is transferred, nor is there any a priori
2046   method of determining the sensitivity of any particular piece of
2047   information within the context of any given request. Therefore,
2048   applications &SHOULD; supply as much control over this information as
2049   possible to the provider of that information. Four header fields are
2050   worth special mention in this context: Server, Via, Referer and From.
2053   Revealing the specific software version of the server might allow the
2054   server machine to become more vulnerable to attacks against software
2055   that is known to contain security holes. Implementors &SHOULD; make the
2056   Server header field a configurable option.
2059   Proxies which serve as a portal through a network firewall &SHOULD;
2060   take special precautions regarding the transfer of header information
2061   that identifies the hosts behind the firewall. In particular, they
2062   &SHOULD; remove, or replace with sanitized versions, any Via fields
2063   generated behind the firewall.
2066   The Referer header allows reading patterns to be studied and reverse
2067   links drawn. Although it can be very useful, its power can be abused
2068   if user details are not separated from the information contained in
2069   the Referer. Even when the personal information has been removed, the
2070   Referer header might indicate a private document's URI whose
2071   publication would be inappropriate.
2074   The information sent in the From field might conflict with the user's
2075   privacy interests or their site's security policy, and hence it
2076   &SHOULD-NOT;  be transmitted without the user being able to disable,
2077   enable, and modify the contents of the field. The user &MUST; be able
2078   to set the contents of this field within a user preference or
2079   application defaults configuration.
2082   We suggest, though do not require, that a convenient toggle interface
2083   be provided for the user to enable or disable the sending of From and
2084   Referer information.
2087   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2088   fields can sometimes be used to determine that a specific client or
2089   server have a particular security hole which might be exploited.
2090   Unfortunately, this same information is often used for other valuable
2091   purposes for which HTTP currently has no better mechanism.
2095<section title="Encoding Sensitive Information in URIs" anchor="">
2097   Because the source of a link might be private information or might
2098   reveal an otherwise private information source, it is strongly
2099   recommended that the user be able to select whether or not the
2100   Referer field is sent. For example, a browser client could have a
2101   toggle switch for browsing openly/anonymously, which would
2102   respectively enable/disable the sending of Referer and From
2103   information.
2106   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2107   HTTP request if the referring page was transferred with a secure
2108   protocol.
2111   Authors of services should not use
2112   GET-based forms for the submission of sensitive data because that
2113   data will be encoded in the Request-URI. Many existing
2114   servers, proxies, and user agents log or display the Request-URI in
2115   places where it might be visible to third parties. Such services can
2116   use POST-based form submission instead.
2120<section title="Location Headers and Spoofing" anchor="location.spoofing">
2122   If a single server supports multiple organizations that do not trust
2123   one another, then it &MUST; check the values of Location and Content-Location
2124   headers in responses that are generated under control of
2125   said organizations to make sure that they do not attempt to
2126   invalidate resources over which they have no authority.
2132<section title="Acknowledgments" anchor="ack">
2137<references title="Normative References">
2139<reference anchor="Part1">
2140  <front>
2141    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2142    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2143      <organization abbrev="Day Software">Day Software</organization>
2144      <address><email></email></address>
2145    </author>
2146    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2147      <organization>One Laptop per Child</organization>
2148      <address><email></email></address>
2149    </author>
2150    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2151      <organization abbrev="HP">Hewlett-Packard Company</organization>
2152      <address><email></email></address>
2153    </author>
2154    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2155      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2156      <address><email></email></address>
2157    </author>
2158    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2159      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2160      <address><email></email></address>
2161    </author>
2162    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2164      <address><email></email></address>
2165    </author>
2166    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2167      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2168      <address><email></email></address>
2169    </author>
2170    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2171      <organization abbrev="W3C">World Wide Web Consortium</organization>
2172      <address><email></email></address>
2173    </author>
2174    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2175      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2176      <address><email></email></address>
2177    </author>
2178    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2179  </front>
2180  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2181  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2184<reference anchor="Part3">
2185  <front>
2186    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2187    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2188      <organization abbrev="Day Software">Day Software</organization>
2189      <address><email></email></address>
2190    </author>
2191    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2192      <organization>One Laptop per Child</organization>
2193      <address><email></email></address>
2194    </author>
2195    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2196      <organization abbrev="HP">Hewlett-Packard Company</organization>
2197      <address><email></email></address>
2198    </author>
2199    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2200      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2201      <address><email></email></address>
2202    </author>
2203    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2204      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2205      <address><email></email></address>
2206    </author>
2207    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2208      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2209      <address><email></email></address>
2210    </author>
2211    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2212      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2213      <address><email></email></address>
2214    </author>
2215    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2216      <organization abbrev="W3C">World Wide Web Consortium</organization>
2217      <address><email></email></address>
2218    </author>
2219    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2220      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2221      <address><email></email></address>
2222    </author>
2223    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2224  </front>
2225  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2226  <x:source href="p3-payload.xml" basename="p3-payload"/>
2229<reference anchor="Part4">
2230  <front>
2231    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2232    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2233      <organization abbrev="Day Software">Day Software</organization>
2234      <address><email></email></address>
2235    </author>
2236    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2237      <organization>One Laptop per Child</organization>
2238      <address><email></email></address>
2239    </author>
2240    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2241      <organization abbrev="HP">Hewlett-Packard Company</organization>
2242      <address><email></email></address>
2243    </author>
2244    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2245      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2246      <address><email></email></address>
2247    </author>
2248    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2249      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2250      <address><email></email></address>
2251    </author>
2252    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2253      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2254      <address><email></email></address>
2255    </author>
2256    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2257      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2258      <address><email></email></address>
2259    </author>
2260    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2261      <organization abbrev="W3C">World Wide Web Consortium</organization>
2262      <address><email></email></address>
2263    </author>
2264    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2265      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2266      <address><email></email></address>
2267    </author>
2268    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2269  </front>
2270  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2271  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2274<reference anchor="Part5">
2275  <front>
2276    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2277    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2278      <organization abbrev="Day Software">Day Software</organization>
2279      <address><email></email></address>
2280    </author>
2281    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2282      <organization>One Laptop per Child</organization>
2283      <address><email></email></address>
2284    </author>
2285    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2286      <organization abbrev="HP">Hewlett-Packard Company</organization>
2287      <address><email></email></address>
2288    </author>
2289    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2290      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2291      <address><email></email></address>
2292    </author>
2293    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2294      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2295      <address><email></email></address>
2296    </author>
2297    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2298      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2299      <address><email></email></address>
2300    </author>
2301    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2302      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2303      <address><email></email></address>
2304    </author>
2305    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2306      <organization abbrev="W3C">World Wide Web Consortium</organization>
2307      <address><email></email></address>
2308    </author>
2309    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2310      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2311      <address><email></email></address>
2312    </author>
2313    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2314  </front>
2315  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2316  <x:source href="p5-range.xml" basename="p5-range"/>
2319<reference anchor="Part6">
2320  <front>
2321    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2322    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2323      <organization abbrev="Day Software">Day Software</organization>
2324      <address><email></email></address>
2325    </author>
2326    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2327      <organization>One Laptop per Child</organization>
2328      <address><email></email></address>
2329    </author>
2330    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2331      <organization abbrev="HP">Hewlett-Packard Company</organization>
2332      <address><email></email></address>
2333    </author>
2334    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2335      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2336      <address><email></email></address>
2337    </author>
2338    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2339      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2340      <address><email></email></address>
2341    </author>
2342    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2343      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2344      <address><email></email></address>
2345    </author>
2346    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2347      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2348      <address><email></email></address>
2349    </author>
2350    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2351      <organization abbrev="W3C">World Wide Web Consortium</organization>
2352      <address><email></email></address>
2353    </author>
2354    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2355      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2356      <address><email></email></address>
2357    </author>
2358    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2359  </front>
2360  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2361  <x:source href="p6-cache.xml" basename="p6-cache"/>
2364<reference anchor="Part7">
2365  <front>
2366    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2367    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2368      <organization abbrev="Day Software">Day Software</organization>
2369      <address><email></email></address>
2370    </author>
2371    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2372      <organization>One Laptop per Child</organization>
2373      <address><email></email></address>
2374    </author>
2375    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2376      <organization abbrev="HP">Hewlett-Packard Company</organization>
2377      <address><email></email></address>
2378    </author>
2379    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2380      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2381      <address><email></email></address>
2382    </author>
2383    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2384      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2385      <address><email></email></address>
2386    </author>
2387    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2388      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2389      <address><email></email></address>
2390    </author>
2391    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2392      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2393      <address><email></email></address>
2394    </author>
2395    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2396      <organization abbrev="W3C">World Wide Web Consortium</organization>
2397      <address><email></email></address>
2398    </author>
2399    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2400      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2401      <address><email></email></address>
2402    </author>
2403    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2404  </front>
2405  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2406  <x:source href="p7-auth.xml" basename="p7-auth"/>
2409<reference anchor="RFC2119">
2410  <front>
2411    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2412    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2413      <organization>Harvard University</organization>
2414      <address><email></email></address>
2415    </author>
2416    <date month="March" year="1997"/>
2417  </front>
2418  <seriesInfo name="BCP" value="14"/>
2419  <seriesInfo name="RFC" value="2119"/>
2424<references title="Informative References">
2426<reference anchor="Luo1998">
2427  <front>
2428    <title>Tunneling TCP based protocols through Web proxy servers</title>
2429    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2430      <organization/>
2431    </author>
2432    <date year="1998" month="August"/>
2433  </front>
2434  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2437<reference anchor="RFC1945">
2438  <front>
2439    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2440    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2441      <organization>MIT, Laboratory for Computer Science</organization>
2442      <address><email></email></address>
2443    </author>
2444    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2445      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2446      <address><email></email></address>
2447    </author>
2448    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2449      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2450      <address><email></email></address>
2451    </author>
2452    <date month="May" year="1996"/>
2453  </front>
2454  <seriesInfo name="RFC" value="1945"/>
2457<reference anchor="RFC2068">
2458  <front>
2459    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2460    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2461      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2462      <address><email></email></address>
2463    </author>
2464    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2465      <organization>MIT Laboratory for Computer Science</organization>
2466      <address><email></email></address>
2467    </author>
2468    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2469      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2470      <address><email></email></address>
2471    </author>
2472    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2473      <organization>MIT Laboratory for Computer Science</organization>
2474      <address><email></email></address>
2475    </author>
2476    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2477      <organization>MIT Laboratory for Computer Science</organization>
2478      <address><email></email></address>
2479    </author>
2480    <date month="January" year="1997"/>
2481  </front>
2482  <seriesInfo name="RFC" value="2068"/>
2485<reference anchor="RFC2616">
2486  <front>
2487    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2488    <author initials="R." surname="Fielding" fullname="R. Fielding">
2489      <organization>University of California, Irvine</organization>
2490      <address><email></email></address>
2491    </author>
2492    <author initials="J." surname="Gettys" fullname="J. Gettys">
2493      <organization>W3C</organization>
2494      <address><email></email></address>
2495    </author>
2496    <author initials="J." surname="Mogul" fullname="J. Mogul">
2497      <organization>Compaq Computer Corporation</organization>
2498      <address><email></email></address>
2499    </author>
2500    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2501      <organization>MIT Laboratory for Computer Science</organization>
2502      <address><email></email></address>
2503    </author>
2504    <author initials="L." surname="Masinter" fullname="L. Masinter">
2505      <organization>Xerox Corporation</organization>
2506      <address><email></email></address>
2507    </author>
2508    <author initials="P." surname="Leach" fullname="P. Leach">
2509      <organization>Microsoft Corporation</organization>
2510      <address><email></email></address>
2511    </author>
2512    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2513      <organization>W3C</organization>
2514      <address><email></email></address>
2515    </author>
2516    <date month="June" year="1999"/>
2517  </front>
2518  <seriesInfo name="RFC" value="2616"/>
2521<reference anchor="RFC2822">
2522  <front>
2523    <title>Internet Message Format</title>
2524    <author initials="P." surname="Resnick" fullname="P. Resnick">
2525      <organization>QUALCOMM Incorporated</organization>
2526    </author>
2527    <date year="2001" month="April"/>
2528  </front>
2529  <seriesInfo name="RFC" value="2822"/>
2534<section title="Compatibility with Previous Versions" anchor="compatibility">
2535<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2537   Clarified which error code should be used for inbound server failures
2538   (e.g. DNS failures). (<xref target="status.504"/>).
2541   201 (Created) had a race that required an Etag be sent when a resource is
2542   first created. (<xref target="status.201"/>).
2545   Rewrite of message transmission requirements to make it much harder
2546   for implementors to get it wrong, as the consequences of errors here
2547   can have significant impact on the Internet, and to deal with the
2548   following problems:
2549  <list style="numbers">
2550      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2551         this was incorrectly placing a requirement on the behavior of
2552         an implementation of a future version of HTTP/1.x</t>
2554      <t>Made it clear that user-agents should retry requests, not
2555         "clients" in general.</t>
2557      <t>Converted requirements for clients to ignore unexpected 100
2558         (Continue) responses, and for proxies to forward 100 responses,
2559         into a general requirement for 1xx responses.</t>
2561      <t>Modified some TCP-specific language, to make it clearer that
2562         non-TCP transports are possible for HTTP.</t>
2564      <t>Require that the origin server &MUST-NOT; wait for the request
2565         body before it sends a required 100 (Continue) response.</t>
2567      <t>Allow, rather than require, a server to omit 100 (Continue) if
2568         it has already seen some of the request body.</t>
2570      <t>Allow servers to defend against denial-of-service attacks and
2571         broken clients.</t>
2572  </list>
2575   This change adds the Expect header and 417 status code.
2578   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2579   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2582   The PATCH<iref item="PATCH method" primary="true"/><iref item="Methods" subitem="PATCH" primary="true"/>, LINK<iref item="LINK method" primary="true"/><iref item="Methods" subitem="LINK" primary="true"/>, UNLINK<iref item="UNLINK method" primary="true"/><iref item="Methods" subitem="UNLINK" primary="true"/> methods were defined but not commonly
2583   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2587<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2589  Clarify definition of POST.
2590  (<xref target="POST"/>)
2593  Failed to consider that there are
2594  many other request methods that are safe to automatically redirect,
2595  and further that the user agent is able to make that determination
2596  based on the request method semantics.
2597  (Sections <xref format="counter" target="status.301"/>,
2598  <xref format="counter" target="status.302"/> and
2599  <xref format="counter" target="status.307"/> )
2602  Correct syntax of Location header to allow fragment,
2603  as referred symbol wasn't what was expected, and add some
2604  clarifications as to when it would not be appropriate.
2605  (<xref target="header.location"/>)
2608  In the description of the Server header, the Via field
2609  was described as a SHOULD. The requirement was and is stated
2610  correctly in the description of the Via header in &header-via;.
2611  (<xref target="header.server"/>)
2617<section title="Change Log (to be removed by RFC Editor before publication)">
2619<section title="Since RFC2616">
2621  Extracted relevant partitions from <xref target="RFC2616"/>.
2625<section title="Since draft-ietf-httpbis-p2-semantics-00">
2627  Closed issues:
2628  <list style="symbols">
2629    <t>
2630      <eref target=""/>:
2631      "Via is a MUST"
2632      (<eref target=""/>)
2633    </t>
2634    <t>
2635      <eref target=""/>:
2636      "Fragments allowed in Location"
2637      (<eref target=""/>)
2638    </t>
2639    <t>
2640      <eref target=""/>:
2641      "Safe Methods vs Redirection"
2642      (<eref target=""/>)
2643    </t>
2644    <t>
2645      <eref target=""/>:
2646      "Revise description of the POST method"
2647      (<eref target=""/>)
2648    </t>
2649    <t>
2650      <eref target=""/>:
2651      "Normative and Informative references"
2652    </t>
2653    <t>
2654      <eref target=""/>:
2655      "RFC2606 Compliance"
2656    </t>
2657    <t>
2658      <eref target=""/>:
2659      "Informative references"
2660    </t>
2661    <t>
2662      <eref target=""/>:
2663      "Redundant cross-references"
2664    </t>
2665  </list>
2668  Other changes:
2669  <list style="symbols">
2670    <t>
2671      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2672    </t>
2673  </list>
2677<section title="Since draft-ietf-httpbis-p2-semantics-01">
2679  Closed issues:
2680  <list style="symbols">
2681    <t>
2682      <eref target=""/>:
2683      "PUT side effects"
2684    </t>
2685    <t>
2686      <eref target=""/>:
2687      "Duplicate Host header requirements"
2688    </t>
2689  </list>
2692  Ongoing work on ABNF conversion (<eref target=""/>):
2693  <list style="symbols">
2694    <t>
2695      Move "Product Tokens" section (back) into Part 1, as "token" is used
2696      in the definition of the Upgrade header.
2697    </t>
2698    <t>
2699      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2700    </t>
2701    <t>
2702      Copy definition of delta-seconds from Part6 instead of referencing it.
2703    </t>
2704  </list>
2708<section title="Since draft-ietf-httpbis-p2-semantics-02">
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