source: draft-ietf-httpbis/latest/p2-semantics.xml @ 144

Last change on this file since 144 was 140, checked in by julian.reschke@…, 15 years ago

Fix (old) typo (?) in Changes section.

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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 "January">
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 diff2045entity             "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
25  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
26  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
27  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
28  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
29  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
30  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
31  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
32  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
33  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
34  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
35  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
36  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
37  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
38  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
39  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
40  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
41  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
42  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
43  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
44  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
45  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
46  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
47  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
48  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
49  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
50  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
51  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
52  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
53  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
54  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
55  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
56  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
57  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
58  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
60<?rfc toc="yes" ?>
61<?rfc symrefs="yes" ?>
62<?rfc sortrefs="yes" ?>
63<?rfc compact="yes"?>
64<?rfc subcompact="no" ?>
65<?rfc linkmailto="no" ?>
66<?rfc editing="no" ?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2068, 2616" category="std"
70     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
71     xmlns:x='' xmlns:ed="">
74  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
76  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
77    <organization abbrev="Day Software">Day Software</organization>
78    <address>
79      <postal>
80        <street>23 Corporate Plaza DR, Suite 280</street>
81        <city>Newport Beach</city>
82        <region>CA</region>
83        <code>92660</code>
84        <country>USA</country>
85      </postal>
86      <phone>+1-949-706-5300</phone>
87      <facsimile>+1-949-706-5305</facsimile>
88      <email></email>
89      <uri></uri>
90    </address>
91  </author>
93  <author initials="J." surname="Gettys" fullname="Jim Gettys">
94    <organization>One Laptop per Child</organization>
95    <address>
96      <postal>
97        <street>21 Oak Knoll Road</street>
98        <city>Carlisle</city>
99        <region>MA</region>
100        <code>01741</code>
101        <country>USA</country>
102      </postal>
103      <email></email>
104      <uri></uri>
105    </address>
106  </author>
108  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
109    <organization abbrev="HP">Hewlett-Packard Company</organization>
110    <address>
111      <postal>
112        <street>HP Labs, Large Scale Systems Group</street>
113        <street>1501 Page Mill Road, MS 1177</street>
114        <city>Palo Alto</city>
115        <region>CA</region>
116        <code>94304</code>
117        <country>USA</country>
118      </postal>
119      <email></email>
120    </address>
121  </author>
123  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
124    <organization abbrev="Microsoft">Microsoft Corporation</organization>
125    <address>
126      <postal>
127        <street>1 Microsoft Way</street>
128        <city>Redmond</city>
129        <region>WA</region>
130        <code>98052</code>
131        <country>USA</country>
132      </postal>
133      <email></email>
134    </address>
135  </author>
137  <author initials="L." surname="Masinter" fullname="Larry Masinter">
138    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
139    <address>
140      <postal>
141        <street>345 Park Ave</street>
142        <city>San Jose</city>
143        <region>CA</region>
144        <code>95110</code>
145        <country>USA</country>
146      </postal>
147      <email></email>
148      <uri></uri>
149    </address>
150  </author>
152  <author initials="P." surname="Leach" fullname="Paul J. Leach">
153    <organization abbrev="Microsoft">Microsoft Corporation</organization>
154    <address>
155      <postal>
156        <street>1 Microsoft Way</street>
157        <city>Redmond</city>
158        <region>WA</region>
159        <code>98052</code>
160      </postal>
161      <email></email>
162    </address>
163  </author>
165  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
166    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
170        <street>The Stata Center, Building 32</street>
171        <street>32 Vassar Street</street>
172        <city>Cambridge</city>
173        <region>MA</region>
174        <code>02139</code>
175        <country>USA</country>
176      </postal>
177      <email></email>
178      <uri></uri>
179    </address>
180  </author>
182  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
183    <organization abbrev="W3C">World Wide Web Consortium</organization>
184    <address>
185      <postal>
186        <street>W3C / ERCIM</street>
187        <street>2004, rte des Lucioles</street>
188        <city>Sophia-Antipolis</city>
189        <region>AM</region>
190        <code>06902</code>
191        <country>France</country>
192      </postal>
193      <email></email>
194      <uri></uri>
195    </address>
196  </author>
198  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
199    <organization abbrev="greenbytes">greenbytes GmbH</organization>
200    <address>
201      <postal>
202        <street>Hafenweg 16</street>
203        <city>Muenster</city><region>NW</region><code>48155</code>
204        <country>Germany</country>
205      </postal>
206      <phone>+49 251 2807760</phone>   
207      <facsimile>+49 251 2807761</facsimile>   
208      <email></email>       
209      <uri></uri>     
210    </address>
211  </author>
213  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
217   The Hypertext Transfer Protocol (HTTP) is an application-level
218   protocol for distributed, collaborative, hypermedia information
219   systems. HTTP has been in use by the World Wide Web global information
220   initiative since 1990. This document is Part 2 of the seven-part specification
221   that defines the protocol referred to as "HTTP/1.1" and, taken together,
222   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
223   as expressed by request methods, request-header fields, response status codes,
224   and response-header fields.
228<note title="Editorial Note (To be removed by RFC Editor)">
229  <t>
230    Discussion of this draft should take place on the HTTPBIS working group
231    mailing list ( The current issues list is
232    at <eref target=""/>
233    and related documents (including fancy diffs) can be found at
234    <eref target=""/>.
235  </t>
239<section title="Introduction" anchor="introduction">
241   This document will define aspects of HTTP related to request and response
242   semantics. Right now it only includes the extracted relevant sections of
243   RFC 2616 with only minor edits.
246   The HTTP protocol is a request/response protocol. A client sends a
247   request to the server in the form of a request method, URI, and
248   protocol version, followed by a MIME-like message containing request
249   modifiers, client information, and possible body content over a
250   connection with a server. The server responds with a status line,
251   including the message's protocol version and a success or error code,
252   followed by a MIME-like message containing server information, entity
253   metainformation, and possible entity-body content. The relationship
254   between HTTP and MIME is described in &diff2045entity;.
257<section title="Requirements" anchor="intro.requirements">
259   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
260   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
261   document are to be interpreted as described in <xref target="RFC2119"/>.
264   An implementation is not compliant if it fails to satisfy one or more
265   of the &MUST; or &REQUIRED; level requirements for the protocols it
266   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
267   level and all the &SHOULD; level requirements for its protocols is said
268   to be "unconditionally compliant"; one that satisfies all the &MUST;
269   level requirements but not all the &SHOULD; level requirements for its
270   protocols is said to be "conditionally compliant."
275<section title="Product Tokens" anchor="product.tokens">
277   Product tokens are used to allow communicating applications to
278   identify themselves by software name and version. Most fields using
279   product tokens also allow sub-products which form a significant part
280   of the application to be listed, separated by white space. By
281   convention, the products are listed in order of their significance
282   for identifying the application.
284<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
285  product         = token ["/" product-version]
286  product-version = token
289   Examples:
291<figure><artwork type="example">
292    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
293    Server: Apache/0.8.4
296   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
297   used for advertising or other non-essential information. Although any
298   token character &MAY; appear in a product-version, this token &SHOULD;
299   only be used for a version identifier (i.e., successive versions of
300   the same product &SHOULD; only differ in the product-version portion of
301   the product value).
305<section title="Method" anchor="method">
307   The Method  token indicates the method to be performed on the
308   resource identified by the Request-URI. The method is case-sensitive.
310<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
311  Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
312                 | "GET"                    ; <xref target="GET"/>
313                 | "HEAD"                   ; <xref target="HEAD"/>
314                 | "POST"                   ; <xref target="POST"/>
315                 | "PUT"                    ; <xref target="PUT"/>
316                 | "DELETE"                 ; <xref target="DELETE"/>
317                 | "TRACE"                  ; <xref target="TRACE"/>
318                 | "CONNECT"                ; <xref target="CONNECT"/>
319                 | extension-method
320  extension-method = token
323   The list of methods allowed by a resource can be specified in an
324   Allow header field (<xref target="header.allow"/>). The return code of the response
325   always notifies the client whether a method is currently allowed on a
326   resource, since the set of allowed methods can change dynamically. An
327   origin server &SHOULD; return the status code 405 (Method Not Allowed)
328   if the method is known by the origin server but not allowed for the
329   requested resource, and 501 (Not Implemented) if the method is
330   unrecognized or not implemented by the origin server. The methods GET
331   and HEAD &MUST; be supported by all general-purpose servers. All other
332   methods are &OPTIONAL;; however, if the above methods are implemented,
333   they &MUST; be implemented with the same semantics as those specified
334   in <xref target="method.definitions"/>.
338<section title="Request Header Fields" anchor="request.header.fields">
340   The request-header fields allow the client to pass additional
341   information about the request, and about the client itself, to the
342   server. These fields act as request modifiers, with semantics
343   equivalent to the parameters on a programming language method
344   invocation.
346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
347  request-header = Accept                   ; &header-accept;
348                 | Accept-Charset           ; &header-accept-charset;
349                 | Accept-Encoding          ; &header-accept-encoding;
350                 | Accept-Language          ; &header-accept-language;
351                 | Authorization            ; &header-authorization;
352                 | Expect                   ; <xref target="header.expect"/>
353                 | From                     ; <xref target="header.from"/>
354                 | Host                     ; &header-host;
355                 | If-Match                 ; &header-if-match;
356                 | If-Modified-Since        ; &header-if-modified-since;
357                 | If-None-Match            ; &header-if-none-match;
358                 | If-Range                 ; &header-if-range;
359                 | If-Unmodified-Since      ; &header-if-unmodified-since;
360                 | Max-Forwards             ; <xref target="header.max-forwards"/>
361                 | Proxy-Authorization      ; &header-proxy-authorization;
362                 | Range                    ; &header-range;
363                 | Referer                  ; <xref target="header.referer"/>
364                 | TE                       ; &header-te;
365                 | User-Agent               ; <xref target="header.user-agent"/>
368   Request-header field names can be extended reliably only in
369   combination with a change in the protocol version. However, new or
370   experimental header fields &MAY; be given the semantics of request-header
371   fields if all parties in the communication recognize them to
372   be request-header fields. Unrecognized header fields are treated as
373   entity-header fields.
377<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
379   The Status-Code element is a 3-digit integer result code of the
380   attempt to understand and satisfy the request. These codes are fully
381   defined in <xref target=""/>. The Reason-Phrase is intended to give a short
382   textual description of the Status-Code. The Status-Code is intended
383   for use by automata and the Reason-Phrase is intended for the human
384   user. The client is not required to examine or display the Reason-Phrase.
387   The individual values of the numeric status codes defined for
388   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
389   presented below. The reason phrases listed here are only
390   recommendations -- they &MAY; be replaced by local equivalents without
391   affecting the protocol.
393<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"/>
394  Status-Code    =
395         "100"  ; <xref target="status.100"/>: Continue
396       | "101"  ; <xref target="status.101"/>: Switching Protocols
397       | "200"  ; <xref target="status.200"/>: OK
398       | "201"  ; <xref target="status.201"/>: Created
399       | "202"  ; <xref target="status.202"/>: Accepted
400       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
401       | "204"  ; <xref target="status.204"/>: No Content
402       | "205"  ; <xref target="status.205"/>: Reset Content
403       | "206"  ; <xref target="status.206"/>: Partial Content
404       | "300"  ; <xref target="status.300"/>: Multiple Choices
405       | "301"  ; <xref target="status.301"/>: Moved Permanently
406       | "302"  ; <xref target="status.302"/>: Found
407       | "303"  ; <xref target="status.303"/>: See Other
408       | "304"  ; <xref target="status.304"/>: Not Modified
409       | "305"  ; <xref target="status.305"/>: Use Proxy
410       | "307"  ; <xref target="status.307"/>: Temporary Redirect
411       | "400"  ; <xref target="status.400"/>: Bad Request
412       | "401"  ; <xref target="status.401"/>: Unauthorized
413       | "402"  ; <xref target="status.402"/>: Payment Required
414       | "403"  ; <xref target="status.403"/>: Forbidden
415       | "404"  ; <xref target="status.404"/>: Not Found
416       | "405"  ; <xref target="status.405"/>: Method Not Allowed
417       | "406"  ; <xref target="status.406"/>: Not Acceptable
418       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
419       | "408"  ; <xref target="status.408"/>: Request Time-out
420       | "409"  ; <xref target="status.409"/>: Conflict
421       | "410"  ; <xref target="status.410"/>: Gone
422       | "411"  ; <xref target="status.411"/>: Length Required
423       | "412"  ; <xref target="status.412"/>: Precondition Failed
424       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
425       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
426       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
427       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
428       | "417"  ; <xref target="status.417"/>: Expectation Failed
429       | "500"  ; <xref target="status.500"/>: Internal Server Error
430       | "501"  ; <xref target="status.501"/>: Not Implemented
431       | "502"  ; <xref target="status.502"/>: Bad Gateway
432       | "503"  ; <xref target="status.503"/>: Service Unavailable
433       | "504"  ; <xref target="status.504"/>: Gateway Time-out
434       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
435       | extension-code
437  extension-code = 3DIGIT
438  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
441   HTTP status codes are extensible. HTTP applications are not required
442   to understand the meaning of all registered status codes, though such
443   understanding is obviously desirable. However, applications &MUST;
444   understand the class of any status code, as indicated by the first
445   digit, and treat any unrecognized response as being equivalent to the
446   x00 status code of that class, with the exception that an
447   unrecognized response &MUST-NOT; be cached. For example, if an
448   unrecognized status code of 431 is received by the client, it can
449   safely assume that there was something wrong with its request and
450   treat the response as if it had received a 400 status code. In such
451   cases, user agents &SHOULD; present to the user the entity returned
452   with the response, since that entity is likely to include human-readable
453   information which will explain the unusual status.
457<section title="Response Header Fields" anchor="response.header.fields">
459   The response-header fields allow the server to pass additional
460   information about the response which cannot be placed in the Status-Line.
461   These header fields give information about the server and about
462   further access to the resource identified by the Request-URI.
464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
465  response-header = Accept-Ranges           ; &header-accept-ranges;
466                  | Age                     ; &header-age;
467                  | ETag                    ; &header-etag;
468                  | Location                ; <xref target="header.location"/>
469                  | Proxy-Authenticate      ; &header-proxy-authenticate;
470                  | Retry-After             ; <xref target="header.retry-after"/>
471                  | Server                  ; <xref target="header.server"/>
472                  | Vary                    ; &header-vary;
473                  | WWW-Authenticate        ; &header-www-authenticate;
476   Response-header field names can be extended reliably only in
477   combination with a change in the protocol version. However, new or
478   experimental header fields &MAY; be given the semantics of response-header
479   fields if all parties in the communication recognize them to
480   be response-header fields. Unrecognized header fields are treated as
481   entity-header fields.
485<section title="Entity" anchor="entity">
487   Request and Response messages &MAY; transfer an entity if not otherwise
488   restricted by the request method or response status code. An entity
489   consists of entity-header fields and an entity-body, although some
490   responses will only include the entity-headers. HTTP entity-body and
491   entity-header fields are defined in &payload;.
494   An entity-body is only present in a message when a message-body is
495   present, as described in &message-body;. The entity-body is obtained
496   from the message-body by decoding any Transfer-Encoding that might
497   have been applied to ensure safe and proper transfer of the message.
502<section title="Method Definitions" anchor="method.definitions">
504   The set of common methods for HTTP/1.1 is defined below. Although
505   this set can be expanded, additional methods cannot be assumed to
506   share the same semantics for separately extended clients and servers.
508   The Host request-header field (&header-host;) &MUST; accompany all
509   HTTP/1.1 requests.
512<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
514<section title="Safe Methods" anchor="safe.methods">
516   Implementors should be aware that the software represents the user in
517   their interactions over the Internet, and should be careful to allow
518   the user to be aware of any actions they might take which may have an
519   unexpected significance to themselves or others.
522   In particular, the convention has been established that the GET and
523   HEAD methods &SHOULD-NOT;  have the significance of taking an action
524   other than retrieval. These methods ought to be considered "safe".
525   This allows user agents to represent other methods, such as POST, PUT
526   and DELETE, in a special way, so that the user is made aware of the
527   fact that a possibly unsafe action is being requested.
530   Naturally, it is not possible to ensure that the server does not
531   generate side-effects as a result of performing a GET request; in
532   fact, some dynamic resources consider that a feature. The important
533   distinction here is that the user did not request the side-effects,
534   so therefore cannot be held accountable for them.
538<section title="Idempotent Methods" anchor="idempotent.methods">
540   Methods can also have the property of "idempotence" in that (aside
541   from error or expiration issues) the side-effects of N &gt; 0 identical
542   requests is the same as for a single request. The methods GET, HEAD,
543   PUT and DELETE share this property. Also, the methods OPTIONS and
544   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
547   However, it is possible that a sequence of several requests is non-idempotent,
548   even if all of the methods executed in that sequence are
549   idempotent. (A sequence is idempotent if a single execution of the
550   entire sequence always yields a result that is not changed by a
551   reexecution of all, or part, of that sequence.) For example, a
552   sequence is non-idempotent if its result depends on a value that is
553   later modified in the same sequence.
556   A sequence that never has side effects is idempotent, by definition
557   (provided that no concurrent operations are being executed on the
558   same set of resources).
563<section title="OPTIONS" anchor="OPTIONS">
564  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
565  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
567   The OPTIONS method represents a request for information about the
568   communication options available on the request/response chain
569   identified by the Request-URI. This method allows the client to
570   determine the options and/or requirements associated with a resource,
571   or the capabilities of a server, without implying a resource action
572   or initiating a resource retrieval.
575   Responses to this method are not cacheable.
578   If the OPTIONS request includes an entity-body (as indicated by the
579   presence of Content-Length or Transfer-Encoding), then the media type
580   &MUST; be indicated by a Content-Type field. Although this
581   specification does not define any use for such a body, future
582   extensions to HTTP might use the OPTIONS body to make more detailed
583   queries on the server. A server that does not support such an
584   extension &MAY; discard the request body.
587   If the Request-URI is an asterisk ("*"), the OPTIONS request is
588   intended to apply to the server in general rather than to a specific
589   resource. Since a server's communication options typically depend on
590   the resource, the "*" request is only useful as a "ping" or "no-op"
591   type of method; it does nothing beyond allowing the client to test
592   the capabilities of the server. For example, this can be used to test
593   a proxy for HTTP/1.1 compliance (or lack thereof).
596   If the Request-URI is not an asterisk, the OPTIONS request applies
597   only to the options that are available when communicating with that
598   resource.
601   A 200 response &SHOULD; include any header fields that indicate
602   optional features implemented by the server and applicable to that
603   resource (e.g., Allow), possibly including extensions not defined by
604   this specification. The response body, if any, &SHOULD; also include
605   information about the communication options. The format for such a
606   body is not defined by this specification, but might be defined by
607   future extensions to HTTP. Content negotiation &MAY; be used to select
608   the appropriate response format. If no response body is included, the
609   response &MUST; include a Content-Length field with a field-value of
610   "0".
613   The Max-Forwards request-header field &MAY; be used to target a
614   specific proxy in the request chain. When a proxy receives an OPTIONS
615   request on an absoluteURI for which request forwarding is permitted,
616   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
617   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
618   instead, the proxy &SHOULD; respond with its own communication options.
619   If the Max-Forwards field-value is an integer greater than zero, the
620   proxy &MUST; decrement the field-value when it forwards the request. If
621   no Max-Forwards field is present in the request, then the forwarded
622   request &MUST-NOT; include a Max-Forwards field.
626<section title="GET" anchor="GET">
627  <iref primary="true" item="GET method" x:for-anchor=""/>
628  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
630   The GET method means retrieve whatever information (in the form of an
631   entity) is identified by the Request-URI. If the Request-URI refers
632   to a data-producing process, it is the produced data which shall be
633   returned as the entity in the response and not the source text of the
634   process, unless that text happens to be the output of the process.
637   The semantics of the GET method change to a "conditional GET" if the
638   request message includes an If-Modified-Since, If-Unmodified-Since,
639   If-Match, If-None-Match, or If-Range header field. A conditional GET
640   method requests that the entity be transferred only under the
641   circumstances described by the conditional header field(s). The
642   conditional GET method is intended to reduce unnecessary network
643   usage by allowing cached entities to be refreshed without requiring
644   multiple requests or transferring data already held by the client.
647   The semantics of the GET method change to a "partial GET" if the
648   request message includes a Range header field. A partial GET requests
649   that only part of the entity be transferred, as described in &header-range;.
650   The partial GET method is intended to reduce unnecessary
651   network usage by allowing partially-retrieved entities to be
652   completed without transferring data already held by the client.
655   The response to a GET request is cacheable if and only if it meets
656   the requirements for HTTP caching described in &caching;.
659   See <xref target=""/> for security considerations when used for forms.
663<section title="HEAD" anchor="HEAD">
664  <iref primary="true" item="HEAD method" x:for-anchor=""/>
665  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
667   The HEAD method is identical to GET except that the server &MUST-NOT;
668   return a message-body in the response. The metainformation contained
669   in the HTTP headers in response to a HEAD request &SHOULD; be identical
670   to the information sent in response to a GET request. This method can
671   be used for obtaining metainformation about the entity implied by the
672   request without transferring the entity-body itself. This method is
673   often used for testing hypertext links for validity, accessibility,
674   and recent modification.
677   The response to a HEAD request &MAY; be cacheable in the sense that the
678   information contained in the response &MAY; be used to update a
679   previously cached entity from that resource. If the new field values
680   indicate that the cached entity differs from the current entity (as
681   would be indicated by a change in Content-Length, Content-MD5, ETag
682   or Last-Modified), then the cache &MUST; treat the cache entry as
683   stale.
687<section title="POST" anchor="POST">
688  <iref primary="true" item="POST method" x:for-anchor=""/>
689  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
691   The POST method is used to request that the origin server accept the
692   entity enclosed in the request as data to be processed by the resource
693   identified by the Request-URI in the Request-Line. POST is designed
694   to allow a uniform method to cover the following functions:
695  <list style="symbols">
696    <t>
697      Annotation of existing resources;
698    </t>
699    <t>
700        Posting a message to a bulletin board, newsgroup, mailing list,
701        or similar group of articles;
702    </t>
703    <t>
704        Providing a block of data, such as the result of submitting a
705        form, to a data-handling process;
706    </t>
707    <t>
708        Extending a database through an append operation.
709    </t>
710  </list>
713   The actual function performed by the POST method is determined by the
714   server and is usually dependent on the Request-URI.
717   The action performed by the POST method might not result in a
718   resource that can be identified by a URI. In this case, either 200
719   (OK) or 204 (No Content) is the appropriate response status,
720   depending on whether or not the response includes an entity that
721   describes the result.
724   If a resource has been created on the origin server, the response
725   &SHOULD; be 201 (Created) and contain an entity which describes the
726   status of the request and refers to the new resource, and a Location
727   header (see <xref target="header.location"/>).
730   Responses to this method are not cacheable, unless the response
731   includes appropriate Cache-Control or Expires header fields. However,
732   the 303 (See Other) response can be used to direct the user agent to
733   retrieve a cacheable resource.
737<section title="PUT" anchor="PUT">
738  <iref primary="true" item="PUT method" x:for-anchor=""/>
739  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
741   The PUT method requests that the enclosed entity be stored under the
742   supplied Request-URI. If the Request-URI refers to an already
743   existing resource, the enclosed entity &SHOULD; be considered as a
744   modified version of the one residing on the origin server. If the
745   Request-URI does not point to an existing resource, and that URI is
746   capable of being defined as a new resource by the requesting user
747   agent, the origin server can create the resource with that URI. If a
748   new resource is created, the origin server &MUST; inform the user agent
749   via the 201 (Created) response. If an existing resource is modified,
750   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
751   to indicate successful completion of the request. If the resource
752   could not be created or modified with the Request-URI, an appropriate
753   error response &SHOULD; be given that reflects the nature of the
754   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
755   (e.g. Content-Range) headers that it does not understand or implement
756   and &MUST; return a 501 (Not Implemented) response in such cases.
759   If the request passes through a cache and the Request-URI identifies
760   one or more currently cached entities, those entries &SHOULD; be
761   treated as stale. Responses to this method are not cacheable.
764   The fundamental difference between the POST and PUT requests is
765   reflected in the different meaning of the Request-URI. The URI in a
766   POST request identifies the resource that will handle the enclosed
767   entity. That resource might be a data-accepting process, a gateway to
768   some other protocol, or a separate entity that accepts annotations.
769   In contrast, the URI in a PUT request identifies the entity enclosed
770   with the request -- the user agent knows what URI is intended and the
771   server &MUST-NOT; attempt to apply the request to some other resource.
772   If the server desires that the request be applied to a different URI,
773   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
774   then make its own decision regarding whether or not to redirect the
775   request.
778   A single resource &MAY; be identified by many different URIs. For
779   example, an article might have a URI for identifying "the current
780   version" which is separate from the URI identifying each particular
781   version. In this case, a PUT request on a general URI might result in
782   several other URIs being defined by the origin server.
785   HTTP/1.1 does not define how a PUT method affects the state of an
786   origin server.
789   Unless otherwise specified for a particular entity-header, the
790   entity-headers in the PUT request &SHOULD; be applied to the resource
791   created or modified by the PUT.
795<section title="DELETE" anchor="DELETE">
796  <iref primary="true" item="DELETE method" x:for-anchor=""/>
797  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
799   The DELETE method requests that the origin server delete the resource
800   identified by the Request-URI. This method &MAY; be overridden by human
801   intervention (or other means) on the origin server. The client cannot
802   be guaranteed that the operation has been carried out, even if the
803   status code returned from the origin server indicates that the action
804   has been completed successfully. However, the server &SHOULD-NOT;
805   indicate success unless, at the time the response is given, it
806   intends to delete the resource or move it to an inaccessible
807   location.
810   A successful response &SHOULD; be 200 (OK) if the response includes an
811   entity describing the status, 202 (Accepted) if the action has not
812   yet been enacted, or 204 (No Content) if the action has been enacted
813   but the response does not include an entity.
816   If the request passes through a cache and the Request-URI identifies
817   one or more currently cached entities, those entries &SHOULD; be
818   treated as stale. Responses to this method are not cacheable.
822<section title="TRACE" anchor="TRACE">
823  <iref primary="true" item="TRACE method" x:for-anchor=""/>
824  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
826   The TRACE method is used to invoke a remote, application-layer loop-back
827   of the request message. The final recipient of the request
828   &SHOULD; reflect the message received back to the client as the
829   entity-body of a 200 (OK) response. The final recipient is either the
830   origin server or the first proxy or gateway to receive a Max-Forwards
831   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
832   &MUST-NOT; include an entity.
835   TRACE allows the client to see what is being received at the other
836   end of the request chain and use that data for testing or diagnostic
837   information. The value of the Via header field (&header-via;) is of
838   particular interest, since it acts as a trace of the request chain.
839   Use of the Max-Forwards header field allows the client to limit the
840   length of the request chain, which is useful for testing a chain of
841   proxies forwarding messages in an infinite loop.
844   If the request is valid, the response &SHOULD; contain the entire
845   request message in the entity-body, with a Content-Type of
846   "message/http". Responses to this method &MUST-NOT; be cached.
850<section title="CONNECT" anchor="CONNECT">
851  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
852  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
854   This specification reserves the method name CONNECT for use with a
855   proxy that can dynamically switch to being a tunnel (e.g. SSL
856   tunneling <xref target="Luo1998"/>).
862<section title="Status Code Definitions" anchor="">
864   Each Status-Code is described below, including a description of which
865   method(s) it can follow and any metainformation required in the
866   response.
869<section title="Informational 1xx" anchor="status.1xx">
871   This class of status code indicates a provisional response,
872   consisting only of the Status-Line and optional headers, and is
873   terminated by an empty line. There are no required headers for this
874   class of status code. Since HTTP/1.0 did not define any 1xx status
875   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
876   except under experimental conditions.
879   A client &MUST; be prepared to accept one or more 1xx status responses
880   prior to a regular response, even if the client does not expect a 100
881   (Continue) status message. Unexpected 1xx status responses &MAY; be
882   ignored by a user agent.
885   Proxies &MUST; forward 1xx responses, unless the connection between the
886   proxy and its client has been closed, or unless the proxy itself
887   requested the generation of the 1xx response. (For example, if a
888   proxy adds a "Expect: 100-continue" field when it forwards a request,
889   then it need not forward the corresponding 100 (Continue)
890   response(s).)
893<section title="100 Continue" anchor="status.100">
894  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
895  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
897   The client &SHOULD; continue with its request. This interim response is
898   used to inform the client that the initial part of the request has
899   been received and has not yet been rejected by the server. The client
900   &SHOULD; continue by sending the remainder of the request or, if the
901   request has already been completed, ignore this response. The server
902   &MUST; send a final response after the request has been completed. See
903   &use100; for detailed discussion of the use and handling of this
904   status code.
908<section title="101 Switching Protocols" anchor="status.101">
909  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
910  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
912   The server understands and is willing to comply with the client's
913   request, via the Upgrade message header field (&header-upgrade;), for a
914   change in the application protocol being used on this connection. The
915   server will switch protocols to those defined by the response's
916   Upgrade header field immediately after the empty line which
917   terminates the 101 response.
920   The protocol &SHOULD; be switched only when it is advantageous to do
921   so. For example, switching to a newer version of HTTP is advantageous
922   over older versions, and switching to a real-time, synchronous
923   protocol might be advantageous when delivering resources that use
924   such features.
929<section title="Successful 2xx" anchor="status.2xx">
931   This class of status code indicates that the client's request was
932   successfully received, understood, and accepted.
935<section title="200 OK" anchor="status.200">
936  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
937  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
939   The request has succeeded. The information returned with the response
940   is dependent on the method used in the request, for example:
941  <list style="hanging">
942    <t hangText="GET">
943          an entity corresponding to the requested resource is sent in
944          the response;
945    </t>
946    <t hangText="HEAD">
947          the entity-header fields corresponding to the requested
948          resource are sent in the response without any message-body;
949    </t>
950    <t hangText="POST">
951      an entity describing or containing the result of the action;
952    </t>
953    <t hangText="TRACE">
954      an entity containing the request message as received by the
955      end server.
956    </t>
957  </list>
961<section title="201 Created" anchor="status.201">
962  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
963  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
965   The request has been fulfilled and resulted in a new resource being
966   created. The newly created resource can be referenced by the URI(s)
967   returned in the entity of the response, with the most specific URI
968   for the resource given by a Location header field. The response
969   &SHOULD; include an entity containing a list of resource
970   characteristics and location(s) from which the user or user agent can
971   choose the one most appropriate. The entity format is specified by
972   the media type given in the Content-Type header field. The origin
973   server &MUST; create the resource before returning the 201 status code.
974   If the action cannot be carried out immediately, the server &SHOULD;
975   respond with 202 (Accepted) response instead.
978   A 201 response &MAY; contain an ETag response header field indicating
979   the current value of the entity tag for the requested variant just
980   created, see &header-etag;.
984<section title="202 Accepted" anchor="status.202">
985  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
986  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
988   The request has been accepted for processing, but the processing has
989   not been completed.  The request might or might not eventually be
990   acted upon, as it might be disallowed when processing actually takes
991   place. There is no facility for re-sending a status code from an
992   asynchronous operation such as this.
995   The 202 response is intentionally non-committal. Its purpose is to
996   allow a server to accept a request for some other process (perhaps a
997   batch-oriented process that is only run once per day) without
998   requiring that the user agent's connection to the server persist
999   until the process is completed. The entity returned with this
1000   response &SHOULD; include an indication of the request's current status
1001   and either a pointer to a status monitor or some estimate of when the
1002   user can expect the request to be fulfilled.
1006<section title="203 Non-Authoritative Information" anchor="status.203">
1007  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1008  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1010   The returned metainformation in the entity-header is not the
1011   definitive set as available from the origin server, but is gathered
1012   from a local or a third-party copy. The set presented &MAY; be a subset
1013   or superset of the original version. For example, including local
1014   annotation information about the resource might result in a superset
1015   of the metainformation known by the origin server. Use of this
1016   response code is not required and is only appropriate when the
1017   response would otherwise be 200 (OK).
1021<section title="204 No Content" anchor="status.204">
1022  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1023  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1025   The server has fulfilled the request but does not need to return an
1026   entity-body, and might want to return updated metainformation. The
1027   response &MAY; include new or updated metainformation in the form of
1028   entity-headers, which if present &SHOULD; be associated with the
1029   requested variant.
1032   If the client is a user agent, it &SHOULD-NOT;  change its document view
1033   from that which caused the request to be sent. This response is
1034   primarily intended to allow input for actions to take place without
1035   causing a change to the user agent's active document view, although
1036   any new or updated metainformation &SHOULD; be applied to the document
1037   currently in the user agent's active view.
1040   The 204 response &MUST-NOT; include a message-body, and thus is always
1041   terminated by the first empty line after the header fields.
1045<section title="205 Reset Content" anchor="status.205">
1046  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1047  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1049   The server has fulfilled the request and the user agent &SHOULD; reset
1050   the document view which caused the request to be sent. This response
1051   is primarily intended to allow input for actions to take place via
1052   user input, followed by a clearing of the form in which the input is
1053   given so that the user can easily initiate another input action. The
1054   response &MUST-NOT; include an entity.
1058<section title="206 Partial Content" anchor="status.206">
1059  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1060  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1062   The server has fulfilled the partial GET request for the resource
1063   and the enclosed entity is a partial representation as defined in &range;.
1068<section title="Redirection 3xx" anchor="status.3xx">
1070   This class of status code indicates that further action needs to be
1071   taken by the user agent in order to fulfill the request.  The action
1072   required &MAY; be carried out by the user agent without interaction
1073   with the user if and only if the method used in the second request is
1074   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1075   such loops generate network traffic for each redirection.
1076  <list><t>
1077      <x:h>Note:</x:h> previous versions of this specification recommended a
1078      maximum of five redirections. Content developers should be aware
1079      that there might be clients that implement such a fixed
1080      limitation.
1081  </t></list>
1084<section title="300 Multiple Choices" anchor="status.300">
1085  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1086  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1088   The requested resource corresponds to any one of a set of
1089   representations, each with its own specific location, and agent-driven
1090   negotiation information (&content-negotiation;) is being provided so that
1091   the user (or user agent) can select a preferred representation and
1092   redirect its request to that location.
1095   Unless it was a HEAD request, the response &SHOULD; include an entity
1096   containing a list of resource characteristics and location(s) from
1097   which the user or user agent can choose the one most appropriate. The
1098   entity format is specified by the media type given in the Content-Type
1099   header field. Depending upon the format and the capabilities of
1100   the user agent, selection of the most appropriate choice &MAY; be
1101   performed automatically. However, this specification does not define
1102   any standard for such automatic selection.
1105   If the server has a preferred choice of representation, it &SHOULD;
1106   include the specific URI for that representation in the Location
1107   field; user agents &MAY; use the Location field value for automatic
1108   redirection. This response is cacheable unless indicated otherwise.
1112<section title="301 Moved Permanently" anchor="status.301">
1113  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1114  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1116   The requested resource has been assigned a new permanent URI and any
1117   future references to this resource &SHOULD; use one of the returned
1118   URIs.  Clients with link editing capabilities ought to automatically
1119   re-link references to the Request-URI to one or more of the new
1120   references returned by the server, where possible. This response is
1121   cacheable unless indicated otherwise.
1124   The new permanent URI &SHOULD; be given by the Location field in the
1125   response. Unless the request method was HEAD, the entity of the
1126   response &SHOULD; contain a short hypertext note with a hyperlink to
1127   the new URI(s).
1130   If the 301 status code is received in response to a request method
1131   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1132   then the request &MAY; be automatically redirected by the user agent without
1133   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1134   request unless it can be confirmed by the user, since this might
1135   change the conditions under which the request was issued.
1136  <list><t>
1137      <x:h>Note:</x:h> When automatically redirecting a POST request after
1138      receiving a 301 status code, some existing HTTP/1.0 user agents
1139      will erroneously change it into a GET request.
1140  </t></list>
1144<section title="302 Found" anchor="status.302">
1145  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1146  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1148   The requested resource resides temporarily under a different URI.
1149   Since the redirection might be altered on occasion, the client &SHOULD;
1150   continue to use the Request-URI for future requests.  This response
1151   is only cacheable if indicated by a Cache-Control or Expires header
1152   field.
1155   The temporary URI &SHOULD; be given by the Location field in the
1156   response. Unless the request method was HEAD, the entity of the
1157   response &SHOULD; contain a short hypertext note with a hyperlink to
1158   the new URI(s).
1161   If the 302 status code is received in response to a request method
1162   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1163   then the request &MAY; be automatically redirected by the user agent without
1164   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1165   request unless it can be confirmed by the user, since this might
1166   change the conditions under which the request was issued.
1167  <list><t>
1168      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1169      to change the method on the redirected request.  However, most
1170      existing user agent implementations treat 302 as if it were a 303
1171      response, performing a GET on the Location field-value regardless
1172      of the original request method. The status codes 303 and 307 have
1173      been added for servers that wish to make unambiguously clear which
1174      kind of reaction is expected of the client.
1175  </t></list>
1179<section title="303 See Other" anchor="status.303">
1180  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1181  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1183   The response to the request can be found under a different URI and
1184   &SHOULD; be retrieved using a GET method on that resource. This method
1185   exists primarily to allow the output of a POST-activated script to
1186   redirect the user agent to a selected resource. The new URI is not a
1187   substitute reference for the originally requested resource. The 303
1188   response &MUST-NOT; be cached, but the response to the second
1189   (redirected) request might be cacheable.
1192   The different URI &SHOULD; be given by the Location field in the
1193   response. Unless the request method was HEAD, the entity of the
1194   response &SHOULD; contain a short hypertext note with a hyperlink to
1195   the new URI(s).
1196  <list><t>
1197      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1198      status. When interoperability with such clients is a concern, the
1199      302 status code may be used instead, since most user agents react
1200      to a 302 response as described here for 303.
1201  </t></list>
1205<section title="304 Not Modified" anchor="status.304">
1206  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1207  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1209   The response to the request has not been modified since the conditions
1210   indicated by the client's conditional GET request, as defined in &conditional;.
1214<section title="305 Use Proxy" anchor="status.305">
1215  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1216  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1218   The requested resource &MUST; be accessed through the proxy given by
1219   the Location field. The Location field gives the URI of the proxy.
1220   The recipient is expected to repeat this single request via the
1221   proxy. 305 responses &MUST; only be generated by origin servers.
1222  <list><t>
1223      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1224      single request, and to be generated by origin servers only.  Not
1225      observing these limitations has significant security consequences.
1226  </t></list>
1230<section title="306 (Unused)" anchor="status.306">
1231  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1234   The 306 status code was used in a previous version of the
1235   specification, is no longer used, and the code is reserved.
1239<section title="307 Temporary Redirect" anchor="status.307">
1240  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1241  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1243   The requested resource resides temporarily under a different URI.
1244   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1245   continue to use the Request-URI for future requests.  This response
1246   is only cacheable if indicated by a Cache-Control or Expires header
1247   field.
1250   The temporary URI &SHOULD; be given by the Location field in the
1251   response. Unless the request method was HEAD, the entity of the
1252   response &SHOULD; contain a short hypertext note with a hyperlink to
1253   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1254   understand the 307 status. Therefore, the note &SHOULD; contain the
1255   information necessary for a user to repeat the original request on
1256   the new URI.
1259   If the 307 status code is received in response to a request method
1260   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1261   then the request &MAY; be automatically redirected by the user agent without
1262   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1263   request unless it can be confirmed by the user, since this might
1264   change the conditions under which the request was issued.
1269<section title="Client Error 4xx" anchor="status.4xx">
1271   The 4xx class of status code is intended for cases in which the
1272   client seems to have erred. Except when responding to a HEAD request,
1273   the server &SHOULD; include an entity containing an explanation of the
1274   error situation, and whether it is a temporary or permanent
1275   condition. These status codes are applicable to any request method.
1276   User agents &SHOULD; display any included entity to the user.
1279   If the client is sending data, a server implementation using TCP
1280   &SHOULD; be careful to ensure that the client acknowledges receipt of
1281   the packet(s) containing the response, before the server closes the
1282   input connection. If the client continues sending data to the server
1283   after the close, the server's TCP stack will send a reset packet to
1284   the client, which may erase the client's unacknowledged input buffers
1285   before they can be read and interpreted by the HTTP application.
1288<section title="400 Bad Request" anchor="status.400">
1289  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1290  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1292   The request could not be understood by the server due to malformed
1293   syntax. The client &SHOULD-NOT;  repeat the request without
1294   modifications.
1298<section title="401 Unauthorized" anchor="status.401">
1299  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1300  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1302   The request requires user authentication (see &auth;).
1306<section title="402 Payment Required" anchor="status.402">
1307  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1308  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1310   This code is reserved for future use.
1314<section title="403 Forbidden" anchor="status.403">
1315  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1316  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1318   The server understood the request, but is refusing to fulfill it.
1319   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1320   If the request method was not HEAD and the server wishes to make
1321   public why the request has not been fulfilled, it &SHOULD; describe the
1322   reason for the refusal in the entity.  If the server does not wish to
1323   make this information available to the client, the status code 404
1324   (Not Found) can be used instead.
1328<section title="404 Not Found" anchor="status.404">
1329  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1330  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1332   The server has not found anything matching the Request-URI. No
1333   indication is given of whether the condition is temporary or
1334   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1335   knows, through some internally configurable mechanism, that an old
1336   resource is permanently unavailable and has no forwarding address.
1337   This status code is commonly used when the server does not wish to
1338   reveal exactly why the request has been refused, or when no other
1339   response is applicable.
1343<section title="405 Method Not Allowed" anchor="status.405">
1344  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1345  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1347   The method specified in the Request-Line is not allowed for the
1348   resource identified by the Request-URI. The response &MUST; include an
1349   Allow header containing a list of valid methods for the requested
1350   resource.
1354<section title="406 Not Acceptable" anchor="status.406">
1355  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1356  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1358   The resource identified by the request is only capable of generating
1359   response entities which have content characteristics not acceptable
1360   according to the accept headers sent in the request.
1363   Unless it was a HEAD request, the response &SHOULD; include an entity
1364   containing a list of available entity characteristics and location(s)
1365   from which the user or user agent can choose the one most
1366   appropriate. The entity format is specified by the media type given
1367   in the Content-Type header field. Depending upon the format and the
1368   capabilities of the user agent, selection of the most appropriate
1369   choice &MAY; be performed automatically. However, this specification
1370   does not define any standard for such automatic selection.
1371  <list><t>
1372      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1373      not acceptable according to the accept headers sent in the
1374      request. In some cases, this may even be preferable to sending a
1375      406 response. User agents are encouraged to inspect the headers of
1376      an incoming response to determine if it is acceptable.
1377  </t></list>
1380   If the response could be unacceptable, a user agent &SHOULD;
1381   temporarily stop receipt of more data and query the user for a
1382   decision on further actions.
1386<section title="407 Proxy Authentication Required" anchor="status.407">
1387  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1388  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1390   This code is similar to 401 (Unauthorized), but indicates that the
1391   client must first authenticate itself with the proxy (see &auth;).
1395<section title="408 Request Timeout" anchor="status.408">
1396  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1397  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1399   The client did not produce a request within the time that the server
1400   was prepared to wait. The client &MAY; repeat the request without
1401   modifications at any later time.
1405<section title="409 Conflict" anchor="status.409">
1406  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1407  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1409   The request could not be completed due to a conflict with the current
1410   state of the resource. This code is only allowed in situations where
1411   it is expected that the user might be able to resolve the conflict
1412   and resubmit the request. The response body &SHOULD; include enough
1413   information for the user to recognize the source of the conflict.
1414   Ideally, the response entity would include enough information for the
1415   user or user agent to fix the problem; however, that might not be
1416   possible and is not required.
1419   Conflicts are most likely to occur in response to a PUT request. For
1420   example, if versioning were being used and the entity being PUT
1421   included changes to a resource which conflict with those made by an
1422   earlier (third-party) request, the server might use the 409 response
1423   to indicate that it can't complete the request. In this case, the
1424   response entity would likely contain a list of the differences
1425   between the two versions in a format defined by the response
1426   Content-Type.
1430<section title="410 Gone" anchor="status.410">
1431  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1432  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1434   The requested resource is no longer available at the server and no
1435   forwarding address is known. This condition is expected to be
1436   considered permanent. Clients with link editing capabilities &SHOULD;
1437   delete references to the Request-URI after user approval. If the
1438   server does not know, or has no facility to determine, whether or not
1439   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1440   used instead. This response is cacheable unless indicated otherwise.
1443   The 410 response is primarily intended to assist the task of web
1444   maintenance by notifying the recipient that the resource is
1445   intentionally unavailable and that the server owners desire that
1446   remote links to that resource be removed. Such an event is common for
1447   limited-time, promotional services and for resources belonging to
1448   individuals no longer working at the server's site. It is not
1449   necessary to mark all permanently unavailable resources as "gone" or
1450   to keep the mark for any length of time -- that is left to the
1451   discretion of the server owner.
1455<section title="411 Length Required" anchor="status.411">
1456  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1457  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1459   The server refuses to accept the request without a defined Content-Length.
1460   The client &MAY; repeat the request if it adds a valid
1461   Content-Length header field containing the length of the message-body
1462   in the request message.
1466<section title="412 Precondition Failed" anchor="status.412">
1467  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1468  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1470   The precondition given in one or more of the request-header fields
1471   evaluated to false when it was tested on the server, as defined in
1472   &conditional;.
1476<section title="413 Request Entity Too Large" anchor="status.413">
1477  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1478  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1480   The server is refusing to process a request because the request
1481   entity is larger than the server is willing or able to process. The
1482   server &MAY; close the connection to prevent the client from continuing
1483   the request.
1486   If the condition is temporary, the server &SHOULD; include a Retry-After
1487   header field to indicate that it is temporary and after what
1488   time the client &MAY; try again.
1492<section title="414 Request-URI Too Long" anchor="status.414">
1493  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1494  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1496   The server is refusing to service the request because the Request-URI
1497   is longer than the server is willing to interpret. This rare
1498   condition is only likely to occur when a client has improperly
1499   converted a POST request to a GET request with long query
1500   information, when the client has descended into a URI "black hole" of
1501   redirection (e.g., a redirected URI prefix that points to a suffix of
1502   itself), or when the server is under attack by a client attempting to
1503   exploit security holes present in some servers using fixed-length
1504   buffers for reading or manipulating the Request-URI.
1508<section title="415 Unsupported Media Type" anchor="status.415">
1509  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1510  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1512   The server is refusing to service the request because the entity of
1513   the request is in a format not supported by the requested resource
1514   for the requested method.
1518<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1519  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1520  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1522   The request included a Range request-header field (&header-range;) and none of
1523   the range-specifier values in this field overlap the current extent
1524   of the selected resource.
1528<section title="417 Expectation Failed" anchor="status.417">
1529  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1530  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1532   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1533   could not be met by this server, or, if the server is a proxy,
1534   the server has unambiguous evidence that the request could not be met
1535   by the next-hop server.
1540<section title="Server Error 5xx" anchor="status.5xx">
1542   Response status codes beginning with the digit "5" indicate cases in
1543   which the server is aware that it has erred or is incapable of
1544   performing the request. Except when responding to a HEAD request, the
1545   server &SHOULD; include an entity containing an explanation of the
1546   error situation, and whether it is a temporary or permanent
1547   condition. User agents &SHOULD; display any included entity to the
1548   user. These response codes are applicable to any request method.
1551<section title="500 Internal Server Error" anchor="status.500">
1552  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1553  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1555   The server encountered an unexpected condition which prevented it
1556   from fulfilling the request.
1560<section title="501 Not Implemented" anchor="status.501">
1561  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1562  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1564   The server does not support the functionality required to fulfill the
1565   request. This is the appropriate response when the server does not
1566   recognize the request method and is not capable of supporting it for
1567   any resource.
1571<section title="502 Bad Gateway" anchor="status.502">
1572  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1573  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1575   The server, while acting as a gateway or proxy, received an invalid
1576   response from the upstream server it accessed in attempting to
1577   fulfill the request.
1581<section title="503 Service Unavailable" anchor="status.503">
1582  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1583  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1585   The server is currently unable to handle the request due to a
1586   temporary overloading or maintenance of the server. The implication
1587   is that this is a temporary condition which will be alleviated after
1588   some delay. If known, the length of the delay &MAY; be indicated in a
1589   Retry-After header. If no Retry-After is given, the client &SHOULD;
1590   handle the response as it would for a 500 response.
1591  <list><t>
1592      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1593      server must use it when becoming overloaded. Some servers may wish
1594      to simply refuse the connection.
1595  </t></list>
1599<section title="504 Gateway Timeout" anchor="status.504">
1600  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1601  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1603   The server, while acting as a gateway or proxy, did not receive a
1604   timely response from the upstream server specified by the URI (e.g.
1605   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1606   to access in attempting to complete the request.
1607  <list><t>
1608      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1609      return 400 or 500 when DNS lookups time out.
1610  </t></list>
1614<section title="505 HTTP Version Not Supported" anchor="status.505">
1615  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1616  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1618   The server does not support, or refuses to support, the HTTP protocol
1619   version that was used in the request message. The server is
1620   indicating that it is unable or unwilling to complete the request
1621   using the same major version as the client, as described in &http-version;,
1622   other than with this error message. The response &SHOULD; contain
1623   an entity describing why that version is not supported and what other
1624   protocols are supported by that server.
1632<section title="Header Field Definitions" anchor="header.fields">
1634   This section defines the syntax and semantics of HTTP/1.1 header fields
1635   related to request and response semantics.
1638   For entity-header fields, both sender and recipient refer to either the
1639   client or the server, depending on who sends and who receives the entity.
1642<section title="Allow" anchor="header.allow">
1643  <iref primary="true" item="Allow header" x:for-anchor=""/>
1644  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1646      The Allow entity-header field lists the set of methods supported
1647      by the resource identified by the Request-URI. The purpose of this
1648      field is strictly to inform the recipient of valid methods
1649      associated with the resource. An Allow header field &MUST; be
1650      present in a 405 (Method Not Allowed) response.
1652<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1653  Allow   = "Allow" ":" #Method
1656      Example of use:
1658<figure><artwork type="example">
1659       Allow: GET, HEAD, PUT
1662      This field cannot prevent a client from trying other methods.
1663      However, the indications given by the Allow header field value
1664      &SHOULD; be followed. The actual set of allowed methods is defined
1665      by the origin server at the time of each request.
1668      The Allow header field &MAY; be provided with a PUT request to
1669      recommend the methods to be supported by the new or modified
1670      resource. The server is not required to support these methods and
1671      &SHOULD; include an Allow header in the response giving the actual
1672      supported methods.
1675      A proxy &MUST-NOT; modify the Allow header field even if it does not
1676      understand all the methods specified, since the user agent might
1677      have other means of communicating with the origin server.
1681<section title="Expect" anchor="header.expect">
1682  <iref primary="true" item="Expect header" x:for-anchor=""/>
1683  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1685   The Expect request-header field is used to indicate that particular
1686   server behaviors are required by the client.
1688<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"/>
1689  Expect       =  "Expect" ":" 1#expectation
1691  expectation  =  "100-continue" | expectation-extension
1692  expectation-extension =  token [ "=" ( token | quoted-string )
1693                           *expect-params ]
1694  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1697   A server that does not understand or is unable to comply with any of
1698   the expectation values in the Expect field of a request &MUST; respond
1699   with appropriate error status. The server &MUST; respond with a 417
1700   (Expectation Failed) status if any of the expectations cannot be met
1701   or, if there are other problems with the request, some other 4xx
1702   status.
1705   This header field is defined with extensible syntax to allow for
1706   future extensions. If a server receives a request containing an
1707   Expect field that includes an expectation-extension that it does not
1708   support, it &MUST; respond with a 417 (Expectation Failed) status.
1711   Comparison of expectation values is case-insensitive for unquoted
1712   tokens (including the 100-continue token), and is case-sensitive for
1713   quoted-string expectation-extensions.
1716   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1717   return a 417 (Expectation Failed) status if it receives a request
1718   with an expectation that it cannot meet. However, the Expect
1719   request-header itself is end-to-end; it &MUST; be forwarded if the
1720   request is forwarded.
1723   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1724   Expect header.
1727   See &use100; for the use of the 100 (Continue) status.
1731<section title="From" anchor="header.from">
1732  <iref primary="true" item="From header" x:for-anchor=""/>
1733  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1735   The From request-header field, if given, &SHOULD; contain an Internet
1736   e-mail address for the human user who controls the requesting user
1737   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1738   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1741  From   = "From" ":" mailbox
1744   An example is:
1746<figure><artwork type="example">
1747    From:
1750   This header field &MAY; be used for logging purposes and as a means for
1751   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1752   be used as an insecure form of access protection. The interpretation
1753   of this field is that the request is being performed on behalf of the
1754   person given, who accepts responsibility for the method performed. In
1755   particular, robot agents &SHOULD; include this header so that the
1756   person responsible for running the robot can be contacted if problems
1757   occur on the receiving end.
1760   The Internet e-mail address in this field &MAY; be separate from the
1761   Internet host which issued the request. For example, when a request
1762   is passed through a proxy the original issuer's address &SHOULD; be
1763   used.
1766   The client &SHOULD-NOT;  send the From header field without the user's
1767   approval, as it might conflict with the user's privacy interests or
1768   their site's security policy. It is strongly recommended that the
1769   user be able to disable, enable, and modify the value of this field
1770   at any time prior to a request.
1774<section title="Location" anchor="header.location">
1775  <iref primary="true" item="Location header" x:for-anchor=""/>
1776  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1778   The Location response-header field is used to redirect the recipient
1779   to a location other than the Request-URI for completion of the
1780   request or identification of a new resource. For 201 (Created)
1781   responses, the Location is that of the new resource which was created
1782   by the request. For 3xx responses, the location &SHOULD; indicate the
1783   server's preferred URI for automatic redirection to the resource. The
1784   field value consists of a single absolute URI.
1786<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1787  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1790   An example is:
1792<figure><artwork type="example">
1793    Location:
1796  <list><t>
1797      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1798      from Location in that the Content-Location identifies the original
1799      location of the entity enclosed in the request. It is therefore
1800      possible for a response to contain header fields for both Location
1801      and Content-Location.
1802  </t></list>
1805   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1806   <list style="symbols">
1807      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1808      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1809      <t>With 305 Use Proxy.</t>
1810   </list>
1814<section title="Max-Forwards" anchor="header.max-forwards">
1815  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1816  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1818   The Max-Forwards request-header field provides a mechanism with the
1819   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1820   number of proxies or gateways that can forward the request to the
1821   next inbound server. This can be useful when the client is attempting
1822   to trace a request chain which appears to be failing or looping in
1823   mid-chain.
1825<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1826  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1829   The Max-Forwards value is a decimal integer indicating the remaining
1830   number of times this request message may be forwarded.
1833   Each proxy or gateway recipient of a TRACE or OPTIONS request
1834   containing a Max-Forwards header field &MUST; check and update its
1835   value prior to forwarding the request. If the received value is zero
1836   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1837   respond as the final recipient. If the received Max-Forwards value is
1838   greater than zero, then the forwarded message &MUST; contain an updated
1839   Max-Forwards field with a value decremented by one (1).
1842   The Max-Forwards header field &MAY; be ignored for all other methods
1843   defined by this specification and for any extension methods for which
1844   it is not explicitly referred to as part of that method definition.
1848<section title="Referer" anchor="header.referer">
1849  <iref primary="true" item="Referer header" x:for-anchor=""/>
1850  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1852   The Referer[sic] request-header field allows the client to specify,
1853   for the server's benefit, the address (URI) of the resource from
1854   which the Request-URI was obtained (the "referrer", although the
1855   header field is misspelled.) The Referer request-header allows a
1856   server to generate lists of back-links to resources for interest,
1857   logging, optimized caching, etc. It also allows obsolete or mistyped
1858   links to be traced for maintenance. The Referer field &MUST-NOT; be
1859   sent if the Request-URI was obtained from a source that does not have
1860   its own URI, such as input from the user keyboard.
1862<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1863  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1866   Example:
1868<figure><artwork type="example">
1869    Referer:
1872   If the field value is a relative URI, it &SHOULD; be interpreted
1873   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1874   <xref target=""/> for security considerations.
1878<section title="Retry-After" anchor="header.retry-after">
1879  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1880  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1882   The Retry-After response-header field can be used with a 503 (Service
1883   Unavailable) response to indicate how long the service is expected to
1884   be unavailable to the requesting client. This field &MAY; also be used
1885   with any 3xx (Redirection) response to indicate the minimum time the
1886   user-agent is asked wait before issuing the redirected request. The
1887   value of this field can be either an HTTP-date or an integer number
1888   of seconds (in decimal) after the time of the response.
1890<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1891  Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1894   Two examples of its use are
1896<figure><artwork type="example">
1897    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1898    Retry-After: 120
1901   In the latter example, the delay is 2 minutes.
1905<section title="Server" anchor="header.server">
1906  <iref primary="true" item="Server header" x:for-anchor=""/>
1907  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1909   The Server response-header field contains information about the
1910   software used by the origin server to handle the request. The field
1911   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1912   identifying the server and any significant subproducts. The product
1913   tokens are listed in order of their significance for identifying the
1914   application.
1916<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1917  Server         = "Server" ":" 1*( product | comment )
1920   Example:
1922<figure><artwork type="example">
1923    Server: CERN/3.0 libwww/2.17
1926   If the response is being forwarded through a proxy, the proxy
1927   application &MUST-NOT; modify the Server response-header. Instead, it
1928   &MUST; include a Via field (as described in &header-via;).
1929  <list><t>
1930      <x:h>Note:</x:h> Revealing the specific software version of the server might
1931      allow the server machine to become more vulnerable to attacks
1932      against software that is known to contain security holes. Server
1933      implementors are encouraged to make this field a configurable
1934      option.
1935  </t></list>
1939<section title="User-Agent" anchor="header.user-agent">
1940  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1941  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1943   The User-Agent request-header field contains information about the
1944   user agent originating the request. This is for statistical purposes,
1945   the tracing of protocol violations, and automated recognition of user
1946   agents for the sake of tailoring responses to avoid particular user
1947   agent limitations. User agents &SHOULD; include this field with
1948   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1949   and comments identifying the agent and any subproducts which form a
1950   significant part of the user agent. By convention, the product tokens
1951   are listed in order of their significance for identifying the
1952   application.
1954<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1955  User-Agent     = "User-Agent" ":" 1*( product | comment )
1958   Example:
1960<figure><artwork type="example">
1961    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1967<section title="IANA Considerations" anchor="IANA.considerations">
1969   TBD.
1973<section title="Security Considerations" anchor="security.considerations">
1975   This section is meant to inform application developers, information
1976   providers, and users of the security limitations in HTTP/1.1 as
1977   described by this document. The discussion does not include
1978   definitive solutions to the problems revealed, though it does make
1979   some suggestions for reducing security risks.
1982<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1984   Like any generic data transfer protocol, HTTP cannot regulate the
1985   content of the data that is transferred, nor is there any a priori
1986   method of determining the sensitivity of any particular piece of
1987   information within the context of any given request. Therefore,
1988   applications &SHOULD; supply as much control over this information as
1989   possible to the provider of that information. Four header fields are
1990   worth special mention in this context: Server, Via, Referer and From.
1993   Revealing the specific software version of the server might allow the
1994   server machine to become more vulnerable to attacks against software
1995   that is known to contain security holes. Implementors &SHOULD; make the
1996   Server header field a configurable option.
1999   Proxies which serve as a portal through a network firewall &SHOULD;
2000   take special precautions regarding the transfer of header information
2001   that identifies the hosts behind the firewall. In particular, they
2002   &SHOULD; remove, or replace with sanitized versions, any Via fields
2003   generated behind the firewall.
2006   The Referer header allows reading patterns to be studied and reverse
2007   links drawn. Although it can be very useful, its power can be abused
2008   if user details are not separated from the information contained in
2009   the Referer. Even when the personal information has been removed, the
2010   Referer header might indicate a private document's URI whose
2011   publication would be inappropriate.
2014   The information sent in the From field might conflict with the user's
2015   privacy interests or their site's security policy, and hence it
2016   &SHOULD-NOT;  be transmitted without the user being able to disable,
2017   enable, and modify the contents of the field. The user &MUST; be able
2018   to set the contents of this field within a user preference or
2019   application defaults configuration.
2022   We suggest, though do not require, that a convenient toggle interface
2023   be provided for the user to enable or disable the sending of From and
2024   Referer information.
2027   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2028   fields can sometimes be used to determine that a specific client or
2029   server have a particular security hole which might be exploited.
2030   Unfortunately, this same information is often used for other valuable
2031   purposes for which HTTP currently has no better mechanism.
2035<section title="Encoding Sensitive Information in URI's" anchor="">
2037   Because the source of a link might be private information or might
2038   reveal an otherwise private information source, it is strongly
2039   recommended that the user be able to select whether or not the
2040   Referer field is sent. For example, a browser client could have a
2041   toggle switch for browsing openly/anonymously, which would
2042   respectively enable/disable the sending of Referer and From
2043   information.
2046   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2047   HTTP request if the referring page was transferred with a secure
2048   protocol.
2051   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2052   based forms for the submission of sensitive data, because this will
2053   cause this data to be encoded in the Request-URI. Many existing
2054   servers, proxies, and user agents will log the request URI in some
2055   place where it might be visible to third parties. Servers can use
2056   POST-based form submission instead
2060<section title="Location Headers and Spoofing" anchor="location.spoofing">
2062   If a single server supports multiple organizations that do not trust
2063   one another, then it &MUST; check the values of Location and Content-Location
2064   headers in responses that are generated under control of
2065   said organizations to make sure that they do not attempt to
2066   invalidate resources over which they have no authority.
2072<section title="Acknowledgments" anchor="ack">
2077<references title="Normative References">
2079<reference anchor="Part1">
2080  <front>
2081    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2082    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2083      <organization abbrev="Day Software">Day Software</organization>
2084      <address><email></email></address>
2085    </author>
2086    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2087      <organization>One Laptop per Child</organization>
2088      <address><email></email></address>
2089    </author>
2090    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2091      <organization abbrev="HP">Hewlett-Packard Company</organization>
2092      <address><email></email></address>
2093    </author>
2094    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2095      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2096      <address><email></email></address>
2097    </author>
2098    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2099      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2100      <address><email></email></address>
2101    </author>
2102    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2103      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2104      <address><email></email></address>
2105    </author>
2106    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2107      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2108      <address><email></email></address>
2109    </author>
2110    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2111      <organization abbrev="W3C">World Wide Web Consortium</organization>
2112      <address><email></email></address>
2113    </author>
2114    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2115      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2116      <address><email></email></address>
2117    </author>
2118    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2119  </front>
2120  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2121  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2124<reference anchor="Part3">
2125  <front>
2126    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2127    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2128      <organization abbrev="Day Software">Day Software</organization>
2129      <address><email></email></address>
2130    </author>
2131    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2132      <organization>One Laptop per Child</organization>
2133      <address><email></email></address>
2134    </author>
2135    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2136      <organization abbrev="HP">Hewlett-Packard Company</organization>
2137      <address><email></email></address>
2138    </author>
2139    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2140      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2141      <address><email></email></address>
2142    </author>
2143    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2144      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2145      <address><email></email></address>
2146    </author>
2147    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2148      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2149      <address><email></email></address>
2150    </author>
2151    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2152      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2153      <address><email></email></address>
2154    </author>
2155    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2156      <organization abbrev="W3C">World Wide Web Consortium</organization>
2157      <address><email></email></address>
2158    </author>
2159    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2160      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2161      <address><email></email></address>
2162    </author>
2163    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2164  </front>
2165  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2166  <x:source href="p3-payload.xml" basename="p3-payload"/>
2169<reference anchor="Part4">
2170  <front>
2171    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2172    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2173      <organization abbrev="Day Software">Day Software</organization>
2174      <address><email></email></address>
2175    </author>
2176    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2177      <organization>One Laptop per Child</organization>
2178      <address><email></email></address>
2179    </author>
2180    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2181      <organization abbrev="HP">Hewlett-Packard Company</organization>
2182      <address><email></email></address>
2183    </author>
2184    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2185      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2186      <address><email></email></address>
2187    </author>
2188    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2189      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2190      <address><email></email></address>
2191    </author>
2192    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2193      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2194      <address><email></email></address>
2195    </author>
2196    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2197      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2198      <address><email></email></address>
2199    </author>
2200    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2201      <organization abbrev="W3C">World Wide Web Consortium</organization>
2202      <address><email></email></address>
2203    </author>
2204    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2205      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2206      <address><email></email></address>
2207    </author>
2208    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2209  </front>
2210  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2211  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2214<reference anchor="Part5">
2215  <front>
2216    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2217    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2218      <organization abbrev="Day Software">Day Software</organization>
2219      <address><email></email></address>
2220    </author>
2221    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2222      <organization>One Laptop per Child</organization>
2223      <address><email></email></address>
2224    </author>
2225    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2226      <organization abbrev="HP">Hewlett-Packard Company</organization>
2227      <address><email></email></address>
2228    </author>
2229    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2230      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2231      <address><email></email></address>
2232    </author>
2233    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2234      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2235      <address><email></email></address>
2236    </author>
2237    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2238      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2239      <address><email></email></address>
2240    </author>
2241    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2242      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2243      <address><email></email></address>
2244    </author>
2245    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2246      <organization abbrev="W3C">World Wide Web Consortium</organization>
2247      <address><email></email></address>
2248    </author>
2249    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2250      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2251      <address><email></email></address>
2252    </author>
2253    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2254  </front>
2255  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2256  <x:source href="p5-range.xml" basename="p5-range"/>
2259<reference anchor="Part6">
2260  <front>
2261    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2262    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2263      <organization abbrev="Day Software">Day Software</organization>
2264      <address><email></email></address>
2265    </author>
2266    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2267      <organization>One Laptop per Child</organization>
2268      <address><email></email></address>
2269    </author>
2270    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2271      <organization abbrev="HP">Hewlett-Packard Company</organization>
2272      <address><email></email></address>
2273    </author>
2274    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2275      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2276      <address><email></email></address>
2277    </author>
2278    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2279      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2280      <address><email></email></address>
2281    </author>
2282    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2283      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2284      <address><email></email></address>
2285    </author>
2286    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2287      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2288      <address><email></email></address>
2289    </author>
2290    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2291      <organization abbrev="W3C">World Wide Web Consortium</organization>
2292      <address><email></email></address>
2293    </author>
2294    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2295      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2296      <address><email></email></address>
2297    </author>
2298    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2299  </front>
2300  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2301  <x:source href="p6-cache.xml" basename="p6-cache"/>
2304<reference anchor="Part7">
2305  <front>
2306    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2307    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2308      <organization abbrev="Day Software">Day Software</organization>
2309      <address><email></email></address>
2310    </author>
2311    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2312      <organization>One Laptop per Child</organization>
2313      <address><email></email></address>
2314    </author>
2315    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2316      <organization abbrev="HP">Hewlett-Packard Company</organization>
2317      <address><email></email></address>
2318    </author>
2319    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2320      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2321      <address><email></email></address>
2322    </author>
2323    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2324      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2325      <address><email></email></address>
2326    </author>
2327    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2328      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2329      <address><email></email></address>
2330    </author>
2331    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2332      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2333      <address><email></email></address>
2334    </author>
2335    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2336      <organization abbrev="W3C">World Wide Web Consortium</organization>
2337      <address><email></email></address>
2338    </author>
2339    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2340      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2341      <address><email></email></address>
2342    </author>
2343    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2344  </front>
2345  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2346  <x:source href="p7-auth.xml" basename="p7-auth"/>
2349<reference anchor="RFC2119">
2350  <front>
2351    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2352    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2353      <organization>Harvard University</organization>
2354      <address><email></email></address>
2355    </author>
2356    <date month="March" year="1997"/>
2357  </front>
2358  <seriesInfo name="BCP" value="14"/>
2359  <seriesInfo name="RFC" value="2119"/>
2364<references title="Informative References">
2366<reference anchor="Luo1998">
2367  <front>
2368    <title>Tunneling TCP based protocols through Web proxy servers</title>
2369    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2370      <organization/>
2371    </author>
2372    <date year="1998" month="August"/>
2373  </front>
2374  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2377<reference anchor="RFC1945">
2378  <front>
2379    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2380    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2381      <organization>MIT, Laboratory for Computer Science</organization>
2382      <address><email></email></address>
2383    </author>
2384    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2385      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2386      <address><email></email></address>
2387    </author>
2388    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2389      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2390      <address><email></email></address>
2391    </author>
2392    <date month="May" year="1996"/>
2393  </front>
2394  <seriesInfo name="RFC" value="1945"/>
2397<reference anchor="RFC2068">
2398  <front>
2399    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2400    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2401      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2402      <address><email></email></address>
2403    </author>
2404    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2405      <organization>MIT Laboratory for Computer Science</organization>
2406      <address><email></email></address>
2407    </author>
2408    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2409      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2410      <address><email></email></address>
2411    </author>
2412    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2413      <organization>MIT Laboratory for Computer Science</organization>
2414      <address><email></email></address>
2415    </author>
2416    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2417      <organization>MIT Laboratory for Computer Science</organization>
2418      <address><email></email></address>
2419    </author>
2420    <date month="January" year="1997"/>
2421  </front>
2422  <seriesInfo name="RFC" value="2068"/>
2425<reference anchor="RFC2616">
2426  <front>
2427    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2428    <author initials="R." surname="Fielding" fullname="R. Fielding">
2429      <organization>University of California, Irvine</organization>
2430      <address><email></email></address>
2431    </author>
2432    <author initials="J." surname="Gettys" fullname="J. Gettys">
2433      <organization>W3C</organization>
2434      <address><email></email></address>
2435    </author>
2436    <author initials="J." surname="Mogul" fullname="J. Mogul">
2437      <organization>Compaq Computer Corporation</organization>
2438      <address><email></email></address>
2439    </author>
2440    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2441      <organization>MIT Laboratory for Computer Science</organization>
2442      <address><email></email></address>
2443    </author>
2444    <author initials="L." surname="Masinter" fullname="L. Masinter">
2445      <organization>Xerox Corporation</organization>
2446      <address><email></email></address>
2447    </author>
2448    <author initials="P." surname="Leach" fullname="P. Leach">
2449      <organization>Microsoft Corporation</organization>
2450      <address><email></email></address>
2451    </author>
2452    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2453      <organization>W3C</organization>
2454      <address><email></email></address>
2455    </author>
2456    <date month="June" year="1999"/>
2457  </front>
2458  <seriesInfo name="RFC" value="2616"/>
2461<reference anchor="RFC2822">
2462  <front>
2463    <title>Internet Message Format</title>
2464    <author initials="P." surname="Resnick" fullname="P. Resnick">
2465      <organization>QUALCOMM Incorporated</organization>
2466    </author>
2467    <date year="2001" month="April"/>
2468  </front>
2469  <seriesInfo name="RFC" value="2822"/>
2474<section title="Compatibility with Previous Versions" anchor="compatibility">
2475<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2477   Clarified which error code should be used for inbound server failures
2478   (e.g. DNS failures). (<xref target="status.504"/>).
2481   201 (Created) had a race that required an Etag be sent when a resource is
2482   first created. (<xref target="status.201"/>).
2485   Rewrite of message transmission requirements to make it much harder
2486   for implementors to get it wrong, as the consequences of errors here
2487   can have significant impact on the Internet, and to deal with the
2488   following problems:
2489  <list style="numbers">
2490      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2491         this was incorrectly placing a requirement on the behavior of
2492         an implementation of a future version of HTTP/1.x</t>
2494      <t>Made it clear that user-agents should retry requests, not
2495         "clients" in general.</t>
2497      <t>Converted requirements for clients to ignore unexpected 100
2498         (Continue) responses, and for proxies to forward 100 responses,
2499         into a general requirement for 1xx responses.</t>
2501      <t>Modified some TCP-specific language, to make it clearer that
2502         non-TCP transports are possible for HTTP.</t>
2504      <t>Require that the origin server &MUST-NOT; wait for the request
2505         body before it sends a required 100 (Continue) response.</t>
2507      <t>Allow, rather than require, a server to omit 100 (Continue) if
2508         it has already seen some of the request body.</t>
2510      <t>Allow servers to defend against denial-of-service attacks and
2511         broken clients.</t>
2512  </list>
2515   This change adds the Expect header and 417 status code.
2518   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2519   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2522   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
2523   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2527<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2529  Clarify definition of POST.
2530  (<xref target="POST"/>)
2533  Failed to consider that there are
2534  many other request methods that are safe to automatically redirect,
2535  and further that the user agent is able to make that determination
2536  based on the request method semantics.
2537  (Sections <xref format="counter" target="status.301"/>,
2538  <xref format="counter" target="status.302"/> and
2539  <xref format="counter" target="status.307"/> )
2542  Correct syntax of Location header to allow fragment,
2543  as referred symbol wasn't what was expected, and add some
2544  clarifications as to when it would not be appropriate.
2545  (<xref target="header.location"/>)
2548  In the description of the Server header, the Via field
2549  was described as a SHOULD. The requirement was and is stated
2550  correctly in the description of the Via header in &header-via;.
2551  (<xref target="header.server"/>)
2557<section title="Change Log (to be removed by RFC Editor before publication)">
2559<section title="Since RFC2616">
2561  Extracted relevant partitions from <xref target="RFC2616"/>.
2565<section title="Since draft-ietf-httpbis-p2-semantics-00">
2567  Closed issues:
2568  <list style="symbols">
2569    <t>
2570      <eref target=""/>:
2571      "Via is a MUST"
2572      (<eref target=""/>)
2573    </t>
2574    <t>
2575      <eref target=""/>:
2576      "Fragments allowed in Location"
2577      (<eref target=""/>)
2578    </t>
2579    <t>
2580      <eref target=""/>:
2581      "Safe Methods vs Redirection"
2582      (<eref target=""/>)
2583    </t>
2584    <t>
2585      <eref target=""/>:
2586      "Revise description of the POST method"
2587      (<eref target=""/>)
2588    </t>
2589    <t>
2590      <eref target=""/>:
2591      "RFC2606 Compliance"
2592    </t>
2593    <t>
2594      <eref target=""/>:
2595      "Informative references"
2596    </t>
2597    <t>
2598      <eref target=""/>:
2599      "Redundant cross-references"
2600    </t>
2601  </list>
2604  Other changes:
2605  <list style="symbols">
2606    <t>
2607      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2608    </t>
2609    <t>
2610      Categorize references as "Normative" or "Informative".
2611    </t>
2612  </list>
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