source: draft-ietf-httpbis/latest/p2-semantics.xml @ 152

Last change on this file since 152 was 152, checked in by julian.reschke@…, 15 years ago

Resolve #35: categorize RFC1737 (URN) as informative, RFC4288 (media type registration procedure) as normative (closes #35). Also update and re-organize media type registration for application/http and message/http to use RFC4288 template (relates to #8).

  • Property svn:eol-style set to native
File size: 119.7 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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="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. The status codes listed
381   below are defined in <xref target=""/>.
382   The Reason-Phrase is intended to give a short
383   textual description of the Status-Code. The Status-Code is intended
384   for use by automata and the Reason-Phrase is intended for the human
385   user. The client is not required to examine or display the Reason-Phrase.
388   The individual values of the numeric status codes defined for
389   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
390   presented below. The reason phrases listed here are only
391   recommendations -- they &MAY; be replaced by local equivalents without
392   affecting the protocol.
394<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"/>
395  Status-Code    =
396         "100"  ; <xref target="status.100"/>: Continue
397       | "101"  ; <xref target="status.101"/>: Switching Protocols
398       | "200"  ; <xref target="status.200"/>: OK
399       | "201"  ; <xref target="status.201"/>: Created
400       | "202"  ; <xref target="status.202"/>: Accepted
401       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
402       | "204"  ; <xref target="status.204"/>: No Content
403       | "205"  ; <xref target="status.205"/>: Reset Content
404       | "206"  ; <xref target="status.206"/>: Partial Content
405       | "300"  ; <xref target="status.300"/>: Multiple Choices
406       | "301"  ; <xref target="status.301"/>: Moved Permanently
407       | "302"  ; <xref target="status.302"/>: Found
408       | "303"  ; <xref target="status.303"/>: See Other
409       | "304"  ; <xref target="status.304"/>: Not Modified
410       | "305"  ; <xref target="status.305"/>: Use Proxy
411       | "307"  ; <xref target="status.307"/>: Temporary Redirect
412       | "400"  ; <xref target="status.400"/>: Bad Request
413       | "401"  ; <xref target="status.401"/>: Unauthorized
414       | "402"  ; <xref target="status.402"/>: Payment Required
415       | "403"  ; <xref target="status.403"/>: Forbidden
416       | "404"  ; <xref target="status.404"/>: Not Found
417       | "405"  ; <xref target="status.405"/>: Method Not Allowed
418       | "406"  ; <xref target="status.406"/>: Not Acceptable
419       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
420       | "408"  ; <xref target="status.408"/>: Request Time-out
421       | "409"  ; <xref target="status.409"/>: Conflict
422       | "410"  ; <xref target="status.410"/>: Gone
423       | "411"  ; <xref target="status.411"/>: Length Required
424       | "412"  ; <xref target="status.412"/>: Precondition Failed
425       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
426       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
427       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
428       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
429       | "417"  ; <xref target="status.417"/>: Expectation Failed
430       | "500"  ; <xref target="status.500"/>: Internal Server Error
431       | "501"  ; <xref target="status.501"/>: Not Implemented
432       | "502"  ; <xref target="status.502"/>: Bad Gateway
433       | "503"  ; <xref target="status.503"/>: Service Unavailable
434       | "504"  ; <xref target="status.504"/>: Gateway Time-out
435       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
436       | extension-code
438  extension-code = 3DIGIT
439  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
442   HTTP status codes are extensible. HTTP applications are not required
443   to understand the meaning of all registered status codes, though such
444   understanding is obviously desirable. However, applications &MUST;
445   understand the class of any status code, as indicated by the first
446   digit, and treat any unrecognized response as being equivalent to the
447   x00 status code of that class, with the exception that an
448   unrecognized response &MUST-NOT; be cached. For example, if an
449   unrecognized status code of 431 is received by the client, it can
450   safely assume that there was something wrong with its request and
451   treat the response as if it had received a 400 status code. In such
452   cases, user agents &SHOULD; present to the user the entity returned
453   with the response, since that entity is likely to include human-readable
454   information which will explain the unusual status.
458<section title="Response Header Fields" anchor="response.header.fields">
460   The response-header fields allow the server to pass additional
461   information about the response which cannot be placed in the Status-Line.
462   These header fields give information about the server and about
463   further access to the resource identified by the Request-URI.
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
466  response-header = Accept-Ranges           ; &header-accept-ranges;
467                  | Age                     ; &header-age;
468                  | ETag                    ; &header-etag;
469                  | Location                ; <xref target="header.location"/>
470                  | Proxy-Authenticate      ; &header-proxy-authenticate;
471                  | Retry-After             ; <xref target="header.retry-after"/>
472                  | Server                  ; <xref target="header.server"/>
473                  | Vary                    ; &header-vary;
474                  | WWW-Authenticate        ; &header-www-authenticate;
477   Response-header field names can be extended reliably only in
478   combination with a change in the protocol version. However, new or
479   experimental header fields &MAY; be given the semantics of response-header
480   fields if all parties in the communication recognize them to
481   be response-header fields. Unrecognized header fields are treated as
482   entity-header fields.
486<section title="Entity" anchor="entity">
488   Request and Response messages &MAY; transfer an entity if not otherwise
489   restricted by the request method or response status code. An entity
490   consists of entity-header fields and an entity-body, although some
491   responses will only include the entity-headers. HTTP entity-body and
492   entity-header fields are defined in &payload;.
495   An entity-body is only present in a message when a message-body is
496   present, as described in &message-body;. The entity-body is obtained
497   from the message-body by decoding any Transfer-Encoding that might
498   have been applied to ensure safe and proper transfer of the message.
503<section title="Method Definitions" anchor="method.definitions">
505   The set of common methods for HTTP/1.1 is defined below. Although
506   this set can be expanded, additional methods cannot be assumed to
507   share the same semantics for separately extended clients and servers.
509   The Host request-header field (&header-host;) &MUST; accompany all
510   HTTP/1.1 requests.
513<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
515<section title="Safe Methods" anchor="safe.methods">
517   Implementors should be aware that the software represents the user in
518   their interactions over the Internet, and should be careful to allow
519   the user to be aware of any actions they might take which may have an
520   unexpected significance to themselves or others.
523   In particular, the convention has been established that the GET and
524   HEAD methods &SHOULD-NOT;  have the significance of taking an action
525   other than retrieval. These methods ought to be considered "safe".
526   This allows user agents to represent other methods, such as POST, PUT
527   and DELETE, in a special way, so that the user is made aware of the
528   fact that a possibly unsafe action is being requested.
531   Naturally, it is not possible to ensure that the server does not
532   generate side-effects as a result of performing a GET request; in
533   fact, some dynamic resources consider that a feature. The important
534   distinction here is that the user did not request the side-effects,
535   so therefore cannot be held accountable for them.
539<section title="Idempotent Methods" anchor="idempotent.methods">
541   Methods can also have the property of "idempotence" in that (aside
542   from error or expiration issues) the side-effects of N &gt; 0 identical
543   requests is the same as for a single request. The methods GET, HEAD,
544   PUT and DELETE share this property. Also, the methods OPTIONS and
545   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
548   However, it is possible that a sequence of several requests is non-idempotent,
549   even if all of the methods executed in that sequence are
550   idempotent. (A sequence is idempotent if a single execution of the
551   entire sequence always yields a result that is not changed by a
552   reexecution of all, or part, of that sequence.) For example, a
553   sequence is non-idempotent if its result depends on a value that is
554   later modified in the same sequence.
557   A sequence that never has side effects is idempotent, by definition
558   (provided that no concurrent operations are being executed on the
559   same set of resources).
564<section title="OPTIONS" anchor="OPTIONS">
565  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
566  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
568   The OPTIONS method represents a request for information about the
569   communication options available on the request/response chain
570   identified by the Request-URI. This method allows the client to
571   determine the options and/or requirements associated with a resource,
572   or the capabilities of a server, without implying a resource action
573   or initiating a resource retrieval.
576   Responses to this method are not cacheable.
579   If the OPTIONS request includes an entity-body (as indicated by the
580   presence of Content-Length or Transfer-Encoding), then the media type
581   &MUST; be indicated by a Content-Type field. Although this
582   specification does not define any use for such a body, future
583   extensions to HTTP might use the OPTIONS body to make more detailed
584   queries on the server. A server that does not support such an
585   extension &MAY; discard the request body.
588   If the Request-URI is an asterisk ("*"), the OPTIONS request is
589   intended to apply to the server in general rather than to a specific
590   resource. Since a server's communication options typically depend on
591   the resource, the "*" request is only useful as a "ping" or "no-op"
592   type of method; it does nothing beyond allowing the client to test
593   the capabilities of the server. For example, this can be used to test
594   a proxy for HTTP/1.1 compliance (or lack thereof).
597   If the Request-URI is not an asterisk, the OPTIONS request applies
598   only to the options that are available when communicating with that
599   resource.
602   A 200 response &SHOULD; include any header fields that indicate
603   optional features implemented by the server and applicable to that
604   resource (e.g., Allow), possibly including extensions not defined by
605   this specification. The response body, if any, &SHOULD; also include
606   information about the communication options. The format for such a
607   body is not defined by this specification, but might be defined by
608   future extensions to HTTP. Content negotiation &MAY; be used to select
609   the appropriate response format. If no response body is included, the
610   response &MUST; include a Content-Length field with a field-value of
611   "0".
614   The Max-Forwards request-header field &MAY; be used to target a
615   specific proxy in the request chain. When a proxy receives an OPTIONS
616   request on an absoluteURI for which request forwarding is permitted,
617   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
618   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
619   instead, the proxy &SHOULD; respond with its own communication options.
620   If the Max-Forwards field-value is an integer greater than zero, the
621   proxy &MUST; decrement the field-value when it forwards the request. If
622   no Max-Forwards field is present in the request, then the forwarded
623   request &MUST-NOT; include a Max-Forwards field.
627<section title="GET" anchor="GET">
628  <iref primary="true" item="GET method" x:for-anchor=""/>
629  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
631   The GET method means retrieve whatever information (in the form of an
632   entity) is identified by the Request-URI. If the Request-URI refers
633   to a data-producing process, it is the produced data which shall be
634   returned as the entity in the response and not the source text of the
635   process, unless that text happens to be the output of the process.
638   The semantics of the GET method change to a "conditional GET" if the
639   request message includes an If-Modified-Since, If-Unmodified-Since,
640   If-Match, If-None-Match, or If-Range header field. A conditional GET
641   method requests that the entity be transferred only under the
642   circumstances described by the conditional header field(s). The
643   conditional GET method is intended to reduce unnecessary network
644   usage by allowing cached entities to be refreshed without requiring
645   multiple requests or transferring data already held by the client.
648   The semantics of the GET method change to a "partial GET" if the
649   request message includes a Range header field. A partial GET requests
650   that only part of the entity be transferred, as described in &header-range;.
651   The partial GET method is intended to reduce unnecessary
652   network usage by allowing partially-retrieved entities to be
653   completed without transferring data already held by the client.
656   The response to a GET request is cacheable if and only if it meets
657   the requirements for HTTP caching described in &caching;.
660   See <xref target=""/> for security considerations when used for forms.
664<section title="HEAD" anchor="HEAD">
665  <iref primary="true" item="HEAD method" x:for-anchor=""/>
666  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
668   The HEAD method is identical to GET except that the server &MUST-NOT;
669   return a message-body in the response. The metainformation contained
670   in the HTTP headers in response to a HEAD request &SHOULD; be identical
671   to the information sent in response to a GET request. This method can
672   be used for obtaining metainformation about the entity implied by the
673   request without transferring the entity-body itself. This method is
674   often used for testing hypertext links for validity, accessibility,
675   and recent modification.
678   The response to a HEAD request &MAY; be cacheable in the sense that the
679   information contained in the response &MAY; be used to update a
680   previously cached entity from that resource. If the new field values
681   indicate that the cached entity differs from the current entity (as
682   would be indicated by a change in Content-Length, Content-MD5, ETag
683   or Last-Modified), then the cache &MUST; treat the cache entry as
684   stale.
688<section title="POST" anchor="POST">
689  <iref primary="true" item="POST method" x:for-anchor=""/>
690  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
692   The POST method is used to request that the origin server accept the
693   entity enclosed in the request as data to be processed by the resource
694   identified by the Request-URI in the Request-Line. POST is designed
695   to allow a uniform method to cover the following functions:
696  <list style="symbols">
697    <t>
698      Annotation of existing resources;
699    </t>
700    <t>
701        Posting a message to a bulletin board, newsgroup, mailing list,
702        or similar group of articles;
703    </t>
704    <t>
705        Providing a block of data, such as the result of submitting a
706        form, to a data-handling process;
707    </t>
708    <t>
709        Extending a database through an append operation.
710    </t>
711  </list>
714   The actual function performed by the POST method is determined by the
715   server and is usually dependent on the Request-URI.
718   The action performed by the POST method might not result in a
719   resource that can be identified by a URI. In this case, either 200
720   (OK) or 204 (No Content) is the appropriate response status,
721   depending on whether or not the response includes an entity that
722   describes the result.
725   If a resource has been created on the origin server, the response
726   &SHOULD; be 201 (Created) and contain an entity which describes the
727   status of the request and refers to the new resource, and a Location
728   header (see <xref target="header.location"/>).
731   Responses to this method are not cacheable, unless the response
732   includes appropriate Cache-Control or Expires header fields. However,
733   the 303 (See Other) response can be used to direct the user agent to
734   retrieve a cacheable resource.
738<section title="PUT" anchor="PUT">
739  <iref primary="true" item="PUT method" x:for-anchor=""/>
740  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
742   The PUT method requests that the enclosed entity be stored under the
743   supplied Request-URI. If the Request-URI refers to an already
744   existing resource, the enclosed entity &SHOULD; be considered as a
745   modified version of the one residing on the origin server. If the
746   Request-URI does not point to an existing resource, and that URI is
747   capable of being defined as a new resource by the requesting user
748   agent, the origin server can create the resource with that URI. If a
749   new resource is created, the origin server &MUST; inform the user agent
750   via the 201 (Created) response. If an existing resource is modified,
751   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
752   to indicate successful completion of the request. If the resource
753   could not be created or modified with the Request-URI, an appropriate
754   error response &SHOULD; be given that reflects the nature of the
755   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
756   (e.g. Content-Range) headers that it does not understand or implement
757   and &MUST; return a 501 (Not Implemented) response in such cases.
760   If the request passes through a cache and the Request-URI identifies
761   one or more currently cached entities, those entries &SHOULD; be
762   treated as stale. Responses to this method are not cacheable.
765   The fundamental difference between the POST and PUT requests is
766   reflected in the different meaning of the Request-URI. The URI in a
767   POST request identifies the resource that will handle the enclosed
768   entity. That resource might be a data-accepting process, a gateway to
769   some other protocol, or a separate entity that accepts annotations.
770   In contrast, the URI in a PUT request identifies the entity enclosed
771   with the request -- the user agent knows what URI is intended and the
772   server &MUST-NOT; attempt to apply the request to some other resource.
773   If the server desires that the request be applied to a different URI,
774   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
775   then make its own decision regarding whether or not to redirect the
776   request.
779   A single resource &MAY; be identified by many different URIs. For
780   example, an article might have a URI for identifying "the current
781   version" which is separate from the URI identifying each particular
782   version. In this case, a PUT request on a general URI might result in
783   several other URIs being defined by the origin server.
786   HTTP/1.1 does not define how a PUT method affects the state of an
787   origin server.
790   Unless otherwise specified for a particular entity-header, the
791   entity-headers in the PUT request &SHOULD; be applied to the resource
792   created or modified by the PUT.
796<section title="DELETE" anchor="DELETE">
797  <iref primary="true" item="DELETE method" x:for-anchor=""/>
798  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
800   The DELETE method requests that the origin server delete the resource
801   identified by the Request-URI. This method &MAY; be overridden by human
802   intervention (or other means) on the origin server. The client cannot
803   be guaranteed that the operation has been carried out, even if the
804   status code returned from the origin server indicates that the action
805   has been completed successfully. However, the server &SHOULD-NOT;
806   indicate success unless, at the time the response is given, it
807   intends to delete the resource or move it to an inaccessible
808   location.
811   A successful response &SHOULD; be 200 (OK) if the response includes an
812   entity describing the status, 202 (Accepted) if the action has not
813   yet been enacted, or 204 (No Content) if the action has been enacted
814   but the response does not include an entity.
817   If the request passes through a cache and the Request-URI identifies
818   one or more currently cached entities, those entries &SHOULD; be
819   treated as stale. Responses to this method are not cacheable.
823<section title="TRACE" anchor="TRACE">
824  <iref primary="true" item="TRACE method" x:for-anchor=""/>
825  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
827   The TRACE method is used to invoke a remote, application-layer loop-back
828   of the request message. The final recipient of the request
829   &SHOULD; reflect the message received back to the client as the
830   entity-body of a 200 (OK) response. The final recipient is either the
831   origin server or the first proxy or gateway to receive a Max-Forwards
832   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
833   &MUST-NOT; include an entity.
836   TRACE allows the client to see what is being received at the other
837   end of the request chain and use that data for testing or diagnostic
838   information. The value of the Via header field (&header-via;) is of
839   particular interest, since it acts as a trace of the request chain.
840   Use of the Max-Forwards header field allows the client to limit the
841   length of the request chain, which is useful for testing a chain of
842   proxies forwarding messages in an infinite loop.
845   If the request is valid, the response &SHOULD; contain the entire
846   request message in the entity-body, with a Content-Type of
847   "message/http". Responses to this method &MUST-NOT; be cached.
851<section title="CONNECT" anchor="CONNECT">
852  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
853  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
855   This specification reserves the method name CONNECT for use with a
856   proxy that can dynamically switch to being a tunnel (e.g. SSL
857   tunneling <xref target="Luo1998"/>).
863<section title="Status Code Definitions" anchor="">
865   Each Status-Code is described below, including a description of which
866   method(s) it can follow and any metainformation required in the
867   response.
870<section title="Informational 1xx" anchor="status.1xx">
872   This class of status code indicates a provisional response,
873   consisting only of the Status-Line and optional headers, and is
874   terminated by an empty line. There are no required headers for this
875   class of status code. Since HTTP/1.0 did not define any 1xx status
876   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
877   except under experimental conditions.
880   A client &MUST; be prepared to accept one or more 1xx status responses
881   prior to a regular response, even if the client does not expect a 100
882   (Continue) status message. Unexpected 1xx status responses &MAY; be
883   ignored by a user agent.
886   Proxies &MUST; forward 1xx responses, unless the connection between the
887   proxy and its client has been closed, or unless the proxy itself
888   requested the generation of the 1xx response. (For example, if a
889   proxy adds a "Expect: 100-continue" field when it forwards a request,
890   then it need not forward the corresponding 100 (Continue)
891   response(s).)
894<section title="100 Continue" anchor="status.100">
895  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
896  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
898   The client &SHOULD; continue with its request. This interim response is
899   used to inform the client that the initial part of the request has
900   been received and has not yet been rejected by the server. The client
901   &SHOULD; continue by sending the remainder of the request or, if the
902   request has already been completed, ignore this response. The server
903   &MUST; send a final response after the request has been completed. See
904   &use100; for detailed discussion of the use and handling of this
905   status code.
909<section title="101 Switching Protocols" anchor="status.101">
910  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
911  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
913   The server understands and is willing to comply with the client's
914   request, via the Upgrade message header field (&header-upgrade;), for a
915   change in the application protocol being used on this connection. The
916   server will switch protocols to those defined by the response's
917   Upgrade header field immediately after the empty line which
918   terminates the 101 response.
921   The protocol &SHOULD; be switched only when it is advantageous to do
922   so. For example, switching to a newer version of HTTP is advantageous
923   over older versions, and switching to a real-time, synchronous
924   protocol might be advantageous when delivering resources that use
925   such features.
930<section title="Successful 2xx" anchor="status.2xx">
932   This class of status code indicates that the client's request was
933   successfully received, understood, and accepted.
936<section title="200 OK" anchor="status.200">
937  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
938  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
940   The request has succeeded. The information returned with the response
941   is dependent on the method used in the request, for example:
942  <list style="hanging">
943    <t hangText="GET">
944          an entity corresponding to the requested resource is sent in
945          the response;
946    </t>
947    <t hangText="HEAD">
948          the entity-header fields corresponding to the requested
949          resource are sent in the response without any message-body;
950    </t>
951    <t hangText="POST">
952      an entity describing or containing the result of the action;
953    </t>
954    <t hangText="TRACE">
955      an entity containing the request message as received by the
956      end server.
957    </t>
958  </list>
962<section title="201 Created" anchor="status.201">
963  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
964  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
966   The request has been fulfilled and resulted in a new resource being
967   created. The newly created resource can be referenced by the URI(s)
968   returned in the entity of the response, with the most specific URI
969   for the resource given by a Location header field. The response
970   &SHOULD; include an entity containing a list of resource
971   characteristics and location(s) from which the user or user agent can
972   choose the one most appropriate. The entity format is specified by
973   the media type given in the Content-Type header field. The origin
974   server &MUST; create the resource before returning the 201 status code.
975   If the action cannot be carried out immediately, the server &SHOULD;
976   respond with 202 (Accepted) response instead.
979   A 201 response &MAY; contain an ETag response header field indicating
980   the current value of the entity tag for the requested variant just
981   created, see &header-etag;.
985<section title="202 Accepted" anchor="status.202">
986  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
987  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
989   The request has been accepted for processing, but the processing has
990   not been completed.  The request might or might not eventually be
991   acted upon, as it might be disallowed when processing actually takes
992   place. There is no facility for re-sending a status code from an
993   asynchronous operation such as this.
996   The 202 response is intentionally non-committal. Its purpose is to
997   allow a server to accept a request for some other process (perhaps a
998   batch-oriented process that is only run once per day) without
999   requiring that the user agent's connection to the server persist
1000   until the process is completed. The entity returned with this
1001   response &SHOULD; include an indication of the request's current status
1002   and either a pointer to a status monitor or some estimate of when the
1003   user can expect the request to be fulfilled.
1007<section title="203 Non-Authoritative Information" anchor="status.203">
1008  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1009  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1011   The returned metainformation in the entity-header is not the
1012   definitive set as available from the origin server, but is gathered
1013   from a local or a third-party copy. The set presented &MAY; be a subset
1014   or superset of the original version. For example, including local
1015   annotation information about the resource might result in a superset
1016   of the metainformation known by the origin server. Use of this
1017   response code is not required and is only appropriate when the
1018   response would otherwise be 200 (OK).
1022<section title="204 No Content" anchor="status.204">
1023  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1024  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1026   The server has fulfilled the request but does not need to return an
1027   entity-body, and might want to return updated metainformation. The
1028   response &MAY; include new or updated metainformation in the form of
1029   entity-headers, which if present &SHOULD; be associated with the
1030   requested variant.
1033   If the client is a user agent, it &SHOULD-NOT;  change its document view
1034   from that which caused the request to be sent. This response is
1035   primarily intended to allow input for actions to take place without
1036   causing a change to the user agent's active document view, although
1037   any new or updated metainformation &SHOULD; be applied to the document
1038   currently in the user agent's active view.
1041   The 204 response &MUST-NOT; include a message-body, and thus is always
1042   terminated by the first empty line after the header fields.
1046<section title="205 Reset Content" anchor="status.205">
1047  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1048  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1050   The server has fulfilled the request and the user agent &SHOULD; reset
1051   the document view which caused the request to be sent. This response
1052   is primarily intended to allow input for actions to take place via
1053   user input, followed by a clearing of the form in which the input is
1054   given so that the user can easily initiate another input action. The
1055   response &MUST-NOT; include an entity.
1059<section title="206 Partial Content" anchor="status.206">
1060  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1061  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1063   The server has fulfilled the partial GET request for the resource
1064   and the enclosed entity is a partial representation as defined in &range;.
1069<section title="Redirection 3xx" anchor="status.3xx">
1071   This class of status code indicates that further action needs to be
1072   taken by the user agent in order to fulfill the request.  The action
1073   required &MAY; be carried out by the user agent without interaction
1074   with the user if and only if the method used in the second request is
1075   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1076   such loops generate network traffic for each redirection.
1077  <list><t>
1078      <x:h>Note:</x:h> previous versions of this specification recommended a
1079      maximum of five redirections. Content developers should be aware
1080      that there might be clients that implement such a fixed
1081      limitation.
1082  </t></list>
1085<section title="300 Multiple Choices" anchor="status.300">
1086  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1087  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1089   The requested resource corresponds to any one of a set of
1090   representations, each with its own specific location, and agent-driven
1091   negotiation information (&content-negotiation;) is being provided so that
1092   the user (or user agent) can select a preferred representation and
1093   redirect its request to that location.
1096   Unless it was a HEAD request, the response &SHOULD; include an entity
1097   containing a list of resource characteristics and location(s) from
1098   which the user or user agent can choose the one most appropriate. The
1099   entity format is specified by the media type given in the Content-Type
1100   header field. Depending upon the format and the capabilities of
1101   the user agent, selection of the most appropriate choice &MAY; be
1102   performed automatically. However, this specification does not define
1103   any standard for such automatic selection.
1106   If the server has a preferred choice of representation, it &SHOULD;
1107   include the specific URI for that representation in the Location
1108   field; user agents &MAY; use the Location field value for automatic
1109   redirection. This response is cacheable unless indicated otherwise.
1113<section title="301 Moved Permanently" anchor="status.301">
1114  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1115  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1117   The requested resource has been assigned a new permanent URI and any
1118   future references to this resource &SHOULD; use one of the returned
1119   URIs.  Clients with link editing capabilities ought to automatically
1120   re-link references to the Request-URI to one or more of the new
1121   references returned by the server, where possible. This response is
1122   cacheable unless indicated otherwise.
1125   The new permanent URI &SHOULD; be given by the Location field in the
1126   response. Unless the request method was HEAD, the entity of the
1127   response &SHOULD; contain a short hypertext note with a hyperlink to
1128   the new URI(s).
1131   If the 301 status code is received in response to a request method
1132   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1133   then the request &MAY; be automatically redirected by the user agent without
1134   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1135   request unless it can be confirmed by the user, since this might
1136   change the conditions under which the request was issued.
1137  <list><t>
1138      <x:h>Note:</x:h> When automatically redirecting a POST request after
1139      receiving a 301 status code, some existing HTTP/1.0 user agents
1140      will erroneously change it into a GET request.
1141  </t></list>
1145<section title="302 Found" anchor="status.302">
1146  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1147  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1149   The requested resource resides temporarily under a different URI.
1150   Since the redirection might be altered on occasion, the client &SHOULD;
1151   continue to use the Request-URI for future requests.  This response
1152   is only cacheable if indicated by a Cache-Control or Expires header
1153   field.
1156   The temporary URI &SHOULD; be given by the Location field in the
1157   response. Unless the request method was HEAD, the entity of the
1158   response &SHOULD; contain a short hypertext note with a hyperlink to
1159   the new URI(s).
1162   If the 302 status code is received in response to a request method
1163   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1164   then the request &MAY; be automatically redirected by the user agent without
1165   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1166   request unless it can be confirmed by the user, since this might
1167   change the conditions under which the request was issued.
1168  <list><t>
1169      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1170      to change the method on the redirected request.  However, most
1171      existing user agent implementations treat 302 as if it were a 303
1172      response, performing a GET on the Location field-value regardless
1173      of the original request method. The status codes 303 and 307 have
1174      been added for servers that wish to make unambiguously clear which
1175      kind of reaction is expected of the client.
1176  </t></list>
1180<section title="303 See Other" anchor="status.303">
1181  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1182  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1184   The response to the request can be found under a different URI and
1185   &SHOULD; be retrieved using a GET method on that resource. This method
1186   exists primarily to allow the output of a POST-activated script to
1187   redirect the user agent to a selected resource. The new URI is not a
1188   substitute reference for the originally requested resource. The 303
1189   response &MUST-NOT; be cached, but the response to the second
1190   (redirected) request might be cacheable.
1193   The different URI &SHOULD; be given by the Location field in the
1194   response. Unless the request method was HEAD, the entity of the
1195   response &SHOULD; contain a short hypertext note with a hyperlink to
1196   the new URI(s).
1197  <list><t>
1198      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1199      status. When interoperability with such clients is a concern, the
1200      302 status code may be used instead, since most user agents react
1201      to a 302 response as described here for 303.
1202  </t></list>
1206<section title="304 Not Modified" anchor="status.304">
1207  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1208  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1210   The response to the request has not been modified since the conditions
1211   indicated by the client's conditional GET request, as defined in &conditional;.
1215<section title="305 Use Proxy" anchor="status.305">
1216  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1217  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1219   The requested resource &MUST; be accessed through the proxy given by
1220   the Location field. The Location field gives the URI of the proxy.
1221   The recipient is expected to repeat this single request via the
1222   proxy. 305 responses &MUST; only be generated by origin servers.
1223  <list><t>
1224      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1225      single request, and to be generated by origin servers only.  Not
1226      observing these limitations has significant security consequences.
1227  </t></list>
1231<section title="306 (Unused)" anchor="status.306">
1232  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1233  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1235   The 306 status code was used in a previous version of the
1236   specification, is no longer used, and the code is reserved.
1240<section title="307 Temporary Redirect" anchor="status.307">
1241  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1242  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1244   The requested resource resides temporarily under a different URI.
1245   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1246   continue to use the Request-URI for future requests.  This response
1247   is only cacheable if indicated by a Cache-Control or Expires header
1248   field.
1251   The temporary URI &SHOULD; be given by the Location field in the
1252   response. Unless the request method was HEAD, the entity of the
1253   response &SHOULD; contain a short hypertext note with a hyperlink to
1254   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1255   understand the 307 status. Therefore, the note &SHOULD; contain the
1256   information necessary for a user to repeat the original request on
1257   the new URI.
1260   If the 307 status code is received in response to a request method
1261   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1262   then the request &MAY; be automatically redirected by the user agent without
1263   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1264   request unless it can be confirmed by the user, since this might
1265   change the conditions under which the request was issued.
1270<section title="Client Error 4xx" anchor="status.4xx">
1272   The 4xx class of status code is intended for cases in which the
1273   client seems to have erred. Except when responding to a HEAD request,
1274   the server &SHOULD; include an entity containing an explanation of the
1275   error situation, and whether it is a temporary or permanent
1276   condition. These status codes are applicable to any request method.
1277   User agents &SHOULD; display any included entity to the user.
1280   If the client is sending data, a server implementation using TCP
1281   &SHOULD; be careful to ensure that the client acknowledges receipt of
1282   the packet(s) containing the response, before the server closes the
1283   input connection. If the client continues sending data to the server
1284   after the close, the server's TCP stack will send a reset packet to
1285   the client, which may erase the client's unacknowledged input buffers
1286   before they can be read and interpreted by the HTTP application.
1289<section title="400 Bad Request" anchor="status.400">
1290  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1291  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1293   The request could not be understood by the server due to malformed
1294   syntax. The client &SHOULD-NOT;  repeat the request without
1295   modifications.
1299<section title="401 Unauthorized" anchor="status.401">
1300  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1301  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1303   The request requires user authentication (see &auth;).
1307<section title="402 Payment Required" anchor="status.402">
1308  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1309  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1311   This code is reserved for future use.
1315<section title="403 Forbidden" anchor="status.403">
1316  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1317  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1319   The server understood the request, but is refusing to fulfill it.
1320   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1321   If the request method was not HEAD and the server wishes to make
1322   public why the request has not been fulfilled, it &SHOULD; describe the
1323   reason for the refusal in the entity.  If the server does not wish to
1324   make this information available to the client, the status code 404
1325   (Not Found) can be used instead.
1329<section title="404 Not Found" anchor="status.404">
1330  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1331  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1333   The server has not found anything matching the Request-URI. No
1334   indication is given of whether the condition is temporary or
1335   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1336   knows, through some internally configurable mechanism, that an old
1337   resource is permanently unavailable and has no forwarding address.
1338   This status code is commonly used when the server does not wish to
1339   reveal exactly why the request has been refused, or when no other
1340   response is applicable.
1344<section title="405 Method Not Allowed" anchor="status.405">
1345  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1346  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1348   The method specified in the Request-Line is not allowed for the
1349   resource identified by the Request-URI. The response &MUST; include an
1350   Allow header containing a list of valid methods for the requested
1351   resource.
1355<section title="406 Not Acceptable" anchor="status.406">
1356  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1357  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1359   The resource identified by the request is only capable of generating
1360   response entities which have content characteristics not acceptable
1361   according to the accept headers sent in the request.
1364   Unless it was a HEAD request, the response &SHOULD; include an entity
1365   containing a list of available entity characteristics and location(s)
1366   from which the user or user agent can choose the one most
1367   appropriate. The entity format is specified by the media type given
1368   in the Content-Type header field. Depending upon the format and the
1369   capabilities of the user agent, selection of the most appropriate
1370   choice &MAY; be performed automatically. However, this specification
1371   does not define any standard for such automatic selection.
1372  <list><t>
1373      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1374      not acceptable according to the accept headers sent in the
1375      request. In some cases, this may even be preferable to sending a
1376      406 response. User agents are encouraged to inspect the headers of
1377      an incoming response to determine if it is acceptable.
1378  </t></list>
1381   If the response could be unacceptable, a user agent &SHOULD;
1382   temporarily stop receipt of more data and query the user for a
1383   decision on further actions.
1387<section title="407 Proxy Authentication Required" anchor="status.407">
1388  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1389  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1391   This code is similar to 401 (Unauthorized), but indicates that the
1392   client must first authenticate itself with the proxy (see &auth;).
1396<section title="408 Request Timeout" anchor="status.408">
1397  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1398  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1400   The client did not produce a request within the time that the server
1401   was prepared to wait. The client &MAY; repeat the request without
1402   modifications at any later time.
1406<section title="409 Conflict" anchor="status.409">
1407  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1408  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1410   The request could not be completed due to a conflict with the current
1411   state of the resource. This code is only allowed in situations where
1412   it is expected that the user might be able to resolve the conflict
1413   and resubmit the request. The response body &SHOULD; include enough
1414   information for the user to recognize the source of the conflict.
1415   Ideally, the response entity would include enough information for the
1416   user or user agent to fix the problem; however, that might not be
1417   possible and is not required.
1420   Conflicts are most likely to occur in response to a PUT request. For
1421   example, if versioning were being used and the entity being PUT
1422   included changes to a resource which conflict with those made by an
1423   earlier (third-party) request, the server might use the 409 response
1424   to indicate that it can't complete the request. In this case, the
1425   response entity would likely contain a list of the differences
1426   between the two versions in a format defined by the response
1427   Content-Type.
1431<section title="410 Gone" anchor="status.410">
1432  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1433  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1435   The requested resource is no longer available at the server and no
1436   forwarding address is known. This condition is expected to be
1437   considered permanent. Clients with link editing capabilities &SHOULD;
1438   delete references to the Request-URI after user approval. If the
1439   server does not know, or has no facility to determine, whether or not
1440   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1441   used instead. This response is cacheable unless indicated otherwise.
1444   The 410 response is primarily intended to assist the task of web
1445   maintenance by notifying the recipient that the resource is
1446   intentionally unavailable and that the server owners desire that
1447   remote links to that resource be removed. Such an event is common for
1448   limited-time, promotional services and for resources belonging to
1449   individuals no longer working at the server's site. It is not
1450   necessary to mark all permanently unavailable resources as "gone" or
1451   to keep the mark for any length of time -- that is left to the
1452   discretion of the server owner.
1456<section title="411 Length Required" anchor="status.411">
1457  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1458  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1460   The server refuses to accept the request without a defined Content-Length.
1461   The client &MAY; repeat the request if it adds a valid
1462   Content-Length header field containing the length of the message-body
1463   in the request message.
1467<section title="412 Precondition Failed" anchor="status.412">
1468  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1469  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1471   The precondition given in one or more of the request-header fields
1472   evaluated to false when it was tested on the server, as defined in
1473   &conditional;.
1477<section title="413 Request Entity Too Large" anchor="status.413">
1478  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1479  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1481   The server is refusing to process a request because the request
1482   entity is larger than the server is willing or able to process. The
1483   server &MAY; close the connection to prevent the client from continuing
1484   the request.
1487   If the condition is temporary, the server &SHOULD; include a Retry-After
1488   header field to indicate that it is temporary and after what
1489   time the client &MAY; try again.
1493<section title="414 Request-URI Too Long" anchor="status.414">
1494  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1495  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1497   The server is refusing to service the request because the Request-URI
1498   is longer than the server is willing to interpret. This rare
1499   condition is only likely to occur when a client has improperly
1500   converted a POST request to a GET request with long query
1501   information, when the client has descended into a URI "black hole" of
1502   redirection (e.g., a redirected URI prefix that points to a suffix of
1503   itself), or when the server is under attack by a client attempting to
1504   exploit security holes present in some servers using fixed-length
1505   buffers for reading or manipulating the Request-URI.
1509<section title="415 Unsupported Media Type" anchor="status.415">
1510  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1511  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1513   The server is refusing to service the request because the entity of
1514   the request is in a format not supported by the requested resource
1515   for the requested method.
1519<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1520  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1521  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1523   The request included a Range request-header field (&header-range;) and none of
1524   the range-specifier values in this field overlap the current extent
1525   of the selected resource.
1529<section title="417 Expectation Failed" anchor="status.417">
1530  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1531  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1533   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1534   could not be met by this server, or, if the server is a proxy,
1535   the server has unambiguous evidence that the request could not be met
1536   by the next-hop server.
1541<section title="Server Error 5xx" anchor="status.5xx">
1543   Response status codes beginning with the digit "5" indicate cases in
1544   which the server is aware that it has erred or is incapable of
1545   performing the request. Except when responding to a HEAD request, the
1546   server &SHOULD; include an entity containing an explanation of the
1547   error situation, and whether it is a temporary or permanent
1548   condition. User agents &SHOULD; display any included entity to the
1549   user. These response codes are applicable to any request method.
1552<section title="500 Internal Server Error" anchor="status.500">
1553  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1554  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1556   The server encountered an unexpected condition which prevented it
1557   from fulfilling the request.
1561<section title="501 Not Implemented" anchor="status.501">
1562  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1563  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1565   The server does not support the functionality required to fulfill the
1566   request. This is the appropriate response when the server does not
1567   recognize the request method and is not capable of supporting it for
1568   any resource.
1572<section title="502 Bad Gateway" anchor="status.502">
1573  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1574  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1576   The server, while acting as a gateway or proxy, received an invalid
1577   response from the upstream server it accessed in attempting to
1578   fulfill the request.
1582<section title="503 Service Unavailable" anchor="status.503">
1583  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1584  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1586   The server is currently unable to handle the request due to a
1587   temporary overloading or maintenance of the server. The implication
1588   is that this is a temporary condition which will be alleviated after
1589   some delay. If known, the length of the delay &MAY; be indicated in a
1590   Retry-After header. If no Retry-After is given, the client &SHOULD;
1591   handle the response as it would for a 500 response.
1592  <list><t>
1593      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1594      server must use it when becoming overloaded. Some servers may wish
1595      to simply refuse the connection.
1596  </t></list>
1600<section title="504 Gateway Timeout" anchor="status.504">
1601  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1602  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1604   The server, while acting as a gateway or proxy, did not receive a
1605   timely response from the upstream server specified by the URI (e.g.
1606   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1607   to access in attempting to complete the request.
1608  <list><t>
1609      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1610      return 400 or 500 when DNS lookups time out.
1611  </t></list>
1615<section title="505 HTTP Version Not Supported" anchor="status.505">
1616  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1617  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1619   The server does not support, or refuses to support, the HTTP protocol
1620   version that was used in the request message. The server is
1621   indicating that it is unable or unwilling to complete the request
1622   using the same major version as the client, as described in &http-version;,
1623   other than with this error message. The response &SHOULD; contain
1624   an entity describing why that version is not supported and what other
1625   protocols are supported by that server.
1633<section title="Header Field Definitions" anchor="header.fields">
1635   This section defines the syntax and semantics of HTTP/1.1 header fields
1636   related to request and response semantics.
1639   For entity-header fields, both sender and recipient refer to either the
1640   client or the server, depending on who sends and who receives the entity.
1643<section title="Allow" anchor="header.allow">
1644  <iref primary="true" item="Allow header" x:for-anchor=""/>
1645  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1647      The Allow entity-header field lists the set of methods supported
1648      by the resource identified by the Request-URI. The purpose of this
1649      field is strictly to inform the recipient of valid methods
1650      associated with the resource. An Allow header field &MUST; be
1651      present in a 405 (Method Not Allowed) response.
1653<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1654  Allow   = "Allow" ":" #Method
1657      Example of use:
1659<figure><artwork type="example">
1660       Allow: GET, HEAD, PUT
1663      This field cannot prevent a client from trying other methods.
1664      However, the indications given by the Allow header field value
1665      &SHOULD; be followed. The actual set of allowed methods is defined
1666      by the origin server at the time of each request.
1669      The Allow header field &MAY; be provided with a PUT request to
1670      recommend the methods to be supported by the new or modified
1671      resource. The server is not required to support these methods and
1672      &SHOULD; include an Allow header in the response giving the actual
1673      supported methods.
1676      A proxy &MUST-NOT; modify the Allow header field even if it does not
1677      understand all the methods specified, since the user agent might
1678      have other means of communicating with the origin server.
1682<section title="Expect" anchor="header.expect">
1683  <iref primary="true" item="Expect header" x:for-anchor=""/>
1684  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1686   The Expect request-header field is used to indicate that particular
1687   server behaviors are required by the client.
1689<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"/>
1690  Expect       =  "Expect" ":" 1#expectation
1692  expectation  =  "100-continue" | expectation-extension
1693  expectation-extension =  token [ "=" ( token | quoted-string )
1694                           *expect-params ]
1695  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1698   A server that does not understand or is unable to comply with any of
1699   the expectation values in the Expect field of a request &MUST; respond
1700   with appropriate error status. The server &MUST; respond with a 417
1701   (Expectation Failed) status if any of the expectations cannot be met
1702   or, if there are other problems with the request, some other 4xx
1703   status.
1706   This header field is defined with extensible syntax to allow for
1707   future extensions. If a server receives a request containing an
1708   Expect field that includes an expectation-extension that it does not
1709   support, it &MUST; respond with a 417 (Expectation Failed) status.
1712   Comparison of expectation values is case-insensitive for unquoted
1713   tokens (including the 100-continue token), and is case-sensitive for
1714   quoted-string expectation-extensions.
1717   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1718   return a 417 (Expectation Failed) status if it receives a request
1719   with an expectation that it cannot meet. However, the Expect
1720   request-header itself is end-to-end; it &MUST; be forwarded if the
1721   request is forwarded.
1724   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1725   Expect header.
1728   See &use100; for the use of the 100 (Continue) status.
1732<section title="From" anchor="header.from">
1733  <iref primary="true" item="From header" x:for-anchor=""/>
1734  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1736   The From request-header field, if given, &SHOULD; contain an Internet
1737   e-mail address for the human user who controls the requesting user
1738   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1739   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1741<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1742  From   = "From" ":" mailbox
1745   An example is:
1747<figure><artwork type="example">
1748    From:
1751   This header field &MAY; be used for logging purposes and as a means for
1752   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1753   be used as an insecure form of access protection. The interpretation
1754   of this field is that the request is being performed on behalf of the
1755   person given, who accepts responsibility for the method performed. In
1756   particular, robot agents &SHOULD; include this header so that the
1757   person responsible for running the robot can be contacted if problems
1758   occur on the receiving end.
1761   The Internet e-mail address in this field &MAY; be separate from the
1762   Internet host which issued the request. For example, when a request
1763   is passed through a proxy the original issuer's address &SHOULD; be
1764   used.
1767   The client &SHOULD-NOT;  send the From header field without the user's
1768   approval, as it might conflict with the user's privacy interests or
1769   their site's security policy. It is strongly recommended that the
1770   user be able to disable, enable, and modify the value of this field
1771   at any time prior to a request.
1775<section title="Location" anchor="header.location">
1776  <iref primary="true" item="Location header" x:for-anchor=""/>
1777  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1779   The Location response-header field is used to redirect the recipient
1780   to a location other than the Request-URI for completion of the
1781   request or identification of a new resource. For 201 (Created)
1782   responses, the Location is that of the new resource which was created
1783   by the request. For 3xx responses, the location &SHOULD; indicate the
1784   server's preferred URI for automatic redirection to the resource. The
1785   field value consists of a single absolute URI.
1787<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1788  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1791   An example is:
1793<figure><artwork type="example">
1794    Location:
1797  <list><t>
1798      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1799      from Location in that the Content-Location identifies the original
1800      location of the entity enclosed in the request. It is therefore
1801      possible for a response to contain header fields for both Location
1802      and Content-Location.
1803  </t></list>
1806   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1807   <list style="symbols">
1808      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1809      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1810      <t>With 305 Use Proxy.</t>
1811   </list>
1815<section title="Max-Forwards" anchor="header.max-forwards">
1816  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1817  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1819   The Max-Forwards request-header field provides a mechanism with the
1820   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1821   number of proxies or gateways that can forward the request to the
1822   next inbound server. This can be useful when the client is attempting
1823   to trace a request chain which appears to be failing or looping in
1824   mid-chain.
1826<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1827  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1830   The Max-Forwards value is a decimal integer indicating the remaining
1831   number of times this request message may be forwarded.
1834   Each proxy or gateway recipient of a TRACE or OPTIONS request
1835   containing a Max-Forwards header field &MUST; check and update its
1836   value prior to forwarding the request. If the received value is zero
1837   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1838   respond as the final recipient. If the received Max-Forwards value is
1839   greater than zero, then the forwarded message &MUST; contain an updated
1840   Max-Forwards field with a value decremented by one (1).
1843   The Max-Forwards header field &MAY; be ignored for all other methods
1844   defined by this specification and for any extension methods for which
1845   it is not explicitly referred to as part of that method definition.
1849<section title="Referer" anchor="header.referer">
1850  <iref primary="true" item="Referer header" x:for-anchor=""/>
1851  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1853   The Referer[sic] request-header field allows the client to specify,
1854   for the server's benefit, the address (URI) of the resource from
1855   which the Request-URI was obtained (the "referrer", although the
1856   header field is misspelled.) The Referer request-header allows a
1857   server to generate lists of back-links to resources for interest,
1858   logging, optimized caching, etc. It also allows obsolete or mistyped
1859   links to be traced for maintenance. The Referer field &MUST-NOT; be
1860   sent if the Request-URI was obtained from a source that does not have
1861   its own URI, such as input from the user keyboard.
1863<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1864  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1867   Example:
1869<figure><artwork type="example">
1870    Referer:
1873   If the field value is a relative URI, it &SHOULD; be interpreted
1874   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1875   <xref target=""/> for security considerations.
1879<section title="Retry-After" anchor="header.retry-after">
1880  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1881  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1883   The Retry-After response-header field can be used with a 503 (Service
1884   Unavailable) response to indicate how long the service is expected to
1885   be unavailable to the requesting client. This field &MAY; also be used
1886   with any 3xx (Redirection) response to indicate the minimum time the
1887   user-agent is asked wait before issuing the redirected request. The
1888   value of this field can be either an HTTP-date or an integer number
1889   of seconds (in decimal) after the time of the response.
1891<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1892  Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1895   Two examples of its use are
1897<figure><artwork type="example">
1898    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1899    Retry-After: 120
1902   In the latter example, the delay is 2 minutes.
1906<section title="Server" anchor="header.server">
1907  <iref primary="true" item="Server header" x:for-anchor=""/>
1908  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1910   The Server response-header field contains information about the
1911   software used by the origin server to handle the request. The field
1912   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1913   identifying the server and any significant subproducts. The product
1914   tokens are listed in order of their significance for identifying the
1915   application.
1917<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1918  Server         = "Server" ":" 1*( product | comment )
1921   Example:
1923<figure><artwork type="example">
1924    Server: CERN/3.0 libwww/2.17
1927   If the response is being forwarded through a proxy, the proxy
1928   application &MUST-NOT; modify the Server response-header. Instead, it
1929   &MUST; include a Via field (as described in &header-via;).
1930  <list><t>
1931      <x:h>Note:</x:h> Revealing the specific software version of the server might
1932      allow the server machine to become more vulnerable to attacks
1933      against software that is known to contain security holes. Server
1934      implementors are encouraged to make this field a configurable
1935      option.
1936  </t></list>
1940<section title="User-Agent" anchor="header.user-agent">
1941  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1942  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1944   The User-Agent request-header field contains information about the
1945   user agent originating the request. This is for statistical purposes,
1946   the tracing of protocol violations, and automated recognition of user
1947   agents for the sake of tailoring responses to avoid particular user
1948   agent limitations. User agents &SHOULD; include this field with
1949   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1950   and comments identifying the agent and any subproducts which form a
1951   significant part of the user agent. By convention, the product tokens
1952   are listed in order of their significance for identifying the
1953   application.
1955<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1956  User-Agent     = "User-Agent" ":" 1*( product | comment )
1959   Example:
1961<figure><artwork type="example">
1962    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1968<section title="IANA Considerations" anchor="IANA.considerations">
1970   TBD.
1974<section title="Security Considerations" anchor="security.considerations">
1976   This section is meant to inform application developers, information
1977   providers, and users of the security limitations in HTTP/1.1 as
1978   described by this document. The discussion does not include
1979   definitive solutions to the problems revealed, though it does make
1980   some suggestions for reducing security risks.
1983<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1985   Like any generic data transfer protocol, HTTP cannot regulate the
1986   content of the data that is transferred, nor is there any a priori
1987   method of determining the sensitivity of any particular piece of
1988   information within the context of any given request. Therefore,
1989   applications &SHOULD; supply as much control over this information as
1990   possible to the provider of that information. Four header fields are
1991   worth special mention in this context: Server, Via, Referer and From.
1994   Revealing the specific software version of the server might allow the
1995   server machine to become more vulnerable to attacks against software
1996   that is known to contain security holes. Implementors &SHOULD; make the
1997   Server header field a configurable option.
2000   Proxies which serve as a portal through a network firewall &SHOULD;
2001   take special precautions regarding the transfer of header information
2002   that identifies the hosts behind the firewall. In particular, they
2003   &SHOULD; remove, or replace with sanitized versions, any Via fields
2004   generated behind the firewall.
2007   The Referer header allows reading patterns to be studied and reverse
2008   links drawn. Although it can be very useful, its power can be abused
2009   if user details are not separated from the information contained in
2010   the Referer. Even when the personal information has been removed, the
2011   Referer header might indicate a private document's URI whose
2012   publication would be inappropriate.
2015   The information sent in the From field might conflict with the user's
2016   privacy interests or their site's security policy, and hence it
2017   &SHOULD-NOT;  be transmitted without the user being able to disable,
2018   enable, and modify the contents of the field. The user &MUST; be able
2019   to set the contents of this field within a user preference or
2020   application defaults configuration.
2023   We suggest, though do not require, that a convenient toggle interface
2024   be provided for the user to enable or disable the sending of From and
2025   Referer information.
2028   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2029   fields can sometimes be used to determine that a specific client or
2030   server have a particular security hole which might be exploited.
2031   Unfortunately, this same information is often used for other valuable
2032   purposes for which HTTP currently has no better mechanism.
2036<section title="Encoding Sensitive Information in URI's" anchor="">
2038   Because the source of a link might be private information or might
2039   reveal an otherwise private information source, it is strongly
2040   recommended that the user be able to select whether or not the
2041   Referer field is sent. For example, a browser client could have a
2042   toggle switch for browsing openly/anonymously, which would
2043   respectively enable/disable the sending of Referer and From
2044   information.
2047   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2048   HTTP request if the referring page was transferred with a secure
2049   protocol.
2052   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2053   based forms for the submission of sensitive data, because this will
2054   cause this data to be encoded in the Request-URI. Many existing
2055   servers, proxies, and user agents will log the request URI in some
2056   place where it might be visible to third parties. Servers can use
2057   POST-based form submission instead
2061<section title="Location Headers and Spoofing" anchor="location.spoofing">
2063   If a single server supports multiple organizations that do not trust
2064   one another, then it &MUST; check the values of Location and Content-Location
2065   headers in responses that are generated under control of
2066   said organizations to make sure that they do not attempt to
2067   invalidate resources over which they have no authority.
2073<section title="Acknowledgments" anchor="ack">
2078<references title="Normative References">
2080<reference anchor="Part1">
2081  <front>
2082    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2083    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2084      <organization abbrev="Day Software">Day Software</organization>
2085      <address><email></email></address>
2086    </author>
2087    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2088      <organization>One Laptop per Child</organization>
2089      <address><email></email></address>
2090    </author>
2091    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2092      <organization abbrev="HP">Hewlett-Packard Company</organization>
2093      <address><email></email></address>
2094    </author>
2095    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2096      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2097      <address><email></email></address>
2098    </author>
2099    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2100      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2101      <address><email></email></address>
2102    </author>
2103    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2104      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2105      <address><email></email></address>
2106    </author>
2107    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2108      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2109      <address><email></email></address>
2110    </author>
2111    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2112      <organization abbrev="W3C">World Wide Web Consortium</organization>
2113      <address><email></email></address>
2114    </author>
2115    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2116      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2117      <address><email></email></address>
2118    </author>
2119    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2120  </front>
2121  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2122  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2125<reference anchor="Part3">
2126  <front>
2127    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2128    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2129      <organization abbrev="Day Software">Day Software</organization>
2130      <address><email></email></address>
2131    </author>
2132    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2133      <organization>One Laptop per Child</organization>
2134      <address><email></email></address>
2135    </author>
2136    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2137      <organization abbrev="HP">Hewlett-Packard Company</organization>
2138      <address><email></email></address>
2139    </author>
2140    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2141      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2142      <address><email></email></address>
2143    </author>
2144    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2145      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2146      <address><email></email></address>
2147    </author>
2148    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2149      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2150      <address><email></email></address>
2151    </author>
2152    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2153      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2154      <address><email></email></address>
2155    </author>
2156    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2157      <organization abbrev="W3C">World Wide Web Consortium</organization>
2158      <address><email></email></address>
2159    </author>
2160    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2161      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2162      <address><email></email></address>
2163    </author>
2164    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2165  </front>
2166  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2167  <x:source href="p3-payload.xml" basename="p3-payload"/>
2170<reference anchor="Part4">
2171  <front>
2172    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2173    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2174      <organization abbrev="Day Software">Day Software</organization>
2175      <address><email></email></address>
2176    </author>
2177    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2178      <organization>One Laptop per Child</organization>
2179      <address><email></email></address>
2180    </author>
2181    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2182      <organization abbrev="HP">Hewlett-Packard Company</organization>
2183      <address><email></email></address>
2184    </author>
2185    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2186      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2187      <address><email></email></address>
2188    </author>
2189    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2190      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2191      <address><email></email></address>
2192    </author>
2193    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2194      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2195      <address><email></email></address>
2196    </author>
2197    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2198      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2199      <address><email></email></address>
2200    </author>
2201    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2202      <organization abbrev="W3C">World Wide Web Consortium</organization>
2203      <address><email></email></address>
2204    </author>
2205    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2206      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2207      <address><email></email></address>
2208    </author>
2209    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2210  </front>
2211  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2212  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2215<reference anchor="Part5">
2216  <front>
2217    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2218    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2219      <organization abbrev="Day Software">Day Software</organization>
2220      <address><email></email></address>
2221    </author>
2222    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2223      <organization>One Laptop per Child</organization>
2224      <address><email></email></address>
2225    </author>
2226    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2227      <organization abbrev="HP">Hewlett-Packard Company</organization>
2228      <address><email></email></address>
2229    </author>
2230    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2231      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2232      <address><email></email></address>
2233    </author>
2234    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2235      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2236      <address><email></email></address>
2237    </author>
2238    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2239      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2240      <address><email></email></address>
2241    </author>
2242    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2243      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2244      <address><email></email></address>
2245    </author>
2246    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2247      <organization abbrev="W3C">World Wide Web Consortium</organization>
2248      <address><email></email></address>
2249    </author>
2250    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2251      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2252      <address><email></email></address>
2253    </author>
2254    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2255  </front>
2256  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2257  <x:source href="p5-range.xml" basename="p5-range"/>
2260<reference anchor="Part6">
2261  <front>
2262    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2263    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2264      <organization abbrev="Day Software">Day Software</organization>
2265      <address><email></email></address>
2266    </author>
2267    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2268      <organization>One Laptop per Child</organization>
2269      <address><email></email></address>
2270    </author>
2271    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2272      <organization abbrev="HP">Hewlett-Packard Company</organization>
2273      <address><email></email></address>
2274    </author>
2275    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2276      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2277      <address><email></email></address>
2278    </author>
2279    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2280      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2281      <address><email></email></address>
2282    </author>
2283    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2284      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2285      <address><email></email></address>
2286    </author>
2287    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2288      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2289      <address><email></email></address>
2290    </author>
2291    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2292      <organization abbrev="W3C">World Wide Web Consortium</organization>
2293      <address><email></email></address>
2294    </author>
2295    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2296      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2297      <address><email></email></address>
2298    </author>
2299    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2300  </front>
2301  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2302  <x:source href="p6-cache.xml" basename="p6-cache"/>
2305<reference anchor="Part7">
2306  <front>
2307    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2308    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2309      <organization abbrev="Day Software">Day Software</organization>
2310      <address><email></email></address>
2311    </author>
2312    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2313      <organization>One Laptop per Child</organization>
2314      <address><email></email></address>
2315    </author>
2316    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2317      <organization abbrev="HP">Hewlett-Packard Company</organization>
2318      <address><email></email></address>
2319    </author>
2320    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2321      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2322      <address><email></email></address>
2323    </author>
2324    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2325      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2326      <address><email></email></address>
2327    </author>
2328    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2329      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2330      <address><email></email></address>
2331    </author>
2332    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2333      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2334      <address><email></email></address>
2335    </author>
2336    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2337      <organization abbrev="W3C">World Wide Web Consortium</organization>
2338      <address><email></email></address>
2339    </author>
2340    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2341      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2342      <address><email></email></address>
2343    </author>
2344    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2345  </front>
2346  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2347  <x:source href="p7-auth.xml" basename="p7-auth"/>
2350<reference anchor="RFC2119">
2351  <front>
2352    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2353    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2354      <organization>Harvard University</organization>
2355      <address><email></email></address>
2356    </author>
2357    <date month="March" year="1997"/>
2358  </front>
2359  <seriesInfo name="BCP" value="14"/>
2360  <seriesInfo name="RFC" value="2119"/>
2365<references title="Informative References">
2367<reference anchor="Luo1998">
2368  <front>
2369    <title>Tunneling TCP based protocols through Web proxy servers</title>
2370    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2371      <organization/>
2372    </author>
2373    <date year="1998" month="August"/>
2374  </front>
2375  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2378<reference anchor="RFC1945">
2379  <front>
2380    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2381    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2382      <organization>MIT, Laboratory for Computer Science</organization>
2383      <address><email></email></address>
2384    </author>
2385    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2386      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2387      <address><email></email></address>
2388    </author>
2389    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2390      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2391      <address><email></email></address>
2392    </author>
2393    <date month="May" year="1996"/>
2394  </front>
2395  <seriesInfo name="RFC" value="1945"/>
2398<reference anchor="RFC2068">
2399  <front>
2400    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2401    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2402      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2403      <address><email></email></address>
2404    </author>
2405    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2406      <organization>MIT Laboratory for Computer Science</organization>
2407      <address><email></email></address>
2408    </author>
2409    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2410      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2411      <address><email></email></address>
2412    </author>
2413    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2414      <organization>MIT Laboratory for Computer Science</organization>
2415      <address><email></email></address>
2416    </author>
2417    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2418      <organization>MIT Laboratory for Computer Science</organization>
2419      <address><email></email></address>
2420    </author>
2421    <date month="January" year="1997"/>
2422  </front>
2423  <seriesInfo name="RFC" value="2068"/>
2426<reference anchor="RFC2616">
2427  <front>
2428    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2429    <author initials="R." surname="Fielding" fullname="R. Fielding">
2430      <organization>University of California, Irvine</organization>
2431      <address><email></email></address>
2432    </author>
2433    <author initials="J." surname="Gettys" fullname="J. Gettys">
2434      <organization>W3C</organization>
2435      <address><email></email></address>
2436    </author>
2437    <author initials="J." surname="Mogul" fullname="J. Mogul">
2438      <organization>Compaq Computer Corporation</organization>
2439      <address><email></email></address>
2440    </author>
2441    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2442      <organization>MIT Laboratory for Computer Science</organization>
2443      <address><email></email></address>
2444    </author>
2445    <author initials="L." surname="Masinter" fullname="L. Masinter">
2446      <organization>Xerox Corporation</organization>
2447      <address><email></email></address>
2448    </author>
2449    <author initials="P." surname="Leach" fullname="P. Leach">
2450      <organization>Microsoft Corporation</organization>
2451      <address><email></email></address>
2452    </author>
2453    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2454      <organization>W3C</organization>
2455      <address><email></email></address>
2456    </author>
2457    <date month="June" year="1999"/>
2458  </front>
2459  <seriesInfo name="RFC" value="2616"/>
2462<reference anchor="RFC2822">
2463  <front>
2464    <title>Internet Message Format</title>
2465    <author initials="P." surname="Resnick" fullname="P. Resnick">
2466      <organization>QUALCOMM Incorporated</organization>
2467    </author>
2468    <date year="2001" month="April"/>
2469  </front>
2470  <seriesInfo name="RFC" value="2822"/>
2475<section title="Compatibility with Previous Versions" anchor="compatibility">
2476<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2478   Clarified which error code should be used for inbound server failures
2479   (e.g. DNS failures). (<xref target="status.504"/>).
2482   201 (Created) had a race that required an Etag be sent when a resource is
2483   first created. (<xref target="status.201"/>).
2486   Rewrite of message transmission requirements to make it much harder
2487   for implementors to get it wrong, as the consequences of errors here
2488   can have significant impact on the Internet, and to deal with the
2489   following problems:
2490  <list style="numbers">
2491      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2492         this was incorrectly placing a requirement on the behavior of
2493         an implementation of a future version of HTTP/1.x</t>
2495      <t>Made it clear that user-agents should retry requests, not
2496         "clients" in general.</t>
2498      <t>Converted requirements for clients to ignore unexpected 100
2499         (Continue) responses, and for proxies to forward 100 responses,
2500         into a general requirement for 1xx responses.</t>
2502      <t>Modified some TCP-specific language, to make it clearer that
2503         non-TCP transports are possible for HTTP.</t>
2505      <t>Require that the origin server &MUST-NOT; wait for the request
2506         body before it sends a required 100 (Continue) response.</t>
2508      <t>Allow, rather than require, a server to omit 100 (Continue) if
2509         it has already seen some of the request body.</t>
2511      <t>Allow servers to defend against denial-of-service attacks and
2512         broken clients.</t>
2513  </list>
2516   This change adds the Expect header and 417 status code.
2519   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2520   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2523   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
2524   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2528<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2530  Clarify definition of POST.
2531  (<xref target="POST"/>)
2534  Failed to consider that there are
2535  many other request methods that are safe to automatically redirect,
2536  and further that the user agent is able to make that determination
2537  based on the request method semantics.
2538  (Sections <xref format="counter" target="status.301"/>,
2539  <xref format="counter" target="status.302"/> and
2540  <xref format="counter" target="status.307"/> )
2543  Correct syntax of Location header to allow fragment,
2544  as referred symbol wasn't what was expected, and add some
2545  clarifications as to when it would not be appropriate.
2546  (<xref target="header.location"/>)
2549  In the description of the Server header, the Via field
2550  was described as a SHOULD. The requirement was and is stated
2551  correctly in the description of the Via header in &header-via;.
2552  (<xref target="header.server"/>)
2558<section title="Change Log (to be removed by RFC Editor before publication)">
2560<section title="Since RFC2616">
2562  Extracted relevant partitions from <xref target="RFC2616"/>.
2566<section title="Since draft-ietf-httpbis-p2-semantics-00">
2568  Closed issues:
2569  <list style="symbols">
2570    <t>
2571      <eref target=""/>:
2572      "Via is a MUST"
2573      (<eref target=""/>)
2574    </t>
2575    <t>
2576      <eref target=""/>:
2577      "Fragments allowed in Location"
2578      (<eref target=""/>)
2579    </t>
2580    <t>
2581      <eref target=""/>:
2582      "Safe Methods vs Redirection"
2583      (<eref target=""/>)
2584    </t>
2585    <t>
2586      <eref target=""/>:
2587      "Revise description of the POST method"
2588      (<eref target=""/>)
2589    </t>
2590    <t>
2591      <eref target=""/>:
2592      "Normative and Informative references"
2593    </t>
2594    <t>
2595      <eref target=""/>:
2596      "RFC2606 Compliance"
2597    </t>
2598    <t>
2599      <eref target=""/>:
2600      "Informative references"
2601    </t>
2602    <t>
2603      <eref target=""/>:
2604      "Redundant cross-references"
2605    </t>
2606  </list>
2609  Other changes:
2610  <list style="symbols">
2611    <t>
2612      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2613    </t>
2614  </list>
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