source: draft-ietf-httpbis/latest/p2-semantics.xml @ 127

Last change on this file since 127 was 124, checked in by julian.reschke@…, 15 years ago

Dates set to Jan 2008.

  • Property svn:eol-style set to native
File size: 120.7 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=''/>">
59  <!ENTITY message-transmission-req   "<xref target='Part1' x:rel='#message.transmission.requirements' xmlns:x=''/>">
61<?rfc toc="yes" ?>
62<?rfc symrefs="yes" ?>
63<?rfc sortrefs="yes" ?>
64<?rfc compact="yes"?>
65<?rfc subcompact="no" ?>
66<?rfc linkmailto="no" ?>
67<?rfc editing="no" ?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2068, 2616" category="std"
71     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
72     xmlns:x='' xmlns:ed="">
75  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
77  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
78    <organization abbrev="Day Software">Day Software</organization>
79    <address>
80      <postal>
81        <street>23 Corporate Plaza DR, Suite 280</street>
82        <city>Newport Beach</city>
83        <region>CA</region>
84        <code>92660</code>
85        <country>USA</country>
86      </postal>
87      <phone>+1-949-706-5300</phone>
88      <facsimile>+1-949-706-5305</facsimile>
89      <email></email>
90      <uri></uri>
91    </address>
92  </author>
94  <author initials="J." surname="Gettys" fullname="Jim Gettys">
95    <organization>One Laptop per Child</organization>
96    <address>
97      <postal>
98        <street>21 Oak Knoll Road</street>
99        <city>Carlisle</city>
100        <region>MA</region>
101        <code>01741</code>
102        <country>USA</country>
103      </postal>
104      <email></email>
105      <uri></uri>
106    </address>
107  </author>
109  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
110    <organization abbrev="HP">Hewlett-Packard Company</organization>
111    <address>
112      <postal>
113        <street>HP Labs, Large Scale Systems Group</street>
114        <street>1501 Page Mill Road, MS 1177</street>
115        <city>Palo Alto</city>
116        <region>CA</region>
117        <code>94304</code>
118        <country>USA</country>
119      </postal>
120      <email></email>
121    </address>
122  </author>
124  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
125    <organization abbrev="Microsoft">Microsoft Corporation</organization>
126    <address>
127      <postal>
128        <street>1 Microsoft Way</street>
129        <city>Redmond</city>
130        <region>WA</region>
131        <code>98052</code>
132        <country>USA</country>
133      </postal>
134      <email></email>
135    </address>
136  </author>
138  <author initials="L." surname="Masinter" fullname="Larry Masinter">
139    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
140    <address>
141      <postal>
142        <street>345 Park Ave</street>
143        <city>San Jose</city>
144        <region>CA</region>
145        <code>95110</code>
146        <country>USA</country>
147      </postal>
148      <email></email>
149      <uri></uri>
150    </address>
151  </author>
153  <author initials="P." surname="Leach" fullname="Paul J. Leach">
154    <organization abbrev="Microsoft">Microsoft Corporation</organization>
155    <address>
156      <postal>
157        <street>1 Microsoft Way</street>
158        <city>Redmond</city>
159        <region>WA</region>
160        <code>98052</code>
161      </postal>
162      <email></email>
163    </address>
164  </author>
166  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
167    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
171        <street>The Stata Center, Building 32</street>
172        <street>32 Vassar Street</street>
173        <city>Cambridge</city>
174        <region>MA</region>
175        <code>02139</code>
176        <country>USA</country>
177      </postal>
178      <email></email>
179      <uri></uri>
180    </address>
181  </author>
183  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
184    <organization abbrev="W3C">World Wide Web Consortium</organization>
185    <address>
186      <postal>
187        <street>W3C / ERCIM</street>
188        <street>2004, rte des Lucioles</street>
189        <city>Sophia-Antipolis</city>
190        <region>AM</region>
191        <code>06902</code>
192        <country>France</country>
193      </postal>
194      <email></email>
195      <uri></uri>
196    </address>
197  </author>
199  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
200    <organization abbrev="greenbytes">greenbytes GmbH</organization>
201    <address>
202      <postal>
203        <street>Hafenweg 16</street>
204        <city>Muenster</city><region>NW</region><code>48155</code>
205        <country>Germany</country>
206      </postal>
207      <phone>+49 251 2807760</phone>   
208      <facsimile>+49 251 2807761</facsimile>   
209      <email></email>       
210      <uri></uri>     
211    </address>
212  </author>
214  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
218   The Hypertext Transfer Protocol (HTTP) is an application-level
219   protocol for distributed, collaborative, hypermedia information
220   systems. HTTP has been in use by the World Wide Web global information
221   initiative since 1990. This document is Part 2 of the seven-part specification
222   that defines the protocol referred to as "HTTP/1.1" and, taken together,
223   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
224   as expressed by request methods, request-header fields, response status codes,
225   and response-header fields.
229<note title="Editorial Note (To be removed by RFC Editor)">
230  <t>
231    Discussion of this draft should take place on the HTTPBIS working group
232    mailing list ( The current issues list is
233    at <eref target=""/>
234    and related documents (including fancy diffs) can be found at
235    <eref target=""/>.
236  </t>
240<section title="Introduction" anchor="introduction">
242   This document will define aspects of HTTP related to request and response
243   semantics. Right now it only includes the extracted relevant sections of
244   RFC 2616 with only minor edits.
247   The HTTP protocol is a request/response protocol. A client sends a
248   request to the server in the form of a request method, URI, and
249   protocol version, followed by a MIME-like message containing request
250   modifiers, client information, and possible body content over a
251   connection with a server. The server responds with a status line,
252   including the message's protocol version and a success or error code,
253   followed by a MIME-like message containing server information, entity
254   metainformation, and possible entity-body content. The relationship
255   between HTTP and MIME is described in &diff2045entity;.
258<section title="Requirements" anchor="intro.requirements">
260   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
261   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
262   document are to be interpreted as described in <xref target="RFC2119"/>.
265   An implementation is not compliant if it fails to satisfy one or more
266   of the &MUST; or &REQUIRED; level requirements for the protocols it
267   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
268   level and all the &SHOULD; level requirements for its protocols is said
269   to be "unconditionally compliant"; one that satisfies all the &MUST;
270   level requirements but not all the &SHOULD; level requirements for its
271   protocols is said to be "conditionally compliant."
276<section title="Product Tokens" anchor="product.tokens">
278   Product tokens are used to allow communicating applications to
279   identify themselves by software name and version. Most fields using
280   product tokens also allow sub-products which form a significant part
281   of the application to be listed, separated by white space. By
282   convention, the products are listed in order of their significance
283   for identifying the application.
285<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
286    product         = token ["/" product-version]
287    product-version = token
290   Examples:
292<figure><artwork type="example">
293    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
294    Server: Apache/0.8.4
297   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
298   used for advertising or other non-essential information. Although any
299   token character &MAY; appear in a product-version, this token &SHOULD;
300   only be used for a version identifier (i.e., successive versions of
301   the same product &SHOULD; only differ in the product-version portion of
302   the product value).
306<section title="Method" anchor="method">
308   The Method  token indicates the method to be performed on the
309   resource identified by the Request-URI. The method is case-sensitive.
311<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
312    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
313                   | "GET"                    ; <xref target="GET"/>
314                   | "HEAD"                   ; <xref target="HEAD"/>
315                   | "POST"                   ; <xref target="POST"/>
316                   | "PUT"                    ; <xref target="PUT"/>
317                   | "DELETE"                 ; <xref target="DELETE"/>
318                   | "TRACE"                  ; <xref target="TRACE"/>
319                   | "CONNECT"                ; <xref target="CONNECT"/>
320                   | extension-method
321    extension-method = token
324   The list of methods allowed by a resource can be specified in an
325   Allow header field (<xref target="header.allow"/>). The return code of the response
326   always notifies the client whether a method is currently allowed on a
327   resource, since the set of allowed methods can change dynamically. An
328   origin server &SHOULD; return the status code 405 (Method Not Allowed)
329   if the method is known by the origin server but not allowed for the
330   requested resource, and 501 (Not Implemented) if the method is
331   unrecognized or not implemented by the origin server. The methods GET
332   and HEAD &MUST; be supported by all general-purpose servers. All other
333   methods are &OPTIONAL;; however, if the above methods are implemented,
334   they &MUST; be implemented with the same semantics as those specified
335   in <xref target="method.definitions"/>.
339<section title="Request Header Fields" anchor="request.header.fields">
341   The request-header fields allow the client to pass additional
342   information about the request, and about the client itself, to the
343   server. These fields act as request modifiers, with semantics
344   equivalent to the parameters on a programming language method
345   invocation.
347<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
348    request-header = Accept                   ; &header-accept;
349                   | Accept-Charset           ; &header-accept-charset;
350                   | Accept-Encoding          ; &header-accept-encoding;
351                   | Accept-Language          ; &header-accept-language;
352                   | Authorization            ; &header-authorization;
353                   | Expect                   ; <xref target="header.expect"/>
354                   | From                     ; <xref target="header.from"/>
355                   | Host                     ; &header-host;
356                   | If-Match                 ; &header-if-match;
357                   | If-Modified-Since        ; &header-if-modified-since;
358                   | If-None-Match            ; &header-if-none-match;
359                   | If-Range                 ; &header-if-range;
360                   | If-Unmodified-Since      ; &header-if-unmodified-since;
361                   | Max-Forwards             ; <xref target="header.max-forwards"/>
362                   | Proxy-Authorization      ; &header-proxy-authorization;
363                   | Range                    ; &header-range;
364                   | Referer                  ; <xref target="header.referer"/>
365                   | TE                       ; &header-te;
366                   | User-Agent               ; <xref target="header.user-agent"/>
369   Request-header field names can be extended reliably only in
370   combination with a change in the protocol version. However, new or
371   experimental header fields &MAY; be given the semantics of request-header
372   fields if all parties in the communication recognize them to
373   be request-header fields. Unrecognized header fields are treated as
374   entity-header fields.
378<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
380   The Status-Code element is a 3-digit integer result code of the
381   attempt to understand and satisfy the request. These codes are fully
382   defined in <xref target=""/>. 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.
737   POST requests &MUST; obey the message transmission requirements set out
738   in &message-transmission-req;.
741   See <xref target=""/> for security considerations.
745<section title="PUT" anchor="PUT">
746  <iref primary="true" item="PUT method" x:for-anchor=""/>
747  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
749   The PUT method requests that the enclosed entity be stored under the
750   supplied Request-URI. If the Request-URI refers to an already
751   existing resource, the enclosed entity &SHOULD; be considered as a
752   modified version of the one residing on the origin server. If the
753   Request-URI does not point to an existing resource, and that URI is
754   capable of being defined as a new resource by the requesting user
755   agent, the origin server can create the resource with that URI. If a
756   new resource is created, the origin server &MUST; inform the user agent
757   via the 201 (Created) response. If an existing resource is modified,
758   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
759   to indicate successful completion of the request. If the resource
760   could not be created or modified with the Request-URI, an appropriate
761   error response &SHOULD; be given that reflects the nature of the
762   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
763   (e.g. Content-Range) headers that it does not understand or implement
764   and &MUST; return a 501 (Not Implemented) response in such cases.
767   If the request passes through a cache and the Request-URI identifies
768   one or more currently cached entities, those entries &SHOULD; be
769   treated as stale. Responses to this method are not cacheable.
772   The fundamental difference between the POST and PUT requests is
773   reflected in the different meaning of the Request-URI. The URI in a
774   POST request identifies the resource that will handle the enclosed
775   entity. That resource might be a data-accepting process, a gateway to
776   some other protocol, or a separate entity that accepts annotations.
777   In contrast, the URI in a PUT request identifies the entity enclosed
778   with the request -- the user agent knows what URI is intended and the
779   server &MUST-NOT; attempt to apply the request to some other resource.
780   If the server desires that the request be applied to a different URI,
781   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
782   then make its own decision regarding whether or not to redirect the
783   request.
786   A single resource &MAY; be identified by many different URIs. For
787   example, an article might have a URI for identifying "the current
788   version" which is separate from the URI identifying each particular
789   version. In this case, a PUT request on a general URI might result in
790   several other URIs being defined by the origin server.
793   HTTP/1.1 does not define how a PUT method affects the state of an
794   origin server.
797   PUT requests &MUST; obey the message transmission requirements set out
798   in &message-transmission-req;.
801   Unless otherwise specified for a particular entity-header, the
802   entity-headers in the PUT request &SHOULD; be applied to the resource
803   created or modified by the PUT.
807<section title="DELETE" anchor="DELETE">
808  <iref primary="true" item="DELETE method" x:for-anchor=""/>
809  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
811   The DELETE method requests that the origin server delete the resource
812   identified by the Request-URI. This method &MAY; be overridden by human
813   intervention (or other means) on the origin server. The client cannot
814   be guaranteed that the operation has been carried out, even if the
815   status code returned from the origin server indicates that the action
816   has been completed successfully. However, the server &SHOULD-NOT;
817   indicate success unless, at the time the response is given, it
818   intends to delete the resource or move it to an inaccessible
819   location.
822   A successful response &SHOULD; be 200 (OK) if the response includes an
823   entity describing the status, 202 (Accepted) if the action has not
824   yet been enacted, or 204 (No Content) if the action has been enacted
825   but the response does not include an entity.
828   If the request passes through a cache and the Request-URI identifies
829   one or more currently cached entities, those entries &SHOULD; be
830   treated as stale. Responses to this method are not cacheable.
834<section title="TRACE" anchor="TRACE">
835  <iref primary="true" item="TRACE method" x:for-anchor=""/>
836  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
838   The TRACE method is used to invoke a remote, application-layer loop-back
839   of the request message. The final recipient of the request
840   &SHOULD; reflect the message received back to the client as the
841   entity-body of a 200 (OK) response. The final recipient is either the
842   origin server or the first proxy or gateway to receive a Max-Forwards
843   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
844   &MUST-NOT; include an entity.
847   TRACE allows the client to see what is being received at the other
848   end of the request chain and use that data for testing or diagnostic
849   information. The value of the Via header field (&header-via;) is of
850   particular interest, since it acts as a trace of the request chain.
851   Use of the Max-Forwards header field allows the client to limit the
852   length of the request chain, which is useful for testing a chain of
853   proxies forwarding messages in an infinite loop.
856   If the request is valid, the response &SHOULD; contain the entire
857   request message in the entity-body, with a Content-Type of
858   "message/http". Responses to this method &MUST-NOT; be cached.
862<section title="CONNECT" anchor="CONNECT">
863  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
864  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
866   This specification reserves the method name CONNECT for use with a
867   proxy that can dynamically switch to being a tunnel (e.g. SSL
868   tunneling <xref target="Luo1998"/>).
874<section title="Status Code Definitions" anchor="">
876   Each Status-Code is described below, including a description of which
877   method(s) it can follow and any metainformation required in the
878   response.
881<section title="Informational 1xx" anchor="status.1xx">
883   This class of status code indicates a provisional response,
884   consisting only of the Status-Line and optional headers, and is
885   terminated by an empty line. There are no required headers for this
886   class of status code. Since HTTP/1.0 did not define any 1xx status
887   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
888   except under experimental conditions.
891   A client &MUST; be prepared to accept one or more 1xx status responses
892   prior to a regular response, even if the client does not expect a 100
893   (Continue) status message. Unexpected 1xx status responses &MAY; be
894   ignored by a user agent.
897   Proxies &MUST; forward 1xx responses, unless the connection between the
898   proxy and its client has been closed, or unless the proxy itself
899   requested the generation of the 1xx response. (For example, if a
900   proxy adds a "Expect: 100-continue" field when it forwards a request,
901   then it need not forward the corresponding 100 (Continue)
902   response(s).)
905<section title="100 Continue" anchor="status.100">
906  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
907  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
909   The client &SHOULD; continue with its request. This interim response is
910   used to inform the client that the initial part of the request has
911   been received and has not yet been rejected by the server. The client
912   &SHOULD; continue by sending the remainder of the request or, if the
913   request has already been completed, ignore this response. The server
914   &MUST; send a final response after the request has been completed. See
915   &use100; for detailed discussion of the use and handling of this
916   status code.
920<section title="101 Switching Protocols" anchor="status.101">
921  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
922  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
924   The server understands and is willing to comply with the client's
925   request, via the Upgrade message header field (&header-upgrade;), for a
926   change in the application protocol being used on this connection. The
927   server will switch protocols to those defined by the response's
928   Upgrade header field immediately after the empty line which
929   terminates the 101 response.
932   The protocol &SHOULD; be switched only when it is advantageous to do
933   so. For example, switching to a newer version of HTTP is advantageous
934   over older versions, and switching to a real-time, synchronous
935   protocol might be advantageous when delivering resources that use
936   such features.
941<section title="Successful 2xx" anchor="status.2xx">
943   This class of status code indicates that the client's request was
944   successfully received, understood, and accepted.
947<section title="200 OK" anchor="status.200">
948  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
949  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
951   The request has succeeded. The information returned with the response
952   is dependent on the method used in the request, for example:
953  <list style="hanging">
954    <t hangText="GET">
955          an entity corresponding to the requested resource is sent in
956          the response;
957    </t>
958    <t hangText="HEAD">
959          the entity-header fields corresponding to the requested
960          resource are sent in the response without any message-body;
961    </t>
962    <t hangText="POST">
963      an entity describing or containing the result of the action;
964    </t>
965    <t hangText="TRACE">
966      an entity containing the request message as received by the
967      end server.
968    </t>
969  </list>
973<section title="201 Created" anchor="status.201">
974  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
975  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
977   The request has been fulfilled and resulted in a new resource being
978   created. The newly created resource can be referenced by the URI(s)
979   returned in the entity of the response, with the most specific URI
980   for the resource given by a Location header field. The response
981   &SHOULD; include an entity containing a list of resource
982   characteristics and location(s) from which the user or user agent can
983   choose the one most appropriate. The entity format is specified by
984   the media type given in the Content-Type header field. The origin
985   server &MUST; create the resource before returning the 201 status code.
986   If the action cannot be carried out immediately, the server &SHOULD;
987   respond with 202 (Accepted) response instead.
990   A 201 response &MAY; contain an ETag response header field indicating
991   the current value of the entity tag for the requested variant just
992   created, see &header-etag;.
996<section title="202 Accepted" anchor="status.202">
997  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
998  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1000   The request has been accepted for processing, but the processing has
1001   not been completed.  The request might or might not eventually be
1002   acted upon, as it might be disallowed when processing actually takes
1003   place. There is no facility for re-sending a status code from an
1004   asynchronous operation such as this.
1007   The 202 response is intentionally non-committal. Its purpose is to
1008   allow a server to accept a request for some other process (perhaps a
1009   batch-oriented process that is only run once per day) without
1010   requiring that the user agent's connection to the server persist
1011   until the process is completed. The entity returned with this
1012   response &SHOULD; include an indication of the request's current status
1013   and either a pointer to a status monitor or some estimate of when the
1014   user can expect the request to be fulfilled.
1018<section title="203 Non-Authoritative Information" anchor="status.203">
1019  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1020  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1022   The returned metainformation in the entity-header is not the
1023   definitive set as available from the origin server, but is gathered
1024   from a local or a third-party copy. The set presented &MAY; be a subset
1025   or superset of the original version. For example, including local
1026   annotation information about the resource might result in a superset
1027   of the metainformation known by the origin server. Use of this
1028   response code is not required and is only appropriate when the
1029   response would otherwise be 200 (OK).
1033<section title="204 No Content" anchor="status.204">
1034  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1035  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1037   The server has fulfilled the request but does not need to return an
1038   entity-body, and might want to return updated metainformation. The
1039   response &MAY; include new or updated metainformation in the form of
1040   entity-headers, which if present &SHOULD; be associated with the
1041   requested variant.
1044   If the client is a user agent, it &SHOULD-NOT;  change its document view
1045   from that which caused the request to be sent. This response is
1046   primarily intended to allow input for actions to take place without
1047   causing a change to the user agent's active document view, although
1048   any new or updated metainformation &SHOULD; be applied to the document
1049   currently in the user agent's active view.
1052   The 204 response &MUST-NOT; include a message-body, and thus is always
1053   terminated by the first empty line after the header fields.
1057<section title="205 Reset Content" anchor="status.205">
1058  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1059  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1061   The server has fulfilled the request and the user agent &SHOULD; reset
1062   the document view which caused the request to be sent. This response
1063   is primarily intended to allow input for actions to take place via
1064   user input, followed by a clearing of the form in which the input is
1065   given so that the user can easily initiate another input action. The
1066   response &MUST-NOT; include an entity.
1070<section title="206 Partial Content" anchor="status.206">
1071  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1072  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1074   The server has fulfilled the partial GET request for the resource
1075   and the enclosed entity is a partial representation as defined in &range;.
1080<section title="Redirection 3xx" anchor="status.3xx">
1082   This class of status code indicates that further action needs to be
1083   taken by the user agent in order to fulfill the request.  The action
1084   required &MAY; be carried out by the user agent without interaction
1085   with the user if and only if the method used in the second request is
1086   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1087   such loops generate network traffic for each redirection.
1088  <list><t>
1089      <x:h>Note:</x:h> previous versions of this specification recommended a
1090      maximum of five redirections. Content developers should be aware
1091      that there might be clients that implement such a fixed
1092      limitation.
1093  </t></list>
1096<section title="300 Multiple Choices" anchor="status.300">
1097  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1098  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1100   The requested resource corresponds to any one of a set of
1101   representations, each with its own specific location, and agent-driven
1102   negotiation information (&content-negotiation;) is being provided so that
1103   the user (or user agent) can select a preferred representation and
1104   redirect its request to that location.
1107   Unless it was a HEAD request, the response &SHOULD; include an entity
1108   containing a list of resource characteristics and location(s) from
1109   which the user or user agent can choose the one most appropriate. The
1110   entity format is specified by the media type given in the Content-Type
1111   header field. Depending upon the format and the capabilities of
1112   the user agent, selection of the most appropriate choice &MAY; be
1113   performed automatically. However, this specification does not define
1114   any standard for such automatic selection.
1117   If the server has a preferred choice of representation, it &SHOULD;
1118   include the specific URI for that representation in the Location
1119   field; user agents &MAY; use the Location field value for automatic
1120   redirection. This response is cacheable unless indicated otherwise.
1124<section title="301 Moved Permanently" anchor="status.301">
1125  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1126  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1128   The requested resource has been assigned a new permanent URI and any
1129   future references to this resource &SHOULD; use one of the returned
1130   URIs.  Clients with link editing capabilities ought to automatically
1131   re-link references to the Request-URI to one or more of the new
1132   references returned by the server, where possible. This response is
1133   cacheable unless indicated otherwise.
1136   The new permanent URI &SHOULD; be given by the Location field in the
1137   response. Unless the request method was HEAD, the entity of the
1138   response &SHOULD; contain a short hypertext note with a hyperlink to
1139   the new URI(s).
1142   If the 301 status code is received in response to a request method
1143   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1144   then the request &MAY; be automatically redirected by the user agent without
1145   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1146   request unless it can be confirmed by the user, since this might
1147   change the conditions under which the request was issued.
1148  <list><t>
1149      <x:h>Note:</x:h> When automatically redirecting a POST request after
1150      receiving a 301 status code, some existing HTTP/1.0 user agents
1151      will erroneously change it into a GET request.
1152  </t></list>
1156<section title="302 Found" anchor="status.302">
1157  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1158  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1160   The requested resource resides temporarily under a different URI.
1161   Since the redirection might be altered on occasion, the client &SHOULD;
1162   continue to use the Request-URI for future requests.  This response
1163   is only cacheable if indicated by a Cache-Control or Expires header
1164   field.
1167   The temporary URI &SHOULD; be given by the Location field in the
1168   response. Unless the request method was HEAD, the entity of the
1169   response &SHOULD; contain a short hypertext note with a hyperlink to
1170   the new URI(s).
1173   If the 302 status code is received in response to a request method
1174   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1175   then the request &MAY; be automatically redirected by the user agent without
1176   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1177   request unless it can be confirmed by the user, since this might
1178   change the conditions under which the request was issued.
1179  <list><t>
1180      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1181      to change the method on the redirected request.  However, most
1182      existing user agent implementations treat 302 as if it were a 303
1183      response, performing a GET on the Location field-value regardless
1184      of the original request method. The status codes 303 and 307 have
1185      been added for servers that wish to make unambiguously clear which
1186      kind of reaction is expected of the client.
1187  </t></list>
1191<section title="303 See Other" anchor="status.303">
1192  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1193  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1195   The response to the request can be found under a different URI and
1196   &SHOULD; be retrieved using a GET method on that resource. This method
1197   exists primarily to allow the output of a POST-activated script to
1198   redirect the user agent to a selected resource. The new URI is not a
1199   substitute reference for the originally requested resource. The 303
1200   response &MUST-NOT; be cached, but the response to the second
1201   (redirected) request might be cacheable.
1204   The different URI &SHOULD; be given by the Location field in the
1205   response. Unless the request method was HEAD, the entity of the
1206   response &SHOULD; contain a short hypertext note with a hyperlink to
1207   the new URI(s).
1208  <list><t>
1209      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1210      status. When interoperability with such clients is a concern, the
1211      302 status code may be used instead, since most user agents react
1212      to a 302 response as described here for 303.
1213  </t></list>
1217<section title="304 Not Modified" anchor="status.304">
1218  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1219  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1221   The response to the request has not been modified since the conditions
1222   indicated by the client's conditional GET request, as defined in &conditional;.
1226<section title="305 Use Proxy" anchor="status.305">
1227  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1228  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1230   The requested resource &MUST; be accessed through the proxy given by
1231   the Location field. The Location field gives the URI of the proxy.
1232   The recipient is expected to repeat this single request via the
1233   proxy. 305 responses &MUST; only be generated by origin servers.
1234  <list><t>
1235      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1236      single request, and to be generated by origin servers only.  Not
1237      observing these limitations has significant security consequences.
1238  </t></list>
1242<section title="306 (Unused)" anchor="status.306">
1243  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1244  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1246   The 306 status code was used in a previous version of the
1247   specification, is no longer used, and the code is reserved.
1251<section title="307 Temporary Redirect" anchor="status.307">
1252  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1253  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1255   The requested resource resides temporarily under a different URI.
1256   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1257   continue to use the Request-URI for future requests.  This response
1258   is only cacheable if indicated by a Cache-Control or Expires header
1259   field.
1262   The temporary URI &SHOULD; be given by the Location field in the
1263   response. Unless the request method was HEAD, the entity of the
1264   response &SHOULD; contain a short hypertext note with a hyperlink to
1265   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1266   understand the 307 status. Therefore, the note &SHOULD; contain the
1267   information necessary for a user to repeat the original request on
1268   the new URI.
1271   If the 307 status code is received in response to a request method
1272   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1273   then the request &MAY; be automatically redirected by the user agent without
1274   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1275   request unless it can be confirmed by the user, since this might
1276   change the conditions under which the request was issued.
1281<section title="Client Error 4xx" anchor="status.4xx">
1283   The 4xx class of status code is intended for cases in which the
1284   client seems to have erred. Except when responding to a HEAD request,
1285   the server &SHOULD; include an entity containing an explanation of the
1286   error situation, and whether it is a temporary or permanent
1287   condition. These status codes are applicable to any request method.
1288   User agents &SHOULD; display any included entity to the user.
1291   If the client is sending data, a server implementation using TCP
1292   &SHOULD; be careful to ensure that the client acknowledges receipt of
1293   the packet(s) containing the response, before the server closes the
1294   input connection. If the client continues sending data to the server
1295   after the close, the server's TCP stack will send a reset packet to
1296   the client, which may erase the client's unacknowledged input buffers
1297   before they can be read and interpreted by the HTTP application.
1300<section title="400 Bad Request" anchor="status.400">
1301  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1302  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1304   The request could not be understood by the server due to malformed
1305   syntax. The client &SHOULD-NOT;  repeat the request without
1306   modifications.
1310<section title="401 Unauthorized" anchor="status.401">
1311  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1312  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1314   The request requires user authentication (see &auth;).
1318<section title="402 Payment Required" anchor="status.402">
1319  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1320  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1322   This code is reserved for future use.
1326<section title="403 Forbidden" anchor="status.403">
1327  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1328  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1330   The server understood the request, but is refusing to fulfill it.
1331   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1332   If the request method was not HEAD and the server wishes to make
1333   public why the request has not been fulfilled, it &SHOULD; describe the
1334   reason for the refusal in the entity.  If the server does not wish to
1335   make this information available to the client, the status code 404
1336   (Not Found) can be used instead.
1340<section title="404 Not Found" anchor="status.404">
1341  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1342  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1344   The server has not found anything matching the Request-URI. No
1345   indication is given of whether the condition is temporary or
1346   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1347   knows, through some internally configurable mechanism, that an old
1348   resource is permanently unavailable and has no forwarding address.
1349   This status code is commonly used when the server does not wish to
1350   reveal exactly why the request has been refused, or when no other
1351   response is applicable.
1355<section title="405 Method Not Allowed" anchor="status.405">
1356  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1357  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1359   The method specified in the Request-Line is not allowed for the
1360   resource identified by the Request-URI. The response &MUST; include an
1361   Allow header containing a list of valid methods for the requested
1362   resource.
1366<section title="406 Not Acceptable" anchor="status.406">
1367  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1368  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1370   The resource identified by the request is only capable of generating
1371   response entities which have content characteristics not acceptable
1372   according to the accept headers sent in the request.
1375   Unless it was a HEAD request, the response &SHOULD; include an entity
1376   containing a list of available entity characteristics and location(s)
1377   from which the user or user agent can choose the one most
1378   appropriate. The entity format is specified by the media type given
1379   in the Content-Type header field. Depending upon the format and the
1380   capabilities of the user agent, selection of the most appropriate
1381   choice &MAY; be performed automatically. However, this specification
1382   does not define any standard for such automatic selection.
1383  <list><t>
1384      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1385      not acceptable according to the accept headers sent in the
1386      request. In some cases, this may even be preferable to sending a
1387      406 response. User agents are encouraged to inspect the headers of
1388      an incoming response to determine if it is acceptable.
1389  </t></list>
1392   If the response could be unacceptable, a user agent &SHOULD;
1393   temporarily stop receipt of more data and query the user for a
1394   decision on further actions.
1398<section title="407 Proxy Authentication Required" anchor="status.407">
1399  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1400  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1402   This code is similar to 401 (Unauthorized), but indicates that the
1403   client must first authenticate itself with the proxy (see &auth;).
1407<section title="408 Request Timeout" anchor="status.408">
1408  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1409  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1411   The client did not produce a request within the time that the server
1412   was prepared to wait. The client &MAY; repeat the request without
1413   modifications at any later time.
1417<section title="409 Conflict" anchor="status.409">
1418  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1419  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1421   The request could not be completed due to a conflict with the current
1422   state of the resource. This code is only allowed in situations where
1423   it is expected that the user might be able to resolve the conflict
1424   and resubmit the request. The response body &SHOULD; include enough
1425   information for the user to recognize the source of the conflict.
1426   Ideally, the response entity would include enough information for the
1427   user or user agent to fix the problem; however, that might not be
1428   possible and is not required.
1431   Conflicts are most likely to occur in response to a PUT request. For
1432   example, if versioning were being used and the entity being PUT
1433   included changes to a resource which conflict with those made by an
1434   earlier (third-party) request, the server might use the 409 response
1435   to indicate that it can't complete the request. In this case, the
1436   response entity would likely contain a list of the differences
1437   between the two versions in a format defined by the response
1438   Content-Type.
1442<section title="410 Gone" anchor="status.410">
1443  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1444  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1446   The requested resource is no longer available at the server and no
1447   forwarding address is known. This condition is expected to be
1448   considered permanent. Clients with link editing capabilities &SHOULD;
1449   delete references to the Request-URI after user approval. If the
1450   server does not know, or has no facility to determine, whether or not
1451   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1452   used instead. This response is cacheable unless indicated otherwise.
1455   The 410 response is primarily intended to assist the task of web
1456   maintenance by notifying the recipient that the resource is
1457   intentionally unavailable and that the server owners desire that
1458   remote links to that resource be removed. Such an event is common for
1459   limited-time, promotional services and for resources belonging to
1460   individuals no longer working at the server's site. It is not
1461   necessary to mark all permanently unavailable resources as "gone" or
1462   to keep the mark for any length of time -- that is left to the
1463   discretion of the server owner.
1467<section title="411 Length Required" anchor="status.411">
1468  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1469  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1471   The server refuses to accept the request without a defined Content-Length.
1472   The client &MAY; repeat the request if it adds a valid
1473   Content-Length header field containing the length of the message-body
1474   in the request message.
1478<section title="412 Precondition Failed" anchor="status.412">
1479  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1480  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1482   The precondition given in one or more of the request-header fields
1483   evaluated to false when it was tested on the server, as defined in
1484   &conditional;.
1488<section title="413 Request Entity Too Large" anchor="status.413">
1489  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1490  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1492   The server is refusing to process a request because the request
1493   entity is larger than the server is willing or able to process. The
1494   server &MAY; close the connection to prevent the client from continuing
1495   the request.
1498   If the condition is temporary, the server &SHOULD; include a Retry-After
1499   header field to indicate that it is temporary and after what
1500   time the client &MAY; try again.
1504<section title="414 Request-URI Too Long" anchor="status.414">
1505  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1506  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1508   The server is refusing to service the request because the Request-URI
1509   is longer than the server is willing to interpret. This rare
1510   condition is only likely to occur when a client has improperly
1511   converted a POST request to a GET request with long query
1512   information, when the client has descended into a URI "black hole" of
1513   redirection (e.g., a redirected URI prefix that points to a suffix of
1514   itself), or when the server is under attack by a client attempting to
1515   exploit security holes present in some servers using fixed-length
1516   buffers for reading or manipulating the Request-URI.
1520<section title="415 Unsupported Media Type" anchor="status.415">
1521  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1522  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1524   The server is refusing to service the request because the entity of
1525   the request is in a format not supported by the requested resource
1526   for the requested method.
1530<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1531  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1532  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1534   The request included a Range request-header field (&header-range;) and none of
1535   the range-specifier values in this field overlap the current extent
1536   of the selected resource.
1540<section title="417 Expectation Failed" anchor="status.417">
1541  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1542  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1544   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1545   could not be met by this server, or, if the server is a proxy,
1546   the server has unambiguous evidence that the request could not be met
1547   by the next-hop server.
1552<section title="Server Error 5xx" anchor="status.5xx">
1554   Response status codes beginning with the digit "5" indicate cases in
1555   which the server is aware that it has erred or is incapable of
1556   performing the request. Except when responding to a HEAD request, the
1557   server &SHOULD; include an entity containing an explanation of the
1558   error situation, and whether it is a temporary or permanent
1559   condition. User agents &SHOULD; display any included entity to the
1560   user. These response codes are applicable to any request method.
1563<section title="500 Internal Server Error" anchor="status.500">
1564  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1565  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1567   The server encountered an unexpected condition which prevented it
1568   from fulfilling the request.
1572<section title="501 Not Implemented" anchor="status.501">
1573  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1574  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1576   The server does not support the functionality required to fulfill the
1577   request. This is the appropriate response when the server does not
1578   recognize the request method and is not capable of supporting it for
1579   any resource.
1583<section title="502 Bad Gateway" anchor="status.502">
1584  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1585  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1587   The server, while acting as a gateway or proxy, received an invalid
1588   response from the upstream server it accessed in attempting to
1589   fulfill the request.
1593<section title="503 Service Unavailable" anchor="status.503">
1594  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1595  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1597   The server is currently unable to handle the request due to a
1598   temporary overloading or maintenance of the server. The implication
1599   is that this is a temporary condition which will be alleviated after
1600   some delay. If known, the length of the delay &MAY; be indicated in a
1601   Retry-After header. If no Retry-After is given, the client &SHOULD;
1602   handle the response as it would for a 500 response.
1603  <list><t>
1604      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1605      server must use it when becoming overloaded. Some servers may wish
1606      to simply refuse the connection.
1607  </t></list>
1611<section title="504 Gateway Timeout" anchor="status.504">
1612  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1613  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1615   The server, while acting as a gateway or proxy, did not receive a
1616   timely response from the upstream server specified by the URI (e.g.
1617   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1618   to access in attempting to complete the request.
1619  <list><t>
1620      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1621      return 400 or 500 when DNS lookups time out.
1622  </t></list>
1626<section title="505 HTTP Version Not Supported" anchor="status.505">
1627  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1628  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1630   The server does not support, or refuses to support, the HTTP protocol
1631   version that was used in the request message. The server is
1632   indicating that it is unable or unwilling to complete the request
1633   using the same major version as the client, as described in &http-version;,
1634   other than with this error message. The response &SHOULD; contain
1635   an entity describing why that version is not supported and what other
1636   protocols are supported by that server.
1644<section title="Header Field Definitions" anchor="header.fields">
1646   This section defines the syntax and semantics of HTTP/1.1 header fields
1647   related to request and response semantics.
1650   For entity-header fields, both sender and recipient refer to either the
1651   client or the server, depending on who sends and who receives the entity.
1654<section title="Allow" anchor="header.allow">
1655  <iref primary="true" item="Allow header" x:for-anchor=""/>
1656  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1658      The Allow entity-header field lists the set of methods supported
1659      by the resource identified by the Request-URI. The purpose of this
1660      field is strictly to inform the recipient of valid methods
1661      associated with the resource. An Allow header field &MUST; be
1662      present in a 405 (Method Not Allowed) response.
1664<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1665       Allow   = "Allow" ":" #Method
1668      Example of use:
1670<figure><artwork type="example">
1671       Allow: GET, HEAD, PUT
1674      This field cannot prevent a client from trying other methods.
1675      However, the indications given by the Allow header field value
1676      &SHOULD; be followed. The actual set of allowed methods is defined
1677      by the origin server at the time of each request.
1680      The Allow header field &MAY; be provided with a PUT request to
1681      recommend the methods to be supported by the new or modified
1682      resource. The server is not required to support these methods and
1683      &SHOULD; include an Allow header in the response giving the actual
1684      supported methods.
1687      A proxy &MUST-NOT; modify the Allow header field even if it does not
1688      understand all the methods specified, since the user agent might
1689      have other means of communicating with the origin server.
1693<section title="Expect" anchor="header.expect">
1694  <iref primary="true" item="Expect header" x:for-anchor=""/>
1695  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1697   The Expect request-header field is used to indicate that particular
1698   server behaviors are required by the client.
1700<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"/>
1701   Expect       =  "Expect" ":" 1#expectation
1703   expectation  =  "100-continue" | expectation-extension
1704   expectation-extension =  token [ "=" ( token | quoted-string )
1705                            *expect-params ]
1706   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1709   A server that does not understand or is unable to comply with any of
1710   the expectation values in the Expect field of a request &MUST; respond
1711   with appropriate error status. The server &MUST; respond with a 417
1712   (Expectation Failed) status if any of the expectations cannot be met
1713   or, if there are other problems with the request, some other 4xx
1714   status.
1717   This header field is defined with extensible syntax to allow for
1718   future extensions. If a server receives a request containing an
1719   Expect field that includes an expectation-extension that it does not
1720   support, it &MUST; respond with a 417 (Expectation Failed) status.
1723   Comparison of expectation values is case-insensitive for unquoted
1724   tokens (including the 100-continue token), and is case-sensitive for
1725   quoted-string expectation-extensions.
1728   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1729   return a 417 (Expectation Failed) status if it receives a request
1730   with an expectation that it cannot meet. However, the Expect
1731   request-header itself is end-to-end; it &MUST; be forwarded if the
1732   request is forwarded.
1735   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1736   Expect header.
1739   See &use100; for the use of the 100 (continue) status.
1743<section title="From" anchor="header.from">
1744  <iref primary="true" item="From header" x:for-anchor=""/>
1745  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1747   The From request-header field, if given, &SHOULD; contain an Internet
1748   e-mail address for the human user who controls the requesting user
1749   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1750   in <xref target="RFC822"/> as updated by <xref target="RFC1123"/>:
1752<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1753    From   = "From" ":" mailbox
1756   An example is:
1758<figure><artwork type="example">
1759    From:
1762   This header field &MAY; be used for logging purposes and as a means for
1763   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1764   be used as an insecure form of access protection. The interpretation
1765   of this field is that the request is being performed on behalf of the
1766   person given, who accepts responsibility for the method performed. In
1767   particular, robot agents &SHOULD; include this header so that the
1768   person responsible for running the robot can be contacted if problems
1769   occur on the receiving end.
1772   The Internet e-mail address in this field &MAY; be separate from the
1773   Internet host which issued the request. For example, when a request
1774   is passed through a proxy the original issuer's address &SHOULD; be
1775   used.
1778   The client &SHOULD-NOT;  send the From header field without the user's
1779   approval, as it might conflict with the user's privacy interests or
1780   their site's security policy. It is strongly recommended that the
1781   user be able to disable, enable, and modify the value of this field
1782   at any time prior to a request.
1786<section title="Location" anchor="header.location">
1787  <iref primary="true" item="Location header" x:for-anchor=""/>
1788  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1790   The Location response-header field is used to redirect the recipient
1791   to a location other than the Request-URI for completion of the
1792   request or identification of a new resource. For 201 (Created)
1793   responses, the Location is that of the new resource which was created
1794   by the request. For 3xx responses, the location &SHOULD; indicate the
1795   server's preferred URI for automatic redirection to the resource. The
1796   field value consists of a single absolute URI.
1798<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1799    Location       = "Location" ":" absoluteURI [ "#" fragment ]
1802   An example is:
1804<figure><artwork type="example">
1805    Location:
1808  <list><t>
1809      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1810      from Location in that the Content-Location identifies the original
1811      location of the entity enclosed in the request. It is therefore
1812      possible for a response to contain header fields for both Location
1813      and Content-Location.
1814  </t></list>
1817   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1818   <list style="symbols">
1819      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1820      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1821      <t>With 305 Use Proxy.</t>
1822   </list>
1826<section title="Max-Forwards" anchor="header.max-forwards">
1827  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1828  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1830   The Max-Forwards request-header field provides a mechanism with the
1831   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1832   number of proxies or gateways that can forward the request to the
1833   next inbound server. This can be useful when the client is attempting
1834   to trace a request chain which appears to be failing or looping in
1835   mid-chain.
1837<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1838    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1841   The Max-Forwards value is a decimal integer indicating the remaining
1842   number of times this request message may be forwarded.
1845   Each proxy or gateway recipient of a TRACE or OPTIONS request
1846   containing a Max-Forwards header field &MUST; check and update its
1847   value prior to forwarding the request. If the received value is zero
1848   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1849   respond as the final recipient. If the received Max-Forwards value is
1850   greater than zero, then the forwarded message &MUST; contain an updated
1851   Max-Forwards field with a value decremented by one (1).
1854   The Max-Forwards header field &MAY; be ignored for all other methods
1855   defined by this specification and for any extension methods for which
1856   it is not explicitly referred to as part of that method definition.
1860<section title="Referer" anchor="header.referer">
1861  <iref primary="true" item="Referer header" x:for-anchor=""/>
1862  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1864   The Referer[sic] request-header field allows the client to specify,
1865   for the server's benefit, the address (URI) of the resource from
1866   which the Request-URI was obtained (the "referrer", although the
1867   header field is misspelled.) The Referer request-header allows a
1868   server to generate lists of back-links to resources for interest,
1869   logging, optimized caching, etc. It also allows obsolete or mistyped
1870   links to be traced for maintenance. The Referer field &MUST-NOT; be
1871   sent if the Request-URI was obtained from a source that does not have
1872   its own URI, such as input from the user keyboard.
1874<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1875    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1878   Example:
1880<figure><artwork type="example">
1881    Referer:
1884   If the field value is a relative URI, it &SHOULD; be interpreted
1885   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1886   <xref target=""/> for security considerations.
1890<section title="Retry-After" anchor="header.retry-after">
1891  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1892  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1894   The Retry-After response-header field can be used with a 503 (Service
1895   Unavailable) response to indicate how long the service is expected to
1896   be unavailable to the requesting client. This field &MAY; also be used
1897   with any 3xx (Redirection) response to indicate the minimum time the
1898   user-agent is asked wait before issuing the redirected request. The
1899   value of this field can be either an HTTP-date or an integer number
1900   of seconds (in decimal) after the time of the response.
1902<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1903    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1906   Two examples of its use are
1908<figure><artwork type="example">
1909    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1910    Retry-After: 120
1913   In the latter example, the delay is 2 minutes.
1917<section title="Server" anchor="header.server">
1918  <iref primary="true" item="Server header" x:for-anchor=""/>
1919  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1921   The Server response-header field contains information about the
1922   software used by the origin server to handle the request. The field
1923   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1924   identifying the server and any significant subproducts. The product
1925   tokens are listed in order of their significance for identifying the
1926   application.
1928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1929    Server         = "Server" ":" 1*( product | comment )
1932   Example:
1934<figure><artwork type="example">
1935    Server: CERN/3.0 libwww/2.17
1938   If the response is being forwarded through a proxy, the proxy
1939   application &MUST-NOT; modify the Server response-header. Instead, it
1940   &MUST; include a Via field (as described in &header-via;).
1941  <list><t>
1942      <x:h>Note:</x:h> Revealing the specific software version of the server might
1943      allow the server machine to become more vulnerable to attacks
1944      against software that is known to contain security holes. Server
1945      implementors are encouraged to make this field a configurable
1946      option.
1947  </t></list>
1951<section title="User-Agent" anchor="header.user-agent">
1952  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1953  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1955   The User-Agent request-header field contains information about the
1956   user agent originating the request. This is for statistical purposes,
1957   the tracing of protocol violations, and automated recognition of user
1958   agents for the sake of tailoring responses to avoid particular user
1959   agent limitations. User agents &SHOULD; include this field with
1960   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1961   and comments identifying the agent and any subproducts which form a
1962   significant part of the user agent. By convention, the product tokens
1963   are listed in order of their significance for identifying the
1964   application.
1966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1967    User-Agent     = "User-Agent" ":" 1*( product | comment )
1970   Example:
1972<figure><artwork type="example">
1973    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1979<section title="IANA Considerations" anchor="IANA.considerations">
1981   TBD.
1985<section title="Security Considerations" anchor="security.considerations">
1987   This section is meant to inform application developers, information
1988   providers, and users of the security limitations in HTTP/1.1 as
1989   described by this document. The discussion does not include
1990   definitive solutions to the problems revealed, though it does make
1991   some suggestions for reducing security risks.
1994<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1996   Like any generic data transfer protocol, HTTP cannot regulate the
1997   content of the data that is transferred, nor is there any a priori
1998   method of determining the sensitivity of any particular piece of
1999   information within the context of any given request. Therefore,
2000   applications &SHOULD; supply as much control over this information as
2001   possible to the provider of that information. Four header fields are
2002   worth special mention in this context: Server, Via, Referer and From.
2005   Revealing the specific software version of the server might allow the
2006   server machine to become more vulnerable to attacks against software
2007   that is known to contain security holes. Implementors &SHOULD; make the
2008   Server header field a configurable option.
2011   Proxies which serve as a portal through a network firewall &SHOULD;
2012   take special precautions regarding the transfer of header information
2013   that identifies the hosts behind the firewall. In particular, they
2014   &SHOULD; remove, or replace with sanitized versions, any Via fields
2015   generated behind the firewall.
2018   The Referer header allows reading patterns to be studied and reverse
2019   links drawn. Although it can be very useful, its power can be abused
2020   if user details are not separated from the information contained in
2021   the Referer. Even when the personal information has been removed, the
2022   Referer header might indicate a private document's URI whose
2023   publication would be inappropriate.
2026   The information sent in the From field might conflict with the user's
2027   privacy interests or their site's security policy, and hence it
2028   &SHOULD-NOT;  be transmitted without the user being able to disable,
2029   enable, and modify the contents of the field. The user &MUST; be able
2030   to set the contents of this field within a user preference or
2031   application defaults configuration.
2034   We suggest, though do not require, that a convenient toggle interface
2035   be provided for the user to enable or disable the sending of From and
2036   Referer information.
2039   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2040   fields can sometimes be used to determine that a specific client or
2041   server have a particular security hole which might be exploited.
2042   Unfortunately, this same information is often used for other valuable
2043   purposes for which HTTP currently has no better mechanism.
2047<section title="Encoding Sensitive Information in URI's" anchor="">
2049   Because the source of a link might be private information or might
2050   reveal an otherwise private information source, it is strongly
2051   recommended that the user be able to select whether or not the
2052   Referer field is sent. For example, a browser client could have a
2053   toggle switch for browsing openly/anonymously, which would
2054   respectively enable/disable the sending of Referer and From
2055   information.
2058   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2059   HTTP request if the referring page was transferred with a secure
2060   protocol.
2063   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2064   based forms for the submission of sensitive data, because this will
2065   cause this data to be encoded in the Request-URI. Many existing
2066   servers, proxies, and user agents will log the request URI in some
2067   place where it might be visible to third parties. Servers can use
2068   POST-based form submission instead
2072<section title="Location Headers and Spoofing" anchor="location.spoofing">
2074   If a single server supports multiple organizations that do not trust
2075   one another, then it &MUST; check the values of Location and Content-Location
2076   headers in responses that are generated under control of
2077   said organizations to make sure that they do not attempt to
2078   invalidate resources over which they have no authority.
2084<section title="Acknowledgments" anchor="ack">
2089<references title="Normative References">
2091<reference anchor="Part1">
2092  <front>
2093    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2094    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2095      <organization abbrev="Day Software">Day Software</organization>
2096      <address><email></email></address>
2097    </author>
2098    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2099      <organization>One Laptop per Child</organization>
2100      <address><email></email></address>
2101    </author>
2102    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2103      <organization abbrev="HP">Hewlett-Packard Company</organization>
2104      <address><email></email></address>
2105    </author>
2106    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2107      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2108      <address><email></email></address>
2109    </author>
2110    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2111      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2112      <address><email></email></address>
2113    </author>
2114    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2115      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2116      <address><email></email></address>
2117    </author>
2118    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2119      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2120      <address><email></email></address>
2121    </author>
2122    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2123      <organization abbrev="W3C">World Wide Web Consortium</organization>
2124      <address><email></email></address>
2125    </author>
2126    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2127      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2128      <address><email></email></address>
2129    </author>
2130    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2131  </front>
2132  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2133  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2136<reference anchor="Part3">
2137  <front>
2138    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2139    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2140      <organization abbrev="Day Software">Day Software</organization>
2141      <address><email></email></address>
2142    </author>
2143    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2144      <organization>One Laptop per Child</organization>
2145      <address><email></email></address>
2146    </author>
2147    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2148      <organization abbrev="HP">Hewlett-Packard Company</organization>
2149      <address><email></email></address>
2150    </author>
2151    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2152      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2153      <address><email></email></address>
2154    </author>
2155    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2156      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2157      <address><email></email></address>
2158    </author>
2159    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2160      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2161      <address><email></email></address>
2162    </author>
2163    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2164      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2165      <address><email></email></address>
2166    </author>
2167    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2168      <organization abbrev="W3C">World Wide Web Consortium</organization>
2169      <address><email></email></address>
2170    </author>
2171    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2172      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2173      <address><email></email></address>
2174    </author>
2175    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2176  </front>
2177  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2178  <x:source href="p3-payload.xml" basename="p3-payload"/>
2181<reference anchor="Part4">
2182  <front>
2183    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2184    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2185      <organization abbrev="Day Software">Day Software</organization>
2186      <address><email></email></address>
2187    </author>
2188    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2189      <organization>One Laptop per Child</organization>
2190      <address><email></email></address>
2191    </author>
2192    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2193      <organization abbrev="HP">Hewlett-Packard Company</organization>
2194      <address><email></email></address>
2195    </author>
2196    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2197      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2198      <address><email></email></address>
2199    </author>
2200    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2201      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2202      <address><email></email></address>
2203    </author>
2204    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2206      <address><email></email></address>
2207    </author>
2208    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2209      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2210      <address><email></email></address>
2211    </author>
2212    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2213      <organization abbrev="W3C">World Wide Web Consortium</organization>
2214      <address><email></email></address>
2215    </author>
2216    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2217      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2218      <address><email></email></address>
2219    </author>
2220    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2221  </front>
2222  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2223  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2226<reference anchor="Part5">
2227  <front>
2228    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2229    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2230      <organization abbrev="Day Software">Day Software</organization>
2231      <address><email></email></address>
2232    </author>
2233    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2234      <organization>One Laptop per Child</organization>
2235      <address><email></email></address>
2236    </author>
2237    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2238      <organization abbrev="HP">Hewlett-Packard Company</organization>
2239      <address><email></email></address>
2240    </author>
2241    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2242      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2243      <address><email></email></address>
2244    </author>
2245    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2246      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2247      <address><email></email></address>
2248    </author>
2249    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2251      <address><email></email></address>
2252    </author>
2253    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2254      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2255      <address><email></email></address>
2256    </author>
2257    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2258      <organization abbrev="W3C">World Wide Web Consortium</organization>
2259      <address><email></email></address>
2260    </author>
2261    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2262      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2263      <address><email></email></address>
2264    </author>
2265    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2266  </front>
2267  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2268  <x:source href="p5-range.xml" basename="p5-range"/>
2271<reference anchor="Part6">
2272  <front>
2273    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2274    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2275      <organization abbrev="Day Software">Day Software</organization>
2276      <address><email></email></address>
2277    </author>
2278    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2279      <organization>One Laptop per Child</organization>
2280      <address><email></email></address>
2281    </author>
2282    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2283      <organization abbrev="HP">Hewlett-Packard Company</organization>
2284      <address><email></email></address>
2285    </author>
2286    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2287      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2288      <address><email></email></address>
2289    </author>
2290    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2291      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2292      <address><email></email></address>
2293    </author>
2294    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2296      <address><email></email></address>
2297    </author>
2298    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2299      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2300      <address><email></email></address>
2301    </author>
2302    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2303      <organization abbrev="W3C">World Wide Web Consortium</organization>
2304      <address><email></email></address>
2305    </author>
2306    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2307      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2308      <address><email></email></address>
2309    </author>
2310    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2311  </front>
2312  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2313  <x:source href="p6-cache.xml" basename="p6-cache"/>
2316<reference anchor="Part7">
2317  <front>
2318    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2319    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2320      <organization abbrev="Day Software">Day Software</organization>
2321      <address><email></email></address>
2322    </author>
2323    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2324      <organization>One Laptop per Child</organization>
2325      <address><email></email></address>
2326    </author>
2327    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2328      <organization abbrev="HP">Hewlett-Packard Company</organization>
2329      <address><email></email></address>
2330    </author>
2331    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2332      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2333      <address><email></email></address>
2334    </author>
2335    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2336      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2337      <address><email></email></address>
2338    </author>
2339    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2340      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2341      <address><email></email></address>
2342    </author>
2343    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2344      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2345      <address><email></email></address>
2346    </author>
2347    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2348      <organization abbrev="W3C">World Wide Web Consortium</organization>
2349      <address><email></email></address>
2350    </author>
2351    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2352      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2353      <address><email></email></address>
2354    </author>
2355    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2356  </front>
2357  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2358  <x:source href="p7-auth.xml" basename="p7-auth"/>
2361<reference anchor="RFC2119">
2362  <front>
2363    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2364    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2365      <organization>Harvard University</organization>
2366      <address><email></email></address>
2367    </author>
2368    <date month="March" year="1997"/>
2369  </front>
2370  <seriesInfo name="BCP" value="14"/>
2371  <seriesInfo name="RFC" value="2119"/>
2376<references title="Informative References">
2378<reference anchor="RFC2068">
2379  <front>
2380    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2381    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2382      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2383      <address><email></email></address>
2384    </author>
2385    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2386      <organization>MIT Laboratory for Computer Science</organization>
2387      <address><email></email></address>
2388    </author>
2389    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2390      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2391      <address><email></email></address>
2392    </author>
2393    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2394      <organization>MIT Laboratory for Computer Science</organization>
2395      <address><email></email></address>
2396    </author>
2397    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2398      <organization>MIT Laboratory for Computer Science</organization>
2399      <address><email></email></address>
2400    </author>
2401    <date month="January" year="1997"/>
2402  </front>
2403  <seriesInfo name="RFC" value="2068"/>
2406<reference anchor="RFC2616">
2407  <front>
2408    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2409    <author initials="R." surname="Fielding" fullname="R. Fielding">
2410      <organization>University of California, Irvine</organization>
2411      <address><email></email></address>
2412    </author>
2413    <author initials="J." surname="Gettys" fullname="J. Gettys">
2414      <organization>W3C</organization>
2415      <address><email></email></address>
2416    </author>
2417    <author initials="J." surname="Mogul" fullname="J. Mogul">
2418      <organization>Compaq Computer Corporation</organization>
2419      <address><email></email></address>
2420    </author>
2421    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2422      <organization>MIT Laboratory for Computer Science</organization>
2423      <address><email></email></address>
2424    </author>
2425    <author initials="L." surname="Masinter" fullname="L. Masinter">
2426      <organization>Xerox Corporation</organization>
2427      <address><email></email></address>
2428    </author>
2429    <author initials="P." surname="Leach" fullname="P. Leach">
2430      <organization>Microsoft Corporation</organization>
2431      <address><email></email></address>
2432    </author>
2433    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2434      <organization>W3C</organization>
2435      <address><email></email></address>
2436    </author>
2437    <date month="June" year="1999"/>
2438  </front>
2439  <seriesInfo name="RFC" value="2616"/>
2444<references title="References (to be categorized)">
2446<reference anchor="RFC1123">
2447  <front>
2448    <title>Requirements for Internet Hosts - Application and Support</title>
2449    <author initials="R." surname="Braden" fullname="Robert Braden">
2450      <organization>University of Southern California (USC), Information Sciences Institute</organization>
2451      <address><email>Braden@ISI.EDU</email></address>
2452    </author>
2453    <date month="October" year="1989"/>
2454  </front>
2455  <seriesInfo name="STD" value="3"/>
2456  <seriesInfo name="RFC" value="1123"/>
2459<reference anchor="RFC822">
2460  <front>
2461    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2462    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2463      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
2464      <address><email>DCrocker@UDel-Relay</email></address>
2465    </author>
2466    <date month="August" day="13" year="1982"/>
2467  </front>
2468  <seriesInfo name="STD" value="11"/>
2469  <seriesInfo name="RFC" value="822"/>
2472<reference anchor="RFC1945">
2473  <front>
2474    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2475    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2476      <organization>MIT, Laboratory for Computer Science</organization>
2477      <address><email></email></address>
2478    </author>
2479    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2481      <address><email></email></address>
2482    </author>
2483    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2484      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2485      <address><email></email></address>
2486    </author>
2487    <date month="May" year="1996"/>
2488  </front>
2489  <seriesInfo name="RFC" value="1945"/>
2492<reference anchor="Luo1998">
2494<title>Tunneling TCP based protocols through Web proxy servers</title>
2495<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2496  <organization/>
2500<seriesInfo name="" value="Work in Progress"/>
2505<section title="Compatibility with Previous Versions" anchor="compatibility">
2506<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2508   Clarified which error code should be used for inbound server failures
2509   (e.g. DNS failures). (<xref target="status.504"/>).
2512   CREATE had a race that required an Etag be sent when a resource is
2513   first created. (<xref target="status.201"/>).
2516   Rewrite of message transmission requirements to make it much harder
2517   for implementors to get it wrong, as the consequences of errors here
2518   can have significant impact on the Internet, and to deal with the
2519   following problems:
2520  <list style="numbers">
2521      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2522         this was incorrectly placing a requirement on the behavior of
2523         an implementation of a future version of HTTP/1.x</t>
2525      <t>Made it clear that user-agents should retry requests, not
2526         "clients" in general.</t>
2528      <t>Converted requirements for clients to ignore unexpected 100
2529         (Continue) responses, and for proxies to forward 100 responses,
2530         into a general requirement for 1xx responses.</t>
2532      <t>Modified some TCP-specific language, to make it clearer that
2533         non-TCP transports are possible for HTTP.</t>
2535      <t>Require that the origin server &MUST-NOT; wait for the request
2536         body before it sends a required 100 (Continue) response.</t>
2538      <t>Allow, rather than require, a server to omit 100 (Continue) if
2539         it has already seen some of the request body.</t>
2541      <t>Allow servers to defend against denial-of-service attacks and
2542         broken clients.</t>
2543  </list>
2546   This change adds the Expect header and 417 status code.
2549   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2550   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2553   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
2554   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2558<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2560  Clarify definition of POST.
2561  (<xref target="POST"/>)
2564  Failed to consider that there are
2565  many other request methods that are safe to automatically redirect,
2566  and further that the user agent is able to make that determination
2567  based on the request method semantics.
2568  (Sections <xref format="counter" target="status.301"/>,
2569  <xref format="counter" target="status.302"/> and
2570  <xref format="counter" target="status.307"/> )
2573  Correct syntax of Location header to allow fragment,
2574  as referred symbol wasn't what was expected, and add some
2575  clarifications as to when it would not be appropriate.
2576  (<xref target="header.location"/>)
2579  In the description of the Server header, the Via field
2580  was described as a SHOULD. The requirement was and is stated
2581  correctly in the description of the Via header in &header-via;.
2582  (<xref target="header.server"/>)
2588<section title="Change Log (to be removed by RFC Editor before publication)">
2590<section title="Since RFC2616">
2592  Extracted relevant partitions from <xref target="RFC2616"/>.
2596<section title="Since draft-ietf-httpbis-p2-semantics-00">
2598  Closed issues:
2599  <list style="symbols">
2600    <t>
2601      <eref target=""/>:
2602      "Via is a MUST"
2603      (<eref target=""/>)
2604    </t>
2605    <t>
2606      <eref target=""/>:
2607      "Fragments allowed in Location"
2608      (<eref target=""/>)
2609    </t>
2610    <t>
2611      <eref target=""/>:
2612      "Safe Methods vs Redirection"
2613      (<eref target=""/>)
2614    </t>
2615    <t>
2616      <eref target=""/>:
2617      "Revise description of the POST method"
2618      (<eref target=""/>)
2619    </t>
2620    <t>
2621      <eref target=""/>:
2622      "RFC2606 Compliance"
2623    </t>
2624  </list>
2627  Other changes:
2628  <list style="symbols">
2629    <t>
2630      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2631    </t>
2632    <t>
2633      Start work on categorizing references as "Normative" or "Informative".
2634    </t>
2635  </list>
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