source: draft-ietf-httpbis/01/p2-semantics.xml @ 164

Last change on this file since 164 was 162, checked in by fielding@…, 15 years ago

editorial: write preliminary introduction to p2 noting future reorg

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x=''/>">
18  <!ENTITY payload                    "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY conditional                "<xref target='Part4' xmlns:x=''/>">
20  <!ENTITY range                      "<xref target='Part5' xmlns:x=''/>">
21  <!ENTITY caching                    "<xref target='Part6' xmlns:x=''/>">
22  <!ENTITY auth                       "<xref target='Part7' xmlns:x=''/>">
23  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
24  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
25  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
26  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
27  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
28  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
29  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
30  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
31  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
32  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
33  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
34  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
35  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
36  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
37  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
38  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
39  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
40  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
41  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
42  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
43  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
44  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
45  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
46  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
47  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
48  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
49  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
50  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
51  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
52  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
53  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
54  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
55  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
56  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
57  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc-ext allow-markup-in-artwork="yes" ?>
67<?rfc-ext include-references-in-index="yes" ?>
68<rfc obsoletes="2616" category="std"
69     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
70     xmlns:x=''>
73  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
75  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
76    <organization abbrev="Day Software">Day Software</organization>
77    <address>
78      <postal>
79        <street>23 Corporate Plaza DR, Suite 280</street>
80        <city>Newport Beach</city>
81        <region>CA</region>
82        <code>92660</code>
83        <country>USA</country>
84      </postal>
85      <phone>+1-949-706-5300</phone>
86      <facsimile>+1-949-706-5305</facsimile>
87      <email></email>
88      <uri></uri>
89    </address>
90  </author>
92  <author initials="J." surname="Gettys" fullname="Jim Gettys">
93    <organization>One Laptop per Child</organization>
94    <address>
95      <postal>
96        <street>21 Oak Knoll Road</street>
97        <city>Carlisle</city>
98        <region>MA</region>
99        <code>01741</code>
100        <country>USA</country>
101      </postal>
102      <email></email>
103      <uri></uri>
104    </address>
105  </author>
107  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
108    <organization abbrev="HP">Hewlett-Packard Company</organization>
109    <address>
110      <postal>
111        <street>HP Labs, Large Scale Systems Group</street>
112        <street>1501 Page Mill Road, MS 1177</street>
113        <city>Palo Alto</city>
114        <region>CA</region>
115        <code>94304</code>
116        <country>USA</country>
117      </postal>
118      <email></email>
119    </address>
120  </author>
122  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
123    <organization abbrev="Microsoft">Microsoft Corporation</organization>
124    <address>
125      <postal>
126        <street>1 Microsoft Way</street>
127        <city>Redmond</city>
128        <region>WA</region>
129        <code>98052</code>
130        <country>USA</country>
131      </postal>
132      <email></email>
133    </address>
134  </author>
136  <author initials="L." surname="Masinter" fullname="Larry Masinter">
137    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
138    <address>
139      <postal>
140        <street>345 Park Ave</street>
141        <city>San Jose</city>
142        <region>CA</region>
143        <code>95110</code>
144        <country>USA</country>
145      </postal>
146      <email></email>
147      <uri></uri>
148    </address>
149  </author>
151  <author initials="P." surname="Leach" fullname="Paul J. Leach">
152    <organization abbrev="Microsoft">Microsoft Corporation</organization>
153    <address>
154      <postal>
155        <street>1 Microsoft Way</street>
156        <city>Redmond</city>
157        <region>WA</region>
158        <code>98052</code>
159      </postal>
160      <email></email>
161    </address>
162  </author>
164  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
165    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
169        <street>The Stata Center, Building 32</street>
170        <street>32 Vassar Street</street>
171        <city>Cambridge</city>
172        <region>MA</region>
173        <code>02139</code>
174        <country>USA</country>
175      </postal>
176      <email></email>
177      <uri></uri>
178    </address>
179  </author>
181  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
182    <organization abbrev="W3C">World Wide Web Consortium</organization>
183    <address>
184      <postal>
185        <street>W3C / ERCIM</street>
186        <street>2004, rte des Lucioles</street>
187        <city>Sophia-Antipolis</city>
188        <region>AM</region>
189        <code>06902</code>
190        <country>France</country>
191      </postal>
192      <email></email>
193      <uri></uri>
194    </address>
195  </author>
197  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
198    <organization abbrev="greenbytes">greenbytes GmbH</organization>
199    <address>
200      <postal>
201        <street>Hafenweg 16</street>
202        <city>Muenster</city><region>NW</region><code>48155</code>
203        <country>Germany</country>
204      </postal>
205      <phone>+49 251 2807760</phone>   
206      <facsimile>+49 251 2807761</facsimile>   
207      <email></email>       
208      <uri></uri>     
209    </address>
210  </author>
212  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
216   The Hypertext Transfer Protocol (HTTP) is an application-level
217   protocol for distributed, collaborative, hypermedia information
218   systems. HTTP has been in use by the World Wide Web global information
219   initiative since 1990. This document is Part 2 of the seven-part specification
220   that defines the protocol referred to as "HTTP/1.1" and, taken together,
221   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
222   as expressed by request methods, request-header fields, response status codes,
223   and response-header fields.
227<note title="Editorial Note (To be removed by RFC Editor)">
228  <t>
229    Discussion of this draft should take place on the HTTPBIS working group
230    mailing list ( The current issues list is
231    at <eref target=""/>
232    and related documents (including fancy diffs) can be found at
233    <eref target=""/>.
234  </t>
235  <t>
236    This draft incorporates those issue resolutions that were either
237    collected in the original RFC2616 errata list (<eref target=""/>),
238    or which were agreed upon on the mailing list between October 2006 and
239    November 2007 (as published in "draft-lafon-rfc2616bis-03").
240  </t>
244<section title="Introduction" anchor="introduction">
246   This document defines HTTP/1.1 request and response semantics.  Each HTTP
247   message, as defined in &messaging;, is in the form of either a request or
248   a response.  An HTTP server listens on a connection for HTTP requests and
249   responds to each request, in the order received on that connection, with
250   one or more HTTP response messages.  This document defines the commonly
251   agreed upon semantics of the HTTP uniform interface, the intentions defined
252   by each request method, and the various response messages that might be
253   expected as a result of applying that method for the requested resource.
256   This document is currently disorganized in order to minimize the changes
257   between drafts and enable reviewers to see the smaller errata changes.
258   The next draft will reorganize the sections to better reflect the content.
259   In particular, the sections will be ordered according to the typical
260   processing of an HTTP request message (after message parsing): resource
261   mapping, general header fields, methods, request modifiers, response
262   status, and resource metadata.  The current mess reflects how widely
263   dispersed these topics and associated requirements had become in
264   <xref target="RFC2616"/>.
267<section title="Requirements" anchor="intro.requirements">
269   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
270   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
271   document are to be interpreted as described in <xref target="RFC2119"/>.
274   An implementation is not compliant if it fails to satisfy one or more
275   of the &MUST; or &REQUIRED; level requirements for the protocols it
276   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
277   level and all the &SHOULD; level requirements for its protocols is said
278   to be "unconditionally compliant"; one that satisfies all the &MUST;
279   level requirements but not all the &SHOULD; level requirements for its
280   protocols is said to be "conditionally compliant."
285<section title="Product Tokens" anchor="product.tokens">
287   Product tokens are used to allow communicating applications to
288   identify themselves by software name and version. Most fields using
289   product tokens also allow sub-products which form a significant part
290   of the application to be listed, separated by white space. By
291   convention, the products are listed in order of their significance
292   for identifying the application.
294<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
295  product         = token ["/" product-version]
296  product-version = token
299   Examples:
301<figure><artwork type="example">
302    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
303    Server: Apache/0.8.4
306   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
307   used for advertising or other non-essential information. Although any
308   token character &MAY; appear in a product-version, this token &SHOULD;
309   only be used for a version identifier (i.e., successive versions of
310   the same product &SHOULD; only differ in the product-version portion of
311   the product value).
315<section title="Method" anchor="method">
317   The Method  token indicates the method to be performed on the
318   resource identified by the Request-URI. The method is case-sensitive.
320<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
321  Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
322                 | "GET"                    ; <xref target="GET"/>
323                 | "HEAD"                   ; <xref target="HEAD"/>
324                 | "POST"                   ; <xref target="POST"/>
325                 | "PUT"                    ; <xref target="PUT"/>
326                 | "DELETE"                 ; <xref target="DELETE"/>
327                 | "TRACE"                  ; <xref target="TRACE"/>
328                 | "CONNECT"                ; <xref target="CONNECT"/>
329                 | extension-method
330  extension-method = token
333   The list of methods allowed by a resource can be specified in an
334   Allow header field (<xref target="header.allow"/>). The return code of the response
335   always notifies the client whether a method is currently allowed on a
336   resource, since the set of allowed methods can change dynamically. An
337   origin server &SHOULD; return the status code 405 (Method Not Allowed)
338   if the method is known by the origin server but not allowed for the
339   requested resource, and 501 (Not Implemented) if the method is
340   unrecognized or not implemented by the origin server. The methods GET
341   and HEAD &MUST; be supported by all general-purpose servers. All other
342   methods are &OPTIONAL;; however, if the above methods are implemented,
343   they &MUST; be implemented with the same semantics as those specified
344   in <xref target="method.definitions"/>.
348<section title="Request Header Fields" anchor="request.header.fields">
350   The request-header fields allow the client to pass additional
351   information about the request, and about the client itself, to the
352   server. These fields act as request modifiers, with semantics
353   equivalent to the parameters on a programming language method
354   invocation.
356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
357  request-header = Accept                   ; &header-accept;
358                 | Accept-Charset           ; &header-accept-charset;
359                 | Accept-Encoding          ; &header-accept-encoding;
360                 | Accept-Language          ; &header-accept-language;
361                 | Authorization            ; &header-authorization;
362                 | Expect                   ; <xref target="header.expect"/>
363                 | From                     ; <xref target="header.from"/>
364                 | Host                     ; &header-host;
365                 | If-Match                 ; &header-if-match;
366                 | If-Modified-Since        ; &header-if-modified-since;
367                 | If-None-Match            ; &header-if-none-match;
368                 | If-Range                 ; &header-if-range;
369                 | If-Unmodified-Since      ; &header-if-unmodified-since;
370                 | Max-Forwards             ; <xref target="header.max-forwards"/>
371                 | Proxy-Authorization      ; &header-proxy-authorization;
372                 | Range                    ; &header-range;
373                 | Referer                  ; <xref target="header.referer"/>
374                 | TE                       ; &header-te;
375                 | User-Agent               ; <xref target="header.user-agent"/>
378   Request-header field names can be extended reliably only in
379   combination with a change in the protocol version. However, new or
380   experimental header fields &MAY; be given the semantics of request-header
381   fields if all parties in the communication recognize them to
382   be request-header fields. Unrecognized header fields are treated as
383   entity-header fields.
387<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
389   The Status-Code element is a 3-digit integer result code of the
390   attempt to understand and satisfy the request. The status codes listed
391   below are defined in <xref target=""/>.
392   The Reason-Phrase is intended to give a short
393   textual description of the Status-Code. The Status-Code is intended
394   for use by automata and the Reason-Phrase is intended for the human
395   user. The client is not required to examine or display the Reason-Phrase.
398   The individual values of the numeric status codes defined for
399   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
400   presented below. The reason phrases listed here are only
401   recommendations -- they &MAY; be replaced by local equivalents without
402   affecting the protocol.
404<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"/>
405  Status-Code    =
406         "100"  ; <xref target="status.100"/>: Continue
407       | "101"  ; <xref target="status.101"/>: Switching Protocols
408       | "200"  ; <xref target="status.200"/>: OK
409       | "201"  ; <xref target="status.201"/>: Created
410       | "202"  ; <xref target="status.202"/>: Accepted
411       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
412       | "204"  ; <xref target="status.204"/>: No Content
413       | "205"  ; <xref target="status.205"/>: Reset Content
414       | "206"  ; <xref target="status.206"/>: Partial Content
415       | "300"  ; <xref target="status.300"/>: Multiple Choices
416       | "301"  ; <xref target="status.301"/>: Moved Permanently
417       | "302"  ; <xref target="status.302"/>: Found
418       | "303"  ; <xref target="status.303"/>: See Other
419       | "304"  ; <xref target="status.304"/>: Not Modified
420       | "305"  ; <xref target="status.305"/>: Use Proxy
421       | "307"  ; <xref target="status.307"/>: Temporary Redirect
422       | "400"  ; <xref target="status.400"/>: Bad Request
423       | "401"  ; <xref target="status.401"/>: Unauthorized
424       | "402"  ; <xref target="status.402"/>: Payment Required
425       | "403"  ; <xref target="status.403"/>: Forbidden
426       | "404"  ; <xref target="status.404"/>: Not Found
427       | "405"  ; <xref target="status.405"/>: Method Not Allowed
428       | "406"  ; <xref target="status.406"/>: Not Acceptable
429       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
430       | "408"  ; <xref target="status.408"/>: Request Time-out
431       | "409"  ; <xref target="status.409"/>: Conflict
432       | "410"  ; <xref target="status.410"/>: Gone
433       | "411"  ; <xref target="status.411"/>: Length Required
434       | "412"  ; <xref target="status.412"/>: Precondition Failed
435       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
436       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
437       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
438       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
439       | "417"  ; <xref target="status.417"/>: Expectation Failed
440       | "500"  ; <xref target="status.500"/>: Internal Server Error
441       | "501"  ; <xref target="status.501"/>: Not Implemented
442       | "502"  ; <xref target="status.502"/>: Bad Gateway
443       | "503"  ; <xref target="status.503"/>: Service Unavailable
444       | "504"  ; <xref target="status.504"/>: Gateway Time-out
445       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
446       | extension-code
448  extension-code = 3DIGIT
449  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
452   HTTP status codes are extensible. HTTP applications are not required
453   to understand the meaning of all registered status codes, though such
454   understanding is obviously desirable. However, applications &MUST;
455   understand the class of any status code, as indicated by the first
456   digit, and treat any unrecognized response as being equivalent to the
457   x00 status code of that class, with the exception that an
458   unrecognized response &MUST-NOT; be cached. For example, if an
459   unrecognized status code of 431 is received by the client, it can
460   safely assume that there was something wrong with its request and
461   treat the response as if it had received a 400 status code. In such
462   cases, user agents &SHOULD; present to the user the entity returned
463   with the response, since that entity is likely to include human-readable
464   information which will explain the unusual status.
468<section title="Response Header Fields" anchor="response.header.fields">
470   The response-header fields allow the server to pass additional
471   information about the response which cannot be placed in the Status-Line.
472   These header fields give information about the server and about
473   further access to the resource identified by the Request-URI.
475<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
476  response-header = Accept-Ranges           ; &header-accept-ranges;
477                  | Age                     ; &header-age;
478                  | ETag                    ; &header-etag;
479                  | Location                ; <xref target="header.location"/>
480                  | Proxy-Authenticate      ; &header-proxy-authenticate;
481                  | Retry-After             ; <xref target="header.retry-after"/>
482                  | Server                  ; <xref target="header.server"/>
483                  | Vary                    ; &header-vary;
484                  | WWW-Authenticate        ; &header-www-authenticate;
487   Response-header field names can be extended reliably only in
488   combination with a change in the protocol version. However, new or
489   experimental header fields &MAY; be given the semantics of response-header
490   fields if all parties in the communication recognize them to
491   be response-header fields. Unrecognized header fields are treated as
492   entity-header fields.
496<section title="Entity" anchor="entity">
498   Request and Response messages &MAY; transfer an entity if not otherwise
499   restricted by the request method or response status code. An entity
500   consists of entity-header fields and an entity-body, although some
501   responses will only include the entity-headers. HTTP entity-body and
502   entity-header fields are defined in &payload;.
505   An entity-body is only present in a message when a message-body is
506   present, as described in &message-body;. The entity-body is obtained
507   from the message-body by decoding any Transfer-Encoding that might
508   have been applied to ensure safe and proper transfer of the message.
513<section title="Method Definitions" anchor="method.definitions">
515   The set of common methods for HTTP/1.1 is defined below. Although
516   this set can be expanded, additional methods cannot be assumed to
517   share the same semantics for separately extended clients and servers.
519   The Host request-header field (&header-host;) &MUST; accompany all
520   HTTP/1.1 requests.
523<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
525<section title="Safe Methods" anchor="safe.methods">
527   Implementors should be aware that the software represents the user in
528   their interactions over the Internet, and should be careful to allow
529   the user to be aware of any actions they might take which may have an
530   unexpected significance to themselves or others.
533   In particular, the convention has been established that the GET and
534   HEAD methods &SHOULD-NOT;  have the significance of taking an action
535   other than retrieval. These methods ought to be considered "safe".
536   This allows user agents to represent other methods, such as POST, PUT
537   and DELETE, in a special way, so that the user is made aware of the
538   fact that a possibly unsafe action is being requested.
541   Naturally, it is not possible to ensure that the server does not
542   generate side-effects as a result of performing a GET request; in
543   fact, some dynamic resources consider that a feature. The important
544   distinction here is that the user did not request the side-effects,
545   so therefore cannot be held accountable for them.
549<section title="Idempotent Methods" anchor="idempotent.methods">
551   Methods can also have the property of "idempotence" in that (aside
552   from error or expiration issues) the side-effects of N &gt; 0 identical
553   requests is the same as for a single request. The methods GET, HEAD,
554   PUT and DELETE share this property. Also, the methods OPTIONS and
555   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
558   However, it is possible that a sequence of several requests is non-idempotent,
559   even if all of the methods executed in that sequence are
560   idempotent. (A sequence is idempotent if a single execution of the
561   entire sequence always yields a result that is not changed by a
562   reexecution of all, or part, of that sequence.) For example, a
563   sequence is non-idempotent if its result depends on a value that is
564   later modified in the same sequence.
567   A sequence that never has side effects is idempotent, by definition
568   (provided that no concurrent operations are being executed on the
569   same set of resources).
574<section title="OPTIONS" anchor="OPTIONS">
575  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
576  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
578   The OPTIONS method represents a request for information about the
579   communication options available on the request/response chain
580   identified by the Request-URI. This method allows the client to
581   determine the options and/or requirements associated with a resource,
582   or the capabilities of a server, without implying a resource action
583   or initiating a resource retrieval.
586   Responses to this method are not cacheable.
589   If the OPTIONS request includes an entity-body (as indicated by the
590   presence of Content-Length or Transfer-Encoding), then the media type
591   &MUST; be indicated by a Content-Type field. Although this
592   specification does not define any use for such a body, future
593   extensions to HTTP might use the OPTIONS body to make more detailed
594   queries on the server. A server that does not support such an
595   extension &MAY; discard the request body.
598   If the Request-URI is an asterisk ("*"), the OPTIONS request is
599   intended to apply to the server in general rather than to a specific
600   resource. Since a server's communication options typically depend on
601   the resource, the "*" request is only useful as a "ping" or "no-op"
602   type of method; it does nothing beyond allowing the client to test
603   the capabilities of the server. For example, this can be used to test
604   a proxy for HTTP/1.1 compliance (or lack thereof).
607   If the Request-URI is not an asterisk, the OPTIONS request applies
608   only to the options that are available when communicating with that
609   resource.
612   A 200 response &SHOULD; include any header fields that indicate
613   optional features implemented by the server and applicable to that
614   resource (e.g., Allow), possibly including extensions not defined by
615   this specification. The response body, if any, &SHOULD; also include
616   information about the communication options. The format for such a
617   body is not defined by this specification, but might be defined by
618   future extensions to HTTP. Content negotiation &MAY; be used to select
619   the appropriate response format. If no response body is included, the
620   response &MUST; include a Content-Length field with a field-value of
621   "0".
624   The Max-Forwards request-header field &MAY; be used to target a
625   specific proxy in the request chain. When a proxy receives an OPTIONS
626   request on an absoluteURI for which request forwarding is permitted,
627   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
628   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
629   instead, the proxy &SHOULD; respond with its own communication options.
630   If the Max-Forwards field-value is an integer greater than zero, the
631   proxy &MUST; decrement the field-value when it forwards the request. If
632   no Max-Forwards field is present in the request, then the forwarded
633   request &MUST-NOT; include a Max-Forwards field.
637<section title="GET" anchor="GET">
638  <iref primary="true" item="GET method" x:for-anchor=""/>
639  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
641   The GET method means retrieve whatever information (in the form of an
642   entity) is identified by the Request-URI. If the Request-URI refers
643   to a data-producing process, it is the produced data which shall be
644   returned as the entity in the response and not the source text of the
645   process, unless that text happens to be the output of the process.
648   The semantics of the GET method change to a "conditional GET" if the
649   request message includes an If-Modified-Since, If-Unmodified-Since,
650   If-Match, If-None-Match, or If-Range header field. A conditional GET
651   method requests that the entity be transferred only under the
652   circumstances described by the conditional header field(s). The
653   conditional GET method is intended to reduce unnecessary network
654   usage by allowing cached entities to be refreshed without requiring
655   multiple requests or transferring data already held by the client.
658   The semantics of the GET method change to a "partial GET" if the
659   request message includes a Range header field. A partial GET requests
660   that only part of the entity be transferred, as described in &header-range;.
661   The partial GET method is intended to reduce unnecessary
662   network usage by allowing partially-retrieved entities to be
663   completed without transferring data already held by the client.
666   The response to a GET request is cacheable if and only if it meets
667   the requirements for HTTP caching described in &caching;.
670   See <xref target=""/> for security considerations when used for forms.
674<section title="HEAD" anchor="HEAD">
675  <iref primary="true" item="HEAD method" x:for-anchor=""/>
676  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
678   The HEAD method is identical to GET except that the server &MUST-NOT;
679   return a message-body in the response. The metainformation contained
680   in the HTTP headers in response to a HEAD request &SHOULD; be identical
681   to the information sent in response to a GET request. This method can
682   be used for obtaining metainformation about the entity implied by the
683   request without transferring the entity-body itself. This method is
684   often used for testing hypertext links for validity, accessibility,
685   and recent modification.
688   The response to a HEAD request &MAY; be cacheable in the sense that the
689   information contained in the response &MAY; be used to update a
690   previously cached entity from that resource. If the new field values
691   indicate that the cached entity differs from the current entity (as
692   would be indicated by a change in Content-Length, Content-MD5, ETag
693   or Last-Modified), then the cache &MUST; treat the cache entry as
694   stale.
698<section title="POST" anchor="POST">
699  <iref primary="true" item="POST method" x:for-anchor=""/>
700  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
702   The POST method is used to request that the origin server accept the
703   entity enclosed in the request as data to be processed by the resource
704   identified by the Request-URI in the Request-Line. POST is designed
705   to allow a uniform method to cover the following functions:
706  <list style="symbols">
707    <t>
708      Annotation of existing resources;
709    </t>
710    <t>
711        Posting a message to a bulletin board, newsgroup, mailing list,
712        or similar group of articles;
713    </t>
714    <t>
715        Providing a block of data, such as the result of submitting a
716        form, to a data-handling process;
717    </t>
718    <t>
719        Extending a database through an append operation.
720    </t>
721  </list>
724   The actual function performed by the POST method is determined by the
725   server and is usually dependent on the Request-URI.
728   The action performed by the POST method might not result in a
729   resource that can be identified by a URI. In this case, either 200
730   (OK) or 204 (No Content) is the appropriate response status,
731   depending on whether or not the response includes an entity that
732   describes the result.
735   If a resource has been created on the origin server, the response
736   &SHOULD; be 201 (Created) and contain an entity which describes the
737   status of the request and refers to the new resource, and a Location
738   header (see <xref target="header.location"/>).
741   Responses to this method are not cacheable, unless the response
742   includes appropriate Cache-Control or Expires header fields. However,
743   the 303 (See Other) response can be used to direct the user agent to
744   retrieve a cacheable resource.
748<section title="PUT" anchor="PUT">
749  <iref primary="true" item="PUT method" x:for-anchor=""/>
750  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
752   The PUT method requests that the enclosed entity be stored under the
753   supplied Request-URI. If the Request-URI refers to an already
754   existing resource, the enclosed entity &SHOULD; be considered as a
755   modified version of the one residing on the origin server. If the
756   Request-URI does not point to an existing resource, and that URI is
757   capable of being defined as a new resource by the requesting user
758   agent, the origin server can create the resource with that URI. If a
759   new resource is created, the origin server &MUST; inform the user agent
760   via the 201 (Created) response. If an existing resource is modified,
761   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
762   to indicate successful completion of the request. If the resource
763   could not be created or modified with the Request-URI, an appropriate
764   error response &SHOULD; be given that reflects the nature of the
765   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
766   (e.g. Content-Range) headers that it does not understand or implement
767   and &MUST; return a 501 (Not Implemented) response in such cases.
770   If the request passes through a cache and the Request-URI identifies
771   one or more currently cached entities, those entries &SHOULD; be
772   treated as stale. Responses to this method are not cacheable.
775   The fundamental difference between the POST and PUT requests is
776   reflected in the different meaning of the Request-URI. The URI in a
777   POST request identifies the resource that will handle the enclosed
778   entity. That resource might be a data-accepting process, a gateway to
779   some other protocol, or a separate entity that accepts annotations.
780   In contrast, the URI in a PUT request identifies the entity enclosed
781   with the request -- the user agent knows what URI is intended and the
782   server &MUST-NOT; attempt to apply the request to some other resource.
783   If the server desires that the request be applied to a different URI,
784   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
785   then make its own decision regarding whether or not to redirect the
786   request.
789   A single resource &MAY; be identified by many different URIs. For
790   example, an article might have a URI for identifying "the current
791   version" which is separate from the URI identifying each particular
792   version. In this case, a PUT request on a general URI might result in
793   several other URIs being defined by the origin server.
796   HTTP/1.1 does not define how a PUT method affects the state of an
797   origin server.
800   Unless otherwise specified for a particular entity-header, the
801   entity-headers in the PUT request &SHOULD; be applied to the resource
802   created or modified by the PUT.
806<section title="DELETE" anchor="DELETE">
807  <iref primary="true" item="DELETE method" x:for-anchor=""/>
808  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
810   The DELETE method requests that the origin server delete the resource
811   identified by the Request-URI. This method &MAY; be overridden by human
812   intervention (or other means) on the origin server. The client cannot
813   be guaranteed that the operation has been carried out, even if the
814   status code returned from the origin server indicates that the action
815   has been completed successfully. However, the server &SHOULD-NOT;
816   indicate success unless, at the time the response is given, it
817   intends to delete the resource or move it to an inaccessible
818   location.
821   A successful response &SHOULD; be 200 (OK) if the response includes an
822   entity describing the status, 202 (Accepted) if the action has not
823   yet been enacted, or 204 (No Content) if the action has been enacted
824   but the response does not include an entity.
827   If the request passes through a cache and the Request-URI identifies
828   one or more currently cached entities, those entries &SHOULD; be
829   treated as stale. Responses to this method are not cacheable.
833<section title="TRACE" anchor="TRACE">
834  <iref primary="true" item="TRACE method" x:for-anchor=""/>
835  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
837   The TRACE method is used to invoke a remote, application-layer loop-back
838   of the request message. The final recipient of the request
839   &SHOULD; reflect the message received back to the client as the
840   entity-body of a 200 (OK) response. The final recipient is either the
841   origin server or the first proxy or gateway to receive a Max-Forwards
842   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
843   &MUST-NOT; include an entity.
846   TRACE allows the client to see what is being received at the other
847   end of the request chain and use that data for testing or diagnostic
848   information. The value of the Via header field (&header-via;) is of
849   particular interest, since it acts as a trace of the request chain.
850   Use of the Max-Forwards header field allows the client to limit the
851   length of the request chain, which is useful for testing a chain of
852   proxies forwarding messages in an infinite loop.
855   If the request is valid, the response &SHOULD; contain the entire
856   request message in the entity-body, with a Content-Type of
857   "message/http". Responses to this method &MUST-NOT; be cached.
861<section title="CONNECT" anchor="CONNECT">
862  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
863  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
865   This specification reserves the method name CONNECT for use with a
866   proxy that can dynamically switch to being a tunnel (e.g. SSL
867   tunneling <xref target="Luo1998"/>).
873<section title="Status Code Definitions" anchor="">
875   Each Status-Code is described below, including a description of which
876   method(s) it can follow and any metainformation required in the
877   response.
880<section title="Informational 1xx" anchor="status.1xx">
882   This class of status code indicates a provisional response,
883   consisting only of the Status-Line and optional headers, and is
884   terminated by an empty line. There are no required headers for this
885   class of status code. Since HTTP/1.0 did not define any 1xx status
886   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
887   except under experimental conditions.
890   A client &MUST; be prepared to accept one or more 1xx status responses
891   prior to a regular response, even if the client does not expect a 100
892   (Continue) status message. Unexpected 1xx status responses &MAY; be
893   ignored by a user agent.
896   Proxies &MUST; forward 1xx responses, unless the connection between the
897   proxy and its client has been closed, or unless the proxy itself
898   requested the generation of the 1xx response. (For example, if a
899   proxy adds a "Expect: 100-continue" field when it forwards a request,
900   then it need not forward the corresponding 100 (Continue)
901   response(s).)
904<section title="100 Continue" anchor="status.100">
905  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
906  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
908   The client &SHOULD; continue with its request. This interim response is
909   used to inform the client that the initial part of the request has
910   been received and has not yet been rejected by the server. The client
911   &SHOULD; continue by sending the remainder of the request or, if the
912   request has already been completed, ignore this response. The server
913   &MUST; send a final response after the request has been completed. See
914   &use100; for detailed discussion of the use and handling of this
915   status code.
919<section title="101 Switching Protocols" anchor="status.101">
920  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
921  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
923   The server understands and is willing to comply with the client's
924   request, via the Upgrade message header field (&header-upgrade;), for a
925   change in the application protocol being used on this connection. The
926   server will switch protocols to those defined by the response's
927   Upgrade header field immediately after the empty line which
928   terminates the 101 response.
931   The protocol &SHOULD; be switched only when it is advantageous to do
932   so. For example, switching to a newer version of HTTP is advantageous
933   over older versions, and switching to a real-time, synchronous
934   protocol might be advantageous when delivering resources that use
935   such features.
940<section title="Successful 2xx" anchor="status.2xx">
942   This class of status code indicates that the client's request was
943   successfully received, understood, and accepted.
946<section title="200 OK" anchor="status.200">
947  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
948  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
950   The request has succeeded. The information returned with the response
951   is dependent on the method used in the request, for example:
952  <list style="hanging">
953    <t hangText="GET">
954          an entity corresponding to the requested resource is sent in
955          the response;
956    </t>
957    <t hangText="HEAD">
958          the entity-header fields corresponding to the requested
959          resource are sent in the response without any message-body;
960    </t>
961    <t hangText="POST">
962      an entity describing or containing the result of the action;
963    </t>
964    <t hangText="TRACE">
965      an entity containing the request message as received by the
966      end server.
967    </t>
968  </list>
972<section title="201 Created" anchor="status.201">
973  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
974  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
976   The request has been fulfilled and resulted in a new resource being
977   created. The newly created resource can be referenced by the URI(s)
978   returned in the entity of the response, with the most specific URI
979   for the resource given by a Location header field. The response
980   &SHOULD; include an entity containing a list of resource
981   characteristics and location(s) from which the user or user agent can
982   choose the one most appropriate. The entity format is specified by
983   the media type given in the Content-Type header field. The origin
984   server &MUST; create the resource before returning the 201 status code.
985   If the action cannot be carried out immediately, the server &SHOULD;
986   respond with 202 (Accepted) response instead.
989   A 201 response &MAY; contain an ETag response header field indicating
990   the current value of the entity tag for the requested variant just
991   created, see &header-etag;.
995<section title="202 Accepted" anchor="status.202">
996  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
997  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
999   The request has been accepted for processing, but the processing has
1000   not been completed.  The request might or might not eventually be
1001   acted upon, as it might be disallowed when processing actually takes
1002   place. There is no facility for re-sending a status code from an
1003   asynchronous operation such as this.
1006   The 202 response is intentionally non-committal. Its purpose is to
1007   allow a server to accept a request for some other process (perhaps a
1008   batch-oriented process that is only run once per day) without
1009   requiring that the user agent's connection to the server persist
1010   until the process is completed. The entity returned with this
1011   response &SHOULD; include an indication of the request's current status
1012   and either a pointer to a status monitor or some estimate of when the
1013   user can expect the request to be fulfilled.
1017<section title="203 Non-Authoritative Information" anchor="status.203">
1018  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1019  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1021   The returned metainformation in the entity-header is not the
1022   definitive set as available from the origin server, but is gathered
1023   from a local or a third-party copy. The set presented &MAY; be a subset
1024   or superset of the original version. For example, including local
1025   annotation information about the resource might result in a superset
1026   of the metainformation known by the origin server. Use of this
1027   response code is not required and is only appropriate when the
1028   response would otherwise be 200 (OK).
1032<section title="204 No Content" anchor="status.204">
1033  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1034  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1036   The server has fulfilled the request but does not need to return an
1037   entity-body, and might want to return updated metainformation. The
1038   response &MAY; include new or updated metainformation in the form of
1039   entity-headers, which if present &SHOULD; be associated with the
1040   requested variant.
1043   If the client is a user agent, it &SHOULD-NOT;  change its document view
1044   from that which caused the request to be sent. This response is
1045   primarily intended to allow input for actions to take place without
1046   causing a change to the user agent's active document view, although
1047   any new or updated metainformation &SHOULD; be applied to the document
1048   currently in the user agent's active view.
1051   The 204 response &MUST-NOT; include a message-body, and thus is always
1052   terminated by the first empty line after the header fields.
1056<section title="205 Reset Content" anchor="status.205">
1057  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1058  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1060   The server has fulfilled the request and the user agent &SHOULD; reset
1061   the document view which caused the request to be sent. This response
1062   is primarily intended to allow input for actions to take place via
1063   user input, followed by a clearing of the form in which the input is
1064   given so that the user can easily initiate another input action. The
1065   response &MUST-NOT; include an entity.
1069<section title="206 Partial Content" anchor="status.206">
1070  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1071  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1073   The server has fulfilled the partial GET request for the resource
1074   and the enclosed entity is a partial representation as defined in &range;.
1079<section title="Redirection 3xx" anchor="status.3xx">
1081   This class of status code indicates that further action needs to be
1082   taken by the user agent in order to fulfill the request.  The action
1083   required &MAY; be carried out by the user agent without interaction
1084   with the user if and only if the method used in the second request is
1085   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1086   such loops generate network traffic for each redirection.
1087  <list><t>
1088      <x:h>Note:</x:h> previous versions of this specification recommended a
1089      maximum of five redirections. Content developers should be aware
1090      that there might be clients that implement such a fixed
1091      limitation.
1092  </t></list>
1095<section title="300 Multiple Choices" anchor="status.300">
1096  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1097  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1099   The requested resource corresponds to any one of a set of
1100   representations, each with its own specific location, and agent-driven
1101   negotiation information (&content-negotiation;) is being provided so that
1102   the user (or user agent) can select a preferred representation and
1103   redirect its request to that location.
1106   Unless it was a HEAD request, the response &SHOULD; include an entity
1107   containing a list of resource characteristics and location(s) from
1108   which the user or user agent can choose the one most appropriate. The
1109   entity format is specified by the media type given in the Content-Type
1110   header field. Depending upon the format and the capabilities of
1111   the user agent, selection of the most appropriate choice &MAY; be
1112   performed automatically. However, this specification does not define
1113   any standard for such automatic selection.
1116   If the server has a preferred choice of representation, it &SHOULD;
1117   include the specific URI for that representation in the Location
1118   field; user agents &MAY; use the Location field value for automatic
1119   redirection. This response is cacheable unless indicated otherwise.
1123<section title="301 Moved Permanently" anchor="status.301">
1124  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1125  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1127   The requested resource has been assigned a new permanent URI and any
1128   future references to this resource &SHOULD; use one of the returned
1129   URIs.  Clients with link editing capabilities ought to automatically
1130   re-link references to the Request-URI to one or more of the new
1131   references returned by the server, where possible. This response is
1132   cacheable unless indicated otherwise.
1135   The new permanent URI &SHOULD; be given by the Location field in the
1136   response. Unless the request method was HEAD, the entity of the
1137   response &SHOULD; contain a short hypertext note with a hyperlink to
1138   the new URI(s).
1141   If the 301 status code is received in response to a request method
1142   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1143   then the request &MAY; be automatically redirected by the user agent without
1144   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1145   request unless it can be confirmed by the user, since this might
1146   change the conditions under which the request was issued.
1147  <list><t>
1148      <x:h>Note:</x:h> When automatically redirecting a POST request after
1149      receiving a 301 status code, some existing HTTP/1.0 user agents
1150      will erroneously change it into a GET request.
1151  </t></list>
1155<section title="302 Found" anchor="status.302">
1156  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1157  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1159   The requested resource resides temporarily under a different URI.
1160   Since the redirection might be altered on occasion, the client &SHOULD;
1161   continue to use the Request-URI for future requests.  This response
1162   is only cacheable if indicated by a Cache-Control or Expires header
1163   field.
1166   The temporary URI &SHOULD; be given by the Location field in the
1167   response. Unless the request method was HEAD, the entity of the
1168   response &SHOULD; contain a short hypertext note with a hyperlink to
1169   the new URI(s).
1172   If the 302 status code is received in response to a request method
1173   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1174   then the request &MAY; be automatically redirected by the user agent without
1175   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1176   request unless it can be confirmed by the user, since this might
1177   change the conditions under which the request was issued.
1178  <list><t>
1179      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1180      to change the method on the redirected request.  However, most
1181      existing user agent implementations treat 302 as if it were a 303
1182      response, performing a GET on the Location field-value regardless
1183      of the original request method. The status codes 303 and 307 have
1184      been added for servers that wish to make unambiguously clear which
1185      kind of reaction is expected of the client.
1186  </t></list>
1190<section title="303 See Other" anchor="status.303">
1191  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1192  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1194   The response to the request can be found under a different URI and
1195   &SHOULD; be retrieved using a GET method on that resource. This method
1196   exists primarily to allow the output of a POST-activated script to
1197   redirect the user agent to a selected resource. The new URI is not a
1198   substitute reference for the originally requested resource. The 303
1199   response &MUST-NOT; be cached, but the response to the second
1200   (redirected) request might be cacheable.
1203   The different URI &SHOULD; be given by the Location field in the
1204   response. Unless the request method was HEAD, the entity of the
1205   response &SHOULD; contain a short hypertext note with a hyperlink to
1206   the new URI(s).
1207  <list><t>
1208      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1209      status. When interoperability with such clients is a concern, the
1210      302 status code may be used instead, since most user agents react
1211      to a 302 response as described here for 303.
1212  </t></list>
1216<section title="304 Not Modified" anchor="status.304">
1217  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1218  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1220   The response to the request has not been modified since the conditions
1221   indicated by the client's conditional GET request, as defined in &conditional;.
1225<section title="305 Use Proxy" anchor="status.305">
1226  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1227  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1229   The requested resource &MUST; be accessed through the proxy given by
1230   the Location field. The Location field gives the URI of the proxy.
1231   The recipient is expected to repeat this single request via the
1232   proxy. 305 responses &MUST; only be generated by origin servers.
1233  <list><t>
1234      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1235      single request, and to be generated by origin servers only.  Not
1236      observing these limitations has significant security consequences.
1237  </t></list>
1241<section title="306 (Unused)" anchor="status.306">
1242  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1243  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1245   The 306 status code was used in a previous version of the
1246   specification, is no longer used, and the code is reserved.
1250<section title="307 Temporary Redirect" anchor="status.307">
1251  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1252  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1254   The requested resource resides temporarily under a different URI.
1255   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1256   continue to use the Request-URI for future requests.  This response
1257   is only cacheable if indicated by a Cache-Control or Expires header
1258   field.
1261   The temporary URI &SHOULD; be given by the Location field in the
1262   response. Unless the request method was HEAD, the entity of the
1263   response &SHOULD; contain a short hypertext note with a hyperlink to
1264   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1265   understand the 307 status. Therefore, the note &SHOULD; contain the
1266   information necessary for a user to repeat the original request on
1267   the new URI.
1270   If the 307 status code is received in response to a request method
1271   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1272   then the request &MAY; be automatically redirected by the user agent without
1273   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1274   request unless it can be confirmed by the user, since this might
1275   change the conditions under which the request was issued.
1280<section title="Client Error 4xx" anchor="status.4xx">
1282   The 4xx class of status code is intended for cases in which the
1283   client seems to have erred. Except when responding to a HEAD request,
1284   the server &SHOULD; include an entity containing an explanation of the
1285   error situation, and whether it is a temporary or permanent
1286   condition. These status codes are applicable to any request method.
1287   User agents &SHOULD; display any included entity to the user.
1290   If the client is sending data, a server implementation using TCP
1291   &SHOULD; be careful to ensure that the client acknowledges receipt of
1292   the packet(s) containing the response, before the server closes the
1293   input connection. If the client continues sending data to the server
1294   after the close, the server's TCP stack will send a reset packet to
1295   the client, which may erase the client's unacknowledged input buffers
1296   before they can be read and interpreted by the HTTP application.
1299<section title="400 Bad Request" anchor="status.400">
1300  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1301  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1303   The request could not be understood by the server due to malformed
1304   syntax. The client &SHOULD-NOT;  repeat the request without
1305   modifications.
1309<section title="401 Unauthorized" anchor="status.401">
1310  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1311  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1313   The request requires user authentication (see &auth;).
1317<section title="402 Payment Required" anchor="status.402">
1318  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1319  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1321   This code is reserved for future use.
1325<section title="403 Forbidden" anchor="status.403">
1326  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1327  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1329   The server understood the request, but is refusing to fulfill it.
1330   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1331   If the request method was not HEAD and the server wishes to make
1332   public why the request has not been fulfilled, it &SHOULD; describe the
1333   reason for the refusal in the entity.  If the server does not wish to
1334   make this information available to the client, the status code 404
1335   (Not Found) can be used instead.
1339<section title="404 Not Found" anchor="status.404">
1340  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1341  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1343   The server has not found anything matching the Request-URI. No
1344   indication is given of whether the condition is temporary or
1345   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1346   knows, through some internally configurable mechanism, that an old
1347   resource is permanently unavailable and has no forwarding address.
1348   This status code is commonly used when the server does not wish to
1349   reveal exactly why the request has been refused, or when no other
1350   response is applicable.
1354<section title="405 Method Not Allowed" anchor="status.405">
1355  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1356  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1358   The method specified in the Request-Line is not allowed for the
1359   resource identified by the Request-URI. The response &MUST; include an
1360   Allow header containing a list of valid methods for the requested
1361   resource.
1365<section title="406 Not Acceptable" anchor="status.406">
1366  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1367  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1369   The resource identified by the request is only capable of generating
1370   response entities which have content characteristics not acceptable
1371   according to the accept headers sent in the request.
1374   Unless it was a HEAD request, the response &SHOULD; include an entity
1375   containing a list of available entity characteristics and location(s)
1376   from which the user or user agent can choose the one most
1377   appropriate. The entity format is specified by the media type given
1378   in the Content-Type header field. Depending upon the format and the
1379   capabilities of the user agent, selection of the most appropriate
1380   choice &MAY; be performed automatically. However, this specification
1381   does not define any standard for such automatic selection.
1382  <list><t>
1383      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1384      not acceptable according to the accept headers sent in the
1385      request. In some cases, this may even be preferable to sending a
1386      406 response. User agents are encouraged to inspect the headers of
1387      an incoming response to determine if it is acceptable.
1388  </t></list>
1391   If the response could be unacceptable, a user agent &SHOULD;
1392   temporarily stop receipt of more data and query the user for a
1393   decision on further actions.
1397<section title="407 Proxy Authentication Required" anchor="status.407">
1398  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1399  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1401   This code is similar to 401 (Unauthorized), but indicates that the
1402   client must first authenticate itself with the proxy (see &auth;).
1406<section title="408 Request Timeout" anchor="status.408">
1407  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1408  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1410   The client did not produce a request within the time that the server
1411   was prepared to wait. The client &MAY; repeat the request without
1412   modifications at any later time.
1416<section title="409 Conflict" anchor="status.409">
1417  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1418  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1420   The request could not be completed due to a conflict with the current
1421   state of the resource. This code is only allowed in situations where
1422   it is expected that the user might be able to resolve the conflict
1423   and resubmit the request. The response body &SHOULD; include enough
1424   information for the user to recognize the source of the conflict.
1425   Ideally, the response entity would include enough information for the
1426   user or user agent to fix the problem; however, that might not be
1427   possible and is not required.
1430   Conflicts are most likely to occur in response to a PUT request. For
1431   example, if versioning were being used and the entity being PUT
1432   included changes to a resource which conflict with those made by an
1433   earlier (third-party) request, the server might use the 409 response
1434   to indicate that it can't complete the request. In this case, the
1435   response entity would likely contain a list of the differences
1436   between the two versions in a format defined by the response
1437   Content-Type.
1441<section title="410 Gone" anchor="status.410">
1442  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1443  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1445   The requested resource is no longer available at the server and no
1446   forwarding address is known. This condition is expected to be
1447   considered permanent. Clients with link editing capabilities &SHOULD;
1448   delete references to the Request-URI after user approval. If the
1449   server does not know, or has no facility to determine, whether or not
1450   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1451   used instead. This response is cacheable unless indicated otherwise.
1454   The 410 response is primarily intended to assist the task of web
1455   maintenance by notifying the recipient that the resource is
1456   intentionally unavailable and that the server owners desire that
1457   remote links to that resource be removed. Such an event is common for
1458   limited-time, promotional services and for resources belonging to
1459   individuals no longer working at the server's site. It is not
1460   necessary to mark all permanently unavailable resources as "gone" or
1461   to keep the mark for any length of time -- that is left to the
1462   discretion of the server owner.
1466<section title="411 Length Required" anchor="status.411">
1467  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1468  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1470   The server refuses to accept the request without a defined Content-Length.
1471   The client &MAY; repeat the request if it adds a valid
1472   Content-Length header field containing the length of the message-body
1473   in the request message.
1477<section title="412 Precondition Failed" anchor="status.412">
1478  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1479  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1481   The precondition given in one or more of the request-header fields
1482   evaluated to false when it was tested on the server, as defined in
1483   &conditional;.
1487<section title="413 Request Entity Too Large" anchor="status.413">
1488  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1489  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1491   The server is refusing to process a request because the request
1492   entity is larger than the server is willing or able to process. The
1493   server &MAY; close the connection to prevent the client from continuing
1494   the request.
1497   If the condition is temporary, the server &SHOULD; include a Retry-After
1498   header field to indicate that it is temporary and after what
1499   time the client &MAY; try again.
1503<section title="414 Request-URI Too Long" anchor="status.414">
1504  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1505  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1507   The server is refusing to service the request because the Request-URI
1508   is longer than the server is willing to interpret. This rare
1509   condition is only likely to occur when a client has improperly
1510   converted a POST request to a GET request with long query
1511   information, when the client has descended into a URI "black hole" of
1512   redirection (e.g., a redirected URI prefix that points to a suffix of
1513   itself), or when the server is under attack by a client attempting to
1514   exploit security holes present in some servers using fixed-length
1515   buffers for reading or manipulating the Request-URI.
1519<section title="415 Unsupported Media Type" anchor="status.415">
1520  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1521  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1523   The server is refusing to service the request because the entity of
1524   the request is in a format not supported by the requested resource
1525   for the requested method.
1529<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1530  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1531  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1533   The request included a Range request-header field (&header-range;) and none of
1534   the range-specifier values in this field overlap the current extent
1535   of the selected resource.
1539<section title="417 Expectation Failed" anchor="status.417">
1540  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1541  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1543   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1544   could not be met by this server, or, if the server is a proxy,
1545   the server has unambiguous evidence that the request could not be met
1546   by the next-hop server.
1551<section title="Server Error 5xx" anchor="status.5xx">
1553   Response status codes beginning with the digit "5" indicate cases in
1554   which the server is aware that it has erred or is incapable of
1555   performing the request. Except when responding to a HEAD request, the
1556   server &SHOULD; include an entity containing an explanation of the
1557   error situation, and whether it is a temporary or permanent
1558   condition. User agents &SHOULD; display any included entity to the
1559   user. These response codes are applicable to any request method.
1562<section title="500 Internal Server Error" anchor="status.500">
1563  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1564  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1566   The server encountered an unexpected condition which prevented it
1567   from fulfilling the request.
1571<section title="501 Not Implemented" anchor="status.501">
1572  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1573  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1575   The server does not support the functionality required to fulfill the
1576   request. This is the appropriate response when the server does not
1577   recognize the request method and is not capable of supporting it for
1578   any resource.
1582<section title="502 Bad Gateway" anchor="status.502">
1583  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1584  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1586   The server, while acting as a gateway or proxy, received an invalid
1587   response from the upstream server it accessed in attempting to
1588   fulfill the request.
1592<section title="503 Service Unavailable" anchor="status.503">
1593  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1594  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1596   The server is currently unable to handle the request due to a
1597   temporary overloading or maintenance of the server. The implication
1598   is that this is a temporary condition which will be alleviated after
1599   some delay. If known, the length of the delay &MAY; be indicated in a
1600   Retry-After header. If no Retry-After is given, the client &SHOULD;
1601   handle the response as it would for a 500 response.
1602  <list><t>
1603      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1604      server must use it when becoming overloaded. Some servers may wish
1605      to simply refuse the connection.
1606  </t></list>
1610<section title="504 Gateway Timeout" anchor="status.504">
1611  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1612  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1614   The server, while acting as a gateway or proxy, did not receive a
1615   timely response from the upstream server specified by the URI (e.g.
1616   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1617   to access in attempting to complete the request.
1618  <list><t>
1619      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1620      return 400 or 500 when DNS lookups time out.
1621  </t></list>
1625<section title="505 HTTP Version Not Supported" anchor="status.505">
1626  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1627  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1629   The server does not support, or refuses to support, the HTTP protocol
1630   version that was used in the request message. The server is
1631   indicating that it is unable or unwilling to complete the request
1632   using the same major version as the client, as described in &http-version;,
1633   other than with this error message. The response &SHOULD; contain
1634   an entity describing why that version is not supported and what other
1635   protocols are supported by that server.
1643<section title="Header Field Definitions" anchor="header.fields">
1645   This section defines the syntax and semantics of HTTP/1.1 header fields
1646   related to request and response semantics.
1649   For entity-header fields, both sender and recipient refer to either the
1650   client or the server, depending on who sends and who receives the entity.
1653<section title="Allow" anchor="header.allow">
1654  <iref primary="true" item="Allow header" x:for-anchor=""/>
1655  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1657      The Allow entity-header field lists the set of methods supported
1658      by the resource identified by the Request-URI. The purpose of this
1659      field is strictly to inform the recipient of valid methods
1660      associated with the resource. An Allow header field &MUST; be
1661      present in a 405 (Method Not Allowed) response.
1663<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1664  Allow   = "Allow" ":" #Method
1667      Example of use:
1669<figure><artwork type="example">
1670       Allow: GET, HEAD, PUT
1673      This field cannot prevent a client from trying other methods.
1674      However, the indications given by the Allow header field value
1675      &SHOULD; be followed. The actual set of allowed methods is defined
1676      by the origin server at the time of each request.
1679      The Allow header field &MAY; be provided with a PUT request to
1680      recommend the methods to be supported by the new or modified
1681      resource. The server is not required to support these methods and
1682      &SHOULD; include an Allow header in the response giving the actual
1683      supported methods.
1686      A proxy &MUST-NOT; modify the Allow header field even if it does not
1687      understand all the methods specified, since the user agent might
1688      have other means of communicating with the origin server.
1692<section title="Expect" anchor="header.expect">
1693  <iref primary="true" item="Expect header" x:for-anchor=""/>
1694  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1696   The Expect request-header field is used to indicate that particular
1697   server behaviors are required by the client.
1699<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"/>
1700  Expect       =  "Expect" ":" 1#expectation
1702  expectation  =  "100-continue" | expectation-extension
1703  expectation-extension =  token [ "=" ( token | quoted-string )
1704                           *expect-params ]
1705  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1708   A server that does not understand or is unable to comply with any of
1709   the expectation values in the Expect field of a request &MUST; respond
1710   with appropriate error status. The server &MUST; respond with a 417
1711   (Expectation Failed) status if any of the expectations cannot be met
1712   or, if there are other problems with the request, some other 4xx
1713   status.
1716   This header field is defined with extensible syntax to allow for
1717   future extensions. If a server receives a request containing an
1718   Expect field that includes an expectation-extension that it does not
1719   support, it &MUST; respond with a 417 (Expectation Failed) status.
1722   Comparison of expectation values is case-insensitive for unquoted
1723   tokens (including the 100-continue token), and is case-sensitive for
1724   quoted-string expectation-extensions.
1727   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1728   return a 417 (Expectation Failed) status if it receives a request
1729   with an expectation that it cannot meet. However, the Expect
1730   request-header itself is end-to-end; it &MUST; be forwarded if the
1731   request is forwarded.
1734   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1735   Expect header.
1738   See &use100; for the use of the 100 (Continue) status.
1742<section title="From" anchor="header.from">
1743  <iref primary="true" item="From header" x:for-anchor=""/>
1744  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1746   The From request-header field, if given, &SHOULD; contain an Internet
1747   e-mail address for the human user who controls the requesting user
1748   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1749   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1751<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1752  From   = "From" ":" mailbox
1755   An example is:
1757<figure><artwork type="example">
1758    From:
1761   This header field &MAY; be used for logging purposes and as a means for
1762   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1763   be used as an insecure form of access protection. The interpretation
1764   of this field is that the request is being performed on behalf of the
1765   person given, who accepts responsibility for the method performed. In
1766   particular, robot agents &SHOULD; include this header so that the
1767   person responsible for running the robot can be contacted if problems
1768   occur on the receiving end.
1771   The Internet e-mail address in this field &MAY; be separate from the
1772   Internet host which issued the request. For example, when a request
1773   is passed through a proxy the original issuer's address &SHOULD; be
1774   used.
1777   The client &SHOULD-NOT;  send the From header field without the user's
1778   approval, as it might conflict with the user's privacy interests or
1779   their site's security policy. It is strongly recommended that the
1780   user be able to disable, enable, and modify the value of this field
1781   at any time prior to a request.
1785<section title="Location" anchor="header.location">
1786  <iref primary="true" item="Location header" x:for-anchor=""/>
1787  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1789   The Location response-header field is used to redirect the recipient
1790   to a location other than the Request-URI for completion of the
1791   request or identification of a new resource. For 201 (Created)
1792   responses, the Location is that of the new resource which was created
1793   by the request. For 3xx responses, the location &SHOULD; indicate the
1794   server's preferred URI for automatic redirection to the resource. The
1795   field value consists of a single absolute URI.
1797<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1798  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1801   An example is:
1803<figure><artwork type="example">
1804    Location:
1807  <list><t>
1808      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1809      from Location in that the Content-Location identifies the original
1810      location of the entity enclosed in the request. It is therefore
1811      possible for a response to contain header fields for both Location
1812      and Content-Location.
1813  </t></list>
1816   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1817   <list style="symbols">
1818      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1819      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1820      <t>With 305 Use Proxy.</t>
1821   </list>
1825<section title="Max-Forwards" anchor="header.max-forwards">
1826  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1827  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1829   The Max-Forwards request-header field provides a mechanism with the
1830   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1831   number of proxies or gateways that can forward the request to the
1832   next inbound server. This can be useful when the client is attempting
1833   to trace a request chain which appears to be failing or looping in
1834   mid-chain.
1836<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1837  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1840   The Max-Forwards value is a decimal integer indicating the remaining
1841   number of times this request message may be forwarded.
1844   Each proxy or gateway recipient of a TRACE or OPTIONS request
1845   containing a Max-Forwards header field &MUST; check and update its
1846   value prior to forwarding the request. If the received value is zero
1847   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1848   respond as the final recipient. If the received Max-Forwards value is
1849   greater than zero, then the forwarded message &MUST; contain an updated
1850   Max-Forwards field with a value decremented by one (1).
1853   The Max-Forwards header field &MAY; be ignored for all other methods
1854   defined by this specification and for any extension methods for which
1855   it is not explicitly referred to as part of that method definition.
1859<section title="Referer" anchor="header.referer">
1860  <iref primary="true" item="Referer header" x:for-anchor=""/>
1861  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1863   The Referer[sic] request-header field allows the client to specify,
1864   for the server's benefit, the address (URI) of the resource from
1865   which the Request-URI was obtained (the "referrer", although the
1866   header field is misspelled.) The Referer request-header allows a
1867   server to generate lists of back-links to resources for interest,
1868   logging, optimized caching, etc. It also allows obsolete or mistyped
1869   links to be traced for maintenance. The Referer field &MUST-NOT; be
1870   sent if the Request-URI was obtained from a source that does not have
1871   its own URI, such as input from the user keyboard.
1873<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1874  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1877   Example:
1879<figure><artwork type="example">
1880    Referer:
1883   If the field value is a relative URI, it &SHOULD; be interpreted
1884   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1885   <xref target=""/> for security considerations.
1889<section title="Retry-After" anchor="header.retry-after">
1890  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1891  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1893   The Retry-After response-header field can be used with a 503 (Service
1894   Unavailable) response to indicate how long the service is expected to
1895   be unavailable to the requesting client. This field &MAY; also be used
1896   with any 3xx (Redirection) response to indicate the minimum time the
1897   user-agent is asked wait before issuing the redirected request. The
1898   value of this field can be either an HTTP-date or an integer number
1899   of seconds (in decimal) after the time of the response.
1901<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1902  Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1905   Two examples of its use are
1907<figure><artwork type="example">
1908    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1909    Retry-After: 120
1912   In the latter example, the delay is 2 minutes.
1916<section title="Server" anchor="header.server">
1917  <iref primary="true" item="Server header" x:for-anchor=""/>
1918  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1920   The Server response-header field contains information about the
1921   software used by the origin server to handle the request. The field
1922   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1923   identifying the server and any significant subproducts. The product
1924   tokens are listed in order of their significance for identifying the
1925   application.
1927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1928  Server         = "Server" ":" 1*( product | comment )
1931   Example:
1933<figure><artwork type="example">
1934    Server: CERN/3.0 libwww/2.17
1937   If the response is being forwarded through a proxy, the proxy
1938   application &MUST-NOT; modify the Server response-header. Instead, it
1939   &MUST; include a Via field (as described in &header-via;).
1940  <list><t>
1941      <x:h>Note:</x:h> Revealing the specific software version of the server might
1942      allow the server machine to become more vulnerable to attacks
1943      against software that is known to contain security holes. Server
1944      implementors are encouraged to make this field a configurable
1945      option.
1946  </t></list>
1950<section title="User-Agent" anchor="header.user-agent">
1951  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1952  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1954   The User-Agent request-header field contains information about the
1955   user agent originating the request. This is for statistical purposes,
1956   the tracing of protocol violations, and automated recognition of user
1957   agents for the sake of tailoring responses to avoid particular user
1958   agent limitations. User agents &SHOULD; include this field with
1959   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1960   and comments identifying the agent and any subproducts which form a
1961   significant part of the user agent. By convention, the product tokens
1962   are listed in order of their significance for identifying the
1963   application.
1965<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1966  User-Agent     = "User-Agent" ":" 1*( product | comment )
1969   Example:
1971<figure><artwork type="example">
1972    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1978<section title="IANA Considerations" anchor="IANA.considerations">
1980   TBD.
1984<section title="Security Considerations" anchor="security.considerations">
1986   This section is meant to inform application developers, information
1987   providers, and users of the security limitations in HTTP/1.1 as
1988   described by this document. The discussion does not include
1989   definitive solutions to the problems revealed, though it does make
1990   some suggestions for reducing security risks.
1993<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1995   Like any generic data transfer protocol, HTTP cannot regulate the
1996   content of the data that is transferred, nor is there any a priori
1997   method of determining the sensitivity of any particular piece of
1998   information within the context of any given request. Therefore,
1999   applications &SHOULD; supply as much control over this information as
2000   possible to the provider of that information. Four header fields are
2001   worth special mention in this context: Server, Via, Referer and From.
2004   Revealing the specific software version of the server might allow the
2005   server machine to become more vulnerable to attacks against software
2006   that is known to contain security holes. Implementors &SHOULD; make the
2007   Server header field a configurable option.
2010   Proxies which serve as a portal through a network firewall &SHOULD;
2011   take special precautions regarding the transfer of header information
2012   that identifies the hosts behind the firewall. In particular, they
2013   &SHOULD; remove, or replace with sanitized versions, any Via fields
2014   generated behind the firewall.
2017   The Referer header allows reading patterns to be studied and reverse
2018   links drawn. Although it can be very useful, its power can be abused
2019   if user details are not separated from the information contained in
2020   the Referer. Even when the personal information has been removed, the
2021   Referer header might indicate a private document's URI whose
2022   publication would be inappropriate.
2025   The information sent in the From field might conflict with the user's
2026   privacy interests or their site's security policy, and hence it
2027   &SHOULD-NOT;  be transmitted without the user being able to disable,
2028   enable, and modify the contents of the field. The user &MUST; be able
2029   to set the contents of this field within a user preference or
2030   application defaults configuration.
2033   We suggest, though do not require, that a convenient toggle interface
2034   be provided for the user to enable or disable the sending of From and
2035   Referer information.
2038   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2039   fields can sometimes be used to determine that a specific client or
2040   server have a particular security hole which might be exploited.
2041   Unfortunately, this same information is often used for other valuable
2042   purposes for which HTTP currently has no better mechanism.
2046<section title="Encoding Sensitive Information in URI's" anchor="">
2048   Because the source of a link might be private information or might
2049   reveal an otherwise private information source, it is strongly
2050   recommended that the user be able to select whether or not the
2051   Referer field is sent. For example, a browser client could have a
2052   toggle switch for browsing openly/anonymously, which would
2053   respectively enable/disable the sending of Referer and From
2054   information.
2057   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2058   HTTP request if the referring page was transferred with a secure
2059   protocol.
2062   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2063   based forms for the submission of sensitive data, because this will
2064   cause this data to be encoded in the Request-URI. Many existing
2065   servers, proxies, and user agents will log the request URI in some
2066   place where it might be visible to third parties. Servers can use
2067   POST-based form submission instead
2071<section title="Location Headers and Spoofing" anchor="location.spoofing">
2073   If a single server supports multiple organizations that do not trust
2074   one another, then it &MUST; check the values of Location and Content-Location
2075   headers in responses that are generated under control of
2076   said organizations to make sure that they do not attempt to
2077   invalidate resources over which they have no authority.
2083<section title="Acknowledgments" anchor="ack">
2088<references title="Normative References">
2090<reference anchor="Part1">
2091  <front>
2092    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2093    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2094      <organization abbrev="Day Software">Day Software</organization>
2095      <address><email></email></address>
2096    </author>
2097    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2098      <organization>One Laptop per Child</organization>
2099      <address><email></email></address>
2100    </author>
2101    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2102      <organization abbrev="HP">Hewlett-Packard Company</organization>
2103      <address><email></email></address>
2104    </author>
2105    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2106      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2107      <address><email></email></address>
2108    </author>
2109    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2110      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2111      <address><email></email></address>
2112    </author>
2113    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2114      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2115      <address><email></email></address>
2116    </author>
2117    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2118      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2119      <address><email></email></address>
2120    </author>
2121    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2122      <organization abbrev="W3C">World Wide Web Consortium</organization>
2123      <address><email></email></address>
2124    </author>
2125    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2126      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2127      <address><email></email></address>
2128    </author>
2129    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2130  </front>
2131  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2132  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2135<reference anchor="Part3">
2136  <front>
2137    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2138    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2139      <organization abbrev="Day Software">Day Software</organization>
2140      <address><email></email></address>
2141    </author>
2142    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2143      <organization>One Laptop per Child</organization>
2144      <address><email></email></address>
2145    </author>
2146    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2147      <organization abbrev="HP">Hewlett-Packard Company</organization>
2148      <address><email></email></address>
2149    </author>
2150    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2151      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2152      <address><email></email></address>
2153    </author>
2154    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2155      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2156      <address><email></email></address>
2157    </author>
2158    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2159      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2160      <address><email></email></address>
2161    </author>
2162    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2163      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2164      <address><email></email></address>
2165    </author>
2166    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2167      <organization abbrev="W3C">World Wide Web Consortium</organization>
2168      <address><email></email></address>
2169    </author>
2170    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2171      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2172      <address><email></email></address>
2173    </author>
2174    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2175  </front>
2176  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2177  <x:source href="p3-payload.xml" basename="p3-payload"/>
2180<reference anchor="Part4">
2181  <front>
2182    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2183    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2184      <organization abbrev="Day Software">Day Software</organization>
2185      <address><email></email></address>
2186    </author>
2187    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2188      <organization>One Laptop per Child</organization>
2189      <address><email></email></address>
2190    </author>
2191    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2192      <organization abbrev="HP">Hewlett-Packard Company</organization>
2193      <address><email></email></address>
2194    </author>
2195    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2196      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2197      <address><email></email></address>
2198    </author>
2199    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2200      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2201      <address><email></email></address>
2202    </author>
2203    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2204      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2205      <address><email></email></address>
2206    </author>
2207    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2208      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2209      <address><email></email></address>
2210    </author>
2211    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2212      <organization abbrev="W3C">World Wide Web Consortium</organization>
2213      <address><email></email></address>
2214    </author>
2215    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2216      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2217      <address><email></email></address>
2218    </author>
2219    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2220  </front>
2221  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2222  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2225<reference anchor="Part5">
2226  <front>
2227    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2228    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2229      <organization abbrev="Day Software">Day Software</organization>
2230      <address><email></email></address>
2231    </author>
2232    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2233      <organization>One Laptop per Child</organization>
2234      <address><email></email></address>
2235    </author>
2236    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2237      <organization abbrev="HP">Hewlett-Packard Company</organization>
2238      <address><email></email></address>
2239    </author>
2240    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2241      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2242      <address><email></email></address>
2243    </author>
2244    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2245      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2246      <address><email></email></address>
2247    </author>
2248    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2249      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2250      <address><email></email></address>
2251    </author>
2252    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2253      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2254      <address><email></email></address>
2255    </author>
2256    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2257      <organization abbrev="W3C">World Wide Web Consortium</organization>
2258      <address><email></email></address>
2259    </author>
2260    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2261      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2262      <address><email></email></address>
2263    </author>
2264    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2265  </front>
2266  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2267  <x:source href="p5-range.xml" basename="p5-range"/>
2270<reference anchor="Part6">
2271  <front>
2272    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2273    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2274      <organization abbrev="Day Software">Day Software</organization>
2275      <address><email></email></address>
2276    </author>
2277    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2278      <organization>One Laptop per Child</organization>
2279      <address><email></email></address>
2280    </author>
2281    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2282      <organization abbrev="HP">Hewlett-Packard Company</organization>
2283      <address><email></email></address>
2284    </author>
2285    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2286      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2287      <address><email></email></address>
2288    </author>
2289    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2290      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2291      <address><email></email></address>
2292    </author>
2293    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2294      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2295      <address><email></email></address>
2296    </author>
2297    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2298      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2299      <address><email></email></address>
2300    </author>
2301    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2302      <organization abbrev="W3C">World Wide Web Consortium</organization>
2303      <address><email></email></address>
2304    </author>
2305    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2306      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2307      <address><email></email></address>
2308    </author>
2309    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2310  </front>
2311  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2312  <x:source href="p6-cache.xml" basename="p6-cache"/>
2315<reference anchor="Part7">
2316  <front>
2317    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2318    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2319      <organization abbrev="Day Software">Day Software</organization>
2320      <address><email></email></address>
2321    </author>
2322    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2323      <organization>One Laptop per Child</organization>
2324      <address><email></email></address>
2325    </author>
2326    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2327      <organization abbrev="HP">Hewlett-Packard Company</organization>
2328      <address><email></email></address>
2329    </author>
2330    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2331      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2332      <address><email></email></address>
2333    </author>
2334    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2335      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2336      <address><email></email></address>
2337    </author>
2338    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2339      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2340      <address><email></email></address>
2341    </author>
2342    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2343      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2344      <address><email></email></address>
2345    </author>
2346    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2347      <organization abbrev="W3C">World Wide Web Consortium</organization>
2348      <address><email></email></address>
2349    </author>
2350    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2351      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2352      <address><email></email></address>
2353    </author>
2354    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2355  </front>
2356  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2357  <x:source href="p7-auth.xml" basename="p7-auth"/>
2360<reference anchor="RFC2119">
2361  <front>
2362    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2363    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2364      <organization>Harvard University</organization>
2365      <address><email></email></address>
2366    </author>
2367    <date month="March" year="1997"/>
2368  </front>
2369  <seriesInfo name="BCP" value="14"/>
2370  <seriesInfo name="RFC" value="2119"/>
2375<references title="Informative References">
2377<reference anchor="Luo1998">
2378  <front>
2379    <title>Tunneling TCP based protocols through Web proxy servers</title>
2380    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2381      <organization/>
2382    </author>
2383    <date year="1998" month="August"/>
2384  </front>
2385  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2388<reference anchor="RFC1945">
2389  <front>
2390    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2391    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2392      <organization>MIT, Laboratory for Computer Science</organization>
2393      <address><email></email></address>
2394    </author>
2395    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2396      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2397      <address><email></email></address>
2398    </author>
2399    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2400      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2401      <address><email></email></address>
2402    </author>
2403    <date month="May" year="1996"/>
2404  </front>
2405  <seriesInfo name="RFC" value="1945"/>
2408<reference anchor="RFC2068">
2409  <front>
2410    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2411    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2412      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2413      <address><email></email></address>
2414    </author>
2415    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2416      <organization>MIT Laboratory for Computer Science</organization>
2417      <address><email></email></address>
2418    </author>
2419    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2420      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2421      <address><email></email></address>
2422    </author>
2423    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2424      <organization>MIT Laboratory for Computer Science</organization>
2425      <address><email></email></address>
2426    </author>
2427    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2428      <organization>MIT Laboratory for Computer Science</organization>
2429      <address><email></email></address>
2430    </author>
2431    <date month="January" year="1997"/>
2432  </front>
2433  <seriesInfo name="RFC" value="2068"/>
2436<reference anchor="RFC2616">
2437  <front>
2438    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2439    <author initials="R." surname="Fielding" fullname="R. Fielding">
2440      <organization>University of California, Irvine</organization>
2441      <address><email></email></address>
2442    </author>
2443    <author initials="J." surname="Gettys" fullname="J. Gettys">
2444      <organization>W3C</organization>
2445      <address><email></email></address>
2446    </author>
2447    <author initials="J." surname="Mogul" fullname="J. Mogul">
2448      <organization>Compaq Computer Corporation</organization>
2449      <address><email></email></address>
2450    </author>
2451    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2452      <organization>MIT Laboratory for Computer Science</organization>
2453      <address><email></email></address>
2454    </author>
2455    <author initials="L." surname="Masinter" fullname="L. Masinter">
2456      <organization>Xerox Corporation</organization>
2457      <address><email></email></address>
2458    </author>
2459    <author initials="P." surname="Leach" fullname="P. Leach">
2460      <organization>Microsoft Corporation</organization>
2461      <address><email></email></address>
2462    </author>
2463    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2464      <organization>W3C</organization>
2465      <address><email></email></address>
2466    </author>
2467    <date month="June" year="1999"/>
2468  </front>
2469  <seriesInfo name="RFC" value="2616"/>
2472<reference anchor="RFC2822">
2473  <front>
2474    <title>Internet Message Format</title>
2475    <author initials="P." surname="Resnick" fullname="P. Resnick">
2476      <organization>QUALCOMM Incorporated</organization>
2477    </author>
2478    <date year="2001" month="April"/>
2479  </front>
2480  <seriesInfo name="RFC" value="2822"/>
2485<section title="Compatibility with Previous Versions" anchor="compatibility">
2486<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2488   Clarified which error code should be used for inbound server failures
2489   (e.g. DNS failures). (<xref target="status.504"/>).
2492   201 (Created) had a race that required an Etag be sent when a resource is
2493   first created. (<xref target="status.201"/>).
2496   Rewrite of message transmission requirements to make it much harder
2497   for implementors to get it wrong, as the consequences of errors here
2498   can have significant impact on the Internet, and to deal with the
2499   following problems:
2500  <list style="numbers">
2501      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2502         this was incorrectly placing a requirement on the behavior of
2503         an implementation of a future version of HTTP/1.x</t>
2505      <t>Made it clear that user-agents should retry requests, not
2506         "clients" in general.</t>
2508      <t>Converted requirements for clients to ignore unexpected 100
2509         (Continue) responses, and for proxies to forward 100 responses,
2510         into a general requirement for 1xx responses.</t>
2512      <t>Modified some TCP-specific language, to make it clearer that
2513         non-TCP transports are possible for HTTP.</t>
2515      <t>Require that the origin server &MUST-NOT; wait for the request
2516         body before it sends a required 100 (Continue) response.</t>
2518      <t>Allow, rather than require, a server to omit 100 (Continue) if
2519         it has already seen some of the request body.</t>
2521      <t>Allow servers to defend against denial-of-service attacks and
2522         broken clients.</t>
2523  </list>
2526   This change adds the Expect header and 417 status code.
2529   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2530   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2533   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
2534   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2538<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2540  Clarify definition of POST.
2541  (<xref target="POST"/>)
2544  Failed to consider that there are
2545  many other request methods that are safe to automatically redirect,
2546  and further that the user agent is able to make that determination
2547  based on the request method semantics.
2548  (Sections <xref format="counter" target="status.301"/>,
2549  <xref format="counter" target="status.302"/> and
2550  <xref format="counter" target="status.307"/> )
2553  Correct syntax of Location header to allow fragment,
2554  as referred symbol wasn't what was expected, and add some
2555  clarifications as to when it would not be appropriate.
2556  (<xref target="header.location"/>)
2559  In the description of the Server header, the Via field
2560  was described as a SHOULD. The requirement was and is stated
2561  correctly in the description of the Via header in &header-via;.
2562  (<xref target="header.server"/>)
2568<section title="Change Log (to be removed by RFC Editor before publication)">
2570<section title="Since RFC2616">
2572  Extracted relevant partitions from <xref target="RFC2616"/>.
2576<section title="Since draft-ietf-httpbis-p2-semantics-00">
2578  Closed issues:
2579  <list style="symbols">
2580    <t>
2581      <eref target=""/>:
2582      "Via is a MUST"
2583      (<eref target=""/>)
2584    </t>
2585    <t>
2586      <eref target=""/>:
2587      "Fragments allowed in Location"
2588      (<eref target=""/>)
2589    </t>
2590    <t>
2591      <eref target=""/>:
2592      "Safe Methods vs Redirection"
2593      (<eref target=""/>)
2594    </t>
2595    <t>
2596      <eref target=""/>:
2597      "Revise description of the POST method"
2598      (<eref target=""/>)
2599    </t>
2600    <t>
2601      <eref target=""/>:
2602      "Normative and Informative references"
2603    </t>
2604    <t>
2605      <eref target=""/>:
2606      "RFC2606 Compliance"
2607    </t>
2608    <t>
2609      <eref target=""/>:
2610      "Informative references"
2611    </t>
2612    <t>
2613      <eref target=""/>:
2614      "Redundant cross-references"
2615    </t>
2616  </list>
2619  Other changes:
2620  <list style="symbols">
2621    <t>
2622      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2623    </t>
2624  </list>
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