source: draft-ietf-httpbis/latest/p2-semantics.xml @ 203

Last change on this file since 203 was 203, checked in by julian.reschke@…, 14 years ago

Add processing instructions for inline comments throughout, and use them for the IANA TBDs.

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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 "February">
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=''/>">
58  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x=''/>">
60<?rfc toc="yes" ?>
61<?rfc symrefs="yes" ?>
62<?rfc sortrefs="yes" ?>
63<?rfc compact="yes"?>
64<?rfc subcompact="no" ?>
65<?rfc linkmailto="no" ?>
66<?rfc editing="no" ?>
67<?rfc comments="yes"?>
68<?rfc inline="yes"?>
69<?rfc-ext allow-markup-in-artwork="yes" ?>
70<?rfc-ext include-references-in-index="yes" ?>
71<rfc obsoletes="2616" category="std"
72     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
73     xmlns:x=''>
76  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
78  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
79    <organization abbrev="Day Software">Day Software</organization>
80    <address>
81      <postal>
82        <street>23 Corporate Plaza DR, Suite 280</street>
83        <city>Newport Beach</city>
84        <region>CA</region>
85        <code>92660</code>
86        <country>USA</country>
87      </postal>
88      <phone>+1-949-706-5300</phone>
89      <facsimile>+1-949-706-5305</facsimile>
90      <email></email>
91      <uri></uri>
92    </address>
93  </author>
95  <author initials="J." surname="Gettys" fullname="Jim Gettys">
96    <organization>One Laptop per Child</organization>
97    <address>
98      <postal>
99        <street>21 Oak Knoll Road</street>
100        <city>Carlisle</city>
101        <region>MA</region>
102        <code>01741</code>
103        <country>USA</country>
104      </postal>
105      <email></email>
106      <uri></uri>
107    </address>
108  </author>
110  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
111    <organization abbrev="HP">Hewlett-Packard Company</organization>
112    <address>
113      <postal>
114        <street>HP Labs, Large Scale Systems Group</street>
115        <street>1501 Page Mill Road, MS 1177</street>
116        <city>Palo Alto</city>
117        <region>CA</region>
118        <code>94304</code>
119        <country>USA</country>
120      </postal>
121      <email></email>
122    </address>
123  </author>
125  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
126    <organization abbrev="Microsoft">Microsoft Corporation</organization>
127    <address>
128      <postal>
129        <street>1 Microsoft Way</street>
130        <city>Redmond</city>
131        <region>WA</region>
132        <code>98052</code>
133        <country>USA</country>
134      </postal>
135      <email></email>
136    </address>
137  </author>
139  <author initials="L." surname="Masinter" fullname="Larry Masinter">
140    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
141    <address>
142      <postal>
143        <street>345 Park Ave</street>
144        <city>San Jose</city>
145        <region>CA</region>
146        <code>95110</code>
147        <country>USA</country>
148      </postal>
149      <email></email>
150      <uri></uri>
151    </address>
152  </author>
154  <author initials="P." surname="Leach" fullname="Paul J. Leach">
155    <organization abbrev="Microsoft">Microsoft Corporation</organization>
156    <address>
157      <postal>
158        <street>1 Microsoft Way</street>
159        <city>Redmond</city>
160        <region>WA</region>
161        <code>98052</code>
162      </postal>
163      <email></email>
164    </address>
165  </author>
167  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
168    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
172        <street>The Stata Center, Building 32</street>
173        <street>32 Vassar Street</street>
174        <city>Cambridge</city>
175        <region>MA</region>
176        <code>02139</code>
177        <country>USA</country>
178      </postal>
179      <email></email>
180      <uri></uri>
181    </address>
182  </author>
184  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
185    <organization abbrev="W3C">World Wide Web Consortium</organization>
186    <address>
187      <postal>
188        <street>W3C / ERCIM</street>
189        <street>2004, rte des Lucioles</street>
190        <city>Sophia-Antipolis</city>
191        <region>AM</region>
192        <code>06902</code>
193        <country>France</country>
194      </postal>
195      <email></email>
196      <uri></uri>
197    </address>
198  </author>
200  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
201    <organization abbrev="greenbytes">greenbytes GmbH</organization>
202    <address>
203      <postal>
204        <street>Hafenweg 16</street>
205        <city>Muenster</city><region>NW</region><code>48155</code>
206        <country>Germany</country>
207      </postal>
208      <phone>+49 251 2807760</phone>   
209      <facsimile>+49 251 2807761</facsimile>   
210      <email></email>       
211      <uri></uri>     
212    </address>
213  </author>
215  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
219   The Hypertext Transfer Protocol (HTTP) is an application-level
220   protocol for distributed, collaborative, hypermedia information
221   systems. HTTP has been in use by the World Wide Web global information
222   initiative since 1990. This document is Part 2 of the seven-part specification
223   that defines the protocol referred to as "HTTP/1.1" and, taken together,
224   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
225   as expressed by request methods, request-header fields, response status codes,
226   and response-header fields.
230<note title="Editorial Note (To be removed by RFC Editor)">
231  <t>
232    Discussion of this draft should take place on the HTTPBIS working group
233    mailing list ( The current issues list is
234    at <eref target=""/>
235    and related documents (including fancy diffs) can be found at
236    <eref target=""/>.
237  </t>
238  <t>
239    This draft incorporates those issue resolutions that were either
240    collected in the original RFC2616 errata list (<eref target=""/>),
241    or which were agreed upon on the mailing list between October 2006 and
242    November 2007 (as published in "draft-lafon-rfc2616bis-03").
243  </t>
247<section title="Introduction" anchor="introduction">
249   This document defines HTTP/1.1 request and response semantics.  Each HTTP
250   message, as defined in &messaging;, is in the form of either a request or
251   a response.  An HTTP server listens on a connection for HTTP requests and
252   responds to each request, in the order received on that connection, with
253   one or more HTTP response messages.  This document defines the commonly
254   agreed upon semantics of the HTTP uniform interface, the intentions defined
255   by each request method, and the various response messages that might be
256   expected as a result of applying that method for the requested resource.
259   This document is currently disorganized in order to minimize the changes
260   between drafts and enable reviewers to see the smaller errata changes.
261   The next draft will reorganize the sections to better reflect the content.
262   In particular, the sections will be ordered according to the typical
263   processing of an HTTP request message (after message parsing): resource
264   mapping, general header fields, methods, request modifiers, response
265   status, and resource metadata.  The current mess reflects how widely
266   dispersed these topics and associated requirements had become in
267   <xref target="RFC2616"/>.
270<section title="Requirements" anchor="intro.requirements">
272   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
273   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
274   document are to be interpreted as described in <xref target="RFC2119"/>.
277   An implementation is not compliant if it fails to satisfy one or more
278   of the &MUST; or &REQUIRED; level requirements for the protocols it
279   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
280   level and all the &SHOULD; level requirements for its protocols is said
281   to be "unconditionally compliant"; one that satisfies all the &MUST;
282   level requirements but not all the &SHOULD; level requirements for its
283   protocols is said to be "conditionally compliant."
288<section title="Method" anchor="method">
290   The Method  token indicates the method to be performed on the
291   resource identified by the Request-URI. The method is case-sensitive.
293<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
294  Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
295                 | "GET"                    ; <xref target="GET"/>
296                 | "HEAD"                   ; <xref target="HEAD"/>
297                 | "POST"                   ; <xref target="POST"/>
298                 | "PUT"                    ; <xref target="PUT"/>
299                 | "DELETE"                 ; <xref target="DELETE"/>
300                 | "TRACE"                  ; <xref target="TRACE"/>
301                 | "CONNECT"                ; <xref target="CONNECT"/>
302                 | extension-method
303  extension-method = token
306   The list of methods allowed by a resource can be specified in an
307   Allow header field (<xref target="header.allow"/>). The return code of the response
308   always notifies the client whether a method is currently allowed on a
309   resource, since the set of allowed methods can change dynamically. An
310   origin server &SHOULD; return the status code 405 (Method Not Allowed)
311   if the method is known by the origin server but not allowed for the
312   requested resource, and 501 (Not Implemented) if the method is
313   unrecognized or not implemented by the origin server. The methods GET
314   and HEAD &MUST; be supported by all general-purpose servers. All other
315   methods are &OPTIONAL;; however, if the above methods are implemented,
316   they &MUST; be implemented with the same semantics as those specified
317   in <xref target="method.definitions"/>.
321<section title="Request Header Fields" anchor="request.header.fields">
323   The request-header fields allow the client to pass additional
324   information about the request, and about the client itself, to the
325   server. These fields act as request modifiers, with semantics
326   equivalent to the parameters on a programming language method
327   invocation.
329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
330  request-header = Accept                   ; &header-accept;
331                 | Accept-Charset           ; &header-accept-charset;
332                 | Accept-Encoding          ; &header-accept-encoding;
333                 | Accept-Language          ; &header-accept-language;
334                 | Authorization            ; &header-authorization;
335                 | Expect                   ; <xref target="header.expect"/>
336                 | From                     ; <xref target="header.from"/>
337                 | Host                     ; &header-host;
338                 | If-Match                 ; &header-if-match;
339                 | If-Modified-Since        ; &header-if-modified-since;
340                 | If-None-Match            ; &header-if-none-match;
341                 | If-Range                 ; &header-if-range;
342                 | If-Unmodified-Since      ; &header-if-unmodified-since;
343                 | Max-Forwards             ; <xref target="header.max-forwards"/>
344                 | Proxy-Authorization      ; &header-proxy-authorization;
345                 | Range                    ; &header-range;
346                 | Referer                  ; <xref target="header.referer"/>
347                 | TE                       ; &header-te;
348                 | User-Agent               ; <xref target="header.user-agent"/>
351   Request-header field names can be extended reliably only in
352   combination with a change in the protocol version. However, new or
353   experimental header fields &MAY; be given the semantics of request-header
354   fields if all parties in the communication recognize them to
355   be request-header fields. Unrecognized header fields are treated as
356   entity-header fields.
360<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
362   The Status-Code element is a 3-digit integer result code of the
363   attempt to understand and satisfy the request. The status codes listed
364   below are defined in <xref target=""/>.
365   The Reason-Phrase is intended to give a short
366   textual description of the Status-Code. The Status-Code is intended
367   for use by automata and the Reason-Phrase is intended for the human
368   user. The client is not required to examine or display the Reason-Phrase.
371   The individual values of the numeric status codes defined for
372   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
373   presented below. The reason phrases listed here are only
374   recommendations -- they &MAY; be replaced by local equivalents without
375   affecting the protocol.
377<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"/>
378  Status-Code    =
379         "100"  ; <xref target="status.100"/>: Continue
380       | "101"  ; <xref target="status.101"/>: Switching Protocols
381       | "200"  ; <xref target="status.200"/>: OK
382       | "201"  ; <xref target="status.201"/>: Created
383       | "202"  ; <xref target="status.202"/>: Accepted
384       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
385       | "204"  ; <xref target="status.204"/>: No Content
386       | "205"  ; <xref target="status.205"/>: Reset Content
387       | "206"  ; <xref target="status.206"/>: Partial Content
388       | "300"  ; <xref target="status.300"/>: Multiple Choices
389       | "301"  ; <xref target="status.301"/>: Moved Permanently
390       | "302"  ; <xref target="status.302"/>: Found
391       | "303"  ; <xref target="status.303"/>: See Other
392       | "304"  ; <xref target="status.304"/>: Not Modified
393       | "305"  ; <xref target="status.305"/>: Use Proxy
394       | "307"  ; <xref target="status.307"/>: Temporary Redirect
395       | "400"  ; <xref target="status.400"/>: Bad Request
396       | "401"  ; <xref target="status.401"/>: Unauthorized
397       | "402"  ; <xref target="status.402"/>: Payment Required
398       | "403"  ; <xref target="status.403"/>: Forbidden
399       | "404"  ; <xref target="status.404"/>: Not Found
400       | "405"  ; <xref target="status.405"/>: Method Not Allowed
401       | "406"  ; <xref target="status.406"/>: Not Acceptable
402       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
403       | "408"  ; <xref target="status.408"/>: Request Time-out
404       | "409"  ; <xref target="status.409"/>: Conflict
405       | "410"  ; <xref target="status.410"/>: Gone
406       | "411"  ; <xref target="status.411"/>: Length Required
407       | "412"  ; <xref target="status.412"/>: Precondition Failed
408       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
409       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
410       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
411       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
412       | "417"  ; <xref target="status.417"/>: Expectation Failed
413       | "500"  ; <xref target="status.500"/>: Internal Server Error
414       | "501"  ; <xref target="status.501"/>: Not Implemented
415       | "502"  ; <xref target="status.502"/>: Bad Gateway
416       | "503"  ; <xref target="status.503"/>: Service Unavailable
417       | "504"  ; <xref target="status.504"/>: Gateway Time-out
418       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
419       | extension-code
421  extension-code = 3DIGIT
422  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
425   HTTP status codes are extensible. HTTP applications are not required
426   to understand the meaning of all registered status codes, though such
427   understanding is obviously desirable. However, applications &MUST;
428   understand the class of any status code, as indicated by the first
429   digit, and treat any unrecognized response as being equivalent to the
430   x00 status code of that class, with the exception that an
431   unrecognized response &MUST-NOT; be cached. For example, if an
432   unrecognized status code of 431 is received by the client, it can
433   safely assume that there was something wrong with its request and
434   treat the response as if it had received a 400 status code. In such
435   cases, user agents &SHOULD; present to the user the entity returned
436   with the response, since that entity is likely to include human-readable
437   information which will explain the unusual status.
441<section title="Response Header Fields" anchor="response.header.fields">
443   The response-header fields allow the server to pass additional
444   information about the response which cannot be placed in the Status-Line.
445   These header fields give information about the server and about
446   further access to the resource identified by the Request-URI.
448<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
449  response-header = Accept-Ranges           ; &header-accept-ranges;
450                  | Age                     ; &header-age;
451                  | ETag                    ; &header-etag;
452                  | Location                ; <xref target="header.location"/>
453                  | Proxy-Authenticate      ; &header-proxy-authenticate;
454                  | Retry-After             ; <xref target="header.retry-after"/>
455                  | Server                  ; <xref target="header.server"/>
456                  | Vary                    ; &header-vary;
457                  | WWW-Authenticate        ; &header-www-authenticate;
460   Response-header field names can be extended reliably only in
461   combination with a change in the protocol version. However, new or
462   experimental header fields &MAY; be given the semantics of response-header
463   fields if all parties in the communication recognize them to
464   be response-header fields. Unrecognized header fields are treated as
465   entity-header fields.
469<section title="Entity" anchor="entity">
471   Request and Response messages &MAY; transfer an entity if not otherwise
472   restricted by the request method or response status code. An entity
473   consists of entity-header fields and an entity-body, although some
474   responses will only include the entity-headers. HTTP entity-body and
475   entity-header fields are defined in &payload;.
478   An entity-body is only present in a message when a message-body is
479   present, as described in &message-body;. The entity-body is obtained
480   from the message-body by decoding any Transfer-Encoding that might
481   have been applied to ensure safe and proper transfer of the message.
486<section title="Method Definitions" anchor="method.definitions">
488   The set of common methods for HTTP/1.1 is defined below. Although
489   this set can be expanded, additional methods cannot be assumed to
490   share the same semantics for separately extended clients and servers.
493<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
495<section title="Safe Methods" anchor="safe.methods">
497   Implementors should be aware that the software represents the user in
498   their interactions over the Internet, and should be careful to allow
499   the user to be aware of any actions they might take which may have an
500   unexpected significance to themselves or others.
503   In particular, the convention has been established that the GET and
504   HEAD methods &SHOULD-NOT;  have the significance of taking an action
505   other than retrieval. These methods ought to be considered "safe".
506   This allows user agents to represent other methods, such as POST, PUT
507   and DELETE, in a special way, so that the user is made aware of the
508   fact that a possibly unsafe action is being requested.
511   Naturally, it is not possible to ensure that the server does not
512   generate side-effects as a result of performing a GET request; in
513   fact, some dynamic resources consider that a feature. The important
514   distinction here is that the user did not request the side-effects,
515   so therefore cannot be held accountable for them.
519<section title="Idempotent Methods" anchor="idempotent.methods">
521   Methods can also have the property of "idempotence" in that (aside
522   from error or expiration issues) the side-effects of N &gt; 0 identical
523   requests is the same as for a single request. The methods GET, HEAD,
524   PUT and DELETE share this property. Also, the methods OPTIONS and
525   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
528   However, it is possible that a sequence of several requests is non-idempotent,
529   even if all of the methods executed in that sequence are
530   idempotent. (A sequence is idempotent if a single execution of the
531   entire sequence always yields a result that is not changed by a
532   reexecution of all, or part, of that sequence.) For example, a
533   sequence is non-idempotent if its result depends on a value that is
534   later modified in the same sequence.
537   A sequence that never has side effects is idempotent, by definition
538   (provided that no concurrent operations are being executed on the
539   same set of resources).
544<section title="OPTIONS" anchor="OPTIONS">
545  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
546  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
548   The OPTIONS method represents a request for information about the
549   communication options available on the request/response chain
550   identified by the Request-URI. This method allows the client to
551   determine the options and/or requirements associated with a resource,
552   or the capabilities of a server, without implying a resource action
553   or initiating a resource retrieval.
556   Responses to this method are not cacheable.
559   If the OPTIONS request includes an entity-body (as indicated by the
560   presence of Content-Length or Transfer-Encoding), then the media type
561   &MUST; be indicated by a Content-Type field. Although this
562   specification does not define any use for such a body, future
563   extensions to HTTP might use the OPTIONS body to make more detailed
564   queries on the server. A server that does not support such an
565   extension &MAY; discard the request body.
568   If the Request-URI is an asterisk ("*"), the OPTIONS request is
569   intended to apply to the server in general rather than to a specific
570   resource. Since a server's communication options typically depend on
571   the resource, the "*" request is only useful as a "ping" or "no-op"
572   type of method; it does nothing beyond allowing the client to test
573   the capabilities of the server. For example, this can be used to test
574   a proxy for HTTP/1.1 compliance (or lack thereof).
577   If the Request-URI is not an asterisk, the OPTIONS request applies
578   only to the options that are available when communicating with that
579   resource.
582   A 200 response &SHOULD; include any header fields that indicate
583   optional features implemented by the server and applicable to that
584   resource (e.g., Allow), possibly including extensions not defined by
585   this specification. The response body, if any, &SHOULD; also include
586   information about the communication options. The format for such a
587   body is not defined by this specification, but might be defined by
588   future extensions to HTTP. Content negotiation &MAY; be used to select
589   the appropriate response format. If no response body is included, the
590   response &MUST; include a Content-Length field with a field-value of
591   "0".
594   The Max-Forwards request-header field &MAY; be used to target a
595   specific proxy in the request chain. When a proxy receives an OPTIONS
596   request on an absoluteURI for which request forwarding is permitted,
597   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
598   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
599   instead, the proxy &SHOULD; respond with its own communication options.
600   If the Max-Forwards field-value is an integer greater than zero, the
601   proxy &MUST; decrement the field-value when it forwards the request. If
602   no Max-Forwards field is present in the request, then the forwarded
603   request &MUST-NOT; include a Max-Forwards field.
607<section title="GET" anchor="GET">
608  <iref primary="true" item="GET method" x:for-anchor=""/>
609  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
611   The GET method means retrieve whatever information (in the form of an
612   entity) is identified by the Request-URI. If the Request-URI refers
613   to a data-producing process, it is the produced data which shall be
614   returned as the entity in the response and not the source text of the
615   process, unless that text happens to be the output of the process.
618   The semantics of the GET method change to a "conditional GET" if the
619   request message includes an If-Modified-Since, If-Unmodified-Since,
620   If-Match, If-None-Match, or If-Range header field. A conditional GET
621   method requests that the entity be transferred only under the
622   circumstances described by the conditional header field(s). The
623   conditional GET method is intended to reduce unnecessary network
624   usage by allowing cached entities to be refreshed without requiring
625   multiple requests or transferring data already held by the client.
628   The semantics of the GET method change to a "partial GET" if the
629   request message includes a Range header field. A partial GET requests
630   that only part of the entity be transferred, as described in &header-range;.
631   The partial GET method is intended to reduce unnecessary
632   network usage by allowing partially-retrieved entities to be
633   completed without transferring data already held by the client.
636   The response to a GET request is cacheable if and only if it meets
637   the requirements for HTTP caching described in &caching;.
640   See <xref target=""/> for security considerations when used for forms.
644<section title="HEAD" anchor="HEAD">
645  <iref primary="true" item="HEAD method" x:for-anchor=""/>
646  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
648   The HEAD method is identical to GET except that the server &MUST-NOT;
649   return a message-body in the response. The metainformation contained
650   in the HTTP headers in response to a HEAD request &SHOULD; be identical
651   to the information sent in response to a GET request. This method can
652   be used for obtaining metainformation about the entity implied by the
653   request without transferring the entity-body itself. This method is
654   often used for testing hypertext links for validity, accessibility,
655   and recent modification.
658   The response to a HEAD request &MAY; be cacheable in the sense that the
659   information contained in the response &MAY; be used to update a
660   previously cached entity from that resource. If the new field values
661   indicate that the cached entity differs from the current entity (as
662   would be indicated by a change in Content-Length, Content-MD5, ETag
663   or Last-Modified), then the cache &MUST; treat the cache entry as
664   stale.
668<section title="POST" anchor="POST">
669  <iref primary="true" item="POST method" x:for-anchor=""/>
670  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
672   The POST method is used to request that the origin server accept the
673   entity enclosed in the request as data to be processed by the resource
674   identified by the Request-URI in the Request-Line. POST is designed
675   to allow a uniform method to cover the following functions:
676  <list style="symbols">
677    <t>
678      Annotation of existing resources;
679    </t>
680    <t>
681        Posting a message to a bulletin board, newsgroup, mailing list,
682        or similar group of articles;
683    </t>
684    <t>
685        Providing a block of data, such as the result of submitting a
686        form, to a data-handling process;
687    </t>
688    <t>
689        Extending a database through an append operation.
690    </t>
691  </list>
694   The actual function performed by the POST method is determined by the
695   server and is usually dependent on the Request-URI.
698   The action performed by the POST method might not result in a
699   resource that can be identified by a URI. In this case, either 200
700   (OK) or 204 (No Content) is the appropriate response status,
701   depending on whether or not the response includes an entity that
702   describes the result.
705   If a resource has been created on the origin server, the response
706   &SHOULD; be 201 (Created) and contain an entity which describes the
707   status of the request and refers to the new resource, and a Location
708   header (see <xref target="header.location"/>).
711   Responses to this method are not cacheable, unless the response
712   includes appropriate Cache-Control or Expires header fields. However,
713   the 303 (See Other) response can be used to direct the user agent to
714   retrieve a cacheable resource.
718<section title="PUT" anchor="PUT">
719  <iref primary="true" item="PUT method" x:for-anchor=""/>
720  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
722   The PUT method requests that the enclosed entity be stored under the
723   supplied Request-URI. If the Request-URI refers to an already
724   existing resource, the enclosed entity &SHOULD; be considered as a
725   modified version of the one residing on the origin server. If the
726   Request-URI does not point to an existing resource, and that URI is
727   capable of being defined as a new resource by the requesting user
728   agent, the origin server can create the resource with that URI. If a
729   new resource is created at the Request-URI, the origin server &MUST;
730         inform the user agent
731   via the 201 (Created) response. If an existing resource is modified,
732   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
733   to indicate successful completion of the request. If the resource
734   could not be created or modified with the Request-URI, an appropriate
735   error response &SHOULD; be given that reflects the nature of the
736   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
737   (e.g. Content-Range) headers that it does not understand or implement
738   and &MUST; return a 501 (Not Implemented) response in such cases.
741   If the request passes through a cache and the Request-URI identifies
742   one or more currently cached entities, those entries &SHOULD; be
743   treated as stale. Responses to this method are not cacheable.
746   The fundamental difference between the POST and PUT requests is
747   reflected in the different meaning of the Request-URI. The URI in a
748   POST request identifies the resource that will handle the enclosed
749   entity. That resource might be a data-accepting process, a gateway to
750   some other protocol, or a separate entity that accepts annotations.
751   In contrast, the URI in a PUT request identifies the entity enclosed
752   with the request -- the user agent knows what URI is intended and the
753   server &MUST-NOT; attempt to apply the request to some other resource.
754   If the server desires that the request be applied to a different URI,
755   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
756   then make its own decision regarding whether or not to redirect the
757   request.
760   A single resource &MAY; be identified by many different URIs. For
761   example, an article might have a URI for identifying "the current
762   version" which is separate from the URI identifying each particular
763   version. In this case, a PUT request on a general URI might result in
764   several other URIs being defined by the origin server.
767   HTTP/1.1 does not define how a PUT method affects the state of an
768   origin server.
771   Unless otherwise specified for a particular entity-header, the
772   entity-headers in the PUT request &SHOULD; be applied to the resource
773   created or modified by the PUT.
777<section title="DELETE" anchor="DELETE">
778  <iref primary="true" item="DELETE method" x:for-anchor=""/>
779  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
781   The DELETE method requests that the origin server delete the resource
782   identified by the Request-URI. This method &MAY; be overridden by human
783   intervention (or other means) on the origin server. The client cannot
784   be guaranteed that the operation has been carried out, even if the
785   status code returned from the origin server indicates that the action
786   has been completed successfully. However, the server &SHOULD-NOT;
787   indicate success unless, at the time the response is given, it
788   intends to delete the resource or move it to an inaccessible
789   location.
792   A successful response &SHOULD; be 200 (OK) if the response includes an
793   entity describing the status, 202 (Accepted) if the action has not
794   yet been enacted, or 204 (No Content) if the action has been enacted
795   but the response does not include an entity.
798   If the request passes through a cache and the Request-URI identifies
799   one or more currently cached entities, those entries &SHOULD; be
800   treated as stale. Responses to this method are not cacheable.
804<section title="TRACE" anchor="TRACE">
805  <iref primary="true" item="TRACE method" x:for-anchor=""/>
806  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
808   The TRACE method is used to invoke a remote, application-layer loop-back
809   of the request message. The final recipient of the request
810   &SHOULD; reflect the message received back to the client as the
811   entity-body of a 200 (OK) response. The final recipient is either the
812   origin server or the first proxy or gateway to receive a Max-Forwards
813   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
814   &MUST-NOT; include an entity.
817   TRACE allows the client to see what is being received at the other
818   end of the request chain and use that data for testing or diagnostic
819   information. The value of the Via header field (&header-via;) is of
820   particular interest, since it acts as a trace of the request chain.
821   Use of the Max-Forwards header field allows the client to limit the
822   length of the request chain, which is useful for testing a chain of
823   proxies forwarding messages in an infinite loop.
826   If the request is valid, the response &SHOULD; contain the entire
827   request message in the entity-body, with a Content-Type of
828   "message/http". Responses to this method &MUST-NOT; be cached.
832<section title="CONNECT" anchor="CONNECT">
833  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
834  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
836   This specification reserves the method name CONNECT for use with a
837   proxy that can dynamically switch to being a tunnel (e.g. SSL
838   tunneling <xref target="Luo1998"/>).
844<section title="Status Code Definitions" anchor="">
846   Each Status-Code is described below, including a description of which
847   method(s) it can follow and any metainformation required in the
848   response.
851<section title="Informational 1xx" anchor="status.1xx">
853   This class of status code indicates a provisional response,
854   consisting only of the Status-Line and optional headers, and is
855   terminated by an empty line. There are no required headers for this
856   class of status code. Since HTTP/1.0 did not define any 1xx status
857   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
858   except under experimental conditions.
861   A client &MUST; be prepared to accept one or more 1xx status responses
862   prior to a regular response, even if the client does not expect a 100
863   (Continue) status message. Unexpected 1xx status responses &MAY; be
864   ignored by a user agent.
867   Proxies &MUST; forward 1xx responses, unless the connection between the
868   proxy and its client has been closed, or unless the proxy itself
869   requested the generation of the 1xx response. (For example, if a
870   proxy adds a "Expect: 100-continue" field when it forwards a request,
871   then it need not forward the corresponding 100 (Continue)
872   response(s).)
875<section title="100 Continue" anchor="status.100">
876  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
877  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
879   The client &SHOULD; continue with its request. This interim response is
880   used to inform the client that the initial part of the request has
881   been received and has not yet been rejected by the server. The client
882   &SHOULD; continue by sending the remainder of the request or, if the
883   request has already been completed, ignore this response. The server
884   &MUST; send a final response after the request has been completed. See
885   &use100; for detailed discussion of the use and handling of this
886   status code.
890<section title="101 Switching Protocols" anchor="status.101">
891  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
892  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
894   The server understands and is willing to comply with the client's
895   request, via the Upgrade message header field (&header-upgrade;), for a
896   change in the application protocol being used on this connection. The
897   server will switch protocols to those defined by the response's
898   Upgrade header field immediately after the empty line which
899   terminates the 101 response.
902   The protocol &SHOULD; be switched only when it is advantageous to do
903   so. For example, switching to a newer version of HTTP is advantageous
904   over older versions, and switching to a real-time, synchronous
905   protocol might be advantageous when delivering resources that use
906   such features.
911<section title="Successful 2xx" anchor="status.2xx">
913   This class of status code indicates that the client's request was
914   successfully received, understood, and accepted.
917<section title="200 OK" anchor="status.200">
918  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
919  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
921   The request has succeeded. The information returned with the response
922   is dependent on the method used in the request, for example:
923  <list style="hanging">
924    <t hangText="GET">
925          an entity corresponding to the requested resource is sent in
926          the response;
927    </t>
928    <t hangText="HEAD">
929          the entity-header fields corresponding to the requested
930          resource are sent in the response without any message-body;
931    </t>
932    <t hangText="POST">
933      an entity describing or containing the result of the action;
934    </t>
935    <t hangText="TRACE">
936      an entity containing the request message as received by the
937      end server.
938    </t>
939  </list>
943<section title="201 Created" anchor="status.201">
944  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
945  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
947   The request has been fulfilled and resulted in a new resource being
948   created. The newly created resource can be referenced by the URI(s)
949   returned in the entity of the response, with the most specific URI
950   for the resource given by a Location header field. The response
951   &SHOULD; include an entity containing a list of resource
952   characteristics and location(s) from which the user or user agent can
953   choose the one most appropriate. The entity format is specified by
954   the media type given in the Content-Type header field. The origin
955   server &MUST; create the resource before returning the 201 status code.
956   If the action cannot be carried out immediately, the server &SHOULD;
957   respond with 202 (Accepted) response instead.
960   A 201 response &MAY; contain an ETag response header field indicating
961   the current value of the entity tag for the requested variant just
962   created, see &header-etag;.
966<section title="202 Accepted" anchor="status.202">
967  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
968  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
970   The request has been accepted for processing, but the processing has
971   not been completed.  The request might or might not eventually be
972   acted upon, as it might be disallowed when processing actually takes
973   place. There is no facility for re-sending a status code from an
974   asynchronous operation such as this.
977   The 202 response is intentionally non-committal. Its purpose is to
978   allow a server to accept a request for some other process (perhaps a
979   batch-oriented process that is only run once per day) without
980   requiring that the user agent's connection to the server persist
981   until the process is completed. The entity returned with this
982   response &SHOULD; include an indication of the request's current status
983   and either a pointer to a status monitor or some estimate of when the
984   user can expect the request to be fulfilled.
988<section title="203 Non-Authoritative Information" anchor="status.203">
989  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
990  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
992   The returned metainformation in the entity-header is not the
993   definitive set as available from the origin server, but is gathered
994   from a local or a third-party copy. The set presented &MAY; be a subset
995   or superset of the original version. For example, including local
996   annotation information about the resource might result in a superset
997   of the metainformation known by the origin server. Use of this
998   response code is not required and is only appropriate when the
999   response would otherwise be 200 (OK).
1003<section title="204 No Content" anchor="status.204">
1004  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1005  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1007   The server has fulfilled the request but does not need to return an
1008   entity-body, and might want to return updated metainformation. The
1009   response &MAY; include new or updated metainformation in the form of
1010   entity-headers, which if present &SHOULD; be associated with the
1011   requested variant.
1014   If the client is a user agent, it &SHOULD-NOT;  change its document view
1015   from that which caused the request to be sent. This response is
1016   primarily intended to allow input for actions to take place without
1017   causing a change to the user agent's active document view, although
1018   any new or updated metainformation &SHOULD; be applied to the document
1019   currently in the user agent's active view.
1022   The 204 response &MUST-NOT; include a message-body, and thus is always
1023   terminated by the first empty line after the header fields.
1027<section title="205 Reset Content" anchor="status.205">
1028  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1029  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1031   The server has fulfilled the request and the user agent &SHOULD; reset
1032   the document view which caused the request to be sent. This response
1033   is primarily intended to allow input for actions to take place via
1034   user input, followed by a clearing of the form in which the input is
1035   given so that the user can easily initiate another input action. The
1036   response &MUST-NOT; include an entity.
1040<section title="206 Partial Content" anchor="status.206">
1041  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1042  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1044   The server has fulfilled the partial GET request for the resource
1045   and the enclosed entity is a partial representation as defined in &range;.
1050<section title="Redirection 3xx" anchor="status.3xx">
1052   This class of status code indicates that further action needs to be
1053   taken by the user agent in order to fulfill the request.  The action
1054   required &MAY; be carried out by the user agent without interaction
1055   with the user if and only if the method used in the second request is
1056   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1057   such loops generate network traffic for each redirection.
1058  <list><t>
1059      <x:h>Note:</x:h> previous versions of this specification recommended a
1060      maximum of five redirections. Content developers should be aware
1061      that there might be clients that implement such a fixed
1062      limitation.
1063  </t></list>
1066<section title="300 Multiple Choices" anchor="status.300">
1067  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1068  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1070   The requested resource corresponds to any one of a set of
1071   representations, each with its own specific location, and agent-driven
1072   negotiation information (&content-negotiation;) is being provided so that
1073   the user (or user agent) can select a preferred representation and
1074   redirect its request to that location.
1077   Unless it was a HEAD request, the response &SHOULD; include an entity
1078   containing a list of resource characteristics and location(s) from
1079   which the user or user agent can choose the one most appropriate. The
1080   entity format is specified by the media type given in the Content-Type
1081   header field. Depending upon the format and the capabilities of
1082   the user agent, selection of the most appropriate choice &MAY; be
1083   performed automatically. However, this specification does not define
1084   any standard for such automatic selection.
1087   If the server has a preferred choice of representation, it &SHOULD;
1088   include the specific URI for that representation in the Location
1089   field; user agents &MAY; use the Location field value for automatic
1090   redirection. This response is cacheable unless indicated otherwise.
1094<section title="301 Moved Permanently" anchor="status.301">
1095  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1096  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1098   The requested resource has been assigned a new permanent URI and any
1099   future references to this resource &SHOULD; use one of the returned
1100   URIs.  Clients with link editing capabilities ought to automatically
1101   re-link references to the Request-URI to one or more of the new
1102   references returned by the server, where possible. This response is
1103   cacheable unless indicated otherwise.
1106   The new permanent URI &SHOULD; be given by the Location field in the
1107   response. Unless the request method was HEAD, the entity of the
1108   response &SHOULD; contain a short hypertext note with a hyperlink to
1109   the new URI(s).
1112   If the 301 status code is received in response to a request method
1113   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1114   then the request &MAY; be automatically redirected by the user agent without
1115   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1116   request unless it can be confirmed by the user, since this might
1117   change the conditions under which the request was issued.
1118  <list><t>
1119      <x:h>Note:</x:h> When automatically redirecting a POST request after
1120      receiving a 301 status code, some existing HTTP/1.0 user agents
1121      will erroneously change it into a GET request.
1122  </t></list>
1126<section title="302 Found" anchor="status.302">
1127  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1128  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1130   The requested resource resides temporarily under a different URI.
1131   Since the redirection might be altered on occasion, the client &SHOULD;
1132   continue to use the Request-URI for future requests.  This response
1133   is only cacheable if indicated by a Cache-Control or Expires header
1134   field.
1137   The temporary URI &SHOULD; be given by the Location field in the
1138   response. Unless the request method was HEAD, the entity of the
1139   response &SHOULD; contain a short hypertext note with a hyperlink to
1140   the new URI(s).
1143   If the 302 status code is received in response to a request method
1144   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1145   then the request &MAY; be automatically redirected by the user agent without
1146   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1147   request unless it can be confirmed by the user, since this might
1148   change the conditions under which the request was issued.
1149  <list><t>
1150      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1151      to change the method on the redirected request.  However, most
1152      existing user agent implementations treat 302 as if it were a 303
1153      response, performing a GET on the Location field-value regardless
1154      of the original request method. The status codes 303 and 307 have
1155      been added for servers that wish to make unambiguously clear which
1156      kind of reaction is expected of the client.
1157  </t></list>
1161<section title="303 See Other" anchor="status.303">
1162  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1163  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1165   The response to the request can be found under a different URI and
1166   &SHOULD; be retrieved using a GET method on that resource. This method
1167   exists primarily to allow the output of a POST-activated script to
1168   redirect the user agent to a selected resource. The new URI is not a
1169   substitute reference for the originally requested resource. The 303
1170   response &MUST-NOT; be cached, but the response to the second
1171   (redirected) request might be cacheable.
1174   The different URI &SHOULD; be given by the Location field in the
1175   response. Unless the request method was HEAD, the entity of the
1176   response &SHOULD; contain a short hypertext note with a hyperlink to
1177   the new URI(s).
1178  <list><t>
1179      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1180      status. When interoperability with such clients is a concern, the
1181      302 status code may be used instead, since most user agents react
1182      to a 302 response as described here for 303.
1183  </t></list>
1187<section title="304 Not Modified" anchor="status.304">
1188  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1189  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1191   The response to the request has not been modified since the conditions
1192   indicated by the client's conditional GET request, as defined in &conditional;.
1196<section title="305 Use Proxy" anchor="status.305">
1197  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1198  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1200   The requested resource &MUST; be accessed through the proxy given by
1201   the Location field. The Location field gives the URI of the proxy.
1202   The recipient is expected to repeat this single request via the
1203   proxy. 305 responses &MUST; only be generated by origin servers.
1204  <list><t>
1205      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1206      single request, and to be generated by origin servers only.  Not
1207      observing these limitations has significant security consequences.
1208  </t></list>
1212<section title="306 (Unused)" anchor="status.306">
1213  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1214  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1216   The 306 status code was used in a previous version of the
1217   specification, is no longer used, and the code is reserved.
1221<section title="307 Temporary Redirect" anchor="status.307">
1222  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1223  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1225   The requested resource resides temporarily under a different URI.
1226   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1227   continue to use the Request-URI for future requests.  This response
1228   is only cacheable if indicated by a Cache-Control or Expires header
1229   field.
1232   The temporary URI &SHOULD; be given by the Location field in the
1233   response. Unless the request method was HEAD, the entity of the
1234   response &SHOULD; contain a short hypertext note with a hyperlink to
1235   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1236   understand the 307 status. Therefore, the note &SHOULD; contain the
1237   information necessary for a user to repeat the original request on
1238   the new URI.
1241   If the 307 status code is received in response to a request method
1242   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1243   then the request &MAY; be automatically redirected by the user agent without
1244   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1245   request unless it can be confirmed by the user, since this might
1246   change the conditions under which the request was issued.
1251<section title="Client Error 4xx" anchor="status.4xx">
1253   The 4xx class of status code is intended for cases in which the
1254   client seems to have erred. Except when responding to a HEAD request,
1255   the server &SHOULD; include an entity containing an explanation of the
1256   error situation, and whether it is a temporary or permanent
1257   condition. These status codes are applicable to any request method.
1258   User agents &SHOULD; display any included entity to the user.
1261   If the client is sending data, a server implementation using TCP
1262   &SHOULD; be careful to ensure that the client acknowledges receipt of
1263   the packet(s) containing the response, before the server closes the
1264   input connection. If the client continues sending data to the server
1265   after the close, the server's TCP stack will send a reset packet to
1266   the client, which may erase the client's unacknowledged input buffers
1267   before they can be read and interpreted by the HTTP application.
1270<section title="400 Bad Request" anchor="status.400">
1271  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1272  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1274   The request could not be understood by the server due to malformed
1275   syntax. The client &SHOULD-NOT;  repeat the request without
1276   modifications.
1280<section title="401 Unauthorized" anchor="status.401">
1281  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1282  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1284   The request requires user authentication (see &auth;).
1288<section title="402 Payment Required" anchor="status.402">
1289  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1290  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1292   This code is reserved for future use.
1296<section title="403 Forbidden" anchor="status.403">
1297  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1298  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1300   The server understood the request, but is refusing to fulfill it.
1301   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1302   If the request method was not HEAD and the server wishes to make
1303   public why the request has not been fulfilled, it &SHOULD; describe the
1304   reason for the refusal in the entity.  If the server does not wish to
1305   make this information available to the client, the status code 404
1306   (Not Found) can be used instead.
1310<section title="404 Not Found" anchor="status.404">
1311  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1312  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1314   The server has not found anything matching the Request-URI. No
1315   indication is given of whether the condition is temporary or
1316   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1317   knows, through some internally configurable mechanism, that an old
1318   resource is permanently unavailable and has no forwarding address.
1319   This status code is commonly used when the server does not wish to
1320   reveal exactly why the request has been refused, or when no other
1321   response is applicable.
1325<section title="405 Method Not Allowed" anchor="status.405">
1326  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1327  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1329   The method specified in the Request-Line is not allowed for the
1330   resource identified by the Request-URI. The response &MUST; include an
1331   Allow header containing a list of valid methods for the requested
1332   resource.
1336<section title="406 Not Acceptable" anchor="status.406">
1337  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1338  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1340   The resource identified by the request is only capable of generating
1341   response entities which have content characteristics not acceptable
1342   according to the accept headers sent in the request.
1345   Unless it was a HEAD request, the response &SHOULD; include an entity
1346   containing a list of available entity characteristics and location(s)
1347   from which the user or user agent can choose the one most
1348   appropriate. The entity format is specified by the media type given
1349   in the Content-Type header field. Depending upon the format and the
1350   capabilities of the user agent, selection of the most appropriate
1351   choice &MAY; be performed automatically. However, this specification
1352   does not define any standard for such automatic selection.
1353  <list><t>
1354      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1355      not acceptable according to the accept headers sent in the
1356      request. In some cases, this may even be preferable to sending a
1357      406 response. User agents are encouraged to inspect the headers of
1358      an incoming response to determine if it is acceptable.
1359  </t></list>
1362   If the response could be unacceptable, a user agent &SHOULD;
1363   temporarily stop receipt of more data and query the user for a
1364   decision on further actions.
1368<section title="407 Proxy Authentication Required" anchor="status.407">
1369  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1370  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1372   This code is similar to 401 (Unauthorized), but indicates that the
1373   client must first authenticate itself with the proxy (see &auth;).
1377<section title="408 Request Timeout" anchor="status.408">
1378  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1379  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1381   The client did not produce a request within the time that the server
1382   was prepared to wait. The client &MAY; repeat the request without
1383   modifications at any later time.
1387<section title="409 Conflict" anchor="status.409">
1388  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1389  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1391   The request could not be completed due to a conflict with the current
1392   state of the resource. This code is only allowed in situations where
1393   it is expected that the user might be able to resolve the conflict
1394   and resubmit the request. The response body &SHOULD; include enough
1395   information for the user to recognize the source of the conflict.
1396   Ideally, the response entity would include enough information for the
1397   user or user agent to fix the problem; however, that might not be
1398   possible and is not required.
1401   Conflicts are most likely to occur in response to a PUT request. For
1402   example, if versioning were being used and the entity being PUT
1403   included changes to a resource which conflict with those made by an
1404   earlier (third-party) request, the server might use the 409 response
1405   to indicate that it can't complete the request. In this case, the
1406   response entity would likely contain a list of the differences
1407   between the two versions in a format defined by the response
1408   Content-Type.
1412<section title="410 Gone" anchor="status.410">
1413  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1414  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1416   The requested resource is no longer available at the server and no
1417   forwarding address is known. This condition is expected to be
1418   considered permanent. Clients with link editing capabilities &SHOULD;
1419   delete references to the Request-URI after user approval. If the
1420   server does not know, or has no facility to determine, whether or not
1421   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1422   used instead. This response is cacheable unless indicated otherwise.
1425   The 410 response is primarily intended to assist the task of web
1426   maintenance by notifying the recipient that the resource is
1427   intentionally unavailable and that the server owners desire that
1428   remote links to that resource be removed. Such an event is common for
1429   limited-time, promotional services and for resources belonging to
1430   individuals no longer working at the server's site. It is not
1431   necessary to mark all permanently unavailable resources as "gone" or
1432   to keep the mark for any length of time -- that is left to the
1433   discretion of the server owner.
1437<section title="411 Length Required" anchor="status.411">
1438  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1439  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1441   The server refuses to accept the request without a defined Content-Length.
1442   The client &MAY; repeat the request if it adds a valid
1443   Content-Length header field containing the length of the message-body
1444   in the request message.
1448<section title="412 Precondition Failed" anchor="status.412">
1449  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1450  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1452   The precondition given in one or more of the request-header fields
1453   evaluated to false when it was tested on the server, as defined in
1454   &conditional;.
1458<section title="413 Request Entity Too Large" anchor="status.413">
1459  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1460  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1462   The server is refusing to process a request because the request
1463   entity is larger than the server is willing or able to process. The
1464   server &MAY; close the connection to prevent the client from continuing
1465   the request.
1468   If the condition is temporary, the server &SHOULD; include a Retry-After
1469   header field to indicate that it is temporary and after what
1470   time the client &MAY; try again.
1474<section title="414 Request-URI Too Long" anchor="status.414">
1475  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1476  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1478   The server is refusing to service the request because the Request-URI
1479   is longer than the server is willing to interpret. This rare
1480   condition is only likely to occur when a client has improperly
1481   converted a POST request to a GET request with long query
1482   information, when the client has descended into a URI "black hole" of
1483   redirection (e.g., a redirected URI prefix that points to a suffix of
1484   itself), or when the server is under attack by a client attempting to
1485   exploit security holes present in some servers using fixed-length
1486   buffers for reading or manipulating the Request-URI.
1490<section title="415 Unsupported Media Type" anchor="status.415">
1491  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1492  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1494   The server is refusing to service the request because the entity of
1495   the request is in a format not supported by the requested resource
1496   for the requested method.
1500<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1501  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1502  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1504   The request included a Range request-header field (&header-range;) and none of
1505   the range-specifier values in this field overlap the current extent
1506   of the selected resource.
1510<section title="417 Expectation Failed" anchor="status.417">
1511  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1512  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1514   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1515   could not be met by this server, or, if the server is a proxy,
1516   the server has unambiguous evidence that the request could not be met
1517   by the next-hop server.
1522<section title="Server Error 5xx" anchor="status.5xx">
1524   Response status codes beginning with the digit "5" indicate cases in
1525   which the server is aware that it has erred or is incapable of
1526   performing the request. Except when responding to a HEAD request, the
1527   server &SHOULD; include an entity containing an explanation of the
1528   error situation, and whether it is a temporary or permanent
1529   condition. User agents &SHOULD; display any included entity to the
1530   user. These response codes are applicable to any request method.
1533<section title="500 Internal Server Error" anchor="status.500">
1534  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1535  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1537   The server encountered an unexpected condition which prevented it
1538   from fulfilling the request.
1542<section title="501 Not Implemented" anchor="status.501">
1543  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1544  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1546   The server does not support the functionality required to fulfill the
1547   request. This is the appropriate response when the server does not
1548   recognize the request method and is not capable of supporting it for
1549   any resource.
1553<section title="502 Bad Gateway" anchor="status.502">
1554  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1555  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1557   The server, while acting as a gateway or proxy, received an invalid
1558   response from the upstream server it accessed in attempting to
1559   fulfill the request.
1563<section title="503 Service Unavailable" anchor="status.503">
1564  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1565  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1567   The server is currently unable to handle the request due to a
1568   temporary overloading or maintenance of the server. The implication
1569   is that this is a temporary condition which will be alleviated after
1570   some delay. If known, the length of the delay &MAY; be indicated in a
1571   Retry-After header. If no Retry-After is given, the client &SHOULD;
1572   handle the response as it would for a 500 response.
1573  <list><t>
1574      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1575      server must use it when becoming overloaded. Some servers may wish
1576      to simply refuse the connection.
1577  </t></list>
1581<section title="504 Gateway Timeout" anchor="status.504">
1582  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1583  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1585   The server, while acting as a gateway or proxy, did not receive a
1586   timely response from the upstream server specified by the URI (e.g.
1587   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1588   to access in attempting to complete the request.
1589  <list><t>
1590      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1591      return 400 or 500 when DNS lookups time out.
1592  </t></list>
1596<section title="505 HTTP Version Not Supported" anchor="status.505">
1597  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1598  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1600   The server does not support, or refuses to support, the protocol
1601   version that was used in the request message. The server is
1602   indicating that it is unable or unwilling to complete the request
1603   using the same major version as the client, as described in &http-version;,
1604   other than with this error message. The response &SHOULD; contain
1605   an entity describing why that version is not supported and what other
1606   protocols are supported by that server.
1614<section title="Header Field Definitions" anchor="header.fields">
1616   This section defines the syntax and semantics of HTTP/1.1 header fields
1617   related to request and response semantics.
1620   For entity-header fields, both sender and recipient refer to either the
1621   client or the server, depending on who sends and who receives the entity.
1624<section title="Allow" anchor="header.allow">
1625  <iref primary="true" item="Allow header" x:for-anchor=""/>
1626  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1628      The Allow entity-header field lists the set of methods supported
1629      by the resource identified by the Request-URI. The purpose of this
1630      field is strictly to inform the recipient of valid methods
1631      associated with the resource. An Allow header field &MUST; be
1632      present in a 405 (Method Not Allowed) response.
1634<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1635  Allow   = "Allow" ":" #Method
1638      Example of use:
1640<figure><artwork type="example">
1641       Allow: GET, HEAD, PUT
1644      This field cannot prevent a client from trying other methods.
1645      However, the indications given by the Allow header field value
1646      &SHOULD; be followed. The actual set of allowed methods is defined
1647      by the origin server at the time of each request.
1650      The Allow header field &MAY; be provided with a PUT request to
1651      recommend the methods to be supported by the new or modified
1652      resource. The server is not required to support these methods and
1653      &SHOULD; include an Allow header in the response giving the actual
1654      supported methods.
1657      A proxy &MUST-NOT; modify the Allow header field even if it does not
1658      understand all the methods specified, since the user agent might
1659      have other means of communicating with the origin server.
1663<section title="Expect" anchor="header.expect">
1664  <iref primary="true" item="Expect header" x:for-anchor=""/>
1665  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1667   The Expect request-header field is used to indicate that particular
1668   server behaviors are required by the client.
1670<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"/>
1671  Expect       =  "Expect" ":" 1#expectation
1673  expectation  =  "100-continue" | expectation-extension
1674  expectation-extension =  token [ "=" ( token | quoted-string )
1675                           *expect-params ]
1676  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1679   A server that does not understand or is unable to comply with any of
1680   the expectation values in the Expect field of a request &MUST; respond
1681   with appropriate error status. The server &MUST; respond with a 417
1682   (Expectation Failed) status if any of the expectations cannot be met
1683   or, if there are other problems with the request, some other 4xx
1684   status.
1687   This header field is defined with extensible syntax to allow for
1688   future extensions. If a server receives a request containing an
1689   Expect field that includes an expectation-extension that it does not
1690   support, it &MUST; respond with a 417 (Expectation Failed) status.
1693   Comparison of expectation values is case-insensitive for unquoted
1694   tokens (including the 100-continue token), and is case-sensitive for
1695   quoted-string expectation-extensions.
1698   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1699   return a 417 (Expectation Failed) status if it receives a request
1700   with an expectation that it cannot meet. However, the Expect
1701   request-header itself is end-to-end; it &MUST; be forwarded if the
1702   request is forwarded.
1705   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1706   Expect header.
1709   See &use100; for the use of the 100 (Continue) status.
1713<section title="From" anchor="header.from">
1714  <iref primary="true" item="From header" x:for-anchor=""/>
1715  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1717   The From request-header field, if given, &SHOULD; contain an Internet
1718   e-mail address for the human user who controls the requesting user
1719   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1720   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1722<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1723  From   = "From" ":" mailbox
1726   An example is:
1728<figure><artwork type="example">
1729    From:
1732   This header field &MAY; be used for logging purposes and as a means for
1733   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1734   be used as an insecure form of access protection. The interpretation
1735   of this field is that the request is being performed on behalf of the
1736   person given, who accepts responsibility for the method performed. In
1737   particular, robot agents &SHOULD; include this header so that the
1738   person responsible for running the robot can be contacted if problems
1739   occur on the receiving end.
1742   The Internet e-mail address in this field &MAY; be separate from the
1743   Internet host which issued the request. For example, when a request
1744   is passed through a proxy the original issuer's address &SHOULD; be
1745   used.
1748   The client &SHOULD-NOT;  send the From header field without the user's
1749   approval, as it might conflict with the user's privacy interests or
1750   their site's security policy. It is strongly recommended that the
1751   user be able to disable, enable, and modify the value of this field
1752   at any time prior to a request.
1756<section title="Location" anchor="header.location">
1757  <iref primary="true" item="Location header" x:for-anchor=""/>
1758  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1760   The Location response-header field is used to redirect the recipient
1761   to a location other than the Request-URI for completion of the
1762   request or identification of a new resource. For 201 (Created)
1763   responses, the Location is that of the new resource which was created
1764   by the request. For 3xx responses, the location &SHOULD; indicate the
1765   server's preferred URI for automatic redirection to the resource. The
1766   field value consists of a single absolute URI.
1768<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1769  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1772   An example is:
1774<figure><artwork type="example">
1775    Location:
1778  <list><t>
1779      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1780      from Location in that the Content-Location identifies the original
1781      location of the entity enclosed in the request. It is therefore
1782      possible for a response to contain header fields for both Location
1783      and Content-Location.
1784  </t></list>
1787   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1788   <list style="symbols">
1789      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1790      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1791      <t>With 305 Use Proxy.</t>
1792   </list>
1796<section title="Max-Forwards" anchor="header.max-forwards">
1797  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1798  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1800   The Max-Forwards request-header field provides a mechanism with the
1801   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1802   number of proxies or gateways that can forward the request to the
1803   next inbound server. This can be useful when the client is attempting
1804   to trace a request chain which appears to be failing or looping in
1805   mid-chain.
1807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1808  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1811   The Max-Forwards value is a decimal integer indicating the remaining
1812   number of times this request message may be forwarded.
1815   Each proxy or gateway recipient of a TRACE or OPTIONS request
1816   containing a Max-Forwards header field &MUST; check and update its
1817   value prior to forwarding the request. If the received value is zero
1818   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1819   respond as the final recipient. If the received Max-Forwards value is
1820   greater than zero, then the forwarded message &MUST; contain an updated
1821   Max-Forwards field with a value decremented by one (1).
1824   The Max-Forwards header field &MAY; be ignored for all other methods
1825   defined by this specification and for any extension methods for which
1826   it is not explicitly referred to as part of that method definition.
1830<section title="Referer" anchor="header.referer">
1831  <iref primary="true" item="Referer header" x:for-anchor=""/>
1832  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1834   The Referer[sic] request-header field allows the client to specify,
1835   for the server's benefit, the address (URI) of the resource from
1836   which the Request-URI was obtained (the "referrer", although the
1837   header field is misspelled.) The Referer request-header allows a
1838   server to generate lists of back-links to resources for interest,
1839   logging, optimized caching, etc. It also allows obsolete or mistyped
1840   links to be traced for maintenance. The Referer field &MUST-NOT; be
1841   sent if the Request-URI was obtained from a source that does not have
1842   its own URI, such as input from the user keyboard.
1844<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1845  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1848   Example:
1850<figure><artwork type="example">
1851    Referer:
1854   If the field value is a relative URI, it &SHOULD; be interpreted
1855   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1856   <xref target=""/> for security considerations.
1860<section title="Retry-After" anchor="header.retry-after">
1861  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1862  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1864   The Retry-After response-header field can be used with a 503 (Service
1865   Unavailable) response to indicate how long the service is expected to
1866   be unavailable to the requesting client. This field &MAY; also be used
1867   with any 3xx (Redirection) response to indicate the minimum time the
1868   user-agent is asked wait before issuing the redirected request. The
1869   value of this field can be either an HTTP-date or an integer number
1870   of seconds (in decimal) after the time of the response.
1872<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1873  Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1876   Two examples of its use are
1878<figure><artwork type="example">
1879    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1880    Retry-After: 120
1883   In the latter example, the delay is 2 minutes.
1887<section title="Server" anchor="header.server">
1888  <iref primary="true" item="Server header" x:for-anchor=""/>
1889  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1891   The Server response-header field contains information about the
1892   software used by the origin server to handle the request. The field
1893   can contain multiple product tokens (&product-tokens;) and comments
1894   identifying the server and any significant subproducts. The product
1895   tokens are listed in order of their significance for identifying the
1896   application.
1898<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1899  Server         = "Server" ":" 1*( product | comment )
1902   Example:
1904<figure><artwork type="example">
1905    Server: CERN/3.0 libwww/2.17
1908   If the response is being forwarded through a proxy, the proxy
1909   application &MUST-NOT; modify the Server response-header. Instead, it
1910   &MUST; include a Via field (as described in &header-via;).
1911  <list><t>
1912      <x:h>Note:</x:h> Revealing the specific software version of the server might
1913      allow the server machine to become more vulnerable to attacks
1914      against software that is known to contain security holes. Server
1915      implementors are encouraged to make this field a configurable
1916      option.
1917  </t></list>
1921<section title="User-Agent" anchor="header.user-agent">
1922  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1923  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1925   The User-Agent request-header field contains information about the
1926   user agent originating the request. This is for statistical purposes,
1927   the tracing of protocol violations, and automated recognition of user
1928   agents for the sake of tailoring responses to avoid particular user
1929   agent limitations. User agents &SHOULD; include this field with
1930   requests. The field can contain multiple product tokens (&product-tokens;)
1931   and comments identifying the agent and any subproducts which form a
1932   significant part of the user agent. By convention, the product tokens
1933   are listed in order of their significance for identifying the
1934   application.
1936<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1937  User-Agent     = "User-Agent" ":" 1*( product | comment )
1940   Example:
1942<figure><artwork type="example">
1943    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1949<section title="IANA Considerations" anchor="IANA.considerations">
1951   <cref>TBD.</cref>
1955<section title="Security Considerations" anchor="security.considerations">
1957   This section is meant to inform application developers, information
1958   providers, and users of the security limitations in HTTP/1.1 as
1959   described by this document. The discussion does not include
1960   definitive solutions to the problems revealed, though it does make
1961   some suggestions for reducing security risks.
1964<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1966   Like any generic data transfer protocol, HTTP cannot regulate the
1967   content of the data that is transferred, nor is there any a priori
1968   method of determining the sensitivity of any particular piece of
1969   information within the context of any given request. Therefore,
1970   applications &SHOULD; supply as much control over this information as
1971   possible to the provider of that information. Four header fields are
1972   worth special mention in this context: Server, Via, Referer and From.
1975   Revealing the specific software version of the server might allow the
1976   server machine to become more vulnerable to attacks against software
1977   that is known to contain security holes. Implementors &SHOULD; make the
1978   Server header field a configurable option.
1981   Proxies which serve as a portal through a network firewall &SHOULD;
1982   take special precautions regarding the transfer of header information
1983   that identifies the hosts behind the firewall. In particular, they
1984   &SHOULD; remove, or replace with sanitized versions, any Via fields
1985   generated behind the firewall.
1988   The Referer header allows reading patterns to be studied and reverse
1989   links drawn. Although it can be very useful, its power can be abused
1990   if user details are not separated from the information contained in
1991   the Referer. Even when the personal information has been removed, the
1992   Referer header might indicate a private document's URI whose
1993   publication would be inappropriate.
1996   The information sent in the From field might conflict with the user's
1997   privacy interests or their site's security policy, and hence it
1998   &SHOULD-NOT;  be transmitted without the user being able to disable,
1999   enable, and modify the contents of the field. The user &MUST; be able
2000   to set the contents of this field within a user preference or
2001   application defaults configuration.
2004   We suggest, though do not require, that a convenient toggle interface
2005   be provided for the user to enable or disable the sending of From and
2006   Referer information.
2009   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2010   fields can sometimes be used to determine that a specific client or
2011   server have a particular security hole which might be exploited.
2012   Unfortunately, this same information is often used for other valuable
2013   purposes for which HTTP currently has no better mechanism.
2017<section title="Encoding Sensitive Information in URIs" anchor="">
2019   Because the source of a link might be private information or might
2020   reveal an otherwise private information source, it is strongly
2021   recommended that the user be able to select whether or not the
2022   Referer field is sent. For example, a browser client could have a
2023   toggle switch for browsing openly/anonymously, which would
2024   respectively enable/disable the sending of Referer and From
2025   information.
2028   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2029   HTTP request if the referring page was transferred with a secure
2030   protocol.
2033   Authors of services should not use
2034   GET-based forms for the submission of sensitive data because that
2035   data will be encoded in the Request-URI. Many existing
2036   servers, proxies, and user agents log or display the Request-URI in
2037   places where it might be visible to third parties. Such services can
2038   use POST-based form submission instead.
2042<section title="Location Headers and Spoofing" anchor="location.spoofing">
2044   If a single server supports multiple organizations that do not trust
2045   one another, then it &MUST; check the values of Location and Content-Location
2046   headers in responses that are generated under control of
2047   said organizations to make sure that they do not attempt to
2048   invalidate resources over which they have no authority.
2054<section title="Acknowledgments" anchor="ack">
2059<references title="Normative References">
2061<reference anchor="Part1">
2062  <front>
2063    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2064    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2065      <organization abbrev="Day Software">Day Software</organization>
2066      <address><email></email></address>
2067    </author>
2068    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2069      <organization>One Laptop per Child</organization>
2070      <address><email></email></address>
2071    </author>
2072    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2073      <organization abbrev="HP">Hewlett-Packard Company</organization>
2074      <address><email></email></address>
2075    </author>
2076    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2077      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2078      <address><email></email></address>
2079    </author>
2080    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2081      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2082      <address><email></email></address>
2083    </author>
2084    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2085      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2086      <address><email></email></address>
2087    </author>
2088    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2089      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2090      <address><email></email></address>
2091    </author>
2092    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2093      <organization abbrev="W3C">World Wide Web Consortium</organization>
2094      <address><email></email></address>
2095    </author>
2096    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2097      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2098      <address><email></email></address>
2099    </author>
2100    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2101  </front>
2102  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2103  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2106<reference anchor="Part3">
2107  <front>
2108    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2109    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2110      <organization abbrev="Day Software">Day Software</organization>
2111      <address><email></email></address>
2112    </author>
2113    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2114      <organization>One Laptop per Child</organization>
2115      <address><email></email></address>
2116    </author>
2117    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2118      <organization abbrev="HP">Hewlett-Packard Company</organization>
2119      <address><email></email></address>
2120    </author>
2121    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2122      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2123      <address><email></email></address>
2124    </author>
2125    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2126      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2127      <address><email></email></address>
2128    </author>
2129    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2130      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2131      <address><email></email></address>
2132    </author>
2133    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2134      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2135      <address><email></email></address>
2136    </author>
2137    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2138      <organization abbrev="W3C">World Wide Web Consortium</organization>
2139      <address><email></email></address>
2140    </author>
2141    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2142      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2143      <address><email></email></address>
2144    </author>
2145    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2146  </front>
2147  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2148  <x:source href="p3-payload.xml" basename="p3-payload"/>
2151<reference anchor="Part4">
2152  <front>
2153    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2154    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2155      <organization abbrev="Day Software">Day Software</organization>
2156      <address><email></email></address>
2157    </author>
2158    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2159      <organization>One Laptop per Child</organization>
2160      <address><email></email></address>
2161    </author>
2162    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2163      <organization abbrev="HP">Hewlett-Packard Company</organization>
2164      <address><email></email></address>
2165    </author>
2166    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2167      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2168      <address><email></email></address>
2169    </author>
2170    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2171      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2172      <address><email></email></address>
2173    </author>
2174    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2175      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2176      <address><email></email></address>
2177    </author>
2178    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2179      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2180      <address><email></email></address>
2181    </author>
2182    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2183      <organization abbrev="W3C">World Wide Web Consortium</organization>
2184      <address><email></email></address>
2185    </author>
2186    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2187      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2188      <address><email></email></address>
2189    </author>
2190    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2191  </front>
2192  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2193  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2196<reference anchor="Part5">
2197  <front>
2198    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2199    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2200      <organization abbrev="Day Software">Day Software</organization>
2201      <address><email></email></address>
2202    </author>
2203    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2204      <organization>One Laptop per Child</organization>
2205      <address><email></email></address>
2206    </author>
2207    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2208      <organization abbrev="HP">Hewlett-Packard Company</organization>
2209      <address><email></email></address>
2210    </author>
2211    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2212      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2213      <address><email></email></address>
2214    </author>
2215    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2216      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2217      <address><email></email></address>
2218    </author>
2219    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2220      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2221      <address><email></email></address>
2222    </author>
2223    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2224      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2225      <address><email></email></address>
2226    </author>
2227    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2228      <organization abbrev="W3C">World Wide Web Consortium</organization>
2229      <address><email></email></address>
2230    </author>
2231    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2232      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2233      <address><email></email></address>
2234    </author>
2235    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2236  </front>
2237  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2238  <x:source href="p5-range.xml" basename="p5-range"/>
2241<reference anchor="Part6">
2242  <front>
2243    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2244    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2245      <organization abbrev="Day Software">Day Software</organization>
2246      <address><email></email></address>
2247    </author>
2248    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2249      <organization>One Laptop per Child</organization>
2250      <address><email></email></address>
2251    </author>
2252    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2253      <organization abbrev="HP">Hewlett-Packard Company</organization>
2254      <address><email></email></address>
2255    </author>
2256    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2257      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2258      <address><email></email></address>
2259    </author>
2260    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2261      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2262      <address><email></email></address>
2263    </author>
2264    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2265      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2266      <address><email></email></address>
2267    </author>
2268    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2269      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2270      <address><email></email></address>
2271    </author>
2272    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2273      <organization abbrev="W3C">World Wide Web Consortium</organization>
2274      <address><email></email></address>
2275    </author>
2276    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2277      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2278      <address><email></email></address>
2279    </author>
2280    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2281  </front>
2282  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2283  <x:source href="p6-cache.xml" basename="p6-cache"/>
2286<reference anchor="Part7">
2287  <front>
2288    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2289    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2290      <organization abbrev="Day Software">Day Software</organization>
2291      <address><email></email></address>
2292    </author>
2293    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2294      <organization>One Laptop per Child</organization>
2295      <address><email></email></address>
2296    </author>
2297    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2298      <organization abbrev="HP">Hewlett-Packard Company</organization>
2299      <address><email></email></address>
2300    </author>
2301    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2302      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2303      <address><email></email></address>
2304    </author>
2305    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2306      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2307      <address><email></email></address>
2308    </author>
2309    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2310      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2311      <address><email></email></address>
2312    </author>
2313    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2314      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2315      <address><email></email></address>
2316    </author>
2317    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2318      <organization abbrev="W3C">World Wide Web Consortium</organization>
2319      <address><email></email></address>
2320    </author>
2321    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2322      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2323      <address><email></email></address>
2324    </author>
2325    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2326  </front>
2327  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2328  <x:source href="p7-auth.xml" basename="p7-auth"/>
2331<reference anchor="RFC2119">
2332  <front>
2333    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2334    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2335      <organization>Harvard University</organization>
2336      <address><email></email></address>
2337    </author>
2338    <date month="March" year="1997"/>
2339  </front>
2340  <seriesInfo name="BCP" value="14"/>
2341  <seriesInfo name="RFC" value="2119"/>
2346<references title="Informative References">
2348<reference anchor="Luo1998">
2349  <front>
2350    <title>Tunneling TCP based protocols through Web proxy servers</title>
2351    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2352      <organization/>
2353    </author>
2354    <date year="1998" month="August"/>
2355  </front>
2356  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2359<reference anchor="RFC1945">
2360  <front>
2361    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2362    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2363      <organization>MIT, Laboratory for Computer Science</organization>
2364      <address><email></email></address>
2365    </author>
2366    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2367      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2368      <address><email></email></address>
2369    </author>
2370    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2371      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2372      <address><email></email></address>
2373    </author>
2374    <date month="May" year="1996"/>
2375  </front>
2376  <seriesInfo name="RFC" value="1945"/>
2379<reference anchor="RFC2068">
2380  <front>
2381    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2382    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2383      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2384      <address><email></email></address>
2385    </author>
2386    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2387      <organization>MIT Laboratory for Computer Science</organization>
2388      <address><email></email></address>
2389    </author>
2390    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2391      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2392      <address><email></email></address>
2393    </author>
2394    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2395      <organization>MIT Laboratory for Computer Science</organization>
2396      <address><email></email></address>
2397    </author>
2398    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2399      <organization>MIT Laboratory for Computer Science</organization>
2400      <address><email></email></address>
2401    </author>
2402    <date month="January" year="1997"/>
2403  </front>
2404  <seriesInfo name="RFC" value="2068"/>
2407<reference anchor="RFC2616">
2408  <front>
2409    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2410    <author initials="R." surname="Fielding" fullname="R. Fielding">
2411      <organization>University of California, Irvine</organization>
2412      <address><email></email></address>
2413    </author>
2414    <author initials="J." surname="Gettys" fullname="J. Gettys">
2415      <organization>W3C</organization>
2416      <address><email></email></address>
2417    </author>
2418    <author initials="J." surname="Mogul" fullname="J. Mogul">
2419      <organization>Compaq Computer Corporation</organization>
2420      <address><email></email></address>
2421    </author>
2422    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2423      <organization>MIT Laboratory for Computer Science</organization>
2424      <address><email></email></address>
2425    </author>
2426    <author initials="L." surname="Masinter" fullname="L. Masinter">
2427      <organization>Xerox Corporation</organization>
2428      <address><email></email></address>
2429    </author>
2430    <author initials="P." surname="Leach" fullname="P. Leach">
2431      <organization>Microsoft Corporation</organization>
2432      <address><email></email></address>
2433    </author>
2434    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2435      <organization>W3C</organization>
2436      <address><email></email></address>
2437    </author>
2438    <date month="June" year="1999"/>
2439  </front>
2440  <seriesInfo name="RFC" value="2616"/>
2443<reference anchor="RFC2822">
2444  <front>
2445    <title>Internet Message Format</title>
2446    <author initials="P." surname="Resnick" fullname="P. Resnick">
2447      <organization>QUALCOMM Incorporated</organization>
2448    </author>
2449    <date year="2001" month="April"/>
2450  </front>
2451  <seriesInfo name="RFC" value="2822"/>
2456<section title="Compatibility with Previous Versions" anchor="compatibility">
2457<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2459   Clarified which error code should be used for inbound server failures
2460   (e.g. DNS failures). (<xref target="status.504"/>).
2463   201 (Created) had a race that required an Etag be sent when a resource is
2464   first created. (<xref target="status.201"/>).
2467   Rewrite of message transmission requirements to make it much harder
2468   for implementors to get it wrong, as the consequences of errors here
2469   can have significant impact on the Internet, and to deal with the
2470   following problems:
2471  <list style="numbers">
2472      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2473         this was incorrectly placing a requirement on the behavior of
2474         an implementation of a future version of HTTP/1.x</t>
2476      <t>Made it clear that user-agents should retry requests, not
2477         "clients" in general.</t>
2479      <t>Converted requirements for clients to ignore unexpected 100
2480         (Continue) responses, and for proxies to forward 100 responses,
2481         into a general requirement for 1xx responses.</t>
2483      <t>Modified some TCP-specific language, to make it clearer that
2484         non-TCP transports are possible for HTTP.</t>
2486      <t>Require that the origin server &MUST-NOT; wait for the request
2487         body before it sends a required 100 (Continue) response.</t>
2489      <t>Allow, rather than require, a server to omit 100 (Continue) if
2490         it has already seen some of the request body.</t>
2492      <t>Allow servers to defend against denial-of-service attacks and
2493         broken clients.</t>
2494  </list>
2497   This change adds the Expect header and 417 status code.
2500   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2501   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2504   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
2505   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2509<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2511  Clarify definition of POST.
2512  (<xref target="POST"/>)
2515  Failed to consider that there are
2516  many other request methods that are safe to automatically redirect,
2517  and further that the user agent is able to make that determination
2518  based on the request method semantics.
2519  (Sections <xref format="counter" target="status.301"/>,
2520  <xref format="counter" target="status.302"/> and
2521  <xref format="counter" target="status.307"/> )
2524  Correct syntax of Location header to allow fragment,
2525  as referred symbol wasn't what was expected, and add some
2526  clarifications as to when it would not be appropriate.
2527  (<xref target="header.location"/>)
2530  In the description of the Server header, the Via field
2531  was described as a SHOULD. The requirement was and is stated
2532  correctly in the description of the Via header in &header-via;.
2533  (<xref target="header.server"/>)
2539<section title="Change Log (to be removed by RFC Editor before publication)">
2541<section title="Since RFC2616">
2543  Extracted relevant partitions from <xref target="RFC2616"/>.
2547<section title="Since draft-ietf-httpbis-p2-semantics-00">
2549  Closed issues:
2550  <list style="symbols">
2551    <t>
2552      <eref target=""/>:
2553      "Via is a MUST"
2554      (<eref target=""/>)
2555    </t>
2556    <t>
2557      <eref target=""/>:
2558      "Fragments allowed in Location"
2559      (<eref target=""/>)
2560    </t>
2561    <t>
2562      <eref target=""/>:
2563      "Safe Methods vs Redirection"
2564      (<eref target=""/>)
2565    </t>
2566    <t>
2567      <eref target=""/>:
2568      "Revise description of the POST method"
2569      (<eref target=""/>)
2570    </t>
2571    <t>
2572      <eref target=""/>:
2573      "Normative and Informative references"
2574    </t>
2575    <t>
2576      <eref target=""/>:
2577      "RFC2606 Compliance"
2578    </t>
2579    <t>
2580      <eref target=""/>:
2581      "Informative references"
2582    </t>
2583    <t>
2584      <eref target=""/>:
2585      "Redundant cross-references"
2586    </t>
2587  </list>
2590  Other changes:
2591  <list style="symbols">
2592    <t>
2593      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2594    </t>
2595  </list>
2599<section title="Since draft-ietf-httpbis-p2-semantics-01">
2601  Closed issues:
2602  <list style="symbols">
2603    <t>
2604      <eref target=""/>:
2605      "PUT side effects"
2606    </t>
2607    <t>
2608      <eref target=""/>:
2609      "Duplicate Host header requirements"
2610    </t>
2611  </list>
2614  Ongoing work on ABNF conversion (<eref target=""/>):
2615  <list style="symbols">
2616    <t>
2617      Move "Product Tokens" section (back) into Part 1, as "token" is used
2618      in the definition of the Upgrade header.
2619    </t>
2620  </list>
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