source: draft-ietf-httpbis/latest/p2-semantics.xml @ 113

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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 "December">
16  <!ENTITY ID-YEAR "2007">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x=''/>">
18  <!ENTITY payload                    "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY conditional                "<xref target='Part4' xmlns:x=''/>">
20  <!ENTITY range                      "<xref target='Part5' xmlns:x=''/>">
21  <!ENTITY caching                    "<xref target='Part6' xmlns:x=''/>">
22  <!ENTITY auth                       "<xref target='Part7' xmlns:x=''/>">
23  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
24  <!ENTITY diff2045entity             "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
25  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
26  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
27  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
28  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
29  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
30  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
31  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
32  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
33  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
34  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
35  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
36  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
37  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
38  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
39  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
40  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
41  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
42  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
43  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
44  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
45  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
46  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
47  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
48  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
49  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
50  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
51  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
52  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
53  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
54  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
55  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
56  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
57  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
58  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
59  <!ENTITY message-transmission-req   "<xref target='Part1' x:rel='#message.transmission.requirements' xmlns:x=''/>">
61<?rfc toc="yes" ?>
62<?rfc symrefs="yes" ?>
63<?rfc sortrefs="yes" ?>
64<?rfc compact="yes"?>
65<?rfc subcompact="no" ?>
66<?rfc linkmailto="no" ?>
67<?rfc editing="no" ?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2068, 2616" category="std"
71     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
72     xmlns:x='' xmlns:ed="">
75  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
77  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
78    <organization abbrev="Day Software">Day Software</organization>
79    <address>
80      <postal>
81        <street>23 Corporate Plaza DR, Suite 280</street>
82        <city>Newport Beach</city>
83        <region>CA</region>
84        <code>92660</code>
85        <country>USA</country>
86      </postal>
87      <phone>+1-949-706-5300</phone>
88      <facsimile>+1-949-706-5305</facsimile>
89      <email></email>
90      <uri></uri>
91    </address>
92  </author>
94  <author initials="J." surname="Gettys" fullname="Jim Gettys">
95    <organization>One Laptop per Child</organization>
96    <address>
97      <postal>
98        <street>21 Oak Knoll Road</street>
99        <city>Carlisle</city>
100        <region>MA</region>
101        <code>01741</code>
102        <country>USA</country>
103      </postal>
104      <email></email>
105      <uri></uri>
106    </address>
107  </author>
109  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
110    <organization abbrev="HP">Hewlett-Packard Company</organization>
111    <address>
112      <postal>
113        <street>HP Labs, Large Scale Systems Group</street>
114        <street>1501 Page Mill Road, MS 1177</street>
115        <city>Palo Alto</city>
116        <region>CA</region>
117        <code>94304</code>
118        <country>USA</country>
119      </postal>
120      <email></email>
121    </address>
122  </author>
124  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
125    <organization abbrev="Microsoft">Microsoft Corporation</organization>
126    <address>
127      <postal>
128        <street>1 Microsoft Way</street>
129        <city>Redmond</city>
130        <region>WA</region>
131        <code>98052</code>
132        <country>USA</country>
133      </postal>
134      <email></email>
135    </address>
136  </author>
138  <author initials="L." surname="Masinter" fullname="Larry Masinter">
139    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
140    <address>
141      <postal>
142        <street>345 Park Ave</street>
143        <city>San Jose</city>
144        <region>CA</region>
145        <code>95110</code>
146        <country>USA</country>
147      </postal>
148      <email></email>
149      <uri></uri>
150    </address>
151  </author>
153  <author initials="P." surname="Leach" fullname="Paul J. Leach">
154    <organization abbrev="Microsoft">Microsoft Corporation</organization>
155    <address>
156      <postal>
157        <street>1 Microsoft Way</street>
158        <city>Redmond</city>
159        <region>WA</region>
160        <code>98052</code>
161      </postal>
162      <email></email>
163    </address>
164  </author>
166  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
167    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
171        <street>The Stata Center, Building 32</street>
172        <street>32 Vassar Street</street>
173        <city>Cambridge</city>
174        <region>MA</region>
175        <code>02139</code>
176        <country>USA</country>
177      </postal>
178      <email></email>
179      <uri></uri>
180    </address>
181  </author>
183  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
184    <organization abbrev="W3C">World Wide Web Consortium</organization>
185    <address>
186      <postal>
187        <street>W3C / ERCIM</street>
188        <street>2004, rte des Lucioles</street>
189        <city>Sophia-Antipolis</city>
190        <region>AM</region>
191        <code>06902</code>
192        <country>France</country>
193      </postal>
194      <email></email>
195      <uri></uri>
196    </address>
197  </author>
199  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
200    <organization abbrev="greenbytes">greenbytes GmbH</organization>
201    <address>
202      <postal>
203        <street>Hafenweg 16</street>
204        <city>Muenster</city><region>NW</region><code>48155</code>
205        <country>Germany</country>
206      </postal>
207      <phone>+49 251 2807760</phone>   
208      <facsimile>+49 251 2807761</facsimile>   
209      <email></email>       
210      <uri></uri>     
211    </address>
212  </author>
214  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
218   The Hypertext Transfer Protocol (HTTP) is an application-level
219   protocol for distributed, collaborative, hypermedia information
220   systems. HTTP has been in use by the World Wide Web global information
221   initiative since 1990. This document is Part 2 of the seven-part specification
222   that defines the protocol referred to as "HTTP/1.1" and, taken together,
223   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
224   as expressed by request methods, request-header fields, response status codes,
225   and response-header fields.
229<note title="Editorial Note (To be removed by RFC Editor)">
230  <t>
231    This version of the HTTP specification contains only minimal editorial
232    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
233    and authors' addresses).  All other changes are due to partitioning the
234    original into seven mostly independent parts.  The intent is for readers
235    of future drafts to able to use draft 00 as the basis for comparison
236    when the WG makes later changes to the specification text.  This draft
237    will shortly be followed by draft 01 (containing the first round of changes
238    that have already been agreed to on the mailing list). There is no point in
239    reviewing this draft other than to verify that the partitioning has been
240    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
241    will be the editors after draft 00 is submitted.
242  </t>
243  <t>
244    Discussion of this draft should take place on the HTTPBIS working group
245    mailing list ( The current issues list is
246    at <eref target=""/>
247    and related documents (including fancy diffs) can be found at
248    <eref target=""/>.
249  </t>
253<section title="Introduction" anchor="introduction">
255   This document will define aspects of HTTP related to request and response
256   semantics. Right now it only includes the extracted relevant sections of
257   RFC 2616 with only minor edits.
260   The HTTP protocol is a request/response protocol. A client sends a
261   request to the server in the form of a request method, URI, and
262   protocol version, followed by a MIME-like message containing request
263   modifiers, client information, and possible body content over a
264   connection with a server. The server responds with a status line,
265   including the message's protocol version and a success or error code,
266   followed by a MIME-like message containing server information, entity
267   metainformation, and possible entity-body content. The relationship
268   between HTTP and MIME is described in &diff2045entity;.
271<section title="Requirements" anchor="intro.requirements">
273   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
274   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
275   document are to be interpreted as described in <xref target="RFC2119"/>.
278   An implementation is not compliant if it fails to satisfy one or more
279   of the &MUST; or &REQUIRED; level requirements for the protocols it
280   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
281   level and all the &SHOULD; level requirements for its protocols is said
282   to be "unconditionally compliant"; one that satisfies all the &MUST;
283   level requirements but not all the &SHOULD; level requirements for its
284   protocols is said to be "conditionally compliant."
289<section title="Product Tokens" anchor="product.tokens">
291   Product tokens are used to allow communicating applications to
292   identify themselves by software name and version. Most fields using
293   product tokens also allow sub-products which form a significant part
294   of the application to be listed, separated by white space. By
295   convention, the products are listed in order of their significance
296   for identifying the application.
298<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
299    product         = token ["/" product-version]
300    product-version = token
303   Examples:
305<figure><artwork type="example">
306    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
307    Server: Apache/0.8.4
310   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
311   used for advertising or other non-essential information. Although any
312   token character &MAY; appear in a product-version, this token &SHOULD;
313   only be used for a version identifier (i.e., successive versions of
314   the same product &SHOULD; only differ in the product-version portion of
315   the product value).
319<section title="Method" anchor="method">
321   The Method  token indicates the method to be performed on the
322   resource identified by the Request-URI. The method is case-sensitive.
324<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
325    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
326                   | "GET"                    ; <xref target="GET"/>
327                   | "HEAD"                   ; <xref target="HEAD"/>
328                   | "POST"                   ; <xref target="POST"/>
329                   | "PUT"                    ; <xref target="PUT"/>
330                   | "DELETE"                 ; <xref target="DELETE"/>
331                   | "TRACE"                  ; <xref target="TRACE"/>
332                   | "CONNECT"                ; <xref target="CONNECT"/>
333                   | extension-method
334    extension-method = token
337   The list of methods allowed by a resource can be specified in an
338   Allow header field (<xref target="header.allow"/>). The return code of the response
339   always notifies the client whether a method is currently allowed on a
340   resource, since the set of allowed methods can change dynamically. An
341   origin server &SHOULD; return the status code 405 (Method Not Allowed)
342   if the method is known by the origin server but not allowed for the
343   requested resource, and 501 (Not Implemented) if the method is
344   unrecognized or not implemented by the origin server. The methods GET
345   and HEAD &MUST; be supported by all general-purpose servers. All other
346   methods are &OPTIONAL;; however, if the above methods are implemented,
347   they &MUST; be implemented with the same semantics as those specified
348   in <xref target="method.definitions"/>.
352<section title="Request Header Fields" anchor="request.header.fields">
354   The request-header fields allow the client to pass additional
355   information about the request, and about the client itself, to the
356   server. These fields act as request modifiers, with semantics
357   equivalent to the parameters on a programming language method
358   invocation.
360<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
361    request-header = Accept                   ; &header-accept;
362                   | Accept-Charset           ; &header-accept-charset;
363                   | Accept-Encoding          ; &header-accept-encoding;
364                   | Accept-Language          ; &header-accept-language;
365                   | Authorization            ; &header-authorization;
366                   | Expect                   ; <xref target="header.expect"/>
367                   | From                     ; <xref target="header.from"/>
368                   | Host                     ; &header-host;
369                   | If-Match                 ; &header-if-match;
370                   | If-Modified-Since        ; &header-if-modified-since;
371                   | If-None-Match            ; &header-if-none-match;
372                   | If-Range                 ; &header-if-range;
373                   | If-Unmodified-Since      ; &header-if-unmodified-since;
374                   | Max-Forwards             ; <xref target="header.max-forwards"/>
375                   | Proxy-Authorization      ; &header-proxy-authorization;
376                   | Range                    ; &header-range;
377                   | Referer                  ; <xref target="header.referer"/>
378                   | TE                       ; &header-te;
379                   | User-Agent               ; <xref target="header.user-agent"/>
382   Request-header field names can be extended reliably only in
383   combination with a change in the protocol version. However, new or
384   experimental header fields &MAY; be given the semantics of request-header
385   fields if all parties in the communication recognize them to
386   be request-header fields. Unrecognized header fields are treated as
387   entity-header fields.
391<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
393   The Status-Code element is a 3-digit integer result code of the
394   attempt to understand and satisfy the request. These codes are fully
395   defined in <xref target=""/>. The Reason-Phrase is intended to give a short
396   textual description of the Status-Code. The Status-Code is intended
397   for use by automata and the Reason-Phrase is intended for the human
398   user. The client is not required to examine or display the Reason-Phrase.
401   The individual values of the numeric status codes defined for
402   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
403   presented below. The reason phrases listed here are only
404   recommendations -- they &MAY; be replaced by local equivalents without
405   affecting the protocol.
407<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"/>
408   Status-Code    =
409         "100"  ; <xref target="status.100"/>: Continue
410       | "101"  ; <xref target="status.101"/>: Switching Protocols
411       | "200"  ; <xref target="status.200"/>: OK
412       | "201"  ; <xref target="status.201"/>: Created
413       | "202"  ; <xref target="status.202"/>: Accepted
414       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
415       | "204"  ; <xref target="status.204"/>: No Content
416       | "205"  ; <xref target="status.205"/>: Reset Content
417       | "206"  ; <xref target="status.206"/>: Partial Content
418       | "300"  ; <xref target="status.300"/>: Multiple Choices
419       | "301"  ; <xref target="status.301"/>: Moved Permanently
420       | "302"  ; <xref target="status.302"/>: Found
421       | "303"  ; <xref target="status.303"/>: See Other
422       | "304"  ; <xref target="status.304"/>: Not Modified
423       | "305"  ; <xref target="status.305"/>: Use Proxy
424       | "307"  ; <xref target="status.307"/>: Temporary Redirect
425       | "400"  ; <xref target="status.400"/>: Bad Request
426       | "401"  ; <xref target="status.401"/>: Unauthorized
427       | "402"  ; <xref target="status.402"/>: Payment Required
428       | "403"  ; <xref target="status.403"/>: Forbidden
429       | "404"  ; <xref target="status.404"/>: Not Found
430       | "405"  ; <xref target="status.405"/>: Method Not Allowed
431       | "406"  ; <xref target="status.406"/>: Not Acceptable
432       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
433       | "408"  ; <xref target="status.408"/>: Request Time-out
434       | "409"  ; <xref target="status.409"/>: Conflict
435       | "410"  ; <xref target="status.410"/>: Gone
436       | "411"  ; <xref target="status.411"/>: Length Required
437       | "412"  ; <xref target="status.412"/>: Precondition Failed
438       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
439       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
440       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
441       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
442       | "417"  ; <xref target="status.417"/>: Expectation Failed
443       | "500"  ; <xref target="status.500"/>: Internal Server Error
444       | "501"  ; <xref target="status.501"/>: Not Implemented
445       | "502"  ; <xref target="status.502"/>: Bad Gateway
446       | "503"  ; <xref target="status.503"/>: Service Unavailable
447       | "504"  ; <xref target="status.504"/>: Gateway Time-out
448       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
449       | extension-code
451   extension-code = 3DIGIT
452   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
455   HTTP status codes are extensible. HTTP applications are not required
456   to understand the meaning of all registered status codes, though such
457   understanding is obviously desirable. However, applications &MUST;
458   understand the class of any status code, as indicated by the first
459   digit, and treat any unrecognized response as being equivalent to the
460   x00 status code of that class, with the exception that an
461   unrecognized response &MUST-NOT; be cached. For example, if an
462   unrecognized status code of 431 is received by the client, it can
463   safely assume that there was something wrong with its request and
464   treat the response as if it had received a 400 status code. In such
465   cases, user agents &SHOULD; present to the user the entity returned
466   with the response, since that entity is likely to include human-readable
467   information which will explain the unusual status.
471<section title="Response Header Fields" anchor="response.header.fields">
473   The response-header fields allow the server to pass additional
474   information about the response which cannot be placed in the Status-Line.
475   These header fields give information about the server and about
476   further access to the resource identified by the Request-URI.
478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
479    response-header = Accept-Ranges           ; &header-accept-ranges;
480                    | Age                     ; &header-age;
481                    | ETag                    ; &header-etag;
482                    | Location                ; <xref target="header.location"/>
483                    | Proxy-Authenticate      ; &header-proxy-authenticate;
484                    | Retry-After             ; <xref target="header.retry-after"/>
485                    | Server                  ; <xref target="header.server"/>
486                    | Vary                    ; &header-vary;
487                    | WWW-Authenticate        ; &header-www-authenticate;
490   Response-header field names can be extended reliably only in
491   combination with a change in the protocol version. However, new or
492   experimental header fields &MAY; be given the semantics of response-header
493   fields if all parties in the communication recognize them to
494   be response-header fields. Unrecognized header fields are treated as
495   entity-header fields.
499<section title="Entity" anchor="entity">
501   Request and Response messages &MAY; transfer an entity if not otherwise
502   restricted by the request method or response status code. An entity
503   consists of entity-header fields and an entity-body, although some
504   responses will only include the entity-headers. HTTP entity-body and
505   entity-header fields are defined in &payload;.
508   An entity-body is only present in a message when a message-body is
509   present, as described in &message-body;. The entity-body is obtained
510   from the message-body by decoding any Transfer-Encoding that might
511   have been applied to ensure safe and proper transfer of the message.
516<section title="Method Definitions" anchor="method.definitions">
518   The set of common methods for HTTP/1.1 is defined below. Although
519   this set can be expanded, additional methods cannot be assumed to
520   share the same semantics for separately extended clients and servers.
522   The Host request-header field (&header-host;) &MUST; accompany all
523   HTTP/1.1 requests.
526<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
528<section title="Safe Methods" anchor="safe.methods">
530   Implementors should be aware that the software represents the user in
531   their interactions over the Internet, and should be careful to allow
532   the user to be aware of any actions they might take which may have an
533   unexpected significance to themselves or others.
536   In particular, the convention has been established that the GET and
537   HEAD methods &SHOULD-NOT;  have the significance of taking an action
538   other than retrieval. These methods ought to be considered "safe".
539   This allows user agents to represent other methods, such as POST, PUT
540   and DELETE, in a special way, so that the user is made aware of the
541   fact that a possibly unsafe action is being requested.
544   Naturally, it is not possible to ensure that the server does not
545   generate side-effects as a result of performing a GET request; in
546   fact, some dynamic resources consider that a feature. The important
547   distinction here is that the user did not request the side-effects,
548   so therefore cannot be held accountable for them.
552<section title="Idempotent Methods" anchor="idempotent.methods">
554   Methods can also have the property of "idempotence" in that (aside
555   from error or expiration issues) the side-effects of N &gt; 0 identical
556   requests is the same as for a single request. The methods GET, HEAD,
557   PUT and DELETE share this property. Also, the methods OPTIONS and
558   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
561   However, it is possible that a sequence of several requests is non-idempotent,
562   even if all of the methods executed in that sequence are
563   idempotent. (A sequence is idempotent if a single execution of the
564   entire sequence always yields a result that is not changed by a
565   reexecution of all, or part, of that sequence.) For example, a
566   sequence is non-idempotent if its result depends on a value that is
567   later modified in the same sequence.
570   A sequence that never has side effects is idempotent, by definition
571   (provided that no concurrent operations are being executed on the
572   same set of resources).
577<section title="OPTIONS" anchor="OPTIONS">
578  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
579  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
581   The OPTIONS method represents a request for information about the
582   communication options available on the request/response chain
583   identified by the Request-URI. This method allows the client to
584   determine the options and/or requirements associated with a resource,
585   or the capabilities of a server, without implying a resource action
586   or initiating a resource retrieval.
589   Responses to this method are not cacheable.
592   If the OPTIONS request includes an entity-body (as indicated by the
593   presence of Content-Length or Transfer-Encoding), then the media type
594   &MUST; be indicated by a Content-Type field. Although this
595   specification does not define any use for such a body, future
596   extensions to HTTP might use the OPTIONS body to make more detailed
597   queries on the server. A server that does not support such an
598   extension &MAY; discard the request body.
601   If the Request-URI is an asterisk ("*"), the OPTIONS request is
602   intended to apply to the server in general rather than to a specific
603   resource. Since a server's communication options typically depend on
604   the resource, the "*" request is only useful as a "ping" or "no-op"
605   type of method; it does nothing beyond allowing the client to test
606   the capabilities of the server. For example, this can be used to test
607   a proxy for HTTP/1.1 compliance (or lack thereof).
610   If the Request-URI is not an asterisk, the OPTIONS request applies
611   only to the options that are available when communicating with that
612   resource.
615   A 200 response &SHOULD; include any header fields that indicate
616   optional features implemented by the server and applicable to that
617   resource (e.g., Allow), possibly including extensions not defined by
618   this specification. The response body, if any, &SHOULD; also include
619   information about the communication options. The format for such a
620   body is not defined by this specification, but might be defined by
621   future extensions to HTTP. Content negotiation &MAY; be used to select
622   the appropriate response format. If no response body is included, the
623   response &MUST; include a Content-Length field with a field-value of
624   "0".
627   The Max-Forwards request-header field &MAY; be used to target a
628   specific proxy in the request chain. When a proxy receives an OPTIONS
629   request on an absoluteURI for which request forwarding is permitted,
630   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
631   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
632   instead, the proxy &SHOULD; respond with its own communication options.
633   If the Max-Forwards field-value is an integer greater than zero, the
634   proxy &MUST; decrement the field-value when it forwards the request. If
635   no Max-Forwards field is present in the request, then the forwarded
636   request &MUST-NOT; include a Max-Forwards field.
640<section title="GET" anchor="GET">
641  <iref primary="true" item="GET method" x:for-anchor=""/>
642  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
644   The GET method means retrieve whatever information (in the form of an
645   entity) is identified by the Request-URI. If the Request-URI refers
646   to a data-producing process, it is the produced data which shall be
647   returned as the entity in the response and not the source text of the
648   process, unless that text happens to be the output of the process.
651   The semantics of the GET method change to a "conditional GET" if the
652   request message includes an If-Modified-Since, If-Unmodified-Since,
653   If-Match, If-None-Match, or If-Range header field. A conditional GET
654   method requests that the entity be transferred only under the
655   circumstances described by the conditional header field(s). The
656   conditional GET method is intended to reduce unnecessary network
657   usage by allowing cached entities to be refreshed without requiring
658   multiple requests or transferring data already held by the client.
661   The semantics of the GET method change to a "partial GET" if the
662   request message includes a Range header field. A partial GET requests
663   that only part of the entity be transferred, as described in &header-range;.
664   The partial GET method is intended to reduce unnecessary
665   network usage by allowing partially-retrieved entities to be
666   completed without transferring data already held by the client.
669   The response to a GET request is cacheable if and only if it meets
670   the requirements for HTTP caching described in &caching;.
673   See <xref target=""/> for security considerations when used for forms.
677<section title="HEAD" anchor="HEAD">
678  <iref primary="true" item="HEAD method" x:for-anchor=""/>
679  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
681   The HEAD method is identical to GET except that the server &MUST-NOT;
682   return a message-body in the response. The metainformation contained
683   in the HTTP headers in response to a HEAD request &SHOULD; be identical
684   to the information sent in response to a GET request. This method can
685   be used for obtaining metainformation about the entity implied by the
686   request without transferring the entity-body itself. This method is
687   often used for testing hypertext links for validity, accessibility,
688   and recent modification.
691   The response to a HEAD request &MAY; be cacheable in the sense that the
692   information contained in the response &MAY; be used to update a
693   previously cached entity from that resource. If the new field values
694   indicate that the cached entity differs from the current entity (as
695   would be indicated by a change in Content-Length, Content-MD5, ETag
696   or Last-Modified), then the cache &MUST; treat the cache entry as
697   stale.
701<section title="POST" anchor="POST">
702  <iref primary="true" item="POST method" x:for-anchor=""/>
703  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
705   The POST method is used to request that the origin server accept the
706   entity enclosed in the request as data to be processed by the resource
707   identified by the Request-URI in the Request-Line. POST is designed
708   to allow a uniform method to cover the following functions:
709  <list style="symbols">
710    <t>
711      Annotation of existing resources;
712    </t>
713    <t>
714        Posting a message to a bulletin board, newsgroup, mailing list,
715        or similar group of articles;
716    </t>
717    <t>
718        Providing a block of data, such as the result of submitting a
719        form, to a data-handling process;
720    </t>
721    <t>
722        Extending a database through an append operation.
723    </t>
724  </list>
727   The actual function performed by the POST method is determined by the
728   server and is usually dependent on the Request-URI.
731   The action performed by the POST method might not result in a
732   resource that can be identified by a URI. In this case, either 200
733   (OK) or 204 (No Content) is the appropriate response status,
734   depending on whether or not the response includes an entity that
735   describes the result.
738   If a resource has been created on the origin server, the response
739   &SHOULD; be 201 (Created) and contain an entity which describes the
740   status of the request and refers to the new resource, and a Location
741   header (see <xref target="header.location"/>).
744   Responses to this method are not cacheable, unless the response
745   includes appropriate Cache-Control or Expires header fields. However,
746   the 303 (See Other) response can be used to direct the user agent to
747   retrieve a cacheable resource.
750   POST requests &MUST; obey the message transmission requirements set out
751   in &message-transmission-req;.
754   See <xref target=""/> for security considerations.
758<section title="PUT" anchor="PUT">
759  <iref primary="true" item="PUT method" x:for-anchor=""/>
760  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
762   The PUT method requests that the enclosed entity be stored under the
763   supplied Request-URI. If the Request-URI refers to an already
764   existing resource, the enclosed entity &SHOULD; be considered as a
765   modified version of the one residing on the origin server. If the
766   Request-URI does not point to an existing resource, and that URI is
767   capable of being defined as a new resource by the requesting user
768   agent, the origin server can create the resource with that URI. If a
769   new resource is created, the origin server &MUST; inform the user agent
770   via the 201 (Created) response. If an existing resource is modified,
771   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
772   to indicate successful completion of the request. If the resource
773   could not be created or modified with the Request-URI, an appropriate
774   error response &SHOULD; be given that reflects the nature of the
775   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
776   (e.g. Content-Range) headers that it does not understand or implement
777   and &MUST; return a 501 (Not Implemented) response in such cases.
780   If the request passes through a cache and the Request-URI identifies
781   one or more currently cached entities, those entries &SHOULD; be
782   treated as stale. Responses to this method are not cacheable.
785   The fundamental difference between the POST and PUT requests is
786   reflected in the different meaning of the Request-URI. The URI in a
787   POST request identifies the resource that will handle the enclosed
788   entity. That resource might be a data-accepting process, a gateway to
789   some other protocol, or a separate entity that accepts annotations.
790   In contrast, the URI in a PUT request identifies the entity enclosed
791   with the request -- the user agent knows what URI is intended and the
792   server &MUST-NOT; attempt to apply the request to some other resource.
793   If the server desires that the request be applied to a different URI,
794   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
795   then make its own decision regarding whether or not to redirect the
796   request.
799   A single resource &MAY; be identified by many different URIs. For
800   example, an article might have a URI for identifying "the current
801   version" which is separate from the URI identifying each particular
802   version. In this case, a PUT request on a general URI might result in
803   several other URIs being defined by the origin server.
806   HTTP/1.1 does not define how a PUT method affects the state of an
807   origin server.
810   PUT requests &MUST; obey the message transmission requirements set out
811   in &message-transmission-req;.
814   Unless otherwise specified for a particular entity-header, the
815   entity-headers in the PUT request &SHOULD; be applied to the resource
816   created or modified by the PUT.
820<section title="DELETE" anchor="DELETE">
821  <iref primary="true" item="DELETE method" x:for-anchor=""/>
822  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
824   The DELETE method requests that the origin server delete the resource
825   identified by the Request-URI. This method &MAY; be overridden by human
826   intervention (or other means) on the origin server. The client cannot
827   be guaranteed that the operation has been carried out, even if the
828   status code returned from the origin server indicates that the action
829   has been completed successfully. However, the server &SHOULD-NOT;
830   indicate success unless, at the time the response is given, it
831   intends to delete the resource or move it to an inaccessible
832   location.
835   A successful response &SHOULD; be 200 (OK) if the response includes an
836   entity describing the status, 202 (Accepted) if the action has not
837   yet been enacted, or 204 (No Content) if the action has been enacted
838   but the response does not include an entity.
841   If the request passes through a cache and the Request-URI identifies
842   one or more currently cached entities, those entries &SHOULD; be
843   treated as stale. Responses to this method are not cacheable.
847<section title="TRACE" anchor="TRACE">
848  <iref primary="true" item="TRACE method" x:for-anchor=""/>
849  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
851   The TRACE method is used to invoke a remote, application-layer loop-back
852   of the request message. The final recipient of the request
853   &SHOULD; reflect the message received back to the client as the
854   entity-body of a 200 (OK) response. The final recipient is either the
855   origin server or the first proxy or gateway to receive a Max-Forwards
856   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
857   &MUST-NOT; include an entity.
860   TRACE allows the client to see what is being received at the other
861   end of the request chain and use that data for testing or diagnostic
862   information. The value of the Via header field (&header-via;) is of
863   particular interest, since it acts as a trace of the request chain.
864   Use of the Max-Forwards header field allows the client to limit the
865   length of the request chain, which is useful for testing a chain of
866   proxies forwarding messages in an infinite loop.
869   If the request is valid, the response &SHOULD; contain the entire
870   request message in the entity-body, with a Content-Type of
871   "message/http". Responses to this method &MUST-NOT; be cached.
875<section title="CONNECT" anchor="CONNECT">
876  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
877  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
879   This specification reserves the method name CONNECT for use with a
880   proxy that can dynamically switch to being a tunnel (e.g. SSL
881   tunneling <xref target="Luo1998"/>).
887<section title="Status Code Definitions" anchor="">
889   Each Status-Code is described below, including a description of which
890   method(s) it can follow and any metainformation required in the
891   response.
894<section title="Informational 1xx" anchor="status.1xx">
896   This class of status code indicates a provisional response,
897   consisting only of the Status-Line and optional headers, and is
898   terminated by an empty line. There are no required headers for this
899   class of status code. Since HTTP/1.0 did not define any 1xx status
900   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
901   except under experimental conditions.
904   A client &MUST; be prepared to accept one or more 1xx status responses
905   prior to a regular response, even if the client does not expect a 100
906   (Continue) status message. Unexpected 1xx status responses &MAY; be
907   ignored by a user agent.
910   Proxies &MUST; forward 1xx responses, unless the connection between the
911   proxy and its client has been closed, or unless the proxy itself
912   requested the generation of the 1xx response. (For example, if a
913   proxy adds a "Expect: 100-continue" field when it forwards a request,
914   then it need not forward the corresponding 100 (Continue)
915   response(s).)
918<section title="100 Continue" anchor="status.100">
919  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
920  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
922   The client &SHOULD; continue with its request. This interim response is
923   used to inform the client that the initial part of the request has
924   been received and has not yet been rejected by the server. The client
925   &SHOULD; continue by sending the remainder of the request or, if the
926   request has already been completed, ignore this response. The server
927   &MUST; send a final response after the request has been completed. See
928   &use100; for detailed discussion of the use and handling of this
929   status code.
933<section title="101 Switching Protocols" anchor="status.101">
934  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
935  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
937   The server understands and is willing to comply with the client's
938   request, via the Upgrade message header field (&header-upgrade;), for a
939   change in the application protocol being used on this connection. The
940   server will switch protocols to those defined by the response's
941   Upgrade header field immediately after the empty line which
942   terminates the 101 response.
945   The protocol &SHOULD; be switched only when it is advantageous to do
946   so. For example, switching to a newer version of HTTP is advantageous
947   over older versions, and switching to a real-time, synchronous
948   protocol might be advantageous when delivering resources that use
949   such features.
954<section title="Successful 2xx" anchor="status.2xx">
956   This class of status code indicates that the client's request was
957   successfully received, understood, and accepted.
960<section title="200 OK" anchor="status.200">
961  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
962  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
964   The request has succeeded. The information returned with the response
965   is dependent on the method used in the request, for example:
966  <list style="hanging">
967    <t hangText="GET">
968          an entity corresponding to the requested resource is sent in
969          the response;
970    </t>
971    <t hangText="HEAD">
972          the entity-header fields corresponding to the requested
973          resource are sent in the response without any message-body;
974    </t>
975    <t hangText="POST">
976      an entity describing or containing the result of the action;
977    </t>
978    <t hangText="TRACE">
979      an entity containing the request message as received by the
980      end server.
981    </t>
982  </list>
986<section title="201 Created" anchor="status.201">
987  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
988  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
990   The request has been fulfilled and resulted in a new resource being
991   created. The newly created resource can be referenced by the URI(s)
992   returned in the entity of the response, with the most specific URI
993   for the resource given by a Location header field. The response
994   &SHOULD; include an entity containing a list of resource
995   characteristics and location(s) from which the user or user agent can
996   choose the one most appropriate. The entity format is specified by
997   the media type given in the Content-Type header field. The origin
998   server &MUST; create the resource before returning the 201 status code.
999   If the action cannot be carried out immediately, the server &SHOULD;
1000   respond with 202 (Accepted) response instead.
1003   A 201 response &MAY; contain an ETag response header field indicating
1004   the current value of the entity tag for the requested variant just
1005   created, see &header-etag;.
1009<section title="202 Accepted" anchor="status.202">
1010  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1011  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1013   The request has been accepted for processing, but the processing has
1014   not been completed.  The request might or might not eventually be
1015   acted upon, as it might be disallowed when processing actually takes
1016   place. There is no facility for re-sending a status code from an
1017   asynchronous operation such as this.
1020   The 202 response is intentionally non-committal. Its purpose is to
1021   allow a server to accept a request for some other process (perhaps a
1022   batch-oriented process that is only run once per day) without
1023   requiring that the user agent's connection to the server persist
1024   until the process is completed. The entity returned with this
1025   response &SHOULD; include an indication of the request's current status
1026   and either a pointer to a status monitor or some estimate of when the
1027   user can expect the request to be fulfilled.
1031<section title="203 Non-Authoritative Information" anchor="status.203">
1032  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1033  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1035   The returned metainformation in the entity-header is not the
1036   definitive set as available from the origin server, but is gathered
1037   from a local or a third-party copy. The set presented &MAY; be a subset
1038   or superset of the original version. For example, including local
1039   annotation information about the resource might result in a superset
1040   of the metainformation known by the origin server. Use of this
1041   response code is not required and is only appropriate when the
1042   response would otherwise be 200 (OK).
1046<section title="204 No Content" anchor="status.204">
1047  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1048  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1050   The server has fulfilled the request but does not need to return an
1051   entity-body, and might want to return updated metainformation. The
1052   response &MAY; include new or updated metainformation in the form of
1053   entity-headers, which if present &SHOULD; be associated with the
1054   requested variant.
1057   If the client is a user agent, it &SHOULD-NOT;  change its document view
1058   from that which caused the request to be sent. This response is
1059   primarily intended to allow input for actions to take place without
1060   causing a change to the user agent's active document view, although
1061   any new or updated metainformation &SHOULD; be applied to the document
1062   currently in the user agent's active view.
1065   The 204 response &MUST-NOT; include a message-body, and thus is always
1066   terminated by the first empty line after the header fields.
1070<section title="205 Reset Content" anchor="status.205">
1071  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1072  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1074   The server has fulfilled the request and the user agent &SHOULD; reset
1075   the document view which caused the request to be sent. This response
1076   is primarily intended to allow input for actions to take place via
1077   user input, followed by a clearing of the form in which the input is
1078   given so that the user can easily initiate another input action. The
1079   response &MUST-NOT; include an entity.
1083<section title="206 Partial Content" anchor="status.206">
1084  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1085  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1087   The server has fulfilled the partial GET request for the resource
1088   and the enclosed entity is a partial representation as defined in &range;.
1093<section title="Redirection 3xx" anchor="status.3xx">
1095   This class of status code indicates that further action needs to be
1096   taken by the user agent in order to fulfill the request.  The action
1097   required &MAY; be carried out by the user agent without interaction
1098   with the user if and only if the method used in the second request is
1099   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1100   such loops generate network traffic for each redirection.
1101  <list><t>
1102      <x:h>Note:</x:h> previous versions of this specification recommended a
1103      maximum of five redirections. Content developers should be aware
1104      that there might be clients that implement such a fixed
1105      limitation.
1106  </t></list>
1109<section title="300 Multiple Choices" anchor="status.300">
1110  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1111  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1113   The requested resource corresponds to any one of a set of
1114   representations, each with its own specific location, and agent-driven
1115   negotiation information (&content-negotiation;) is being provided so that
1116   the user (or user agent) can select a preferred representation and
1117   redirect its request to that location.
1120   Unless it was a HEAD request, the response &SHOULD; include an entity
1121   containing a list of resource characteristics and location(s) from
1122   which the user or user agent can choose the one most appropriate. The
1123   entity format is specified by the media type given in the Content-Type
1124   header field. Depending upon the format and the capabilities of
1125   the user agent, selection of the most appropriate choice &MAY; be
1126   performed automatically. However, this specification does not define
1127   any standard for such automatic selection.
1130   If the server has a preferred choice of representation, it &SHOULD;
1131   include the specific URI for that representation in the Location
1132   field; user agents &MAY; use the Location field value for automatic
1133   redirection. This response is cacheable unless indicated otherwise.
1137<section title="301 Moved Permanently" anchor="status.301">
1138  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1139  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1141   The requested resource has been assigned a new permanent URI and any
1142   future references to this resource &SHOULD; use one of the returned
1143   URIs.  Clients with link editing capabilities ought to automatically
1144   re-link references to the Request-URI to one or more of the new
1145   references returned by the server, where possible. This response is
1146   cacheable unless indicated otherwise.
1149   The new permanent URI &SHOULD; be given by the Location field in the
1150   response. Unless the request method was HEAD, the entity of the
1151   response &SHOULD; contain a short hypertext note with a hyperlink to
1152   the new URI(s).
1155   If the 301 status code is received in response to a request method
1156   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1157   then the request &MAY; be automatically redirected by the user agent without
1158   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1159   request unless it can be confirmed by the user, since this might
1160   change the conditions under which the request was issued.
1161  <list><t>
1162      <x:h>Note:</x:h> When automatically redirecting a POST request after
1163      receiving a 301 status code, some existing HTTP/1.0 user agents
1164      will erroneously change it into a GET request.
1165  </t></list>
1169<section title="302 Found" anchor="status.302">
1170  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1171  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1173   The requested resource resides temporarily under a different URI.
1174   Since the redirection might be altered on occasion, the client &SHOULD;
1175   continue to use the Request-URI for future requests.  This response
1176   is only cacheable if indicated by a Cache-Control or Expires header
1177   field.
1180   The temporary URI &SHOULD; be given by the Location field in the
1181   response. Unless the request method was HEAD, the entity of the
1182   response &SHOULD; contain a short hypertext note with a hyperlink to
1183   the new URI(s).
1186   If the 302 status code is received in response to a request method
1187   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1188   then the request &MAY; be automatically redirected by the user agent without
1189   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1190   request unless it can be confirmed by the user, since this might
1191   change the conditions under which the request was issued.
1192  <list><t>
1193      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1194      to change the method on the redirected request.  However, most
1195      existing user agent implementations treat 302 as if it were a 303
1196      response, performing a GET on the Location field-value regardless
1197      of the original request method. The status codes 303 and 307 have
1198      been added for servers that wish to make unambiguously clear which
1199      kind of reaction is expected of the client.
1200  </t></list>
1204<section title="303 See Other" anchor="status.303">
1205  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1206  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1208   The response to the request can be found under a different URI and
1209   &SHOULD; be retrieved using a GET method on that resource. This method
1210   exists primarily to allow the output of a POST-activated script to
1211   redirect the user agent to a selected resource. The new URI is not a
1212   substitute reference for the originally requested resource. The 303
1213   response &MUST-NOT; be cached, but the response to the second
1214   (redirected) request might be cacheable.
1217   The different URI &SHOULD; be given by the Location field in the
1218   response. Unless the request method was HEAD, the entity of the
1219   response &SHOULD; contain a short hypertext note with a hyperlink to
1220   the new URI(s).
1221  <list><t>
1222      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1223      status. When interoperability with such clients is a concern, the
1224      302 status code may be used instead, since most user agents react
1225      to a 302 response as described here for 303.
1226  </t></list>
1230<section title="304 Not Modified" anchor="status.304">
1231  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1234   The response to the request has not been modified since the conditions
1235   indicated by the client's conditional GET request, as defined in &conditional;.
1239<section title="305 Use Proxy" anchor="status.305">
1240  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1241  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1243   The requested resource &MUST; be accessed through the proxy given by
1244   the Location field. The Location field gives the URI of the proxy.
1245   The recipient is expected to repeat this single request via the
1246   proxy. 305 responses &MUST; only be generated by origin servers.
1247  <list><t>
1248      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1249      single request, and to be generated by origin servers only.  Not
1250      observing these limitations has significant security consequences.
1251  </t></list>
1255<section title="306 (Unused)" anchor="status.306">
1256  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1257  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1259   The 306 status code was used in a previous version of the
1260   specification, is no longer used, and the code is reserved.
1264<section title="307 Temporary Redirect" anchor="status.307">
1265  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1266  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1268   The requested resource resides temporarily under a different URI.
1269   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1270   continue to use the Request-URI for future requests.  This response
1271   is only cacheable if indicated by a Cache-Control or Expires header
1272   field.
1275   The temporary URI &SHOULD; be given by the Location field in the
1276   response. Unless the request method was HEAD, the entity of the
1277   response &SHOULD; contain a short hypertext note with a hyperlink to
1278   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1279   understand the 307 status. Therefore, the note &SHOULD; contain the
1280   information necessary for a user to repeat the original request on
1281   the new URI.
1284   If the 307 status code is received in response to a request method
1285   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1286   then the request &MAY; be automatically redirected by the user agent without
1287   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1288   request unless it can be confirmed by the user, since this might
1289   change the conditions under which the request was issued.
1294<section title="Client Error 4xx" anchor="status.4xx">
1296   The 4xx class of status code is intended for cases in which the
1297   client seems to have erred. Except when responding to a HEAD request,
1298   the server &SHOULD; include an entity containing an explanation of the
1299   error situation, and whether it is a temporary or permanent
1300   condition. These status codes are applicable to any request method.
1301   User agents &SHOULD; display any included entity to the user.
1304   If the client is sending data, a server implementation using TCP
1305   &SHOULD; be careful to ensure that the client acknowledges receipt of
1306   the packet(s) containing the response, before the server closes the
1307   input connection. If the client continues sending data to the server
1308   after the close, the server's TCP stack will send a reset packet to
1309   the client, which may erase the client's unacknowledged input buffers
1310   before they can be read and interpreted by the HTTP application.
1313<section title="400 Bad Request" anchor="status.400">
1314  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1315  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1317   The request could not be understood by the server due to malformed
1318   syntax. The client &SHOULD-NOT;  repeat the request without
1319   modifications.
1323<section title="401 Unauthorized" anchor="status.401">
1324  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1325  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1327   The request requires user authentication (see &auth;).
1331<section title="402 Payment Required" anchor="status.402">
1332  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1333  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1335   This code is reserved for future use.
1339<section title="403 Forbidden" anchor="status.403">
1340  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1341  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1343   The server understood the request, but is refusing to fulfill it.
1344   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1345   If the request method was not HEAD and the server wishes to make
1346   public why the request has not been fulfilled, it &SHOULD; describe the
1347   reason for the refusal in the entity.  If the server does not wish to
1348   make this information available to the client, the status code 404
1349   (Not Found) can be used instead.
1353<section title="404 Not Found" anchor="status.404">
1354  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1355  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1357   The server has not found anything matching the Request-URI. No
1358   indication is given of whether the condition is temporary or
1359   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1360   knows, through some internally configurable mechanism, that an old
1361   resource is permanently unavailable and has no forwarding address.
1362   This status code is commonly used when the server does not wish to
1363   reveal exactly why the request has been refused, or when no other
1364   response is applicable.
1368<section title="405 Method Not Allowed" anchor="status.405">
1369  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1370  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1372   The method specified in the Request-Line is not allowed for the
1373   resource identified by the Request-URI. The response &MUST; include an
1374   Allow header containing a list of valid methods for the requested
1375   resource.
1379<section title="406 Not Acceptable" anchor="status.406">
1380  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1381  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1383   The resource identified by the request is only capable of generating
1384   response entities which have content characteristics not acceptable
1385   according to the accept headers sent in the request.
1388   Unless it was a HEAD request, the response &SHOULD; include an entity
1389   containing a list of available entity characteristics and location(s)
1390   from which the user or user agent can choose the one most
1391   appropriate. The entity format is specified by the media type given
1392   in the Content-Type header field. Depending upon the format and the
1393   capabilities of the user agent, selection of the most appropriate
1394   choice &MAY; be performed automatically. However, this specification
1395   does not define any standard for such automatic selection.
1396  <list><t>
1397      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1398      not acceptable according to the accept headers sent in the
1399      request. In some cases, this may even be preferable to sending a
1400      406 response. User agents are encouraged to inspect the headers of
1401      an incoming response to determine if it is acceptable.
1402  </t></list>
1405   If the response could be unacceptable, a user agent &SHOULD;
1406   temporarily stop receipt of more data and query the user for a
1407   decision on further actions.
1411<section title="407 Proxy Authentication Required" anchor="status.407">
1412  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1413  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1415   This code is similar to 401 (Unauthorized), but indicates that the
1416   client must first authenticate itself with the proxy (see &auth;).
1420<section title="408 Request Timeout" anchor="status.408">
1421  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1422  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1424   The client did not produce a request within the time that the server
1425   was prepared to wait. The client &MAY; repeat the request without
1426   modifications at any later time.
1430<section title="409 Conflict" anchor="status.409">
1431  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1432  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1434   The request could not be completed due to a conflict with the current
1435   state of the resource. This code is only allowed in situations where
1436   it is expected that the user might be able to resolve the conflict
1437   and resubmit the request. The response body &SHOULD; include enough
1438   information for the user to recognize the source of the conflict.
1439   Ideally, the response entity would include enough information for the
1440   user or user agent to fix the problem; however, that might not be
1441   possible and is not required.
1444   Conflicts are most likely to occur in response to a PUT request. For
1445   example, if versioning were being used and the entity being PUT
1446   included changes to a resource which conflict with those made by an
1447   earlier (third-party) request, the server might use the 409 response
1448   to indicate that it can't complete the request. In this case, the
1449   response entity would likely contain a list of the differences
1450   between the two versions in a format defined by the response
1451   Content-Type.
1455<section title="410 Gone" anchor="status.410">
1456  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1457  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1459   The requested resource is no longer available at the server and no
1460   forwarding address is known. This condition is expected to be
1461   considered permanent. Clients with link editing capabilities &SHOULD;
1462   delete references to the Request-URI after user approval. If the
1463   server does not know, or has no facility to determine, whether or not
1464   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1465   used instead. This response is cacheable unless indicated otherwise.
1468   The 410 response is primarily intended to assist the task of web
1469   maintenance by notifying the recipient that the resource is
1470   intentionally unavailable and that the server owners desire that
1471   remote links to that resource be removed. Such an event is common for
1472   limited-time, promotional services and for resources belonging to
1473   individuals no longer working at the server's site. It is not
1474   necessary to mark all permanently unavailable resources as "gone" or
1475   to keep the mark for any length of time -- that is left to the
1476   discretion of the server owner.
1480<section title="411 Length Required" anchor="status.411">
1481  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1482  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1484   The server refuses to accept the request without a defined Content-Length.
1485   The client &MAY; repeat the request if it adds a valid
1486   Content-Length header field containing the length of the message-body
1487   in the request message.
1491<section title="412 Precondition Failed" anchor="status.412">
1492  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1493  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1495   The precondition given in one or more of the request-header fields
1496   evaluated to false when it was tested on the server, as defined in
1497   &conditional;.
1501<section title="413 Request Entity Too Large" anchor="status.413">
1502  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1503  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1505   The server is refusing to process a request because the request
1506   entity is larger than the server is willing or able to process. The
1507   server &MAY; close the connection to prevent the client from continuing
1508   the request.
1511   If the condition is temporary, the server &SHOULD; include a Retry-After
1512   header field to indicate that it is temporary and after what
1513   time the client &MAY; try again.
1517<section title="414 Request-URI Too Long" anchor="status.414">
1518  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1521   The server is refusing to service the request because the Request-URI
1522   is longer than the server is willing to interpret. This rare
1523   condition is only likely to occur when a client has improperly
1524   converted a POST request to a GET request with long query
1525   information, when the client has descended into a URI "black hole" of
1526   redirection (e.g., a redirected URI prefix that points to a suffix of
1527   itself), or when the server is under attack by a client attempting to
1528   exploit security holes present in some servers using fixed-length
1529   buffers for reading or manipulating the Request-URI.
1533<section title="415 Unsupported Media Type" anchor="status.415">
1534  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1535  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1537   The server is refusing to service the request because the entity of
1538   the request is in a format not supported by the requested resource
1539   for the requested method.
1543<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1544  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1545  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1547   The request included a Range request-header field (&header-range;) and none of
1548   the range-specifier values in this field overlap the current extent
1549   of the selected resource.
1553<section title="417 Expectation Failed" anchor="status.417">
1554  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1555  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1557   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1558   could not be met by this server, or, if the server is a proxy,
1559   the server has unambiguous evidence that the request could not be met
1560   by the next-hop server.
1565<section title="Server Error 5xx" anchor="status.5xx">
1567   Response status codes beginning with the digit "5" indicate cases in
1568   which the server is aware that it has erred or is incapable of
1569   performing the request. Except when responding to a HEAD request, the
1570   server &SHOULD; include an entity containing an explanation of the
1571   error situation, and whether it is a temporary or permanent
1572   condition. User agents &SHOULD; display any included entity to the
1573   user. These response codes are applicable to any request method.
1576<section title="500 Internal Server Error" anchor="status.500">
1577  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1578  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1580   The server encountered an unexpected condition which prevented it
1581   from fulfilling the request.
1585<section title="501 Not Implemented" anchor="status.501">
1586  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1587  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1589   The server does not support the functionality required to fulfill the
1590   request. This is the appropriate response when the server does not
1591   recognize the request method and is not capable of supporting it for
1592   any resource.
1596<section title="502 Bad Gateway" anchor="status.502">
1597  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1598  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1600   The server, while acting as a gateway or proxy, received an invalid
1601   response from the upstream server it accessed in attempting to
1602   fulfill the request.
1606<section title="503 Service Unavailable" anchor="status.503">
1607  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1608  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1610   The server is currently unable to handle the request due to a
1611   temporary overloading or maintenance of the server. The implication
1612   is that this is a temporary condition which will be alleviated after
1613   some delay. If known, the length of the delay &MAY; be indicated in a
1614   Retry-After header. If no Retry-After is given, the client &SHOULD;
1615   handle the response as it would for a 500 response.
1616  <list><t>
1617      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1618      server must use it when becoming overloaded. Some servers may wish
1619      to simply refuse the connection.
1620  </t></list>
1624<section title="504 Gateway Timeout" anchor="status.504">
1625  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1626  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1628   The server, while acting as a gateway or proxy, did not receive a
1629   timely response from the upstream server specified by the URI (e.g.
1630   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1631   to access in attempting to complete the request.
1632  <list><t>
1633      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1634      return 400 or 500 when DNS lookups time out.
1635  </t></list>
1639<section title="505 HTTP Version Not Supported" anchor="status.505">
1640  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1641  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1643   The server does not support, or refuses to support, the HTTP protocol
1644   version that was used in the request message. The server is
1645   indicating that it is unable or unwilling to complete the request
1646   using the same major version as the client, as described in &http-version;,
1647   other than with this error message. The response &SHOULD; contain
1648   an entity describing why that version is not supported and what other
1649   protocols are supported by that server.
1657<section title="Header Field Definitions" anchor="header.fields">
1659   This section defines the syntax and semantics of all standard
1660   HTTP/1.1 header fields. For entity-header fields, both sender and
1661   recipient refer to either the client or the server, depending on who
1662   sends and who receives the entity.
1665<section title="Allow" anchor="header.allow">
1666  <iref primary="true" item="Allow header" x:for-anchor=""/>
1667  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1669      The Allow entity-header field lists the set of methods supported
1670      by the resource identified by the Request-URI. The purpose of this
1671      field is strictly to inform the recipient of valid methods
1672      associated with the resource. An Allow header field &MUST; be
1673      present in a 405 (Method Not Allowed) response.
1675<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1676       Allow   = "Allow" ":" #Method
1679      Example of use:
1681<figure><artwork type="example">
1682       Allow: GET, HEAD, PUT
1685      This field cannot prevent a client from trying other methods.
1686      However, the indications given by the Allow header field value
1687      &SHOULD; be followed. The actual set of allowed methods is defined
1688      by the origin server at the time of each request.
1691      The Allow header field &MAY; be provided with a PUT request to
1692      recommend the methods to be supported by the new or modified
1693      resource. The server is not required to support these methods and
1694      &SHOULD; include an Allow header in the response giving the actual
1695      supported methods.
1698      A proxy &MUST-NOT; modify the Allow header field even if it does not
1699      understand all the methods specified, since the user agent might
1700      have other means of communicating with the origin server.
1704<section title="Expect" anchor="header.expect">
1705  <iref primary="true" item="Expect header" x:for-anchor=""/>
1706  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1708   The Expect request-header field is used to indicate that particular
1709   server behaviors are required by the client.
1711<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"/>
1712   Expect       =  "Expect" ":" 1#expectation
1714   expectation  =  "100-continue" | expectation-extension
1715   expectation-extension =  token [ "=" ( token | quoted-string )
1716                            *expect-params ]
1717   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1720   A server that does not understand or is unable to comply with any of
1721   the expectation values in the Expect field of a request &MUST; respond
1722   with appropriate error status. The server &MUST; respond with a 417
1723   (Expectation Failed) status if any of the expectations cannot be met
1724   or, if there are other problems with the request, some other 4xx
1725   status.
1728   This header field is defined with extensible syntax to allow for
1729   future extensions. If a server receives a request containing an
1730   Expect field that includes an expectation-extension that it does not
1731   support, it &MUST; respond with a 417 (Expectation Failed) status.
1734   Comparison of expectation values is case-insensitive for unquoted
1735   tokens (including the 100-continue token), and is case-sensitive for
1736   quoted-string expectation-extensions.
1739   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1740   return a 417 (Expectation Failed) status if it receives a request
1741   with an expectation that it cannot meet. However, the Expect
1742   request-header itself is end-to-end; it &MUST; be forwarded if the
1743   request is forwarded.
1746   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1747   Expect header.
1750   See &use100; for the use of the 100 (continue) status.
1754<section title="From" anchor="header.from">
1755  <iref primary="true" item="From header" x:for-anchor=""/>
1756  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1758   The From request-header field, if given, &SHOULD; contain an Internet
1759   e-mail address for the human user who controls the requesting user
1760   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1761   in <xref target="RFC822"/> as updated by <xref target="RFC1123"/>:
1763<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1764    From   = "From" ":" mailbox
1767   An example is:
1769<figure><artwork type="example">
1770    From:
1773   This header field &MAY; be used for logging purposes and as a means for
1774   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1775   be used as an insecure form of access protection. The interpretation
1776   of this field is that the request is being performed on behalf of the
1777   person given, who accepts responsibility for the method performed. In
1778   particular, robot agents &SHOULD; include this header so that the
1779   person responsible for running the robot can be contacted if problems
1780   occur on the receiving end.
1783   The Internet e-mail address in this field &MAY; be separate from the
1784   Internet host which issued the request. For example, when a request
1785   is passed through a proxy the original issuer's address &SHOULD; be
1786   used.
1789   The client &SHOULD-NOT;  send the From header field without the user's
1790   approval, as it might conflict with the user's privacy interests or
1791   their site's security policy. It is strongly recommended that the
1792   user be able to disable, enable, and modify the value of this field
1793   at any time prior to a request.
1797<section title="Location" anchor="header.location">
1798  <iref primary="true" item="Location header" x:for-anchor=""/>
1799  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1801   The Location response-header field is used to redirect the recipient
1802   to a location other than the Request-URI for completion of the
1803   request or identification of a new resource. For 201 (Created)
1804   responses, the Location is that of the new resource which was created
1805   by the request. For 3xx responses, the location &SHOULD; indicate the
1806   server's preferred URI for automatic redirection to the resource. The
1807   field value consists of a single absolute URI.
1809<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1810    Location       = "Location" ":" absoluteURI [ "#" fragment ]
1813   An example is:
1815<figure><artwork type="example">
1816    Location:
1819  <list><t>
1820      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1821      from Location in that the Content-Location identifies the original
1822      location of the entity enclosed in the request. It is therefore
1823      possible for a response to contain header fields for both Location
1824      and Content-Location.
1825  </t></list>
1829<section title="Max-Forwards" anchor="header.max-forwards">
1830  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1831  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1833   The Max-Forwards request-header field provides a mechanism with the
1834   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1835   number of proxies or gateways that can forward the request to the
1836   next inbound server. This can be useful when the client is attempting
1837   to trace a request chain which appears to be failing or looping in
1838   mid-chain.
1840<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1841    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1844   The Max-Forwards value is a decimal integer indicating the remaining
1845   number of times this request message may be forwarded.
1848   Each proxy or gateway recipient of a TRACE or OPTIONS request
1849   containing a Max-Forwards header field &MUST; check and update its
1850   value prior to forwarding the request. If the received value is zero
1851   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1852   respond as the final recipient. If the received Max-Forwards value is
1853   greater than zero, then the forwarded message &MUST; contain an updated
1854   Max-Forwards field with a value decremented by one (1).
1857   The Max-Forwards header field &MAY; be ignored for all other methods
1858   defined by this specification and for any extension methods for which
1859   it is not explicitly referred to as part of that method definition.
1863<section title="Referer" anchor="header.referer">
1864  <iref primary="true" item="Referer header" x:for-anchor=""/>
1865  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1867   The Referer[sic] request-header field allows the client to specify,
1868   for the server's benefit, the address (URI) of the resource from
1869   which the Request-URI was obtained (the "referrer", although the
1870   header field is misspelled.) The Referer request-header allows a
1871   server to generate lists of back-links to resources for interest,
1872   logging, optimized caching, etc. It also allows obsolete or mistyped
1873   links to be traced for maintenance. The Referer field &MUST-NOT; be
1874   sent if the Request-URI was obtained from a source that does not have
1875   its own URI, such as input from the user keyboard.
1877<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1878    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1881   Example:
1883<figure><artwork type="example">
1884    Referer:
1887   If the field value is a relative URI, it &SHOULD; be interpreted
1888   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1889   <xref target=""/> for security considerations.
1893<section title="Retry-After" anchor="header.retry-after">
1894  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1895  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1897   The Retry-After response-header field can be used with a 503 (Service
1898   Unavailable) response to indicate how long the service is expected to
1899   be unavailable to the requesting client. This field &MAY; also be used
1900   with any 3xx (Redirection) response to indicate the minimum time the
1901   user-agent is asked wait before issuing the redirected request. The
1902   value of this field can be either an HTTP-date or an integer number
1903   of seconds (in decimal) after the time of the response.
1905<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1906    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1909   Two examples of its use are
1911<figure><artwork type="example">
1912    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1913    Retry-After: 120
1916   In the latter example, the delay is 2 minutes.
1920<section title="Server" anchor="header.server">
1921  <iref primary="true" item="Server header" x:for-anchor=""/>
1922  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1924   The Server response-header field contains information about the
1925   software used by the origin server to handle the request. The field
1926   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1927   identifying the server and any significant subproducts. The product
1928   tokens are listed in order of their significance for identifying the
1929   application.
1931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1932    Server         = "Server" ":" 1*( product | comment )
1935   Example:
1937<figure><artwork type="example">
1938    Server: CERN/3.0 libwww/2.17
1941   If the response is being forwarded through a proxy, the proxy
1942   application &MUST-NOT; modify the Server response-header. Instead, it
1943   &MUST; include a Via field (as described in &header-via;).
1944  <list><t>
1945      <x:h>Note:</x:h> Revealing the specific software version of the server might
1946      allow the server machine to become more vulnerable to attacks
1947      against software that is known to contain security holes. Server
1948      implementors are encouraged to make this field a configurable
1949      option.
1950  </t></list>
1954<section title="User-Agent" anchor="header.user-agent">
1955  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1956  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1958   The User-Agent request-header field contains information about the
1959   user agent originating the request. This is for statistical purposes,
1960   the tracing of protocol violations, and automated recognition of user
1961   agents for the sake of tailoring responses to avoid particular user
1962   agent limitations. User agents &SHOULD; include this field with
1963   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1964   and comments identifying the agent and any subproducts which form a
1965   significant part of the user agent. By convention, the product tokens
1966   are listed in order of their significance for identifying the
1967   application.
1969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1970    User-Agent     = "User-Agent" ":" 1*( product | comment )
1973   Example:
1975<figure><artwork type="example">
1976    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1982<section title="IANA Considerations" anchor="IANA.considerations">
1984   TBD.
1988<section title="Security Considerations" anchor="security.considerations">
1990   This section is meant to inform application developers, information
1991   providers, and users of the security limitations in HTTP/1.1 as
1992   described by this document. The discussion does not include
1993   definitive solutions to the problems revealed, though it does make
1994   some suggestions for reducing security risks.
1997<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1999   Like any generic data transfer protocol, HTTP cannot regulate the
2000   content of the data that is transferred, nor is there any a priori
2001   method of determining the sensitivity of any particular piece of
2002   information within the context of any given request. Therefore,
2003   applications &SHOULD; supply as much control over this information as
2004   possible to the provider of that information. Four header fields are
2005   worth special mention in this context: Server, Via, Referer and From.
2008   Revealing the specific software version of the server might allow the
2009   server machine to become more vulnerable to attacks against software
2010   that is known to contain security holes. Implementors &SHOULD; make the
2011   Server header field a configurable option.
2014   Proxies which serve as a portal through a network firewall &SHOULD;
2015   take special precautions regarding the transfer of header information
2016   that identifies the hosts behind the firewall. In particular, they
2017   &SHOULD; remove, or replace with sanitized versions, any Via fields
2018   generated behind the firewall.
2021   The Referer header allows reading patterns to be studied and reverse
2022   links drawn. Although it can be very useful, its power can be abused
2023   if user details are not separated from the information contained in
2024   the Referer. Even when the personal information has been removed, the
2025   Referer header might indicate a private document's URI whose
2026   publication would be inappropriate.
2029   The information sent in the From field might conflict with the user's
2030   privacy interests or their site's security policy, and hence it
2031   &SHOULD-NOT;  be transmitted without the user being able to disable,
2032   enable, and modify the contents of the field. The user &MUST; be able
2033   to set the contents of this field within a user preference or
2034   application defaults configuration.
2037   We suggest, though do not require, that a convenient toggle interface
2038   be provided for the user to enable or disable the sending of From and
2039   Referer information.
2042   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2043   fields can sometimes be used to determine that a specific client or
2044   server have a particular security hole which might be exploited.
2045   Unfortunately, this same information is often used for other valuable
2046   purposes for which HTTP currently has no better mechanism.
2050<section title="Encoding Sensitive Information in URI's" anchor="">
2052   Because the source of a link might be private information or might
2053   reveal an otherwise private information source, it is strongly
2054   recommended that the user be able to select whether or not the
2055   Referer field is sent. For example, a browser client could have a
2056   toggle switch for browsing openly/anonymously, which would
2057   respectively enable/disable the sending of Referer and From
2058   information.
2061   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2062   HTTP request if the referring page was transferred with a secure
2063   protocol.
2066   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2067   based forms for the submission of sensitive data, because this will
2068   cause this data to be encoded in the Request-URI. Many existing
2069   servers, proxies, and user agents will log the request URI in some
2070   place where it might be visible to third parties. Servers can use
2071   POST-based form submission instead
2075<section title="Location Headers and Spoofing" anchor="location.spoofing">
2077   If a single server supports multiple organizations that do not trust
2078   one another, then it &MUST; check the values of Location and Content-Location
2079   headers in responses that are generated under control of
2080   said organizations to make sure that they do not attempt to
2081   invalidate resources over which they have no authority.
2087<section title="Acknowledgments" anchor="ack">
2093<reference anchor="Part1">
2094   <front>
2095      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2096      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2097         <organization abbrev="Day Software">Day Software</organization>
2098         <address><email></email></address>
2099      </author>
2100      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2101         <organization>One Laptop per Child</organization>
2102         <address><email></email></address>
2103      </author>
2104      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2105         <organization abbrev="HP">Hewlett-Packard Company</organization>
2106         <address><email></email></address>
2107      </author>
2108      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2109         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2110         <address><email></email></address>
2111      </author>
2112      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2113         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2114         <address><email></email></address>
2115      </author>
2116      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2117         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2118         <address><email></email></address>
2119      </author>
2120      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2121         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2122         <address><email></email></address>
2123      </author>
2124      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2125         <organization abbrev="W3C">World Wide Web Consortium</organization>
2126         <address><email></email></address>
2127      </author>
2128      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2129         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2130         <address><email></email></address>
2131      </author>
2132      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2133   </front>
2134   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2135   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2138<reference anchor="Part3">
2139   <front>
2140      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2141      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2142         <organization abbrev="Day Software">Day Software</organization>
2143         <address><email></email></address>
2144      </author>
2145      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2146         <organization>One Laptop per Child</organization>
2147         <address><email></email></address>
2148      </author>
2149      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2150         <organization abbrev="HP">Hewlett-Packard Company</organization>
2151         <address><email></email></address>
2152      </author>
2153      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2154         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2155         <address><email></email></address>
2156      </author>
2157      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2158         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2159         <address><email></email></address>
2160      </author>
2161      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2162         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2163         <address><email></email></address>
2164      </author>
2165      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2166         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2167         <address><email></email></address>
2168      </author>
2169      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2170         <organization abbrev="W3C">World Wide Web Consortium</organization>
2171         <address><email></email></address>
2172      </author>
2173      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2174         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2175         <address><email></email></address>
2176      </author>
2177      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2178   </front>
2179   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2180   <x:source href="p3-payload.xml" basename="p3-payload"/>
2183<reference anchor="Part4">
2184   <front>
2185      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2186      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2187         <organization abbrev="Day Software">Day Software</organization>
2188         <address><email></email></address>
2189      </author>
2190      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2191         <organization>One Laptop per Child</organization>
2192         <address><email></email></address>
2193      </author>
2194      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2195         <organization abbrev="HP">Hewlett-Packard Company</organization>
2196         <address><email></email></address>
2197      </author>
2198      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2199         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2200         <address><email></email></address>
2201      </author>
2202      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2203         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2204         <address><email></email></address>
2205      </author>
2206      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2207         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2208         <address><email></email></address>
2209      </author>
2210      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2211         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2212         <address><email></email></address>
2213      </author>
2214      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2215         <organization abbrev="W3C">World Wide Web Consortium</organization>
2216         <address><email></email></address>
2217      </author>
2218      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2219         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2220         <address><email></email></address>
2221      </author>
2222      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2223   </front>
2224   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2225   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2228<reference anchor="Part5">
2229   <front>
2230      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2231      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2232         <organization abbrev="Day Software">Day Software</organization>
2233         <address><email></email></address>
2234      </author>
2235      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2236         <organization>One Laptop per Child</organization>
2237         <address><email></email></address>
2238      </author>
2239      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2240         <organization abbrev="HP">Hewlett-Packard Company</organization>
2241         <address><email></email></address>
2242      </author>
2243      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2244         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2245         <address><email></email></address>
2246      </author>
2247      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2248         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2249         <address><email></email></address>
2250      </author>
2251      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2252         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2253         <address><email></email></address>
2254      </author>
2255      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2256         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2257         <address><email></email></address>
2258      </author>
2259      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2260         <organization abbrev="W3C">World Wide Web Consortium</organization>
2261         <address><email></email></address>
2262      </author>
2263      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2264         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2265         <address><email></email></address>
2266      </author>
2267      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2268   </front>
2269   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2270   <x:source href="p5-range.xml" basename="p5-range"/>
2273<reference anchor="Part6">
2274   <front>
2275      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2276      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2277         <organization abbrev="Day Software">Day Software</organization>
2278         <address><email></email></address>
2279      </author>
2280      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2281         <organization>One Laptop per Child</organization>
2282         <address><email></email></address>
2283      </author>
2284      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2285         <organization abbrev="HP">Hewlett-Packard Company</organization>
2286         <address><email></email></address>
2287      </author>
2288      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2289         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2290         <address><email></email></address>
2291      </author>
2292      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2293         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2294         <address><email></email></address>
2295      </author>
2296      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2297         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2298         <address><email></email></address>
2299      </author>
2300      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2301         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2302         <address><email></email></address>
2303      </author>
2304      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2305         <organization abbrev="W3C">World Wide Web Consortium</organization>
2306         <address><email></email></address>
2307      </author>
2308      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2309         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2310         <address><email></email></address>
2311      </author>
2312      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2313   </front>
2314   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2315   <x:source href="p6-cache.xml" basename="p6-cache"/>
2318<reference anchor="Part7">
2319   <front>
2320      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2321      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2322         <organization abbrev="Day Software">Day Software</organization>
2323         <address><email></email></address>
2324      </author>
2325      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2326         <organization>One Laptop per Child</organization>
2327         <address><email></email></address>
2328      </author>
2329      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2330         <organization abbrev="HP">Hewlett-Packard Company</organization>
2331         <address><email></email></address>
2332      </author>
2333      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2334         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2335         <address><email></email></address>
2336      </author>
2337      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2338         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2339         <address><email></email></address>
2340      </author>
2341      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2342         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2343         <address><email></email></address>
2344      </author>
2345      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2346         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2347         <address><email></email></address>
2348      </author>
2349      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2350         <organization abbrev="W3C">World Wide Web Consortium</organization>
2351         <address><email></email></address>
2352      </author>
2353      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2354         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2355         <address><email></email></address>
2356      </author>
2357      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2358   </front>
2359   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2360   <x:source href="p7-auth.xml" basename="p7-auth"/>
2363<reference anchor="RFC2616">
2364   <front>
2365      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2366      <author initials="R." surname="Fielding" fullname="R. Fielding">
2367         <organization>University of California, Irvine</organization>
2368         <address><email></email></address>
2369      </author>
2370      <author initials="J." surname="Gettys" fullname="J. Gettys">
2371         <organization>W3C</organization>
2372         <address><email></email></address>
2373      </author>
2374      <author initials="J." surname="Mogul" fullname="J. Mogul">
2375         <organization>Compaq Computer Corporation</organization>
2376         <address><email></email></address>
2377      </author>
2378      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2379         <organization>MIT Laboratory for Computer Science</organization>
2380         <address><email></email></address>
2381      </author>
2382      <author initials="L." surname="Masinter" fullname="L. Masinter">
2383         <organization>Xerox Corporation</organization>
2384         <address><email></email></address>
2385      </author>
2386      <author initials="P." surname="Leach" fullname="P. Leach">
2387         <organization>Microsoft Corporation</organization>
2388         <address><email></email></address>
2389      </author>
2390      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2391         <organization>W3C</organization>
2392         <address><email></email></address>
2393      </author>
2394      <date month="June" year="1999"/>
2395   </front>
2396   <seriesInfo name="RFC" value="2616"/>
2399<reference anchor="RFC1123">
2400  <front>
2401    <title>Requirements for Internet Hosts - Application and Support</title>
2402    <author initials="R." surname="Braden" fullname="Robert Braden">
2403      <organization>University of Southern California (USC), Information Sciences Institute</organization>
2404      <address><email>Braden@ISI.EDU</email></address>
2405    </author>
2406    <date month="October" year="1989"/>
2407  </front>
2408  <seriesInfo name="STD" value="3"/>
2409  <seriesInfo name="RFC" value="1123"/>
2412<reference anchor="RFC822">
2413  <front>
2414    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2415    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2416      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
2417      <address><email>DCrocker@UDel-Relay</email></address>
2418    </author>
2419    <date month="August" day="13" year="1982"/>
2420  </front>
2421  <seriesInfo name="STD" value="11"/>
2422  <seriesInfo name="RFC" value="822"/>
2425<reference anchor="RFC1945">
2426  <front>
2427    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2428    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2429      <organization>MIT, Laboratory for Computer Science</organization>
2430      <address><email></email></address>
2431    </author>
2432    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2433      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2434      <address><email></email></address>
2435    </author>
2436    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2437      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2438      <address><email></email></address>
2439    </author>
2440    <date month="May" year="1996"/>
2441  </front>
2442  <seriesInfo name="RFC" value="1945"/>
2445<reference anchor="RFC2068">
2446  <front>
2447    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2448    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2449      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2450      <address><email></email></address>
2451    </author>
2452    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2453      <organization>MIT Laboratory for Computer Science</organization>
2454      <address><email></email></address>
2455    </author>
2456    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2457      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2458      <address><email></email></address>
2459    </author>
2460    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2461      <organization>MIT Laboratory for Computer Science</organization>
2462      <address><email></email></address>
2463    </author>
2464    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2465      <organization>MIT Laboratory for Computer Science</organization>
2466      <address><email></email></address>
2467    </author>
2468    <date month="January" year="1997"/>
2469  </front>
2470  <seriesInfo name="RFC" value="2068"/>
2473<reference anchor="RFC2119">
2474  <front>
2475    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2476    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2477      <organization>Harvard University</organization>
2478      <address><email></email></address>
2479    </author>
2480    <date month="March" year="1997"/>
2481  </front>
2482  <seriesInfo name="BCP" value="14"/>
2483  <seriesInfo name="RFC" value="2119"/>
2486<reference anchor="Luo1998">
2488<title>Tunneling TCP based protocols through Web proxy servers</title>
2489<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2490  <organization/>
2494<seriesInfo name="" value="Work in Progress"/>
2499<section title="Compatibility with Previous Versions" anchor="compatibility">
2500<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2502   Clarified which error code should be used for inbound server failures
2503   (e.g. DNS failures). (<xref target="status.504"/>).
2506   CREATE had a race that required an Etag be sent when a resource is
2507   first created. (<xref target="status.201"/>).
2510   Rewrite of message transmission requirements to make it much harder
2511   for implementors to get it wrong, as the consequences of errors here
2512   can have significant impact on the Internet, and to deal with the
2513   following problems:
2514  <list style="numbers">
2515      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2516         this was incorrectly placing a requirement on the behavior of
2517         an implementation of a future version of HTTP/1.x</t>
2519      <t>Made it clear that user-agents should retry requests, not
2520         "clients" in general.</t>
2522      <t>Converted requirements for clients to ignore unexpected 100
2523         (Continue) responses, and for proxies to forward 100 responses,
2524         into a general requirement for 1xx responses.</t>
2526      <t>Modified some TCP-specific language, to make it clearer that
2527         non-TCP transports are possible for HTTP.</t>
2529      <t>Require that the origin server &MUST-NOT; wait for the request
2530         body before it sends a required 100 (Continue) response.</t>
2532      <t>Allow, rather than require, a server to omit 100 (Continue) if
2533         it has already seen some of the request body.</t>
2535      <t>Allow servers to defend against denial-of-service attacks and
2536         broken clients.</t>
2537  </list>
2540   This change adds the Expect header and 417 status code.
2543   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2544   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2547   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
2548   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2552<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2554  Clarify definition of POST.
2555  (<xref target="POST"/>)
2558  Failed to consider that there are
2559  many other request methods that are safe to automatically redirect,
2560  and further that the user agent is able to make that determination
2561  based on the request method semantics.
2562  (Sections <xref format="counter" target="status.301"/>,
2563  <xref format="counter" target="status.302"/> and
2564  <xref format="counter" target="status.307"/> )
2567  In the description of the Server header, the Via field
2568  was described as a SHOULD. The requirement was and is stated
2569  correctly in the description of the Via header in &header-via;.
2570  (<xref target="header.server"/>)
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