source: draft-ietf-httpbis/latest/p2-semantics.xml @ 38

Last change on this file since 38 was 38, checked in by julian.reschke@…, 12 years ago

Restore links from Part2 into "Clockless Origin Server Operation" in Part1.

  • Property svn:eol-style set to native
File size: 119.8 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity             "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY message-transmission-req   "<xref target='Part1' x:rel='#message.transmission.requirements' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY clockless                  "<xref target='Part1' x:rel='#clockless.origin.server.operation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60]>
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, 2617" category="std"
71     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
72     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
73<front>
74
75  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
76
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>fielding@gbiv.com</email>
90      <uri>http://roy.gbiv.com/</uri>
91    </address>
92  </author>
93
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>jg@laptop.org</email>
105      <uri>http://www.laptop.org/</uri>
106    </address>
107  </author>
108 
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>JeffMogul@acm.org</email>
121    </address>
122  </author>
123
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>henrikn@microsoft.com</email>
135    </address>
136  </author>
137
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>LMM@acm.org</email>
149      <uri>http://larry.masinter.net/</uri>
150    </address>
151  </author>
152 
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>paulle@microsoft.com</email>
163    </address>
164  </author>
165   
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>timbl@w3.org</email>
179      <uri>http://www.w3.org/People/Berners-Lee/</uri>
180    </address>
181  </author>
182
183  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
184
185<abstract>
186<t>
187   The Hypertext Transfer Protocol (HTTP) is an application-level
188   protocol for distributed, collaborative, hypermedia information
189   systems. HTTP has been in use by the World Wide Web global information
190   initiative since 1990. This document is Part 2 of the seven-part specification
191   that defines the protocol referred to as "HTTP/1.1" and, taken together,
192   obsoletes RFC 2616 and RFC 2617.  Part 2 defines the semantics of HTTP messages
193   as expressed by request methods, request-header fields, response status codes,
194   and response-header fields.
195</t>
196</abstract>
197
198<note title="Editorial Note (To be removed by RFC Editor)">
199  <t>
200    This version of the HTTP specification contains only minimal editorial
201    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
202    and authors' addresses).  All other changes are due to partitioning the
203    original into seven mostly independent parts.  The intent is for readers
204    of future drafts to able to use draft 00 as the basis for comparison
205    when the WG makes later changes to the specification text.  This draft
206    will shortly be followed by draft 01 (containing the first round of changes
207    that have already been agreed to on the mailing list). There is no point in
208    reviewing this draft other than to verify that the partitioning has been
209    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
210    will be the editors after draft 00 is submitted.
211  </t>
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (ietf-http-wg@w3.org). The current issues list is
215    at <eref target="http://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/"/>
216    and related documents (including fancy diffs) can be found at
217    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
218  </t>
219</note>
220</front>
221<middle>
222<section title="Introduction" anchor="introduction">
223<t>
224   This document will define aspects of HTTP related to request and response
225   semantics. Right now it only includes the extracted relevant sections of
226   RFC 2616 with only minor edits.
227</t>
228<t>
229   The HTTP protocol is a request/response protocol. A client sends a
230   request to the server in the form of a request method, URI, and
231   protocol version, followed by a MIME-like message containing request
232   modifiers, client information, and possible body content over a
233   connection with a server. The server responds with a status line,
234   including the message's protocol version and a success or error code,
235   followed by a MIME-like message containing server information, entity
236   metainformation, and possible entity-body content. The relationship
237   between HTTP and MIME is described in &diff2045entity;.
238</t>
239</section>
240
241<section title="Product Tokens" anchor="product.tokens">
242<t>
243   Product tokens are used to allow communicating applications to
244   identify themselves by software name and version. Most fields using
245   product tokens also allow sub-products which form a significant part
246   of the application to be listed, separated by white space. By
247   convention, the products are listed in order of their significance
248   for identifying the application.
249</t>
250<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
251    product         = token ["/" product-version]
252    product-version = token
253</artwork></figure>
254<t>
255   Examples:
256</t>
257<figure><artwork type="example">
258    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
259    Server: Apache/0.8.4
260</artwork></figure>
261<t>
262   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
263   used for advertising or other non-essential information. Although any
264   token character &MAY; appear in a product-version, this token &SHOULD;
265   only be used for a version identifier (i.e., successive versions of
266   the same product &SHOULD; only differ in the product-version portion of
267   the product value).
268</t>
269</section>
270
271<section title="Method" anchor="method">
272<t>
273   The Method  token indicates the method to be performed on the
274   resource identified by the Request-URI. The method is case-sensitive.
275</t>
276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
277    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
278                   | "GET"                    ; <xref target="GET"/>
279                   | "HEAD"                   ; <xref target="HEAD"/>
280                   | "POST"                   ; <xref target="POST"/>
281                   | "PUT"                    ; <xref target="PUT"/>
282                   | "DELETE"                 ; <xref target="DELETE"/>
283                   | "TRACE"                  ; <xref target="TRACE"/>
284                   | "CONNECT"                ; <xref target="CONNECT"/>
285                   | extension-method
286    extension-method = token
287</artwork></figure>
288<t>
289   The list of methods allowed by a resource can be specified in an
290   Allow header field (<xref target="header.allow"/>). The return code of the response
291   always notifies the client whether a method is currently allowed on a
292   resource, since the set of allowed methods can change dynamically. An
293   origin server &SHOULD; return the status code 405 (Method Not Allowed)
294   if the method is known by the origin server but not allowed for the
295   requested resource, and 501 (Not Implemented) if the method is
296   unrecognized or not implemented by the origin server. The methods GET
297   and HEAD &MUST; be supported by all general-purpose servers. All other
298   methods are &OPTIONAL;; however, if the above methods are implemented,
299   they &MUST; be implemented with the same semantics as those specified
300   in <xref target="method.definitions"/>.
301</t>
302</section>
303
304<section title="Request Header Fields" anchor="request.header.fields">
305<t>
306   The request-header fields allow the client to pass additional
307   information about the request, and about the client itself, to the
308   server. These fields act as request modifiers, with semantics
309   equivalent to the parameters on a programming language method
310   invocation.
311</t>
312<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
313    request-header = Accept                   ; &header-accept;
314                   | Accept-Charset           ; &header-accept-charset;
315                   | Accept-Encoding          ; &header-accept-encoding;
316                   | Accept-Language          ; &header-accept-language;
317                   | Authorization            ; &header-authorization;
318                   | Expect                   ; <xref target="header.expect"/>
319                   | From                     ; <xref target="header.from"/>
320                   | Host                     ; &header-host;
321                   | If-Match                 ; &header-if-match;
322                   | If-Modified-Since        ; &header-if-modified-since;
323                   | If-None-Match            ; &header-if-none-match;
324                   | If-Range                 ; &header-if-range;
325                   | If-Unmodified-Since      ; &header-if-unmodified-since;
326                   | Max-Forwards             ; <xref target="header.max-forwards"/>
327                   | Proxy-Authorization      ; &header-proxy-authorization;
328                   | Range                    ; &header-range;
329                   | Referer                  ; <xref target="header.referer"/>
330                   | TE                       ; &header-te;
331                   | User-Agent               ; <xref target="header.user-agent"/>
332</artwork></figure>
333<t>
334   Request-header field names can be extended reliably only in
335   combination with a change in the protocol version. However, new or
336   experimental header fields &MAY; be given the semantics of request-header
337   fields if all parties in the communication recognize them to
338   be request-header fields. Unrecognized header fields are treated as
339   entity-header fields.
340</t>
341</section>
342
343<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
344<t>
345   The Status-Code element is a 3-digit integer result code of the
346   attempt to understand and satisfy the request. These codes are fully
347   defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
348   textual description of the Status-Code. The Status-Code is intended
349   for use by automata and the Reason-Phrase is intended for the human
350   user. The client is not required to examine or display the Reason-Phrase.
351</t>
352<t> 
353   The individual values of the numeric status codes defined for
354   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
355   presented below. The reason phrases listed here are only
356   recommendations -- they &MAY; be replaced by local equivalents without
357   affecting the protocol.
358</t>
359<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"/>
360   Status-Code    =
361         "100"  ; <xref target="status.100"/>: Continue
362       | "101"  ; <xref target="status.101"/>: Switching Protocols
363       | "200"  ; <xref target="status.200"/>: OK
364       | "201"  ; <xref target="status.201"/>: Created
365       | "202"  ; <xref target="status.202"/>: Accepted
366       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
367       | "204"  ; <xref target="status.204"/>: No Content
368       | "205"  ; <xref target="status.205"/>: Reset Content
369       | "206"  ; <xref target="status.206"/>: Partial Content
370       | "300"  ; <xref target="status.300"/>: Multiple Choices
371       | "301"  ; <xref target="status.301"/>: Moved Permanently
372       | "302"  ; <xref target="status.302"/>: Found
373       | "303"  ; <xref target="status.303"/>: See Other
374       | "304"  ; <xref target="status.304"/>: Not Modified
375       | "305"  ; <xref target="status.305"/>: Use Proxy
376       | "307"  ; <xref target="status.307"/>: Temporary Redirect
377       | "400"  ; <xref target="status.400"/>: Bad Request
378       | "401"  ; <xref target="status.401"/>: Unauthorized
379       | "402"  ; <xref target="status.402"/>: Payment Required
380       | "403"  ; <xref target="status.403"/>: Forbidden
381       | "404"  ; <xref target="status.404"/>: Not Found
382       | "405"  ; <xref target="status.405"/>: Method Not Allowed
383       | "406"  ; <xref target="status.406"/>: Not Acceptable
384       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
385       | "408"  ; <xref target="status.408"/>: Request Time-out
386       | "409"  ; <xref target="status.409"/>: Conflict
387       | "410"  ; <xref target="status.410"/>: Gone
388       | "411"  ; <xref target="status.411"/>: Length Required
389       | "412"  ; <xref target="status.412"/>: Precondition Failed
390       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
391       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
392       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
393       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
394       | "417"  ; <xref target="status.417"/>: Expectation Failed
395       | "500"  ; <xref target="status.500"/>: Internal Server Error
396       | "501"  ; <xref target="status.501"/>: Not Implemented
397       | "502"  ; <xref target="status.502"/>: Bad Gateway
398       | "503"  ; <xref target="status.503"/>: Service Unavailable
399       | "504"  ; <xref target="status.504"/>: Gateway Time-out
400       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
401       | extension-code
402
403   extension-code = 3DIGIT
404   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
405</artwork></figure>
406<t>
407   HTTP status codes are extensible. HTTP applications are not required
408   to understand the meaning of all registered status codes, though such
409   understanding is obviously desirable. However, applications &MUST;
410   understand the class of any status code, as indicated by the first
411   digit, and treat any unrecognized response as being equivalent to the
412   x00 status code of that class, with the exception that an
413   unrecognized response &MUST-NOT; be cached. For example, if an
414   unrecognized status code of 431 is received by the client, it can
415   safely assume that there was something wrong with its request and
416   treat the response as if it had received a 400 status code. In such
417   cases, user agents &SHOULD; present to the user the entity returned
418   with the response, since that entity is likely to include human-readable
419   information which will explain the unusual status.
420</t>
421</section>
422
423<section title="Response Header Fields" anchor="response.header.fields">
424<t>
425   The response-header fields allow the server to pass additional
426   information about the response which cannot be placed in the Status-Line.
427   These header fields give information about the server and about
428   further access to the resource identified by the Request-URI.
429</t>
430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
431    response-header = Accept-Ranges           ; &header-accept-ranges;
432                    | Age                     ; &header-age;
433                    | ETag                    ; &header-etag;
434                    | Location                ; <xref target="header.location"/>
435                    | Proxy-Authenticate      ; &header-proxy-authenticate;
436                    | Retry-After             ; <xref target="header.retry-after"/>
437                    | Server                  ; <xref target="header.server"/>
438                    | Vary                    ; &header-vary;
439                    | WWW-Authenticate        ; &header-www-authenticate;
440</artwork></figure>
441<t>
442   Response-header field names can be extended reliably only in
443   combination with a change in the protocol version. However, new or
444   experimental header fields &MAY; be given the semantics of response-header
445   fields if all parties in the communication recognize them to
446   be response-header fields. Unrecognized header fields are treated as
447   entity-header fields.
448</t>
449</section>
450
451<section title="Entity" anchor="entity">
452<t>
453   Request and Response messages &MAY; transfer an entity if not otherwise
454   restricted by the request method or response status code. An entity
455   consists of entity-header fields and an entity-body, although some
456   responses will only include the entity-headers. HTTP entity-body and
457   entity-header fields are defined in &payload;.
458</t>
459<t>
460   An entity-body is only present in a message when a message-body is
461   present, as described in &message-body;. The entity-body is obtained
462   from the message-body by decoding any Transfer-Encoding that might
463   have been applied to ensure safe and proper transfer of the message.
464</t>
465</section>
466
467
468<section title="Method Definitions" anchor="method.definitions">
469<t>
470   The set of common methods for HTTP/1.1 is defined below. Although
471   this set can be expanded, additional methods cannot be assumed to
472   share the same semantics for separately extended clients and servers.
473
474   The Host request-header field (&header-host;) &MUST; accompany all
475   HTTP/1.1 requests.
476</t>
477
478<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
479
480<section title="Safe Methods" anchor="safe.methods">
481<t>
482   Implementors should be aware that the software represents the user in
483   their interactions over the Internet, and should be careful to allow
484   the user to be aware of any actions they might take which may have an
485   unexpected significance to themselves or others.
486</t>
487<t>
488   In particular, the convention has been established that the GET and
489   HEAD methods &SHOULD-NOT;  have the significance of taking an action
490   other than retrieval. These methods ought to be considered "safe".
491   This allows user agents to represent other methods, such as POST, PUT
492   and DELETE, in a special way, so that the user is made aware of the
493   fact that a possibly unsafe action is being requested.
494</t>
495<t>
496   Naturally, it is not possible to ensure that the server does not
497   generate side-effects as a result of performing a GET request; in
498   fact, some dynamic resources consider that a feature. The important
499   distinction here is that the user did not request the side-effects,
500   so therefore cannot be held accountable for them.
501</t>
502</section>
503
504<section title="Idempotent Methods" anchor="idempotent.methods">
505<t>
506   Methods can also have the property of "idempotence" in that (aside
507   from error or expiration issues) the side-effects of N &gt; 0 identical
508   requests is the same as for a single request. The methods GET, HEAD,
509   PUT and DELETE share this property. Also, the methods OPTIONS and
510   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
511</t>
512<t>
513   However, it is possible that a sequence of several requests is non-idempotent,
514   even if all of the methods executed in that sequence are
515   idempotent. (A sequence is idempotent if a single execution of the
516   entire sequence always yields a result that is not changed by a
517   reexecution of all, or part, of that sequence.) For example, a
518   sequence is non-idempotent if its result depends on a value that is
519   later modified in the same sequence.
520</t>
521<t>
522   A sequence that never has side effects is idempotent, by definition
523   (provided that no concurrent operations are being executed on the
524   same set of resources).
525</t>
526</section>
527</section>
528
529<section title="OPTIONS" anchor="OPTIONS">
530  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
531  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
532<t>
533   The OPTIONS method represents a request for information about the
534   communication options available on the request/response chain
535   identified by the Request-URI. This method allows the client to
536   determine the options and/or requirements associated with a resource,
537   or the capabilities of a server, without implying a resource action
538   or initiating a resource retrieval.
539</t>
540<t>
541   Responses to this method are not cacheable.
542</t>
543<t>
544   If the OPTIONS request includes an entity-body (as indicated by the
545   presence of Content-Length or Transfer-Encoding), then the media type
546   &MUST; be indicated by a Content-Type field. Although this
547   specification does not define any use for such a body, future
548   extensions to HTTP might use the OPTIONS body to make more detailed
549   queries on the server. A server that does not support such an
550   extension &MAY; discard the request body.
551</t>
552<t>
553   If the Request-URI is an asterisk ("*"), the OPTIONS request is
554   intended to apply to the server in general rather than to a specific
555   resource. Since a server's communication options typically depend on
556   the resource, the "*" request is only useful as a "ping" or "no-op"
557   type of method; it does nothing beyond allowing the client to test
558   the capabilities of the server. For example, this can be used to test
559   a proxy for HTTP/1.1 compliance (or lack thereof).
560</t>
561<t>
562   If the Request-URI is not an asterisk, the OPTIONS request applies
563   only to the options that are available when communicating with that
564   resource.
565</t>
566<t>
567   A 200 response &SHOULD; include any header fields that indicate
568   optional features implemented by the server and applicable to that
569   resource (e.g., Allow), possibly including extensions not defined by
570   this specification. The response body, if any, &SHOULD; also include
571   information about the communication options. The format for such a
572   body is not defined by this specification, but might be defined by
573   future extensions to HTTP. Content negotiation &MAY; be used to select
574   the appropriate response format. If no response body is included, the
575   response &MUST; include a Content-Length field with a field-value of
576   "0".
577</t>
578<t>
579   The Max-Forwards request-header field &MAY; be used to target a
580   specific proxy in the request chain. When a proxy receives an OPTIONS
581   request on an absoluteURI for which request forwarding is permitted,
582   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
583   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
584   instead, the proxy &SHOULD; respond with its own communication options.
585   If the Max-Forwards field-value is an integer greater than zero, the
586   proxy &MUST; decrement the field-value when it forwards the request. If
587   no Max-Forwards field is present in the request, then the forwarded
588   request &MUST-NOT; include a Max-Forwards field.
589</t>
590</section>
591
592<section title="GET" anchor="GET">
593  <iref primary="true" item="GET method" x:for-anchor=""/>
594  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
595<t>
596   The GET method means retrieve whatever information (in the form of an
597   entity) is identified by the Request-URI. If the Request-URI refers
598   to a data-producing process, it is the produced data which shall be
599   returned as the entity in the response and not the source text of the
600   process, unless that text happens to be the output of the process.
601</t>
602<t>
603   The semantics of the GET method change to a "conditional GET" if the
604   request message includes an If-Modified-Since, If-Unmodified-Since,
605   If-Match, If-None-Match, or If-Range header field. A conditional GET
606   method requests that the entity be transferred only under the
607   circumstances described by the conditional header field(s). The
608   conditional GET method is intended to reduce unnecessary network
609   usage by allowing cached entities to be refreshed without requiring
610   multiple requests or transferring data already held by the client.
611</t>
612<t>
613   The semantics of the GET method change to a "partial GET" if the
614   request message includes a Range header field. A partial GET requests
615   that only part of the entity be transferred, as described in &header-range;.
616   The partial GET method is intended to reduce unnecessary
617   network usage by allowing partially-retrieved entities to be
618   completed without transferring data already held by the client.
619</t>
620<t>
621   The response to a GET request is cacheable if and only if it meets
622   the requirements for HTTP caching described in &caching;.
623</t>
624<t>
625   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
626</t>
627</section>
628
629<section title="HEAD" anchor="HEAD">
630  <iref primary="true" item="HEAD method" x:for-anchor=""/>
631  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
632<t>
633   The HEAD method is identical to GET except that the server &MUST-NOT;
634   return a message-body in the response. The metainformation contained
635   in the HTTP headers in response to a HEAD request &SHOULD; be identical
636   to the information sent in response to a GET request. This method can
637   be used for obtaining metainformation about the entity implied by the
638   request without transferring the entity-body itself. This method is
639   often used for testing hypertext links for validity, accessibility,
640   and recent modification.
641</t>
642<t>
643   The response to a HEAD request &MAY; be cacheable in the sense that the
644   information contained in the response &MAY; be used to update a
645   previously cached entity from that resource. If the new field values
646   indicate that the cached entity differs from the current entity (as
647   would be indicated by a change in Content-Length, Content-MD5, ETag
648   or Last-Modified), then the cache &MUST; treat the cache entry as
649   stale.
650</t>
651</section>
652
653<section title="POST" anchor="POST">
654  <iref primary="true" item="POST method" x:for-anchor=""/>
655  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
656<t>
657   The POST method is used to request that the origin server accept the
658   entity enclosed in the request as a new subordinate of the resource
659   identified by the Request-URI in the Request-Line. POST is designed
660   to allow a uniform method to cover the following functions:
661  <list style="symbols">
662    <t>
663      Annotation of existing resources;
664    </t>
665    <t>
666        Posting a message to a bulletin board, newsgroup, mailing list,
667        or similar group of articles;
668    </t>
669    <t>
670        Providing a block of data, such as the result of submitting a
671        form, to a data-handling process;
672    </t>
673    <t>
674        Extending a database through an append operation.
675    </t>
676  </list>
677</t>
678<t>
679   The actual function performed by the POST method is determined by the
680   server and is usually dependent on the Request-URI. The posted entity
681   is subordinate to that URI in the same way that a file is subordinate
682   to a directory containing it, a news article is subordinate to a
683   newsgroup to which it is posted, or a record is subordinate to a
684   database.
685</t>
686<t>
687   The action performed by the POST method might not result in a
688   resource that can be identified by a URI. In this case, either 200
689   (OK) or 204 (No Content) is the appropriate response status,
690   depending on whether or not the response includes an entity that
691   describes the result.
692</t>
693<t>
694   If a resource has been created on the origin server, the response
695   &SHOULD; be 201 (Created) and contain an entity which describes the
696   status of the request and refers to the new resource, and a Location
697   header (see <xref target="header.location"/>).
698</t>
699<t>
700   Responses to this method are not cacheable, unless the response
701   includes appropriate Cache-Control or Expires header fields. However,
702   the 303 (See Other) response can be used to direct the user agent to
703   retrieve a cacheable resource.
704</t>
705<t>
706   POST requests &MUST; obey the message transmission requirements set out
707   in &message-transmission-req;.
708</t>
709<t>
710   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
711</t>
712</section>
713
714<section title="PUT" anchor="PUT">
715  <iref primary="true" item="PUT method" x:for-anchor=""/>
716  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
717<t>
718   The PUT method requests that the enclosed entity be stored under the
719   supplied Request-URI. If the Request-URI refers to an already
720   existing resource, the enclosed entity &SHOULD; be considered as a
721   modified version of the one residing on the origin server. If the
722   Request-URI does not point to an existing resource, and that URI is
723   capable of being defined as a new resource by the requesting user
724   agent, the origin server can create the resource with that URI. If a
725   new resource is created, the origin server &MUST; inform the user agent
726   via the 201 (Created) response. If an existing resource is modified,
727   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
728   to indicate successful completion of the request. If the resource
729   could not be created or modified with the Request-URI, an appropriate
730   error response &SHOULD; be given that reflects the nature of the
731   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
732   (e.g. Content-Range) headers that it does not understand or implement
733   and &MUST; return a 501 (Not Implemented) response in such cases.
734</t>
735<t>
736   If the request passes through a cache and the Request-URI identifies
737   one or more currently cached entities, those entries &SHOULD; be
738   treated as stale. Responses to this method are not cacheable.
739</t>
740<t>
741   The fundamental difference between the POST and PUT requests is
742   reflected in the different meaning of the Request-URI. The URI in a
743   POST request identifies the resource that will handle the enclosed
744   entity. That resource might be a data-accepting process, a gateway to
745   some other protocol, or a separate entity that accepts annotations.
746   In contrast, the URI in a PUT request identifies the entity enclosed
747   with the request -- the user agent knows what URI is intended and the
748   server &MUST-NOT; attempt to apply the request to some other resource.
749   If the server desires that the request be applied to a different URI,
750   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
751   then make its own decision regarding whether or not to redirect the
752   request.
753</t>
754<t>
755   A single resource &MAY; be identified by many different URIs. For
756   example, an article might have a URI for identifying "the current
757   version" which is separate from the URI identifying each particular
758   version. In this case, a PUT request on a general URI might result in
759   several other URIs being defined by the origin server.
760</t>
761<t>
762   HTTP/1.1 does not define how a PUT method affects the state of an
763   origin server.
764</t>
765<t>
766   PUT requests &MUST; obey the message transmission requirements set out
767   in &message-transmission-req;.
768</t>
769<t>
770   Unless otherwise specified for a particular entity-header, the
771   entity-headers in the PUT request &SHOULD; be applied to the resource
772   created or modified by the PUT.
773</t>
774</section>
775
776<section title="DELETE" anchor="DELETE">
777  <iref primary="true" item="DELETE method" x:for-anchor=""/>
778  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
779<t>
780   The DELETE method requests that the origin server delete the resource
781   identified by the Request-URI. This method &MAY; be overridden by human
782   intervention (or other means) on the origin server. The client cannot
783   be guaranteed that the operation has been carried out, even if the
784   status code returned from the origin server indicates that the action
785   has been completed successfully. However, the server &SHOULD-NOT; 
786   indicate success unless, at the time the response is given, it
787   intends to delete the resource or move it to an inaccessible
788   location.
789</t>
790<t>
791   A successful response &SHOULD; be 200 (OK) if the response includes an
792   entity describing the status, 202 (Accepted) if the action has not
793   yet been enacted, or 204 (No Content) if the action has been enacted
794   but the response does not include an entity.
795</t>
796<t>
797   If the request passes through a cache and the Request-URI identifies
798   one or more currently cached entities, those entries &SHOULD; be
799   treated as stale. Responses to this method are not cacheable.
800</t>
801</section>
802
803<section title="TRACE" anchor="TRACE">
804  <iref primary="true" item="TRACE method" x:for-anchor=""/>
805  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
806<t>
807   The TRACE method is used to invoke a remote, application-layer loop-back
808   of the request message. The final recipient of the request
809   &SHOULD; reflect the message received back to the client as the
810   entity-body of a 200 (OK) response. The final recipient is either the
811   origin server or the first proxy or gateway to receive a Max-Forwards
812   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
813   &MUST-NOT; include an entity.
814</t>
815<t>
816   TRACE allows the client to see what is being received at the other
817   end of the request chain and use that data for testing or diagnostic
818   information. The value of the Via header field (&header-via;) is of
819   particular interest, since it acts as a trace of the request chain.
820   Use of the Max-Forwards header field allows the client to limit the
821   length of the request chain, which is useful for testing a chain of
822   proxies forwarding messages in an infinite loop.
823</t>
824<t>
825   If the request is valid, the response &SHOULD; contain the entire
826   request message in the entity-body, with a Content-Type of
827   "message/http". Responses to this method &MUST-NOT; be cached.
828</t>
829</section>
830
831<section title="CONNECT" anchor="CONNECT">
832  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
833  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
834<t>
835   This specification reserves the method name CONNECT for use with a
836   proxy that can dynamically switch to being a tunnel (e.g. SSL
837   tunneling <xref target="Luo1998"/>).
838</t>
839</section>
840</section>
841
842
843<section title="Status Code Definitions" anchor="status.codes">
844<t>
845   Each Status-Code is described below, including a description of which
846   method(s) it can follow and any metainformation required in the
847   response.
848</t>
849
850<section title="Informational 1xx" anchor="status.1xx">
851<t>
852   This class of status code indicates a provisional response,
853   consisting only of the Status-Line and optional headers, and is
854   terminated by an empty line. There are no required headers for this
855   class of status code. Since HTTP/1.0 did not define any 1xx status
856   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
857   except under experimental conditions.
858</t>
859<t>
860   A client &MUST; be prepared to accept one or more 1xx status responses
861   prior to a regular response, even if the client does not expect a 100
862   (Continue) status message. Unexpected 1xx status responses &MAY; be
863   ignored by a user agent.
864</t>
865<t>
866   Proxies &MUST; forward 1xx responses, unless the connection between the
867   proxy and its client has been closed, or unless the proxy itself
868   requested the generation of the 1xx response. (For example, if a
869   proxy adds a "Expect: 100-continue" field when it forwards a request,
870   then it need not forward the corresponding 100 (Continue)
871   response(s).)
872</t>
873
874<section title="100 Continue" anchor="status.100">
875  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
876  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
877<t>
878   The client &SHOULD; continue with its request. This interim response is
879   used to inform the client that the initial part of the request has
880   been received and has not yet been rejected by the server. The client
881   &SHOULD; continue by sending the remainder of the request or, if the
882   request has already been completed, ignore this response. The server
883   &MUST; send a final response after the request has been completed. See
884   &use100; for detailed discussion of the use and handling of this
885   status code.
886</t>
887</section>
888
889<section title="101 Switching Protocols" anchor="status.101">
890  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
891  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
892<t>
893   The server understands and is willing to comply with the client's
894   request, via the Upgrade message header field (&header-upgrade;), for a
895   change in the application protocol being used on this connection. The
896   server will switch protocols to those defined by the response's
897   Upgrade header field immediately after the empty line which
898   terminates the 101 response.
899</t>
900<t>
901   The protocol &SHOULD; be switched only when it is advantageous to do
902   so. For example, switching to a newer version of HTTP is advantageous
903   over older versions, and switching to a real-time, synchronous
904   protocol might be advantageous when delivering resources that use
905   such features.
906</t>
907</section>
908</section>
909
910<section title="Successful 2xx" anchor="status.2xx">
911<t>
912   This class of status code indicates that the client's request was
913   successfully received, understood, and accepted.
914</t>
915
916<section title="200 OK" anchor="status.200">
917  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
918  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
919<t>
920   The request has succeeded. The information returned with the response
921   is dependent on the method used in the request, for example:
922  <list style="hanging">
923    <t hangText="GET">
924          an entity corresponding to the requested resource is sent in
925          the response;
926    </t>
927    <t hangText="HEAD">
928          the entity-header fields corresponding to the requested
929          resource are sent in the response without any message-body;
930    </t>
931    <t hangText="POST">
932      an entity describing or containing the result of the action;
933    </t>
934    <t hangText="TRACE">
935      an entity containing the request message as received by the
936      end server.
937    </t>
938  </list>
939</t>
940</section>
941
942<section title="201 Created" anchor="status.201">
943  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
944  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
945<t>
946   The request has been fulfilled and resulted in a new resource being
947   created. The newly created resource can be referenced by the URI(s)
948   returned in the entity of the response, with the most specific URI
949   for the resource given by a Location header field. The response
950   &SHOULD; include an entity containing a list of resource
951   characteristics and location(s) from which the user or user agent can
952   choose the one most appropriate. The entity format is specified by
953   the media type given in the Content-Type header field. The origin
954   server &MUST; create the resource before returning the 201 status code.
955   If the action cannot be carried out immediately, the server &SHOULD;
956   respond with 202 (Accepted) response instead.
957</t>
958<t>
959   A 201 response &MAY; contain an ETag response header field indicating
960   the current value of the entity tag for the requested variant just
961   created, see &header-etag;.
962</t>
963</section>
964
965<section title="202 Accepted" anchor="status.202">
966  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
967  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
968<t>
969   The request has been accepted for processing, but the processing has
970   not been completed.  The request might or might not eventually be
971   acted upon, as it might be disallowed when processing actually takes
972   place. There is no facility for re-sending a status code from an
973   asynchronous operation such as this.
974</t>
975<t>
976   The 202 response is intentionally non-committal. Its purpose is to
977   allow a server to accept a request for some other process (perhaps a
978   batch-oriented process that is only run once per day) without
979   requiring that the user agent's connection to the server persist
980   until the process is completed. The entity returned with this
981   response &SHOULD; include an indication of the request's current status
982   and either a pointer to a status monitor or some estimate of when the
983   user can expect the request to be fulfilled.
984</t>
985</section>
986
987<section title="203 Non-Authoritative Information" anchor="status.203">
988  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
989  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
990<t>
991   The returned metainformation in the entity-header is not the
992   definitive set as available from the origin server, but is gathered
993   from a local or a third-party copy. The set presented &MAY; be a subset
994   or superset of the original version. For example, including local
995   annotation information about the resource might result in a superset
996   of the metainformation known by the origin server. Use of this
997   response code is not required and is only appropriate when the
998   response would otherwise be 200 (OK).
999</t>
1000</section>
1001
1002<section title="204 No Content" anchor="status.204">
1003  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1004  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1005<t>
1006   The server has fulfilled the request but does not need to return an
1007   entity-body, and might want to return updated metainformation. The
1008   response &MAY; include new or updated metainformation in the form of
1009   entity-headers, which if present &SHOULD; be associated with the
1010   requested variant.
1011</t>
1012<t>
1013   If the client is a user agent, it &SHOULD-NOT;  change its document view
1014   from that which caused the request to be sent. This response is
1015   primarily intended to allow input for actions to take place without
1016   causing a change to the user agent's active document view, although
1017   any new or updated metainformation &SHOULD; be applied to the document
1018   currently in the user agent's active view.
1019</t>
1020<t>
1021   The 204 response &MUST-NOT; include a message-body, and thus is always
1022   terminated by the first empty line after the header fields.
1023</t>
1024</section>
1025
1026<section title="205 Reset Content" anchor="status.205">
1027  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1028  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1029<t>
1030   The server has fulfilled the request and the user agent &SHOULD; reset
1031   the document view which caused the request to be sent. This response
1032   is primarily intended to allow input for actions to take place via
1033   user input, followed by a clearing of the form in which the input is
1034   given so that the user can easily initiate another input action. The
1035   response &MUST-NOT; include an entity.
1036</t>
1037</section>
1038
1039<section title="206 Partial Content" anchor="status.206">
1040  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1041  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1042<t>
1043   The server has fulfilled the partial GET request for the resource
1044   and the enclosed entity is a partial representation as defined in &range;.
1045</t>
1046</section>
1047</section>
1048
1049<section title="Redirection 3xx" anchor="status.3xx">
1050<t>
1051   This class of status code indicates that further action needs to be
1052   taken by the user agent in order to fulfill the request.  The action
1053   required &MAY; be carried out by the user agent without interaction
1054   with the user if and only if the method used in the second request is
1055   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1056   such loops generate network traffic for each redirection.
1057  <list><t>
1058      <x:h>Note:</x:h> previous versions of this specification recommended a
1059      maximum of five redirections. Content developers should be aware
1060      that there might be clients that implement such a fixed
1061      limitation.
1062  </t></list>
1063</t>
1064
1065<section title="300 Multiple Choices" anchor="status.300">
1066  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1067  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1068<t>
1069   The requested resource corresponds to any one of a set of
1070   representations, each with its own specific location, and agent-driven
1071   negotiation information (&content-negotiation;) is being provided so that
1072   the user (or user agent) can select a preferred representation and
1073   redirect its request to that location.
1074</t>
1075<t>
1076   Unless it was a HEAD request, the response &SHOULD; include an entity
1077   containing a list of resource characteristics and location(s) from
1078   which the user or user agent can choose the one most appropriate. The
1079   entity format is specified by the media type given in the Content-Type
1080   header field. Depending upon the format and the capabilities of
1081   the user agent, selection of the most appropriate choice &MAY; be
1082   performed automatically. However, this specification does not define
1083   any standard for such automatic selection.
1084</t>
1085<t>
1086   If the server has a preferred choice of representation, it &SHOULD;
1087   include the specific URI for that representation in the Location
1088   field; user agents &MAY; use the Location field value for automatic
1089   redirection. This response is cacheable unless indicated otherwise.
1090</t>
1091</section>
1092
1093<section title="301 Moved Permanently" anchor="status.301">
1094  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1095  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1096<t>
1097   The requested resource has been assigned a new permanent URI and any
1098   future references to this resource &SHOULD; use one of the returned
1099   URIs.  Clients with link editing capabilities ought to automatically
1100   re-link references to the Request-URI to one or more of the new
1101   references returned by the server, where possible. This response is
1102   cacheable unless indicated otherwise.
1103</t>
1104<t>
1105   The new permanent URI &SHOULD; be given by the Location field in the
1106   response. Unless the request method was HEAD, the entity of the
1107   response &SHOULD; contain a short hypertext note with a hyperlink to
1108   the new URI(s).
1109</t>
1110<t>
1111   If the 301 status code is received in response to a request other
1112   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1113   request unless it can be confirmed by the user, since this might
1114   change the conditions under which the request was issued.
1115  <list><t>
1116      <x:h>Note:</x:h> When automatically redirecting a POST request after
1117      receiving a 301 status code, some existing HTTP/1.0 user agents
1118      will erroneously change it into a GET request.
1119  </t></list>
1120</t>
1121</section>
1122
1123<section title="302 Found" anchor="status.302">
1124  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1125  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1126<t>
1127   The requested resource resides temporarily under a different URI.
1128   Since the redirection might be altered on occasion, the client &SHOULD;
1129   continue to use the Request-URI for future requests.  This response
1130   is only cacheable if indicated by a Cache-Control or Expires header
1131   field.
1132</t>
1133<t>
1134   The temporary URI &SHOULD; be given by the Location field in the
1135   response. Unless the request method was HEAD, the entity of the
1136   response &SHOULD; contain a short hypertext note with a hyperlink to
1137   the new URI(s).
1138</t>
1139<t>
1140   If the 302 status code is received in response to a request other
1141   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1142   request unless it can be confirmed by the user, since this might
1143   change the conditions under which the request was issued.
1144  <list><t>
1145      <x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
1146      to change the method on the redirected request.  However, most
1147      existing user agent implementations treat 302 as if it were a 303
1148      response, performing a GET on the Location field-value regardless
1149      of the original request method. The status codes 303 and 307 have
1150      been added for servers that wish to make unambiguously clear which
1151      kind of reaction is expected of the client.
1152  </t></list>
1153</t>
1154</section>
1155
1156<section title="303 See Other" anchor="status.303">
1157  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1158  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1159<t>
1160   The response to the request can be found under a different URI and
1161   &SHOULD; be retrieved using a GET method on that resource. This method
1162   exists primarily to allow the output of a POST-activated script to
1163   redirect the user agent to a selected resource. The new URI is not a
1164   substitute reference for the originally requested resource. The 303
1165   response &MUST-NOT; be cached, but the response to the second
1166   (redirected) request might be cacheable.
1167</t>
1168<t>
1169   The different URI &SHOULD; be given by the Location field in the
1170   response. Unless the request method was HEAD, the entity of the
1171   response &SHOULD; contain a short hypertext note with a hyperlink to
1172   the new URI(s).
1173  <list><t>
1174      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1175      status. When interoperability with such clients is a concern, the
1176      302 status code may be used instead, since most user agents react
1177      to a 302 response as described here for 303.
1178  </t></list>
1179</t>
1180</section>
1181
1182<section title="304 Not Modified" anchor="status.304">
1183  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1184  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1185<t>
1186   If the client has performed a conditional GET request and access is
1187   allowed, but the document has not been modified, the server &SHOULD;
1188   respond with this status code. The 304 response &MUST-NOT; contain a
1189   message-body, and thus is always terminated by the first empty line
1190   after the header fields.
1191</t>
1192<t>
1193   The response &MUST; include the following header fields:
1194  <list style="symbols">
1195    <t>Date, unless its omission is required by &clockless;</t>
1196  </list>
1197</t>
1198<t>
1199   If a clockless origin server obeys these rules, and proxies and
1200   clients add their own Date to any response received without one (as
1201   already specified by [RFC 2068], section <xref target="RFC2068" x:sec="14.19" x:fmt="number"/>), caches will operate
1202   correctly.
1203  <list style="symbols">
1204    <t>ETag and/or Content-Location, if the header would have been sent
1205        in a 200 response to the same request</t>
1206    <t>Expires, Cache-Control, and/or Vary, if the field-value might
1207        differ from that sent in any previous response for the same
1208        variant</t>
1209  </list>
1210</t>
1211<t>
1212   If the conditional GET used a strong cache validator (see &caching;),
1213   the response &SHOULD-NOT;  include other entity-headers.
1214   Otherwise (i.e., the conditional GET used a weak validator), the
1215   response &MUST-NOT; include other entity-headers; this prevents
1216   inconsistencies between cached entity-bodies and updated headers.
1217</t>
1218<t>
1219   If a 304 response indicates an entity not currently cached, then the
1220   cache &MUST; disregard the response and repeat the request without the
1221   conditional.
1222</t>
1223<t>
1224   If a cache uses a received 304 response to update a cache entry, the
1225   cache &MUST; update the entry to reflect any new field values given in
1226   the response.
1227</t>
1228</section>
1229
1230<section title="305 Use Proxy" anchor="status.305">
1231  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1233<t>
1234   The requested resource &MUST; be accessed through the proxy given by
1235   the Location field. The Location field gives the URI of the proxy.
1236   The recipient is expected to repeat this single request via the
1237   proxy. 305 responses &MUST; only be generated by origin servers.
1238  <list><t>
1239      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1240      single request, and to be generated by origin servers only.  Not
1241      observing these limitations has significant security consequences.
1242  </t></list>
1243</t>
1244</section>
1245
1246<section title="306 (Unused)" anchor="status.306">
1247  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1248  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1249<t>
1250   The 306 status code was used in a previous version of the
1251   specification, is no longer used, and the code is reserved.
1252</t>
1253</section>
1254
1255<section title="307 Temporary Redirect" anchor="status.307">
1256  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1257  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1258<t>
1259   The requested resource resides temporarily under a different URI.
1260   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1261   continue to use the Request-URI for future requests.  This response
1262   is only cacheable if indicated by a Cache-Control or Expires header
1263   field.
1264</t>
1265<t>
1266   The temporary URI &SHOULD; be given by the Location field in the
1267   response. Unless the request method was HEAD, the entity of the
1268   response &SHOULD; contain a short hypertext note with a hyperlink to
1269   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1270   understand the 307 status. Therefore, the note &SHOULD; contain the
1271   information necessary for a user to repeat the original request on
1272   the new URI.
1273</t>
1274<t>
1275   If the 307 status code is received in response to a request other
1276   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1277   request unless it can be confirmed by the user, since this might
1278   change the conditions under which the request was issued.
1279</t>
1280</section>
1281</section>
1282
1283<section title="Client Error 4xx" anchor="status.4xx">
1284<t>
1285   The 4xx class of status code is intended for cases in which the
1286   client seems to have erred. Except when responding to a HEAD request,
1287   the server &SHOULD; include an entity containing an explanation of the
1288   error situation, and whether it is a temporary or permanent
1289   condition. These status codes are applicable to any request method.
1290   User agents &SHOULD; display any included entity to the user.
1291</t>
1292<t>
1293   If the client is sending data, a server implementation using TCP
1294   &SHOULD; be careful to ensure that the client acknowledges receipt of
1295   the packet(s) containing the response, before the server closes the
1296   input connection. If the client continues sending data to the server
1297   after the close, the server's TCP stack will send a reset packet to
1298   the client, which may erase the client's unacknowledged input buffers
1299   before they can be read and interpreted by the HTTP application.
1300</t>
1301
1302<section title="400 Bad Request" anchor="status.400">
1303  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1304  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1305<t>
1306   The request could not be understood by the server due to malformed
1307   syntax. The client &SHOULD-NOT;  repeat the request without
1308   modifications.
1309</t>
1310</section>
1311
1312<section title="401 Unauthorized" anchor="status.401">
1313  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1314  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1315<t>
1316   The request requires user authentication. The response &MUST; include a
1317   WWW-Authenticate header field (&header-www-authenticate;) containing a challenge
1318   applicable to the requested resource. The client &MAY; repeat the
1319   request with a suitable Authorization header field (&header-authorization;). If
1320   the request already included Authorization credentials, then the 401
1321   response indicates that authorization has been refused for those
1322   credentials. If the 401 response contains the same challenge as the
1323   prior response, and the user agent has already attempted
1324   authentication at least once, then the user &SHOULD; be presented the
1325   entity that was given in the response, since that entity might
1326   include relevant diagnostic information. HTTP access authentication
1327   is explained in "HTTP Authentication: Basic and Digest Access
1328   Authentication" <xref target="RFC2617"/>.
1329</t>
1330</section>
1331
1332<section title="402 Payment Required" anchor="status.402">
1333  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1334  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1335<t>
1336   This code is reserved for future use.
1337</t>
1338</section>
1339
1340<section title="403 Forbidden" anchor="status.403">
1341  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1342  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1343<t>
1344   The server understood the request, but is refusing to fulfill it.
1345   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1346   If the request method was not HEAD and the server wishes to make
1347   public why the request has not been fulfilled, it &SHOULD; describe the
1348   reason for the refusal in the entity.  If the server does not wish to
1349   make this information available to the client, the status code 404
1350   (Not Found) can be used instead.
1351</t>
1352</section>
1353
1354<section title="404 Not Found" anchor="status.404">
1355  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1356  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1357<t>
1358   The server has not found anything matching the Request-URI. No
1359   indication is given of whether the condition is temporary or
1360   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1361   knows, through some internally configurable mechanism, that an old
1362   resource is permanently unavailable and has no forwarding address.
1363   This status code is commonly used when the server does not wish to
1364   reveal exactly why the request has been refused, or when no other
1365   response is applicable.
1366</t>
1367</section>
1368
1369<section title="405 Method Not Allowed" anchor="status.405">
1370  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1371  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1372<t>
1373   The method specified in the Request-Line is not allowed for the
1374   resource identified by the Request-URI. The response &MUST; include an
1375   Allow header containing a list of valid methods for the requested
1376   resource.
1377</t>
1378</section>
1379
1380<section title="406 Not Acceptable" anchor="status.406">
1381  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1382  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1383<t>
1384   The resource identified by the request is only capable of generating
1385   response entities which have content characteristics not acceptable
1386   according to the accept headers sent in the request.
1387</t>
1388<t>
1389   Unless it was a HEAD request, the response &SHOULD; include an entity
1390   containing a list of available entity characteristics and location(s)
1391   from which the user or user agent can choose the one most
1392   appropriate. The entity format is specified by the media type given
1393   in the Content-Type header field. Depending upon the format and the
1394   capabilities of the user agent, selection of the most appropriate
1395   choice &MAY; be performed automatically. However, this specification
1396   does not define any standard for such automatic selection.
1397  <list><t>
1398      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1399      not acceptable according to the accept headers sent in the
1400      request. In some cases, this may even be preferable to sending a
1401      406 response. User agents are encouraged to inspect the headers of
1402      an incoming response to determine if it is acceptable.
1403  </t></list>
1404</t>
1405<t>
1406   If the response could be unacceptable, a user agent &SHOULD;
1407   temporarily stop receipt of more data and query the user for a
1408   decision on further actions.
1409</t>
1410</section>
1411
1412<section title="407 Proxy Authentication Required" anchor="status.407">
1413  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1414  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1415<t>
1416   This code is similar to 401 (Unauthorized), but indicates that the
1417   client must first authenticate itself with the proxy. The proxy &MUST;
1418   return a Proxy-Authenticate header field (&header-proxy-authenticate;) containing a
1419   challenge applicable to the proxy for the requested resource. The
1420   client &MAY; repeat the request with a suitable Proxy-Authorization
1421   header field (&header-proxy-authorization;). HTTP access authentication is explained
1422   in "HTTP Authentication: Basic and Digest Access Authentication"
1423   <xref target="RFC2617"/>.
1424</t>
1425</section>
1426
1427<section title="408 Request Timeout" anchor="status.408">
1428  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1429  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1430<t>
1431   The client did not produce a request within the time that the server
1432   was prepared to wait. The client &MAY; repeat the request without
1433   modifications at any later time.
1434</t>
1435</section>
1436
1437<section title="409 Conflict" anchor="status.409">
1438  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1439  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1440<t>
1441   The request could not be completed due to a conflict with the current
1442   state of the resource. This code is only allowed in situations where
1443   it is expected that the user might be able to resolve the conflict
1444   and resubmit the request. The response body &SHOULD; include enough
1445   information for the user to recognize the source of the conflict.
1446   Ideally, the response entity would include enough information for the
1447   user or user agent to fix the problem; however, that might not be
1448   possible and is not required.
1449</t>
1450<t>
1451   Conflicts are most likely to occur in response to a PUT request. For
1452   example, if versioning were being used and the entity being PUT
1453   included changes to a resource which conflict with those made by an
1454   earlier (third-party) request, the server might use the 409 response
1455   to indicate that it can't complete the request. In this case, the
1456   response entity would likely contain a list of the differences
1457   between the two versions in a format defined by the response
1458   Content-Type.
1459</t>
1460</section>
1461
1462<section title="410 Gone" anchor="status.410">
1463  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1464  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1465<t>
1466   The requested resource is no longer available at the server and no
1467   forwarding address is known. This condition is expected to be
1468   considered permanent. Clients with link editing capabilities &SHOULD;
1469   delete references to the Request-URI after user approval. If the
1470   server does not know, or has no facility to determine, whether or not
1471   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1472   used instead. This response is cacheable unless indicated otherwise.
1473</t>
1474<t>
1475   The 410 response is primarily intended to assist the task of web
1476   maintenance by notifying the recipient that the resource is
1477   intentionally unavailable and that the server owners desire that
1478   remote links to that resource be removed. Such an event is common for
1479   limited-time, promotional services and for resources belonging to
1480   individuals no longer working at the server's site. It is not
1481   necessary to mark all permanently unavailable resources as "gone" or
1482   to keep the mark for any length of time -- that is left to the
1483   discretion of the server owner.
1484</t>
1485</section>
1486
1487<section title="411 Length Required" anchor="status.411">
1488  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1489  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1490<t>
1491   The server refuses to accept the request without a defined Content-Length.
1492   The client &MAY; repeat the request if it adds a valid
1493   Content-Length header field containing the length of the message-body
1494   in the request message.
1495</t>
1496</section>
1497
1498<section title="412 Precondition Failed" anchor="status.412">
1499  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1500  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1501<t>
1502   The precondition given in one or more of the request-header fields
1503   evaluated to false when it was tested on the server. This response
1504   code allows the client to place preconditions on the current resource
1505   metainformation (header field data) and thus prevent the requested
1506   method from being applied to a resource other than the one intended.
1507</t>
1508</section>
1509
1510<section title="413 Request Entity Too Large" anchor="status.413">
1511  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1512  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1513<t>
1514   The server is refusing to process a request because the request
1515   entity is larger than the server is willing or able to process. The
1516   server &MAY; close the connection to prevent the client from continuing
1517   the request.
1518</t>
1519<t>
1520   If the condition is temporary, the server &SHOULD; include a Retry-After
1521   header field to indicate that it is temporary and after what
1522   time the client &MAY; try again.
1523</t>
1524</section>
1525
1526<section title="414 Request-URI Too Long" anchor="status.414">
1527  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1528  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1529<t>
1530   The server is refusing to service the request because the Request-URI
1531   is longer than the server is willing to interpret. This rare
1532   condition is only likely to occur when a client has improperly
1533   converted a POST request to a GET request with long query
1534   information, when the client has descended into a URI "black hole" of
1535   redirection (e.g., a redirected URI prefix that points to a suffix of
1536   itself), or when the server is under attack by a client attempting to
1537   exploit security holes present in some servers using fixed-length
1538   buffers for reading or manipulating the Request-URI.
1539</t>
1540</section>
1541
1542<section title="415 Unsupported Media Type" anchor="status.415">
1543  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1544  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1545<t>
1546   The server is refusing to service the request because the entity of
1547   the request is in a format not supported by the requested resource
1548   for the requested method.
1549</t>
1550</section>
1551
1552<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1553  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1554  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1555<t>
1556   The request included a Range request-header field (&header-range;) and none of
1557   the range-specifier values in this field overlap the current extent
1558   of the selected resource.
1559</t>
1560</section>
1561
1562<section title="417 Expectation Failed" anchor="status.417">
1563  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1564  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1565<t>
1566   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1567   could not be met by this server, or, if the server is a proxy,
1568   the server has unambiguous evidence that the request could not be met
1569   by the next-hop server.
1570</t>
1571</section>
1572</section>
1573
1574<section title="Server Error 5xx" anchor="status.5xx">
1575<t>
1576   Response status codes beginning with the digit "5" indicate cases in
1577   which the server is aware that it has erred or is incapable of
1578   performing the request. Except when responding to a HEAD request, the
1579   server &SHOULD; include an entity containing an explanation of the
1580   error situation, and whether it is a temporary or permanent
1581   condition. User agents &SHOULD; display any included entity to the
1582   user. These response codes are applicable to any request method.
1583</t>
1584
1585<section title="500 Internal Server Error" anchor="status.500">
1586  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1587  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1588<t>
1589   The server encountered an unexpected condition which prevented it
1590   from fulfilling the request.
1591</t>
1592</section>
1593
1594<section title="501 Not Implemented" anchor="status.501">
1595  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1596  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1597<t>
1598   The server does not support the functionality required to fulfill the
1599   request. This is the appropriate response when the server does not
1600   recognize the request method and is not capable of supporting it for
1601   any resource.
1602</t>
1603</section>
1604
1605<section title="502 Bad Gateway" anchor="status.502">
1606  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1607  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1608<t>
1609   The server, while acting as a gateway or proxy, received an invalid
1610   response from the upstream server it accessed in attempting to
1611   fulfill the request.
1612</t>
1613</section>
1614
1615<section title="503 Service Unavailable" anchor="status.503">
1616  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1617  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1618<t>
1619   The server is currently unable to handle the request due to a
1620   temporary overloading or maintenance of the server. The implication
1621   is that this is a temporary condition which will be alleviated after
1622   some delay. If known, the length of the delay &MAY; be indicated in a
1623   Retry-After header. If no Retry-After is given, the client &SHOULD;
1624   handle the response as it would for a 500 response.
1625  <list><t>
1626      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1627      server must use it when becoming overloaded. Some servers may wish
1628      to simply refuse the connection.
1629  </t></list>
1630</t>
1631</section>
1632
1633<section title="504 Gateway Timeout" anchor="status.504">
1634  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1635  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1636<t>
1637   The server, while acting as a gateway or proxy, did not receive a
1638   timely response from the upstream server specified by the URI (e.g.
1639   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1640   to access in attempting to complete the request.
1641  <list><t>
1642      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1643      return 400 or 500 when DNS lookups time out.
1644  </t></list>
1645</t>
1646</section>
1647
1648<section title="505 HTTP Version Not Supported" anchor="status.505">
1649  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1650  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1651<t>
1652   The server does not support, or refuses to support, the HTTP protocol
1653   version that was used in the request message. The server is
1654   indicating that it is unable or unwilling to complete the request
1655   using the same major version as the client, as described in &http-version;,
1656   other than with this error message. The response &SHOULD; contain
1657   an entity describing why that version is not supported and what other
1658   protocols are supported by that server.
1659</t>
1660
1661</section>
1662</section>
1663</section>
1664
1665
1666<section title="Header Field Definitions" anchor="header.fields">
1667<t>
1668   This section defines the syntax and semantics of all standard
1669   HTTP/1.1 header fields. For entity-header fields, both sender and
1670   recipient refer to either the client or the server, depending on who
1671   sends and who receives the entity.
1672</t>
1673
1674<section title="Allow" anchor="header.allow">
1675  <iref primary="true" item="Allow header" x:for-anchor=""/>
1676  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1677<t>
1678      The Allow entity-header field lists the set of methods supported
1679      by the resource identified by the Request-URI. The purpose of this
1680      field is strictly to inform the recipient of valid methods
1681      associated with the resource. An Allow header field &MUST; be
1682      present in a 405 (Method Not Allowed) response.
1683</t>
1684<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1685       Allow   = "Allow" ":" #Method
1686</artwork></figure>
1687<t>
1688      Example of use:
1689</t>
1690<figure><artwork type="example">
1691       Allow: GET, HEAD, PUT
1692</artwork></figure>
1693<t>
1694      This field cannot prevent a client from trying other methods.
1695      However, the indications given by the Allow header field value
1696      &SHOULD; be followed. The actual set of allowed methods is defined
1697      by the origin server at the time of each request.
1698</t>
1699<t>
1700      The Allow header field &MAY; be provided with a PUT request to
1701      recommend the methods to be supported by the new or modified
1702      resource. The server is not required to support these methods and
1703      &SHOULD; include an Allow header in the response giving the actual
1704      supported methods.
1705</t>
1706<t>
1707      A proxy &MUST-NOT; modify the Allow header field even if it does not
1708      understand all the methods specified, since the user agent might
1709      have other means of communicating with the origin server.
1710</t>
1711</section>
1712
1713<section title="Expect" anchor="header.expect">
1714  <iref primary="true" item="Expect header" x:for-anchor=""/>
1715  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1716<t>
1717   The Expect request-header field is used to indicate that particular
1718   server behaviors are required by the client.
1719</t>
1720<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"/>
1721   Expect       =  "Expect" ":" 1#expectation
1722
1723   expectation  =  "100-continue" | expectation-extension
1724   expectation-extension =  token [ "=" ( token | quoted-string )
1725                            *expect-params ]
1726   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1727</artwork></figure>
1728<t>
1729   A server that does not understand or is unable to comply with any of
1730   the expectation values in the Expect field of a request &MUST; respond
1731   with appropriate error status. The server &MUST; respond with a 417
1732   (Expectation Failed) status if any of the expectations cannot be met
1733   or, if there are other problems with the request, some other 4xx
1734   status.
1735</t>
1736<t>
1737   This header field is defined with extensible syntax to allow for
1738   future extensions. If a server receives a request containing an
1739   Expect field that includes an expectation-extension that it does not
1740   support, it &MUST; respond with a 417 (Expectation Failed) status.
1741</t>
1742<t>
1743   Comparison of expectation values is case-insensitive for unquoted
1744   tokens (including the 100-continue token), and is case-sensitive for
1745   quoted-string expectation-extensions.
1746</t>
1747<t>
1748   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1749   return a 417 (Expectation Failed) status if it receives a request
1750   with an expectation that it cannot meet. However, the Expect
1751   request-header itself is end-to-end; it &MUST; be forwarded if the
1752   request is forwarded.
1753</t>
1754<t>
1755   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1756   Expect header.
1757</t>
1758<t>
1759   See &use100; for the use of the 100 (continue) status.
1760</t>
1761</section>
1762
1763<section title="From" anchor="header.from">
1764  <iref primary="true" item="From header" x:for-anchor=""/>
1765  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1766<t>
1767   The From request-header field, if given, &SHOULD; contain an Internet
1768   e-mail address for the human user who controls the requesting user
1769   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1770   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1771</t>
1772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1773    From   = "From" ":" mailbox
1774</artwork></figure>
1775<t>
1776   An example is:
1777</t>
1778<figure><artwork type="example">
1779    From: webmaster@w3.org
1780</artwork></figure>
1781<t>
1782   This header field &MAY; be used for logging purposes and as a means for
1783   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1784   be used as an insecure form of access protection. The interpretation
1785   of this field is that the request is being performed on behalf of the
1786   person given, who accepts responsibility for the method performed. In
1787   particular, robot agents &SHOULD; include this header so that the
1788   person responsible for running the robot can be contacted if problems
1789   occur on the receiving end.
1790</t>
1791<t>
1792   The Internet e-mail address in this field &MAY; be separate from the
1793   Internet host which issued the request. For example, when a request
1794   is passed through a proxy the original issuer's address &SHOULD; be
1795   used.
1796</t>
1797<t>
1798   The client &SHOULD-NOT;  send the From header field without the user's
1799   approval, as it might conflict with the user's privacy interests or
1800   their site's security policy. It is strongly recommended that the
1801   user be able to disable, enable, and modify the value of this field
1802   at any time prior to a request.
1803</t>
1804</section>
1805
1806<section title="Location" anchor="header.location">
1807  <iref primary="true" item="Location header" x:for-anchor=""/>
1808  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1809<t>
1810   The Location response-header field is used to redirect the recipient
1811   to a location other than the Request-URI for completion of the
1812   request or identification of a new resource. For 201 (Created)
1813   responses, the Location is that of the new resource which was created
1814   by the request. For 3xx responses, the location &SHOULD; indicate the
1815   server's preferred URI for automatic redirection to the resource. The
1816   field value consists of a single absolute URI.
1817</t>
1818<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1819    Location       = "Location" ":" absoluteURI
1820</artwork></figure>
1821<t>
1822   An example is:
1823</t>
1824<figure><artwork type="example">
1825    Location: http://www.w3.org/pub/WWW/People.html
1826</artwork></figure>
1827<t>
1828  <list><t>
1829      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1830      from Location in that the Content-Location identifies the original
1831      location of the entity enclosed in the request. It is therefore
1832      possible for a response to contain header fields for both Location
1833      and Content-Location.
1834  </t></list>
1835</t>
1836</section>
1837
1838<section title="Max-Forwards" anchor="header.max-forwards">
1839  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1840  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1841<t>
1842   The Max-Forwards request-header field provides a mechanism with the
1843   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1844   number of proxies or gateways that can forward the request to the
1845   next inbound server. This can be useful when the client is attempting
1846   to trace a request chain which appears to be failing or looping in
1847   mid-chain.
1848</t>
1849<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1850    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1851</artwork></figure>
1852<t>
1853   The Max-Forwards value is a decimal integer indicating the remaining
1854   number of times this request message may be forwarded.
1855</t>
1856<t>
1857   Each proxy or gateway recipient of a TRACE or OPTIONS request
1858   containing a Max-Forwards header field &MUST; check and update its
1859   value prior to forwarding the request. If the received value is zero
1860   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1861   respond as the final recipient. If the received Max-Forwards value is
1862   greater than zero, then the forwarded message &MUST; contain an updated
1863   Max-Forwards field with a value decremented by one (1).
1864</t>
1865<t>
1866   The Max-Forwards header field &MAY; be ignored for all other methods
1867   defined by this specification and for any extension methods for which
1868   it is not explicitly referred to as part of that method definition.
1869</t>
1870</section>
1871
1872<section title="Referer" anchor="header.referer">
1873  <iref primary="true" item="Referer header" x:for-anchor=""/>
1874  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1875<t>
1876   The Referer[sic] request-header field allows the client to specify,
1877   for the server's benefit, the address (URI) of the resource from
1878   which the Request-URI was obtained (the "referrer", although the
1879   header field is misspelled.) The Referer request-header allows a
1880   server to generate lists of back-links to resources for interest,
1881   logging, optimized caching, etc. It also allows obsolete or mistyped
1882   links to be traced for maintenance. The Referer field &MUST-NOT; be
1883   sent if the Request-URI was obtained from a source that does not have
1884   its own URI, such as input from the user keyboard.
1885</t>
1886<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1887    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1888</artwork></figure>
1889<t>
1890   Example:
1891</t>
1892<figure><artwork type="example">
1893    Referer: http://www.w3.org/hypertext/DataSources/Overview.html
1894</artwork></figure>
1895<t>
1896   If the field value is a relative URI, it &SHOULD; be interpreted
1897   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1898   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1899</t>
1900</section>
1901
1902<section title="Retry-After" anchor="header.retry-after">
1903  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1904  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1905<t>
1906   The Retry-After response-header field can be used with a 503 (Service
1907   Unavailable) response to indicate how long the service is expected to
1908   be unavailable to the requesting client. This field &MAY; also be used
1909   with any 3xx (Redirection) response to indicate the minimum time the
1910   user-agent is asked wait before issuing the redirected request. The
1911   value of this field can be either an HTTP-date or an integer number
1912   of seconds (in decimal) after the time of the response.
1913</t>
1914<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1915    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1916</artwork></figure>
1917<t>
1918   Two examples of its use are
1919</t>
1920<figure><artwork type="example">
1921    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1922    Retry-After: 120
1923</artwork></figure>
1924<t>
1925   In the latter example, the delay is 2 minutes.
1926</t>
1927</section>
1928
1929<section title="Server" anchor="header.server">
1930  <iref primary="true" item="Server header" x:for-anchor=""/>
1931  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1932<t>
1933   The Server response-header field contains information about the
1934   software used by the origin server to handle the request. The field
1935   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1936   identifying the server and any significant subproducts. The product
1937   tokens are listed in order of their significance for identifying the
1938   application.
1939</t>
1940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1941    Server         = "Server" ":" 1*( product | comment )
1942</artwork></figure>
1943<t>
1944   Example:
1945</t>
1946<figure><artwork type="example">
1947    Server: CERN/3.0 libwww/2.17
1948</artwork></figure>
1949<t>
1950   If the response is being forwarded through a proxy, the proxy
1951   application &MUST-NOT; modify the Server response-header. Instead, it
1952   &SHOULD; include a Via field (as described in &header-via;).
1953  <list><t>
1954      <x:h>Note:</x:h> Revealing the specific software version of the server might
1955      allow the server machine to become more vulnerable to attacks
1956      against software that is known to contain security holes. Server
1957      implementors are encouraged to make this field a configurable
1958      option.
1959  </t></list>
1960</t>
1961</section>
1962
1963<section title="User-Agent" anchor="header.user-agent">
1964  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1965  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1966<t>
1967   The User-Agent request-header field contains information about the
1968   user agent originating the request. This is for statistical purposes,
1969   the tracing of protocol violations, and automated recognition of user
1970   agents for the sake of tailoring responses to avoid particular user
1971   agent limitations. User agents &SHOULD; include this field with
1972   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1973   and comments identifying the agent and any subproducts which form a
1974   significant part of the user agent. By convention, the product tokens
1975   are listed in order of their significance for identifying the
1976   application.
1977</t>
1978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1979    User-Agent     = "User-Agent" ":" 1*( product | comment )
1980</artwork></figure>
1981<t>
1982   Example:
1983</t>
1984<figure><artwork type="example">
1985    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1986</artwork></figure>
1987</section>
1988
1989</section>
1990
1991<section title="IANA Considerations" anchor="IANA.considerations">
1992<t>
1993   TBD.
1994</t>
1995</section>
1996
1997<section title="Security Considerations" anchor="security.considerations">
1998<t>
1999   This section is meant to inform application developers, information
2000   providers, and users of the security limitations in HTTP/1.1 as
2001   described by this document. The discussion does not include
2002   definitive solutions to the problems revealed, though it does make
2003   some suggestions for reducing security risks.
2004</t>
2005
2006<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2007<t>
2008   Like any generic data transfer protocol, HTTP cannot regulate the
2009   content of the data that is transferred, nor is there any a priori
2010   method of determining the sensitivity of any particular piece of
2011   information within the context of any given request. Therefore,
2012   applications &SHOULD; supply as much control over this information as
2013   possible to the provider of that information. Four header fields are
2014   worth special mention in this context: Server, Via, Referer and From.
2015</t>
2016<t>
2017   Revealing the specific software version of the server might allow the
2018   server machine to become more vulnerable to attacks against software
2019   that is known to contain security holes. Implementors &SHOULD; make the
2020   Server header field a configurable option.
2021</t>
2022<t>
2023   Proxies which serve as a portal through a network firewall &SHOULD;
2024   take special precautions regarding the transfer of header information
2025   that identifies the hosts behind the firewall. In particular, they
2026   &SHOULD; remove, or replace with sanitized versions, any Via fields
2027   generated behind the firewall.
2028</t>
2029<t>
2030   The Referer header allows reading patterns to be studied and reverse
2031   links drawn. Although it can be very useful, its power can be abused
2032   if user details are not separated from the information contained in
2033   the Referer. Even when the personal information has been removed, the
2034   Referer header might indicate a private document's URI whose
2035   publication would be inappropriate.
2036</t>
2037<t>
2038   The information sent in the From field might conflict with the user's
2039   privacy interests or their site's security policy, and hence it
2040   &SHOULD-NOT;  be transmitted without the user being able to disable,
2041   enable, and modify the contents of the field. The user &MUST; be able
2042   to set the contents of this field within a user preference or
2043   application defaults configuration.
2044</t>
2045<t>
2046   We suggest, though do not require, that a convenient toggle interface
2047   be provided for the user to enable or disable the sending of From and
2048   Referer information.
2049</t>
2050<t>
2051   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2052   fields can sometimes be used to determine that a specific client or
2053   server have a particular security hole which might be exploited.
2054   Unfortunately, this same information is often used for other valuable
2055   purposes for which HTTP currently has no better mechanism.
2056</t>
2057</section>
2058
2059<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2060<t>
2061   Because the source of a link might be private information or might
2062   reveal an otherwise private information source, it is strongly
2063   recommended that the user be able to select whether or not the
2064   Referer field is sent. For example, a browser client could have a
2065   toggle switch for browsing openly/anonymously, which would
2066   respectively enable/disable the sending of Referer and From
2067   information.
2068</t>
2069<t>
2070   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2071   HTTP request if the referring page was transferred with a secure
2072   protocol.
2073</t>
2074<t>
2075   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2076   based forms for the submission of sensitive data, because this will
2077   cause this data to be encoded in the Request-URI. Many existing
2078   servers, proxies, and user agents will log the request URI in some
2079   place where it might be visible to third parties. Servers can use
2080   POST-based form submission instead
2081</t>
2082</section>
2083
2084<section title="Location Headers and Spoofing" anchor="location.spoofing">
2085<t>
2086   If a single server supports multiple organizations that do not trust
2087   one another, then it &MUST; check the values of Location and Content-Location
2088   headers in responses that are generated under control of
2089   said organizations to make sure that they do not attempt to
2090   invalidate resources over which they have no authority.
2091</t>
2092</section>
2093
2094</section>
2095
2096<section title="Acknowledgments" anchor="ack">
2097<t>
2098   Based on an XML translation of RFC 2616 by Julian Reschke.
2099</t>
2100</section>
2101</middle>
2102<back>
2103<references>
2104
2105<reference anchor="Part1">
2106   <front>
2107      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2108      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2109         <organization abbrev="Day Software">Day Software</organization>
2110         <address><email>fielding@gbiv.com</email></address>
2111      </author>
2112      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2113         <organization>One Laptop per Child</organization>
2114         <address><email>jg@laptop.org</email></address>
2115      </author>
2116      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2117         <organization abbrev="HP">Hewlett-Packard Company</organization>
2118         <address><email>JeffMogul@acm.org</email></address>
2119      </author>
2120      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2121         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2122         <address><email>henrikn@microsoft.com</email></address>
2123      </author>
2124      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2125         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2126         <address><email>LMM@acm.org</email></address>
2127      </author>
2128      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2129         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2130         <address><email>paulle@microsoft.com</email></address>
2131      </author>
2132      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2133         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2134         <address><email>timbl@w3.org</email></address>
2135      </author>
2136      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2137   </front>
2138   <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
2139   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2140</reference>
2141
2142<reference anchor="Part3">
2143   <front>
2144      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2145      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2146         <organization abbrev="Day Software">Day Software</organization>
2147         <address><email>fielding@gbiv.com</email></address>
2148      </author>
2149      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2150         <organization>One Laptop per Child</organization>
2151         <address><email>jg@laptop.org</email></address>
2152      </author>
2153      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2154         <organization abbrev="HP">Hewlett-Packard Company</organization>
2155         <address><email>JeffMogul@acm.org</email></address>
2156      </author>
2157      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2158         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2159         <address><email>henrikn@microsoft.com</email></address>
2160      </author>
2161      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2162         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2163         <address><email>LMM@acm.org</email></address>
2164      </author>
2165      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2166         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2167         <address><email>paulle@microsoft.com</email></address>
2168      </author>
2169      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2170         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2171         <address><email>timbl@w3.org</email></address>
2172      </author>
2173      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2174   </front>
2175   <seriesInfo name="Internet-Draft" value="draft-fielding-p3-payload-&ID-VERSION;"/>
2176   <x:source href="p3-payload.xml" basename="p3-payload"/>
2177</reference>
2178
2179<reference anchor="Part4">
2180   <front>
2181      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2182      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2183         <organization abbrev="Day Software">Day Software</organization>
2184         <address><email>fielding@gbiv.com</email></address>
2185      </author>
2186      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2187         <organization>One Laptop per Child</organization>
2188         <address><email>jg@laptop.org</email></address>
2189      </author>
2190      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2191         <organization abbrev="HP">Hewlett-Packard Company</organization>
2192         <address><email>JeffMogul@acm.org</email></address>
2193      </author>
2194      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2195         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2196         <address><email>henrikn@microsoft.com</email></address>
2197      </author>
2198      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2199         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2200         <address><email>LMM@acm.org</email></address>
2201      </author>
2202      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2203         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2204         <address><email>paulle@microsoft.com</email></address>
2205      </author>
2206      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2207         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2208         <address><email>timbl@w3.org</email></address>
2209      </author>
2210      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2211   </front>
2212   <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
2213   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2214</reference>
2215
2216<reference anchor="Part5">
2217   <front>
2218      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2219      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2220         <organization abbrev="Day Software">Day Software</organization>
2221         <address><email>fielding@gbiv.com</email></address>
2222      </author>
2223      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2224         <organization>One Laptop per Child</organization>
2225         <address><email>jg@laptop.org</email></address>
2226      </author>
2227      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2228         <organization abbrev="HP">Hewlett-Packard Company</organization>
2229         <address><email>JeffMogul@acm.org</email></address>
2230      </author>
2231      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2232         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2233         <address><email>henrikn@microsoft.com</email></address>
2234      </author>
2235      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2236         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2237         <address><email>LMM@acm.org</email></address>
2238      </author>
2239      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2240         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2241         <address><email>paulle@microsoft.com</email></address>
2242      </author>
2243      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2244         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2245         <address><email>timbl@w3.org</email></address>
2246      </author>
2247      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2248   </front>
2249   <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
2250   <x:source href="p5-range.xml" basename="p5-range"/>
2251</reference>
2252
2253<reference anchor="Part6">
2254   <front>
2255      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2256      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2257         <organization abbrev="Day Software">Day Software</organization>
2258         <address><email>fielding@gbiv.com</email></address>
2259      </author>
2260      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2261         <organization>One Laptop per Child</organization>
2262         <address><email>jg@laptop.org</email></address>
2263      </author>
2264      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2265         <organization abbrev="HP">Hewlett-Packard Company</organization>
2266         <address><email>JeffMogul@acm.org</email></address>
2267      </author>
2268      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2269         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2270         <address><email>henrikn@microsoft.com</email></address>
2271      </author>
2272      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2273         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2274         <address><email>LMM@acm.org</email></address>
2275      </author>
2276      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2277         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2278         <address><email>paulle@microsoft.com</email></address>
2279      </author>
2280      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2281         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2282         <address><email>timbl@w3.org</email></address>
2283      </author>
2284      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2285   </front>
2286   <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
2287   <x:source href="p6-cache.xml" basename="p6-cache"/>
2288</reference>
2289
2290<reference anchor="Part7">
2291   <front>
2292      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2293      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2294         <organization abbrev="Day Software">Day Software</organization>
2295         <address><email>fielding@gbiv.com</email></address>
2296      </author>
2297      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2298         <organization>One Laptop per Child</organization>
2299         <address><email>jg@laptop.org</email></address>
2300      </author>
2301      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2302         <organization abbrev="HP">Hewlett-Packard Company</organization>
2303         <address><email>JeffMogul@acm.org</email></address>
2304      </author>
2305      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2306         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2307         <address><email>henrikn@microsoft.com</email></address>
2308      </author>
2309      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2310         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2311         <address><email>LMM@acm.org</email></address>
2312      </author>
2313      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2314         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2315         <address><email>paulle@microsoft.com</email></address>
2316      </author>
2317      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2318         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2319         <address><email>timbl@w3.org</email></address>
2320      </author>
2321      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2322   </front>
2323   <seriesInfo name="Internet-Draft" value="draft-fielding-p7-auth-&ID-VERSION;"/>
2324   <x:source href="p7-auth.xml" basename="p7-auth"/>
2325</reference>
2326
2327<reference anchor="RFC2616">
2328   <front>
2329      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2330      <author initials="R." surname="Fielding" fullname="R. Fielding">
2331         <organization>University of California, Irvine</organization>
2332         <address><email>fielding@ics.uci.edu</email></address>
2333      </author>
2334      <author initials="J." surname="Gettys" fullname="J. Gettys">
2335         <organization>W3C</organization>
2336         <address><email>jg@w3.org</email></address>
2337      </author>
2338      <author initials="J." surname="Mogul" fullname="J. Mogul">
2339         <organization>Compaq Computer Corporation</organization>
2340         <address><email>mogul@wrl.dec.com</email></address>
2341      </author>
2342      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2343         <organization>MIT Laboratory for Computer Science</organization>
2344         <address><email>frystyk@w3.org</email></address>
2345      </author>
2346      <author initials="L." surname="Masinter" fullname="L. Masinter">
2347         <organization>Xerox Corporation</organization>
2348         <address><email>masinter@parc.xerox.com</email></address>
2349      </author>
2350      <author initials="P." surname="Leach" fullname="P. Leach">
2351         <organization>Microsoft Corporation</organization>
2352         <address><email>paulle@microsoft.com</email></address>
2353      </author>
2354      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2355         <organization>W3C</organization>
2356         <address><email>timbl@w3.org</email></address>
2357      </author>
2358      <date month="June" year="1999"/>
2359   </front>
2360   <seriesInfo name="RFC" value="2616"/>
2361</reference>
2362
2363<reference anchor="RFC1123">
2364<front>
2365<title>Requirements for Internet Hosts - Application and Support</title>
2366<author initials="R." surname="Braden" fullname="Robert Braden">
2367<organization>University of Southern California (USC), Information Sciences Institute</organization>
2368<address>
2369<postal>
2370<street>4676 Admiralty Way</street>
2371<city>Marina del Rey</city>
2372<region>CA</region>
2373<code>90292-6695</code>
2374<country>US</country></postal>
2375<phone>+1 213 822 1511</phone>
2376<email>Braden@ISI.EDU</email></address></author>
2377<date month="October" year="1989"/></front>
2378<seriesInfo name="STD" value="3"/>
2379<seriesInfo name="RFC" value="1123"/>
2380</reference>
2381
2382<reference anchor="RFC822">
2383<front>
2384<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2385<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2386<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2387<address>
2388<postal>
2389<street/>
2390<city>Newark</city>
2391<region>DE</region>
2392<code>19711</code>
2393<country>US</country></postal>
2394<email>DCrocker@UDel-Relay</email></address></author>
2395<date month="August" day="13" year="1982"/></front>
2396<seriesInfo name="STD" value="11"/>
2397<seriesInfo name="RFC" value="822"/>
2398</reference>
2399
2400<reference anchor="RFC2068">
2401<front>
2402<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2403<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2404<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2405<address>
2406<postal>
2407<street/>
2408<city>Irvine</city>
2409<region>CA</region>
2410<code>92717-3425</code>
2411<country>US</country></postal>
2412<facsimile>+1 714 824 4056</facsimile>
2413<email>fielding@ics.uci.edu</email></address></author>
2414<author initials="J." surname="Gettys" fullname="Jim Gettys">
2415<organization>MIT Laboratory for Computer Science</organization>
2416<address>
2417<postal>
2418<street>545 Technology Square</street>
2419<city>Cambridge</city>
2420<region>MA</region>
2421<code>02139</code>
2422<country>US</country></postal>
2423<facsimile>+1 617 258 8682</facsimile>
2424<email>jg@w3.org</email></address></author>
2425<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2426<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2427<address>
2428<postal>
2429<street>250 University Avenue</street>
2430<city>Palo Alto</city>
2431<region>CA</region>
2432<code>94301</code>
2433<country>US</country></postal>
2434<email>mogul@wrl.dec.com</email></address></author>
2435<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2436<organization>MIT Laboratory for Computer Science</organization>
2437<address>
2438<postal>
2439<street>545 Technology Square</street>
2440<city>Cambridge</city>
2441<region>MA</region>
2442<code>02139</code>
2443<country>US</country></postal>
2444<facsimile>+1 617 258 8682</facsimile>
2445<email>frystyk@w3.org</email></address></author>
2446<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2447<organization>MIT Laboratory for Computer Science</organization>
2448<address>
2449<postal>
2450<street>545 Technology Square</street>
2451<city>Cambridge</city>
2452<region>MA</region>
2453<code>02139</code>
2454<country>US</country></postal>
2455<facsimile>+1 617 258 8682</facsimile>
2456<email>timbl@w3.org</email></address></author>
2457<date month="January" year="1997"/>
2458<abstract>
2459<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
2460<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
2461<seriesInfo name="RFC" value="2068"/>
2462</reference>
2463
2464<reference anchor="RFC2617">
2465<front>
2466<title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
2467<author initials="J." surname="Franks" fullname="John Franks">
2468<organization>Northwestern University, Department of Mathematics</organization>
2469<address>
2470<postal>
2471<street/>
2472<city>Evanston</city>
2473<region>IL</region>
2474<code>60208-2730</code>
2475<country>US</country></postal>
2476<email>john@math.nwu.edu</email></address></author>
2477<author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
2478<organization>Verisign Inc.</organization>
2479<address>
2480<postal>
2481<street>301 Edgewater Place</street>
2482<street>Suite 210</street>
2483<city>Wakefield</city>
2484<region>MA</region>
2485<code>01880</code>
2486<country>US</country></postal>
2487<email>pbaker@verisign.com</email></address></author>
2488<author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
2489<organization>AbiSource, Inc.</organization>
2490<address>
2491<postal>
2492<street>6 Dunlap Court</street>
2493<city>Savoy</city>
2494<region>IL</region>
2495<code>61874</code>
2496<country>US</country></postal>
2497<email>jeff@AbiSource.com</email></address></author>
2498<author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
2499<organization>Agranat Systems, Inc.</organization>
2500<address>
2501<postal>
2502<street>5 Clocktower Place</street>
2503<street>Suite 400</street>
2504<city>Maynard</city>
2505<region>MA</region>
2506<code>01754</code>
2507<country>US</country></postal>
2508<email>lawrence@agranat.com</email></address></author>
2509<author initials="P.J." surname="Leach" fullname="Paul J. Leach">
2510<organization>Microsoft Corporation</organization>
2511<address>
2512<postal>
2513<street>1 Microsoft Way</street>
2514<city>Redmond</city>
2515<region>WA</region>
2516<code>98052</code>
2517<country>US</country></postal>
2518<email>paulle@microsoft.com</email></address></author>
2519<author initials="A." surname="Luotonen" fullname="Ari Luotonen">
2520<organization>Netscape Communications Corporation</organization>
2521<address>
2522<postal>
2523<street>501 East Middlefield Road</street>
2524<city>Mountain View</city>
2525<region>CA</region>
2526<code>94043</code>
2527<country>US</country></postal></address></author>
2528<author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
2529<organization>Open Market, Inc.</organization>
2530<address>
2531<postal>
2532<street>215 First Street</street>
2533<city>Cambridge</city>
2534<region>MA</region>
2535<code>02142</code>
2536<country>US</country></postal>
2537<email>stewart@OpenMarket.com</email></address></author>
2538<date month="June" year="1999"/>
2539</front>
2540<seriesInfo name="RFC" value="2617"/>
2541</reference>
2542
2543<reference anchor="Luo1998">
2544<front>
2545<title>Tunneling TCP based protocols through Web proxy servers</title>
2546<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2547  <organization/>
2548</author>
2549<date/>
2550</front>
2551<seriesInfo name="" value="Work in Progress"/>
2552</reference>
2553
2554</references>
2555
2556<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2557<t>
2558   Clarified which error code should be used for inbound server failures
2559   (e.g. DNS failures). (<xref target="status.504"/>).
2560</t>
2561<t>
2562   CREATE had a race that required an Etag be sent when a resource is
2563   first created. (<xref target="status.201"/>).
2564</t>
2565<t>
2566   Rewrite of message transmission requirements to make it much harder
2567   for implementors to get it wrong, as the consequences of errors here
2568   can have significant impact on the Internet, and to deal with the
2569   following problems:
2570  <list style="numbers">
2571      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2572         this was incorrectly placing a requirement on the behavior of
2573         an implementation of a future version of HTTP/1.x</t>
2574
2575      <t>Made it clear that user-agents should retry requests, not
2576         "clients" in general.</t>
2577
2578      <t>Converted requirements for clients to ignore unexpected 100
2579         (Continue) responses, and for proxies to forward 100 responses,
2580         into a general requirement for 1xx responses.</t>
2581
2582      <t>Modified some TCP-specific language, to make it clearer that
2583         non-TCP transports are possible for HTTP.</t>
2584
2585      <t>Require that the origin server &MUST-NOT; wait for the request
2586         body before it sends a required 100 (Continue) response.</t>
2587
2588      <t>Allow, rather than require, a server to omit 100 (Continue) if
2589         it has already seen some of the request body.</t>
2590
2591      <t>Allow servers to defend against denial-of-service attacks and
2592         broken clients.</t>
2593  </list>
2594</t>
2595<t>
2596   This change adds the Expect header and 417 status code.
2597</t>
2598<t>
2599   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2600   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2601</t>
2602<t>
2603   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
2604   implemented in previous versions of this specification. See RFC 2068
2605   <xref target="RFC2068"/>.
2606</t>
2607</section>
2608</back>
2609</rfc>
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