source: draft-ietf-httpbis/latest/p2-semantics.xml @ 37

Last change on this file since 37 was 37, checked in by julian.reschke@…, 12 years ago

Restore links from Part2 into "Message Transmission Requirements" in Part1.

  • Property svn:eol-style set to native
File size: 119.7 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]>
60<?rfc toc="yes" ?>
61<?rfc symrefs="yes" ?>
62<?rfc sortrefs="yes" ?>
63<?rfc compact="yes"?>
64<?rfc subcompact="no" ?>
65<?rfc linkmailto="no" ?>
66<?rfc editing="no" ?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2068, 2616, 2617" category="std"
70     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
72<front>
73
74  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
75
76  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
77    <organization abbrev="Day Software">Day Software</organization>
78    <address>
79      <postal>
80        <street>23 Corporate Plaza DR, Suite 280</street>
81        <city>Newport Beach</city>
82        <region>CA</region>
83        <code>92660</code>
84        <country>USA</country>
85      </postal>
86      <phone>+1-949-706-5300</phone>
87      <facsimile>+1-949-706-5305</facsimile>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="J." surname="Gettys" fullname="Jim Gettys">
94    <organization>One Laptop per Child</organization>
95    <address>
96      <postal>
97        <street>21 Oak Knoll Road</street>
98        <city>Carlisle</city>
99        <region>MA</region>
100        <code>01741</code>
101        <country>USA</country>
102      </postal>
103      <email>jg@laptop.org</email>
104      <uri>http://www.laptop.org/</uri>
105    </address>
106  </author>
107 
108  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
109    <organization abbrev="HP">Hewlett-Packard Company</organization>
110    <address>
111      <postal>
112        <street>HP Labs, Large Scale Systems Group</street>
113        <street>1501 Page Mill Road, MS 1177</street>
114        <city>Palo Alto</city>
115        <region>CA</region>
116        <code>94304</code>
117        <country>USA</country>
118      </postal>
119      <email>JeffMogul@acm.org</email>
120    </address>
121  </author>
122
123  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
124    <organization abbrev="Microsoft">Microsoft Corporation</organization>
125    <address>
126      <postal>
127        <street>1 Microsoft Way</street>
128        <city>Redmond</city>
129        <region>WA</region>
130        <code>98052</code>
131        <country>USA</country>
132      </postal>
133      <email>henrikn@microsoft.com</email>
134    </address>
135  </author>
136
137  <author initials="L." surname="Masinter" fullname="Larry Masinter">
138    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
139    <address>
140      <postal>
141        <street>345 Park Ave</street>
142        <city>San Jose</city>
143        <region>CA</region>
144        <code>95110</code>
145        <country>USA</country>
146      </postal>
147      <email>LMM@acm.org</email>
148      <uri>http://larry.masinter.net/</uri>
149    </address>
150  </author>
151 
152  <author initials="P." surname="Leach" fullname="Paul J. Leach">
153    <organization abbrev="Microsoft">Microsoft Corporation</organization>
154    <address>
155      <postal>
156        <street>1 Microsoft Way</street>
157        <city>Redmond</city>
158        <region>WA</region>
159        <code>98052</code>
160      </postal>
161      <email>paulle@microsoft.com</email>
162    </address>
163  </author>
164   
165  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
166    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
170        <street>The Stata Center, Building 32</street>
171        <street>32 Vassar Street</street>
172        <city>Cambridge</city>
173        <region>MA</region>
174        <code>02139</code>
175        <country>USA</country>
176      </postal>
177      <email>timbl@w3.org</email>
178      <uri>http://www.w3.org/People/Berners-Lee/</uri>
179    </address>
180  </author>
181
182  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
183
184<abstract>
185<t>
186   The Hypertext Transfer Protocol (HTTP) is an application-level
187   protocol for distributed, collaborative, hypermedia information
188   systems. HTTP has been in use by the World Wide Web global information
189   initiative since 1990. This document is Part 2 of the seven-part specification
190   that defines the protocol referred to as "HTTP/1.1" and, taken together,
191   obsoletes RFC 2616 and RFC 2617.  Part 2 defines the semantics of HTTP messages
192   as expressed by request methods, request-header fields, response status codes,
193   and response-header fields.
194</t>
195</abstract>
196
197<note title="Editorial Note (To be removed by RFC Editor)">
198  <t>
199    This version of the HTTP specification contains only minimal editorial
200    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
201    and authors' addresses).  All other changes are due to partitioning the
202    original into seven mostly independent parts.  The intent is for readers
203    of future drafts to able to use draft 00 as the basis for comparison
204    when the WG makes later changes to the specification text.  This draft
205    will shortly be followed by draft 01 (containing the first round of changes
206    that have already been agreed to on the mailing list). There is no point in
207    reviewing this draft other than to verify that the partitioning has been
208    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
209    will be the editors after draft 00 is submitted.
210  </t>
211  <t>
212    Discussion of this draft should take place on the HTTPBIS working group
213    mailing list (ietf-http-wg@w3.org). The current issues list is
214    at <eref target="http://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/"/>
215    and related documents (including fancy diffs) can be found at
216    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
217  </t>
218</note>
219</front>
220<middle>
221<section title="Introduction" anchor="introduction">
222<t>
223   This document will define aspects of HTTP related to request and response
224   semantics. Right now it only includes the extracted relevant sections of
225   RFC 2616 with only minor edits.
226</t>
227<t>
228   The HTTP protocol is a request/response protocol. A client sends a
229   request to the server in the form of a request method, URI, and
230   protocol version, followed by a MIME-like message containing request
231   modifiers, client information, and possible body content over a
232   connection with a server. The server responds with a status line,
233   including the message's protocol version and a success or error code,
234   followed by a MIME-like message containing server information, entity
235   metainformation, and possible entity-body content. The relationship
236   between HTTP and MIME is described in &diff2045entity;.
237</t>
238</section>
239
240<section title="Product Tokens" anchor="product.tokens">
241<t>
242   Product tokens are used to allow communicating applications to
243   identify themselves by software name and version. Most fields using
244   product tokens also allow sub-products which form a significant part
245   of the application to be listed, separated by white space. By
246   convention, the products are listed in order of their significance
247   for identifying the application.
248</t>
249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
250    product         = token ["/" product-version]
251    product-version = token
252</artwork></figure>
253<t>
254   Examples:
255</t>
256<figure><artwork type="example">
257    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
258    Server: Apache/0.8.4
259</artwork></figure>
260<t>
261   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
262   used for advertising or other non-essential information. Although any
263   token character &MAY; appear in a product-version, this token &SHOULD;
264   only be used for a version identifier (i.e., successive versions of
265   the same product &SHOULD; only differ in the product-version portion of
266   the product value).
267</t>
268</section>
269
270<section title="Method" anchor="method">
271<t>
272   The Method  token indicates the method to be performed on the
273   resource identified by the Request-URI. The method is case-sensitive.
274</t>
275<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
276    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
277                   | "GET"                    ; <xref target="GET"/>
278                   | "HEAD"                   ; <xref target="HEAD"/>
279                   | "POST"                   ; <xref target="POST"/>
280                   | "PUT"                    ; <xref target="PUT"/>
281                   | "DELETE"                 ; <xref target="DELETE"/>
282                   | "TRACE"                  ; <xref target="TRACE"/>
283                   | "CONNECT"                ; <xref target="CONNECT"/>
284                   | extension-method
285    extension-method = token
286</artwork></figure>
287<t>
288   The list of methods allowed by a resource can be specified in an
289   Allow header field (<xref target="header.allow"/>). The return code of the response
290   always notifies the client whether a method is currently allowed on a
291   resource, since the set of allowed methods can change dynamically. An
292   origin server &SHOULD; return the status code 405 (Method Not Allowed)
293   if the method is known by the origin server but not allowed for the
294   requested resource, and 501 (Not Implemented) if the method is
295   unrecognized or not implemented by the origin server. The methods GET
296   and HEAD &MUST; be supported by all general-purpose servers. All other
297   methods are &OPTIONAL;; however, if the above methods are implemented,
298   they &MUST; be implemented with the same semantics as those specified
299   in <xref target="method.definitions"/>.
300</t>
301</section>
302
303<section title="Request Header Fields" anchor="request.header.fields">
304<t>
305   The request-header fields allow the client to pass additional
306   information about the request, and about the client itself, to the
307   server. These fields act as request modifiers, with semantics
308   equivalent to the parameters on a programming language method
309   invocation.
310</t>
311<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
312    request-header = Accept                   ; &header-accept;
313                   | Accept-Charset           ; &header-accept-charset;
314                   | Accept-Encoding          ; &header-accept-encoding;
315                   | Accept-Language          ; &header-accept-language;
316                   | Authorization            ; &header-authorization;
317                   | Expect                   ; <xref target="header.expect"/>
318                   | From                     ; <xref target="header.from"/>
319                   | Host                     ; &header-host;
320                   | If-Match                 ; &header-if-match;
321                   | If-Modified-Since        ; &header-if-modified-since;
322                   | If-None-Match            ; &header-if-none-match;
323                   | If-Range                 ; &header-if-range;
324                   | If-Unmodified-Since      ; &header-if-unmodified-since;
325                   | Max-Forwards             ; <xref target="header.max-forwards"/>
326                   | Proxy-Authorization      ; &header-proxy-authorization;
327                   | Range                    ; &header-range;
328                   | Referer                  ; <xref target="header.referer"/>
329                   | TE                       ; &header-te;
330                   | User-Agent               ; <xref target="header.user-agent"/>
331</artwork></figure>
332<t>
333   Request-header field names can be extended reliably only in
334   combination with a change in the protocol version. However, new or
335   experimental header fields &MAY; be given the semantics of request-header
336   fields if all parties in the communication recognize them to
337   be request-header fields. Unrecognized header fields are treated as
338   entity-header fields.
339</t>
340</section>
341
342<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
343<t>
344   The Status-Code element is a 3-digit integer result code of the
345   attempt to understand and satisfy the request. These codes are fully
346   defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
347   textual description of the Status-Code. The Status-Code is intended
348   for use by automata and the Reason-Phrase is intended for the human
349   user. The client is not required to examine or display the Reason-Phrase.
350</t>
351<t> 
352   The individual values of the numeric status codes defined for
353   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
354   presented below. The reason phrases listed here are only
355   recommendations -- they &MAY; be replaced by local equivalents without
356   affecting the protocol.
357</t>
358<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"/>
359   Status-Code    =
360         "100"  ; <xref target="status.100"/>: Continue
361       | "101"  ; <xref target="status.101"/>: Switching Protocols
362       | "200"  ; <xref target="status.200"/>: OK
363       | "201"  ; <xref target="status.201"/>: Created
364       | "202"  ; <xref target="status.202"/>: Accepted
365       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
366       | "204"  ; <xref target="status.204"/>: No Content
367       | "205"  ; <xref target="status.205"/>: Reset Content
368       | "206"  ; <xref target="status.206"/>: Partial Content
369       | "300"  ; <xref target="status.300"/>: Multiple Choices
370       | "301"  ; <xref target="status.301"/>: Moved Permanently
371       | "302"  ; <xref target="status.302"/>: Found
372       | "303"  ; <xref target="status.303"/>: See Other
373       | "304"  ; <xref target="status.304"/>: Not Modified
374       | "305"  ; <xref target="status.305"/>: Use Proxy
375       | "307"  ; <xref target="status.307"/>: Temporary Redirect
376       | "400"  ; <xref target="status.400"/>: Bad Request
377       | "401"  ; <xref target="status.401"/>: Unauthorized
378       | "402"  ; <xref target="status.402"/>: Payment Required
379       | "403"  ; <xref target="status.403"/>: Forbidden
380       | "404"  ; <xref target="status.404"/>: Not Found
381       | "405"  ; <xref target="status.405"/>: Method Not Allowed
382       | "406"  ; <xref target="status.406"/>: Not Acceptable
383       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
384       | "408"  ; <xref target="status.408"/>: Request Time-out
385       | "409"  ; <xref target="status.409"/>: Conflict
386       | "410"  ; <xref target="status.410"/>: Gone
387       | "411"  ; <xref target="status.411"/>: Length Required
388       | "412"  ; <xref target="status.412"/>: Precondition Failed
389       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
390       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
391       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
392       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
393       | "417"  ; <xref target="status.417"/>: Expectation Failed
394       | "500"  ; <xref target="status.500"/>: Internal Server Error
395       | "501"  ; <xref target="status.501"/>: Not Implemented
396       | "502"  ; <xref target="status.502"/>: Bad Gateway
397       | "503"  ; <xref target="status.503"/>: Service Unavailable
398       | "504"  ; <xref target="status.504"/>: Gateway Time-out
399       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
400       | extension-code
401
402   extension-code = 3DIGIT
403   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
404</artwork></figure>
405<t>
406   HTTP status codes are extensible. HTTP applications are not required
407   to understand the meaning of all registered status codes, though such
408   understanding is obviously desirable. However, applications &MUST;
409   understand the class of any status code, as indicated by the first
410   digit, and treat any unrecognized response as being equivalent to the
411   x00 status code of that class, with the exception that an
412   unrecognized response &MUST-NOT; be cached. For example, if an
413   unrecognized status code of 431 is received by the client, it can
414   safely assume that there was something wrong with its request and
415   treat the response as if it had received a 400 status code. In such
416   cases, user agents &SHOULD; present to the user the entity returned
417   with the response, since that entity is likely to include human-readable
418   information which will explain the unusual status.
419</t>
420</section>
421
422<section title="Response Header Fields" anchor="response.header.fields">
423<t>
424   The response-header fields allow the server to pass additional
425   information about the response which cannot be placed in the Status-Line.
426   These header fields give information about the server and about
427   further access to the resource identified by the Request-URI.
428</t>
429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
430    response-header = Accept-Ranges           ; &header-accept-ranges;
431                    | Age                     ; &header-age;
432                    | ETag                    ; &header-etag;
433                    | Location                ; <xref target="header.location"/>
434                    | Proxy-Authenticate      ; &header-proxy-authenticate;
435                    | Retry-After             ; <xref target="header.retry-after"/>
436                    | Server                  ; <xref target="header.server"/>
437                    | Vary                    ; &header-vary;
438                    | WWW-Authenticate        ; &header-www-authenticate;
439</artwork></figure>
440<t>
441   Response-header field names can be extended reliably only in
442   combination with a change in the protocol version. However, new or
443   experimental header fields &MAY; be given the semantics of response-header
444   fields if all parties in the communication recognize them to
445   be response-header fields. Unrecognized header fields are treated as
446   entity-header fields.
447</t>
448</section>
449
450<section title="Entity" anchor="entity">
451<t>
452   Request and Response messages &MAY; transfer an entity if not otherwise
453   restricted by the request method or response status code. An entity
454   consists of entity-header fields and an entity-body, although some
455   responses will only include the entity-headers. HTTP entity-body and
456   entity-header fields are defined in &payload;.
457</t>
458<t>
459   An entity-body is only present in a message when a message-body is
460   present, as described in &message-body;. The entity-body is obtained
461   from the message-body by decoding any Transfer-Encoding that might
462   have been applied to ensure safe and proper transfer of the message.
463</t>
464</section>
465
466
467<section title="Method Definitions" anchor="method.definitions">
468<t>
469   The set of common methods for HTTP/1.1 is defined below. Although
470   this set can be expanded, additional methods cannot be assumed to
471   share the same semantics for separately extended clients and servers.
472
473   The Host request-header field (&header-host;) &MUST; accompany all
474   HTTP/1.1 requests.
475</t>
476
477<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
478
479<section title="Safe Methods" anchor="safe.methods">
480<t>
481   Implementors should be aware that the software represents the user in
482   their interactions over the Internet, and should be careful to allow
483   the user to be aware of any actions they might take which may have an
484   unexpected significance to themselves or others.
485</t>
486<t>
487   In particular, the convention has been established that the GET and
488   HEAD methods &SHOULD-NOT;  have the significance of taking an action
489   other than retrieval. These methods ought to be considered "safe".
490   This allows user agents to represent other methods, such as POST, PUT
491   and DELETE, in a special way, so that the user is made aware of the
492   fact that a possibly unsafe action is being requested.
493</t>
494<t>
495   Naturally, it is not possible to ensure that the server does not
496   generate side-effects as a result of performing a GET request; in
497   fact, some dynamic resources consider that a feature. The important
498   distinction here is that the user did not request the side-effects,
499   so therefore cannot be held accountable for them.
500</t>
501</section>
502
503<section title="Idempotent Methods" anchor="idempotent.methods">
504<t>
505   Methods can also have the property of "idempotence" in that (aside
506   from error or expiration issues) the side-effects of N &gt; 0 identical
507   requests is the same as for a single request. The methods GET, HEAD,
508   PUT and DELETE share this property. Also, the methods OPTIONS and
509   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
510</t>
511<t>
512   However, it is possible that a sequence of several requests is non-idempotent,
513   even if all of the methods executed in that sequence are
514   idempotent. (A sequence is idempotent if a single execution of the
515   entire sequence always yields a result that is not changed by a
516   reexecution of all, or part, of that sequence.) For example, a
517   sequence is non-idempotent if its result depends on a value that is
518   later modified in the same sequence.
519</t>
520<t>
521   A sequence that never has side effects is idempotent, by definition
522   (provided that no concurrent operations are being executed on the
523   same set of resources).
524</t>
525</section>
526</section>
527
528<section title="OPTIONS" anchor="OPTIONS">
529  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
530  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
531<t>
532   The OPTIONS method represents a request for information about the
533   communication options available on the request/response chain
534   identified by the Request-URI. This method allows the client to
535   determine the options and/or requirements associated with a resource,
536   or the capabilities of a server, without implying a resource action
537   or initiating a resource retrieval.
538</t>
539<t>
540   Responses to this method are not cacheable.
541</t>
542<t>
543   If the OPTIONS request includes an entity-body (as indicated by the
544   presence of Content-Length or Transfer-Encoding), then the media type
545   &MUST; be indicated by a Content-Type field. Although this
546   specification does not define any use for such a body, future
547   extensions to HTTP might use the OPTIONS body to make more detailed
548   queries on the server. A server that does not support such an
549   extension &MAY; discard the request body.
550</t>
551<t>
552   If the Request-URI is an asterisk ("*"), the OPTIONS request is
553   intended to apply to the server in general rather than to a specific
554   resource. Since a server's communication options typically depend on
555   the resource, the "*" request is only useful as a "ping" or "no-op"
556   type of method; it does nothing beyond allowing the client to test
557   the capabilities of the server. For example, this can be used to test
558   a proxy for HTTP/1.1 compliance (or lack thereof).
559</t>
560<t>
561   If the Request-URI is not an asterisk, the OPTIONS request applies
562   only to the options that are available when communicating with that
563   resource.
564</t>
565<t>
566   A 200 response &SHOULD; include any header fields that indicate
567   optional features implemented by the server and applicable to that
568   resource (e.g., Allow), possibly including extensions not defined by
569   this specification. The response body, if any, &SHOULD; also include
570   information about the communication options. The format for such a
571   body is not defined by this specification, but might be defined by
572   future extensions to HTTP. Content negotiation &MAY; be used to select
573   the appropriate response format. If no response body is included, the
574   response &MUST; include a Content-Length field with a field-value of
575   "0".
576</t>
577<t>
578   The Max-Forwards request-header field &MAY; be used to target a
579   specific proxy in the request chain. When a proxy receives an OPTIONS
580   request on an absoluteURI for which request forwarding is permitted,
581   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
582   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
583   instead, the proxy &SHOULD; respond with its own communication options.
584   If the Max-Forwards field-value is an integer greater than zero, the
585   proxy &MUST; decrement the field-value when it forwards the request. If
586   no Max-Forwards field is present in the request, then the forwarded
587   request &MUST-NOT; include a Max-Forwards field.
588</t>
589</section>
590
591<section title="GET" anchor="GET">
592  <iref primary="true" item="GET method" x:for-anchor=""/>
593  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
594<t>
595   The GET method means retrieve whatever information (in the form of an
596   entity) is identified by the Request-URI. If the Request-URI refers
597   to a data-producing process, it is the produced data which shall be
598   returned as the entity in the response and not the source text of the
599   process, unless that text happens to be the output of the process.
600</t>
601<t>
602   The semantics of the GET method change to a "conditional GET" if the
603   request message includes an If-Modified-Since, If-Unmodified-Since,
604   If-Match, If-None-Match, or If-Range header field. A conditional GET
605   method requests that the entity be transferred only under the
606   circumstances described by the conditional header field(s). The
607   conditional GET method is intended to reduce unnecessary network
608   usage by allowing cached entities to be refreshed without requiring
609   multiple requests or transferring data already held by the client.
610</t>
611<t>
612   The semantics of the GET method change to a "partial GET" if the
613   request message includes a Range header field. A partial GET requests
614   that only part of the entity be transferred, as described in &header-range;.
615   The partial GET method is intended to reduce unnecessary
616   network usage by allowing partially-retrieved entities to be
617   completed without transferring data already held by the client.
618</t>
619<t>
620   The response to a GET request is cacheable if and only if it meets
621   the requirements for HTTP caching described in &caching;.
622</t>
623<t>
624   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
625</t>
626</section>
627
628<section title="HEAD" anchor="HEAD">
629  <iref primary="true" item="HEAD method" x:for-anchor=""/>
630  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
631<t>
632   The HEAD method is identical to GET except that the server &MUST-NOT;
633   return a message-body in the response. The metainformation contained
634   in the HTTP headers in response to a HEAD request &SHOULD; be identical
635   to the information sent in response to a GET request. This method can
636   be used for obtaining metainformation about the entity implied by the
637   request without transferring the entity-body itself. This method is
638   often used for testing hypertext links for validity, accessibility,
639   and recent modification.
640</t>
641<t>
642   The response to a HEAD request &MAY; be cacheable in the sense that the
643   information contained in the response &MAY; be used to update a
644   previously cached entity from that resource. If the new field values
645   indicate that the cached entity differs from the current entity (as
646   would be indicated by a change in Content-Length, Content-MD5, ETag
647   or Last-Modified), then the cache &MUST; treat the cache entry as
648   stale.
649</t>
650</section>
651
652<section title="POST" anchor="POST">
653  <iref primary="true" item="POST method" x:for-anchor=""/>
654  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
655<t>
656   The POST method is used to request that the origin server accept the
657   entity enclosed in the request as a new subordinate of the resource
658   identified by the Request-URI in the Request-Line. POST is designed
659   to allow a uniform method to cover the following functions:
660  <list style="symbols">
661    <t>
662      Annotation of existing resources;
663    </t>
664    <t>
665        Posting a message to a bulletin board, newsgroup, mailing list,
666        or similar group of articles;
667    </t>
668    <t>
669        Providing a block of data, such as the result of submitting a
670        form, to a data-handling process;
671    </t>
672    <t>
673        Extending a database through an append operation.
674    </t>
675  </list>
676</t>
677<t>
678   The actual function performed by the POST method is determined by the
679   server and is usually dependent on the Request-URI. The posted entity
680   is subordinate to that URI in the same way that a file is subordinate
681   to a directory containing it, a news article is subordinate to a
682   newsgroup to which it is posted, or a record is subordinate to a
683   database.
684</t>
685<t>
686   The action performed by the POST method might not result in a
687   resource that can be identified by a URI. In this case, either 200
688   (OK) or 204 (No Content) is the appropriate response status,
689   depending on whether or not the response includes an entity that
690   describes the result.
691</t>
692<t>
693   If a resource has been created on the origin server, the response
694   &SHOULD; be 201 (Created) and contain an entity which describes the
695   status of the request and refers to the new resource, and a Location
696   header (see <xref target="header.location"/>).
697</t>
698<t>
699   Responses to this method are not cacheable, unless the response
700   includes appropriate Cache-Control or Expires header fields. However,
701   the 303 (See Other) response can be used to direct the user agent to
702   retrieve a cacheable resource.
703</t>
704<t>
705   POST requests &MUST; obey the message transmission requirements set out
706   in &message-transmission-req;.
707</t>
708<t>
709   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
710</t>
711</section>
712
713<section title="PUT" anchor="PUT">
714  <iref primary="true" item="PUT method" x:for-anchor=""/>
715  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
716<t>
717   The PUT method requests that the enclosed entity be stored under the
718   supplied Request-URI. If the Request-URI refers to an already
719   existing resource, the enclosed entity &SHOULD; be considered as a
720   modified version of the one residing on the origin server. If the
721   Request-URI does not point to an existing resource, and that URI is
722   capable of being defined as a new resource by the requesting user
723   agent, the origin server can create the resource with that URI. If a
724   new resource is created, the origin server &MUST; inform the user agent
725   via the 201 (Created) response. If an existing resource is modified,
726   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
727   to indicate successful completion of the request. If the resource
728   could not be created or modified with the Request-URI, an appropriate
729   error response &SHOULD; be given that reflects the nature of the
730   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
731   (e.g. Content-Range) headers that it does not understand or implement
732   and &MUST; return a 501 (Not Implemented) response in such cases.
733</t>
734<t>
735   If the request passes through a cache and the Request-URI identifies
736   one or more currently cached entities, those entries &SHOULD; be
737   treated as stale. Responses to this method are not cacheable.
738</t>
739<t>
740   The fundamental difference between the POST and PUT requests is
741   reflected in the different meaning of the Request-URI. The URI in a
742   POST request identifies the resource that will handle the enclosed
743   entity. That resource might be a data-accepting process, a gateway to
744   some other protocol, or a separate entity that accepts annotations.
745   In contrast, the URI in a PUT request identifies the entity enclosed
746   with the request -- the user agent knows what URI is intended and the
747   server &MUST-NOT; attempt to apply the request to some other resource.
748   If the server desires that the request be applied to a different URI,
749   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
750   then make its own decision regarding whether or not to redirect the
751   request.
752</t>
753<t>
754   A single resource &MAY; be identified by many different URIs. For
755   example, an article might have a URI for identifying "the current
756   version" which is separate from the URI identifying each particular
757   version. In this case, a PUT request on a general URI might result in
758   several other URIs being defined by the origin server.
759</t>
760<t>
761   HTTP/1.1 does not define how a PUT method affects the state of an
762   origin server.
763</t>
764<t>
765   PUT requests &MUST; obey the message transmission requirements set out
766   in &message-transmission-req;.
767</t>
768<t>
769   Unless otherwise specified for a particular entity-header, the
770   entity-headers in the PUT request &SHOULD; be applied to the resource
771   created or modified by the PUT.
772</t>
773</section>
774
775<section title="DELETE" anchor="DELETE">
776  <iref primary="true" item="DELETE method" x:for-anchor=""/>
777  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
778<t>
779   The DELETE method requests that the origin server delete the resource
780   identified by the Request-URI. This method &MAY; be overridden by human
781   intervention (or other means) on the origin server. The client cannot
782   be guaranteed that the operation has been carried out, even if the
783   status code returned from the origin server indicates that the action
784   has been completed successfully. However, the server &SHOULD-NOT; 
785   indicate success unless, at the time the response is given, it
786   intends to delete the resource or move it to an inaccessible
787   location.
788</t>
789<t>
790   A successful response &SHOULD; be 200 (OK) if the response includes an
791   entity describing the status, 202 (Accepted) if the action has not
792   yet been enacted, or 204 (No Content) if the action has been enacted
793   but the response does not include an entity.
794</t>
795<t>
796   If the request passes through a cache and the Request-URI identifies
797   one or more currently cached entities, those entries &SHOULD; be
798   treated as stale. Responses to this method are not cacheable.
799</t>
800</section>
801
802<section title="TRACE" anchor="TRACE">
803  <iref primary="true" item="TRACE method" x:for-anchor=""/>
804  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
805<t>
806   The TRACE method is used to invoke a remote, application-layer loop-back
807   of the request message. The final recipient of the request
808   &SHOULD; reflect the message received back to the client as the
809   entity-body of a 200 (OK) response. The final recipient is either the
810   origin server or the first proxy or gateway to receive a Max-Forwards
811   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
812   &MUST-NOT; include an entity.
813</t>
814<t>
815   TRACE allows the client to see what is being received at the other
816   end of the request chain and use that data for testing or diagnostic
817   information. The value of the Via header field (&header-via;) is of
818   particular interest, since it acts as a trace of the request chain.
819   Use of the Max-Forwards header field allows the client to limit the
820   length of the request chain, which is useful for testing a chain of
821   proxies forwarding messages in an infinite loop.
822</t>
823<t>
824   If the request is valid, the response &SHOULD; contain the entire
825   request message in the entity-body, with a Content-Type of
826   "message/http". Responses to this method &MUST-NOT; be cached.
827</t>
828</section>
829
830<section title="CONNECT" anchor="CONNECT">
831  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
832  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
833<t>
834   This specification reserves the method name CONNECT for use with a
835   proxy that can dynamically switch to being a tunnel (e.g. SSL
836   tunneling <xref target="Luo1998"/>).
837</t>
838</section>
839</section>
840
841
842<section title="Status Code Definitions" anchor="status.codes">
843<t>
844   Each Status-Code is described below, including a description of which
845   method(s) it can follow and any metainformation required in the
846   response.
847</t>
848
849<section title="Informational 1xx" anchor="status.1xx">
850<t>
851   This class of status code indicates a provisional response,
852   consisting only of the Status-Line and optional headers, and is
853   terminated by an empty line. There are no required headers for this
854   class of status code. Since HTTP/1.0 did not define any 1xx status
855   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
856   except under experimental conditions.
857</t>
858<t>
859   A client &MUST; be prepared to accept one or more 1xx status responses
860   prior to a regular response, even if the client does not expect a 100
861   (Continue) status message. Unexpected 1xx status responses &MAY; be
862   ignored by a user agent.
863</t>
864<t>
865   Proxies &MUST; forward 1xx responses, unless the connection between the
866   proxy and its client has been closed, or unless the proxy itself
867   requested the generation of the 1xx response. (For example, if a
868   proxy adds a "Expect: 100-continue" field when it forwards a request,
869   then it need not forward the corresponding 100 (Continue)
870   response(s).)
871</t>
872
873<section title="100 Continue" anchor="status.100">
874  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
875  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
876<t>
877   The client &SHOULD; continue with its request. This interim response is
878   used to inform the client that the initial part of the request has
879   been received and has not yet been rejected by the server. The client
880   &SHOULD; continue by sending the remainder of the request or, if the
881   request has already been completed, ignore this response. The server
882   &MUST; send a final response after the request has been completed. See
883   &use100; for detailed discussion of the use and handling of this
884   status code.
885</t>
886</section>
887
888<section title="101 Switching Protocols" anchor="status.101">
889  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
890  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
891<t>
892   The server understands and is willing to comply with the client's
893   request, via the Upgrade message header field (&header-upgrade;), for a
894   change in the application protocol being used on this connection. The
895   server will switch protocols to those defined by the response's
896   Upgrade header field immediately after the empty line which
897   terminates the 101 response.
898</t>
899<t>
900   The protocol &SHOULD; be switched only when it is advantageous to do
901   so. For example, switching to a newer version of HTTP is advantageous
902   over older versions, and switching to a real-time, synchronous
903   protocol might be advantageous when delivering resources that use
904   such features.
905</t>
906</section>
907</section>
908
909<section title="Successful 2xx" anchor="status.2xx">
910<t>
911   This class of status code indicates that the client's request was
912   successfully received, understood, and accepted.
913</t>
914
915<section title="200 OK" anchor="status.200">
916  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
917  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
918<t>
919   The request has succeeded. The information returned with the response
920   is dependent on the method used in the request, for example:
921  <list style="hanging">
922    <t hangText="GET">
923          an entity corresponding to the requested resource is sent in
924          the response;
925    </t>
926    <t hangText="HEAD">
927          the entity-header fields corresponding to the requested
928          resource are sent in the response without any message-body;
929    </t>
930    <t hangText="POST">
931      an entity describing or containing the result of the action;
932    </t>
933    <t hangText="TRACE">
934      an entity containing the request message as received by the
935      end server.
936    </t>
937  </list>
938</t>
939</section>
940
941<section title="201 Created" anchor="status.201">
942  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
943  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
944<t>
945   The request has been fulfilled and resulted in a new resource being
946   created. The newly created resource can be referenced by the URI(s)
947   returned in the entity of the response, with the most specific URI
948   for the resource given by a Location header field. The response
949   &SHOULD; include an entity containing a list of resource
950   characteristics and location(s) from which the user or user agent can
951   choose the one most appropriate. The entity format is specified by
952   the media type given in the Content-Type header field. The origin
953   server &MUST; create the resource before returning the 201 status code.
954   If the action cannot be carried out immediately, the server &SHOULD;
955   respond with 202 (Accepted) response instead.
956</t>
957<t>
958   A 201 response &MAY; contain an ETag response header field indicating
959   the current value of the entity tag for the requested variant just
960   created, see &header-etag;.
961</t>
962</section>
963
964<section title="202 Accepted" anchor="status.202">
965  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
966  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
967<t>
968   The request has been accepted for processing, but the processing has
969   not been completed.  The request might or might not eventually be
970   acted upon, as it might be disallowed when processing actually takes
971   place. There is no facility for re-sending a status code from an
972   asynchronous operation such as this.
973</t>
974<t>
975   The 202 response is intentionally non-committal. Its purpose is to
976   allow a server to accept a request for some other process (perhaps a
977   batch-oriented process that is only run once per day) without
978   requiring that the user agent's connection to the server persist
979   until the process is completed. The entity returned with this
980   response &SHOULD; include an indication of the request's current status
981   and either a pointer to a status monitor or some estimate of when the
982   user can expect the request to be fulfilled.
983</t>
984</section>
985
986<section title="203 Non-Authoritative Information" anchor="status.203">
987  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
988  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
989<t>
990   The returned metainformation in the entity-header is not the
991   definitive set as available from the origin server, but is gathered
992   from a local or a third-party copy. The set presented &MAY; be a subset
993   or superset of the original version. For example, including local
994   annotation information about the resource might result in a superset
995   of the metainformation known by the origin server. Use of this
996   response code is not required and is only appropriate when the
997   response would otherwise be 200 (OK).
998</t>
999</section>
1000
1001<section title="204 No Content" anchor="status.204">
1002  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1003  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1004<t>
1005   The server has fulfilled the request but does not need to return an
1006   entity-body, and might want to return updated metainformation. The
1007   response &MAY; include new or updated metainformation in the form of
1008   entity-headers, which if present &SHOULD; be associated with the
1009   requested variant.
1010</t>
1011<t>
1012   If the client is a user agent, it &SHOULD-NOT;  change its document view
1013   from that which caused the request to be sent. This response is
1014   primarily intended to allow input for actions to take place without
1015   causing a change to the user agent's active document view, although
1016   any new or updated metainformation &SHOULD; be applied to the document
1017   currently in the user agent's active view.
1018</t>
1019<t>
1020   The 204 response &MUST-NOT; include a message-body, and thus is always
1021   terminated by the first empty line after the header fields.
1022</t>
1023</section>
1024
1025<section title="205 Reset Content" anchor="status.205">
1026  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1027  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1028<t>
1029   The server has fulfilled the request and the user agent &SHOULD; reset
1030   the document view which caused the request to be sent. This response
1031   is primarily intended to allow input for actions to take place via
1032   user input, followed by a clearing of the form in which the input is
1033   given so that the user can easily initiate another input action. The
1034   response &MUST-NOT; include an entity.
1035</t>
1036</section>
1037
1038<section title="206 Partial Content" anchor="status.206">
1039  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1040  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1041<t>
1042   The server has fulfilled the partial GET request for the resource
1043   and the enclosed entity is a partial representation as defined in &range;.
1044</t>
1045</section>
1046</section>
1047
1048<section title="Redirection 3xx" anchor="status.3xx">
1049<t>
1050   This class of status code indicates that further action needs to be
1051   taken by the user agent in order to fulfill the request.  The action
1052   required &MAY; be carried out by the user agent without interaction
1053   with the user if and only if the method used in the second request is
1054   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1055   such loops generate network traffic for each redirection.
1056  <list><t>
1057      <x:h>Note:</x:h> previous versions of this specification recommended a
1058      maximum of five redirections. Content developers should be aware
1059      that there might be clients that implement such a fixed
1060      limitation.
1061  </t></list>
1062</t>
1063
1064<section title="300 Multiple Choices" anchor="status.300">
1065  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1066  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1067<t>
1068   The requested resource corresponds to any one of a set of
1069   representations, each with its own specific location, and agent-driven
1070   negotiation information (&content-negotiation;) is being provided so that
1071   the user (or user agent) can select a preferred representation and
1072   redirect its request to that location.
1073</t>
1074<t>
1075   Unless it was a HEAD request, the response &SHOULD; include an entity
1076   containing a list of resource characteristics and location(s) from
1077   which the user or user agent can choose the one most appropriate. The
1078   entity format is specified by the media type given in the Content-Type
1079   header field. Depending upon the format and the capabilities of
1080   the user agent, selection of the most appropriate choice &MAY; be
1081   performed automatically. However, this specification does not define
1082   any standard for such automatic selection.
1083</t>
1084<t>
1085   If the server has a preferred choice of representation, it &SHOULD;
1086   include the specific URI for that representation in the Location
1087   field; user agents &MAY; use the Location field value for automatic
1088   redirection. This response is cacheable unless indicated otherwise.
1089</t>
1090</section>
1091
1092<section title="301 Moved Permanently" anchor="status.301">
1093  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1094  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1095<t>
1096   The requested resource has been assigned a new permanent URI and any
1097   future references to this resource &SHOULD; use one of the returned
1098   URIs.  Clients with link editing capabilities ought to automatically
1099   re-link references to the Request-URI to one or more of the new
1100   references returned by the server, where possible. This response is
1101   cacheable unless indicated otherwise.
1102</t>
1103<t>
1104   The new permanent URI &SHOULD; be given by the Location field in the
1105   response. Unless the request method was HEAD, the entity of the
1106   response &SHOULD; contain a short hypertext note with a hyperlink to
1107   the new URI(s).
1108</t>
1109<t>
1110   If the 301 status code is received in response to a request other
1111   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1112   request unless it can be confirmed by the user, since this might
1113   change the conditions under which the request was issued.
1114  <list><t>
1115      <x:h>Note:</x:h> When automatically redirecting a POST request after
1116      receiving a 301 status code, some existing HTTP/1.0 user agents
1117      will erroneously change it into a GET request.
1118  </t></list>
1119</t>
1120</section>
1121
1122<section title="302 Found" anchor="status.302">
1123  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1124  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1125<t>
1126   The requested resource resides temporarily under a different URI.
1127   Since the redirection might be altered on occasion, the client &SHOULD;
1128   continue to use the Request-URI for future requests.  This response
1129   is only cacheable if indicated by a Cache-Control or Expires header
1130   field.
1131</t>
1132<t>
1133   The temporary URI &SHOULD; be given by the Location field in the
1134   response. Unless the request method was HEAD, the entity of the
1135   response &SHOULD; contain a short hypertext note with a hyperlink to
1136   the new URI(s).
1137</t>
1138<t>
1139   If the 302 status code is received in response to a request other
1140   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1141   request unless it can be confirmed by the user, since this might
1142   change the conditions under which the request was issued.
1143  <list><t>
1144      <x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
1145      to change the method on the redirected request.  However, most
1146      existing user agent implementations treat 302 as if it were a 303
1147      response, performing a GET on the Location field-value regardless
1148      of the original request method. The status codes 303 and 307 have
1149      been added for servers that wish to make unambiguously clear which
1150      kind of reaction is expected of the client.
1151  </t></list>
1152</t>
1153</section>
1154
1155<section title="303 See Other" anchor="status.303">
1156  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1157  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1158<t>
1159   The response to the request can be found under a different URI and
1160   &SHOULD; be retrieved using a GET method on that resource. This method
1161   exists primarily to allow the output of a POST-activated script to
1162   redirect the user agent to a selected resource. The new URI is not a
1163   substitute reference for the originally requested resource. The 303
1164   response &MUST-NOT; be cached, but the response to the second
1165   (redirected) request might be cacheable.
1166</t>
1167<t>
1168   The different URI &SHOULD; be given by the Location field in the
1169   response. Unless the request method was HEAD, the entity of the
1170   response &SHOULD; contain a short hypertext note with a hyperlink to
1171   the new URI(s).
1172  <list><t>
1173      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1174      status. When interoperability with such clients is a concern, the
1175      302 status code may be used instead, since most user agents react
1176      to a 302 response as described here for 303.
1177  </t></list>
1178</t>
1179</section>
1180
1181<section title="304 Not Modified" anchor="status.304">
1182  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1183  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1184<t>
1185   If the client has performed a conditional GET request and access is
1186   allowed, but the document has not been modified, the server &SHOULD;
1187   respond with this status code. The 304 response &MUST-NOT; contain a
1188   message-body, and thus is always terminated by the first empty line
1189   after the header fields.
1190</t>
1191<t>
1192   The response &MUST; include the following header fields:
1193  <list style="symbols">
1194    <t>Date, unless its omission is required by [clockless.origin.server.operation]</t>
1195  </list>
1196</t>
1197<t>
1198   If a clockless origin server obeys these rules, and proxies and
1199   clients add their own Date to any response received without one (as
1200   already specified by [RFC 2068], section <xref target="RFC2068" x:sec="14.19" x:fmt="number"/>), caches will operate
1201   correctly.
1202  <list style="symbols">
1203    <t>ETag and/or Content-Location, if the header would have been sent
1204        in a 200 response to the same request</t>
1205    <t>Expires, Cache-Control, and/or Vary, if the field-value might
1206        differ from that sent in any previous response for the same
1207        variant</t>
1208  </list>
1209</t>
1210<t>
1211   If the conditional GET used a strong cache validator (see &caching;),
1212   the response &SHOULD-NOT;  include other entity-headers.
1213   Otherwise (i.e., the conditional GET used a weak validator), the
1214   response &MUST-NOT; include other entity-headers; this prevents
1215   inconsistencies between cached entity-bodies and updated headers.
1216</t>
1217<t>
1218   If a 304 response indicates an entity not currently cached, then the
1219   cache &MUST; disregard the response and repeat the request without the
1220   conditional.
1221</t>
1222<t>
1223   If a cache uses a received 304 response to update a cache entry, the
1224   cache &MUST; update the entry to reflect any new field values given in
1225   the response.
1226</t>
1227</section>
1228
1229<section title="305 Use Proxy" anchor="status.305">
1230  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1231  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1232<t>
1233   The requested resource &MUST; be accessed through the proxy given by
1234   the Location field. The Location field gives the URI of the proxy.
1235   The recipient is expected to repeat this single request via the
1236   proxy. 305 responses &MUST; only be generated by origin servers.
1237  <list><t>
1238      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1239      single request, and to be generated by origin servers only.  Not
1240      observing these limitations has significant security consequences.
1241  </t></list>
1242</t>
1243</section>
1244
1245<section title="306 (Unused)" anchor="status.306">
1246  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1247  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1248<t>
1249   The 306 status code was used in a previous version of the
1250   specification, is no longer used, and the code is reserved.
1251</t>
1252</section>
1253
1254<section title="307 Temporary Redirect" anchor="status.307">
1255  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1256  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1257<t>
1258   The requested resource resides temporarily under a different URI.
1259   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1260   continue to use the Request-URI for future requests.  This response
1261   is only cacheable if indicated by a Cache-Control or Expires header
1262   field.
1263</t>
1264<t>
1265   The temporary URI &SHOULD; be given by the Location field in the
1266   response. Unless the request method was HEAD, the entity of the
1267   response &SHOULD; contain a short hypertext note with a hyperlink to
1268   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1269   understand the 307 status. Therefore, the note &SHOULD; contain the
1270   information necessary for a user to repeat the original request on
1271   the new URI.
1272</t>
1273<t>
1274   If the 307 status code is received in response to a request other
1275   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1276   request unless it can be confirmed by the user, since this might
1277   change the conditions under which the request was issued.
1278</t>
1279</section>
1280</section>
1281
1282<section title="Client Error 4xx" anchor="status.4xx">
1283<t>
1284   The 4xx class of status code is intended for cases in which the
1285   client seems to have erred. Except when responding to a HEAD request,
1286   the server &SHOULD; include an entity containing an explanation of the
1287   error situation, and whether it is a temporary or permanent
1288   condition. These status codes are applicable to any request method.
1289   User agents &SHOULD; display any included entity to the user.
1290</t>
1291<t>
1292   If the client is sending data, a server implementation using TCP
1293   &SHOULD; be careful to ensure that the client acknowledges receipt of
1294   the packet(s) containing the response, before the server closes the
1295   input connection. If the client continues sending data to the server
1296   after the close, the server's TCP stack will send a reset packet to
1297   the client, which may erase the client's unacknowledged input buffers
1298   before they can be read and interpreted by the HTTP application.
1299</t>
1300
1301<section title="400 Bad Request" anchor="status.400">
1302  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1303  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1304<t>
1305   The request could not be understood by the server due to malformed
1306   syntax. The client &SHOULD-NOT;  repeat the request without
1307   modifications.
1308</t>
1309</section>
1310
1311<section title="401 Unauthorized" anchor="status.401">
1312  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1313  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1314<t>
1315   The request requires user authentication. The response &MUST; include a
1316   WWW-Authenticate header field (&header-www-authenticate;) containing a challenge
1317   applicable to the requested resource. The client &MAY; repeat the
1318   request with a suitable Authorization header field (&header-authorization;). If
1319   the request already included Authorization credentials, then the 401
1320   response indicates that authorization has been refused for those
1321   credentials. If the 401 response contains the same challenge as the
1322   prior response, and the user agent has already attempted
1323   authentication at least once, then the user &SHOULD; be presented the
1324   entity that was given in the response, since that entity might
1325   include relevant diagnostic information. HTTP access authentication
1326   is explained in "HTTP Authentication: Basic and Digest Access
1327   Authentication" <xref target="RFC2617"/>.
1328</t>
1329</section>
1330
1331<section title="402 Payment Required" anchor="status.402">
1332  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1333  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1334<t>
1335   This code is reserved for future use.
1336</t>
1337</section>
1338
1339<section title="403 Forbidden" anchor="status.403">
1340  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1341  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1342<t>
1343   The server understood the request, but is refusing to fulfill it.
1344   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1345   If the request method was not HEAD and the server wishes to make
1346   public why the request has not been fulfilled, it &SHOULD; describe the
1347   reason for the refusal in the entity.  If the server does not wish to
1348   make this information available to the client, the status code 404
1349   (Not Found) can be used instead.
1350</t>
1351</section>
1352
1353<section title="404 Not Found" anchor="status.404">
1354  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1355  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1356<t>
1357   The server has not found anything matching the Request-URI. No
1358   indication is given of whether the condition is temporary or
1359   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1360   knows, through some internally configurable mechanism, that an old
1361   resource is permanently unavailable and has no forwarding address.
1362   This status code is commonly used when the server does not wish to
1363   reveal exactly why the request has been refused, or when no other
1364   response is applicable.
1365</t>
1366</section>
1367
1368<section title="405 Method Not Allowed" anchor="status.405">
1369  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1370  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1371<t>
1372   The method specified in the Request-Line is not allowed for the
1373   resource identified by the Request-URI. The response &MUST; include an
1374   Allow header containing a list of valid methods for the requested
1375   resource.
1376</t>
1377</section>
1378
1379<section title="406 Not Acceptable" anchor="status.406">
1380  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1381  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1382<t>
1383   The resource identified by the request is only capable of generating
1384   response entities which have content characteristics not acceptable
1385   according to the accept headers sent in the request.
1386</t>
1387<t>
1388   Unless it was a HEAD request, the response &SHOULD; include an entity
1389   containing a list of available entity characteristics and location(s)
1390   from which the user or user agent can choose the one most
1391   appropriate. The entity format is specified by the media type given
1392   in the Content-Type header field. Depending upon the format and the
1393   capabilities of the user agent, selection of the most appropriate
1394   choice &MAY; be performed automatically. However, this specification
1395   does not define any standard for such automatic selection.
1396  <list><t>
1397      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1398      not acceptable according to the accept headers sent in the
1399      request. In some cases, this may even be preferable to sending a
1400      406 response. User agents are encouraged to inspect the headers of
1401      an incoming response to determine if it is acceptable.
1402  </t></list>
1403</t>
1404<t>
1405   If the response could be unacceptable, a user agent &SHOULD;
1406   temporarily stop receipt of more data and query the user for a
1407   decision on further actions.
1408</t>
1409</section>
1410
1411<section title="407 Proxy Authentication Required" anchor="status.407">
1412  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1413  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1414<t>
1415   This code is similar to 401 (Unauthorized), but indicates that the
1416   client must first authenticate itself with the proxy. The proxy &MUST;
1417   return a Proxy-Authenticate header field (&header-proxy-authenticate;) containing a
1418   challenge applicable to the proxy for the requested resource. The
1419   client &MAY; repeat the request with a suitable Proxy-Authorization
1420   header field (&header-proxy-authorization;). HTTP access authentication is explained
1421   in "HTTP Authentication: Basic and Digest Access Authentication"
1422   <xref target="RFC2617"/>.
1423</t>
1424</section>
1425
1426<section title="408 Request Timeout" anchor="status.408">
1427  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1428  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1429<t>
1430   The client did not produce a request within the time that the server
1431   was prepared to wait. The client &MAY; repeat the request without
1432   modifications at any later time.
1433</t>
1434</section>
1435
1436<section title="409 Conflict" anchor="status.409">
1437  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1438  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1439<t>
1440   The request could not be completed due to a conflict with the current
1441   state of the resource. This code is only allowed in situations where
1442   it is expected that the user might be able to resolve the conflict
1443   and resubmit the request. The response body &SHOULD; include enough
1444   information for the user to recognize the source of the conflict.
1445   Ideally, the response entity would include enough information for the
1446   user or user agent to fix the problem; however, that might not be
1447   possible and is not required.
1448</t>
1449<t>
1450   Conflicts are most likely to occur in response to a PUT request. For
1451   example, if versioning were being used and the entity being PUT
1452   included changes to a resource which conflict with those made by an
1453   earlier (third-party) request, the server might use the 409 response
1454   to indicate that it can't complete the request. In this case, the
1455   response entity would likely contain a list of the differences
1456   between the two versions in a format defined by the response
1457   Content-Type.
1458</t>
1459</section>
1460
1461<section title="410 Gone" anchor="status.410">
1462  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1463  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1464<t>
1465   The requested resource is no longer available at the server and no
1466   forwarding address is known. This condition is expected to be
1467   considered permanent. Clients with link editing capabilities &SHOULD;
1468   delete references to the Request-URI after user approval. If the
1469   server does not know, or has no facility to determine, whether or not
1470   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1471   used instead. This response is cacheable unless indicated otherwise.
1472</t>
1473<t>
1474   The 410 response is primarily intended to assist the task of web
1475   maintenance by notifying the recipient that the resource is
1476   intentionally unavailable and that the server owners desire that
1477   remote links to that resource be removed. Such an event is common for
1478   limited-time, promotional services and for resources belonging to
1479   individuals no longer working at the server's site. It is not
1480   necessary to mark all permanently unavailable resources as "gone" or
1481   to keep the mark for any length of time -- that is left to the
1482   discretion of the server owner.
1483</t>
1484</section>
1485
1486<section title="411 Length Required" anchor="status.411">
1487  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1488  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1489<t>
1490   The server refuses to accept the request without a defined Content-Length.
1491   The client &MAY; repeat the request if it adds a valid
1492   Content-Length header field containing the length of the message-body
1493   in the request message.
1494</t>
1495</section>
1496
1497<section title="412 Precondition Failed" anchor="status.412">
1498  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1499  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1500<t>
1501   The precondition given in one or more of the request-header fields
1502   evaluated to false when it was tested on the server. This response
1503   code allows the client to place preconditions on the current resource
1504   metainformation (header field data) and thus prevent the requested
1505   method from being applied to a resource other than the one intended.
1506</t>
1507</section>
1508
1509<section title="413 Request Entity Too Large" anchor="status.413">
1510  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1511  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1512<t>
1513   The server is refusing to process a request because the request
1514   entity is larger than the server is willing or able to process. The
1515   server &MAY; close the connection to prevent the client from continuing
1516   the request.
1517</t>
1518<t>
1519   If the condition is temporary, the server &SHOULD; include a Retry-After
1520   header field to indicate that it is temporary and after what
1521   time the client &MAY; try again.
1522</t>
1523</section>
1524
1525<section title="414 Request-URI Too Long" anchor="status.414">
1526  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1527  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1528<t>
1529   The server is refusing to service the request because the Request-URI
1530   is longer than the server is willing to interpret. This rare
1531   condition is only likely to occur when a client has improperly
1532   converted a POST request to a GET request with long query
1533   information, when the client has descended into a URI "black hole" of
1534   redirection (e.g., a redirected URI prefix that points to a suffix of
1535   itself), or when the server is under attack by a client attempting to
1536   exploit security holes present in some servers using fixed-length
1537   buffers for reading or manipulating the Request-URI.
1538</t>
1539</section>
1540
1541<section title="415 Unsupported Media Type" anchor="status.415">
1542  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1543  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1544<t>
1545   The server is refusing to service the request because the entity of
1546   the request is in a format not supported by the requested resource
1547   for the requested method.
1548</t>
1549</section>
1550
1551<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1552  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1553  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1554<t>
1555   The request included a Range request-header field (&header-range;) and none of
1556   the range-specifier values in this field overlap the current extent
1557   of the selected resource.
1558</t>
1559</section>
1560
1561<section title="417 Expectation Failed" anchor="status.417">
1562  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1563  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1564<t>
1565   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1566   could not be met by this server, or, if the server is a proxy,
1567   the server has unambiguous evidence that the request could not be met
1568   by the next-hop server.
1569</t>
1570</section>
1571</section>
1572
1573<section title="Server Error 5xx" anchor="status.5xx">
1574<t>
1575   Response status codes beginning with the digit "5" indicate cases in
1576   which the server is aware that it has erred or is incapable of
1577   performing the request. Except when responding to a HEAD request, the
1578   server &SHOULD; include an entity containing an explanation of the
1579   error situation, and whether it is a temporary or permanent
1580   condition. User agents &SHOULD; display any included entity to the
1581   user. These response codes are applicable to any request method.
1582</t>
1583
1584<section title="500 Internal Server Error" anchor="status.500">
1585  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1586  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1587<t>
1588   The server encountered an unexpected condition which prevented it
1589   from fulfilling the request.
1590</t>
1591</section>
1592
1593<section title="501 Not Implemented" anchor="status.501">
1594  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1595  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1596<t>
1597   The server does not support the functionality required to fulfill the
1598   request. This is the appropriate response when the server does not
1599   recognize the request method and is not capable of supporting it for
1600   any resource.
1601</t>
1602</section>
1603
1604<section title="502 Bad Gateway" anchor="status.502">
1605  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1606  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1607<t>
1608   The server, while acting as a gateway or proxy, received an invalid
1609   response from the upstream server it accessed in attempting to
1610   fulfill the request.
1611</t>
1612</section>
1613
1614<section title="503 Service Unavailable" anchor="status.503">
1615  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1616  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1617<t>
1618   The server is currently unable to handle the request due to a
1619   temporary overloading or maintenance of the server. The implication
1620   is that this is a temporary condition which will be alleviated after
1621   some delay. If known, the length of the delay &MAY; be indicated in a
1622   Retry-After header. If no Retry-After is given, the client &SHOULD;
1623   handle the response as it would for a 500 response.
1624  <list><t>
1625      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1626      server must use it when becoming overloaded. Some servers may wish
1627      to simply refuse the connection.
1628  </t></list>
1629</t>
1630</section>
1631
1632<section title="504 Gateway Timeout" anchor="status.504">
1633  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1634  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1635<t>
1636   The server, while acting as a gateway or proxy, did not receive a
1637   timely response from the upstream server specified by the URI (e.g.
1638   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1639   to access in attempting to complete the request.
1640  <list><t>
1641      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1642      return 400 or 500 when DNS lookups time out.
1643  </t></list>
1644</t>
1645</section>
1646
1647<section title="505 HTTP Version Not Supported" anchor="status.505">
1648  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1649  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1650<t>
1651   The server does not support, or refuses to support, the HTTP protocol
1652   version that was used in the request message. The server is
1653   indicating that it is unable or unwilling to complete the request
1654   using the same major version as the client, as described in &http-version;,
1655   other than with this error message. The response &SHOULD; contain
1656   an entity describing why that version is not supported and what other
1657   protocols are supported by that server.
1658</t>
1659
1660</section>
1661</section>
1662</section>
1663
1664
1665<section title="Header Field Definitions" anchor="header.fields">
1666<t>
1667   This section defines the syntax and semantics of all standard
1668   HTTP/1.1 header fields. For entity-header fields, both sender and
1669   recipient refer to either the client or the server, depending on who
1670   sends and who receives the entity.
1671</t>
1672
1673<section title="Allow" anchor="header.allow">
1674  <iref primary="true" item="Allow header" x:for-anchor=""/>
1675  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1676<t>
1677      The Allow entity-header field lists the set of methods supported
1678      by the resource identified by the Request-URI. The purpose of this
1679      field is strictly to inform the recipient of valid methods
1680      associated with the resource. An Allow header field &MUST; be
1681      present in a 405 (Method Not Allowed) response.
1682</t>
1683<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1684       Allow   = "Allow" ":" #Method
1685</artwork></figure>
1686<t>
1687      Example of use:
1688</t>
1689<figure><artwork type="example">
1690       Allow: GET, HEAD, PUT
1691</artwork></figure>
1692<t>
1693      This field cannot prevent a client from trying other methods.
1694      However, the indications given by the Allow header field value
1695      &SHOULD; be followed. The actual set of allowed methods is defined
1696      by the origin server at the time of each request.
1697</t>
1698<t>
1699      The Allow header field &MAY; be provided with a PUT request to
1700      recommend the methods to be supported by the new or modified
1701      resource. The server is not required to support these methods and
1702      &SHOULD; include an Allow header in the response giving the actual
1703      supported methods.
1704</t>
1705<t>
1706      A proxy &MUST-NOT; modify the Allow header field even if it does not
1707      understand all the methods specified, since the user agent might
1708      have other means of communicating with the origin server.
1709</t>
1710</section>
1711
1712<section title="Expect" anchor="header.expect">
1713  <iref primary="true" item="Expect header" x:for-anchor=""/>
1714  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1715<t>
1716   The Expect request-header field is used to indicate that particular
1717   server behaviors are required by the client.
1718</t>
1719<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"/>
1720   Expect       =  "Expect" ":" 1#expectation
1721
1722   expectation  =  "100-continue" | expectation-extension
1723   expectation-extension =  token [ "=" ( token | quoted-string )
1724                            *expect-params ]
1725   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1726</artwork></figure>
1727<t>
1728   A server that does not understand or is unable to comply with any of
1729   the expectation values in the Expect field of a request &MUST; respond
1730   with appropriate error status. The server &MUST; respond with a 417
1731   (Expectation Failed) status if any of the expectations cannot be met
1732   or, if there are other problems with the request, some other 4xx
1733   status.
1734</t>
1735<t>
1736   This header field is defined with extensible syntax to allow for
1737   future extensions. If a server receives a request containing an
1738   Expect field that includes an expectation-extension that it does not
1739   support, it &MUST; respond with a 417 (Expectation Failed) status.
1740</t>
1741<t>
1742   Comparison of expectation values is case-insensitive for unquoted
1743   tokens (including the 100-continue token), and is case-sensitive for
1744   quoted-string expectation-extensions.
1745</t>
1746<t>
1747   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1748   return a 417 (Expectation Failed) status if it receives a request
1749   with an expectation that it cannot meet. However, the Expect
1750   request-header itself is end-to-end; it &MUST; be forwarded if the
1751   request is forwarded.
1752</t>
1753<t>
1754   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1755   Expect header.
1756</t>
1757<t>
1758   See &use100; for the use of the 100 (continue) status.
1759</t>
1760</section>
1761
1762<section title="From" anchor="header.from">
1763  <iref primary="true" item="From header" x:for-anchor=""/>
1764  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1765<t>
1766   The From request-header field, if given, &SHOULD; contain an Internet
1767   e-mail address for the human user who controls the requesting user
1768   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1769   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1770</t>
1771<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1772    From   = "From" ":" mailbox
1773</artwork></figure>
1774<t>
1775   An example is:
1776</t>
1777<figure><artwork type="example">
1778    From: webmaster@w3.org
1779</artwork></figure>
1780<t>
1781   This header field &MAY; be used for logging purposes and as a means for
1782   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1783   be used as an insecure form of access protection. The interpretation
1784   of this field is that the request is being performed on behalf of the
1785   person given, who accepts responsibility for the method performed. In
1786   particular, robot agents &SHOULD; include this header so that the
1787   person responsible for running the robot can be contacted if problems
1788   occur on the receiving end.
1789</t>
1790<t>
1791   The Internet e-mail address in this field &MAY; be separate from the
1792   Internet host which issued the request. For example, when a request
1793   is passed through a proxy the original issuer's address &SHOULD; be
1794   used.
1795</t>
1796<t>
1797   The client &SHOULD-NOT;  send the From header field without the user's
1798   approval, as it might conflict with the user's privacy interests or
1799   their site's security policy. It is strongly recommended that the
1800   user be able to disable, enable, and modify the value of this field
1801   at any time prior to a request.
1802</t>
1803</section>
1804
1805<section title="Location" anchor="header.location">
1806  <iref primary="true" item="Location header" x:for-anchor=""/>
1807  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1808<t>
1809   The Location response-header field is used to redirect the recipient
1810   to a location other than the Request-URI for completion of the
1811   request or identification of a new resource. For 201 (Created)
1812   responses, the Location is that of the new resource which was created
1813   by the request. For 3xx responses, the location &SHOULD; indicate the
1814   server's preferred URI for automatic redirection to the resource. The
1815   field value consists of a single absolute URI.
1816</t>
1817<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1818    Location       = "Location" ":" absoluteURI
1819</artwork></figure>
1820<t>
1821   An example is:
1822</t>
1823<figure><artwork type="example">
1824    Location: http://www.w3.org/pub/WWW/People.html
1825</artwork></figure>
1826<t>
1827  <list><t>
1828      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1829      from Location in that the Content-Location identifies the original
1830      location of the entity enclosed in the request. It is therefore
1831      possible for a response to contain header fields for both Location
1832      and Content-Location.
1833  </t></list>
1834</t>
1835</section>
1836
1837<section title="Max-Forwards" anchor="header.max-forwards">
1838  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1839  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1840<t>
1841   The Max-Forwards request-header field provides a mechanism with the
1842   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1843   number of proxies or gateways that can forward the request to the
1844   next inbound server. This can be useful when the client is attempting
1845   to trace a request chain which appears to be failing or looping in
1846   mid-chain.
1847</t>
1848<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1849    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1850</artwork></figure>
1851<t>
1852   The Max-Forwards value is a decimal integer indicating the remaining
1853   number of times this request message may be forwarded.
1854</t>
1855<t>
1856   Each proxy or gateway recipient of a TRACE or OPTIONS request
1857   containing a Max-Forwards header field &MUST; check and update its
1858   value prior to forwarding the request. If the received value is zero
1859   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1860   respond as the final recipient. If the received Max-Forwards value is
1861   greater than zero, then the forwarded message &MUST; contain an updated
1862   Max-Forwards field with a value decremented by one (1).
1863</t>
1864<t>
1865   The Max-Forwards header field &MAY; be ignored for all other methods
1866   defined by this specification and for any extension methods for which
1867   it is not explicitly referred to as part of that method definition.
1868</t>
1869</section>
1870
1871<section title="Referer" anchor="header.referer">
1872  <iref primary="true" item="Referer header" x:for-anchor=""/>
1873  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1874<t>
1875   The Referer[sic] request-header field allows the client to specify,
1876   for the server's benefit, the address (URI) of the resource from
1877   which the Request-URI was obtained (the "referrer", although the
1878   header field is misspelled.) The Referer request-header allows a
1879   server to generate lists of back-links to resources for interest,
1880   logging, optimized caching, etc. It also allows obsolete or mistyped
1881   links to be traced for maintenance. The Referer field &MUST-NOT; be
1882   sent if the Request-URI was obtained from a source that does not have
1883   its own URI, such as input from the user keyboard.
1884</t>
1885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1886    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1887</artwork></figure>
1888<t>
1889   Example:
1890</t>
1891<figure><artwork type="example">
1892    Referer: http://www.w3.org/hypertext/DataSources/Overview.html
1893</artwork></figure>
1894<t>
1895   If the field value is a relative URI, it &SHOULD; be interpreted
1896   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1897   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1898</t>
1899</section>
1900
1901<section title="Retry-After" anchor="header.retry-after">
1902  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1903  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1904<t>
1905   The Retry-After response-header field can be used with a 503 (Service
1906   Unavailable) response to indicate how long the service is expected to
1907   be unavailable to the requesting client. This field &MAY; also be used
1908   with any 3xx (Redirection) response to indicate the minimum time the
1909   user-agent is asked wait before issuing the redirected request. The
1910   value of this field can be either an HTTP-date or an integer number
1911   of seconds (in decimal) after the time of the response.
1912</t>
1913<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1914    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1915</artwork></figure>
1916<t>
1917   Two examples of its use are
1918</t>
1919<figure><artwork type="example">
1920    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1921    Retry-After: 120
1922</artwork></figure>
1923<t>
1924   In the latter example, the delay is 2 minutes.
1925</t>
1926</section>
1927
1928<section title="Server" anchor="header.server">
1929  <iref primary="true" item="Server header" x:for-anchor=""/>
1930  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1931<t>
1932   The Server response-header field contains information about the
1933   software used by the origin server to handle the request. The field
1934   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1935   identifying the server and any significant subproducts. The product
1936   tokens are listed in order of their significance for identifying the
1937   application.
1938</t>
1939<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1940    Server         = "Server" ":" 1*( product | comment )
1941</artwork></figure>
1942<t>
1943   Example:
1944</t>
1945<figure><artwork type="example">
1946    Server: CERN/3.0 libwww/2.17
1947</artwork></figure>
1948<t>
1949   If the response is being forwarded through a proxy, the proxy
1950   application &MUST-NOT; modify the Server response-header. Instead, it
1951   &SHOULD; include a Via field (as described in &header-via;).
1952  <list><t>
1953      <x:h>Note:</x:h> Revealing the specific software version of the server might
1954      allow the server machine to become more vulnerable to attacks
1955      against software that is known to contain security holes. Server
1956      implementors are encouraged to make this field a configurable
1957      option.
1958  </t></list>
1959</t>
1960</section>
1961
1962<section title="User-Agent" anchor="header.user-agent">
1963  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1964  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1965<t>
1966   The User-Agent request-header field contains information about the
1967   user agent originating the request. This is for statistical purposes,
1968   the tracing of protocol violations, and automated recognition of user
1969   agents for the sake of tailoring responses to avoid particular user
1970   agent limitations. User agents &SHOULD; include this field with
1971   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1972   and comments identifying the agent and any subproducts which form a
1973   significant part of the user agent. By convention, the product tokens
1974   are listed in order of their significance for identifying the
1975   application.
1976</t>
1977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1978    User-Agent     = "User-Agent" ":" 1*( product | comment )
1979</artwork></figure>
1980<t>
1981   Example:
1982</t>
1983<figure><artwork type="example">
1984    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1985</artwork></figure>
1986</section>
1987
1988</section>
1989
1990<section title="IANA Considerations" anchor="IANA.considerations">
1991<t>
1992   TBD.
1993</t>
1994</section>
1995
1996<section title="Security Considerations" anchor="security.considerations">
1997<t>
1998   This section is meant to inform application developers, information
1999   providers, and users of the security limitations in HTTP/1.1 as
2000   described by this document. The discussion does not include
2001   definitive solutions to the problems revealed, though it does make
2002   some suggestions for reducing security risks.
2003</t>
2004
2005<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2006<t>
2007   Like any generic data transfer protocol, HTTP cannot regulate the
2008   content of the data that is transferred, nor is there any a priori
2009   method of determining the sensitivity of any particular piece of
2010   information within the context of any given request. Therefore,
2011   applications &SHOULD; supply as much control over this information as
2012   possible to the provider of that information. Four header fields are
2013   worth special mention in this context: Server, Via, Referer and From.
2014</t>
2015<t>
2016   Revealing the specific software version of the server might allow the
2017   server machine to become more vulnerable to attacks against software
2018   that is known to contain security holes. Implementors &SHOULD; make the
2019   Server header field a configurable option.
2020</t>
2021<t>
2022   Proxies which serve as a portal through a network firewall &SHOULD;
2023   take special precautions regarding the transfer of header information
2024   that identifies the hosts behind the firewall. In particular, they
2025   &SHOULD; remove, or replace with sanitized versions, any Via fields
2026   generated behind the firewall.
2027</t>
2028<t>
2029   The Referer header allows reading patterns to be studied and reverse
2030   links drawn. Although it can be very useful, its power can be abused
2031   if user details are not separated from the information contained in
2032   the Referer. Even when the personal information has been removed, the
2033   Referer header might indicate a private document's URI whose
2034   publication would be inappropriate.
2035</t>
2036<t>
2037   The information sent in the From field might conflict with the user's
2038   privacy interests or their site's security policy, and hence it
2039   &SHOULD-NOT;  be transmitted without the user being able to disable,
2040   enable, and modify the contents of the field. The user &MUST; be able
2041   to set the contents of this field within a user preference or
2042   application defaults configuration.
2043</t>
2044<t>
2045   We suggest, though do not require, that a convenient toggle interface
2046   be provided for the user to enable or disable the sending of From and
2047   Referer information.
2048</t>
2049<t>
2050   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2051   fields can sometimes be used to determine that a specific client or
2052   server have a particular security hole which might be exploited.
2053   Unfortunately, this same information is often used for other valuable
2054   purposes for which HTTP currently has no better mechanism.
2055</t>
2056</section>
2057
2058<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2059<t>
2060   Because the source of a link might be private information or might
2061   reveal an otherwise private information source, it is strongly
2062   recommended that the user be able to select whether or not the
2063   Referer field is sent. For example, a browser client could have a
2064   toggle switch for browsing openly/anonymously, which would
2065   respectively enable/disable the sending of Referer and From
2066   information.
2067</t>
2068<t>
2069   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2070   HTTP request if the referring page was transferred with a secure
2071   protocol.
2072</t>
2073<t>
2074   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2075   based forms for the submission of sensitive data, because this will
2076   cause this data to be encoded in the Request-URI. Many existing
2077   servers, proxies, and user agents will log the request URI in some
2078   place where it might be visible to third parties. Servers can use
2079   POST-based form submission instead
2080</t>
2081</section>
2082
2083<section title="Location Headers and Spoofing" anchor="location.spoofing">
2084<t>
2085   If a single server supports multiple organizations that do not trust
2086   one another, then it &MUST; check the values of Location and Content-Location
2087   headers in responses that are generated under control of
2088   said organizations to make sure that they do not attempt to
2089   invalidate resources over which they have no authority.
2090</t>
2091</section>
2092
2093</section>
2094
2095<section title="Acknowledgments" anchor="ack">
2096<t>
2097   Based on an XML translation of RFC 2616 by Julian Reschke.
2098</t>
2099</section>
2100</middle>
2101<back>
2102<references>
2103
2104<reference anchor="Part1">
2105   <front>
2106      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2107      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2108         <organization abbrev="Day Software">Day Software</organization>
2109         <address><email>fielding@gbiv.com</email></address>
2110      </author>
2111      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2112         <organization>One Laptop per Child</organization>
2113         <address><email>jg@laptop.org</email></address>
2114      </author>
2115      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2116         <organization abbrev="HP">Hewlett-Packard Company</organization>
2117         <address><email>JeffMogul@acm.org</email></address>
2118      </author>
2119      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2120         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2121         <address><email>henrikn@microsoft.com</email></address>
2122      </author>
2123      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2124         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2125         <address><email>LMM@acm.org</email></address>
2126      </author>
2127      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2128         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2129         <address><email>paulle@microsoft.com</email></address>
2130      </author>
2131      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2132         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2133         <address><email>timbl@w3.org</email></address>
2134      </author>
2135      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2136   </front>
2137   <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
2138   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2139</reference>
2140
2141<reference anchor="Part3">
2142   <front>
2143      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2144      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2145         <organization abbrev="Day Software">Day Software</organization>
2146         <address><email>fielding@gbiv.com</email></address>
2147      </author>
2148      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2149         <organization>One Laptop per Child</organization>
2150         <address><email>jg@laptop.org</email></address>
2151      </author>
2152      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2153         <organization abbrev="HP">Hewlett-Packard Company</organization>
2154         <address><email>JeffMogul@acm.org</email></address>
2155      </author>
2156      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2157         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2158         <address><email>henrikn@microsoft.com</email></address>
2159      </author>
2160      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2161         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2162         <address><email>LMM@acm.org</email></address>
2163      </author>
2164      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2165         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2166         <address><email>paulle@microsoft.com</email></address>
2167      </author>
2168      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2169         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2170         <address><email>timbl@w3.org</email></address>
2171      </author>
2172      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2173   </front>
2174   <seriesInfo name="Internet-Draft" value="draft-fielding-p3-payload-&ID-VERSION;"/>
2175   <x:source href="p3-payload.xml" basename="p3-payload"/>
2176</reference>
2177
2178<reference anchor="Part4">
2179   <front>
2180      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2181      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2182         <organization abbrev="Day Software">Day Software</organization>
2183         <address><email>fielding@gbiv.com</email></address>
2184      </author>
2185      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2186         <organization>One Laptop per Child</organization>
2187         <address><email>jg@laptop.org</email></address>
2188      </author>
2189      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2190         <organization abbrev="HP">Hewlett-Packard Company</organization>
2191         <address><email>JeffMogul@acm.org</email></address>
2192      </author>
2193      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2194         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2195         <address><email>henrikn@microsoft.com</email></address>
2196      </author>
2197      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2198         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2199         <address><email>LMM@acm.org</email></address>
2200      </author>
2201      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2202         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2203         <address><email>paulle@microsoft.com</email></address>
2204      </author>
2205      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2206         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2207         <address><email>timbl@w3.org</email></address>
2208      </author>
2209      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2210   </front>
2211   <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
2212   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2213</reference>
2214
2215<reference anchor="Part5">
2216   <front>
2217      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2218      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2219         <organization abbrev="Day Software">Day Software</organization>
2220         <address><email>fielding@gbiv.com</email></address>
2221      </author>
2222      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2223         <organization>One Laptop per Child</organization>
2224         <address><email>jg@laptop.org</email></address>
2225      </author>
2226      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2227         <organization abbrev="HP">Hewlett-Packard Company</organization>
2228         <address><email>JeffMogul@acm.org</email></address>
2229      </author>
2230      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2231         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2232         <address><email>henrikn@microsoft.com</email></address>
2233      </author>
2234      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2235         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2236         <address><email>LMM@acm.org</email></address>
2237      </author>
2238      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2239         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2240         <address><email>paulle@microsoft.com</email></address>
2241      </author>
2242      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2243         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2244         <address><email>timbl@w3.org</email></address>
2245      </author>
2246      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2247   </front>
2248   <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
2249   <x:source href="p5-range.xml" basename="p5-range"/>
2250</reference>
2251
2252<reference anchor="Part6">
2253   <front>
2254      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2255      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2256         <organization abbrev="Day Software">Day Software</organization>
2257         <address><email>fielding@gbiv.com</email></address>
2258      </author>
2259      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2260         <organization>One Laptop per Child</organization>
2261         <address><email>jg@laptop.org</email></address>
2262      </author>
2263      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2264         <organization abbrev="HP">Hewlett-Packard Company</organization>
2265         <address><email>JeffMogul@acm.org</email></address>
2266      </author>
2267      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2268         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2269         <address><email>henrikn@microsoft.com</email></address>
2270      </author>
2271      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2272         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2273         <address><email>LMM@acm.org</email></address>
2274      </author>
2275      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2276         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2277         <address><email>paulle@microsoft.com</email></address>
2278      </author>
2279      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2280         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2281         <address><email>timbl@w3.org</email></address>
2282      </author>
2283      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2284   </front>
2285   <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
2286   <x:source href="p6-cache.xml" basename="p6-cache"/>
2287</reference>
2288
2289<reference anchor="Part7">
2290   <front>
2291      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2292      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2293         <organization abbrev="Day Software">Day Software</organization>
2294         <address><email>fielding@gbiv.com</email></address>
2295      </author>
2296      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2297         <organization>One Laptop per Child</organization>
2298         <address><email>jg@laptop.org</email></address>
2299      </author>
2300      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2301         <organization abbrev="HP">Hewlett-Packard Company</organization>
2302         <address><email>JeffMogul@acm.org</email></address>
2303      </author>
2304      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2305         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2306         <address><email>henrikn@microsoft.com</email></address>
2307      </author>
2308      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2309         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2310         <address><email>LMM@acm.org</email></address>
2311      </author>
2312      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2313         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2314         <address><email>paulle@microsoft.com</email></address>
2315      </author>
2316      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2317         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2318         <address><email>timbl@w3.org</email></address>
2319      </author>
2320      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2321   </front>
2322   <seriesInfo name="Internet-Draft" value="draft-fielding-p7-auth-&ID-VERSION;"/>
2323   <x:source href="p7-auth.xml" basename="p7-auth"/>
2324</reference>
2325
2326<reference anchor="RFC2616">
2327   <front>
2328      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2329      <author initials="R." surname="Fielding" fullname="R. Fielding">
2330         <organization>University of California, Irvine</organization>
2331         <address><email>fielding@ics.uci.edu</email></address>
2332      </author>
2333      <author initials="J." surname="Gettys" fullname="J. Gettys">
2334         <organization>W3C</organization>
2335         <address><email>jg@w3.org</email></address>
2336      </author>
2337      <author initials="J." surname="Mogul" fullname="J. Mogul">
2338         <organization>Compaq Computer Corporation</organization>
2339         <address><email>mogul@wrl.dec.com</email></address>
2340      </author>
2341      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2342         <organization>MIT Laboratory for Computer Science</organization>
2343         <address><email>frystyk@w3.org</email></address>
2344      </author>
2345      <author initials="L." surname="Masinter" fullname="L. Masinter">
2346         <organization>Xerox Corporation</organization>
2347         <address><email>masinter@parc.xerox.com</email></address>
2348      </author>
2349      <author initials="P." surname="Leach" fullname="P. Leach">
2350         <organization>Microsoft Corporation</organization>
2351         <address><email>paulle@microsoft.com</email></address>
2352      </author>
2353      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2354         <organization>W3C</organization>
2355         <address><email>timbl@w3.org</email></address>
2356      </author>
2357      <date month="June" year="1999"/>
2358   </front>
2359   <seriesInfo name="RFC" value="2616"/>
2360</reference>
2361
2362<reference anchor="RFC1123">
2363<front>
2364<title>Requirements for Internet Hosts - Application and Support</title>
2365<author initials="R." surname="Braden" fullname="Robert Braden">
2366<organization>University of Southern California (USC), Information Sciences Institute</organization>
2367<address>
2368<postal>
2369<street>4676 Admiralty Way</street>
2370<city>Marina del Rey</city>
2371<region>CA</region>
2372<code>90292-6695</code>
2373<country>US</country></postal>
2374<phone>+1 213 822 1511</phone>
2375<email>Braden@ISI.EDU</email></address></author>
2376<date month="October" year="1989"/></front>
2377<seriesInfo name="STD" value="3"/>
2378<seriesInfo name="RFC" value="1123"/>
2379</reference>
2380
2381<reference anchor="RFC822">
2382<front>
2383<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2384<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2385<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2386<address>
2387<postal>
2388<street/>
2389<city>Newark</city>
2390<region>DE</region>
2391<code>19711</code>
2392<country>US</country></postal>
2393<email>DCrocker@UDel-Relay</email></address></author>
2394<date month="August" day="13" year="1982"/></front>
2395<seriesInfo name="STD" value="11"/>
2396<seriesInfo name="RFC" value="822"/>
2397</reference>
2398
2399<reference anchor="RFC2068">
2400<front>
2401<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2402<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2403<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2404<address>
2405<postal>
2406<street/>
2407<city>Irvine</city>
2408<region>CA</region>
2409<code>92717-3425</code>
2410<country>US</country></postal>
2411<facsimile>+1 714 824 4056</facsimile>
2412<email>fielding@ics.uci.edu</email></address></author>
2413<author initials="J." surname="Gettys" fullname="Jim Gettys">
2414<organization>MIT Laboratory for Computer Science</organization>
2415<address>
2416<postal>
2417<street>545 Technology Square</street>
2418<city>Cambridge</city>
2419<region>MA</region>
2420<code>02139</code>
2421<country>US</country></postal>
2422<facsimile>+1 617 258 8682</facsimile>
2423<email>jg@w3.org</email></address></author>
2424<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2425<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2426<address>
2427<postal>
2428<street>250 University Avenue</street>
2429<city>Palo Alto</city>
2430<region>CA</region>
2431<code>94301</code>
2432<country>US</country></postal>
2433<email>mogul@wrl.dec.com</email></address></author>
2434<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2435<organization>MIT Laboratory for Computer Science</organization>
2436<address>
2437<postal>
2438<street>545 Technology Square</street>
2439<city>Cambridge</city>
2440<region>MA</region>
2441<code>02139</code>
2442<country>US</country></postal>
2443<facsimile>+1 617 258 8682</facsimile>
2444<email>frystyk@w3.org</email></address></author>
2445<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2446<organization>MIT Laboratory for Computer Science</organization>
2447<address>
2448<postal>
2449<street>545 Technology Square</street>
2450<city>Cambridge</city>
2451<region>MA</region>
2452<code>02139</code>
2453<country>US</country></postal>
2454<facsimile>+1 617 258 8682</facsimile>
2455<email>timbl@w3.org</email></address></author>
2456<date month="January" year="1997"/>
2457<abstract>
2458<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>
2459<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>
2460<seriesInfo name="RFC" value="2068"/>
2461</reference>
2462
2463<reference anchor="RFC2617">
2464<front>
2465<title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
2466<author initials="J." surname="Franks" fullname="John Franks">
2467<organization>Northwestern University, Department of Mathematics</organization>
2468<address>
2469<postal>
2470<street/>
2471<city>Evanston</city>
2472<region>IL</region>
2473<code>60208-2730</code>
2474<country>US</country></postal>
2475<email>john@math.nwu.edu</email></address></author>
2476<author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
2477<organization>Verisign Inc.</organization>
2478<address>
2479<postal>
2480<street>301 Edgewater Place</street>
2481<street>Suite 210</street>
2482<city>Wakefield</city>
2483<region>MA</region>
2484<code>01880</code>
2485<country>US</country></postal>
2486<email>pbaker@verisign.com</email></address></author>
2487<author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
2488<organization>AbiSource, Inc.</organization>
2489<address>
2490<postal>
2491<street>6 Dunlap Court</street>
2492<city>Savoy</city>
2493<region>IL</region>
2494<code>61874</code>
2495<country>US</country></postal>
2496<email>jeff@AbiSource.com</email></address></author>
2497<author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
2498<organization>Agranat Systems, Inc.</organization>
2499<address>
2500<postal>
2501<street>5 Clocktower Place</street>
2502<street>Suite 400</street>
2503<city>Maynard</city>
2504<region>MA</region>
2505<code>01754</code>
2506<country>US</country></postal>
2507<email>lawrence@agranat.com</email></address></author>
2508<author initials="P.J." surname="Leach" fullname="Paul J. Leach">
2509<organization>Microsoft Corporation</organization>
2510<address>
2511<postal>
2512<street>1 Microsoft Way</street>
2513<city>Redmond</city>
2514<region>WA</region>
2515<code>98052</code>
2516<country>US</country></postal>
2517<email>paulle@microsoft.com</email></address></author>
2518<author initials="A." surname="Luotonen" fullname="Ari Luotonen">
2519<organization>Netscape Communications Corporation</organization>
2520<address>
2521<postal>
2522<street>501 East Middlefield Road</street>
2523<city>Mountain View</city>
2524<region>CA</region>
2525<code>94043</code>
2526<country>US</country></postal></address></author>
2527<author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
2528<organization>Open Market, Inc.</organization>
2529<address>
2530<postal>
2531<street>215 First Street</street>
2532<city>Cambridge</city>
2533<region>MA</region>
2534<code>02142</code>
2535<country>US</country></postal>
2536<email>stewart@OpenMarket.com</email></address></author>
2537<date month="June" year="1999"/>
2538</front>
2539<seriesInfo name="RFC" value="2617"/>
2540</reference>
2541
2542<reference anchor="Luo1998">
2543<front>
2544<title>Tunneling TCP based protocols through Web proxy servers</title>
2545<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2546  <organization/>
2547</author>
2548<date/>
2549</front>
2550<seriesInfo name="" value="Work in Progress"/>
2551</reference>
2552
2553</references>
2554
2555<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2556<t>
2557   Clarified which error code should be used for inbound server failures
2558   (e.g. DNS failures). (<xref target="status.504"/>).
2559</t>
2560<t>
2561   CREATE had a race that required an Etag be sent when a resource is
2562   first created. (<xref target="status.201"/>).
2563</t>
2564<t>
2565   Rewrite of message transmission requirements to make it much harder
2566   for implementors to get it wrong, as the consequences of errors here
2567   can have significant impact on the Internet, and to deal with the
2568   following problems:
2569  <list style="numbers">
2570      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2571         this was incorrectly placing a requirement on the behavior of
2572         an implementation of a future version of HTTP/1.x</t>
2573
2574      <t>Made it clear that user-agents should retry requests, not
2575         "clients" in general.</t>
2576
2577      <t>Converted requirements for clients to ignore unexpected 100
2578         (Continue) responses, and for proxies to forward 100 responses,
2579         into a general requirement for 1xx responses.</t>
2580
2581      <t>Modified some TCP-specific language, to make it clearer that
2582         non-TCP transports are possible for HTTP.</t>
2583
2584      <t>Require that the origin server &MUST-NOT; wait for the request
2585         body before it sends a required 100 (Continue) response.</t>
2586
2587      <t>Allow, rather than require, a server to omit 100 (Continue) if
2588         it has already seen some of the request body.</t>
2589
2590      <t>Allow servers to defend against denial-of-service attacks and
2591         broken clients.</t>
2592  </list>
2593</t>
2594<t>
2595   This change adds the Expect header and 417 status code.
2596</t>
2597<t>
2598   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2599   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2600</t>
2601<t>
2602   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
2603   implemented in previous versions of this specification. See RFC 2068
2604   <xref target="RFC2068"/>.
2605</t>
2606</section>
2607</back>
2608</rfc>
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