source: draft-ietf-httpbis/latest/p2-semantics.xml @ 91

Last change on this file since 91 was 90, checked in by fielding@…, 12 years ago

Resolve #42: RFC2606 compliance

Use example.org, example.com, and example.net instead
of real domains in examples.

  • Property svn:eol-style set to native
File size: 114.5 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" 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.  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://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
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 data to be processed by 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.
680</t>
681<t>
682   The action performed by the POST method might not result in a
683   resource that can be identified by a URI. In this case, either 200
684   (OK) or 204 (No Content) is the appropriate response status,
685   depending on whether or not the response includes an entity that
686   describes the result.
687</t>
688<t>
689   If a resource has been created on the origin server, the response
690   &SHOULD; be 201 (Created) and contain an entity which describes the
691   status of the request and refers to the new resource, and a Location
692   header (see <xref target="header.location"/>).
693</t>
694<t>
695   Responses to this method are not cacheable, unless the response
696   includes appropriate Cache-Control or Expires header fields. However,
697   the 303 (See Other) response can be used to direct the user agent to
698   retrieve a cacheable resource.
699</t>
700<t>
701   POST requests &MUST; obey the message transmission requirements set out
702   in &message-transmission-req;.
703</t>
704<t>
705   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
706</t>
707</section>
708
709<section title="PUT" anchor="PUT">
710  <iref primary="true" item="PUT method" x:for-anchor=""/>
711  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
712<t>
713   The PUT method requests that the enclosed entity be stored under the
714   supplied Request-URI. If the Request-URI refers to an already
715   existing resource, the enclosed entity &SHOULD; be considered as a
716   modified version of the one residing on the origin server. If the
717   Request-URI does not point to an existing resource, and that URI is
718   capable of being defined as a new resource by the requesting user
719   agent, the origin server can create the resource with that URI. If a
720   new resource is created, the origin server &MUST; inform the user agent
721   via the 201 (Created) response. If an existing resource is modified,
722   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
723   to indicate successful completion of the request. If the resource
724   could not be created or modified with the Request-URI, an appropriate
725   error response &SHOULD; be given that reflects the nature of the
726   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
727   (e.g. Content-Range) headers that it does not understand or implement
728   and &MUST; return a 501 (Not Implemented) response in such cases.
729</t>
730<t>
731   If the request passes through a cache and the Request-URI identifies
732   one or more currently cached entities, those entries &SHOULD; be
733   treated as stale. Responses to this method are not cacheable.
734</t>
735<t>
736   The fundamental difference between the POST and PUT requests is
737   reflected in the different meaning of the Request-URI. The URI in a
738   POST request identifies the resource that will handle the enclosed
739   entity. That resource might be a data-accepting process, a gateway to
740   some other protocol, or a separate entity that accepts annotations.
741   In contrast, the URI in a PUT request identifies the entity enclosed
742   with the request -- the user agent knows what URI is intended and the
743   server &MUST-NOT; attempt to apply the request to some other resource.
744   If the server desires that the request be applied to a different URI,
745   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
746   then make its own decision regarding whether or not to redirect the
747   request.
748</t>
749<t>
750   A single resource &MAY; be identified by many different URIs. For
751   example, an article might have a URI for identifying "the current
752   version" which is separate from the URI identifying each particular
753   version. In this case, a PUT request on a general URI might result in
754   several other URIs being defined by the origin server.
755</t>
756<t>
757   HTTP/1.1 does not define how a PUT method affects the state of an
758   origin server.
759</t>
760<t>
761   PUT requests &MUST; obey the message transmission requirements set out
762   in &message-transmission-req;.
763</t>
764<t>
765   Unless otherwise specified for a particular entity-header, the
766   entity-headers in the PUT request &SHOULD; be applied to the resource
767   created or modified by the PUT.
768</t>
769</section>
770
771<section title="DELETE" anchor="DELETE">
772  <iref primary="true" item="DELETE method" x:for-anchor=""/>
773  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
774<t>
775   The DELETE method requests that the origin server delete the resource
776   identified by the Request-URI. This method &MAY; be overridden by human
777   intervention (or other means) on the origin server. The client cannot
778   be guaranteed that the operation has been carried out, even if the
779   status code returned from the origin server indicates that the action
780   has been completed successfully. However, the server &SHOULD-NOT; 
781   indicate success unless, at the time the response is given, it
782   intends to delete the resource or move it to an inaccessible
783   location.
784</t>
785<t>
786   A successful response &SHOULD; be 200 (OK) if the response includes an
787   entity describing the status, 202 (Accepted) if the action has not
788   yet been enacted, or 204 (No Content) if the action has been enacted
789   but the response does not include an entity.
790</t>
791<t>
792   If the request passes through a cache and the Request-URI identifies
793   one or more currently cached entities, those entries &SHOULD; be
794   treated as stale. Responses to this method are not cacheable.
795</t>
796</section>
797
798<section title="TRACE" anchor="TRACE">
799  <iref primary="true" item="TRACE method" x:for-anchor=""/>
800  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
801<t>
802   The TRACE method is used to invoke a remote, application-layer loop-back
803   of the request message. The final recipient of the request
804   &SHOULD; reflect the message received back to the client as the
805   entity-body of a 200 (OK) response. The final recipient is either the
806   origin server or the first proxy or gateway to receive a Max-Forwards
807   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
808   &MUST-NOT; include an entity.
809</t>
810<t>
811   TRACE allows the client to see what is being received at the other
812   end of the request chain and use that data for testing or diagnostic
813   information. The value of the Via header field (&header-via;) is of
814   particular interest, since it acts as a trace of the request chain.
815   Use of the Max-Forwards header field allows the client to limit the
816   length of the request chain, which is useful for testing a chain of
817   proxies forwarding messages in an infinite loop.
818</t>
819<t>
820   If the request is valid, the response &SHOULD; contain the entire
821   request message in the entity-body, with a Content-Type of
822   "message/http". Responses to this method &MUST-NOT; be cached.
823</t>
824</section>
825
826<section title="CONNECT" anchor="CONNECT">
827  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
828  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
829<t>
830   This specification reserves the method name CONNECT for use with a
831   proxy that can dynamically switch to being a tunnel (e.g. SSL
832   tunneling <xref target="Luo1998"/>).
833</t>
834</section>
835</section>
836
837
838<section title="Status Code Definitions" anchor="status.codes">
839<t>
840   Each Status-Code is described below, including a description of which
841   method(s) it can follow and any metainformation required in the
842   response.
843</t>
844
845<section title="Informational 1xx" anchor="status.1xx">
846<t>
847   This class of status code indicates a provisional response,
848   consisting only of the Status-Line and optional headers, and is
849   terminated by an empty line. There are no required headers for this
850   class of status code. Since HTTP/1.0 did not define any 1xx status
851   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
852   except under experimental conditions.
853</t>
854<t>
855   A client &MUST; be prepared to accept one or more 1xx status responses
856   prior to a regular response, even if the client does not expect a 100
857   (Continue) status message. Unexpected 1xx status responses &MAY; be
858   ignored by a user agent.
859</t>
860<t>
861   Proxies &MUST; forward 1xx responses, unless the connection between the
862   proxy and its client has been closed, or unless the proxy itself
863   requested the generation of the 1xx response. (For example, if a
864   proxy adds a "Expect: 100-continue" field when it forwards a request,
865   then it need not forward the corresponding 100 (Continue)
866   response(s).)
867</t>
868
869<section title="100 Continue" anchor="status.100">
870  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
871  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
872<t>
873   The client &SHOULD; continue with its request. This interim response is
874   used to inform the client that the initial part of the request has
875   been received and has not yet been rejected by the server. The client
876   &SHOULD; continue by sending the remainder of the request or, if the
877   request has already been completed, ignore this response. The server
878   &MUST; send a final response after the request has been completed. See
879   &use100; for detailed discussion of the use and handling of this
880   status code.
881</t>
882</section>
883
884<section title="101 Switching Protocols" anchor="status.101">
885  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
886  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
887<t>
888   The server understands and is willing to comply with the client's
889   request, via the Upgrade message header field (&header-upgrade;), for a
890   change in the application protocol being used on this connection. The
891   server will switch protocols to those defined by the response's
892   Upgrade header field immediately after the empty line which
893   terminates the 101 response.
894</t>
895<t>
896   The protocol &SHOULD; be switched only when it is advantageous to do
897   so. For example, switching to a newer version of HTTP is advantageous
898   over older versions, and switching to a real-time, synchronous
899   protocol might be advantageous when delivering resources that use
900   such features.
901</t>
902</section>
903</section>
904
905<section title="Successful 2xx" anchor="status.2xx">
906<t>
907   This class of status code indicates that the client's request was
908   successfully received, understood, and accepted.
909</t>
910
911<section title="200 OK" anchor="status.200">
912  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
913  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
914<t>
915   The request has succeeded. The information returned with the response
916   is dependent on the method used in the request, for example:
917  <list style="hanging">
918    <t hangText="GET">
919          an entity corresponding to the requested resource is sent in
920          the response;
921    </t>
922    <t hangText="HEAD">
923          the entity-header fields corresponding to the requested
924          resource are sent in the response without any message-body;
925    </t>
926    <t hangText="POST">
927      an entity describing or containing the result of the action;
928    </t>
929    <t hangText="TRACE">
930      an entity containing the request message as received by the
931      end server.
932    </t>
933  </list>
934</t>
935</section>
936
937<section title="201 Created" anchor="status.201">
938  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
939  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
940<t>
941   The request has been fulfilled and resulted in a new resource being
942   created. The newly created resource can be referenced by the URI(s)
943   returned in the entity of the response, with the most specific URI
944   for the resource given by a Location header field. The response
945   &SHOULD; include an entity containing a list of resource
946   characteristics and location(s) from which the user or user agent can
947   choose the one most appropriate. The entity format is specified by
948   the media type given in the Content-Type header field. The origin
949   server &MUST; create the resource before returning the 201 status code.
950   If the action cannot be carried out immediately, the server &SHOULD;
951   respond with 202 (Accepted) response instead.
952</t>
953<t>
954   A 201 response &MAY; contain an ETag response header field indicating
955   the current value of the entity tag for the requested variant just
956   created, see &header-etag;.
957</t>
958</section>
959
960<section title="202 Accepted" anchor="status.202">
961  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
962  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
963<t>
964   The request has been accepted for processing, but the processing has
965   not been completed.  The request might or might not eventually be
966   acted upon, as it might be disallowed when processing actually takes
967   place. There is no facility for re-sending a status code from an
968   asynchronous operation such as this.
969</t>
970<t>
971   The 202 response is intentionally non-committal. Its purpose is to
972   allow a server to accept a request for some other process (perhaps a
973   batch-oriented process that is only run once per day) without
974   requiring that the user agent's connection to the server persist
975   until the process is completed. The entity returned with this
976   response &SHOULD; include an indication of the request's current status
977   and either a pointer to a status monitor or some estimate of when the
978   user can expect the request to be fulfilled.
979</t>
980</section>
981
982<section title="203 Non-Authoritative Information" anchor="status.203">
983  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
984  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
985<t>
986   The returned metainformation in the entity-header is not the
987   definitive set as available from the origin server, but is gathered
988   from a local or a third-party copy. The set presented &MAY; be a subset
989   or superset of the original version. For example, including local
990   annotation information about the resource might result in a superset
991   of the metainformation known by the origin server. Use of this
992   response code is not required and is only appropriate when the
993   response would otherwise be 200 (OK).
994</t>
995</section>
996
997<section title="204 No Content" anchor="status.204">
998  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
999  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1000<t>
1001   The server has fulfilled the request but does not need to return an
1002   entity-body, and might want to return updated metainformation. The
1003   response &MAY; include new or updated metainformation in the form of
1004   entity-headers, which if present &SHOULD; be associated with the
1005   requested variant.
1006</t>
1007<t>
1008   If the client is a user agent, it &SHOULD-NOT;  change its document view
1009   from that which caused the request to be sent. This response is
1010   primarily intended to allow input for actions to take place without
1011   causing a change to the user agent's active document view, although
1012   any new or updated metainformation &SHOULD; be applied to the document
1013   currently in the user agent's active view.
1014</t>
1015<t>
1016   The 204 response &MUST-NOT; include a message-body, and thus is always
1017   terminated by the first empty line after the header fields.
1018</t>
1019</section>
1020
1021<section title="205 Reset Content" anchor="status.205">
1022  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1023  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1024<t>
1025   The server has fulfilled the request and the user agent &SHOULD; reset
1026   the document view which caused the request to be sent. This response
1027   is primarily intended to allow input for actions to take place via
1028   user input, followed by a clearing of the form in which the input is
1029   given so that the user can easily initiate another input action. The
1030   response &MUST-NOT; include an entity.
1031</t>
1032</section>
1033
1034<section title="206 Partial Content" anchor="status.206">
1035  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1036  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1037<t>
1038   The server has fulfilled the partial GET request for the resource
1039   and the enclosed entity is a partial representation as defined in &range;.
1040</t>
1041</section>
1042</section>
1043
1044<section title="Redirection 3xx" anchor="status.3xx">
1045<t>
1046   This class of status code indicates that further action needs to be
1047   taken by the user agent in order to fulfill the request.  The action
1048   required &MAY; be carried out by the user agent without interaction
1049   with the user if and only if the method used in the second request is
1050   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1051   such loops generate network traffic for each redirection.
1052  <list><t>
1053      <x:h>Note:</x:h> previous versions of this specification recommended a
1054      maximum of five redirections. Content developers should be aware
1055      that there might be clients that implement such a fixed
1056      limitation.
1057  </t></list>
1058</t>
1059
1060<section title="300 Multiple Choices" anchor="status.300">
1061  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1062  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1063<t>
1064   The requested resource corresponds to any one of a set of
1065   representations, each with its own specific location, and agent-driven
1066   negotiation information (&content-negotiation;) is being provided so that
1067   the user (or user agent) can select a preferred representation and
1068   redirect its request to that location.
1069</t>
1070<t>
1071   Unless it was a HEAD request, the response &SHOULD; include an entity
1072   containing a list of resource characteristics and location(s) from
1073   which the user or user agent can choose the one most appropriate. The
1074   entity format is specified by the media type given in the Content-Type
1075   header field. Depending upon the format and the capabilities of
1076   the user agent, selection of the most appropriate choice &MAY; be
1077   performed automatically. However, this specification does not define
1078   any standard for such automatic selection.
1079</t>
1080<t>
1081   If the server has a preferred choice of representation, it &SHOULD;
1082   include the specific URI for that representation in the Location
1083   field; user agents &MAY; use the Location field value for automatic
1084   redirection. This response is cacheable unless indicated otherwise.
1085</t>
1086</section>
1087
1088<section title="301 Moved Permanently" anchor="status.301">
1089  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1090  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1091<t>
1092   The requested resource has been assigned a new permanent URI and any
1093   future references to this resource &SHOULD; use one of the returned
1094   URIs.  Clients with link editing capabilities ought to automatically
1095   re-link references to the Request-URI to one or more of the new
1096   references returned by the server, where possible. This response is
1097   cacheable unless indicated otherwise.
1098</t>
1099<t>
1100   The new permanent URI &SHOULD; be given by the Location field in the
1101   response. Unless the request method was HEAD, the entity of the
1102   response &SHOULD; contain a short hypertext note with a hyperlink to
1103   the new URI(s).
1104</t>
1105<t>
1106   If the 301 status code is received in response to a request method
1107   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1108   then the request MAY be automatically redirected by the user agent without
1109   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1110   request unless it can be confirmed by the user, since this might
1111   change the conditions under which the request was issued.
1112  <list><t>
1113      <x:h>Note:</x:h> When automatically redirecting a POST request after
1114      receiving a 301 status code, some existing HTTP/1.0 user agents
1115      will erroneously change it into a GET request.
1116  </t></list>
1117</t>
1118</section>
1119
1120<section title="302 Found" anchor="status.302">
1121  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1122  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1123<t>
1124   The requested resource resides temporarily under a different URI.
1125   Since the redirection might be altered on occasion, the client &SHOULD;
1126   continue to use the Request-URI for future requests.  This response
1127   is only cacheable if indicated by a Cache-Control or Expires header
1128   field.
1129</t>
1130<t>
1131   The temporary URI &SHOULD; be given by the Location field in the
1132   response. Unless the request method was HEAD, the entity of the
1133   response &SHOULD; contain a short hypertext note with a hyperlink to
1134   the new URI(s).
1135</t>
1136<t>
1137   If the 302 status code is received in response to a request method
1138   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1139   then the request MAY be automatically redirected by the user agent without
1140   confirmation.  Otherwise, 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   The response to the request has not been modified since the conditions
1186   indicated by the client's conditional GET request, as defined in &conditional;.
1187</t>
1188</section>
1189
1190<section title="305 Use Proxy" anchor="status.305">
1191  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1192  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1193<t>
1194   The requested resource &MUST; be accessed through the proxy given by
1195   the Location field. The Location field gives the URI of the proxy.
1196   The recipient is expected to repeat this single request via the
1197   proxy. 305 responses &MUST; only be generated by origin servers.
1198  <list><t>
1199      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1200      single request, and to be generated by origin servers only.  Not
1201      observing these limitations has significant security consequences.
1202  </t></list>
1203</t>
1204</section>
1205
1206<section title="306 (Unused)" anchor="status.306">
1207  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1208  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1209<t>
1210   The 306 status code was used in a previous version of the
1211   specification, is no longer used, and the code is reserved.
1212</t>
1213</section>
1214
1215<section title="307 Temporary Redirect" anchor="status.307">
1216  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1217  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1218<t>
1219   The requested resource resides temporarily under a different URI.
1220   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1221   continue to use the Request-URI for future requests.  This response
1222   is only cacheable if indicated by a Cache-Control or Expires header
1223   field.
1224</t>
1225<t>
1226   The temporary URI &SHOULD; be given by the Location field in the
1227   response. Unless the request method was HEAD, the entity of the
1228   response &SHOULD; contain a short hypertext note with a hyperlink to
1229   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1230   understand the 307 status. Therefore, the note &SHOULD; contain the
1231   information necessary for a user to repeat the original request on
1232   the new URI.
1233</t>
1234<t>
1235   If the 307 status code is received in response to a request method
1236   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1237   then the request MAY be automatically redirected by the user agent without
1238   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1239   request unless it can be confirmed by the user, since this might
1240   change the conditions under which the request was issued.
1241</t>
1242</section>
1243</section>
1244
1245<section title="Client Error 4xx" anchor="status.4xx">
1246<t>
1247   The 4xx class of status code is intended for cases in which the
1248   client seems to have erred. Except when responding to a HEAD request,
1249   the server &SHOULD; include an entity containing an explanation of the
1250   error situation, and whether it is a temporary or permanent
1251   condition. These status codes are applicable to any request method.
1252   User agents &SHOULD; display any included entity to the user.
1253</t>
1254<t>
1255   If the client is sending data, a server implementation using TCP
1256   &SHOULD; be careful to ensure that the client acknowledges receipt of
1257   the packet(s) containing the response, before the server closes the
1258   input connection. If the client continues sending data to the server
1259   after the close, the server's TCP stack will send a reset packet to
1260   the client, which may erase the client's unacknowledged input buffers
1261   before they can be read and interpreted by the HTTP application.
1262</t>
1263
1264<section title="400 Bad Request" anchor="status.400">
1265  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1266  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1267<t>
1268   The request could not be understood by the server due to malformed
1269   syntax. The client &SHOULD-NOT;  repeat the request without
1270   modifications.
1271</t>
1272</section>
1273
1274<section title="401 Unauthorized" anchor="status.401">
1275  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1276  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1277<t>
1278   The request requires user authentication (see &auth;).
1279</t>
1280</section>
1281
1282<section title="402 Payment Required" anchor="status.402">
1283  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1284  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1285<t>
1286   This code is reserved for future use.
1287</t>
1288</section>
1289
1290<section title="403 Forbidden" anchor="status.403">
1291  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1292  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1293<t>
1294   The server understood the request, but is refusing to fulfill it.
1295   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1296   If the request method was not HEAD and the server wishes to make
1297   public why the request has not been fulfilled, it &SHOULD; describe the
1298   reason for the refusal in the entity.  If the server does not wish to
1299   make this information available to the client, the status code 404
1300   (Not Found) can be used instead.
1301</t>
1302</section>
1303
1304<section title="404 Not Found" anchor="status.404">
1305  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1306  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1307<t>
1308   The server has not found anything matching the Request-URI. No
1309   indication is given of whether the condition is temporary or
1310   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1311   knows, through some internally configurable mechanism, that an old
1312   resource is permanently unavailable and has no forwarding address.
1313   This status code is commonly used when the server does not wish to
1314   reveal exactly why the request has been refused, or when no other
1315   response is applicable.
1316</t>
1317</section>
1318
1319<section title="405 Method Not Allowed" anchor="status.405">
1320  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1321  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1322<t>
1323   The method specified in the Request-Line is not allowed for the
1324   resource identified by the Request-URI. The response &MUST; include an
1325   Allow header containing a list of valid methods for the requested
1326   resource.
1327</t>
1328</section>
1329
1330<section title="406 Not Acceptable" anchor="status.406">
1331  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1332  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1333<t>
1334   The resource identified by the request is only capable of generating
1335   response entities which have content characteristics not acceptable
1336   according to the accept headers sent in the request.
1337</t>
1338<t>
1339   Unless it was a HEAD request, the response &SHOULD; include an entity
1340   containing a list of available entity characteristics and location(s)
1341   from which the user or user agent can choose the one most
1342   appropriate. The entity format is specified by the media type given
1343   in the Content-Type header field. Depending upon the format and the
1344   capabilities of the user agent, selection of the most appropriate
1345   choice &MAY; be performed automatically. However, this specification
1346   does not define any standard for such automatic selection.
1347  <list><t>
1348      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1349      not acceptable according to the accept headers sent in the
1350      request. In some cases, this may even be preferable to sending a
1351      406 response. User agents are encouraged to inspect the headers of
1352      an incoming response to determine if it is acceptable.
1353  </t></list>
1354</t>
1355<t>
1356   If the response could be unacceptable, a user agent &SHOULD;
1357   temporarily stop receipt of more data and query the user for a
1358   decision on further actions.
1359</t>
1360</section>
1361
1362<section title="407 Proxy Authentication Required" anchor="status.407">
1363  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1364  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1365<t>
1366   This code is similar to 401 (Unauthorized), but indicates that the
1367   client must first authenticate itself with the proxy (see &auth;).
1368</t>
1369</section>
1370
1371<section title="408 Request Timeout" anchor="status.408">
1372  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1373  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1374<t>
1375   The client did not produce a request within the time that the server
1376   was prepared to wait. The client &MAY; repeat the request without
1377   modifications at any later time.
1378</t>
1379</section>
1380
1381<section title="409 Conflict" anchor="status.409">
1382  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1383  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1384<t>
1385   The request could not be completed due to a conflict with the current
1386   state of the resource. This code is only allowed in situations where
1387   it is expected that the user might be able to resolve the conflict
1388   and resubmit the request. The response body &SHOULD; include enough
1389   information for the user to recognize the source of the conflict.
1390   Ideally, the response entity would include enough information for the
1391   user or user agent to fix the problem; however, that might not be
1392   possible and is not required.
1393</t>
1394<t>
1395   Conflicts are most likely to occur in response to a PUT request. For
1396   example, if versioning were being used and the entity being PUT
1397   included changes to a resource which conflict with those made by an
1398   earlier (third-party) request, the server might use the 409 response
1399   to indicate that it can't complete the request. In this case, the
1400   response entity would likely contain a list of the differences
1401   between the two versions in a format defined by the response
1402   Content-Type.
1403</t>
1404</section>
1405
1406<section title="410 Gone" anchor="status.410">
1407  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1408  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1409<t>
1410   The requested resource is no longer available at the server and no
1411   forwarding address is known. This condition is expected to be
1412   considered permanent. Clients with link editing capabilities &SHOULD;
1413   delete references to the Request-URI after user approval. If the
1414   server does not know, or has no facility to determine, whether or not
1415   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1416   used instead. This response is cacheable unless indicated otherwise.
1417</t>
1418<t>
1419   The 410 response is primarily intended to assist the task of web
1420   maintenance by notifying the recipient that the resource is
1421   intentionally unavailable and that the server owners desire that
1422   remote links to that resource be removed. Such an event is common for
1423   limited-time, promotional services and for resources belonging to
1424   individuals no longer working at the server's site. It is not
1425   necessary to mark all permanently unavailable resources as "gone" or
1426   to keep the mark for any length of time -- that is left to the
1427   discretion of the server owner.
1428</t>
1429</section>
1430
1431<section title="411 Length Required" anchor="status.411">
1432  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1433  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1434<t>
1435   The server refuses to accept the request without a defined Content-Length.
1436   The client &MAY; repeat the request if it adds a valid
1437   Content-Length header field containing the length of the message-body
1438   in the request message.
1439</t>
1440</section>
1441
1442<section title="412 Precondition Failed" anchor="status.412">
1443  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1444  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1445<t>
1446   The precondition given in one or more of the request-header fields
1447   evaluated to false when it was tested on the server, as defined in
1448   &conditional;.
1449</t>
1450</section>
1451
1452<section title="413 Request Entity Too Large" anchor="status.413">
1453  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1454  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1455<t>
1456   The server is refusing to process a request because the request
1457   entity is larger than the server is willing or able to process. The
1458   server &MAY; close the connection to prevent the client from continuing
1459   the request.
1460</t>
1461<t>
1462   If the condition is temporary, the server &SHOULD; include a Retry-After
1463   header field to indicate that it is temporary and after what
1464   time the client &MAY; try again.
1465</t>
1466</section>
1467
1468<section title="414 Request-URI Too Long" anchor="status.414">
1469  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1470  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1471<t>
1472   The server is refusing to service the request because the Request-URI
1473   is longer than the server is willing to interpret. This rare
1474   condition is only likely to occur when a client has improperly
1475   converted a POST request to a GET request with long query
1476   information, when the client has descended into a URI "black hole" of
1477   redirection (e.g., a redirected URI prefix that points to a suffix of
1478   itself), or when the server is under attack by a client attempting to
1479   exploit security holes present in some servers using fixed-length
1480   buffers for reading or manipulating the Request-URI.
1481</t>
1482</section>
1483
1484<section title="415 Unsupported Media Type" anchor="status.415">
1485  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1486  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1487<t>
1488   The server is refusing to service the request because the entity of
1489   the request is in a format not supported by the requested resource
1490   for the requested method.
1491</t>
1492</section>
1493
1494<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1495  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1496  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1497<t>
1498   The request included a Range request-header field (&header-range;) and none of
1499   the range-specifier values in this field overlap the current extent
1500   of the selected resource.
1501</t>
1502</section>
1503
1504<section title="417 Expectation Failed" anchor="status.417">
1505  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1506  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1507<t>
1508   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1509   could not be met by this server, or, if the server is a proxy,
1510   the server has unambiguous evidence that the request could not be met
1511   by the next-hop server.
1512</t>
1513</section>
1514</section>
1515
1516<section title="Server Error 5xx" anchor="status.5xx">
1517<t>
1518   Response status codes beginning with the digit "5" indicate cases in
1519   which the server is aware that it has erred or is incapable of
1520   performing the request. Except when responding to a HEAD request, the
1521   server &SHOULD; include an entity containing an explanation of the
1522   error situation, and whether it is a temporary or permanent
1523   condition. User agents &SHOULD; display any included entity to the
1524   user. These response codes are applicable to any request method.
1525</t>
1526
1527<section title="500 Internal Server Error" anchor="status.500">
1528  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1529  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1530<t>
1531   The server encountered an unexpected condition which prevented it
1532   from fulfilling the request.
1533</t>
1534</section>
1535
1536<section title="501 Not Implemented" anchor="status.501">
1537  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1538  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1539<t>
1540   The server does not support the functionality required to fulfill the
1541   request. This is the appropriate response when the server does not
1542   recognize the request method and is not capable of supporting it for
1543   any resource.
1544</t>
1545</section>
1546
1547<section title="502 Bad Gateway" anchor="status.502">
1548  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1549  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1550<t>
1551   The server, while acting as a gateway or proxy, received an invalid
1552   response from the upstream server it accessed in attempting to
1553   fulfill the request.
1554</t>
1555</section>
1556
1557<section title="503 Service Unavailable" anchor="status.503">
1558  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1559  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1560<t>
1561   The server is currently unable to handle the request due to a
1562   temporary overloading or maintenance of the server. The implication
1563   is that this is a temporary condition which will be alleviated after
1564   some delay. If known, the length of the delay &MAY; be indicated in a
1565   Retry-After header. If no Retry-After is given, the client &SHOULD;
1566   handle the response as it would for a 500 response.
1567  <list><t>
1568      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1569      server must use it when becoming overloaded. Some servers may wish
1570      to simply refuse the connection.
1571  </t></list>
1572</t>
1573</section>
1574
1575<section title="504 Gateway Timeout" anchor="status.504">
1576  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1577  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1578<t>
1579   The server, while acting as a gateway or proxy, did not receive a
1580   timely response from the upstream server specified by the URI (e.g.
1581   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1582   to access in attempting to complete the request.
1583  <list><t>
1584      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1585      return 400 or 500 when DNS lookups time out.
1586  </t></list>
1587</t>
1588</section>
1589
1590<section title="505 HTTP Version Not Supported" anchor="status.505">
1591  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1592  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1593<t>
1594   The server does not support, or refuses to support, the HTTP protocol
1595   version that was used in the request message. The server is
1596   indicating that it is unable or unwilling to complete the request
1597   using the same major version as the client, as described in &http-version;,
1598   other than with this error message. The response &SHOULD; contain
1599   an entity describing why that version is not supported and what other
1600   protocols are supported by that server.
1601</t>
1602
1603</section>
1604</section>
1605</section>
1606
1607
1608<section title="Header Field Definitions" anchor="header.fields">
1609<t>
1610   This section defines the syntax and semantics of all standard
1611   HTTP/1.1 header fields. For entity-header fields, both sender and
1612   recipient refer to either the client or the server, depending on who
1613   sends and who receives the entity.
1614</t>
1615
1616<section title="Allow" anchor="header.allow">
1617  <iref primary="true" item="Allow header" x:for-anchor=""/>
1618  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1619<t>
1620      The Allow entity-header field lists the set of methods supported
1621      by the resource identified by the Request-URI. The purpose of this
1622      field is strictly to inform the recipient of valid methods
1623      associated with the resource. An Allow header field &MUST; be
1624      present in a 405 (Method Not Allowed) response.
1625</t>
1626<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1627       Allow   = "Allow" ":" #Method
1628</artwork></figure>
1629<t>
1630      Example of use:
1631</t>
1632<figure><artwork type="example">
1633       Allow: GET, HEAD, PUT
1634</artwork></figure>
1635<t>
1636      This field cannot prevent a client from trying other methods.
1637      However, the indications given by the Allow header field value
1638      &SHOULD; be followed. The actual set of allowed methods is defined
1639      by the origin server at the time of each request.
1640</t>
1641<t>
1642      The Allow header field &MAY; be provided with a PUT request to
1643      recommend the methods to be supported by the new or modified
1644      resource. The server is not required to support these methods and
1645      &SHOULD; include an Allow header in the response giving the actual
1646      supported methods.
1647</t>
1648<t>
1649      A proxy &MUST-NOT; modify the Allow header field even if it does not
1650      understand all the methods specified, since the user agent might
1651      have other means of communicating with the origin server.
1652</t>
1653</section>
1654
1655<section title="Expect" anchor="header.expect">
1656  <iref primary="true" item="Expect header" x:for-anchor=""/>
1657  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1658<t>
1659   The Expect request-header field is used to indicate that particular
1660   server behaviors are required by the client.
1661</t>
1662<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"/>
1663   Expect       =  "Expect" ":" 1#expectation
1664
1665   expectation  =  "100-continue" | expectation-extension
1666   expectation-extension =  token [ "=" ( token | quoted-string )
1667                            *expect-params ]
1668   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1669</artwork></figure>
1670<t>
1671   A server that does not understand or is unable to comply with any of
1672   the expectation values in the Expect field of a request &MUST; respond
1673   with appropriate error status. The server &MUST; respond with a 417
1674   (Expectation Failed) status if any of the expectations cannot be met
1675   or, if there are other problems with the request, some other 4xx
1676   status.
1677</t>
1678<t>
1679   This header field is defined with extensible syntax to allow for
1680   future extensions. If a server receives a request containing an
1681   Expect field that includes an expectation-extension that it does not
1682   support, it &MUST; respond with a 417 (Expectation Failed) status.
1683</t>
1684<t>
1685   Comparison of expectation values is case-insensitive for unquoted
1686   tokens (including the 100-continue token), and is case-sensitive for
1687   quoted-string expectation-extensions.
1688</t>
1689<t>
1690   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1691   return a 417 (Expectation Failed) status if it receives a request
1692   with an expectation that it cannot meet. However, the Expect
1693   request-header itself is end-to-end; it &MUST; be forwarded if the
1694   request is forwarded.
1695</t>
1696<t>
1697   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1698   Expect header.
1699</t>
1700<t>
1701   See &use100; for the use of the 100 (continue) status.
1702</t>
1703</section>
1704
1705<section title="From" anchor="header.from">
1706  <iref primary="true" item="From header" x:for-anchor=""/>
1707  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1708<t>
1709   The From request-header field, if given, &SHOULD; contain an Internet
1710   e-mail address for the human user who controls the requesting user
1711   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1712   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1713</t>
1714<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1715    From   = "From" ":" mailbox
1716</artwork></figure>
1717<t>
1718   An example is:
1719</t>
1720<figure><artwork type="example">
1721    From: webmaster@example.org
1722</artwork></figure>
1723<t>
1724   This header field &MAY; be used for logging purposes and as a means for
1725   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1726   be used as an insecure form of access protection. The interpretation
1727   of this field is that the request is being performed on behalf of the
1728   person given, who accepts responsibility for the method performed. In
1729   particular, robot agents &SHOULD; include this header so that the
1730   person responsible for running the robot can be contacted if problems
1731   occur on the receiving end.
1732</t>
1733<t>
1734   The Internet e-mail address in this field &MAY; be separate from the
1735   Internet host which issued the request. For example, when a request
1736   is passed through a proxy the original issuer's address &SHOULD; be
1737   used.
1738</t>
1739<t>
1740   The client &SHOULD-NOT;  send the From header field without the user's
1741   approval, as it might conflict with the user's privacy interests or
1742   their site's security policy. It is strongly recommended that the
1743   user be able to disable, enable, and modify the value of this field
1744   at any time prior to a request.
1745</t>
1746</section>
1747
1748<section title="Location" anchor="header.location">
1749  <iref primary="true" item="Location header" x:for-anchor=""/>
1750  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1751<t>
1752   The Location response-header field is used to redirect the recipient
1753   to a location other than the Request-URI for completion of the
1754   request or identification of a new resource. For 201 (Created)
1755   responses, the Location is that of the new resource which was created
1756   by the request. For 3xx responses, the location &SHOULD; indicate the
1757   server's preferred URI for automatic redirection to the resource. The
1758   field value consists of a single absolute URI.
1759</t>
1760<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1761    Location       = "Location" ":" absoluteURI [ "#" fragment ]
1762</artwork></figure>
1763<t>
1764   An example is:
1765</t>
1766<figure><artwork type="example">
1767    Location: http://www.example.org/pub/WWW/People.html
1768</artwork></figure>
1769<t>
1770  <list><t>
1771      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1772      from Location in that the Content-Location identifies the original
1773      location of the entity enclosed in the request. It is therefore
1774      possible for a response to contain header fields for both Location
1775      and Content-Location.
1776  </t></list>
1777</t>
1778</section>
1779
1780<section title="Max-Forwards" anchor="header.max-forwards">
1781  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1782  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1783<t>
1784   The Max-Forwards request-header field provides a mechanism with the
1785   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1786   number of proxies or gateways that can forward the request to the
1787   next inbound server. This can be useful when the client is attempting
1788   to trace a request chain which appears to be failing or looping in
1789   mid-chain.
1790</t>
1791<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1792    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1793</artwork></figure>
1794<t>
1795   The Max-Forwards value is a decimal integer indicating the remaining
1796   number of times this request message may be forwarded.
1797</t>
1798<t>
1799   Each proxy or gateway recipient of a TRACE or OPTIONS request
1800   containing a Max-Forwards header field &MUST; check and update its
1801   value prior to forwarding the request. If the received value is zero
1802   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1803   respond as the final recipient. If the received Max-Forwards value is
1804   greater than zero, then the forwarded message &MUST; contain an updated
1805   Max-Forwards field with a value decremented by one (1).
1806</t>
1807<t>
1808   The Max-Forwards header field &MAY; be ignored for all other methods
1809   defined by this specification and for any extension methods for which
1810   it is not explicitly referred to as part of that method definition.
1811</t>
1812</section>
1813
1814<section title="Referer" anchor="header.referer">
1815  <iref primary="true" item="Referer header" x:for-anchor=""/>
1816  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1817<t>
1818   The Referer[sic] request-header field allows the client to specify,
1819   for the server's benefit, the address (URI) of the resource from
1820   which the Request-URI was obtained (the "referrer", although the
1821   header field is misspelled.) The Referer request-header allows a
1822   server to generate lists of back-links to resources for interest,
1823   logging, optimized caching, etc. It also allows obsolete or mistyped
1824   links to be traced for maintenance. The Referer field &MUST-NOT; be
1825   sent if the Request-URI was obtained from a source that does not have
1826   its own URI, such as input from the user keyboard.
1827</t>
1828<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1829    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1830</artwork></figure>
1831<t>
1832   Example:
1833</t>
1834<figure><artwork type="example">
1835    Referer: http://www.example.org/hypertext/Overview.html
1836</artwork></figure>
1837<t>
1838   If the field value is a relative URI, it &SHOULD; be interpreted
1839   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1840   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1841</t>
1842</section>
1843
1844<section title="Retry-After" anchor="header.retry-after">
1845  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1846  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1847<t>
1848   The Retry-After response-header field can be used with a 503 (Service
1849   Unavailable) response to indicate how long the service is expected to
1850   be unavailable to the requesting client. This field &MAY; also be used
1851   with any 3xx (Redirection) response to indicate the minimum time the
1852   user-agent is asked wait before issuing the redirected request. The
1853   value of this field can be either an HTTP-date or an integer number
1854   of seconds (in decimal) after the time of the response.
1855</t>
1856<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1857    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1858</artwork></figure>
1859<t>
1860   Two examples of its use are
1861</t>
1862<figure><artwork type="example">
1863    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1864    Retry-After: 120
1865</artwork></figure>
1866<t>
1867   In the latter example, the delay is 2 minutes.
1868</t>
1869</section>
1870
1871<section title="Server" anchor="header.server">
1872  <iref primary="true" item="Server header" x:for-anchor=""/>
1873  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1874<t>
1875   The Server response-header field contains information about the
1876   software used by the origin server to handle the request. The field
1877   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1878   identifying the server and any significant subproducts. The product
1879   tokens are listed in order of their significance for identifying the
1880   application.
1881</t>
1882<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1883    Server         = "Server" ":" 1*( product | comment )
1884</artwork></figure>
1885<t>
1886   Example:
1887</t>
1888<figure><artwork type="example">
1889    Server: CERN/3.0 libwww/2.17
1890</artwork></figure>
1891<t>
1892   If the response is being forwarded through a proxy, the proxy
1893   application &MUST-NOT; modify the Server response-header. Instead, it
1894   &MUST; include a Via field (as described in &header-via;).
1895  <list><t>
1896      <x:h>Note:</x:h> Revealing the specific software version of the server might
1897      allow the server machine to become more vulnerable to attacks
1898      against software that is known to contain security holes. Server
1899      implementors are encouraged to make this field a configurable
1900      option.
1901  </t></list>
1902</t>
1903</section>
1904
1905<section title="User-Agent" anchor="header.user-agent">
1906  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1907  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1908<t>
1909   The User-Agent request-header field contains information about the
1910   user agent originating the request. This is for statistical purposes,
1911   the tracing of protocol violations, and automated recognition of user
1912   agents for the sake of tailoring responses to avoid particular user
1913   agent limitations. User agents &SHOULD; include this field with
1914   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1915   and comments identifying the agent and any subproducts which form a
1916   significant part of the user agent. By convention, the product tokens
1917   are listed in order of their significance for identifying the
1918   application.
1919</t>
1920<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1921    User-Agent     = "User-Agent" ":" 1*( product | comment )
1922</artwork></figure>
1923<t>
1924   Example:
1925</t>
1926<figure><artwork type="example">
1927    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1928</artwork></figure>
1929</section>
1930
1931</section>
1932
1933<section title="IANA Considerations" anchor="IANA.considerations">
1934<t>
1935   TBD.
1936</t>
1937</section>
1938
1939<section title="Security Considerations" anchor="security.considerations">
1940<t>
1941   This section is meant to inform application developers, information
1942   providers, and users of the security limitations in HTTP/1.1 as
1943   described by this document. The discussion does not include
1944   definitive solutions to the problems revealed, though it does make
1945   some suggestions for reducing security risks.
1946</t>
1947
1948<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1949<t>
1950   Like any generic data transfer protocol, HTTP cannot regulate the
1951   content of the data that is transferred, nor is there any a priori
1952   method of determining the sensitivity of any particular piece of
1953   information within the context of any given request. Therefore,
1954   applications &SHOULD; supply as much control over this information as
1955   possible to the provider of that information. Four header fields are
1956   worth special mention in this context: Server, Via, Referer and From.
1957</t>
1958<t>
1959   Revealing the specific software version of the server might allow the
1960   server machine to become more vulnerable to attacks against software
1961   that is known to contain security holes. Implementors &SHOULD; make the
1962   Server header field a configurable option.
1963</t>
1964<t>
1965   Proxies which serve as a portal through a network firewall &SHOULD;
1966   take special precautions regarding the transfer of header information
1967   that identifies the hosts behind the firewall. In particular, they
1968   &SHOULD; remove, or replace with sanitized versions, any Via fields
1969   generated behind the firewall.
1970</t>
1971<t>
1972   The Referer header allows reading patterns to be studied and reverse
1973   links drawn. Although it can be very useful, its power can be abused
1974   if user details are not separated from the information contained in
1975   the Referer. Even when the personal information has been removed, the
1976   Referer header might indicate a private document's URI whose
1977   publication would be inappropriate.
1978</t>
1979<t>
1980   The information sent in the From field might conflict with the user's
1981   privacy interests or their site's security policy, and hence it
1982   &SHOULD-NOT;  be transmitted without the user being able to disable,
1983   enable, and modify the contents of the field. The user &MUST; be able
1984   to set the contents of this field within a user preference or
1985   application defaults configuration.
1986</t>
1987<t>
1988   We suggest, though do not require, that a convenient toggle interface
1989   be provided for the user to enable or disable the sending of From and
1990   Referer information.
1991</t>
1992<t>
1993   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
1994   fields can sometimes be used to determine that a specific client or
1995   server have a particular security hole which might be exploited.
1996   Unfortunately, this same information is often used for other valuable
1997   purposes for which HTTP currently has no better mechanism.
1998</t>
1999</section>
2000
2001<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2002<t>
2003   Because the source of a link might be private information or might
2004   reveal an otherwise private information source, it is strongly
2005   recommended that the user be able to select whether or not the
2006   Referer field is sent. For example, a browser client could have a
2007   toggle switch for browsing openly/anonymously, which would
2008   respectively enable/disable the sending of Referer and From
2009   information.
2010</t>
2011<t>
2012   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2013   HTTP request if the referring page was transferred with a secure
2014   protocol.
2015</t>
2016<t>
2017   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2018   based forms for the submission of sensitive data, because this will
2019   cause this data to be encoded in the Request-URI. Many existing
2020   servers, proxies, and user agents will log the request URI in some
2021   place where it might be visible to third parties. Servers can use
2022   POST-based form submission instead
2023</t>
2024</section>
2025
2026<section title="Location Headers and Spoofing" anchor="location.spoofing">
2027<t>
2028   If a single server supports multiple organizations that do not trust
2029   one another, then it &MUST; check the values of Location and Content-Location
2030   headers in responses that are generated under control of
2031   said organizations to make sure that they do not attempt to
2032   invalidate resources over which they have no authority.
2033</t>
2034</section>
2035
2036</section>
2037
2038<section title="Acknowledgments" anchor="ack">
2039<t>
2040   Based on an XML translation of RFC 2616 by Julian Reschke.
2041</t>
2042</section>
2043</middle>
2044<back>
2045<references>
2046
2047<reference anchor="Part1">
2048   <front>
2049      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2050      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2051         <organization abbrev="Day Software">Day Software</organization>
2052         <address><email>fielding@gbiv.com</email></address>
2053      </author>
2054      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2055         <organization>One Laptop per Child</organization>
2056         <address><email>jg@laptop.org</email></address>
2057      </author>
2058      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2059         <organization abbrev="HP">Hewlett-Packard Company</organization>
2060         <address><email>JeffMogul@acm.org</email></address>
2061      </author>
2062      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2063         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2064         <address><email>henrikn@microsoft.com</email></address>
2065      </author>
2066      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2067         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2068         <address><email>LMM@acm.org</email></address>
2069      </author>
2070      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2071         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2072         <address><email>paulle@microsoft.com</email></address>
2073      </author>
2074      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2075         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2076         <address><email>timbl@w3.org</email></address>
2077      </author>
2078      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2079   </front>
2080   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2081   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2082</reference>
2083
2084<reference anchor="Part3">
2085   <front>
2086      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2087      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2088         <organization abbrev="Day Software">Day Software</organization>
2089         <address><email>fielding@gbiv.com</email></address>
2090      </author>
2091      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2092         <organization>One Laptop per Child</organization>
2093         <address><email>jg@laptop.org</email></address>
2094      </author>
2095      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2096         <organization abbrev="HP">Hewlett-Packard Company</organization>
2097         <address><email>JeffMogul@acm.org</email></address>
2098      </author>
2099      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2100         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2101         <address><email>henrikn@microsoft.com</email></address>
2102      </author>
2103      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2104         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2105         <address><email>LMM@acm.org</email></address>
2106      </author>
2107      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2108         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2109         <address><email>paulle@microsoft.com</email></address>
2110      </author>
2111      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2112         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2113         <address><email>timbl@w3.org</email></address>
2114      </author>
2115      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2116   </front>
2117   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2118   <x:source href="p3-payload.xml" basename="p3-payload"/>
2119</reference>
2120
2121<reference anchor="Part4">
2122   <front>
2123      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2124      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2125         <organization abbrev="Day Software">Day Software</organization>
2126         <address><email>fielding@gbiv.com</email></address>
2127      </author>
2128      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2129         <organization>One Laptop per Child</organization>
2130         <address><email>jg@laptop.org</email></address>
2131      </author>
2132      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2133         <organization abbrev="HP">Hewlett-Packard Company</organization>
2134         <address><email>JeffMogul@acm.org</email></address>
2135      </author>
2136      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2137         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2138         <address><email>henrikn@microsoft.com</email></address>
2139      </author>
2140      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2141         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2142         <address><email>LMM@acm.org</email></address>
2143      </author>
2144      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2145         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2146         <address><email>paulle@microsoft.com</email></address>
2147      </author>
2148      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2149         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2150         <address><email>timbl@w3.org</email></address>
2151      </author>
2152      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2153   </front>
2154   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2155   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2156</reference>
2157
2158<reference anchor="Part5">
2159   <front>
2160      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2161      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2162         <organization abbrev="Day Software">Day Software</organization>
2163         <address><email>fielding@gbiv.com</email></address>
2164      </author>
2165      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2166         <organization>One Laptop per Child</organization>
2167         <address><email>jg@laptop.org</email></address>
2168      </author>
2169      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2170         <organization abbrev="HP">Hewlett-Packard Company</organization>
2171         <address><email>JeffMogul@acm.org</email></address>
2172      </author>
2173      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2174         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2175         <address><email>henrikn@microsoft.com</email></address>
2176      </author>
2177      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2178         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2179         <address><email>LMM@acm.org</email></address>
2180      </author>
2181      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2182         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2183         <address><email>paulle@microsoft.com</email></address>
2184      </author>
2185      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2186         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2187         <address><email>timbl@w3.org</email></address>
2188      </author>
2189      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2190   </front>
2191   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2192   <x:source href="p5-range.xml" basename="p5-range"/>
2193</reference>
2194
2195<reference anchor="Part6">
2196   <front>
2197      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2198      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2199         <organization abbrev="Day Software">Day Software</organization>
2200         <address><email>fielding@gbiv.com</email></address>
2201      </author>
2202      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2203         <organization>One Laptop per Child</organization>
2204         <address><email>jg@laptop.org</email></address>
2205      </author>
2206      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2207         <organization abbrev="HP">Hewlett-Packard Company</organization>
2208         <address><email>JeffMogul@acm.org</email></address>
2209      </author>
2210      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2211         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2212         <address><email>henrikn@microsoft.com</email></address>
2213      </author>
2214      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2215         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2216         <address><email>LMM@acm.org</email></address>
2217      </author>
2218      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2219         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2220         <address><email>paulle@microsoft.com</email></address>
2221      </author>
2222      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2223         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2224         <address><email>timbl@w3.org</email></address>
2225      </author>
2226      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2227   </front>
2228   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2229   <x:source href="p6-cache.xml" basename="p6-cache"/>
2230</reference>
2231
2232<reference anchor="Part7">
2233   <front>
2234      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2235      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2236         <organization abbrev="Day Software">Day Software</organization>
2237         <address><email>fielding@gbiv.com</email></address>
2238      </author>
2239      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2240         <organization>One Laptop per Child</organization>
2241         <address><email>jg@laptop.org</email></address>
2242      </author>
2243      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2244         <organization abbrev="HP">Hewlett-Packard Company</organization>
2245         <address><email>JeffMogul@acm.org</email></address>
2246      </author>
2247      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2248         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2249         <address><email>henrikn@microsoft.com</email></address>
2250      </author>
2251      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2252         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2253         <address><email>LMM@acm.org</email></address>
2254      </author>
2255      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2256         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2257         <address><email>paulle@microsoft.com</email></address>
2258      </author>
2259      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2260         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2261         <address><email>timbl@w3.org</email></address>
2262      </author>
2263      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2264   </front>
2265   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2266   <x:source href="p7-auth.xml" basename="p7-auth"/>
2267</reference>
2268
2269<reference anchor="RFC2616">
2270   <front>
2271      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2272      <author initials="R." surname="Fielding" fullname="R. Fielding">
2273         <organization>University of California, Irvine</organization>
2274         <address><email>fielding@ics.uci.edu</email></address>
2275      </author>
2276      <author initials="J." surname="Gettys" fullname="J. Gettys">
2277         <organization>W3C</organization>
2278         <address><email>jg@w3.org</email></address>
2279      </author>
2280      <author initials="J." surname="Mogul" fullname="J. Mogul">
2281         <organization>Compaq Computer Corporation</organization>
2282         <address><email>mogul@wrl.dec.com</email></address>
2283      </author>
2284      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2285         <organization>MIT Laboratory for Computer Science</organization>
2286         <address><email>frystyk@w3.org</email></address>
2287      </author>
2288      <author initials="L." surname="Masinter" fullname="L. Masinter">
2289         <organization>Xerox Corporation</organization>
2290         <address><email>masinter@parc.xerox.com</email></address>
2291      </author>
2292      <author initials="P." surname="Leach" fullname="P. Leach">
2293         <organization>Microsoft Corporation</organization>
2294         <address><email>paulle@microsoft.com</email></address>
2295      </author>
2296      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2297         <organization>W3C</organization>
2298         <address><email>timbl@w3.org</email></address>
2299      </author>
2300      <date month="June" year="1999"/>
2301   </front>
2302   <seriesInfo name="RFC" value="2616"/>
2303</reference>
2304
2305<reference anchor="RFC1123">
2306<front>
2307<title>Requirements for Internet Hosts - Application and Support</title>
2308<author initials="R." surname="Braden" fullname="Robert Braden">
2309<organization>University of Southern California (USC), Information Sciences Institute</organization>
2310<address>
2311<postal>
2312<street>4676 Admiralty Way</street>
2313<city>Marina del Rey</city>
2314<region>CA</region>
2315<code>90292-6695</code>
2316<country>US</country></postal>
2317<phone>+1 213 822 1511</phone>
2318<email>Braden@ISI.EDU</email></address></author>
2319<date month="October" year="1989"/></front>
2320<seriesInfo name="STD" value="3"/>
2321<seriesInfo name="RFC" value="1123"/>
2322</reference>
2323
2324<reference anchor="RFC822">
2325<front>
2326<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2327<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2328<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2329<address>
2330<postal>
2331<street/>
2332<city>Newark</city>
2333<region>DE</region>
2334<code>19711</code>
2335<country>US</country></postal>
2336<email>DCrocker@UDel-Relay</email></address></author>
2337<date month="August" day="13" year="1982"/></front>
2338<seriesInfo name="STD" value="11"/>
2339<seriesInfo name="RFC" value="822"/>
2340</reference>
2341
2342<reference anchor="RFC2068">
2343<front>
2344<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2345<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2346<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2347<address>
2348<postal>
2349<street/>
2350<city>Irvine</city>
2351<region>CA</region>
2352<code>92717-3425</code>
2353<country>US</country></postal>
2354<facsimile>+1 714 824 4056</facsimile>
2355<email>fielding@ics.uci.edu</email></address></author>
2356<author initials="J." surname="Gettys" fullname="Jim Gettys">
2357<organization>MIT Laboratory for Computer Science</organization>
2358<address>
2359<postal>
2360<street>545 Technology Square</street>
2361<city>Cambridge</city>
2362<region>MA</region>
2363<code>02139</code>
2364<country>US</country></postal>
2365<facsimile>+1 617 258 8682</facsimile>
2366<email>jg@w3.org</email></address></author>
2367<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2368<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2369<address>
2370<postal>
2371<street>250 University Avenue</street>
2372<city>Palo Alto</city>
2373<region>CA</region>
2374<code>94301</code>
2375<country>US</country></postal>
2376<email>mogul@wrl.dec.com</email></address></author>
2377<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2378<organization>MIT Laboratory for Computer Science</organization>
2379<address>
2380<postal>
2381<street>545 Technology Square</street>
2382<city>Cambridge</city>
2383<region>MA</region>
2384<code>02139</code>
2385<country>US</country></postal>
2386<facsimile>+1 617 258 8682</facsimile>
2387<email>frystyk@w3.org</email></address></author>
2388<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2389<organization>MIT Laboratory for Computer Science</organization>
2390<address>
2391<postal>
2392<street>545 Technology Square</street>
2393<city>Cambridge</city>
2394<region>MA</region>
2395<code>02139</code>
2396<country>US</country></postal>
2397<facsimile>+1 617 258 8682</facsimile>
2398<email>timbl@w3.org</email></address></author>
2399<date month="January" year="1997"/>
2400<abstract>
2401<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>
2402<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>
2403<seriesInfo name="RFC" value="2068"/>
2404</reference>
2405
2406<reference anchor="Luo1998">
2407<front>
2408<title>Tunneling TCP based protocols through Web proxy servers</title>
2409<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2410  <organization/>
2411</author>
2412<date/>
2413</front>
2414<seriesInfo name="" value="Work in Progress"/>
2415</reference>
2416
2417</references>
2418
2419<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2420<t>
2421   Clarified which error code should be used for inbound server failures
2422   (e.g. DNS failures). (<xref target="status.504"/>).
2423</t>
2424<t>
2425   CREATE had a race that required an Etag be sent when a resource is
2426   first created. (<xref target="status.201"/>).
2427</t>
2428<t>
2429   Rewrite of message transmission requirements to make it much harder
2430   for implementors to get it wrong, as the consequences of errors here
2431   can have significant impact on the Internet, and to deal with the
2432   following problems:
2433  <list style="numbers">
2434      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2435         this was incorrectly placing a requirement on the behavior of
2436         an implementation of a future version of HTTP/1.x</t>
2437
2438      <t>Made it clear that user-agents should retry requests, not
2439         "clients" in general.</t>
2440
2441      <t>Converted requirements for clients to ignore unexpected 100
2442         (Continue) responses, and for proxies to forward 100 responses,
2443         into a general requirement for 1xx responses.</t>
2444
2445      <t>Modified some TCP-specific language, to make it clearer that
2446         non-TCP transports are possible for HTTP.</t>
2447
2448      <t>Require that the origin server &MUST-NOT; wait for the request
2449         body before it sends a required 100 (Continue) response.</t>
2450
2451      <t>Allow, rather than require, a server to omit 100 (Continue) if
2452         it has already seen some of the request body.</t>
2453
2454      <t>Allow servers to defend against denial-of-service attacks and
2455         broken clients.</t>
2456  </list>
2457</t>
2458<t>
2459   This change adds the Expect header and 417 status code.
2460</t>
2461<t>
2462   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2463   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2464</t>
2465<t>
2466   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
2467   implemented in previous versions of this specification. See RFC 2068
2468   <xref target="RFC2068"/>.
2469</t>
2470</section>
2471</back>
2472</rfc>
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