source: draft-ietf-httpbis/latest/p2-semantics.xml @ 36

Last change on this file since 36 was 36, checked in by fielding@…, 12 years ago

Add an editorial note about status and list.
Streamline the new references and place them up front.

  • Property svn:eol-style set to native
File size: 119.6 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]>
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc-ext allow-markup-in-artwork="yes" ?>
67<?rfc-ext include-references-in-index="yes" ?>
68<rfc obsoletes="2068, 2616, 2617" category="std"
69     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
70     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
71<front>
72
73  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
74
75  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
76    <organization abbrev="Day Software">Day Software</organization>
77    <address>
78      <postal>
79        <street>23 Corporate Plaza DR, Suite 280</street>
80        <city>Newport Beach</city>
81        <region>CA</region>
82        <code>92660</code>
83        <country>USA</country>
84      </postal>
85      <phone>+1-949-706-5300</phone>
86      <facsimile>+1-949-706-5305</facsimile>
87      <email>fielding@gbiv.com</email>
88      <uri>http://roy.gbiv.com/</uri>
89    </address>
90  </author>
91
92  <author initials="J." surname="Gettys" fullname="Jim Gettys">
93    <organization>One Laptop per Child</organization>
94    <address>
95      <postal>
96        <street>21 Oak Knoll Road</street>
97        <city>Carlisle</city>
98        <region>MA</region>
99        <code>01741</code>
100        <country>USA</country>
101      </postal>
102      <email>jg@laptop.org</email>
103      <uri>http://www.laptop.org/</uri>
104    </address>
105  </author>
106 
107  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
108    <organization abbrev="HP">Hewlett-Packard Company</organization>
109    <address>
110      <postal>
111        <street>HP Labs, Large Scale Systems Group</street>
112        <street>1501 Page Mill Road, MS 1177</street>
113        <city>Palo Alto</city>
114        <region>CA</region>
115        <code>94304</code>
116        <country>USA</country>
117      </postal>
118      <email>JeffMogul@acm.org</email>
119    </address>
120  </author>
121
122  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
123    <organization abbrev="Microsoft">Microsoft Corporation</organization>
124    <address>
125      <postal>
126        <street>1 Microsoft Way</street>
127        <city>Redmond</city>
128        <region>WA</region>
129        <code>98052</code>
130        <country>USA</country>
131      </postal>
132      <email>henrikn@microsoft.com</email>
133    </address>
134  </author>
135
136  <author initials="L." surname="Masinter" fullname="Larry Masinter">
137    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
138    <address>
139      <postal>
140        <street>345 Park Ave</street>
141        <city>San Jose</city>
142        <region>CA</region>
143        <code>95110</code>
144        <country>USA</country>
145      </postal>
146      <email>LMM@acm.org</email>
147      <uri>http://larry.masinter.net/</uri>
148    </address>
149  </author>
150 
151  <author initials="P." surname="Leach" fullname="Paul J. Leach">
152    <organization abbrev="Microsoft">Microsoft Corporation</organization>
153    <address>
154      <postal>
155        <street>1 Microsoft Way</street>
156        <city>Redmond</city>
157        <region>WA</region>
158        <code>98052</code>
159      </postal>
160      <email>paulle@microsoft.com</email>
161    </address>
162  </author>
163   
164  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
165    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
169        <street>The Stata Center, Building 32</street>
170        <street>32 Vassar Street</street>
171        <city>Cambridge</city>
172        <region>MA</region>
173        <code>02139</code>
174        <country>USA</country>
175      </postal>
176      <email>timbl@w3.org</email>
177      <uri>http://www.w3.org/People/Berners-Lee/</uri>
178    </address>
179  </author>
180
181  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
182
183<abstract>
184<t>
185   The Hypertext Transfer Protocol (HTTP) is an application-level
186   protocol for distributed, collaborative, hypermedia information
187   systems. HTTP has been in use by the World Wide Web global information
188   initiative since 1990. This document is Part 2 of the seven-part specification
189   that defines the protocol referred to as "HTTP/1.1" and, taken together,
190   obsoletes RFC 2616 and RFC 2617.  Part 2 defines the semantics of HTTP messages
191   as expressed by request methods, request-header fields, response status codes,
192   and response-header fields.
193</t>
194</abstract>
195
196<note title="Editorial Note (To be removed by RFC Editor)">
197  <t>
198    This version of the HTTP specification contains only minimal editorial
199    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
200    and authors' addresses).  All other changes are due to partitioning the
201    original into seven mostly independent parts.  The intent is for readers
202    of future drafts to able to use draft 00 as the basis for comparison
203    when the WG makes later changes to the specification text.  This draft
204    will shortly be followed by draft 01 (containing the first round of changes
205    that have already been agreed to on the mailing list). There is no point in
206    reviewing this draft other than to verify that the partitioning has been
207    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
208    will be the editors after draft 00 is submitted.
209  </t>
210  <t>
211    Discussion of this draft should take place on the HTTPBIS working group
212    mailing list (ietf-http-wg@w3.org). The current issues list is
213    at <eref target="http://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/"/>
214    and related documents (including fancy diffs) can be found at
215    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
216  </t>
217</note>
218</front>
219<middle>
220<section title="Introduction" anchor="introduction">
221<t>
222   This document will define aspects of HTTP related to request and response
223   semantics. Right now it only includes the extracted relevant sections of
224   RFC 2616 with only minor edits.
225</t>
226<t>
227   The HTTP protocol is a request/response protocol. A client sends a
228   request to the server in the form of a request method, URI, and
229   protocol version, followed by a MIME-like message containing request
230   modifiers, client information, and possible body content over a
231   connection with a server. The server responds with a status line,
232   including the message's protocol version and a success or error code,
233   followed by a MIME-like message containing server information, entity
234   metainformation, and possible entity-body content. The relationship
235   between HTTP and MIME is described in &diff2045entity;.
236</t>
237</section>
238
239<section title="Product Tokens" anchor="product.tokens">
240<t>
241   Product tokens are used to allow communicating applications to
242   identify themselves by software name and version. Most fields using
243   product tokens also allow sub-products which form a significant part
244   of the application to be listed, separated by white space. By
245   convention, the products are listed in order of their significance
246   for identifying the application.
247</t>
248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
249    product         = token ["/" product-version]
250    product-version = token
251</artwork></figure>
252<t>
253   Examples:
254</t>
255<figure><artwork type="example">
256    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
257    Server: Apache/0.8.4
258</artwork></figure>
259<t>
260   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
261   used for advertising or other non-essential information. Although any
262   token character &MAY; appear in a product-version, this token &SHOULD;
263   only be used for a version identifier (i.e., successive versions of
264   the same product &SHOULD; only differ in the product-version portion of
265   the product value).
266</t>
267</section>
268
269<section title="Method" anchor="method">
270<t>
271   The Method  token indicates the method to be performed on the
272   resource identified by the Request-URI. The method is case-sensitive.
273</t>
274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
275    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
276                   | "GET"                    ; <xref target="GET"/>
277                   | "HEAD"                   ; <xref target="HEAD"/>
278                   | "POST"                   ; <xref target="POST"/>
279                   | "PUT"                    ; <xref target="PUT"/>
280                   | "DELETE"                 ; <xref target="DELETE"/>
281                   | "TRACE"                  ; <xref target="TRACE"/>
282                   | "CONNECT"                ; <xref target="CONNECT"/>
283                   | extension-method
284    extension-method = token
285</artwork></figure>
286<t>
287   The list of methods allowed by a resource can be specified in an
288   Allow header field (<xref target="header.allow"/>). The return code of the response
289   always notifies the client whether a method is currently allowed on a
290   resource, since the set of allowed methods can change dynamically. An
291   origin server &SHOULD; return the status code 405 (Method Not Allowed)
292   if the method is known by the origin server but not allowed for the
293   requested resource, and 501 (Not Implemented) if the method is
294   unrecognized or not implemented by the origin server. The methods GET
295   and HEAD &MUST; be supported by all general-purpose servers. All other
296   methods are &OPTIONAL;; however, if the above methods are implemented,
297   they &MUST; be implemented with the same semantics as those specified
298   in <xref target="method.definitions"/>.
299</t>
300</section>
301
302<section title="Request Header Fields" anchor="request.header.fields">
303<t>
304   The request-header fields allow the client to pass additional
305   information about the request, and about the client itself, to the
306   server. These fields act as request modifiers, with semantics
307   equivalent to the parameters on a programming language method
308   invocation.
309</t>
310<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
311    request-header = Accept                   ; &header-accept;
312                   | Accept-Charset           ; &header-accept-charset;
313                   | Accept-Encoding          ; &header-accept-encoding;
314                   | Accept-Language          ; &header-accept-language;
315                   | Authorization            ; &header-authorization;
316                   | Expect                   ; <xref target="header.expect"/>
317                   | From                     ; <xref target="header.from"/>
318                   | Host                     ; &header-host;
319                   | If-Match                 ; &header-if-match;
320                   | If-Modified-Since        ; &header-if-modified-since;
321                   | If-None-Match            ; &header-if-none-match;
322                   | If-Range                 ; &header-if-range;
323                   | If-Unmodified-Since      ; &header-if-unmodified-since;
324                   | Max-Forwards             ; <xref target="header.max-forwards"/>
325                   | Proxy-Authorization      ; &header-proxy-authorization;
326                   | Range                    ; &header-range;
327                   | Referer                  ; <xref target="header.referer"/>
328                   | TE                       ; &header-te;
329                   | User-Agent               ; <xref target="header.user-agent"/>
330</artwork></figure>
331<t>
332   Request-header field names can be extended reliably only in
333   combination with a change in the protocol version. However, new or
334   experimental header fields &MAY; be given the semantics of request-header
335   fields if all parties in the communication recognize them to
336   be request-header fields. Unrecognized header fields are treated as
337   entity-header fields.
338</t>
339</section>
340
341<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
342<t>
343   The Status-Code element is a 3-digit integer result code of the
344   attempt to understand and satisfy the request. These codes are fully
345   defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
346   textual description of the Status-Code. The Status-Code is intended
347   for use by automata and the Reason-Phrase is intended for the human
348   user. The client is not required to examine or display the Reason-Phrase.
349</t>
350<t> 
351   The individual values of the numeric status codes defined for
352   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
353   presented below. The reason phrases listed here are only
354   recommendations -- they &MAY; be replaced by local equivalents without
355   affecting the protocol.
356</t>
357<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"/>
358   Status-Code    =
359         "100"  ; <xref target="status.100"/>: Continue
360       | "101"  ; <xref target="status.101"/>: Switching Protocols
361       | "200"  ; <xref target="status.200"/>: OK
362       | "201"  ; <xref target="status.201"/>: Created
363       | "202"  ; <xref target="status.202"/>: Accepted
364       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
365       | "204"  ; <xref target="status.204"/>: No Content
366       | "205"  ; <xref target="status.205"/>: Reset Content
367       | "206"  ; <xref target="status.206"/>: Partial Content
368       | "300"  ; <xref target="status.300"/>: Multiple Choices
369       | "301"  ; <xref target="status.301"/>: Moved Permanently
370       | "302"  ; <xref target="status.302"/>: Found
371       | "303"  ; <xref target="status.303"/>: See Other
372       | "304"  ; <xref target="status.304"/>: Not Modified
373       | "305"  ; <xref target="status.305"/>: Use Proxy
374       | "307"  ; <xref target="status.307"/>: Temporary Redirect
375       | "400"  ; <xref target="status.400"/>: Bad Request
376       | "401"  ; <xref target="status.401"/>: Unauthorized
377       | "402"  ; <xref target="status.402"/>: Payment Required
378       | "403"  ; <xref target="status.403"/>: Forbidden
379       | "404"  ; <xref target="status.404"/>: Not Found
380       | "405"  ; <xref target="status.405"/>: Method Not Allowed
381       | "406"  ; <xref target="status.406"/>: Not Acceptable
382       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
383       | "408"  ; <xref target="status.408"/>: Request Time-out
384       | "409"  ; <xref target="status.409"/>: Conflict
385       | "410"  ; <xref target="status.410"/>: Gone
386       | "411"  ; <xref target="status.411"/>: Length Required
387       | "412"  ; <xref target="status.412"/>: Precondition Failed
388       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
389       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
390       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
391       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
392       | "417"  ; <xref target="status.417"/>: Expectation Failed
393       | "500"  ; <xref target="status.500"/>: Internal Server Error
394       | "501"  ; <xref target="status.501"/>: Not Implemented
395       | "502"  ; <xref target="status.502"/>: Bad Gateway
396       | "503"  ; <xref target="status.503"/>: Service Unavailable
397       | "504"  ; <xref target="status.504"/>: Gateway Time-out
398       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
399       | extension-code
400
401   extension-code = 3DIGIT
402   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
403</artwork></figure>
404<t>
405   HTTP status codes are extensible. HTTP applications are not required
406   to understand the meaning of all registered status codes, though such
407   understanding is obviously desirable. However, applications &MUST;
408   understand the class of any status code, as indicated by the first
409   digit, and treat any unrecognized response as being equivalent to the
410   x00 status code of that class, with the exception that an
411   unrecognized response &MUST-NOT; be cached. For example, if an
412   unrecognized status code of 431 is received by the client, it can
413   safely assume that there was something wrong with its request and
414   treat the response as if it had received a 400 status code. In such
415   cases, user agents &SHOULD; present to the user the entity returned
416   with the response, since that entity is likely to include human-readable
417   information which will explain the unusual status.
418</t>
419</section>
420
421<section title="Response Header Fields" anchor="response.header.fields">
422<t>
423   The response-header fields allow the server to pass additional
424   information about the response which cannot be placed in the Status-Line.
425   These header fields give information about the server and about
426   further access to the resource identified by the Request-URI.
427</t>
428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
429    response-header = Accept-Ranges           ; &header-accept-ranges;
430                    | Age                     ; &header-age;
431                    | ETag                    ; &header-etag;
432                    | Location                ; <xref target="header.location"/>
433                    | Proxy-Authenticate      ; &header-proxy-authenticate;
434                    | Retry-After             ; <xref target="header.retry-after"/>
435                    | Server                  ; <xref target="header.server"/>
436                    | Vary                    ; &header-vary;
437                    | WWW-Authenticate        ; &header-www-authenticate;
438</artwork></figure>
439<t>
440   Response-header field names can be extended reliably only in
441   combination with a change in the protocol version. However, new or
442   experimental header fields &MAY; be given the semantics of response-header
443   fields if all parties in the communication recognize them to
444   be response-header fields. Unrecognized header fields are treated as
445   entity-header fields.
446</t>
447</section>
448
449<section title="Entity" anchor="entity">
450<t>
451   Request and Response messages &MAY; transfer an entity if not otherwise
452   restricted by the request method or response status code. An entity
453   consists of entity-header fields and an entity-body, although some
454   responses will only include the entity-headers. HTTP entity-body and
455   entity-header fields are defined in &payload;.
456</t>
457<t>
458   An entity-body is only present in a message when a message-body is
459   present, as described in &message-body;. The entity-body is obtained
460   from the message-body by decoding any Transfer-Encoding that might
461   have been applied to ensure safe and proper transfer of the message.
462</t>
463</section>
464
465
466<section title="Method Definitions" anchor="method.definitions">
467<t>
468   The set of common methods for HTTP/1.1 is defined below. Although
469   this set can be expanded, additional methods cannot be assumed to
470   share the same semantics for separately extended clients and servers.
471
472   The Host request-header field (&header-host;) &MUST; accompany all
473   HTTP/1.1 requests.
474</t>
475
476<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
477
478<section title="Safe Methods" anchor="safe.methods">
479<t>
480   Implementors should be aware that the software represents the user in
481   their interactions over the Internet, and should be careful to allow
482   the user to be aware of any actions they might take which may have an
483   unexpected significance to themselves or others.
484</t>
485<t>
486   In particular, the convention has been established that the GET and
487   HEAD methods &SHOULD-NOT;  have the significance of taking an action
488   other than retrieval. These methods ought to be considered "safe".
489   This allows user agents to represent other methods, such as POST, PUT
490   and DELETE, in a special way, so that the user is made aware of the
491   fact that a possibly unsafe action is being requested.
492</t>
493<t>
494   Naturally, it is not possible to ensure that the server does not
495   generate side-effects as a result of performing a GET request; in
496   fact, some dynamic resources consider that a feature. The important
497   distinction here is that the user did not request the side-effects,
498   so therefore cannot be held accountable for them.
499</t>
500</section>
501
502<section title="Idempotent Methods" anchor="idempotent.methods">
503<t>
504   Methods can also have the property of "idempotence" in that (aside
505   from error or expiration issues) the side-effects of N &gt; 0 identical
506   requests is the same as for a single request. The methods GET, HEAD,
507   PUT and DELETE share this property. Also, the methods OPTIONS and
508   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
509</t>
510<t>
511   However, it is possible that a sequence of several requests is non-idempotent,
512   even if all of the methods executed in that sequence are
513   idempotent. (A sequence is idempotent if a single execution of the
514   entire sequence always yields a result that is not changed by a
515   reexecution of all, or part, of that sequence.) For example, a
516   sequence is non-idempotent if its result depends on a value that is
517   later modified in the same sequence.
518</t>
519<t>
520   A sequence that never has side effects is idempotent, by definition
521   (provided that no concurrent operations are being executed on the
522   same set of resources).
523</t>
524</section>
525</section>
526
527<section title="OPTIONS" anchor="OPTIONS">
528  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
529  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
530<t>
531   The OPTIONS method represents a request for information about the
532   communication options available on the request/response chain
533   identified by the Request-URI. This method allows the client to
534   determine the options and/or requirements associated with a resource,
535   or the capabilities of a server, without implying a resource action
536   or initiating a resource retrieval.
537</t>
538<t>
539   Responses to this method are not cacheable.
540</t>
541<t>
542   If the OPTIONS request includes an entity-body (as indicated by the
543   presence of Content-Length or Transfer-Encoding), then the media type
544   &MUST; be indicated by a Content-Type field. Although this
545   specification does not define any use for such a body, future
546   extensions to HTTP might use the OPTIONS body to make more detailed
547   queries on the server. A server that does not support such an
548   extension &MAY; discard the request body.
549</t>
550<t>
551   If the Request-URI is an asterisk ("*"), the OPTIONS request is
552   intended to apply to the server in general rather than to a specific
553   resource. Since a server's communication options typically depend on
554   the resource, the "*" request is only useful as a "ping" or "no-op"
555   type of method; it does nothing beyond allowing the client to test
556   the capabilities of the server. For example, this can be used to test
557   a proxy for HTTP/1.1 compliance (or lack thereof).
558</t>
559<t>
560   If the Request-URI is not an asterisk, the OPTIONS request applies
561   only to the options that are available when communicating with that
562   resource.
563</t>
564<t>
565   A 200 response &SHOULD; include any header fields that indicate
566   optional features implemented by the server and applicable to that
567   resource (e.g., Allow), possibly including extensions not defined by
568   this specification. The response body, if any, &SHOULD; also include
569   information about the communication options. The format for such a
570   body is not defined by this specification, but might be defined by
571   future extensions to HTTP. Content negotiation &MAY; be used to select
572   the appropriate response format. If no response body is included, the
573   response &MUST; include a Content-Length field with a field-value of
574   "0".
575</t>
576<t>
577   The Max-Forwards request-header field &MAY; be used to target a
578   specific proxy in the request chain. When a proxy receives an OPTIONS
579   request on an absoluteURI for which request forwarding is permitted,
580   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
581   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
582   instead, the proxy &SHOULD; respond with its own communication options.
583   If the Max-Forwards field-value is an integer greater than zero, the
584   proxy &MUST; decrement the field-value when it forwards the request. If
585   no Max-Forwards field is present in the request, then the forwarded
586   request &MUST-NOT; include a Max-Forwards field.
587</t>
588</section>
589
590<section title="GET" anchor="GET">
591  <iref primary="true" item="GET method" x:for-anchor=""/>
592  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
593<t>
594   The GET method means retrieve whatever information (in the form of an
595   entity) is identified by the Request-URI. If the Request-URI refers
596   to a data-producing process, it is the produced data which shall be
597   returned as the entity in the response and not the source text of the
598   process, unless that text happens to be the output of the process.
599</t>
600<t>
601   The semantics of the GET method change to a "conditional GET" if the
602   request message includes an If-Modified-Since, If-Unmodified-Since,
603   If-Match, If-None-Match, or If-Range header field. A conditional GET
604   method requests that the entity be transferred only under the
605   circumstances described by the conditional header field(s). The
606   conditional GET method is intended to reduce unnecessary network
607   usage by allowing cached entities to be refreshed without requiring
608   multiple requests or transferring data already held by the client.
609</t>
610<t>
611   The semantics of the GET method change to a "partial GET" if the
612   request message includes a Range header field. A partial GET requests
613   that only part of the entity be transferred, as described in &header-range;.
614   The partial GET method is intended to reduce unnecessary
615   network usage by allowing partially-retrieved entities to be
616   completed without transferring data already held by the client.
617</t>
618<t>
619   The response to a GET request is cacheable if and only if it meets
620   the requirements for HTTP caching described in &caching;.
621</t>
622<t>
623   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
624</t>
625</section>
626
627<section title="HEAD" anchor="HEAD">
628  <iref primary="true" item="HEAD method" x:for-anchor=""/>
629  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
630<t>
631   The HEAD method is identical to GET except that the server &MUST-NOT;
632   return a message-body in the response. The metainformation contained
633   in the HTTP headers in response to a HEAD request &SHOULD; be identical
634   to the information sent in response to a GET request. This method can
635   be used for obtaining metainformation about the entity implied by the
636   request without transferring the entity-body itself. This method is
637   often used for testing hypertext links for validity, accessibility,
638   and recent modification.
639</t>
640<t>
641   The response to a HEAD request &MAY; be cacheable in the sense that the
642   information contained in the response &MAY; be used to update a
643   previously cached entity from that resource. If the new field values
644   indicate that the cached entity differs from the current entity (as
645   would be indicated by a change in Content-Length, Content-MD5, ETag
646   or Last-Modified), then the cache &MUST; treat the cache entry as
647   stale.
648</t>
649</section>
650
651<section title="POST" anchor="POST">
652  <iref primary="true" item="POST method" x:for-anchor=""/>
653  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
654<t>
655   The POST method is used to request that the origin server accept the
656   entity enclosed in the request as a new subordinate of the resource
657   identified by the Request-URI in the Request-Line. POST is designed
658   to allow a uniform method to cover the following functions:
659  <list style="symbols">
660    <t>
661      Annotation of existing resources;
662    </t>
663    <t>
664        Posting a message to a bulletin board, newsgroup, mailing list,
665        or similar group of articles;
666    </t>
667    <t>
668        Providing a block of data, such as the result of submitting a
669        form, to a data-handling process;
670    </t>
671    <t>
672        Extending a database through an append operation.
673    </t>
674  </list>
675</t>
676<t>
677   The actual function performed by the POST method is determined by the
678   server and is usually dependent on the Request-URI. The posted entity
679   is subordinate to that URI in the same way that a file is subordinate
680   to a directory containing it, a news article is subordinate to a
681   newsgroup to which it is posted, or a record is subordinate to a
682   database.
683</t>
684<t>
685   The action performed by the POST method might not result in a
686   resource that can be identified by a URI. In this case, either 200
687   (OK) or 204 (No Content) is the appropriate response status,
688   depending on whether or not the response includes an entity that
689   describes the result.
690</t>
691<t>
692   If a resource has been created on the origin server, the response
693   &SHOULD; be 201 (Created) and contain an entity which describes the
694   status of the request and refers to the new resource, and a Location
695   header (see <xref target="header.location"/>).
696</t>
697<t>
698   Responses to this method are not cacheable, unless the response
699   includes appropriate Cache-Control or Expires header fields. However,
700   the 303 (See Other) response can be used to direct the user agent to
701   retrieve a cacheable resource.
702</t>
703<t>
704   POST requests &MUST; obey the message transmission requirements set out
705   in [message.transmission.requirements].
706</t>
707<t>
708   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
709</t>
710</section>
711
712<section title="PUT" anchor="PUT">
713  <iref primary="true" item="PUT method" x:for-anchor=""/>
714  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
715<t>
716   The PUT method requests that the enclosed entity be stored under the
717   supplied Request-URI. If the Request-URI refers to an already
718   existing resource, the enclosed entity &SHOULD; be considered as a
719   modified version of the one residing on the origin server. If the
720   Request-URI does not point to an existing resource, and that URI is
721   capable of being defined as a new resource by the requesting user
722   agent, the origin server can create the resource with that URI. If a
723   new resource is created, the origin server &MUST; inform the user agent
724   via the 201 (Created) response. If an existing resource is modified,
725   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
726   to indicate successful completion of the request. If the resource
727   could not be created or modified with the Request-URI, an appropriate
728   error response &SHOULD; be given that reflects the nature of the
729   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
730   (e.g. Content-Range) headers that it does not understand or implement
731   and &MUST; return a 501 (Not Implemented) response in such cases.
732</t>
733<t>
734   If the request passes through a cache and the Request-URI identifies
735   one or more currently cached entities, those entries &SHOULD; be
736   treated as stale. Responses to this method are not cacheable.
737</t>
738<t>
739   The fundamental difference between the POST and PUT requests is
740   reflected in the different meaning of the Request-URI. The URI in a
741   POST request identifies the resource that will handle the enclosed
742   entity. That resource might be a data-accepting process, a gateway to
743   some other protocol, or a separate entity that accepts annotations.
744   In contrast, the URI in a PUT request identifies the entity enclosed
745   with the request -- the user agent knows what URI is intended and the
746   server &MUST-NOT; attempt to apply the request to some other resource.
747   If the server desires that the request be applied to a different URI,
748   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
749   then make its own decision regarding whether or not to redirect the
750   request.
751</t>
752<t>
753   A single resource &MAY; be identified by many different URIs. For
754   example, an article might have a URI for identifying "the current
755   version" which is separate from the URI identifying each particular
756   version. In this case, a PUT request on a general URI might result in
757   several other URIs being defined by the origin server.
758</t>
759<t>
760   HTTP/1.1 does not define how a PUT method affects the state of an
761   origin server.
762</t>
763<t>
764   PUT requests &MUST; obey the message transmission requirements set out
765   in [message.transmission.requirements].
766</t>
767<t>
768   Unless otherwise specified for a particular entity-header, the
769   entity-headers in the PUT request &SHOULD; be applied to the resource
770   created or modified by the PUT.
771</t>
772</section>
773
774<section title="DELETE" anchor="DELETE">
775  <iref primary="true" item="DELETE method" x:for-anchor=""/>
776  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
777<t>
778   The DELETE method requests that the origin server delete the resource
779   identified by the Request-URI. This method &MAY; be overridden by human
780   intervention (or other means) on the origin server. The client cannot
781   be guaranteed that the operation has been carried out, even if the
782   status code returned from the origin server indicates that the action
783   has been completed successfully. However, the server &SHOULD-NOT; 
784   indicate success unless, at the time the response is given, it
785   intends to delete the resource or move it to an inaccessible
786   location.
787</t>
788<t>
789   A successful response &SHOULD; be 200 (OK) if the response includes an
790   entity describing the status, 202 (Accepted) if the action has not
791   yet been enacted, or 204 (No Content) if the action has been enacted
792   but the response does not include an entity.
793</t>
794<t>
795   If the request passes through a cache and the Request-URI identifies
796   one or more currently cached entities, those entries &SHOULD; be
797   treated as stale. Responses to this method are not cacheable.
798</t>
799</section>
800
801<section title="TRACE" anchor="TRACE">
802  <iref primary="true" item="TRACE method" x:for-anchor=""/>
803  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
804<t>
805   The TRACE method is used to invoke a remote, application-layer loop-back
806   of the request message. The final recipient of the request
807   &SHOULD; reflect the message received back to the client as the
808   entity-body of a 200 (OK) response. The final recipient is either the
809   origin server or the first proxy or gateway to receive a Max-Forwards
810   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
811   &MUST-NOT; include an entity.
812</t>
813<t>
814   TRACE allows the client to see what is being received at the other
815   end of the request chain and use that data for testing or diagnostic
816   information. The value of the Via header field (&header-via;) is of
817   particular interest, since it acts as a trace of the request chain.
818   Use of the Max-Forwards header field allows the client to limit the
819   length of the request chain, which is useful for testing a chain of
820   proxies forwarding messages in an infinite loop.
821</t>
822<t>
823   If the request is valid, the response &SHOULD; contain the entire
824   request message in the entity-body, with a Content-Type of
825   "message/http". Responses to this method &MUST-NOT; be cached.
826</t>
827</section>
828
829<section title="CONNECT" anchor="CONNECT">
830  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
831  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
832<t>
833   This specification reserves the method name CONNECT for use with a
834   proxy that can dynamically switch to being a tunnel (e.g. SSL
835   tunneling <xref target="Luo1998"/>).
836</t>
837</section>
838</section>
839
840
841<section title="Status Code Definitions" anchor="status.codes">
842<t>
843   Each Status-Code is described below, including a description of which
844   method(s) it can follow and any metainformation required in the
845   response.
846</t>
847
848<section title="Informational 1xx" anchor="status.1xx">
849<t>
850   This class of status code indicates a provisional response,
851   consisting only of the Status-Line and optional headers, and is
852   terminated by an empty line. There are no required headers for this
853   class of status code. Since HTTP/1.0 did not define any 1xx status
854   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
855   except under experimental conditions.
856</t>
857<t>
858   A client &MUST; be prepared to accept one or more 1xx status responses
859   prior to a regular response, even if the client does not expect a 100
860   (Continue) status message. Unexpected 1xx status responses &MAY; be
861   ignored by a user agent.
862</t>
863<t>
864   Proxies &MUST; forward 1xx responses, unless the connection between the
865   proxy and its client has been closed, or unless the proxy itself
866   requested the generation of the 1xx response. (For example, if a
867   proxy adds a "Expect: 100-continue" field when it forwards a request,
868   then it need not forward the corresponding 100 (Continue)
869   response(s).)
870</t>
871
872<section title="100 Continue" anchor="status.100">
873  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
874  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
875<t>
876   The client &SHOULD; continue with its request. This interim response is
877   used to inform the client that the initial part of the request has
878   been received and has not yet been rejected by the server. The client
879   &SHOULD; continue by sending the remainder of the request or, if the
880   request has already been completed, ignore this response. The server
881   &MUST; send a final response after the request has been completed. See
882   &use100; for detailed discussion of the use and handling of this
883   status code.
884</t>
885</section>
886
887<section title="101 Switching Protocols" anchor="status.101">
888  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
889  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
890<t>
891   The server understands and is willing to comply with the client's
892   request, via the Upgrade message header field (&header-upgrade;), for a
893   change in the application protocol being used on this connection. The
894   server will switch protocols to those defined by the response's
895   Upgrade header field immediately after the empty line which
896   terminates the 101 response.
897</t>
898<t>
899   The protocol &SHOULD; be switched only when it is advantageous to do
900   so. For example, switching to a newer version of HTTP is advantageous
901   over older versions, and switching to a real-time, synchronous
902   protocol might be advantageous when delivering resources that use
903   such features.
904</t>
905</section>
906</section>
907
908<section title="Successful 2xx" anchor="status.2xx">
909<t>
910   This class of status code indicates that the client's request was
911   successfully received, understood, and accepted.
912</t>
913
914<section title="200 OK" anchor="status.200">
915  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
916  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
917<t>
918   The request has succeeded. The information returned with the response
919   is dependent on the method used in the request, for example:
920  <list style="hanging">
921    <t hangText="GET">
922          an entity corresponding to the requested resource is sent in
923          the response;
924    </t>
925    <t hangText="HEAD">
926          the entity-header fields corresponding to the requested
927          resource are sent in the response without any message-body;
928    </t>
929    <t hangText="POST">
930      an entity describing or containing the result of the action;
931    </t>
932    <t hangText="TRACE">
933      an entity containing the request message as received by the
934      end server.
935    </t>
936  </list>
937</t>
938</section>
939
940<section title="201 Created" anchor="status.201">
941  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
942  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
943<t>
944   The request has been fulfilled and resulted in a new resource being
945   created. The newly created resource can be referenced by the URI(s)
946   returned in the entity of the response, with the most specific URI
947   for the resource given by a Location header field. The response
948   &SHOULD; include an entity containing a list of resource
949   characteristics and location(s) from which the user or user agent can
950   choose the one most appropriate. The entity format is specified by
951   the media type given in the Content-Type header field. The origin
952   server &MUST; create the resource before returning the 201 status code.
953   If the action cannot be carried out immediately, the server &SHOULD;
954   respond with 202 (Accepted) response instead.
955</t>
956<t>
957   A 201 response &MAY; contain an ETag response header field indicating
958   the current value of the entity tag for the requested variant just
959   created, see &header-etag;.
960</t>
961</section>
962
963<section title="202 Accepted" anchor="status.202">
964  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
965  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
966<t>
967   The request has been accepted for processing, but the processing has
968   not been completed.  The request might or might not eventually be
969   acted upon, as it might be disallowed when processing actually takes
970   place. There is no facility for re-sending a status code from an
971   asynchronous operation such as this.
972</t>
973<t>
974   The 202 response is intentionally non-committal. Its purpose is to
975   allow a server to accept a request for some other process (perhaps a
976   batch-oriented process that is only run once per day) without
977   requiring that the user agent's connection to the server persist
978   until the process is completed. The entity returned with this
979   response &SHOULD; include an indication of the request's current status
980   and either a pointer to a status monitor or some estimate of when the
981   user can expect the request to be fulfilled.
982</t>
983</section>
984
985<section title="203 Non-Authoritative Information" anchor="status.203">
986  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
987  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
988<t>
989   The returned metainformation in the entity-header is not the
990   definitive set as available from the origin server, but is gathered
991   from a local or a third-party copy. The set presented &MAY; be a subset
992   or superset of the original version. For example, including local
993   annotation information about the resource might result in a superset
994   of the metainformation known by the origin server. Use of this
995   response code is not required and is only appropriate when the
996   response would otherwise be 200 (OK).
997</t>
998</section>
999
1000<section title="204 No Content" anchor="status.204">
1001  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1002  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1003<t>
1004   The server has fulfilled the request but does not need to return an
1005   entity-body, and might want to return updated metainformation. The
1006   response &MAY; include new or updated metainformation in the form of
1007   entity-headers, which if present &SHOULD; be associated with the
1008   requested variant.
1009</t>
1010<t>
1011   If the client is a user agent, it &SHOULD-NOT;  change its document view
1012   from that which caused the request to be sent. This response is
1013   primarily intended to allow input for actions to take place without
1014   causing a change to the user agent's active document view, although
1015   any new or updated metainformation &SHOULD; be applied to the document
1016   currently in the user agent's active view.
1017</t>
1018<t>
1019   The 204 response &MUST-NOT; include a message-body, and thus is always
1020   terminated by the first empty line after the header fields.
1021</t>
1022</section>
1023
1024<section title="205 Reset Content" anchor="status.205">
1025  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1026  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1027<t>
1028   The server has fulfilled the request and the user agent &SHOULD; reset
1029   the document view which caused the request to be sent. This response
1030   is primarily intended to allow input for actions to take place via
1031   user input, followed by a clearing of the form in which the input is
1032   given so that the user can easily initiate another input action. The
1033   response &MUST-NOT; include an entity.
1034</t>
1035</section>
1036
1037<section title="206 Partial Content" anchor="status.206">
1038  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1039  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1040<t>
1041   The server has fulfilled the partial GET request for the resource
1042   and the enclosed entity is a partial representation as defined in &range;.
1043</t>
1044</section>
1045</section>
1046
1047<section title="Redirection 3xx" anchor="status.3xx">
1048<t>
1049   This class of status code indicates that further action needs to be
1050   taken by the user agent in order to fulfill the request.  The action
1051   required &MAY; be carried out by the user agent without interaction
1052   with the user if and only if the method used in the second request is
1053   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1054   such loops generate network traffic for each redirection.
1055  <list><t>
1056      <x:h>Note:</x:h> previous versions of this specification recommended a
1057      maximum of five redirections. Content developers should be aware
1058      that there might be clients that implement such a fixed
1059      limitation.
1060  </t></list>
1061</t>
1062
1063<section title="300 Multiple Choices" anchor="status.300">
1064  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1065  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1066<t>
1067   The requested resource corresponds to any one of a set of
1068   representations, each with its own specific location, and agent-driven
1069   negotiation information (&content-negotiation;) is being provided so that
1070   the user (or user agent) can select a preferred representation and
1071   redirect its request to that location.
1072</t>
1073<t>
1074   Unless it was a HEAD request, the response &SHOULD; include an entity
1075   containing a list of resource characteristics and location(s) from
1076   which the user or user agent can choose the one most appropriate. The
1077   entity format is specified by the media type given in the Content-Type
1078   header field. Depending upon the format and the capabilities of
1079   the user agent, selection of the most appropriate choice &MAY; be
1080   performed automatically. However, this specification does not define
1081   any standard for such automatic selection.
1082</t>
1083<t>
1084   If the server has a preferred choice of representation, it &SHOULD;
1085   include the specific URI for that representation in the Location
1086   field; user agents &MAY; use the Location field value for automatic
1087   redirection. This response is cacheable unless indicated otherwise.
1088</t>
1089</section>
1090
1091<section title="301 Moved Permanently" anchor="status.301">
1092  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1093  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1094<t>
1095   The requested resource has been assigned a new permanent URI and any
1096   future references to this resource &SHOULD; use one of the returned
1097   URIs.  Clients with link editing capabilities ought to automatically
1098   re-link references to the Request-URI to one or more of the new
1099   references returned by the server, where possible. This response is
1100   cacheable unless indicated otherwise.
1101</t>
1102<t>
1103   The new permanent URI &SHOULD; be given by the Location field in the
1104   response. Unless the request method was HEAD, the entity of the
1105   response &SHOULD; contain a short hypertext note with a hyperlink to
1106   the new URI(s).
1107</t>
1108<t>
1109   If the 301 status code is received in response to a request other
1110   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1111   request unless it can be confirmed by the user, since this might
1112   change the conditions under which the request was issued.
1113  <list><t>
1114      <x:h>Note:</x:h> When automatically redirecting a POST request after
1115      receiving a 301 status code, some existing HTTP/1.0 user agents
1116      will erroneously change it into a GET request.
1117  </t></list>
1118</t>
1119</section>
1120
1121<section title="302 Found" anchor="status.302">
1122  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1123  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1124<t>
1125   The requested resource resides temporarily under a different URI.
1126   Since the redirection might be altered on occasion, the client &SHOULD;
1127   continue to use the Request-URI for future requests.  This response
1128   is only cacheable if indicated by a Cache-Control or Expires header
1129   field.
1130</t>
1131<t>
1132   The temporary URI &SHOULD; be given by the Location field in the
1133   response. Unless the request method was HEAD, the entity of the
1134   response &SHOULD; contain a short hypertext note with a hyperlink to
1135   the new URI(s).
1136</t>
1137<t>
1138   If the 302 status code is received in response to a request other
1139   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1140   request unless it can be confirmed by the user, since this might
1141   change the conditions under which the request was issued.
1142  <list><t>
1143      <x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
1144      to change the method on the redirected request.  However, most
1145      existing user agent implementations treat 302 as if it were a 303
1146      response, performing a GET on the Location field-value regardless
1147      of the original request method. The status codes 303 and 307 have
1148      been added for servers that wish to make unambiguously clear which
1149      kind of reaction is expected of the client.
1150  </t></list>
1151</t>
1152</section>
1153
1154<section title="303 See Other" anchor="status.303">
1155  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1156  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1157<t>
1158   The response to the request can be found under a different URI and
1159   &SHOULD; be retrieved using a GET method on that resource. This method
1160   exists primarily to allow the output of a POST-activated script to
1161   redirect the user agent to a selected resource. The new URI is not a
1162   substitute reference for the originally requested resource. The 303
1163   response &MUST-NOT; be cached, but the response to the second
1164   (redirected) request might be cacheable.
1165</t>
1166<t>
1167   The different URI &SHOULD; be given by the Location field in the
1168   response. Unless the request method was HEAD, the entity of the
1169   response &SHOULD; contain a short hypertext note with a hyperlink to
1170   the new URI(s).
1171  <list><t>
1172      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1173      status. When interoperability with such clients is a concern, the
1174      302 status code may be used instead, since most user agents react
1175      to a 302 response as described here for 303.
1176  </t></list>
1177</t>
1178</section>
1179
1180<section title="304 Not Modified" anchor="status.304">
1181  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1182  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1183<t>
1184   If the client has performed a conditional GET request and access is
1185   allowed, but the document has not been modified, the server &SHOULD;
1186   respond with this status code. The 304 response &MUST-NOT; contain a
1187   message-body, and thus is always terminated by the first empty line
1188   after the header fields.
1189</t>
1190<t>
1191   The response &MUST; include the following header fields:
1192  <list style="symbols">
1193    <t>Date, unless its omission is required by [clockless.origin.server.operation]</t>
1194  </list>
1195</t>
1196<t>
1197   If a clockless origin server obeys these rules, and proxies and
1198   clients add their own Date to any response received without one (as
1199   already specified by [RFC 2068], section <xref target="RFC2068" x:sec="14.19" x:fmt="number"/>), caches will operate
1200   correctly.
1201  <list style="symbols">
1202    <t>ETag and/or Content-Location, if the header would have been sent
1203        in a 200 response to the same request</t>
1204    <t>Expires, Cache-Control, and/or Vary, if the field-value might
1205        differ from that sent in any previous response for the same
1206        variant</t>
1207  </list>
1208</t>
1209<t>
1210   If the conditional GET used a strong cache validator (see &caching;),
1211   the response &SHOULD-NOT;  include other entity-headers.
1212   Otherwise (i.e., the conditional GET used a weak validator), the
1213   response &MUST-NOT; include other entity-headers; this prevents
1214   inconsistencies between cached entity-bodies and updated headers.
1215</t>
1216<t>
1217   If a 304 response indicates an entity not currently cached, then the
1218   cache &MUST; disregard the response and repeat the request without the
1219   conditional.
1220</t>
1221<t>
1222   If a cache uses a received 304 response to update a cache entry, the
1223   cache &MUST; update the entry to reflect any new field values given in
1224   the response.
1225</t>
1226</section>
1227
1228<section title="305 Use Proxy" anchor="status.305">
1229  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1230  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1231<t>
1232   The requested resource &MUST; be accessed through the proxy given by
1233   the Location field. The Location field gives the URI of the proxy.
1234   The recipient is expected to repeat this single request via the
1235   proxy. 305 responses &MUST; only be generated by origin servers.
1236  <list><t>
1237      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1238      single request, and to be generated by origin servers only.  Not
1239      observing these limitations has significant security consequences.
1240  </t></list>
1241</t>
1242</section>
1243
1244<section title="306 (Unused)" anchor="status.306">
1245  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1246  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1247<t>
1248   The 306 status code was used in a previous version of the
1249   specification, is no longer used, and the code is reserved.
1250</t>
1251</section>
1252
1253<section title="307 Temporary Redirect" anchor="status.307">
1254  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1255  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1256<t>
1257   The requested resource resides temporarily under a different URI.
1258   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1259   continue to use the Request-URI for future requests.  This response
1260   is only cacheable if indicated by a Cache-Control or Expires header
1261   field.
1262</t>
1263<t>
1264   The temporary URI &SHOULD; be given by the Location field in the
1265   response. Unless the request method was HEAD, the entity of the
1266   response &SHOULD; contain a short hypertext note with a hyperlink to
1267   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1268   understand the 307 status. Therefore, the note &SHOULD; contain the
1269   information necessary for a user to repeat the original request on
1270   the new URI.
1271</t>
1272<t>
1273   If the 307 status code is received in response to a request other
1274   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1275   request unless it can be confirmed by the user, since this might
1276   change the conditions under which the request was issued.
1277</t>
1278</section>
1279</section>
1280
1281<section title="Client Error 4xx" anchor="status.4xx">
1282<t>
1283   The 4xx class of status code is intended for cases in which the
1284   client seems to have erred. Except when responding to a HEAD request,
1285   the server &SHOULD; include an entity containing an explanation of the
1286   error situation, and whether it is a temporary or permanent
1287   condition. These status codes are applicable to any request method.
1288   User agents &SHOULD; display any included entity to the user.
1289</t>
1290<t>
1291   If the client is sending data, a server implementation using TCP
1292   &SHOULD; be careful to ensure that the client acknowledges receipt of
1293   the packet(s) containing the response, before the server closes the
1294   input connection. If the client continues sending data to the server
1295   after the close, the server's TCP stack will send a reset packet to
1296   the client, which may erase the client's unacknowledged input buffers
1297   before they can be read and interpreted by the HTTP application.
1298</t>
1299
1300<section title="400 Bad Request" anchor="status.400">
1301  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1302  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1303<t>
1304   The request could not be understood by the server due to malformed
1305   syntax. The client &SHOULD-NOT;  repeat the request without
1306   modifications.
1307</t>
1308</section>
1309
1310<section title="401 Unauthorized" anchor="status.401">
1311  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1312  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1313<t>
1314   The request requires user authentication. The response &MUST; include a
1315   WWW-Authenticate header field (&header-www-authenticate;) containing a challenge
1316   applicable to the requested resource. The client &MAY; repeat the
1317   request with a suitable Authorization header field (&header-authorization;). If
1318   the request already included Authorization credentials, then the 401
1319   response indicates that authorization has been refused for those
1320   credentials. If the 401 response contains the same challenge as the
1321   prior response, and the user agent has already attempted
1322   authentication at least once, then the user &SHOULD; be presented the
1323   entity that was given in the response, since that entity might
1324   include relevant diagnostic information. HTTP access authentication
1325   is explained in "HTTP Authentication: Basic and Digest Access
1326   Authentication" <xref target="RFC2617"/>.
1327</t>
1328</section>
1329
1330<section title="402 Payment Required" anchor="status.402">
1331  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1332  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1333<t>
1334   This code is reserved for future use.
1335</t>
1336</section>
1337
1338<section title="403 Forbidden" anchor="status.403">
1339  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1340  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1341<t>
1342   The server understood the request, but is refusing to fulfill it.
1343   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1344   If the request method was not HEAD and the server wishes to make
1345   public why the request has not been fulfilled, it &SHOULD; describe the
1346   reason for the refusal in the entity.  If the server does not wish to
1347   make this information available to the client, the status code 404
1348   (Not Found) can be used instead.
1349</t>
1350</section>
1351
1352<section title="404 Not Found" anchor="status.404">
1353  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1354  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1355<t>
1356   The server has not found anything matching the Request-URI. No
1357   indication is given of whether the condition is temporary or
1358   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1359   knows, through some internally configurable mechanism, that an old
1360   resource is permanently unavailable and has no forwarding address.
1361   This status code is commonly used when the server does not wish to
1362   reveal exactly why the request has been refused, or when no other
1363   response is applicable.
1364</t>
1365</section>
1366
1367<section title="405 Method Not Allowed" anchor="status.405">
1368  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1369  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1370<t>
1371   The method specified in the Request-Line is not allowed for the
1372   resource identified by the Request-URI. The response &MUST; include an
1373   Allow header containing a list of valid methods for the requested
1374   resource.
1375</t>
1376</section>
1377
1378<section title="406 Not Acceptable" anchor="status.406">
1379  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1380  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1381<t>
1382   The resource identified by the request is only capable of generating
1383   response entities which have content characteristics not acceptable
1384   according to the accept headers sent in the request.
1385</t>
1386<t>
1387   Unless it was a HEAD request, the response &SHOULD; include an entity
1388   containing a list of available entity characteristics and location(s)
1389   from which the user or user agent can choose the one most
1390   appropriate. The entity format is specified by the media type given
1391   in the Content-Type header field. Depending upon the format and the
1392   capabilities of the user agent, selection of the most appropriate
1393   choice &MAY; be performed automatically. However, this specification
1394   does not define any standard for such automatic selection.
1395  <list><t>
1396      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1397      not acceptable according to the accept headers sent in the
1398      request. In some cases, this may even be preferable to sending a
1399      406 response. User agents are encouraged to inspect the headers of
1400      an incoming response to determine if it is acceptable.
1401  </t></list>
1402</t>
1403<t>
1404   If the response could be unacceptable, a user agent &SHOULD;
1405   temporarily stop receipt of more data and query the user for a
1406   decision on further actions.
1407</t>
1408</section>
1409
1410<section title="407 Proxy Authentication Required" anchor="status.407">
1411  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1412  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1413<t>
1414   This code is similar to 401 (Unauthorized), but indicates that the
1415   client must first authenticate itself with the proxy. The proxy &MUST;
1416   return a Proxy-Authenticate header field (&header-proxy-authenticate;) containing a
1417   challenge applicable to the proxy for the requested resource. The
1418   client &MAY; repeat the request with a suitable Proxy-Authorization
1419   header field (&header-proxy-authorization;). HTTP access authentication is explained
1420   in "HTTP Authentication: Basic and Digest Access Authentication"
1421   <xref target="RFC2617"/>.
1422</t>
1423</section>
1424
1425<section title="408 Request Timeout" anchor="status.408">
1426  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1427  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1428<t>
1429   The client did not produce a request within the time that the server
1430   was prepared to wait. The client &MAY; repeat the request without
1431   modifications at any later time.
1432</t>
1433</section>
1434
1435<section title="409 Conflict" anchor="status.409">
1436  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1437  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1438<t>
1439   The request could not be completed due to a conflict with the current
1440   state of the resource. This code is only allowed in situations where
1441   it is expected that the user might be able to resolve the conflict
1442   and resubmit the request. The response body &SHOULD; include enough
1443   information for the user to recognize the source of the conflict.
1444   Ideally, the response entity would include enough information for the
1445   user or user agent to fix the problem; however, that might not be
1446   possible and is not required.
1447</t>
1448<t>
1449   Conflicts are most likely to occur in response to a PUT request. For
1450   example, if versioning were being used and the entity being PUT
1451   included changes to a resource which conflict with those made by an
1452   earlier (third-party) request, the server might use the 409 response
1453   to indicate that it can't complete the request. In this case, the
1454   response entity would likely contain a list of the differences
1455   between the two versions in a format defined by the response
1456   Content-Type.
1457</t>
1458</section>
1459
1460<section title="410 Gone" anchor="status.410">
1461  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1462  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1463<t>
1464   The requested resource is no longer available at the server and no
1465   forwarding address is known. This condition is expected to be
1466   considered permanent. Clients with link editing capabilities &SHOULD;
1467   delete references to the Request-URI after user approval. If the
1468   server does not know, or has no facility to determine, whether or not
1469   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1470   used instead. This response is cacheable unless indicated otherwise.
1471</t>
1472<t>
1473   The 410 response is primarily intended to assist the task of web
1474   maintenance by notifying the recipient that the resource is
1475   intentionally unavailable and that the server owners desire that
1476   remote links to that resource be removed. Such an event is common for
1477   limited-time, promotional services and for resources belonging to
1478   individuals no longer working at the server's site. It is not
1479   necessary to mark all permanently unavailable resources as "gone" or
1480   to keep the mark for any length of time -- that is left to the
1481   discretion of the server owner.
1482</t>
1483</section>
1484
1485<section title="411 Length Required" anchor="status.411">
1486  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1487  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1488<t>
1489   The server refuses to accept the request without a defined Content-Length.
1490   The client &MAY; repeat the request if it adds a valid
1491   Content-Length header field containing the length of the message-body
1492   in the request message.
1493</t>
1494</section>
1495
1496<section title="412 Precondition Failed" anchor="status.412">
1497  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1498  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1499<t>
1500   The precondition given in one or more of the request-header fields
1501   evaluated to false when it was tested on the server. This response
1502   code allows the client to place preconditions on the current resource
1503   metainformation (header field data) and thus prevent the requested
1504   method from being applied to a resource other than the one intended.
1505</t>
1506</section>
1507
1508<section title="413 Request Entity Too Large" anchor="status.413">
1509  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1510  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1511<t>
1512   The server is refusing to process a request because the request
1513   entity is larger than the server is willing or able to process. The
1514   server &MAY; close the connection to prevent the client from continuing
1515   the request.
1516</t>
1517<t>
1518   If the condition is temporary, the server &SHOULD; include a Retry-After
1519   header field to indicate that it is temporary and after what
1520   time the client &MAY; try again.
1521</t>
1522</section>
1523
1524<section title="414 Request-URI Too Long" anchor="status.414">
1525  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1526  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1527<t>
1528   The server is refusing to service the request because the Request-URI
1529   is longer than the server is willing to interpret. This rare
1530   condition is only likely to occur when a client has improperly
1531   converted a POST request to a GET request with long query
1532   information, when the client has descended into a URI "black hole" of
1533   redirection (e.g., a redirected URI prefix that points to a suffix of
1534   itself), or when the server is under attack by a client attempting to
1535   exploit security holes present in some servers using fixed-length
1536   buffers for reading or manipulating the Request-URI.
1537</t>
1538</section>
1539
1540<section title="415 Unsupported Media Type" anchor="status.415">
1541  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1542  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1543<t>
1544   The server is refusing to service the request because the entity of
1545   the request is in a format not supported by the requested resource
1546   for the requested method.
1547</t>
1548</section>
1549
1550<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1551  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1552  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1553<t>
1554   The request included a Range request-header field (&header-range;) and none of
1555   the range-specifier values in this field overlap the current extent
1556   of the selected resource.
1557</t>
1558</section>
1559
1560<section title="417 Expectation Failed" anchor="status.417">
1561  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1562  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1563<t>
1564   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1565   could not be met by this server, or, if the server is a proxy,
1566   the server has unambiguous evidence that the request could not be met
1567   by the next-hop server.
1568</t>
1569</section>
1570</section>
1571
1572<section title="Server Error 5xx" anchor="status.5xx">
1573<t>
1574   Response status codes beginning with the digit "5" indicate cases in
1575   which the server is aware that it has erred or is incapable of
1576   performing the request. Except when responding to a HEAD request, the
1577   server &SHOULD; include an entity containing an explanation of the
1578   error situation, and whether it is a temporary or permanent
1579   condition. User agents &SHOULD; display any included entity to the
1580   user. These response codes are applicable to any request method.
1581</t>
1582
1583<section title="500 Internal Server Error" anchor="status.500">
1584  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1585  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1586<t>
1587   The server encountered an unexpected condition which prevented it
1588   from fulfilling the request.
1589</t>
1590</section>
1591
1592<section title="501 Not Implemented" anchor="status.501">
1593  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1594  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1595<t>
1596   The server does not support the functionality required to fulfill the
1597   request. This is the appropriate response when the server does not
1598   recognize the request method and is not capable of supporting it for
1599   any resource.
1600</t>
1601</section>
1602
1603<section title="502 Bad Gateway" anchor="status.502">
1604  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1605  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1606<t>
1607   The server, while acting as a gateway or proxy, received an invalid
1608   response from the upstream server it accessed in attempting to
1609   fulfill the request.
1610</t>
1611</section>
1612
1613<section title="503 Service Unavailable" anchor="status.503">
1614  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1615  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1616<t>
1617   The server is currently unable to handle the request due to a
1618   temporary overloading or maintenance of the server. The implication
1619   is that this is a temporary condition which will be alleviated after
1620   some delay. If known, the length of the delay &MAY; be indicated in a
1621   Retry-After header. If no Retry-After is given, the client &SHOULD;
1622   handle the response as it would for a 500 response.
1623  <list><t>
1624      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1625      server must use it when becoming overloaded. Some servers may wish
1626      to simply refuse the connection.
1627  </t></list>
1628</t>
1629</section>
1630
1631<section title="504 Gateway Timeout" anchor="status.504">
1632  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1633  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1634<t>
1635   The server, while acting as a gateway or proxy, did not receive a
1636   timely response from the upstream server specified by the URI (e.g.
1637   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1638   to access in attempting to complete the request.
1639  <list><t>
1640      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1641      return 400 or 500 when DNS lookups time out.
1642  </t></list>
1643</t>
1644</section>
1645
1646<section title="505 HTTP Version Not Supported" anchor="status.505">
1647  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1648  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1649<t>
1650   The server does not support, or refuses to support, the HTTP protocol
1651   version that was used in the request message. The server is
1652   indicating that it is unable or unwilling to complete the request
1653   using the same major version as the client, as described in &http-version;,
1654   other than with this error message. The response &SHOULD; contain
1655   an entity describing why that version is not supported and what other
1656   protocols are supported by that server.
1657</t>
1658
1659</section>
1660</section>
1661</section>
1662
1663
1664<section title="Header Field Definitions" anchor="header.fields">
1665<t>
1666   This section defines the syntax and semantics of all standard
1667   HTTP/1.1 header fields. For entity-header fields, both sender and
1668   recipient refer to either the client or the server, depending on who
1669   sends and who receives the entity.
1670</t>
1671
1672<section title="Allow" anchor="header.allow">
1673  <iref primary="true" item="Allow header" x:for-anchor=""/>
1674  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1675<t>
1676      The Allow entity-header field lists the set of methods supported
1677      by the resource identified by the Request-URI. The purpose of this
1678      field is strictly to inform the recipient of valid methods
1679      associated with the resource. An Allow header field &MUST; be
1680      present in a 405 (Method Not Allowed) response.
1681</t>
1682<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1683       Allow   = "Allow" ":" #Method
1684</artwork></figure>
1685<t>
1686      Example of use:
1687</t>
1688<figure><artwork type="example">
1689       Allow: GET, HEAD, PUT
1690</artwork></figure>
1691<t>
1692      This field cannot prevent a client from trying other methods.
1693      However, the indications given by the Allow header field value
1694      &SHOULD; be followed. The actual set of allowed methods is defined
1695      by the origin server at the time of each request.
1696</t>
1697<t>
1698      The Allow header field &MAY; be provided with a PUT request to
1699      recommend the methods to be supported by the new or modified
1700      resource. The server is not required to support these methods and
1701      &SHOULD; include an Allow header in the response giving the actual
1702      supported methods.
1703</t>
1704<t>
1705      A proxy &MUST-NOT; modify the Allow header field even if it does not
1706      understand all the methods specified, since the user agent might
1707      have other means of communicating with the origin server.
1708</t>
1709</section>
1710
1711<section title="Expect" anchor="header.expect">
1712  <iref primary="true" item="Expect header" x:for-anchor=""/>
1713  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1714<t>
1715   The Expect request-header field is used to indicate that particular
1716   server behaviors are required by the client.
1717</t>
1718<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"/>
1719   Expect       =  "Expect" ":" 1#expectation
1720
1721   expectation  =  "100-continue" | expectation-extension
1722   expectation-extension =  token [ "=" ( token | quoted-string )
1723                            *expect-params ]
1724   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1725</artwork></figure>
1726<t>
1727   A server that does not understand or is unable to comply with any of
1728   the expectation values in the Expect field of a request &MUST; respond
1729   with appropriate error status. The server &MUST; respond with a 417
1730   (Expectation Failed) status if any of the expectations cannot be met
1731   or, if there are other problems with the request, some other 4xx
1732   status.
1733</t>
1734<t>
1735   This header field is defined with extensible syntax to allow for
1736   future extensions. If a server receives a request containing an
1737   Expect field that includes an expectation-extension that it does not
1738   support, it &MUST; respond with a 417 (Expectation Failed) status.
1739</t>
1740<t>
1741   Comparison of expectation values is case-insensitive for unquoted
1742   tokens (including the 100-continue token), and is case-sensitive for
1743   quoted-string expectation-extensions.
1744</t>
1745<t>
1746   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1747   return a 417 (Expectation Failed) status if it receives a request
1748   with an expectation that it cannot meet. However, the Expect
1749   request-header itself is end-to-end; it &MUST; be forwarded if the
1750   request is forwarded.
1751</t>
1752<t>
1753   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1754   Expect header.
1755</t>
1756<t>
1757   See &use100; for the use of the 100 (continue) status.
1758</t>
1759</section>
1760
1761<section title="From" anchor="header.from">
1762  <iref primary="true" item="From header" x:for-anchor=""/>
1763  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1764<t>
1765   The From request-header field, if given, &SHOULD; contain an Internet
1766   e-mail address for the human user who controls the requesting user
1767   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1768   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1769</t>
1770<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1771    From   = "From" ":" mailbox
1772</artwork></figure>
1773<t>
1774   An example is:
1775</t>
1776<figure><artwork type="example">
1777    From: webmaster@w3.org
1778</artwork></figure>
1779<t>
1780   This header field &MAY; be used for logging purposes and as a means for
1781   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1782   be used as an insecure form of access protection. The interpretation
1783   of this field is that the request is being performed on behalf of the
1784   person given, who accepts responsibility for the method performed. In
1785   particular, robot agents &SHOULD; include this header so that the
1786   person responsible for running the robot can be contacted if problems
1787   occur on the receiving end.
1788</t>
1789<t>
1790   The Internet e-mail address in this field &MAY; be separate from the
1791   Internet host which issued the request. For example, when a request
1792   is passed through a proxy the original issuer's address &SHOULD; be
1793   used.
1794</t>
1795<t>
1796   The client &SHOULD-NOT;  send the From header field without the user's
1797   approval, as it might conflict with the user's privacy interests or
1798   their site's security policy. It is strongly recommended that the
1799   user be able to disable, enable, and modify the value of this field
1800   at any time prior to a request.
1801</t>
1802</section>
1803
1804<section title="Location" anchor="header.location">
1805  <iref primary="true" item="Location header" x:for-anchor=""/>
1806  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1807<t>
1808   The Location response-header field is used to redirect the recipient
1809   to a location other than the Request-URI for completion of the
1810   request or identification of a new resource. For 201 (Created)
1811   responses, the Location is that of the new resource which was created
1812   by the request. For 3xx responses, the location &SHOULD; indicate the
1813   server's preferred URI for automatic redirection to the resource. The
1814   field value consists of a single absolute URI.
1815</t>
1816<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1817    Location       = "Location" ":" absoluteURI
1818</artwork></figure>
1819<t>
1820   An example is:
1821</t>
1822<figure><artwork type="example">
1823    Location: http://www.w3.org/pub/WWW/People.html
1824</artwork></figure>
1825<t>
1826  <list><t>
1827      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1828      from Location in that the Content-Location identifies the original
1829      location of the entity enclosed in the request. It is therefore
1830      possible for a response to contain header fields for both Location
1831      and Content-Location.
1832  </t></list>
1833</t>
1834</section>
1835
1836<section title="Max-Forwards" anchor="header.max-forwards">
1837  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1838  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1839<t>
1840   The Max-Forwards request-header field provides a mechanism with the
1841   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1842   number of proxies or gateways that can forward the request to the
1843   next inbound server. This can be useful when the client is attempting
1844   to trace a request chain which appears to be failing or looping in
1845   mid-chain.
1846</t>
1847<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1848    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1849</artwork></figure>
1850<t>
1851   The Max-Forwards value is a decimal integer indicating the remaining
1852   number of times this request message may be forwarded.
1853</t>
1854<t>
1855   Each proxy or gateway recipient of a TRACE or OPTIONS request
1856   containing a Max-Forwards header field &MUST; check and update its
1857   value prior to forwarding the request. If the received value is zero
1858   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1859   respond as the final recipient. If the received Max-Forwards value is
1860   greater than zero, then the forwarded message &MUST; contain an updated
1861   Max-Forwards field with a value decremented by one (1).
1862</t>
1863<t>
1864   The Max-Forwards header field &MAY; be ignored for all other methods
1865   defined by this specification and for any extension methods for which
1866   it is not explicitly referred to as part of that method definition.
1867</t>
1868</section>
1869
1870<section title="Referer" anchor="header.referer">
1871  <iref primary="true" item="Referer header" x:for-anchor=""/>
1872  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1873<t>
1874   The Referer[sic] request-header field allows the client to specify,
1875   for the server's benefit, the address (URI) of the resource from
1876   which the Request-URI was obtained (the "referrer", although the
1877   header field is misspelled.) The Referer request-header allows a
1878   server to generate lists of back-links to resources for interest,
1879   logging, optimized caching, etc. It also allows obsolete or mistyped
1880   links to be traced for maintenance. The Referer field &MUST-NOT; be
1881   sent if the Request-URI was obtained from a source that does not have
1882   its own URI, such as input from the user keyboard.
1883</t>
1884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1885    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1886</artwork></figure>
1887<t>
1888   Example:
1889</t>
1890<figure><artwork type="example">
1891    Referer: http://www.w3.org/hypertext/DataSources/Overview.html
1892</artwork></figure>
1893<t>
1894   If the field value is a relative URI, it &SHOULD; be interpreted
1895   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1896   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1897</t>
1898</section>
1899
1900<section title="Retry-After" anchor="header.retry-after">
1901  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1902  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1903<t>
1904   The Retry-After response-header field can be used with a 503 (Service
1905   Unavailable) response to indicate how long the service is expected to
1906   be unavailable to the requesting client. This field &MAY; also be used
1907   with any 3xx (Redirection) response to indicate the minimum time the
1908   user-agent is asked wait before issuing the redirected request. The
1909   value of this field can be either an HTTP-date or an integer number
1910   of seconds (in decimal) after the time of the response.
1911</t>
1912<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1913    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1914</artwork></figure>
1915<t>
1916   Two examples of its use are
1917</t>
1918<figure><artwork type="example">
1919    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1920    Retry-After: 120
1921</artwork></figure>
1922<t>
1923   In the latter example, the delay is 2 minutes.
1924</t>
1925</section>
1926
1927<section title="Server" anchor="header.server">
1928  <iref primary="true" item="Server header" x:for-anchor=""/>
1929  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1930<t>
1931   The Server response-header field contains information about the
1932   software used by the origin server to handle the request. The field
1933   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1934   identifying the server and any significant subproducts. The product
1935   tokens are listed in order of their significance for identifying the
1936   application.
1937</t>
1938<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1939    Server         = "Server" ":" 1*( product | comment )
1940</artwork></figure>
1941<t>
1942   Example:
1943</t>
1944<figure><artwork type="example">
1945    Server: CERN/3.0 libwww/2.17
1946</artwork></figure>
1947<t>
1948   If the response is being forwarded through a proxy, the proxy
1949   application &MUST-NOT; modify the Server response-header. Instead, it
1950   &SHOULD; include a Via field (as described in &header-via;).
1951  <list><t>
1952      <x:h>Note:</x:h> Revealing the specific software version of the server might
1953      allow the server machine to become more vulnerable to attacks
1954      against software that is known to contain security holes. Server
1955      implementors are encouraged to make this field a configurable
1956      option.
1957  </t></list>
1958</t>
1959</section>
1960
1961<section title="User-Agent" anchor="header.user-agent">
1962  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1963  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1964<t>
1965   The User-Agent request-header field contains information about the
1966   user agent originating the request. This is for statistical purposes,
1967   the tracing of protocol violations, and automated recognition of user
1968   agents for the sake of tailoring responses to avoid particular user
1969   agent limitations. User agents &SHOULD; include this field with
1970   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1971   and comments identifying the agent and any subproducts which form a
1972   significant part of the user agent. By convention, the product tokens
1973   are listed in order of their significance for identifying the
1974   application.
1975</t>
1976<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1977    User-Agent     = "User-Agent" ":" 1*( product | comment )
1978</artwork></figure>
1979<t>
1980   Example:
1981</t>
1982<figure><artwork type="example">
1983    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1984</artwork></figure>
1985</section>
1986
1987</section>
1988
1989<section title="IANA Considerations" anchor="IANA.considerations">
1990<t>
1991   TBD.
1992</t>
1993</section>
1994
1995<section title="Security Considerations" anchor="security.considerations">
1996<t>
1997   This section is meant to inform application developers, information
1998   providers, and users of the security limitations in HTTP/1.1 as
1999   described by this document. The discussion does not include
2000   definitive solutions to the problems revealed, though it does make
2001   some suggestions for reducing security risks.
2002</t>
2003
2004<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2005<t>
2006   Like any generic data transfer protocol, HTTP cannot regulate the
2007   content of the data that is transferred, nor is there any a priori
2008   method of determining the sensitivity of any particular piece of
2009   information within the context of any given request. Therefore,
2010   applications &SHOULD; supply as much control over this information as
2011   possible to the provider of that information. Four header fields are
2012   worth special mention in this context: Server, Via, Referer and From.
2013</t>
2014<t>
2015   Revealing the specific software version of the server might allow the
2016   server machine to become more vulnerable to attacks against software
2017   that is known to contain security holes. Implementors &SHOULD; make the
2018   Server header field a configurable option.
2019</t>
2020<t>
2021   Proxies which serve as a portal through a network firewall &SHOULD;
2022   take special precautions regarding the transfer of header information
2023   that identifies the hosts behind the firewall. In particular, they
2024   &SHOULD; remove, or replace with sanitized versions, any Via fields
2025   generated behind the firewall.
2026</t>
2027<t>
2028   The Referer header allows reading patterns to be studied and reverse
2029   links drawn. Although it can be very useful, its power can be abused
2030   if user details are not separated from the information contained in
2031   the Referer. Even when the personal information has been removed, the
2032   Referer header might indicate a private document's URI whose
2033   publication would be inappropriate.
2034</t>
2035<t>
2036   The information sent in the From field might conflict with the user's
2037   privacy interests or their site's security policy, and hence it
2038   &SHOULD-NOT;  be transmitted without the user being able to disable,
2039   enable, and modify the contents of the field. The user &MUST; be able
2040   to set the contents of this field within a user preference or
2041   application defaults configuration.
2042</t>
2043<t>
2044   We suggest, though do not require, that a convenient toggle interface
2045   be provided for the user to enable or disable the sending of From and
2046   Referer information.
2047</t>
2048<t>
2049   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2050   fields can sometimes be used to determine that a specific client or
2051   server have a particular security hole which might be exploited.
2052   Unfortunately, this same information is often used for other valuable
2053   purposes for which HTTP currently has no better mechanism.
2054</t>
2055</section>
2056
2057<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2058<t>
2059   Because the source of a link might be private information or might
2060   reveal an otherwise private information source, it is strongly
2061   recommended that the user be able to select whether or not the
2062   Referer field is sent. For example, a browser client could have a
2063   toggle switch for browsing openly/anonymously, which would
2064   respectively enable/disable the sending of Referer and From
2065   information.
2066</t>
2067<t>
2068   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2069   HTTP request if the referring page was transferred with a secure
2070   protocol.
2071</t>
2072<t>
2073   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2074   based forms for the submission of sensitive data, because this will
2075   cause this data to be encoded in the Request-URI. Many existing
2076   servers, proxies, and user agents will log the request URI in some
2077   place where it might be visible to third parties. Servers can use
2078   POST-based form submission instead
2079</t>
2080</section>
2081
2082<section title="Location Headers and Spoofing" anchor="location.spoofing">
2083<t>
2084   If a single server supports multiple organizations that do not trust
2085   one another, then it &MUST; check the values of Location and Content-Location
2086   headers in responses that are generated under control of
2087   said organizations to make sure that they do not attempt to
2088   invalidate resources over which they have no authority.
2089</t>
2090</section>
2091
2092</section>
2093
2094<section title="Acknowledgments" anchor="ack">
2095<t>
2096   Based on an XML translation of RFC 2616 by Julian Reschke.
2097</t>
2098</section>
2099</middle>
2100<back>
2101<references>
2102
2103<reference anchor="Part1">
2104   <front>
2105      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2106      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2107         <organization abbrev="Day Software">Day Software</organization>
2108         <address><email>fielding@gbiv.com</email></address>
2109      </author>
2110      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2111         <organization>One Laptop per Child</organization>
2112         <address><email>jg@laptop.org</email></address>
2113      </author>
2114      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2115         <organization abbrev="HP">Hewlett-Packard Company</organization>
2116         <address><email>JeffMogul@acm.org</email></address>
2117      </author>
2118      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2119         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2120         <address><email>henrikn@microsoft.com</email></address>
2121      </author>
2122      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2123         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2124         <address><email>LMM@acm.org</email></address>
2125      </author>
2126      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2127         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2128         <address><email>paulle@microsoft.com</email></address>
2129      </author>
2130      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2131         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2132         <address><email>timbl@w3.org</email></address>
2133      </author>
2134      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2135   </front>
2136   <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
2137   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2138</reference>
2139
2140<reference anchor="Part3">
2141   <front>
2142      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2143      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2144         <organization abbrev="Day Software">Day Software</organization>
2145         <address><email>fielding@gbiv.com</email></address>
2146      </author>
2147      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2148         <organization>One Laptop per Child</organization>
2149         <address><email>jg@laptop.org</email></address>
2150      </author>
2151      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2152         <organization abbrev="HP">Hewlett-Packard Company</organization>
2153         <address><email>JeffMogul@acm.org</email></address>
2154      </author>
2155      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2156         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2157         <address><email>henrikn@microsoft.com</email></address>
2158      </author>
2159      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2160         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2161         <address><email>LMM@acm.org</email></address>
2162      </author>
2163      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2164         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2165         <address><email>paulle@microsoft.com</email></address>
2166      </author>
2167      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2168         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2169         <address><email>timbl@w3.org</email></address>
2170      </author>
2171      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2172   </front>
2173   <seriesInfo name="Internet-Draft" value="draft-fielding-p3-payload-&ID-VERSION;"/>
2174   <x:source href="p3-payload.xml" basename="p3-payload"/>
2175</reference>
2176
2177<reference anchor="Part4">
2178   <front>
2179      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2180      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2181         <organization abbrev="Day Software">Day Software</organization>
2182         <address><email>fielding@gbiv.com</email></address>
2183      </author>
2184      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2185         <organization>One Laptop per Child</organization>
2186         <address><email>jg@laptop.org</email></address>
2187      </author>
2188      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2189         <organization abbrev="HP">Hewlett-Packard Company</organization>
2190         <address><email>JeffMogul@acm.org</email></address>
2191      </author>
2192      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2193         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2194         <address><email>henrikn@microsoft.com</email></address>
2195      </author>
2196      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2197         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2198         <address><email>LMM@acm.org</email></address>
2199      </author>
2200      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2201         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2202         <address><email>paulle@microsoft.com</email></address>
2203      </author>
2204      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2205         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2206         <address><email>timbl@w3.org</email></address>
2207      </author>
2208      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2209   </front>
2210   <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
2211   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2212</reference>
2213
2214<reference anchor="Part5">
2215   <front>
2216      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2217      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2218         <organization abbrev="Day Software">Day Software</organization>
2219         <address><email>fielding@gbiv.com</email></address>
2220      </author>
2221      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2222         <organization>One Laptop per Child</organization>
2223         <address><email>jg@laptop.org</email></address>
2224      </author>
2225      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2226         <organization abbrev="HP">Hewlett-Packard Company</organization>
2227         <address><email>JeffMogul@acm.org</email></address>
2228      </author>
2229      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2230         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2231         <address><email>henrikn@microsoft.com</email></address>
2232      </author>
2233      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2234         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2235         <address><email>LMM@acm.org</email></address>
2236      </author>
2237      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2238         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2239         <address><email>paulle@microsoft.com</email></address>
2240      </author>
2241      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2242         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2243         <address><email>timbl@w3.org</email></address>
2244      </author>
2245      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2246   </front>
2247   <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
2248   <x:source href="p5-range.xml" basename="p5-range"/>
2249</reference>
2250
2251<reference anchor="Part6">
2252   <front>
2253      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2254      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2255         <organization abbrev="Day Software">Day Software</organization>
2256         <address><email>fielding@gbiv.com</email></address>
2257      </author>
2258      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2259         <organization>One Laptop per Child</organization>
2260         <address><email>jg@laptop.org</email></address>
2261      </author>
2262      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2263         <organization abbrev="HP">Hewlett-Packard Company</organization>
2264         <address><email>JeffMogul@acm.org</email></address>
2265      </author>
2266      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2267         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2268         <address><email>henrikn@microsoft.com</email></address>
2269      </author>
2270      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2271         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2272         <address><email>LMM@acm.org</email></address>
2273      </author>
2274      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2275         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2276         <address><email>paulle@microsoft.com</email></address>
2277      </author>
2278      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2279         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2280         <address><email>timbl@w3.org</email></address>
2281      </author>
2282      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2283   </front>
2284   <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
2285   <x:source href="p6-cache.xml" basename="p6-cache"/>
2286</reference>
2287
2288<reference anchor="Part7">
2289   <front>
2290      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2291      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2292         <organization abbrev="Day Software">Day Software</organization>
2293         <address><email>fielding@gbiv.com</email></address>
2294      </author>
2295      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2296         <organization>One Laptop per Child</organization>
2297         <address><email>jg@laptop.org</email></address>
2298      </author>
2299      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2300         <organization abbrev="HP">Hewlett-Packard Company</organization>
2301         <address><email>JeffMogul@acm.org</email></address>
2302      </author>
2303      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2304         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2305         <address><email>henrikn@microsoft.com</email></address>
2306      </author>
2307      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2308         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2309         <address><email>LMM@acm.org</email></address>
2310      </author>
2311      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2312         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2313         <address><email>paulle@microsoft.com</email></address>
2314      </author>
2315      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2316         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2317         <address><email>timbl@w3.org</email></address>
2318      </author>
2319      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2320   </front>
2321   <seriesInfo name="Internet-Draft" value="draft-fielding-p7-auth-&ID-VERSION;"/>
2322   <x:source href="p7-auth.xml" basename="p7-auth"/>
2323</reference>
2324
2325<reference anchor="RFC2616">
2326   <front>
2327      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2328      <author initials="R." surname="Fielding" fullname="R. Fielding">
2329         <organization>University of California, Irvine</organization>
2330         <address><email>fielding@ics.uci.edu</email></address>
2331      </author>
2332      <author initials="J." surname="Gettys" fullname="J. Gettys">
2333         <organization>W3C</organization>
2334         <address><email>jg@w3.org</email></address>
2335      </author>
2336      <author initials="J." surname="Mogul" fullname="J. Mogul">
2337         <organization>Compaq Computer Corporation</organization>
2338         <address><email>mogul@wrl.dec.com</email></address>
2339      </author>
2340      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2341         <organization>MIT Laboratory for Computer Science</organization>
2342         <address><email>frystyk@w3.org</email></address>
2343      </author>
2344      <author initials="L." surname="Masinter" fullname="L. Masinter">
2345         <organization>Xerox Corporation</organization>
2346         <address><email>masinter@parc.xerox.com</email></address>
2347      </author>
2348      <author initials="P." surname="Leach" fullname="P. Leach">
2349         <organization>Microsoft Corporation</organization>
2350         <address><email>paulle@microsoft.com</email></address>
2351      </author>
2352      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2353         <organization>W3C</organization>
2354         <address><email>timbl@w3.org</email></address>
2355      </author>
2356      <date month="June" year="1999"/>
2357   </front>
2358   <seriesInfo name="RFC" value="2616"/>
2359</reference>
2360
2361<reference anchor="RFC1123">
2362<front>
2363<title>Requirements for Internet Hosts - Application and Support</title>
2364<author initials="R." surname="Braden" fullname="Robert Braden">
2365<organization>University of Southern California (USC), Information Sciences Institute</organization>
2366<address>
2367<postal>
2368<street>4676 Admiralty Way</street>
2369<city>Marina del Rey</city>
2370<region>CA</region>
2371<code>90292-6695</code>
2372<country>US</country></postal>
2373<phone>+1 213 822 1511</phone>
2374<email>Braden@ISI.EDU</email></address></author>
2375<date month="October" year="1989"/></front>
2376<seriesInfo name="STD" value="3"/>
2377<seriesInfo name="RFC" value="1123"/>
2378</reference>
2379
2380<reference anchor="RFC822">
2381<front>
2382<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2383<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2384<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2385<address>
2386<postal>
2387<street/>
2388<city>Newark</city>
2389<region>DE</region>
2390<code>19711</code>
2391<country>US</country></postal>
2392<email>DCrocker@UDel-Relay</email></address></author>
2393<date month="August" day="13" year="1982"/></front>
2394<seriesInfo name="STD" value="11"/>
2395<seriesInfo name="RFC" value="822"/>
2396</reference>
2397
2398<reference anchor="RFC2068">
2399<front>
2400<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2401<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2402<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2403<address>
2404<postal>
2405<street/>
2406<city>Irvine</city>
2407<region>CA</region>
2408<code>92717-3425</code>
2409<country>US</country></postal>
2410<facsimile>+1 714 824 4056</facsimile>
2411<email>fielding@ics.uci.edu</email></address></author>
2412<author initials="J." surname="Gettys" fullname="Jim Gettys">
2413<organization>MIT Laboratory for Computer Science</organization>
2414<address>
2415<postal>
2416<street>545 Technology Square</street>
2417<city>Cambridge</city>
2418<region>MA</region>
2419<code>02139</code>
2420<country>US</country></postal>
2421<facsimile>+1 617 258 8682</facsimile>
2422<email>jg@w3.org</email></address></author>
2423<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2424<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2425<address>
2426<postal>
2427<street>250 University Avenue</street>
2428<city>Palo Alto</city>
2429<region>CA</region>
2430<code>94301</code>
2431<country>US</country></postal>
2432<email>mogul@wrl.dec.com</email></address></author>
2433<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2434<organization>MIT Laboratory for Computer Science</organization>
2435<address>
2436<postal>
2437<street>545 Technology Square</street>
2438<city>Cambridge</city>
2439<region>MA</region>
2440<code>02139</code>
2441<country>US</country></postal>
2442<facsimile>+1 617 258 8682</facsimile>
2443<email>frystyk@w3.org</email></address></author>
2444<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2445<organization>MIT Laboratory for Computer Science</organization>
2446<address>
2447<postal>
2448<street>545 Technology Square</street>
2449<city>Cambridge</city>
2450<region>MA</region>
2451<code>02139</code>
2452<country>US</country></postal>
2453<facsimile>+1 617 258 8682</facsimile>
2454<email>timbl@w3.org</email></address></author>
2455<date month="January" year="1997"/>
2456<abstract>
2457<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>
2458<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>
2459<seriesInfo name="RFC" value="2068"/>
2460</reference>
2461
2462<reference anchor="RFC2617">
2463<front>
2464<title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
2465<author initials="J." surname="Franks" fullname="John Franks">
2466<organization>Northwestern University, Department of Mathematics</organization>
2467<address>
2468<postal>
2469<street/>
2470<city>Evanston</city>
2471<region>IL</region>
2472<code>60208-2730</code>
2473<country>US</country></postal>
2474<email>john@math.nwu.edu</email></address></author>
2475<author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
2476<organization>Verisign Inc.</organization>
2477<address>
2478<postal>
2479<street>301 Edgewater Place</street>
2480<street>Suite 210</street>
2481<city>Wakefield</city>
2482<region>MA</region>
2483<code>01880</code>
2484<country>US</country></postal>
2485<email>pbaker@verisign.com</email></address></author>
2486<author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
2487<organization>AbiSource, Inc.</organization>
2488<address>
2489<postal>
2490<street>6 Dunlap Court</street>
2491<city>Savoy</city>
2492<region>IL</region>
2493<code>61874</code>
2494<country>US</country></postal>
2495<email>jeff@AbiSource.com</email></address></author>
2496<author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
2497<organization>Agranat Systems, Inc.</organization>
2498<address>
2499<postal>
2500<street>5 Clocktower Place</street>
2501<street>Suite 400</street>
2502<city>Maynard</city>
2503<region>MA</region>
2504<code>01754</code>
2505<country>US</country></postal>
2506<email>lawrence@agranat.com</email></address></author>
2507<author initials="P.J." surname="Leach" fullname="Paul J. Leach">
2508<organization>Microsoft Corporation</organization>
2509<address>
2510<postal>
2511<street>1 Microsoft Way</street>
2512<city>Redmond</city>
2513<region>WA</region>
2514<code>98052</code>
2515<country>US</country></postal>
2516<email>paulle@microsoft.com</email></address></author>
2517<author initials="A." surname="Luotonen" fullname="Ari Luotonen">
2518<organization>Netscape Communications Corporation</organization>
2519<address>
2520<postal>
2521<street>501 East Middlefield Road</street>
2522<city>Mountain View</city>
2523<region>CA</region>
2524<code>94043</code>
2525<country>US</country></postal></address></author>
2526<author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
2527<organization>Open Market, Inc.</organization>
2528<address>
2529<postal>
2530<street>215 First Street</street>
2531<city>Cambridge</city>
2532<region>MA</region>
2533<code>02142</code>
2534<country>US</country></postal>
2535<email>stewart@OpenMarket.com</email></address></author>
2536<date month="June" year="1999"/>
2537</front>
2538<seriesInfo name="RFC" value="2617"/>
2539</reference>
2540
2541<reference anchor="Luo1998">
2542<front>
2543<title>Tunneling TCP based protocols through Web proxy servers</title>
2544<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2545  <organization/>
2546</author>
2547<date/>
2548</front>
2549<seriesInfo name="" value="Work in Progress"/>
2550</reference>
2551
2552</references>
2553
2554<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2555<t>
2556   Clarified which error code should be used for inbound server failures
2557   (e.g. DNS failures). (<xref target="status.504"/>).
2558</t>
2559<t>
2560   CREATE had a race that required an Etag be sent when a resource is
2561   first created. (<xref target="status.201"/>).
2562</t>
2563<t>
2564   Rewrite of message transmission requirements to make it much harder
2565   for implementors to get it wrong, as the consequences of errors here
2566   can have significant impact on the Internet, and to deal with the
2567   following problems:
2568  <list style="numbers">
2569      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2570         this was incorrectly placing a requirement on the behavior of
2571         an implementation of a future version of HTTP/1.x</t>
2572
2573      <t>Made it clear that user-agents should retry requests, not
2574         "clients" in general.</t>
2575
2576      <t>Converted requirements for clients to ignore unexpected 100
2577         (Continue) responses, and for proxies to forward 100 responses,
2578         into a general requirement for 1xx responses.</t>
2579
2580      <t>Modified some TCP-specific language, to make it clearer that
2581         non-TCP transports are possible for HTTP.</t>
2582
2583      <t>Require that the origin server &MUST-NOT; wait for the request
2584         body before it sends a required 100 (Continue) response.</t>
2585
2586      <t>Allow, rather than require, a server to omit 100 (Continue) if
2587         it has already seen some of the request body.</t>
2588
2589      <t>Allow servers to defend against denial-of-service attacks and
2590         broken clients.</t>
2591  </list>
2592</t>
2593<t>
2594   This change adds the Expect header and 417 status code.
2595</t>
2596<t>
2597   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2598   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2599</t>
2600<t>
2601   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
2602   implemented in previous versions of this specification. See RFC 2068
2603   <xref target="RFC2068"/>.
2604</t>
2605</section>
2606</back>
2607</rfc>
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