source: draft-ietf-httpbis/latest/p2-semantics.xml @ 689

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Bump up document dates, update to latest version of rfc2629.xslt

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65]>
66<?rfc toc="yes" ?>
67<?rfc symrefs="yes" ?>
68<?rfc sortrefs="yes" ?>
69<?rfc compact="yes"?>
70<?rfc subcompact="no" ?>
71<?rfc linkmailto="no" ?>
72<?rfc editing="no" ?>
73<?rfc comments="yes"?>
74<?rfc inline="yes"?>
75<?rfc-ext allow-markup-in-artwork="yes" ?>
76<?rfc-ext include-references-in-index="yes" ?>
77<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
78     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
79     xmlns:x='http://purl.org/net/xml2rfc/ext'
80     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
81<front>
82
83  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
84
85  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
86    <organization abbrev="Day Software">Day Software</organization>
87    <address>
88      <postal>
89        <street>23 Corporate Plaza DR, Suite 280</street>
90        <city>Newport Beach</city>
91        <region>CA</region>
92        <code>92660</code>
93        <country>USA</country>
94      </postal>
95      <phone>+1-949-706-5300</phone>
96      <facsimile>+1-949-706-5305</facsimile>
97      <email>fielding@gbiv.com</email>
98      <uri>http://roy.gbiv.com/</uri>
99    </address>
100  </author>
101
102  <author initials="J." surname="Gettys" fullname="Jim Gettys">
103    <organization>One Laptop per Child</organization>
104    <address>
105      <postal>
106        <street>21 Oak Knoll Road</street>
107        <city>Carlisle</city>
108        <region>MA</region>
109        <code>01741</code>
110        <country>USA</country>
111      </postal>
112      <email>jg@laptop.org</email>
113      <uri>http://www.laptop.org/</uri>
114    </address>
115  </author>
116 
117  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
118    <organization abbrev="HP">Hewlett-Packard Company</organization>
119    <address>
120      <postal>
121        <street>HP Labs, Large Scale Systems Group</street>
122        <street>1501 Page Mill Road, MS 1177</street>
123        <city>Palo Alto</city>
124        <region>CA</region>
125        <code>94304</code>
126        <country>USA</country>
127      </postal>
128      <email>JeffMogul@acm.org</email>
129    </address>
130  </author>
131
132  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
133    <organization abbrev="Microsoft">Microsoft Corporation</organization>
134    <address>
135      <postal>
136        <street>1 Microsoft Way</street>
137        <city>Redmond</city>
138        <region>WA</region>
139        <code>98052</code>
140        <country>USA</country>
141      </postal>
142      <email>henrikn@microsoft.com</email>
143    </address>
144  </author>
145
146  <author initials="L." surname="Masinter" fullname="Larry Masinter">
147    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
148    <address>
149      <postal>
150        <street>345 Park Ave</street>
151        <city>San Jose</city>
152        <region>CA</region>
153        <code>95110</code>
154        <country>USA</country>
155      </postal>
156      <email>LMM@acm.org</email>
157      <uri>http://larry.masinter.net/</uri>
158    </address>
159  </author>
160 
161  <author initials="P." surname="Leach" fullname="Paul J. Leach">
162    <organization abbrev="Microsoft">Microsoft Corporation</organization>
163    <address>
164      <postal>
165        <street>1 Microsoft Way</street>
166        <city>Redmond</city>
167        <region>WA</region>
168        <code>98052</code>
169      </postal>
170      <email>paulle@microsoft.com</email>
171    </address>
172  </author>
173   
174  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
175    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
176    <address>
177      <postal>
178        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
179        <street>The Stata Center, Building 32</street>
180        <street>32 Vassar Street</street>
181        <city>Cambridge</city>
182        <region>MA</region>
183        <code>02139</code>
184        <country>USA</country>
185      </postal>
186      <email>timbl@w3.org</email>
187      <uri>http://www.w3.org/People/Berners-Lee/</uri>
188    </address>
189  </author>
190
191  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
192    <organization abbrev="W3C">World Wide Web Consortium</organization>
193    <address>
194      <postal>
195        <street>W3C / ERCIM</street>
196        <street>2004, rte des Lucioles</street>
197        <city>Sophia-Antipolis</city>
198        <region>AM</region>
199        <code>06902</code>
200        <country>France</country>
201      </postal>
202      <email>ylafon@w3.org</email>
203      <uri>http://www.raubacapeu.net/people/yves/</uri>
204    </address>
205  </author>
206
207  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
208    <organization abbrev="greenbytes">greenbytes GmbH</organization>
209    <address>
210      <postal>
211        <street>Hafenweg 16</street>
212        <city>Muenster</city><region>NW</region><code>48155</code>
213        <country>Germany</country>
214      </postal>
215      <phone>+49 251 2807760</phone>
216      <facsimile>+49 251 2807761</facsimile>
217      <email>julian.reschke@greenbytes.de</email>
218      <uri>http://greenbytes.de/tech/webdav/</uri>
219    </address>
220  </author>
221
222  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
223  <workgroup>HTTPbis Working Group</workgroup>
224
225<abstract>
226<t>
227   The Hypertext Transfer Protocol (HTTP) is an application-level
228   protocol for distributed, collaborative, hypermedia information
229   systems. HTTP has been in use by the World Wide Web global information
230   initiative since 1990. This document is Part 2 of the seven-part specification
231   that defines the protocol referred to as "HTTP/1.1" and, taken together,
232   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
233   as expressed by request methods, request-header fields, response status codes,
234   and response-header fields.
235</t>
236</abstract>
237
238<note title="Editorial Note (To be removed by RFC Editor)">
239  <t>
240    Discussion of this draft should take place on the HTTPBIS working group
241    mailing list (ietf-http-wg@w3.org). The current issues list is
242    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
243    and related documents (including fancy diffs) can be found at
244    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
245  </t>
246  <t>
247    The changes in this draft are summarized in <xref target="changes.since.07"/>.
248  </t>
249</note>
250</front>
251<middle>
252<section title="Introduction" anchor="introduction">
253<t>
254   This document defines HTTP/1.1 request and response semantics.  Each HTTP
255   message, as defined in &messaging;, is in the form of either a request or
256   a response.  An HTTP server listens on a connection for HTTP requests and
257   responds to each request, in the order received on that connection, with
258   one or more HTTP response messages.  This document defines the commonly
259   agreed upon semantics of the HTTP uniform interface, the intentions defined
260   by each request method, and the various response messages that might be
261   expected as a result of applying that method for the requested resource.
262</t>
263<t>
264   This document is currently disorganized in order to minimize the changes
265   between drafts and enable reviewers to see the smaller errata changes.
266   The next draft will reorganize the sections to better reflect the content.
267   In particular, the sections will be ordered according to the typical
268   processing of an HTTP request message (after message parsing): resource
269   mapping, general header fields, methods, request modifiers, response
270   status, and resource metadata.  The current mess reflects how widely
271   dispersed these topics and associated requirements had become in
272   <xref target="RFC2616"/>.
273</t>
274
275<section title="Requirements" anchor="intro.requirements">
276<t>
277   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
278   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
279   document are to be interpreted as described in <xref target="RFC2119"/>.
280</t>
281<t>
282   An implementation is not compliant if it fails to satisfy one or more
283   of the &MUST; or &REQUIRED; level requirements for the protocols it
284   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
285   level and all the &SHOULD; level requirements for its protocols is said
286   to be "unconditionally compliant"; one that satisfies all the &MUST;
287   level requirements but not all the &SHOULD; level requirements for its
288   protocols is said to be "conditionally compliant."
289</t>
290</section>
291
292<section title="Syntax Notation" anchor="notation">
293  <x:anchor-alias value="CR"/>
294  <x:anchor-alias value="DIGIT"/>
295  <x:anchor-alias value="LF"/>
296  <x:anchor-alias value="VCHAR"/>
297  <x:anchor-alias value="WSP"/>
298<t>
299  This specification uses the ABNF syntax defined in &notation; (which
300  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
301  <xref target="collected.abnf"/> shows the collected ABNF, with the list
302  rule expanded.
303</t>
304<t>
305  The following core rules are included by
306  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
307  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
308  DIGIT (decimal 0-9), DQUOTE (double quote),
309  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
310  OCTET (any 8-bit sequence of data), SP (space),
311  VCHAR (any visible USASCII character),
312  and WSP (whitespace).
313</t>
314
315<section title="Core Rules" anchor="core.rules">
316  <x:anchor-alias value="obs-text"/>
317  <x:anchor-alias value="quoted-string"/>
318  <x:anchor-alias value="token"/>
319  <x:anchor-alias value="OWS"/>
320  <x:anchor-alias value="RWS"/>
321<t>
322  The core rules below are defined in &basic-rules;:
323</t>
324<figure><artwork type="abnf2616">
325  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
326  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
327  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
328  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
329  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
330</artwork></figure>
331</section>
332
333<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
334  <x:anchor-alias value="absolute-URI"/>
335  <x:anchor-alias value="Accept"/>
336  <x:anchor-alias value="Accept-Charset"/>
337  <x:anchor-alias value="Accept-Encoding"/>
338  <x:anchor-alias value="Accept-Language"/>
339  <x:anchor-alias value="Accept-Ranges"/>
340  <x:anchor-alias value="Age"/>
341  <x:anchor-alias value="Authorization"/>
342  <x:anchor-alias value="comment"/>
343  <x:anchor-alias value="ETag"/>
344  <x:anchor-alias value="Host"/>
345  <x:anchor-alias value="HTTP-date"/>
346  <x:anchor-alias value="If-Match"/>
347  <x:anchor-alias value="If-Modified-Since"/>
348  <x:anchor-alias value="If-None-Match"/>
349  <x:anchor-alias value="If-Range"/>
350  <x:anchor-alias value="If-Unmodified-Since"/>
351  <x:anchor-alias value="partial-URI"/>
352  <x:anchor-alias value="product"/>
353  <x:anchor-alias value="Proxy-Authenticate"/>
354  <x:anchor-alias value="Proxy-Authorization"/>
355  <x:anchor-alias value="Range"/>
356  <x:anchor-alias value="TE"/>
357  <x:anchor-alias value="URI"/>
358  <x:anchor-alias value="Vary"/>
359  <x:anchor-alias value="WWW-Authenticate"/>
360<t>
361  The ABNF rules below are defined in other parts:
362</t>
363<figure><!--Part1--><artwork type="abnf2616">
364  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
365  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
366  <x:ref>Host</x:ref>          = &lt;Host, defined in &uri;&gt;
367  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
368  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
369  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
370  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
371  <x:ref>URI</x:ref>           = &lt;URI, defined in &uri;&gt;
372</artwork></figure>
373<figure><!--Part3--><artwork type="abnf2616">
374  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
375  <x:ref>Accept-Charset</x:ref> =
376             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
377  <x:ref>Accept-Encoding</x:ref> =
378             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
379  <x:ref>Accept-Language</x:ref> =
380             &lt;Accept-Language, defined in &header-accept-language;&gt;
381</artwork></figure>
382<figure><!--Part4--><artwork type="abnf2616">
383  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
384  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
385  <x:ref>If-Modified-Since</x:ref> =
386             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
387  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
388  <x:ref>If-Unmodified-Since</x:ref> =
389             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
390</artwork></figure>
391<figure><!--Part5--><artwork type="abnf2616">
392  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
393  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
394  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
395</artwork></figure>
396<figure><!--Part6--><artwork type="abnf2616">
397  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
398  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
399</artwork><!--Part7--></figure>
400<figure><artwork type="abnf2616">
401  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
402  <x:ref>Proxy-Authenticate</x:ref> =
403             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
404  <x:ref>Proxy-Authorization</x:ref> =
405             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
406  <x:ref>WWW-Authenticate</x:ref> =
407             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
408</artwork></figure>
409</section>
410</section>
411</section>
412
413<section title="Method" anchor="method">
414  <x:anchor-alias value="Method"/>
415  <x:anchor-alias value="extension-method"/>
416<t>
417   The Method  token indicates the method to be performed on the
418   resource identified by the request-target. The method is case-sensitive.
419</t>
420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
421  <x:ref>Method</x:ref>         = <x:abnf-char-sequence>"OPTIONS"</x:abnf-char-sequence>   ; "OPTIONS", <xref target="OPTIONS"/>
422                 / <x:abnf-char-sequence>"GET"</x:abnf-char-sequence>               ; "GET", <xref target="GET"/>
423                 / <x:abnf-char-sequence>"HEAD"</x:abnf-char-sequence>            ; "HEAD", <xref target="HEAD"/>
424                 / <x:abnf-char-sequence>"POST"</x:abnf-char-sequence>            ; "POST", <xref target="POST"/>
425                 / <x:abnf-char-sequence>"PUT"</x:abnf-char-sequence>               ; "PUT", <xref target="PUT"/>
426                 / <x:abnf-char-sequence>"DELETE"</x:abnf-char-sequence>      ; "DELETE", <xref target="DELETE"/>
427                 / <x:abnf-char-sequence>"TRACE"</x:abnf-char-sequence>         ; "TRACE", <xref target="TRACE"/>
428                 / <x:abnf-char-sequence>"CONNECT"</x:abnf-char-sequence>   ; "CONNECT", <xref target="CONNECT"/>
429                 / <x:ref>extension-method</x:ref>
430  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
431</artwork></figure>
432<t>
433   The list of methods allowed by a resource can be specified in an
434   Allow header field (<xref target="header.allow"/>). The return code of the response
435   always notifies the client whether a method is currently allowed on a
436   resource, since the set of allowed methods can change dynamically. An
437   origin server &SHOULD; return the status code 405 (Method Not Allowed)
438   if the method is known by the origin server but not allowed for the
439   requested resource, and 501 (Not Implemented) if the method is
440   unrecognized or not implemented by the origin server. The methods GET
441   and HEAD &MUST; be supported by all general-purpose servers. All other
442   methods are &OPTIONAL;; however, if the above methods are implemented,
443   they &MUST; be implemented with the same semantics as those specified
444   in <xref target="method.definitions"/>.
445</t>
446
447<section title="Method Registry" anchor="method.registry">
448<t>
449  The HTTP Method Registry defines the name space for the Method token in the
450  Request line of an HTTP request.
451</t>
452<t>
453  Registrations &MUST; include the following fields:
454  <list style="symbols">
455    <t>Method Name (see <xref target="method"/>)</t>
456    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
457    <t>Pointer to specification text</t>
458  </list>
459</t>
460<t>
461  Values to be added to this name space are subject to IETF review
462  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
463</t>
464<t>
465  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
466</t>
467</section>
468</section>
469
470<section title="Request Header Fields" anchor="request.header.fields">
471  <x:anchor-alias value="request-header"/>
472<t>
473   The request-header fields allow the client to pass additional
474   information about the request, and about the client itself, to the
475   server. These fields act as request modifiers, with semantics
476   equivalent to the parameters on a programming language method
477   invocation.
478</t>
479<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
480  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
481                 / <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
482                 / <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
483                 / <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
484                 / <x:ref>Authorization</x:ref>            ; &header-authorization;
485                 / <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
486                 / <x:ref>From</x:ref>                     ; <xref target="header.from"/>
487                 / <x:ref>Host</x:ref>                     ; &header-host;
488                 / <x:ref>If-Match</x:ref>                 ; &header-if-match;
489                 / <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
490                 / <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
491                 / <x:ref>If-Range</x:ref>                 ; &header-if-range;
492                 / <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
493                 / <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
494                 / <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
495                 / <x:ref>Range</x:ref>                    ; &header-range;
496                 / <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
497                 / <x:ref>TE</x:ref>                       ; &header-te;
498                 / <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
499</artwork></figure>
500<t>
501   Request-header field names can be extended reliably only in
502   combination with a change in the protocol version. However, new or
503   experimental header fields &MAY; be given the semantics of request-header
504   fields if all parties in the communication recognize them to
505   be request-header fields. Unrecognized header fields are treated as
506   entity-header fields.
507</t>
508</section>
509
510<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
511  <x:anchor-alias value="Reason-Phrase"/>
512  <x:anchor-alias value="Status-Code"/>
513  <x:anchor-alias value="extension-code"/>
514<t>
515   The Status-Code element is a 3-digit integer result code of the
516   attempt to understand and satisfy the request. The status codes listed
517   below are defined in <xref target="status.codes"/>.
518   The Reason-Phrase is intended to give a short
519   textual description of the Status-Code. The Status-Code is intended
520   for use by automata and the Reason-Phrase is intended for the human
521   user. The client is not required to examine or display the Reason-Phrase.
522</t>
523<t> 
524   The individual values of the numeric status codes defined for
525   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
526   presented below. The reason phrases listed here are only
527   recommendations -- they &MAY; be replaced by local equivalents without
528   affecting the protocol.
529</t>
530<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"/>
531  <x:ref>Status-Code</x:ref>    =
532         "100"  ; <xref target="status.100"/>: Continue
533       / "101"  ; <xref target="status.101"/>: Switching Protocols
534       / "200"  ; <xref target="status.200"/>: OK
535       / "201"  ; <xref target="status.201"/>: Created
536       / "202"  ; <xref target="status.202"/>: Accepted
537       / "203"  ; <xref target="status.203"/>: Non-Authoritative Information
538       / "204"  ; <xref target="status.204"/>: No Content
539       / "205"  ; <xref target="status.205"/>: Reset Content
540       / "206"  ; <xref target="status.206"/>: Partial Content
541       / "300"  ; <xref target="status.300"/>: Multiple Choices
542       / "301"  ; <xref target="status.301"/>: Moved Permanently
543       / "302"  ; <xref target="status.302"/>: Found
544       / "303"  ; <xref target="status.303"/>: See Other
545       / "304"  ; <xref target="status.304"/>: Not Modified
546       / "305"  ; <xref target="status.305"/>: Use Proxy
547       / "307"  ; <xref target="status.307"/>: Temporary Redirect
548       / "400"  ; <xref target="status.400"/>: Bad Request
549       / "401"  ; <xref target="status.401"/>: Unauthorized
550       / "402"  ; <xref target="status.402"/>: Payment Required
551       / "403"  ; <xref target="status.403"/>: Forbidden
552       / "404"  ; <xref target="status.404"/>: Not Found
553       / "405"  ; <xref target="status.405"/>: Method Not Allowed
554       / "406"  ; <xref target="status.406"/>: Not Acceptable
555       / "407"  ; <xref target="status.407"/>: Proxy Authentication Required
556       / "408"  ; <xref target="status.408"/>: Request Time-out
557       / "409"  ; <xref target="status.409"/>: Conflict
558       / "410"  ; <xref target="status.410"/>: Gone
559       / "411"  ; <xref target="status.411"/>: Length Required
560       / "412"  ; <xref target="status.412"/>: Precondition Failed
561       / "413"  ; <xref target="status.413"/>: Request Entity Too Large
562       / "414"  ; <xref target="status.414"/>: URI Too Long
563       / "415"  ; <xref target="status.415"/>: Unsupported Media Type
564       / "416"  ; <xref target="status.416"/>: Requested range not satisfiable
565       / "417"  ; <xref target="status.417"/>: Expectation Failed
566       / "500"  ; <xref target="status.500"/>: Internal Server Error
567       / "501"  ; <xref target="status.501"/>: Not Implemented
568       / "502"  ; <xref target="status.502"/>: Bad Gateway
569       / "503"  ; <xref target="status.503"/>: Service Unavailable
570       / "504"  ; <xref target="status.504"/>: Gateway Time-out
571       / "505"  ; <xref target="status.505"/>: HTTP Version not supported
572       / <x:ref>extension-code</x:ref>
573
574  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
575  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
576</artwork></figure>
577<t>
578   HTTP status codes are extensible. HTTP applications are not required
579   to understand the meaning of all registered status codes, though such
580   understanding is obviously desirable. However, applications &MUST;
581   understand the class of any status code, as indicated by the first
582   digit, and treat any unrecognized response as being equivalent to the
583   x00 status code of that class, with the exception that an
584   unrecognized response &MUST-NOT; be cached. For example, if an
585   unrecognized status code of 431 is received by the client, it can
586   safely assume that there was something wrong with its request and
587   treat the response as if it had received a 400 status code. In such
588   cases, user agents &SHOULD; present to the user the entity returned
589   with the response, since that entity is likely to include human-readable
590   information which will explain the unusual status.
591</t>
592
593<section title="Status Code Registry" anchor="status.code.registry">
594<t>
595  The HTTP Status Code Registry defines the name space for the Status-Code
596  token in the Status line of an HTTP response.
597</t>
598<t>
599  Values to be added to this name space are subject to IETF review
600  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
601</t>
602<t>
603  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
604</t>
605</section>
606
607</section>
608
609<section title="Response Header Fields" anchor="response.header.fields">
610  <x:anchor-alias value="response-header"/>
611<t>
612   The response-header fields allow the server to pass additional
613   information about the response which cannot be placed in the Status-Line.
614   These header fields give information about the server and about
615   further access to the resource identified by the request-target.
616</t>
617<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
618  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
619                  / <x:ref>Age</x:ref>                     ; &header-age;
620                  / <x:ref>Allow</x:ref>                   ; <xref target="header.allow"/>
621                  / <x:ref>ETag</x:ref>                    ; &header-etag;
622                  / <x:ref>Location</x:ref>                ; <xref target="header.location"/>
623                  / <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
624                  / <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
625                  / <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
626                  / <x:ref>Vary</x:ref>                    ; &header-vary;
627                  / <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
628</artwork></figure>
629<t>
630   Response-header field names can be extended reliably only in
631   combination with a change in the protocol version. However, new or
632   experimental header fields &MAY; be given the semantics of response-header
633   fields if all parties in the communication recognize them to
634   be response-header fields. Unrecognized header fields are treated as
635   entity-header fields.
636</t>
637</section>
638
639<section title="Entity" anchor="entity">
640<t>
641   Request and Response messages &MAY; transfer an entity if not otherwise
642   restricted by the request method or response status code. An entity
643   consists of entity-header fields and an entity-body, although some
644   responses will only include the entity-headers. HTTP entity-body and
645   entity-header fields are defined in &payload;.
646</t>
647<t>
648   An entity-body is only present in a message when a message-body is
649   present, as described in &message-body;. The entity-body is obtained
650   from the message-body by decoding any Transfer-Encoding that might
651   have been applied to ensure safe and proper transfer of the message.
652</t>
653</section>
654
655
656<section title="Method Definitions" anchor="method.definitions">
657<t>
658   The set of common methods for HTTP/1.1 is defined below. Although
659   this set can be expanded, additional methods cannot be assumed to
660   share the same semantics for separately extended clients and servers.
661</t>
662
663<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
664
665<section title="Safe Methods" anchor="safe.methods">
666<iref item="Safe Methods" primary="true"/>
667<t>
668   Implementors should be aware that the software represents the user in
669   their interactions over the Internet, and should be careful to allow
670   the user to be aware of any actions they might take which may have an
671   unexpected significance to themselves or others.
672</t>
673<t>
674   In particular, the convention has been established that the GET and
675   HEAD methods &SHOULD-NOT;  have the significance of taking an action
676   other than retrieval. These methods ought to be considered "<x:dfn anchor="safe">safe</x:dfn>".
677   This allows user agents to represent other methods, such as POST, PUT
678   and DELETE, in a special way, so that the user is made aware of the
679   fact that a possibly unsafe action is being requested.
680</t>
681<t>
682   Naturally, it is not possible to ensure that the server does not
683   generate side-effects as a result of performing a GET request; in
684   fact, some dynamic resources consider that a feature. The important
685   distinction here is that the user did not request the side-effects,
686   so therefore cannot be held accountable for them.
687</t>
688</section>
689
690<section title="Idempotent Methods" anchor="idempotent.methods">
691<iref item="Idempotent Methods" primary="true"/>
692<t>
693   Methods can also have the property of "idempotence" in that, aside
694   from error or expiration issues, the intended effect of multiple
695   identical requests is the same as for a single request.
696   The methods PUT, DELETE, and all safe methods are idempotent.
697   It is important to note that idempotence refers only to changes
698   requested by the client: a server is free to change its state due
699   to multiple requests for the purpose of tracking those requests,
700   versioning of results, etc.
701</t>
702</section>
703</section>
704
705<section title="OPTIONS" anchor="OPTIONS">
706  <rdf:Description>
707    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
708  </rdf:Description>
709  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
710  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
711<t>
712   The OPTIONS method represents a request for information about the
713   communication options available on the request/response chain
714   identified by the request-target. This method allows the client to
715   determine the options and/or requirements associated with a resource,
716   or the capabilities of a server, without implying a resource action
717   or initiating a resource retrieval.
718</t>
719<t>
720   Responses to this method are not cacheable.
721</t>
722<t>
723   If the OPTIONS request includes an entity-body (as indicated by the
724   presence of Content-Length or Transfer-Encoding), then the media type
725   &MUST; be indicated by a Content-Type field. Although this
726   specification does not define any use for such a body, future
727   extensions to HTTP might use the OPTIONS body to make more detailed
728   queries on the server.
729</t>
730<t>
731   If the request-target is an asterisk ("*"), the OPTIONS request is
732   intended to apply to the server in general rather than to a specific
733   resource. Since a server's communication options typically depend on
734   the resource, the "*" request is only useful as a "ping" or "no-op"
735   type of method; it does nothing beyond allowing the client to test
736   the capabilities of the server. For example, this can be used to test
737   a proxy for HTTP/1.1 compliance (or lack thereof).
738</t>
739<t>
740   If the request-target is not an asterisk, the OPTIONS request applies
741   only to the options that are available when communicating with that
742   resource.
743</t>
744<t>
745   A 200 response &SHOULD; include any header fields that indicate
746   optional features implemented by the server and applicable to that
747   resource (e.g., Allow), possibly including extensions not defined by
748   this specification. The response body, if any, &SHOULD; also include
749   information about the communication options. The format for such a
750   body is not defined by this specification, but might be defined by
751   future extensions to HTTP. Content negotiation &MAY; be used to select
752   the appropriate response format. If no response body is included, the
753   response &MUST; include a Content-Length field with a field-value of
754   "0".
755</t>
756<t>
757   The Max-Forwards request-header field &MAY; be used to target a
758   specific proxy in the request chain. When a proxy receives an OPTIONS
759   request on an absolute-URI for which request forwarding is permitted,
760   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
761   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
762   instead, the proxy &SHOULD; respond with its own communication options.
763   If the Max-Forwards field-value is an integer greater than zero, the
764   proxy &MUST; decrement the field-value when it forwards the request. If
765   no Max-Forwards field is present in the request, then the forwarded
766   request &MUST-NOT; include a Max-Forwards field.
767</t>
768</section>
769
770<section title="GET" anchor="GET">
771  <rdf:Description>
772    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
773  </rdf:Description>
774  <iref primary="true" item="GET method" x:for-anchor=""/>
775  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
776<t>
777   The GET method means retrieve whatever information (in the form of an
778   entity) is identified by the request-target. If the request-target refers
779   to a data-producing process, it is the produced data which shall be
780   returned as the entity in the response and not the source text of the
781   process, unless that text happens to be the output of the process.
782</t>
783<t>
784   The semantics of the GET method change to a "conditional GET" if the
785   request message includes an If-Modified-Since, If-Unmodified-Since,
786   If-Match, If-None-Match, or If-Range header field. A conditional GET
787   method requests that the entity be transferred only under the
788   circumstances described by the conditional header field(s). The
789   conditional GET method is intended to reduce unnecessary network
790   usage by allowing cached entities to be refreshed without requiring
791   multiple requests or transferring data already held by the client.
792</t>
793<t>
794   The semantics of the GET method change to a "partial GET" if the
795   request message includes a Range header field. A partial GET requests
796   that only part of the entity be transferred, as described in &header-range;.
797   The partial GET method is intended to reduce unnecessary
798   network usage by allowing partially-retrieved entities to be
799   completed without transferring data already held by the client.
800</t>
801<t>
802   The response to a GET request is cacheable if and only if it meets
803   the requirements for HTTP caching described in &caching;.
804</t>
805<t>
806   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
807</t>
808</section>
809
810<section title="HEAD" anchor="HEAD">
811  <rdf:Description>
812    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
813  </rdf:Description>
814  <iref primary="true" item="HEAD method" x:for-anchor=""/>
815  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
816<t>
817   The HEAD method is identical to GET except that the server &MUST-NOT;
818   return a message-body in the response. The metainformation contained
819   in the HTTP headers in response to a HEAD request &SHOULD; be identical
820   to the information sent in response to a GET request. This method can
821   be used for obtaining metainformation about the entity implied by the
822   request without transferring the entity-body itself. This method is
823   often used for testing hypertext links for validity, accessibility,
824   and recent modification.
825</t>
826<t>
827   The response to a HEAD request &MAY; be cacheable in the sense that the
828   information contained in the response &MAY; be used to update a
829   previously cached entity from that resource. If the new field values
830   indicate that the cached entity differs from the current entity (as
831   would be indicated by a change in Content-Length, Content-MD5, ETag
832   or Last-Modified), then the cache &MUST; treat the cache entry as
833   stale.
834</t>
835</section>
836
837<section title="POST" anchor="POST">
838  <iref primary="true" item="POST method" x:for-anchor=""/>
839  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
840<t>
841   The POST method is used to request that the origin server accept the
842   entity enclosed in the request as data to be processed by the resource
843   identified by the request-target in the Request-Line. POST is designed
844   to allow a uniform method to cover the following functions:
845  <list style="symbols">
846    <t>
847      Annotation of existing resources;
848    </t>
849    <t>
850        Posting a message to a bulletin board, newsgroup, mailing list,
851        or similar group of articles;
852    </t>
853    <t>
854        Providing a block of data, such as the result of submitting a
855        form, to a data-handling process;
856    </t>
857    <t>
858        Extending a database through an append operation.
859    </t>
860  </list>
861</t>
862<t>
863   The actual function performed by the POST method is determined by the
864   server and is usually dependent on the request-target.
865</t>
866<t>
867   The action performed by the POST method might not result in a
868   resource that can be identified by a URI. In this case, either 200
869   (OK) or 204 (No Content) is the appropriate response status,
870   depending on whether or not the response includes an entity that
871   describes the result.
872</t>
873<t>
874   If a resource has been created on the origin server, the response
875   &SHOULD; be 201 (Created) and contain an entity which describes the
876   status of the request and refers to the new resource, and a Location
877   header (see <xref target="header.location"/>).
878</t>
879<t>
880   Responses to this method are not cacheable, unless the response
881   includes appropriate Cache-Control or Expires header fields. However,
882   the 303 (See Other) response can be used to direct the user agent to
883   retrieve a cacheable resource.
884</t>
885</section>
886
887<section title="PUT" anchor="PUT">
888  <iref primary="true" item="PUT method" x:for-anchor=""/>
889  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
890<t>
891   The PUT method requests that the enclosed entity be stored at the
892   supplied request-target. If the request-target refers to an already
893   existing resource, the enclosed entity &SHOULD; be considered as a
894   modified version of the one residing on the origin server. If the
895   request-target does not point to an existing resource, and that URI is
896   capable of being defined as a new resource by the requesting user
897   agent, the origin server can create the resource with that URI. If a
898   new resource is created at the request-target, the origin server &MUST;
899   inform the user agent
900   via the 201 (Created) response. If an existing resource is modified,
901   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
902   to indicate successful completion of the request. If the resource
903   could not be created or modified with the request-target, an appropriate
904   error response &SHOULD; be given that reflects the nature of the
905   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
906   headers (headers starting with the prefix 'Content-') that it does
907   not understand or implement
908   and &MUST; return a 501 (Not Implemented) response in such cases.
909</t>
910<t>
911   If the request passes through a cache and the request-target identifies
912   one or more currently cached entities, those entries &SHOULD; be
913   treated as stale. Responses to this method are not cacheable.
914</t>
915<t>
916   The fundamental difference between the POST and PUT requests is
917   reflected in the different meaning of the request-target. The URI in a
918   POST request identifies the resource that will handle the enclosed
919   entity. That resource might be a data-accepting process, a gateway to
920   some other protocol, or a separate entity that accepts annotations.
921   In contrast, the URI in a PUT request identifies the entity enclosed
922   with the request -- the user agent knows what URI is intended and the
923   server &MUST-NOT; attempt to apply the request to some other resource.
924   If the server desires that the request be applied to a different URI,
925   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
926   then make its own decision regarding whether or not to redirect the
927   request.
928</t>
929<t>
930   A single resource &MAY; be identified by many different URIs. For
931   example, an article might have a URI for identifying "the current
932   version" which is separate from the URI identifying each particular
933   version. In this case, a PUT request on a general URI might result in
934   several other URIs being defined by the origin server.
935</t>
936<t>
937   HTTP/1.1 does not define how a PUT method affects the state of an
938   origin server.
939</t>
940<t>
941   Unless otherwise specified for a particular entity-header, the
942   entity-headers in the PUT request &SHOULD; be applied to the resource
943   created or modified by the PUT.
944</t>
945</section>
946
947<section title="DELETE" anchor="DELETE">
948  <iref primary="true" item="DELETE method" x:for-anchor=""/>
949  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
950<t>
951   The DELETE method requests that the origin server delete the resource
952   identified by the request-target. This method &MAY; be overridden by human
953   intervention (or other means) on the origin server. The client cannot
954   be guaranteed that the operation has been carried out, even if the
955   status code returned from the origin server indicates that the action
956   has been completed successfully. However, the server &SHOULD-NOT; 
957   indicate success unless, at the time the response is given, it
958   intends to delete the resource or move it to an inaccessible
959   location.
960</t>
961<t>
962   A successful response &SHOULD; be 200 (OK) if the response includes an
963   entity describing the status, 202 (Accepted) if the action has not
964   yet been enacted, or 204 (No Content) if the action has been enacted
965   but the response does not include an entity.
966</t>
967<t>
968   If the request passes through a cache and the request-target identifies
969   one or more currently cached entities, those entries &SHOULD; be
970   treated as stale. Responses to this method are not cacheable.
971</t>
972</section>
973
974<section title="TRACE" anchor="TRACE">
975  <rdf:Description>
976    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
977  </rdf:Description>
978  <iref primary="true" item="TRACE method" x:for-anchor=""/>
979  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
980<t>
981   The TRACE method is used to invoke a remote, application-layer loop-back
982   of the request message. The final recipient of the request
983   &SHOULD; reflect the message received back to the client as the
984   entity-body of a 200 (OK) response. The final recipient is either the
985   origin server or the first proxy or gateway to receive a Max-Forwards
986   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
987   &MUST-NOT; include an entity.
988</t>
989<t>
990   TRACE allows the client to see what is being received at the other
991   end of the request chain and use that data for testing or diagnostic
992   information. The value of the Via header field (&header-via;) is of
993   particular interest, since it acts as a trace of the request chain.
994   Use of the Max-Forwards header field allows the client to limit the
995   length of the request chain, which is useful for testing a chain of
996   proxies forwarding messages in an infinite loop.
997</t>
998<t>
999   If the request is valid, the response &SHOULD; contain the entire
1000   request message in the entity-body, with a Content-Type of
1001   "message/http" (see &media-type-message-http;). Responses to this method
1002   &MUST-NOT; be cached.
1003</t>
1004</section>
1005
1006<section title="CONNECT" anchor="CONNECT">
1007  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1008  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1009<t>
1010   This specification reserves the method name CONNECT for use with a
1011   proxy that can dynamically switch to being a tunnel (e.g. SSL
1012   tunneling <xref target="RFC2817"/>).
1013</t>
1014</section>
1015</section>
1016
1017
1018<section title="Status Code Definitions" anchor="status.codes">
1019<t>
1020   Each Status-Code is described below, including any metainformation required
1021   in the response.
1022</t>
1023
1024<section title="Informational 1xx" anchor="status.1xx">
1025<t>
1026   This class of status code indicates a provisional response,
1027   consisting only of the Status-Line and optional headers, and is
1028   terminated by an empty line. There are no required headers for this
1029   class of status code. Since HTTP/1.0 did not define any 1xx status
1030   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1031   except under experimental conditions.
1032</t>
1033<t>
1034   A client &MUST; be prepared to accept one or more 1xx status responses
1035   prior to a regular response, even if the client does not expect a 100
1036   (Continue) status message. Unexpected 1xx status responses &MAY; be
1037   ignored by a user agent.
1038</t>
1039<t>
1040   Proxies &MUST; forward 1xx responses, unless the connection between the
1041   proxy and its client has been closed, or unless the proxy itself
1042   requested the generation of the 1xx response. (For example, if a
1043   proxy adds a "Expect: 100-continue" field when it forwards a request,
1044   then it need not forward the corresponding 100 (Continue)
1045   response(s).)
1046</t>
1047
1048<section title="100 Continue" anchor="status.100">
1049  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1050  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1051<t>
1052   The client &SHOULD; continue with its request. This interim response is
1053   used to inform the client that the initial part of the request has
1054   been received and has not yet been rejected by the server. The client
1055   &SHOULD; continue by sending the remainder of the request or, if the
1056   request has already been completed, ignore this response. The server
1057   &MUST; send a final response after the request has been completed. See
1058   &use100; for detailed discussion of the use and handling of this
1059   status code.
1060</t>
1061</section>
1062
1063<section title="101 Switching Protocols" anchor="status.101">
1064  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1065  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1066<t>
1067   The server understands and is willing to comply with the client's
1068   request, via the Upgrade message header field (&header-upgrade;), for a
1069   change in the application protocol being used on this connection. The
1070   server will switch protocols to those defined by the response's
1071   Upgrade header field immediately after the empty line which
1072   terminates the 101 response.
1073</t>
1074<t>
1075   The protocol &SHOULD; be switched only when it is advantageous to do
1076   so. For example, switching to a newer version of HTTP is advantageous
1077   over older versions, and switching to a real-time, synchronous
1078   protocol might be advantageous when delivering resources that use
1079   such features.
1080</t>
1081</section>
1082</section>
1083
1084<section title="Successful 2xx" anchor="status.2xx">
1085<t>
1086   This class of status code indicates that the client's request was
1087   successfully received, understood, and accepted.
1088</t>
1089
1090<section title="200 OK" anchor="status.200">
1091  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1092  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1093<t>
1094   The request has succeeded. The information returned with the response
1095   is dependent on the method used in the request, for example:
1096  <list style="hanging">
1097    <t hangText="GET">
1098          an entity corresponding to the requested resource is sent in
1099          the response;
1100    </t>
1101    <t hangText="HEAD">
1102          the entity-header fields corresponding to the requested
1103          resource are sent in the response without any message-body;
1104    </t>
1105    <t hangText="POST">
1106      an entity describing or containing the result of the action;
1107    </t>
1108    <t hangText="TRACE">
1109      an entity containing the request message as received by the
1110      end server.
1111    </t>
1112  </list>
1113</t>
1114</section>
1115
1116<section title="201 Created" anchor="status.201">
1117  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1118  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1119<t>
1120   The request has been fulfilled and resulted in a new resource being
1121   created. The newly created resource can be referenced by the URI(s)
1122   returned in the entity of the response, with the most specific URI
1123   for the resource given by a Location header field. The response
1124   &SHOULD; include an entity containing a list of resource
1125   characteristics and location(s) from which the user or user agent can
1126   choose the one most appropriate. The entity format is specified by
1127   the media type given in the Content-Type header field. The origin
1128   server &MUST; create the resource before returning the 201 status code.
1129   If the action cannot be carried out immediately, the server &SHOULD;
1130   respond with 202 (Accepted) response instead.
1131</t>
1132<t>
1133   A 201 response &MAY; contain an ETag response header field indicating
1134   the current value of the entity tag for the requested variant just
1135   created, see &header-etag;.
1136</t>
1137</section>
1138
1139<section title="202 Accepted" anchor="status.202">
1140  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1141  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1142<t>
1143   The request has been accepted for processing, but the processing has
1144   not been completed.  The request might or might not eventually be
1145   acted upon, as it might be disallowed when processing actually takes
1146   place. There is no facility for re-sending a status code from an
1147   asynchronous operation such as this.
1148</t>
1149<t>
1150   The 202 response is intentionally non-committal. Its purpose is to
1151   allow a server to accept a request for some other process (perhaps a
1152   batch-oriented process that is only run once per day) without
1153   requiring that the user agent's connection to the server persist
1154   until the process is completed. The entity returned with this
1155   response &SHOULD; include an indication of the request's current status
1156   and either a pointer to a status monitor or some estimate of when the
1157   user can expect the request to be fulfilled.
1158</t>
1159</section>
1160
1161<section title="203 Non-Authoritative Information" anchor="status.203">
1162  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1163  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1164<t>
1165   The returned metainformation in the entity-header is not the
1166   definitive set as available from the origin server, but is gathered
1167   from a local or a third-party copy. The set presented &MAY; be a subset
1168   or superset of the original version. For example, including local
1169   annotation information about the resource might result in a superset
1170   of the metainformation known by the origin server. Use of this
1171   response code is not required and is only appropriate when the
1172   response would otherwise be 200 (OK).
1173</t>
1174</section>
1175
1176<section title="204 No Content" anchor="status.204">
1177  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1178  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1179<t>
1180   The server has fulfilled the request but does not need to return an
1181   entity-body, and might want to return updated metainformation. The
1182   response &MAY; include new or updated metainformation in the form of
1183   entity-headers, which if present &SHOULD; be associated with the
1184   requested variant.
1185</t>
1186<t>
1187   If the client is a user agent, it &SHOULD-NOT;  change its document view
1188   from that which caused the request to be sent. This response is
1189   primarily intended to allow input for actions to take place without
1190   causing a change to the user agent's active document view, although
1191   any new or updated metainformation &SHOULD; be applied to the document
1192   currently in the user agent's active view.
1193</t>
1194<t>
1195   The 204 response &MUST-NOT; include a message-body, and thus is always
1196   terminated by the first empty line after the header fields.
1197</t>
1198</section>
1199
1200<section title="205 Reset Content" anchor="status.205">
1201  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1202  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1203<t>
1204   The server has fulfilled the request and the user agent &SHOULD; reset
1205   the document view which caused the request to be sent. This response
1206   is primarily intended to allow input for actions to take place via
1207   user input, followed by a clearing of the form in which the input is
1208   given so that the user can easily initiate another input action. The
1209   response &MUST-NOT; include an entity.
1210</t>
1211</section>
1212
1213<section title="206 Partial Content" anchor="status.206">
1214  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1215  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1216<t>
1217   The server has fulfilled the partial GET request for the resource
1218   and the enclosed entity is a partial representation as defined in &range;.
1219</t>
1220</section>
1221</section>
1222
1223<section title="Redirection 3xx" anchor="status.3xx">
1224<t>
1225   This class of status code indicates that further action needs to be
1226   taken by the user agent in order to fulfill the request.  The action
1227   required &MAY; be carried out by the user agent without interaction
1228   with the user if and only if the method used in the second request is
1229   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1230   such loops generate network traffic for each redirection.
1231</t>
1232<x:note>
1233  <t>
1234    <x:h>Note:</x:h> an earlier version of this specification recommended a
1235    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1236    Content developers should be aware that there might be clients that
1237    implement such a fixed limitation.
1238  </t>
1239</x:note>
1240
1241<section title="300 Multiple Choices" anchor="status.300">
1242  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1243  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1244<t>
1245   The requested resource corresponds to any one of a set of
1246   representations, each with its own specific location, and agent-driven
1247   negotiation information (&content-negotiation;) is being provided so that
1248   the user (or user agent) can select a preferred representation and
1249   redirect its request to that location.
1250</t>
1251<t>
1252   Unless it was a HEAD request, the response &SHOULD; include an entity
1253   containing a list of resource characteristics and location(s) from
1254   which the user or user agent can choose the one most appropriate. The
1255   entity format is specified by the media type given in the Content-Type
1256   header field. Depending upon the format and the capabilities of
1257   the user agent, selection of the most appropriate choice &MAY; be
1258   performed automatically. However, this specification does not define
1259   any standard for such automatic selection.
1260</t>
1261<t>
1262   If the server has a preferred choice of representation, it &SHOULD;
1263   include the specific URI for that representation in the Location
1264   field; user agents &MAY; use the Location field value for automatic
1265   redirection. This response is cacheable unless indicated otherwise.
1266</t>
1267</section>
1268
1269<section title="301 Moved Permanently" anchor="status.301">
1270  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1271  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1272<t>
1273   The requested resource has been assigned a new permanent URI and any
1274   future references to this resource &SHOULD; use one of the returned
1275   URIs.  Clients with link editing capabilities ought to automatically
1276   re-link references to the request-target to one or more of the new
1277   references returned by the server, where possible. This response is
1278   cacheable unless indicated otherwise.
1279</t>
1280<t>
1281   The new permanent URI &SHOULD; be given by the Location field in the
1282   response. Unless the request method was HEAD, the entity of the
1283   response &SHOULD; contain a short hypertext note with a hyperlink to
1284   the new URI(s).
1285</t>
1286<t>
1287   If the 301 status code is received in response to a request method
1288   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1289   then the request &MAY; be automatically redirected by the user agent without
1290   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1291   request unless it can be confirmed by the user, since this might
1292   change the conditions under which the request was issued.
1293</t>
1294<x:note>
1295  <t>
1296    <x:h>Note:</x:h> When automatically redirecting a POST request after
1297    receiving a 301 status code, some existing HTTP/1.0 user agents
1298    will erroneously change it into a GET request.
1299  </t>
1300</x:note>
1301</section>
1302
1303<section title="302 Found" anchor="status.302">
1304  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1305  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1306<t>
1307   The requested resource resides temporarily under a different URI.
1308   Since the redirection might be altered on occasion, the client &SHOULD;
1309   continue to use the request-target for future requests.  This response
1310   is only cacheable if indicated by a Cache-Control or Expires header
1311   field.
1312</t>
1313<t>
1314   The temporary URI &SHOULD; be given by the Location field in the
1315   response. Unless the request method was HEAD, the entity of the
1316   response &SHOULD; contain a short hypertext note with a hyperlink to
1317   the new URI(s).
1318</t>
1319<t>
1320   If the 302 status code is received in response to a request method
1321   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1322   then the request &MAY; be automatically redirected by the user agent without
1323   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1324   request unless it can be confirmed by the user, since this might
1325   change the conditions under which the request was issued.
1326</t>
1327<x:note>
1328  <t>
1329    <x:h>Note:</x:h> HTTP/1.0 (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>)
1330    and the first version of HTTP/1.1 (<xref target="RFC2068" x:fmt="," x:sec ="10.3.3"/>)
1331    specify that the client is not allowed to change the method on the
1332    redirected request.  However, most existing user agent implementations
1333    treat 302 as if it were a 303 response, performing a GET on the Location
1334    field-value regardless of the original request method. Therefore, a
1335    previous version of this specification
1336    (<xref target="RFC2616" x:fmt="," x:sec="10.3.3"/>) has added the
1337    status codes
1338    <xref target="status.303" format="none">303</xref> and
1339    <xref target="status.307" format="none">307</xref> for servers that wish
1340    to make unambiguously clear which kind of reaction is expected of the
1341    client.
1342  </t>
1343</x:note>
1344</section>
1345
1346<section title="303 See Other" anchor="status.303">
1347  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1348  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1349<t>
1350   The server directs the user agent to a different resource, indicated
1351   by a URI in the Location header field, that provides an indirect
1352   response to the original request.  The user agent &MAY; perform a GET
1353   request on the URI in the Location field in order to obtain a
1354   representation corresponding to the response, be redirected again,
1355   or end with an error status.  The Location URI is not a substitute
1356   reference for the originally requested resource.
1357</t>
1358<t>
1359   The 303 status is generally applicable to any HTTP method.  It is
1360   primarily used to allow the output of a POST action to redirect
1361   the user agent to a selected resource, since doing so provides the
1362   information corresponding to the POST response in a form that
1363   can be separately identified, bookmarked, and cached independent
1364   of the original request.
1365</t>
1366<t>
1367   A 303 response to a GET request indicates that the requested
1368   resource does not have a representation of its own that can be
1369   transferred by the server over HTTP.  The Location URI indicates a
1370   resource that is descriptive of the requested resource such that
1371   the follow-on representation may be useful without implying that
1372   it adequately represents the previously requested resource.
1373   Note that answers to the questions of what can be represented, what
1374   representations are adequate, and what might be a useful description
1375   are outside the scope of HTTP and thus entirely determined by the
1376   URI owner(s).
1377</t>
1378<t>
1379   A 303 response &SHOULD-NOT; be cached unless it is indicated as
1380   cacheable by Cache-Control or Expires header fields.  Except for
1381   responses to a HEAD request, the entity of a 303 response &SHOULD;
1382   contain a short hypertext note with a hyperlink to the Location URI.
1383</t>
1384</section>
1385
1386<section title="304 Not Modified" anchor="status.304">
1387  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1388  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1389<t>
1390   The response to the request has not been modified since the conditions
1391   indicated by the client's conditional GET request, as defined in &conditional;.
1392</t>
1393</section>
1394
1395<section title="305 Use Proxy" anchor="status.305">
1396  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1397  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1398<t>
1399   The 305 status was defined in a previous version of this specification
1400   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1401</t>
1402</section>
1403
1404<section title="306 (Unused)" anchor="status.306">
1405  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1406  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1407<t>
1408   The 306 status code was used in a previous version of the
1409   specification, is no longer used, and the code is reserved.
1410</t>
1411</section>
1412
1413<section title="307 Temporary Redirect" anchor="status.307">
1414  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1415  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1416<t>
1417   The requested resource resides temporarily under a different URI.
1418   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1419   continue to use the request-target for future requests.  This response
1420   is only cacheable if indicated by a Cache-Control or Expires header
1421   field.
1422</t>
1423<t>
1424   The temporary URI &SHOULD; be given by the Location field in the
1425   response. Unless the request method was HEAD, the entity of the
1426   response &SHOULD; contain a short hypertext note with a hyperlink to
1427   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1428   understand the 307 status. Therefore, the note &SHOULD; contain the
1429   information necessary for a user to repeat the original request on
1430   the new URI.
1431</t>
1432<t>
1433   If the 307 status code is received in response to a request method
1434   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1435   then the request &MAY; be automatically redirected by the user agent without
1436   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1437   request unless it can be confirmed by the user, since this might
1438   change the conditions under which the request was issued.
1439</t>
1440</section>
1441</section>
1442
1443<section title="Client Error 4xx" anchor="status.4xx">
1444<t>
1445   The 4xx class of status code is intended for cases in which the
1446   client seems to have erred. Except when responding to a HEAD request,
1447   the server &SHOULD; include an entity containing an explanation of the
1448   error situation, and whether it is a temporary or permanent
1449   condition. These status codes are applicable to any request method.
1450   User agents &SHOULD; display any included entity to the user.
1451</t>
1452<t>
1453   If the client is sending data, a server implementation using TCP
1454   &SHOULD; be careful to ensure that the client acknowledges receipt of
1455   the packet(s) containing the response, before the server closes the
1456   input connection. If the client continues sending data to the server
1457   after the close, the server's TCP stack will send a reset packet to
1458   the client, which may erase the client's unacknowledged input buffers
1459   before they can be read and interpreted by the HTTP application.
1460</t>
1461
1462<section title="400 Bad Request" anchor="status.400">
1463  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1464  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1465<t>
1466   The request could not be understood by the server due to malformed
1467   syntax. The client &SHOULD-NOT;  repeat the request without
1468   modifications.
1469</t>
1470</section>
1471
1472<section title="401 Unauthorized" anchor="status.401">
1473  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1474  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1475<t>
1476   The request requires user authentication (see &auth;).
1477</t>
1478</section>
1479
1480<section title="402 Payment Required" anchor="status.402">
1481  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1482  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1483<t>
1484   This code is reserved for future use.
1485</t>
1486</section>
1487
1488<section title="403 Forbidden" anchor="status.403">
1489  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1490  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1491<t>
1492   The server understood the request, but is refusing to fulfill it.
1493   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1494   If the request method was not HEAD and the server wishes to make
1495   public why the request has not been fulfilled, it &SHOULD; describe the
1496   reason for the refusal in the entity.  If the server does not wish to
1497   make this information available to the client, the status code 404
1498   (Not Found) can be used instead.
1499</t>
1500</section>
1501
1502<section title="404 Not Found" anchor="status.404">
1503  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1504  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1505<t>
1506   The server has not found anything matching the request-target. No
1507   indication is given of whether the condition is temporary or
1508   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1509   knows, through some internally configurable mechanism, that an old
1510   resource is permanently unavailable and has no forwarding address.
1511   This status code is commonly used when the server does not wish to
1512   reveal exactly why the request has been refused, or when no other
1513   response is applicable.
1514</t>
1515</section>
1516
1517<section title="405 Method Not Allowed" anchor="status.405">
1518  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1520<t>
1521   The method specified in the Request-Line is not allowed for the
1522   resource identified by the request-target. The response &MUST; include an
1523   Allow header containing a list of valid methods for the requested
1524   resource.
1525</t>
1526</section>
1527
1528<section title="406 Not Acceptable" anchor="status.406">
1529  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1530  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1531<t>
1532   The resource identified by the request is only capable of generating
1533   response entities which have content characteristics not acceptable
1534   according to the accept headers sent in the request.
1535</t>
1536<t>
1537   Unless it was a HEAD request, the response &SHOULD; include an entity
1538   containing a list of available entity characteristics and location(s)
1539   from which the user or user agent can choose the one most
1540   appropriate. The entity format is specified by the media type given
1541   in the Content-Type header field. Depending upon the format and the
1542   capabilities of the user agent, selection of the most appropriate
1543   choice &MAY; be performed automatically. However, this specification
1544   does not define any standard for such automatic selection.
1545</t>
1546<x:note>
1547  <t>
1548    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1549    not acceptable according to the accept headers sent in the
1550    request. In some cases, this may even be preferable to sending a
1551    406 response. User agents are encouraged to inspect the headers of
1552    an incoming response to determine if it is acceptable.
1553  </t>
1554</x:note>
1555<t>
1556   If the response could be unacceptable, a user agent &SHOULD;
1557   temporarily stop receipt of more data and query the user for a
1558   decision on further actions.
1559</t>
1560</section>
1561
1562<section title="407 Proxy Authentication Required" anchor="status.407">
1563  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1564  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1565<t>
1566   This code is similar to 401 (Unauthorized), but indicates that the
1567   client must first authenticate itself with the proxy (see &auth;).
1568</t>
1569</section>
1570
1571<section title="408 Request Timeout" anchor="status.408">
1572  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1573  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1574<t>
1575   The client did not produce a request within the time that the server
1576   was prepared to wait. The client &MAY; repeat the request without
1577   modifications at any later time.
1578</t>
1579</section>
1580
1581<section title="409 Conflict" anchor="status.409">
1582  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1583  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1584<t>
1585   The request could not be completed due to a conflict with the current
1586   state of the resource. This code is only allowed in situations where
1587   it is expected that the user might be able to resolve the conflict
1588   and resubmit the request. The response body &SHOULD; include enough
1589   information for the user to recognize the source of the conflict.
1590   Ideally, the response entity would include enough information for the
1591   user or user agent to fix the problem; however, that might not be
1592   possible and is not required.
1593</t>
1594<t>
1595   Conflicts are most likely to occur in response to a PUT request. For
1596   example, if versioning were being used and the entity being PUT
1597   included changes to a resource which conflict with those made by an
1598   earlier (third-party) request, the server might use the 409 response
1599   to indicate that it can't complete the request. In this case, the
1600   response entity would likely contain a list of the differences
1601   between the two versions in a format defined by the response
1602   Content-Type.
1603</t>
1604</section>
1605
1606<section title="410 Gone" anchor="status.410">
1607  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1608  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1609<t>
1610   The requested resource is no longer available at the server and no
1611   forwarding address is known. This condition is expected to be
1612   considered permanent. Clients with link editing capabilities &SHOULD;
1613   delete references to the request-target after user approval. If the
1614   server does not know, or has no facility to determine, whether or not
1615   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1616   used instead. This response is cacheable unless indicated otherwise.
1617</t>
1618<t>
1619   The 410 response is primarily intended to assist the task of web
1620   maintenance by notifying the recipient that the resource is
1621   intentionally unavailable and that the server owners desire that
1622   remote links to that resource be removed. Such an event is common for
1623   limited-time, promotional services and for resources belonging to
1624   individuals no longer working at the server's site. It is not
1625   necessary to mark all permanently unavailable resources as "gone" or
1626   to keep the mark for any length of time -- that is left to the
1627   discretion of the server owner.
1628</t>
1629</section>
1630
1631<section title="411 Length Required" anchor="status.411">
1632  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1633  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1634<t>
1635   The server refuses to accept the request without a defined Content-Length.
1636   The client &MAY; repeat the request if it adds a valid
1637   Content-Length header field containing the length of the message-body
1638   in the request message.
1639</t>
1640</section>
1641
1642<section title="412 Precondition Failed" anchor="status.412">
1643  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1644  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1645<t>
1646   The precondition given in one or more of the request-header fields
1647   evaluated to false when it was tested on the server, as defined in
1648   &conditional;.
1649</t>
1650</section>
1651
1652<section title="413 Request Entity Too Large" anchor="status.413">
1653  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1654  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1655<t>
1656   The server is refusing to process a request because the request
1657   entity is larger than the server is willing or able to process. The
1658   server &MAY; close the connection to prevent the client from continuing
1659   the request.
1660</t>
1661<t>
1662   If the condition is temporary, the server &SHOULD; include a Retry-After
1663   header field to indicate that it is temporary and after what
1664   time the client &MAY; try again.
1665</t>
1666</section>
1667
1668<section title="414 URI Too Long" anchor="status.414">
1669  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1670  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1671<t>
1672   The server is refusing to service the request because the request-target
1673   is longer than the server is willing to interpret. This rare
1674   condition is only likely to occur when a client has improperly
1675   converted a POST request to a GET request with long query
1676   information, when the client has descended into a URI "black hole" of
1677   redirection (e.g., a redirected URI prefix that points to a suffix of
1678   itself), or when the server is under attack by a client attempting to
1679   exploit security holes present in some servers using fixed-length
1680   buffers for reading or manipulating the request-target.
1681</t>
1682</section>
1683
1684<section title="415 Unsupported Media Type" anchor="status.415">
1685  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1686  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1687<t>
1688   The server is refusing to service the request because the entity of
1689   the request is in a format not supported by the requested resource
1690   for the requested method.
1691</t>
1692</section>
1693
1694<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1695  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1696  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1697<t>
1698   The request included a Range request-header field (&header-range;) and none of
1699   the range-specifier values in this field overlap the current extent
1700   of the selected resource.
1701</t>
1702</section>
1703
1704<section title="417 Expectation Failed" anchor="status.417">
1705  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1706  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1707<t>
1708   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1709   could not be met by this server, or, if the server is a proxy,
1710   the server has unambiguous evidence that the request could not be met
1711   by the next-hop server.
1712</t>
1713</section>
1714</section>
1715
1716<section title="Server Error 5xx" anchor="status.5xx">
1717<t>
1718   Response status codes beginning with the digit "5" indicate cases in
1719   which the server is aware that it has erred or is incapable of
1720   performing the request. Except when responding to a HEAD request, the
1721   server &SHOULD; include an entity containing an explanation of the
1722   error situation, and whether it is a temporary or permanent
1723   condition. User agents &SHOULD; display any included entity to the
1724   user. These response codes are applicable to any request method.
1725</t>
1726
1727<section title="500 Internal Server Error" anchor="status.500">
1728  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1729  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1730<t>
1731   The server encountered an unexpected condition which prevented it
1732   from fulfilling the request.
1733</t>
1734</section>
1735
1736<section title="501 Not Implemented" anchor="status.501">
1737  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1738  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1739<t>
1740   The server does not support the functionality required to fulfill the
1741   request. This is the appropriate response when the server does not
1742   recognize the request method and is not capable of supporting it for
1743   any resource.
1744</t>
1745</section>
1746
1747<section title="502 Bad Gateway" anchor="status.502">
1748  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1749  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1750<t>
1751   The server, while acting as a gateway or proxy, received an invalid
1752   response from the upstream server it accessed in attempting to
1753   fulfill the request.
1754</t>
1755</section>
1756
1757<section title="503 Service Unavailable" anchor="status.503">
1758  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1759  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1760<t>
1761   The server is currently unable to handle the request due to a
1762   temporary overloading or maintenance of the server. The implication
1763   is that this is a temporary condition which will be alleviated after
1764   some delay. If known, the length of the delay &MAY; be indicated in a
1765   Retry-After header. If no Retry-After is given, the client &SHOULD;
1766   handle the response as it would for a 500 response.
1767</t>
1768<x:note>
1769  <t>
1770    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1771    server must use it when becoming overloaded. Some servers may wish
1772    to simply refuse the connection.
1773  </t>
1774</x:note>
1775</section>
1776
1777<section title="504 Gateway Timeout" anchor="status.504">
1778  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1779  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1780<t>
1781   The server, while acting as a gateway or proxy, did not receive a
1782   timely response from the upstream server specified by the URI (e.g.
1783   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1784   to access in attempting to complete the request.
1785</t>
1786<x:note>
1787  <t>
1788    <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1789    return 400 or 500 when DNS lookups time out.
1790  </t>
1791</x:note>
1792</section>
1793
1794<section title="505 HTTP Version Not Supported" anchor="status.505">
1795  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1796  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1797<t>
1798   The server does not support, or refuses to support, the protocol
1799   version that was used in the request message. The server is
1800   indicating that it is unable or unwilling to complete the request
1801   using the same major version as the client, as described in &http-version;,
1802   other than with this error message. The response &SHOULD; contain
1803   an entity describing why that version is not supported and what other
1804   protocols are supported by that server.
1805</t>
1806
1807</section>
1808</section>
1809</section>
1810
1811
1812<section title="Header Field Definitions" anchor="header.fields">
1813<t>
1814   This section defines the syntax and semantics of HTTP/1.1 header fields
1815   related to request and response semantics.
1816</t>
1817<t>
1818   For entity-header fields, both sender and recipient refer to either the
1819   client or the server, depending on who sends and who receives the entity.
1820</t>
1821
1822<section title="Allow" anchor="header.allow">
1823  <iref primary="true" item="Allow header" x:for-anchor=""/>
1824  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1825  <x:anchor-alias value="Allow"/>
1826  <x:anchor-alias value="Allow-v"/>
1827<t>
1828      The response-header field "Allow" lists the set of methods advertised as
1829      supported by the resource identified by the request-target. The purpose of
1830      this field is strictly to inform the recipient of valid methods
1831      associated with the resource. An Allow header field &MUST; be
1832      present in a 405 (Method Not Allowed) response.
1833</t>
1834<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/>
1835  <x:ref>Allow</x:ref>   = "Allow" ":" <x:ref>OWS</x:ref> <x:ref>Allow-v</x:ref>
1836  <x:ref>Allow-v</x:ref> = #<x:ref>Method</x:ref>
1837</artwork></figure>
1838<t>
1839      Example of use:
1840</t>
1841<figure><artwork type="example">
1842  Allow: GET, HEAD, PUT
1843</artwork></figure>
1844<t>
1845      The actual set of allowed methods is defined
1846      by the origin server at the time of each request.
1847</t>
1848<t>
1849      A proxy &MUST-NOT; modify the Allow header field even if it does not
1850      understand all the methods specified, since the user agent might
1851      have other means of communicating with the origin server.
1852</t>
1853</section>
1854
1855<section title="Expect" anchor="header.expect">
1856  <iref primary="true" item="Expect header" x:for-anchor=""/>
1857  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1858  <x:anchor-alias value="Expect"/>
1859  <x:anchor-alias value="Expect-v"/>
1860  <x:anchor-alias value="expectation"/>
1861  <x:anchor-alias value="expectation-extension"/>
1862  <x:anchor-alias value="expect-params"/>
1863<t>
1864   The request-header field "Expect" is used to indicate that particular
1865   server behaviors are required by the client.
1866</t>
1867<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="Expect-v"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
1868  <x:ref>Expect</x:ref>       = "Expect" ":" <x:ref>OWS</x:ref> <x:ref>Expect-v</x:ref>
1869  <x:ref>Expect-v</x:ref>     = 1#<x:ref>expectation</x:ref>
1870 
1871  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
1872  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
1873                           *<x:ref>expect-params</x:ref> ]
1874  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
1875</artwork></figure>
1876<t>
1877   A server that does not understand or is unable to comply with any of
1878   the expectation values in the Expect field of a request &MUST; respond
1879   with appropriate error status. The server &MUST; respond with a 417
1880   (Expectation Failed) status if any of the expectations cannot be met
1881   or, if there are other problems with the request, some other 4xx
1882   status.
1883</t>
1884<t>
1885   This header field is defined with extensible syntax to allow for
1886   future extensions. If a server receives a request containing an
1887   Expect field that includes an expectation-extension that it does not
1888   support, it &MUST; respond with a 417 (Expectation Failed) status.
1889</t>
1890<t>
1891   Comparison of expectation values is case-insensitive for unquoted
1892   tokens (including the 100-continue token), and is case-sensitive for
1893   quoted-string expectation-extensions.
1894</t>
1895<t>
1896   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1897   return a 417 (Expectation Failed) status if it receives a request
1898   with an expectation that it cannot meet. However, the Expect
1899   request-header itself is end-to-end; it &MUST; be forwarded if the
1900   request is forwarded.
1901</t>
1902<t>
1903   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1904   Expect header.
1905</t>
1906<t>
1907   See &use100; for the use of the 100 (Continue) status.
1908</t>
1909</section>
1910
1911<section title="From" anchor="header.from">
1912  <iref primary="true" item="From header" x:for-anchor=""/>
1913  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1914  <x:anchor-alias value="From"/>
1915  <x:anchor-alias value="From-v"/>
1916  <x:anchor-alias value="mailbox"/>
1917<t>
1918   The request-header field "From", if given, &SHOULD; contain an Internet
1919   e-mail address for the human user who controls the requesting user
1920   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1921   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
1922</t>
1923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/>
1924  <x:ref>From</x:ref>    = "From" ":" <x:ref>OWS</x:ref> <x:ref>From-v</x:ref>
1925  <x:ref>From-v</x:ref>  = <x:ref>mailbox</x:ref>
1926 
1927  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
1928</artwork></figure>
1929<t>
1930   An example is:
1931</t>
1932<figure><artwork type="example">
1933  From: webmaster@example.org
1934</artwork></figure>
1935<t>
1936   This header field &MAY; be used for logging purposes and as a means for
1937   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1938   be used as an insecure form of access protection. The interpretation
1939   of this field is that the request is being performed on behalf of the
1940   person given, who accepts responsibility for the method performed. In
1941   particular, robot agents &SHOULD; include this header so that the
1942   person responsible for running the robot can be contacted if problems
1943   occur on the receiving end.
1944</t>
1945<t>
1946   The Internet e-mail address in this field &MAY; be separate from the
1947   Internet host which issued the request. For example, when a request
1948   is passed through a proxy the original issuer's address &SHOULD; be
1949   used.
1950</t>
1951<t>
1952   The client &SHOULD-NOT;  send the From header field without the user's
1953   approval, as it might conflict with the user's privacy interests or
1954   their site's security policy. It is strongly recommended that the
1955   user be able to disable, enable, and modify the value of this field
1956   at any time prior to a request.
1957</t>
1958</section>
1959
1960<section title="Location" anchor="header.location">
1961  <iref primary="true" item="Location header" x:for-anchor=""/>
1962  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1963  <x:anchor-alias value="Location"/>
1964  <x:anchor-alias value="Location-v"/>
1965<t>
1966   The response-header field "Location" is used for the identification of a
1967   new resource or to redirect the recipient to a location other than the
1968   request-target for completion of the request.  For 201 (Created)
1969   responses, the Location is that of the new resource which was created
1970   by the request. For 3xx responses, the location &SHOULD; indicate the
1971   server's preferred URI for automatic redirection to the resource. The
1972   field value consists of a single URI.
1973</t>
1974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/>
1975  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>OWS</x:ref> <x:ref>Location-v</x:ref>
1976  <x:ref>Location-v</x:ref>     = <x:ref>URI</x:ref>
1977</artwork></figure>
1978<t>
1979   An example is:
1980</t>
1981<figure><artwork type="example">
1982  Location: http://www.example.org/pub/WWW/People.html
1983</artwork></figure>
1984<t>
1985   There are circumstances in which a fragment identifier in a Location URI would not be appropriate:
1986   <list style="symbols">
1987      <t>With a 201 Created response, because in this usage the Location header specifies the URI for the entire created resource.</t>
1988      <t>With 305 Use Proxy.</t>
1989   </list>
1990</t>
1991<x:note>
1992  <t>
1993    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1994    from Location in that the Content-Location identifies the original
1995    location of the entity enclosed in the response. It is therefore
1996    possible for a response to contain header fields for both Location
1997    and Content-Location.
1998  </t>
1999</x:note>
2000</section>
2001
2002<section title="Max-Forwards" anchor="header.max-forwards">
2003  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
2004  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
2005  <x:anchor-alias value="Max-Forwards"/>
2006  <x:anchor-alias value="Max-Forwards-v"/>
2007<t>
2008   The request-header "Max-Forwards" field provides a mechanism with the
2009   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
2010   number of proxies or gateways that can forward the request to the
2011   next inbound server. This can be useful when the client is attempting
2012   to trace a request chain which appears to be failing or looping in
2013   mid-chain.
2014</t>
2015<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/>
2016  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" <x:ref>OWS</x:ref> <x:ref>Max-Forwards-v</x:ref>
2017  <x:ref>Max-Forwards-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2018</artwork></figure>
2019<t>
2020   The Max-Forwards value is a decimal integer indicating the remaining
2021   number of times this request message may be forwarded.
2022</t>
2023<t>
2024   Each proxy or gateway recipient of a TRACE or OPTIONS request
2025   containing a Max-Forwards header field &MUST; check and update its
2026   value prior to forwarding the request. If the received value is zero
2027   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2028   respond as the final recipient. If the received Max-Forwards value is
2029   greater than zero, then the forwarded message &MUST; contain an updated
2030   Max-Forwards field with a value decremented by one (1).
2031</t>
2032<t>
2033   The Max-Forwards header field &MAY; be ignored for all other methods
2034   defined by this specification and for any extension methods for which
2035   it is not explicitly referred to as part of that method definition.
2036</t>
2037</section>
2038
2039<section title="Referer" anchor="header.referer">
2040  <iref primary="true" item="Referer header" x:for-anchor=""/>
2041  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
2042  <x:anchor-alias value="Referer"/>
2043  <x:anchor-alias value="Referer-v"/>
2044<t>
2045   The request-header field "Referer" [sic] allows the client to specify, for
2046   the server's benefit, the address (URI) of the resource from which the
2047   request-target was obtained (the "referrer", although the header field is
2048   misspelled.).
2049</t>
2050<t>
2051   The Referer header allows servers to generate lists of back-links to
2052   resources for interest, logging, optimized caching, etc. It also allows
2053   obsolete or mistyped links to be traced for maintenance. Some servers use
2054   Referer as a means of controlling where they allow links from (so-called
2055   "deep linking"), but it should be noted that legitimate requests are not
2056   required to contain a Referer header field.
2057</t>
2058<t>
2059   If the request-target was obtained from a source that does not have its own
2060   URI (e.g., input from the user keyboard), the Referer field MUST either be
2061   sent with the value "about:blank", or not be sent at all. Note that this
2062   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2063</t>
2064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/>
2065  <x:ref>Referer</x:ref>        = "Referer" ":" <x:ref>OWS</x:ref> <x:ref>Referer-v</x:ref>
2066  <x:ref>Referer-v</x:ref>      = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2067</artwork></figure>
2068<t>
2069   Example:
2070</t>
2071<figure><artwork type="example">
2072  Referer: http://www.example.org/hypertext/Overview.html
2073</artwork></figure>
2074<t>
2075   If the field value is a relative URI, it &SHOULD; be interpreted
2076   relative to the request-target. The URI &MUST-NOT; include a fragment. See
2077   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2078</t>
2079</section>
2080
2081<section title="Retry-After" anchor="header.retry-after">
2082  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
2083  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
2084  <x:anchor-alias value="Retry-After"/>
2085  <x:anchor-alias value="Retry-After-v"/>
2086<t>
2087   The response-header "Retry-After" field can be used with a 503 (Service
2088   Unavailable) response to indicate how long the service is expected to
2089   be unavailable to the requesting client. This field &MAY; also be used
2090   with any 3xx (Redirection) response to indicate the minimum time the
2091   user-agent is asked wait before issuing the redirected request. The
2092   value of this field can be either an HTTP-date or an integer number
2093   of seconds (in decimal) after the time of the response.
2094</t>
2095<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/>
2096  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" <x:ref>OWS</x:ref> <x:ref>Retry-After-v</x:ref>
2097  <x:ref>Retry-After-v</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2098</artwork></figure>
2099<t anchor="rule.delta-seconds">
2100  <x:anchor-alias value="delta-seconds"/>
2101   Time spans are non-negative decimal integers, representing time in
2102   seconds.
2103</t>
2104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2105  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2106</artwork></figure>
2107<t>
2108   Two examples of its use are
2109</t>
2110<figure><artwork type="example">
2111  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2112  Retry-After: 120
2113</artwork></figure>
2114<t>
2115   In the latter example, the delay is 2 minutes.
2116</t>
2117</section>
2118
2119<section title="Server" anchor="header.server">
2120  <iref primary="true" item="Server header" x:for-anchor=""/>
2121  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2122  <x:anchor-alias value="Server"/>
2123  <x:anchor-alias value="Server-v"/>
2124<t>
2125   The response-header field "Server" contains information about the
2126   software used by the origin server to handle the request. The field
2127   can contain multiple product tokens (&product-tokens;) and comments
2128   identifying the server and any significant subproducts. The product
2129   tokens are listed in order of their significance for identifying the
2130   application.
2131</t>
2132<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/>
2133  <x:ref>Server</x:ref>         = "Server" ":" <x:ref>OWS</x:ref> <x:ref>Server-v</x:ref>
2134  <x:ref>Server-v</x:ref>       = <x:ref>product</x:ref>
2135                   *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2136</artwork></figure>
2137<t>
2138   Example:
2139</t>
2140<figure><artwork type="example">
2141  Server: CERN/3.0 libwww/2.17
2142</artwork></figure>
2143<t>
2144   If the response is being forwarded through a proxy, the proxy
2145   application &MUST-NOT; modify the Server response-header. Instead, it
2146   &MUST; include a Via field (as described in &header-via;).
2147</t>
2148<x:note>
2149  <t>
2150    <x:h>Note:</x:h> Revealing the specific software version of the server might
2151    allow the server machine to become more vulnerable to attacks
2152    against software that is known to contain security holes. Server
2153    implementors are encouraged to make this field a configurable
2154    option.
2155  </t>
2156</x:note>
2157</section>
2158
2159<section title="User-Agent" anchor="header.user-agent">
2160  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2161  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2162  <x:anchor-alias value="User-Agent"/>
2163  <x:anchor-alias value="User-Agent-v"/>
2164<t>
2165   The request-header field "User-Agent" contains information about the
2166   user agent originating the request. This is for statistical purposes,
2167   the tracing of protocol violations, and automated recognition of user
2168   agents for the sake of tailoring responses to avoid particular user
2169   agent limitations. User agents &SHOULD; include this field with
2170   requests. The field can contain multiple product tokens (&product-tokens;)
2171   and comments identifying the agent and any subproducts which form a
2172   significant part of the user agent. By convention, the product tokens
2173   are listed in order of their significance for identifying the
2174   application.
2175</t>
2176<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/>
2177  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" <x:ref>OWS</x:ref> <x:ref>User-Agent-v</x:ref>
2178  <x:ref>User-Agent-v</x:ref>   = <x:ref>product</x:ref>
2179                   *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2180</artwork></figure>
2181<t>
2182   Example:
2183</t>
2184<figure><artwork type="example">
2185  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2186</artwork></figure>
2187</section>
2188
2189</section>
2190
2191<section title="IANA Considerations" anchor="IANA.considerations">
2192
2193<section title="Method Registry" anchor="method.registration">
2194<t>
2195  The registration procedure for HTTP Methods is defined by
2196  <xref target="method.registry"/> of this document.
2197</t>
2198<t>
2199   The HTTP Method Registry located at <eref target="http://www.iana.org/assignments/http-methods"/>
2200   should be populated with the registrations below:
2201</t>
2202<?BEGININC p2-semantics.iana-methods ?>
2203<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2204<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2205   <ttcol>Method</ttcol>
2206   <ttcol>Safe</ttcol>
2207   <ttcol>Reference</ttcol>
2208   <c>CONNECT</c>
2209   <c>no</c>
2210   <c>
2211      <xref target="CONNECT"/>
2212   </c>
2213   <c>DELETE</c>
2214   <c>no</c>
2215   <c>
2216      <xref target="DELETE"/>
2217   </c>
2218   <c>GET</c>
2219   <c>yes</c>
2220   <c>
2221      <xref target="GET"/>
2222   </c>
2223   <c>HEAD</c>
2224   <c>yes</c>
2225   <c>
2226      <xref target="HEAD"/>
2227   </c>
2228   <c>OPTIONS</c>
2229   <c>yes</c>
2230   <c>
2231      <xref target="OPTIONS"/>
2232   </c>
2233   <c>POST</c>
2234   <c>no</c>
2235   <c>
2236      <xref target="POST"/>
2237   </c>
2238   <c>PUT</c>
2239   <c>no</c>
2240   <c>
2241      <xref target="PUT"/>
2242   </c>
2243   <c>TRACE</c>
2244   <c>yes</c>
2245   <c>
2246      <xref target="TRACE"/>
2247   </c>
2248</texttable>
2249<!--(END)-->
2250<?ENDINC p2-semantics.iana-methods ?>
2251</section>
2252
2253<section title="Status Code Registry" anchor="status.code.registration">
2254<t>
2255   The registration procedure for HTTP Status Codes -- previously defined
2256   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> -- is now defined
2257   by <xref target="status.code.registry"/> of this document.
2258</t>
2259<t>
2260   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2261   should be updated with the registrations below:
2262</t>
2263<?BEGININC p2-semantics.iana-status-codes ?>
2264<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2265<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2266   <ttcol>Value</ttcol>
2267   <ttcol>Description</ttcol>
2268   <ttcol>Reference</ttcol>
2269   <c>100</c>
2270   <c>Continue</c>
2271   <c>
2272      <xref target="status.100"/>
2273   </c>
2274   <c>101</c>
2275   <c>Switching Protocols</c>
2276   <c>
2277      <xref target="status.101"/>
2278   </c>
2279   <c>200</c>
2280   <c>OK</c>
2281   <c>
2282      <xref target="status.200"/>
2283   </c>
2284   <c>201</c>
2285   <c>Created</c>
2286   <c>
2287      <xref target="status.201"/>
2288   </c>
2289   <c>202</c>
2290   <c>Accepted</c>
2291   <c>
2292      <xref target="status.202"/>
2293   </c>
2294   <c>203</c>
2295   <c>Non-Authoritative Information</c>
2296   <c>
2297      <xref target="status.203"/>
2298   </c>
2299   <c>204</c>
2300   <c>No Content</c>
2301   <c>
2302      <xref target="status.204"/>
2303   </c>
2304   <c>205</c>
2305   <c>Reset Content</c>
2306   <c>
2307      <xref target="status.205"/>
2308   </c>
2309   <c>206</c>
2310   <c>Partial Content</c>
2311   <c>
2312      <xref target="status.206"/>
2313   </c>
2314   <c>300</c>
2315   <c>Multiple Choices</c>
2316   <c>
2317      <xref target="status.300"/>
2318   </c>
2319   <c>301</c>
2320   <c>Moved Permanently</c>
2321   <c>
2322      <xref target="status.301"/>
2323   </c>
2324   <c>302</c>
2325   <c>Found</c>
2326   <c>
2327      <xref target="status.302"/>
2328   </c>
2329   <c>303</c>
2330   <c>See Other</c>
2331   <c>
2332      <xref target="status.303"/>
2333   </c>
2334   <c>304</c>
2335   <c>Not Modified</c>
2336   <c>
2337      <xref target="status.304"/>
2338   </c>
2339   <c>305</c>
2340   <c>Use Proxy</c>
2341   <c>
2342      <xref target="status.305"/>
2343   </c>
2344   <c>306</c>
2345   <c>(Unused)</c>
2346   <c>
2347      <xref target="status.306"/>
2348   </c>
2349   <c>307</c>
2350   <c>Temporary Redirect</c>
2351   <c>
2352      <xref target="status.307"/>
2353   </c>
2354   <c>400</c>
2355   <c>Bad Request</c>
2356   <c>
2357      <xref target="status.400"/>
2358   </c>
2359   <c>401</c>
2360   <c>Unauthorized</c>
2361   <c>
2362      <xref target="status.401"/>
2363   </c>
2364   <c>402</c>
2365   <c>Payment Required</c>
2366   <c>
2367      <xref target="status.402"/>
2368   </c>
2369   <c>403</c>
2370   <c>Forbidden</c>
2371   <c>
2372      <xref target="status.403"/>
2373   </c>
2374   <c>404</c>
2375   <c>Not Found</c>
2376   <c>
2377      <xref target="status.404"/>
2378   </c>
2379   <c>405</c>
2380   <c>Method Not Allowed</c>
2381   <c>
2382      <xref target="status.405"/>
2383   </c>
2384   <c>406</c>
2385   <c>Not Acceptable</c>
2386   <c>
2387      <xref target="status.406"/>
2388   </c>
2389   <c>407</c>
2390   <c>Proxy Authentication Required</c>
2391   <c>
2392      <xref target="status.407"/>
2393   </c>
2394   <c>408</c>
2395   <c>Request Timeout</c>
2396   <c>
2397      <xref target="status.408"/>
2398   </c>
2399   <c>409</c>
2400   <c>Conflict</c>
2401   <c>
2402      <xref target="status.409"/>
2403   </c>
2404   <c>410</c>
2405   <c>Gone</c>
2406   <c>
2407      <xref target="status.410"/>
2408   </c>
2409   <c>411</c>
2410   <c>Length Required</c>
2411   <c>
2412      <xref target="status.411"/>
2413   </c>
2414   <c>412</c>
2415   <c>Precondition Failed</c>
2416   <c>
2417      <xref target="status.412"/>
2418   </c>
2419   <c>413</c>
2420   <c>Request Entity Too Large</c>
2421   <c>
2422      <xref target="status.413"/>
2423   </c>
2424   <c>414</c>
2425   <c>URI Too Long</c>
2426   <c>
2427      <xref target="status.414"/>
2428   </c>
2429   <c>415</c>
2430   <c>Unsupported Media Type</c>
2431   <c>
2432      <xref target="status.415"/>
2433   </c>
2434   <c>416</c>
2435   <c>Requested Range Not Satisfiable</c>
2436   <c>
2437      <xref target="status.416"/>
2438   </c>
2439   <c>417</c>
2440   <c>Expectation Failed</c>
2441   <c>
2442      <xref target="status.417"/>
2443   </c>
2444   <c>500</c>
2445   <c>Internal Server Error</c>
2446   <c>
2447      <xref target="status.500"/>
2448   </c>
2449   <c>501</c>
2450   <c>Not Implemented</c>
2451   <c>
2452      <xref target="status.501"/>
2453   </c>
2454   <c>502</c>
2455   <c>Bad Gateway</c>
2456   <c>
2457      <xref target="status.502"/>
2458   </c>
2459   <c>503</c>
2460   <c>Service Unavailable</c>
2461   <c>
2462      <xref target="status.503"/>
2463   </c>
2464   <c>504</c>
2465   <c>Gateway Timeout</c>
2466   <c>
2467      <xref target="status.504"/>
2468   </c>
2469   <c>505</c>
2470   <c>HTTP Version Not Supported</c>
2471   <c>
2472      <xref target="status.505"/>
2473   </c>
2474</texttable>
2475<!--(END)-->
2476<?ENDINC p2-semantics.iana-status-codes ?>
2477</section>
2478<section title="Message Header Registration" anchor="message.header.registration">
2479<t>
2480   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2481   with the permanent registrations below (see <xref target="RFC3864"/>):
2482</t>
2483<?BEGININC p2-semantics.iana-headers ?>
2484<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2485<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2486   <ttcol>Header Field Name</ttcol>
2487   <ttcol>Protocol</ttcol>
2488   <ttcol>Status</ttcol>
2489   <ttcol>Reference</ttcol>
2490
2491   <c>Allow</c>
2492   <c>http</c>
2493   <c>standard</c>
2494   <c>
2495      <xref target="header.allow"/>
2496   </c>
2497   <c>Expect</c>
2498   <c>http</c>
2499   <c>standard</c>
2500   <c>
2501      <xref target="header.expect"/>
2502   </c>
2503   <c>From</c>
2504   <c>http</c>
2505   <c>standard</c>
2506   <c>
2507      <xref target="header.from"/>
2508   </c>
2509   <c>Location</c>
2510   <c>http</c>
2511   <c>standard</c>
2512   <c>
2513      <xref target="header.location"/>
2514   </c>
2515   <c>Max-Forwards</c>
2516   <c>http</c>
2517   <c>standard</c>
2518   <c>
2519      <xref target="header.max-forwards"/>
2520   </c>
2521   <c>Referer</c>
2522   <c>http</c>
2523   <c>standard</c>
2524   <c>
2525      <xref target="header.referer"/>
2526   </c>
2527   <c>Retry-After</c>
2528   <c>http</c>
2529   <c>standard</c>
2530   <c>
2531      <xref target="header.retry-after"/>
2532   </c>
2533   <c>Server</c>
2534   <c>http</c>
2535   <c>standard</c>
2536   <c>
2537      <xref target="header.server"/>
2538   </c>
2539   <c>User-Agent</c>
2540   <c>http</c>
2541   <c>standard</c>
2542   <c>
2543      <xref target="header.user-agent"/>
2544   </c>
2545</texttable>
2546<!--(END)-->
2547<?ENDINC p2-semantics.iana-headers ?>
2548<t>
2549   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2550</t>
2551</section>
2552</section>
2553
2554<section title="Security Considerations" anchor="security.considerations">
2555<t>
2556   This section is meant to inform application developers, information
2557   providers, and users of the security limitations in HTTP/1.1 as
2558   described by this document. The discussion does not include
2559   definitive solutions to the problems revealed, though it does make
2560   some suggestions for reducing security risks.
2561</t>
2562
2563<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2564<t>
2565   Like any generic data transfer protocol, HTTP cannot regulate the
2566   content of the data that is transferred, nor is there any a priori
2567   method of determining the sensitivity of any particular piece of
2568   information within the context of any given request. Therefore,
2569   applications &SHOULD; supply as much control over this information as
2570   possible to the provider of that information. Four header fields are
2571   worth special mention in this context: Server, Via, Referer and From.
2572</t>
2573<t>
2574   Revealing the specific software version of the server might allow the
2575   server machine to become more vulnerable to attacks against software
2576   that is known to contain security holes. Implementors &SHOULD; make the
2577   Server header field a configurable option.
2578</t>
2579<t>
2580   Proxies which serve as a portal through a network firewall &SHOULD;
2581   take special precautions regarding the transfer of header information
2582   that identifies the hosts behind the firewall. In particular, they
2583   &SHOULD; remove, or replace with sanitized versions, any Via fields
2584   generated behind the firewall.
2585</t>
2586<t>
2587   The Referer header allows reading patterns to be studied and reverse
2588   links drawn. Although it can be very useful, its power can be abused
2589   if user details are not separated from the information contained in
2590   the Referer. Even when the personal information has been removed, the
2591   Referer header might indicate a private document's URI whose
2592   publication would be inappropriate.
2593</t>
2594<t>
2595   The information sent in the From field might conflict with the user's
2596   privacy interests or their site's security policy, and hence it
2597   &SHOULD-NOT;  be transmitted without the user being able to disable,
2598   enable, and modify the contents of the field. The user &MUST; be able
2599   to set the contents of this field within a user preference or
2600   application defaults configuration.
2601</t>
2602<t>
2603   We suggest, though do not require, that a convenient toggle interface
2604   be provided for the user to enable or disable the sending of From and
2605   Referer information.
2606</t>
2607<t>
2608   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2609   fields can sometimes be used to determine that a specific client or
2610   server have a particular security hole which might be exploited.
2611   Unfortunately, this same information is often used for other valuable
2612   purposes for which HTTP currently has no better mechanism.
2613</t>
2614<t>
2615   Some methods, like TRACE (<xref target="TRACE"/>) may expose
2616   information sent in request headers in the response entity.
2617   Clients &SHOULD; be careful with sensitive information, like Cookies,
2618   Authorization credentials and other headers that might be used to
2619   collect data from the client.
2620</t> 
2621</section>
2622
2623<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2624<t>
2625   Because the source of a link might be private information or might
2626   reveal an otherwise private information source, it is strongly
2627   recommended that the user be able to select whether or not the
2628   Referer field is sent. For example, a browser client could have a
2629   toggle switch for browsing openly/anonymously, which would
2630   respectively enable/disable the sending of Referer and From
2631   information.
2632</t>
2633<t>
2634   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2635   HTTP request if the referring page was transferred with a secure
2636   protocol.
2637</t>
2638<t>
2639   Authors of services should not use
2640   GET-based forms for the submission of sensitive data because that
2641   data will be encoded in the Request-target. Many existing
2642   servers, proxies, and user agents log or display the Request-target in
2643   places where it might be visible to third parties. Such services can
2644   use POST-based form submission instead.
2645</t>
2646</section>
2647
2648<section title="Location Headers and Spoofing" anchor="location.spoofing">
2649<t>
2650   If a single server supports multiple organizations that do not trust
2651   one another, then it &MUST; check the values of Location and Content-Location
2652   headers in responses that are generated under control of
2653   said organizations to make sure that they do not attempt to
2654   invalidate resources over which they have no authority.
2655</t>
2656</section>
2657
2658</section>
2659
2660<section title="Acknowledgments" anchor="ack">
2661</section>
2662</middle>
2663<back>
2664
2665<references title="Normative References">
2666
2667<reference anchor="Part1">
2668  <front>
2669    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2670    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2671      <organization abbrev="Day Software">Day Software</organization>
2672      <address><email>fielding@gbiv.com</email></address>
2673    </author>
2674    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2675      <organization>One Laptop per Child</organization>
2676      <address><email>jg@laptop.org</email></address>
2677    </author>
2678    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2679      <organization abbrev="HP">Hewlett-Packard Company</organization>
2680      <address><email>JeffMogul@acm.org</email></address>
2681    </author>
2682    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2683      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2684      <address><email>henrikn@microsoft.com</email></address>
2685    </author>
2686    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2687      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2688      <address><email>LMM@acm.org</email></address>
2689    </author>
2690    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2691      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2692      <address><email>paulle@microsoft.com</email></address>
2693    </author>
2694    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2695      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2696      <address><email>timbl@w3.org</email></address>
2697    </author>
2698    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2699      <organization abbrev="W3C">World Wide Web Consortium</organization>
2700      <address><email>ylafon@w3.org</email></address>
2701    </author>
2702    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2703      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2704      <address><email>julian.reschke@greenbytes.de</email></address>
2705    </author>
2706    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2707  </front>
2708  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2709  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2710</reference>
2711
2712<reference anchor="Part3">
2713  <front>
2714    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2715    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2716      <organization abbrev="Day Software">Day Software</organization>
2717      <address><email>fielding@gbiv.com</email></address>
2718    </author>
2719    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2720      <organization>One Laptop per Child</organization>
2721      <address><email>jg@laptop.org</email></address>
2722    </author>
2723    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2724      <organization abbrev="HP">Hewlett-Packard Company</organization>
2725      <address><email>JeffMogul@acm.org</email></address>
2726    </author>
2727    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2728      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2729      <address><email>henrikn@microsoft.com</email></address>
2730    </author>
2731    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2732      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2733      <address><email>LMM@acm.org</email></address>
2734    </author>
2735    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2736      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2737      <address><email>paulle@microsoft.com</email></address>
2738    </author>
2739    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2740      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2741      <address><email>timbl@w3.org</email></address>
2742    </author>
2743    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2744      <organization abbrev="W3C">World Wide Web Consortium</organization>
2745      <address><email>ylafon@w3.org</email></address>
2746    </author>
2747    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2748      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2749      <address><email>julian.reschke@greenbytes.de</email></address>
2750    </author>
2751    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2752  </front>
2753  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2754  <x:source href="p3-payload.xml" basename="p3-payload"/>
2755</reference>
2756
2757<reference anchor="Part4">
2758  <front>
2759    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2760    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2761      <organization abbrev="Day Software">Day Software</organization>
2762      <address><email>fielding@gbiv.com</email></address>
2763    </author>
2764    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2765      <organization>One Laptop per Child</organization>
2766      <address><email>jg@laptop.org</email></address>
2767    </author>
2768    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2769      <organization abbrev="HP">Hewlett-Packard Company</organization>
2770      <address><email>JeffMogul@acm.org</email></address>
2771    </author>
2772    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2773      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2774      <address><email>henrikn@microsoft.com</email></address>
2775    </author>
2776    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2777      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2778      <address><email>LMM@acm.org</email></address>
2779    </author>
2780    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2781      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2782      <address><email>paulle@microsoft.com</email></address>
2783    </author>
2784    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2785      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2786      <address><email>timbl@w3.org</email></address>
2787    </author>
2788    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2789      <organization abbrev="W3C">World Wide Web Consortium</organization>
2790      <address><email>ylafon@w3.org</email></address>
2791    </author>
2792    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2793      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2794      <address><email>julian.reschke@greenbytes.de</email></address>
2795    </author>
2796    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2797  </front>
2798  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2799  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2800</reference>
2801
2802<reference anchor="Part5">
2803  <front>
2804    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2805    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2806      <organization abbrev="Day Software">Day Software</organization>
2807      <address><email>fielding@gbiv.com</email></address>
2808    </author>
2809    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2810      <organization>One Laptop per Child</organization>
2811      <address><email>jg@laptop.org</email></address>
2812    </author>
2813    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2814      <organization abbrev="HP">Hewlett-Packard Company</organization>
2815      <address><email>JeffMogul@acm.org</email></address>
2816    </author>
2817    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2818      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2819      <address><email>henrikn@microsoft.com</email></address>
2820    </author>
2821    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2822      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2823      <address><email>LMM@acm.org</email></address>
2824    </author>
2825    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2826      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2827      <address><email>paulle@microsoft.com</email></address>
2828    </author>
2829    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2830      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2831      <address><email>timbl@w3.org</email></address>
2832    </author>
2833    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2834      <organization abbrev="W3C">World Wide Web Consortium</organization>
2835      <address><email>ylafon@w3.org</email></address>
2836    </author>
2837    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2838      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2839      <address><email>julian.reschke@greenbytes.de</email></address>
2840    </author>
2841    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2842  </front>
2843  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2844  <x:source href="p5-range.xml" basename="p5-range"/>
2845</reference>
2846
2847<reference anchor="Part6">
2848  <front>
2849    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2850    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2851      <organization abbrev="Day Software">Day Software</organization>
2852      <address><email>fielding@gbiv.com</email></address>
2853    </author>
2854    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2855      <organization>One Laptop per Child</organization>
2856      <address><email>jg@laptop.org</email></address>
2857    </author>
2858    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2859      <organization abbrev="HP">Hewlett-Packard Company</organization>
2860      <address><email>JeffMogul@acm.org</email></address>
2861    </author>
2862    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2863      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2864      <address><email>henrikn@microsoft.com</email></address>
2865    </author>
2866    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2867      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2868      <address><email>LMM@acm.org</email></address>
2869    </author>
2870    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2871      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2872      <address><email>paulle@microsoft.com</email></address>
2873    </author>
2874    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2875      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2876      <address><email>timbl@w3.org</email></address>
2877    </author>
2878    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2879      <organization abbrev="W3C">World Wide Web Consortium</organization>
2880      <address><email>ylafon@w3.org</email></address>
2881    </author>
2882    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2883      <organization />
2884      <address><email>mnot@mnot.net</email></address>
2885    </author>
2886    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2887      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2888      <address><email>julian.reschke@greenbytes.de</email></address>
2889    </author>
2890    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2891  </front>
2892  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2893  <x:source href="p6-cache.xml" basename="p6-cache"/>
2894</reference>
2895
2896<reference anchor="Part7">
2897  <front>
2898    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2899    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2900      <organization abbrev="Day Software">Day Software</organization>
2901      <address><email>fielding@gbiv.com</email></address>
2902    </author>
2903    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2904      <organization>One Laptop per Child</organization>
2905      <address><email>jg@laptop.org</email></address>
2906    </author>
2907    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2908      <organization abbrev="HP">Hewlett-Packard Company</organization>
2909      <address><email>JeffMogul@acm.org</email></address>
2910    </author>
2911    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2912      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2913      <address><email>henrikn@microsoft.com</email></address>
2914    </author>
2915    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2916      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2917      <address><email>LMM@acm.org</email></address>
2918    </author>
2919    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2920      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2921      <address><email>paulle@microsoft.com</email></address>
2922    </author>
2923    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2924      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2925      <address><email>timbl@w3.org</email></address>
2926    </author>
2927    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2928      <organization abbrev="W3C">World Wide Web Consortium</organization>
2929      <address><email>ylafon@w3.org</email></address>
2930    </author>
2931    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2932      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2933      <address><email>julian.reschke@greenbytes.de</email></address>
2934    </author>
2935    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2936  </front>
2937  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2938  <x:source href="p7-auth.xml" basename="p7-auth"/>
2939</reference>
2940
2941<reference anchor="RFC2119">
2942  <front>
2943    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2944    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2945      <organization>Harvard University</organization>
2946      <address><email>sob@harvard.edu</email></address>
2947    </author>
2948    <date month="March" year="1997"/>
2949  </front>
2950  <seriesInfo name="BCP" value="14"/>
2951  <seriesInfo name="RFC" value="2119"/>
2952</reference>
2953
2954<reference anchor="RFC5234">
2955  <front>
2956    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2957    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2958      <organization>Brandenburg InternetWorking</organization>
2959      <address>
2960      <postal>
2961      <street>675 Spruce Dr.</street>
2962      <city>Sunnyvale</city>
2963      <region>CA</region>
2964      <code>94086</code>
2965      <country>US</country></postal>
2966      <phone>+1.408.246.8253</phone>
2967      <email>dcrocker@bbiw.net</email></address> 
2968    </author>
2969    <author initials="P." surname="Overell" fullname="Paul Overell">
2970      <organization>THUS plc.</organization>
2971      <address>
2972      <postal>
2973      <street>1/2 Berkeley Square</street>
2974      <street>99 Berkely Street</street>
2975      <city>Glasgow</city>
2976      <code>G3 7HR</code>
2977      <country>UK</country></postal>
2978      <email>paul.overell@thus.net</email></address>
2979    </author>
2980    <date month="January" year="2008"/>
2981  </front>
2982  <seriesInfo name="STD" value="68"/>
2983  <seriesInfo name="RFC" value="5234"/>
2984</reference>
2985
2986</references>
2987
2988<references title="Informative References">
2989
2990<reference anchor="RFC1945">
2991  <front>
2992    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2993    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2994      <organization>MIT, Laboratory for Computer Science</organization>
2995      <address><email>timbl@w3.org</email></address>
2996    </author>
2997    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2998      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2999      <address><email>fielding@ics.uci.edu</email></address>
3000    </author>
3001    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3002      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3003      <address><email>frystyk@w3.org</email></address>
3004    </author>
3005    <date month="May" year="1996"/>
3006  </front>
3007  <seriesInfo name="RFC" value="1945"/>
3008</reference>
3009
3010<reference anchor="RFC2068">
3011  <front>
3012    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3013    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3014      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3015      <address><email>fielding@ics.uci.edu</email></address>
3016    </author>
3017    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3018      <organization>MIT Laboratory for Computer Science</organization>
3019      <address><email>jg@w3.org</email></address>
3020    </author>
3021    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3022      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3023      <address><email>mogul@wrl.dec.com</email></address>
3024    </author>
3025    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3026      <organization>MIT Laboratory for Computer Science</organization>
3027      <address><email>frystyk@w3.org</email></address>
3028    </author>
3029    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3030      <organization>MIT Laboratory for Computer Science</organization>
3031      <address><email>timbl@w3.org</email></address>
3032    </author>
3033    <date month="January" year="1997"/>
3034  </front>
3035  <seriesInfo name="RFC" value="2068"/>
3036</reference>
3037
3038<reference anchor="RFC2616">
3039  <front>
3040    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3041    <author initials="R." surname="Fielding" fullname="R. Fielding">
3042      <organization>University of California, Irvine</organization>
3043      <address><email>fielding@ics.uci.edu</email></address>
3044    </author>
3045    <author initials="J." surname="Gettys" fullname="J. Gettys">
3046      <organization>W3C</organization>
3047      <address><email>jg@w3.org</email></address>
3048    </author>
3049    <author initials="J." surname="Mogul" fullname="J. Mogul">
3050      <organization>Compaq Computer Corporation</organization>
3051      <address><email>mogul@wrl.dec.com</email></address>
3052    </author>
3053    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3054      <organization>MIT Laboratory for Computer Science</organization>
3055      <address><email>frystyk@w3.org</email></address>
3056    </author>
3057    <author initials="L." surname="Masinter" fullname="L. Masinter">
3058      <organization>Xerox Corporation</organization>
3059      <address><email>masinter@parc.xerox.com</email></address>
3060    </author>
3061    <author initials="P." surname="Leach" fullname="P. Leach">
3062      <organization>Microsoft Corporation</organization>
3063      <address><email>paulle@microsoft.com</email></address>
3064    </author>
3065    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3066      <organization>W3C</organization>
3067      <address><email>timbl@w3.org</email></address>
3068    </author>
3069    <date month="June" year="1999"/>
3070  </front>
3071  <seriesInfo name="RFC" value="2616"/>
3072</reference>
3073
3074<reference anchor='RFC2817'>
3075  <front>
3076    <title>Upgrading to TLS Within HTTP/1.1</title>
3077    <author initials='R.' surname='Khare' fullname='R. Khare'>
3078      <organization>4K Associates / UC Irvine</organization>
3079      <address><email>rohit@4K-associates.com</email></address>
3080    </author>
3081    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3082      <organization>Agranat Systems, Inc.</organization>
3083      <address><email>lawrence@agranat.com</email></address>
3084    </author>
3085    <date year='2000' month='May' />
3086  </front>
3087  <seriesInfo name='RFC' value='2817' />
3088</reference>
3089
3090<reference anchor='RFC3864'>
3091  <front>
3092    <title>Registration Procedures for Message Header Fields</title>
3093    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3094      <organization>Nine by Nine</organization>
3095      <address><email>GK-IETF@ninebynine.org</email></address>
3096    </author>
3097    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3098      <organization>BEA Systems</organization>
3099      <address><email>mnot@pobox.com</email></address>
3100    </author>
3101    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3102      <organization>HP Labs</organization>
3103      <address><email>JeffMogul@acm.org</email></address>
3104    </author>
3105    <date year='2004' month='September' />
3106  </front>
3107  <seriesInfo name='BCP' value='90' />
3108  <seriesInfo name='RFC' value='3864' />
3109</reference>
3110
3111<reference anchor='RFC5226'>
3112  <front>
3113    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3114    <author initials='T.' surname='Narten' fullname='T. Narten'>
3115      <organization>IBM</organization>
3116      <address><email>narten@us.ibm.com</email></address>
3117    </author>
3118    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3119      <organization>Google</organization>
3120      <address><email>Harald@Alvestrand.no</email></address>
3121    </author>
3122    <date year='2008' month='May' />
3123  </front>
3124  <seriesInfo name='BCP' value='26' />
3125  <seriesInfo name='RFC' value='5226' />
3126</reference>
3127
3128<reference anchor="RFC5322">
3129  <front>
3130    <title>Internet Message Format</title>
3131    <author initials="P." surname="Resnick" fullname="P. Resnick">
3132      <organization>Qualcomm Incorporated</organization>
3133    </author>
3134    <date year="2008" month="October"/>
3135  </front> 
3136  <seriesInfo name="RFC" value="5322"/>
3137</reference>
3138
3139</references>
3140
3141<section title="Compatibility with Previous Versions" anchor="compatibility">
3142<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3143<t>
3144   Clarified which error code should be used for inbound server failures
3145   (e.g. DNS failures). (<xref target="status.504"/>).
3146</t>
3147<t>
3148   201 (Created) had a race that required an Etag be sent when a resource is
3149   first created. (<xref target="status.201"/>).
3150</t>
3151<t>
3152   303 (See Also) and 307 (Temporary Redirect) added to address user agent
3153   failure to implement status code 302 properly.
3154   (Section <xref target="status.303" format="counter"/> and <xref target="status.307" format="counter"/>)
3155</t>
3156<t>
3157   Rewrite of message transmission requirements to make it much harder
3158   for implementors to get it wrong, as the consequences of errors here
3159   can have significant impact on the Internet, and to deal with the
3160   following problems:
3161  <list style="numbers">
3162      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
3163         this was incorrectly placing a requirement on the behavior of
3164         an implementation of a future version of HTTP/1.x</t>
3165
3166      <t>Made it clear that user-agents should retry requests, not
3167         "clients" in general.</t>
3168
3169      <t>Converted requirements for clients to ignore unexpected 100
3170         (Continue) responses, and for proxies to forward 100 responses,
3171         into a general requirement for 1xx responses.</t>
3172
3173      <t>Modified some TCP-specific language, to make it clearer that
3174         non-TCP transports are possible for HTTP.</t>
3175
3176      <t>Require that the origin server &MUST-NOT; wait for the request
3177         body before it sends a required 100 (Continue) response.</t>
3178
3179      <t>Allow, rather than require, a server to omit 100 (Continue) if
3180         it has already seen some of the request body.</t>
3181
3182      <t>Allow servers to defend against denial-of-service attacks and
3183         broken clients.</t>
3184  </list>
3185</t>
3186<t>
3187   This change adds the Expect header and 417 status code.
3188</t>
3189<t>
3190   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3191   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3192</t>
3193<t>
3194   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
3195   implemented in previous versions of this specification. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.1"/>.
3196</t>
3197</section>
3198
3199<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3200<t>
3201  This document takes over the Status Code Registry, previously defined
3202  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3203  (<xref target="status.code.registry"/>)
3204</t>
3205<t>
3206  Clarify definition of POST.
3207  (<xref target="POST"/>)
3208</t>
3209<t>
3210  Failed to consider that there are
3211  many other request methods that are safe to automatically redirect,
3212  and further that the user agent is able to make that determination
3213  based on the request method semantics.
3214  (Sections <xref format="counter" target="status.301"/>,
3215  <xref format="counter" target="status.302"/> and
3216  <xref format="counter" target="status.307"/>)
3217</t>
3218<t>
3219  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3220  It used to indicate that the requested resource must be accessed through the
3221  proxy given by the Location field. The Location field gave the URI of the
3222  proxy. The recipient was expected to repeat this single request via the proxy.
3223  (<xref target="status.305"/>)
3224</t>
3225<t>
3226  Reclassify Allow header as response header, removing the option to
3227  specify it in a PUT request.
3228  Relax the server requirement on the contents of the Allow header and
3229  remove requirement on clients to always trust the header value.
3230  (<xref target="header.allow"/>)
3231</t>
3232<t>
3233  Correct syntax of Location header to allow fragment,
3234  as referred symbol wasn't what was expected, and add some
3235  clarifications as to when it would not be appropriate.
3236  (<xref target="header.location"/>)
3237</t>
3238<t>
3239  Allow Referer value of "about:blank" as alternative to not specifying it.
3240  (<xref target="header.referer"/>)
3241</t>
3242<t>
3243  In the description of the Server header, the Via field
3244  was described as a SHOULD. The requirement was and is stated
3245  correctly in the description of the Via header in &header-via;.
3246  (<xref target="header.server"/>)
3247</t>
3248</section>
3249
3250</section>
3251
3252<?BEGININC p2-semantics.abnf-appendix ?>
3253<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3254<figure>
3255<artwork type="abnf" name="p2-semantics.parsed-abnf">
3256<x:ref>Accept</x:ref> = &lt;Accept, defined in [Part3], Section 5.1&gt;
3257<x:ref>Accept-Charset</x:ref> = &lt;Accept-Charset, defined in [Part3], Section 5.2&gt;
3258<x:ref>Accept-Encoding</x:ref> = &lt;Accept-Encoding, defined in [Part3], Section 5.3&gt;
3259<x:ref>Accept-Language</x:ref> = &lt;Accept-Language, defined in [Part3], Section 5.4&gt;
3260<x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in [Part5], Section 5.1&gt;
3261<x:ref>Age</x:ref> = &lt;Age, defined in [Part6], Section 3.1&gt;
3262<x:ref>Allow</x:ref> = "Allow:" OWS Allow-v
3263<x:ref>Allow-v</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3264<x:ref>Authorization</x:ref> = &lt;Authorization, defined in [Part7], Section 3.1&gt;
3265
3266<x:ref>ETag</x:ref> = &lt;ETag, defined in [Part4], Section 6.1&gt;
3267<x:ref>Expect</x:ref> = "Expect:" OWS Expect-v
3268<x:ref>Expect-v</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3269
3270<x:ref>From</x:ref> = "From:" OWS From-v
3271<x:ref>From-v</x:ref> = mailbox
3272
3273<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
3274<x:ref>Host</x:ref> = &lt;Host, defined in [Part1], Section 2.6&gt;
3275
3276<x:ref>If-Match</x:ref> = &lt;If-Match, defined in [Part4], Section 6.2&gt;
3277If-Modified-Since =
3278 &lt;If-Modified-Since, defined in [Part4], Section 6.3&gt;
3279<x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in [Part4], Section 6.4&gt;
3280<x:ref>If-Range</x:ref> = &lt;If-Range, defined in [Part5], Section 5.3&gt;
3281If-Unmodified-Since =
3282 &lt;If-Unmodified-Since, defined in [Part4], Section 6.5&gt;
3283
3284<x:ref>Location</x:ref> = "Location:" OWS Location-v
3285<x:ref>Location-v</x:ref> = URI
3286
3287<x:ref>Max-Forwards</x:ref> = "Max-Forwards:" OWS Max-Forwards-v
3288<x:ref>Max-Forwards-v</x:ref> = 1*DIGIT
3289<x:ref>Method</x:ref> = %x4F.50.54.49.4F.4E.53 ; OPTIONS
3290 / %x47.45.54 ; GET
3291 / %x48.45.41.44 ; HEAD
3292 / %x50.4F.53.54 ; POST
3293 / %x50.55.54 ; PUT
3294 / %x44.45.4C.45.54.45 ; DELETE
3295 / %x54.52.41.43.45 ; TRACE
3296 / %x43.4F.4E.4E.45.43.54 ; CONNECT
3297 / extension-method
3298
3299<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
3300
3301Proxy-Authenticate =
3302 &lt;Proxy-Authenticate, defined in [Part7], Section 3.2&gt;
3303Proxy-Authorization =
3304 &lt;Proxy-Authorization, defined in [Part7], Section 3.3&gt;
3305
3306<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
3307<x:ref>Range</x:ref> = &lt;Range, defined in [Part5], Section 5.4&gt;
3308<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
3309<x:ref>Referer</x:ref> = "Referer:" OWS Referer-v
3310<x:ref>Referer-v</x:ref> = absolute-URI / partial-URI
3311<x:ref>Retry-After</x:ref> = "Retry-After:" OWS Retry-After-v
3312<x:ref>Retry-After-v</x:ref> = HTTP-date / delta-seconds
3313
3314<x:ref>Server</x:ref> = "Server:" OWS Server-v
3315<x:ref>Server-v</x:ref> = product *( RWS ( product / comment ) )
3316<x:ref>Status-Code</x:ref> = "100" / "101" / "200" / "201" / "202" / "203" / "204" /
3317 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" /
3318 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" /
3319 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" /
3320 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" /
3321 "505" / extension-code
3322
3323<x:ref>TE</x:ref> = &lt;TE, defined in [Part1], Section 9.8&gt;
3324
3325<x:ref>URI</x:ref> = &lt;URI, defined in [Part1], Section 2.6&gt;
3326<x:ref>User-Agent</x:ref> = "User-Agent:" OWS User-Agent-v
3327<x:ref>User-Agent-v</x:ref> = product *( RWS ( product / comment ) )
3328
3329<x:ref>Vary</x:ref> = &lt;Vary, defined in [Part6], Section 3.5&gt;
3330
3331WWW-Authenticate =
3332 &lt;WWW-Authenticate, defined in [Part7], Section 3.4&gt;
3333
3334<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
3335
3336<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
3337
3338<x:ref>delta-seconds</x:ref> = 1*DIGIT
3339
3340<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
3341<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
3342<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
3343 *expect-params ]
3344<x:ref>extension-code</x:ref> = 3DIGIT
3345<x:ref>extension-method</x:ref> = token
3346
3347<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3348
3349<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
3350
3351<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
3352<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 6.3&gt;
3353
3354<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
3355
3356<x:ref>request-header</x:ref> = Accept / Accept-Charset / Accept-Encoding /
3357 Accept-Language / Authorization / Expect / From / Host / If-Match /
3358 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since /
3359 Max-Forwards / Proxy-Authorization / Range / Referer / TE /
3360 User-Agent
3361<x:ref>response-header</x:ref> = Accept-Ranges / Age / Allow / ETag / Location /
3362 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate
3363
3364<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
3365</artwork>
3366</figure>
3367<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3368; Reason-Phrase defined but not used
3369; Status-Code defined but not used
3370; request-header defined but not used
3371; response-header defined but not used
3372</artwork></figure></section>
3373<?ENDINC p2-semantics.abnf-appendix ?>
3374
3375<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3376
3377<section title="Since RFC2616">
3378<t>
3379  Extracted relevant partitions from <xref target="RFC2616"/>.
3380</t>
3381</section>
3382
3383<section title="Since draft-ietf-httpbis-p2-semantics-00">
3384<t>
3385  Closed issues:
3386  <list style="symbols"> 
3387    <t>
3388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3389      "Via is a MUST"
3390      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3391    </t>
3392    <t>
3393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3394      "Fragments allowed in Location"
3395      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3396    </t>
3397    <t>
3398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3399      "Safe Methods vs Redirection"
3400      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3401    </t>
3402    <t>
3403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3404      "Revise description of the POST method"
3405      (<eref target="http://purl.org/NET/http-errata#post"/>)
3406    </t>
3407    <t>
3408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3409      "Normative and Informative references"
3410    </t>
3411    <t>
3412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3413      "RFC2606 Compliance"
3414    </t>
3415    <t>
3416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3417      "Informative references"
3418    </t>
3419    <t>
3420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3421      "Redundant cross-references"
3422    </t>
3423  </list>
3424</t>
3425<t>
3426  Other changes:
3427  <list style="symbols"> 
3428    <t>
3429      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3430    </t>
3431  </list>
3432</t>
3433</section>
3434
3435<section title="Since draft-ietf-httpbis-p2-semantics-01">
3436<t>
3437  Closed issues:
3438  <list style="symbols"> 
3439    <t>
3440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3441      "PUT side effects"
3442    </t>
3443    <t>
3444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3445      "Duplicate Host header requirements"
3446    </t>
3447  </list>
3448</t>
3449<t>
3450  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3451  <list style="symbols"> 
3452    <t>
3453      Move "Product Tokens" section (back) into Part 1, as "token" is used
3454      in the definition of the Upgrade header.
3455    </t>
3456    <t>
3457      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3458    </t>
3459    <t>
3460      Copy definition of delta-seconds from Part6 instead of referencing it.
3461    </t>
3462  </list>
3463</t>
3464</section>
3465
3466<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3467<t>
3468  Closed issues:
3469  <list style="symbols"> 
3470    <t>
3471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3472      "Requiring Allow in 405 responses"
3473    </t>
3474    <t>
3475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3476      "Status Code Registry"
3477    </t>
3478    <t>
3479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3480      "Redirection vs. Location"
3481    </t>
3482    <t>
3483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3484      "Cacheability of 303 response"
3485    </t>
3486    <t>
3487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3488      "305 Use Proxy"
3489    </t>
3490    <t>
3491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3492      "Classification for Allow header"
3493    </t>
3494    <t>
3495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3496      "PUT - 'store under' vs 'store at'"
3497    </t>
3498  </list>
3499</t>
3500<t>
3501  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3502  <list style="symbols"> 
3503    <t>
3504      Reference RFC 3984, and update header registrations for headers defined
3505      in this document.
3506    </t>
3507  </list>
3508</t>
3509<t>
3510  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3511  <list style="symbols"> 
3512    <t>
3513      Replace string literals when the string really is case-sensitive (method).
3514    </t>
3515  </list>
3516</t>
3517</section>
3518
3519<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3520<t>
3521  Closed issues:
3522  <list style="symbols"> 
3523    <t>
3524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3525      "OPTIONS request bodies"
3526    </t>
3527    <t>
3528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3529      "Description of CONNECT should refer to RFC2817"
3530    </t>
3531    <t>
3532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3533      "Location Content-Location reference request/response mixup"
3534    </t>
3535  </list>
3536</t>
3537<t>
3538  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3539  <list style="symbols"> 
3540    <t>
3541      Added initial proposal for registration process, plus initial
3542      content (non-HTTP/1.1 methods to be added by a separate specification).
3543    </t>
3544  </list>
3545</t>
3546</section>
3547
3548<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3549<t>
3550  Closed issues:
3551  <list style="symbols"> 
3552    <t>
3553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3554      "Content-*"
3555    </t>
3556    <t>
3557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3558      "RFC 2822 is updated by RFC 5322"
3559    </t>
3560  </list>
3561</t>
3562<t>
3563  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3564  <list style="symbols"> 
3565    <t>
3566      Use "/" instead of "|" for alternatives.
3567    </t>
3568    <t>
3569      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3570      whitespace ("OWS") and required whitespace ("RWS").
3571    </t>
3572    <t>
3573      Rewrite ABNFs to spell out whitespace rules, factor out
3574      header value format definitions.
3575    </t>
3576  </list>
3577</t>
3578</section>
3579
3580<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3581<t>
3582  Closed issues:
3583  <list style="symbols"> 
3584    <t>
3585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3586      "Reason-Phrase BNF"
3587    </t>
3588  </list>
3589</t>
3590<t>
3591  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3592  <list style="symbols"> 
3593    <t>
3594      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3595    </t>
3596  </list>
3597</t>
3598</section>
3599
3600<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3601<t>
3602  Closed issues:
3603  <list style="symbols"> 
3604    <t>
3605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3606      "Clarify when Referer is sent"
3607    </t>
3608    <t>
3609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3610      "status codes vs methods"
3611    </t>
3612    <t>
3613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3614      "Do not require "updates" relation for specs that register status codes or method names"
3615    </t>
3616  </list>
3617</t>
3618</section>
3619
3620<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
3621<t>
3622  Closed issues:
3623  <list style="symbols"> 
3624    <t>
3625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
3626      "Idempotency"
3627    </t>
3628    <t>
3629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
3630      "TRACE security considerations"
3631    </t>
3632    <t>
3633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
3634      "update note citing RFC 1945 and 2068"
3635    </t>
3636    <t>
3637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
3638      "update note about redirect limit"
3639    </t>
3640    <t>
3641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
3642      "Location header ABNF should use 'URI'"
3643    </t>
3644    <t>
3645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
3646      "fragments in Location vs status 303"
3647    </t>
3648  </list>
3649</t>
3650</section>
3651
3652</section>
3653
3654</back>
3655</rfc>
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