source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1161

Last change on this file since 1161 was 1161, checked in by fielding@…, 9 years ago

editorial consistency:
Use "request method" when talking about HTTP method tokens
unless it is obvious from context.
Make method descriptions a bit more consistent.

  • Property svn:eol-style set to native
File size: 174.4 KB
Line 
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 "March">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY combining-responses        "<xref target='Part6' x:rel='#combining.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81]>
82<?rfc toc="yes" ?>
83<?rfc symrefs="yes" ?>
84<?rfc sortrefs="yes" ?>
85<?rfc compact="yes"?>
86<?rfc subcompact="no" ?>
87<?rfc linkmailto="no" ?>
88<?rfc editing="no" ?>
89<?rfc comments="yes"?>
90<?rfc inline="yes"?>
91<?rfc rfcedstyle="yes"?>
92<?rfc-ext allow-markup-in-artwork="yes" ?>
93<?rfc-ext include-references-in-index="yes" ?>
94<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
95     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
96     xmlns:x='http://purl.org/net/xml2rfc/ext'
97     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
98<front>
99
100  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
101
102  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
103    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
104    <address>
105      <postal>
106        <street>345 Park Ave</street>
107        <city>San Jose</city>
108        <region>CA</region>
109        <code>95110</code>
110        <country>USA</country>
111      </postal>
112      <email>fielding@gbiv.com</email>
113      <uri>http://roy.gbiv.com/</uri>
114    </address>
115  </author>
116
117  <author initials="J." surname="Gettys" fullname="Jim Gettys">
118    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
119    <address>
120      <postal>
121        <street>21 Oak Knoll Road</street>
122        <city>Carlisle</city>
123        <region>MA</region>
124        <code>01741</code>
125        <country>USA</country>
126      </postal>
127      <email>jg@freedesktop.org</email>
128      <uri>http://gettys.wordpress.com/</uri>
129    </address>
130  </author>
131 
132  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
133    <organization abbrev="HP">Hewlett-Packard Company</organization>
134    <address>
135      <postal>
136        <street>HP Labs, Large Scale Systems Group</street>
137        <street>1501 Page Mill Road, MS 1177</street>
138        <city>Palo Alto</city>
139        <region>CA</region>
140        <code>94304</code>
141        <country>USA</country>
142      </postal>
143      <email>JeffMogul@acm.org</email>
144    </address>
145  </author>
146
147  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
148    <organization abbrev="Microsoft">Microsoft Corporation</organization>
149    <address>
150      <postal>
151        <street>1 Microsoft Way</street>
152        <city>Redmond</city>
153        <region>WA</region>
154        <code>98052</code>
155        <country>USA</country>
156      </postal>
157      <email>henrikn@microsoft.com</email>
158    </address>
159  </author>
160
161  <author initials="L." surname="Masinter" fullname="Larry Masinter">
162    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
163    <address>
164      <postal>
165        <street>345 Park Ave</street>
166        <city>San Jose</city>
167        <region>CA</region>
168        <code>95110</code>
169        <country>USA</country>
170      </postal>
171      <email>LMM@acm.org</email>
172      <uri>http://larry.masinter.net/</uri>
173    </address>
174  </author>
175 
176  <author initials="P." surname="Leach" fullname="Paul J. Leach">
177    <organization abbrev="Microsoft">Microsoft Corporation</organization>
178    <address>
179      <postal>
180        <street>1 Microsoft Way</street>
181        <city>Redmond</city>
182        <region>WA</region>
183        <code>98052</code>
184      </postal>
185      <email>paulle@microsoft.com</email>
186    </address>
187  </author>
188   
189  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
190    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
191    <address>
192      <postal>
193        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
194        <street>The Stata Center, Building 32</street>
195        <street>32 Vassar Street</street>
196        <city>Cambridge</city>
197        <region>MA</region>
198        <code>02139</code>
199        <country>USA</country>
200      </postal>
201      <email>timbl@w3.org</email>
202      <uri>http://www.w3.org/People/Berners-Lee/</uri>
203    </address>
204  </author>
205
206  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
207    <organization abbrev="W3C">World Wide Web Consortium</organization>
208    <address>
209      <postal>
210        <street>W3C / ERCIM</street>
211        <street>2004, rte des Lucioles</street>
212        <city>Sophia-Antipolis</city>
213        <region>AM</region>
214        <code>06902</code>
215        <country>France</country>
216      </postal>
217      <email>ylafon@w3.org</email>
218      <uri>http://www.raubacapeu.net/people/yves/</uri>
219    </address>
220  </author>
221
222  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
223    <organization abbrev="greenbytes">greenbytes GmbH</organization>
224    <address>
225      <postal>
226        <street>Hafenweg 16</street>
227        <city>Muenster</city><region>NW</region><code>48155</code>
228        <country>Germany</country>
229      </postal>
230      <phone>+49 251 2807760</phone>
231      <facsimile>+49 251 2807761</facsimile>
232      <email>julian.reschke@greenbytes.de</email>
233      <uri>http://greenbytes.de/tech/webdav/</uri>
234    </address>
235  </author>
236
237  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
238  <workgroup>HTTPbis Working Group</workgroup>
239
240<abstract>
241<t>
242   The Hypertext Transfer Protocol (HTTP) is an application-level
243   protocol for distributed, collaborative, hypermedia information
244   systems. HTTP has been in use by the World Wide Web global information
245   initiative since 1990. This document is Part 2 of the seven-part specification
246   that defines the protocol referred to as "HTTP/1.1" and, taken together,
247   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
248   as expressed by request methods, request-header fields, response status codes,
249   and response-header fields.
250</t>
251</abstract>
252
253<note title="Editorial Note (To be removed by RFC Editor)">
254  <t>
255    Discussion of this draft should take place on the HTTPBIS working group
256    mailing list (ietf-http-wg@w3.org). The current issues list is
257    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
258    and related documents (including fancy diffs) can be found at
259    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
260  </t>
261  <t>
262    The changes in this draft are summarized in <xref target="changes.since.12"/>.
263  </t>
264</note>
265</front>
266<middle>
267<section title="Introduction" anchor="introduction">
268<t>
269   This document defines HTTP/1.1 request and response semantics.  Each HTTP
270   message, as defined in &messaging;, is in the form of either a request or
271   a response.  An HTTP server listens on a connection for HTTP requests and
272   responds to each request, in the order received on that connection, with
273   one or more HTTP response messages.  This document defines the commonly
274   agreed upon semantics of the HTTP uniform interface, the intentions defined
275   by each request method, and the various response messages that might be
276   expected as a result of applying that method to the target resource.
277</t>
278<t>
279   This document is currently disorganized in order to minimize the changes
280   between drafts and enable reviewers to see the smaller errata changes.
281   A future draft will reorganize the sections to better reflect the content.
282   In particular, the sections will be ordered according to the typical
283   processing of an HTTP request message (after message parsing): resource
284   mapping, general header fields, methods, request modifiers, response
285   status, and resource metadata.  The current mess reflects how widely
286   dispersed these topics and associated requirements had become in
287   <xref target="RFC2616"/>.
288</t>
289
290<section title="Requirements" anchor="intro.requirements">
291<t>
292   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
293   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
294   document are to be interpreted as described in <xref target="RFC2119"/>.
295</t>
296<t>
297   An implementation is not compliant if it fails to satisfy one or more
298   of the "MUST" or "REQUIRED" level requirements for the protocols it
299   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
300   level and all the "SHOULD" level requirements for its protocols is said
301   to be "unconditionally compliant"; one that satisfies all the "MUST"
302   level requirements but not all the "SHOULD" level requirements for its
303   protocols is said to be "conditionally compliant".
304</t>
305</section>
306
307<section title="Syntax Notation" anchor="notation">
308  <x:anchor-alias value="CR"/>
309  <x:anchor-alias value="DIGIT"/>
310  <x:anchor-alias value="LF"/>
311  <x:anchor-alias value="VCHAR"/>
312  <x:anchor-alias value="WSP"/>
313<t>
314  This specification uses the ABNF syntax defined in &notation; (which
315  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
316  <xref target="collected.abnf"/> shows the collected ABNF, with the list
317  rule expanded.
318</t>
319<t>
320  The following core rules are included by
321  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
322  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
323  DIGIT (decimal 0-9), DQUOTE (double quote),
324  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
325  OCTET (any 8-bit sequence of data), SP (space),
326  VCHAR (any visible USASCII character),
327  and WSP (whitespace).
328</t>
329
330<section title="Core Rules" anchor="core.rules">
331  <x:anchor-alias value="obs-text"/>
332  <x:anchor-alias value="quoted-string"/>
333  <x:anchor-alias value="token"/>
334  <x:anchor-alias value="OWS"/>
335  <x:anchor-alias value="RWS"/>
336<t>
337  The core rules below are defined in &basic-rules;:
338</t>
339<figure><artwork type="abnf2616">
340  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
341  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
342  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
343  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
344  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
345</artwork></figure>
346</section>
347
348<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
349  <x:anchor-alias value="absolute-URI"/>
350  <x:anchor-alias value="Accept"/>
351  <x:anchor-alias value="Accept-Charset"/>
352  <x:anchor-alias value="Accept-Encoding"/>
353  <x:anchor-alias value="Accept-Language"/>
354  <x:anchor-alias value="Accept-Ranges"/>
355  <x:anchor-alias value="Age"/>
356  <x:anchor-alias value="Authorization"/>
357  <x:anchor-alias value="comment"/>
358  <x:anchor-alias value="ETag"/>
359  <x:anchor-alias value="Host"/>
360  <x:anchor-alias value="HTTP-date"/>
361  <x:anchor-alias value="If-Match"/>
362  <x:anchor-alias value="If-Modified-Since"/>
363  <x:anchor-alias value="If-None-Match"/>
364  <x:anchor-alias value="If-Range"/>
365  <x:anchor-alias value="If-Unmodified-Since"/>
366  <x:anchor-alias value="partial-URI"/>
367  <x:anchor-alias value="product"/>
368  <x:anchor-alias value="Proxy-Authenticate"/>
369  <x:anchor-alias value="Proxy-Authorization"/>
370  <x:anchor-alias value="Range"/>
371  <x:anchor-alias value="TE"/>
372  <x:anchor-alias value="URI-reference"/>
373  <x:anchor-alias value="Vary"/>
374  <x:anchor-alias value="WWW-Authenticate"/>
375<t>
376  The ABNF rules below are defined in other parts:
377</t>
378<figure><!--Part1--><artwork type="abnf2616">
379  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
380  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
381  <x:ref>Host</x:ref>          = &lt;Host, defined in &uri;&gt;
382  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
383  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
384  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
385  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
386  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
387</artwork></figure>
388<figure><!--Part3--><artwork type="abnf2616">
389  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
390  <x:ref>Accept-Charset</x:ref> =
391             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
392  <x:ref>Accept-Encoding</x:ref> =
393             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
394  <x:ref>Accept-Language</x:ref> =
395             &lt;Accept-Language, defined in &header-accept-language;&gt;
396</artwork></figure>
397<figure><!--Part4--><artwork type="abnf2616">
398  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
399  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
400  <x:ref>If-Modified-Since</x:ref> =
401             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
402  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
403  <x:ref>If-Unmodified-Since</x:ref> =
404             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
405</artwork></figure>
406<figure><!--Part5--><artwork type="abnf2616">
407  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
408  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
409  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
410</artwork></figure>
411<figure><!--Part6--><artwork type="abnf2616">
412  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
413  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
414</artwork><!--Part7--></figure>
415<figure><artwork type="abnf2616">
416  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
417  <x:ref>Proxy-Authenticate</x:ref> =
418             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
419  <x:ref>Proxy-Authorization</x:ref> =
420             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
421  <x:ref>WWW-Authenticate</x:ref> =
422             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
423</artwork></figure>
424</section>
425</section>
426</section>
427
428<section title="Method" anchor="method">
429  <x:anchor-alias value="Method"/>
430  <x:anchor-alias value="extension-method"/>
431<t>
432   The Method token indicates the request method to be performed on the target
433   resource (&effective-request-uri;). The method is case-sensitive.
434</t>
435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
436  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
437</artwork></figure>
438<t>
439   The list of methods allowed by a resource can be specified in an
440   Allow header field (<xref target="header.allow"/>). The status code of the response
441   always notifies the client whether a method is currently allowed on a
442   resource, since the set of allowed methods can change dynamically. An
443   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
444   if the method is known by the origin server but not allowed for the
445   resource, and 501 (Not Implemented) if the method is
446   unrecognized or not implemented by the origin server. The methods GET
447   and HEAD &MUST; be supported by all general-purpose servers. All other
448   methods are &OPTIONAL;; however, if the above methods are implemented,
449   they &MUST; be implemented with the same semantics as those specified
450   in <xref target="method.definitions"/>.
451</t>
452
453<section title="Overview of Methods" anchor="overview.of.methods">
454<t>
455  The methods listed below are defined in <xref target="method.definitions"/>.
456</t>
457<texttable align="left">
458  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
459 
460  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
461  <c>GET</c> <c><xref target="GET"/></c>
462  <c>HEAD</c> <c><xref target="HEAD"/></c>
463  <c>POST</c> <c><xref target="POST"/></c>
464  <c>PUT</c> <c><xref target="PUT"/></c>
465  <c>DELETE</c> <c><xref target="DELETE"/></c>
466  <c>TRACE</c> <c><xref target="TRACE"/></c>
467  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
468</texttable>
469<t>
470  Note that this list is not exhaustive &mdash; it does not include request methods defined
471  in other specifications.
472</t>
473</section>
474
475<section title="Method Registry" anchor="method.registry">
476<t>
477  The HTTP Method Registry defines the name space for the Method token in the
478  Request line of an HTTP request.
479</t>
480<t>
481  Registrations &MUST; include the following fields:
482  <list style="symbols">
483    <t>Method Name (see <xref target="method"/>)</t>
484    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
485    <t>Pointer to specification text</t>
486  </list>
487</t>
488<t>
489  Values to be added to this name space are subject to IETF review
490  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
491</t>
492<t>
493  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
494</t>
495
496<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
497<t>
498   When it is necessary to express new semantics for a HTTP request that
499   aren't specific to a single application or media type, and currently defined
500   methods are inadequate, it may be appropriate to register a new method.
501</t>
502<t>
503   HTTP methods are generic; that is, they are potentially applicable to any
504   resource, not just one particular media type, "type" of resource, or
505   application. As such, it is preferred that new HTTP methods be registered
506   in a document that isn't specific to a single application, so that this is
507   clear.
508</t>
509<t>
510   Due to the parsing rules defined in &message-body;, definitions of HTTP
511   methods cannot prohibit the presence of a message-body on either the request
512   or the response message (with responses to HEAD requests being the single
513   exception). Definitions of new methods cannot change this rule, but they can
514   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
515</t>
516<t>
517   New method definitions need to indicate whether they are safe (<xref
518   target="safe.methods"/>) and whether they are idempotent (<xref
519   target="idempotent.methods"/>). They also need to state whether they can be
520   cached (&caching;); in particular what conditions a cache may store the
521   response, and under what conditions such a stored response may be used to
522   satisfy a subsequent request.
523</t>
524</section>
525
526</section>
527</section>
528
529<section title="Request Header Fields" anchor="request.header.fields">
530  <x:anchor-alias value="request-header"/>
531<t>
532   The request-header fields allow the client to pass additional
533   information about the request, and about the client itself, to the
534   server. These fields act as request modifiers, with semantics
535   equivalent to the parameters on a programming language method
536   invocation.
537</t>
538<texttable align="left">
539  <ttcol>Header Field Name</ttcol>
540  <ttcol>Defined in...</ttcol>
541
542  <c>Accept</c> <c>&header-accept;</c>
543  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
544  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
545  <c>Accept-Language</c> <c>&header-accept-language;</c>
546  <c>Authorization</c> <c>&header-authorization;</c>
547  <c>Expect</c> <c><xref target="header.expect"/></c>
548  <c>From</c> <c><xref target="header.from"/></c>
549  <c>Host</c> <c>&header-host;</c>
550  <c>If-Match</c> <c>&header-if-match;</c>
551  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
552  <c>If-None-Match</c> <c>&header-if-none-match;</c>
553  <c>If-Range</c> <c>&header-if-range;</c>
554  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
555  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
556  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
557  <c>Range</c> <c>&header-range;</c>
558  <c>Referer</c> <c><xref target="header.referer"/></c>
559  <c>TE</c> <c>&header-te;</c>
560  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
561</texttable>
562<t>
563   Request-header field names can be extended reliably only in
564   combination with a change in the protocol version. However, new or
565   experimental header fields &MAY; be given the semantics of request-header
566   fields if all parties in the communication recognize them to
567   be request-header fields.
568</t>
569</section>
570
571<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
572  <x:anchor-alias value="Reason-Phrase"/>
573  <x:anchor-alias value="Status-Code"/>
574  <x:anchor-alias value="extension-code"/>
575<t>
576   The Status-Code element is a 3-digit integer result code of the attempt to
577   understand and satisfy the request.
578</t>
579<t>
580   The Reason-Phrase is intended to give a short textual description of the
581   Status-Code and is intended for a human user. The client does not need
582   to examine or display the Reason-Phrase.
583</t>
584<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"/>
585  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
586  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
587</artwork></figure>
588<t>
589   HTTP status codes are extensible. HTTP applications are not required
590   to understand the meaning of all registered status codes, though such
591   understanding is obviously desirable. However, applications &MUST;
592   understand the class of any status code, as indicated by the first
593   digit, and treat any unrecognized response as being equivalent to the
594   x00 status code of that class, with the exception that an
595   unrecognized response &MUST-NOT; be cached. For example, if an
596   unrecognized status code of 431 is received by the client, it can
597   safely assume that there was something wrong with its request and
598   treat the response as if it had received a 400 status code. In such
599   cases, user agents &SHOULD; present to the user the representation enclosed
600   with the response, since that representation is likely to include human-readable
601   information which will explain the unusual status.
602</t>
603
604<section title="Overview of Status Codes" anchor="overview.of.status.codes">
605<t> 
606   The status codes listed below are defined in <xref target="status.codes"/>
607   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
608   The reason phrases listed here are only recommendations &mdash; they can be
609   replaced by local equivalents without affecting the protocol.
610</t>
611<texttable align="left">
612  <ttcol>Status-Code</ttcol>
613  <ttcol>Reason-Phrase</ttcol>
614  <ttcol>Defined in...</ttcol>
615 
616  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
617  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
618
619  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
620  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
621  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
622  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
623  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
624  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
625  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
626
627  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
628  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
629  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
630  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
631  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
632  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
633  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
634
635  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
636  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
637  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
638  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
639  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
640  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
641  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
642  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
643  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
644  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
645  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
646  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
647  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
648  <c>413</c> <c>Request Entity Too Large</c> <c><xref target="status.413"/></c>
649  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
650  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
651  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
652  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
653  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
654
655  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
656  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
657  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
658  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
659  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
660  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
661</texttable>
662<t>
663   Note that this list is not exhaustive &mdash; it does not include
664   extension status codes defined in other specifications.
665</t>
666</section>
667
668<section title="Status Code Registry" anchor="status.code.registry">
669<t>
670  The HTTP Status Code Registry defines the name space for the Status-Code
671  token in the Status-Line of an HTTP response.
672</t>
673<t>
674  Values to be added to this name space are subject to IETF review
675  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
676</t>
677<t>
678  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
679</t>
680
681<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
682<t>
683   When it is necessary to express new semantics for a HTTP response that
684   aren't specific to a single application or media type, and currently defined
685   status codes are inadequate, a new status code can be registered.
686</t>
687<t>
688   HTTP status codes are generic; that is, they are potentially applicable to
689   any resource, not just one particular media type, "type" of resource, or
690   application. As such, it is preferred that new HTTP status codes be
691   registered in a document that isn't specific to a single application, so
692   that this is clear.
693</t>
694<t>
695   Definitions of new HTTP status codes typically explain the request
696   conditions that produce a response containing the status code (e.g.,
697   combinations of request headers and/or method(s)), along with any
698   interactions with response headers (e.g., those that are required, those
699   that modify the semantics of the response).
700</t>
701<t>
702   New HTTP status codes are required to fall under one of the categories
703   defined in <xref target="status.codes"/>. To allow existing parsers to
704   properly handle them, new status codes cannot disallow a response body,
705   although they can mandate a zero-length response body. They can require the
706   presence of one or more particular HTTP response header(s).
707</t>
708<t>
709   Likewise, their definitions can specify that caches are allowed to use
710   heuristics to determine their freshness (see &caching;; by default, it is
711   not allowed), and can define how to determine the resource which they
712   carry a representation for (see <xref
713   target="identifying.response.associated.with.representation"/>; by default,
714   it is anonymous).
715</t>
716</section>
717
718</section>
719
720</section>
721
722<section title="Response Header Fields" anchor="response.header.fields">
723  <x:anchor-alias value="response-header"/>
724<t>
725   The response-header fields allow the server to pass additional
726   information about the response which cannot be placed in the Status-Line.
727   These header fields give information about the server and about
728   further access to the target resource (&effective-request-uri;).
729</t>
730<texttable align="left">
731  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
732
733  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
734  <c>Age</c> <c>&header-age;</c>
735  <c>Allow</c> <c><xref target="header.allow"/></c>
736  <c>ETag</c> <c>&header-etag;</c>
737  <c>Location</c> <c><xref target="header.location"/></c>
738  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
739  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
740  <c>Server</c> <c><xref target="header.server"/></c>
741  <c>Vary</c> <c>&header-vary;</c>
742  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
743</texttable>
744<t>
745   Response-header field names can be extended reliably only in
746   combination with a change in the protocol version. However, new or
747   experimental header fields &MAY; be given the semantics of response-header
748   fields if all parties in the communication recognize them to
749   be response-header fields.
750</t>
751</section>
752
753<section title="Representation" anchor="representation">
754<t>
755   Request and Response messages &MAY; transfer a representation if not otherwise
756   restricted by the request method or response status code. A representation
757   consists of metadata (representation header fields) and data (representation
758   body).  When a complete or partial representation is enclosed in an HTTP message,
759   it is referred to as the payload of the message. HTTP representations
760   are defined in &payload;.
761</t>
762<t>
763   A representation body is only present in a message when a message-body is
764   present, as described in &message-body;. The representation body is obtained
765   from the message-body by decoding any Transfer-Encoding that might
766   have been applied to ensure safe and proper transfer of the message.
767</t>
768
769<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
770<t>
771   It is sometimes necessary to determine an identifier for the resource
772   associated with a representation.
773</t>
774<t>
775   An HTTP request representation, when present, is always associated with an
776   anonymous (i.e., unidentified) resource.
777</t>
778<t>
779   In the common case, an HTTP response is a representation of the target
780   resource (see &effective-request-uri;). However, this is not always the
781   case. To determine the URI of the resource a response is associated with,
782   the following rules are used (with the first applicable one being selected):
783</t>
784<t><list style="numbers">
785   <t>If the response status code is 200 or 203 and the request method was GET,
786   the response payload is a representation of the target resource.</t>
787   <t>If the response status code is 204, 206, or 304 and the request method was GET
788   or HEAD, the response payload is a partial representation of the target
789   resource (see &combining-responses;).</t>
790   <t>If the response has a Content-Location header field, and that URI is the same
791   as the effective request URI, the response payload is a representation of the
792   target resource.</t>
793   <t>If the response has a Content-Location header field, and that URI is not the
794   same as the effective request URI, then the response asserts that its
795   payload is a representation of the resource identified by the
796   Content-Location URI. However, such an assertion cannot be trusted unless
797   it can be verified by other means (not defined by HTTP).</t>
798   <t>Otherwise, the response is a representation of an anonymous (i.e.,
799   unidentified) resource.</t>
800</list></t>
801<t>
802  <cref anchor="TODO-req-uri">
803   The comparison function is going to have to be defined somewhere,
804   because we already need to compare URIs for things like cache invalidation.</cref>
805</t>
806</section>
807
808</section>
809
810
811<section title="Method Definitions" anchor="method.definitions">
812<t>
813   The set of common request methods for HTTP/1.1 is defined below. Although
814   this set can be expanded, additional methods cannot be assumed to
815   share the same semantics for separately extended clients and servers.
816</t>
817
818<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
819
820<section title="Safe Methods" anchor="safe.methods">
821<iref item="Safe Methods" primary="true"/>
822<t>
823   Implementors need to be aware that the software represents the user in
824   their interactions over the Internet, and need to allow
825   the user to be aware of any actions they take which might have an
826   unexpected significance to themselves or others.
827</t>
828<t>
829   In particular, the convention has been established that the GET, HEAD,
830   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
831   of taking an action other than retrieval. These request methods ought
832   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
833   This allows user agents to represent other methods, such as POST, PUT
834   and DELETE, in a special way, so that the user is made aware of the
835   fact that a possibly unsafe action is being requested.
836</t>
837<t>
838   Naturally, it is not possible to ensure that the server does not
839   generate side-effects as a result of performing a GET request; in
840   fact, some dynamic resources consider that a feature. The important
841   distinction here is that the user did not request the side-effects,
842   so therefore cannot be held accountable for them.
843</t>
844</section>
845
846<section title="Idempotent Methods" anchor="idempotent.methods">
847<iref item="Idempotent Methods" primary="true"/>
848<t>
849   Request methods can also have the property of "idempotence" in that,
850   aside from error or expiration issues, the intended effect of multiple
851   identical requests is the same as for a single request.
852   PUT, DELETE, and all safe request methods are idempotent.
853   It is important to note that idempotence refers only to changes
854   requested by the client: a server is free to change its state due
855   to multiple requests for the purpose of tracking those requests,
856   versioning of results, etc.
857</t>
858</section>
859</section>
860
861<section title="OPTIONS" anchor="OPTIONS">
862  <rdf:Description>
863    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
864  </rdf:Description>
865  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
866  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
867<t>
868   The OPTIONS method requests information about the
869   communication options available on the request/response chain
870   identified by the effective request URI. This method allows a client to
871   determine the options and/or requirements associated with a resource,
872   or the capabilities of a server, without implying a resource action
873   or initiating a resource retrieval.
874</t>
875<t>
876   Responses to the OPTIONS method are not cacheable.
877</t>
878<t>
879   If the OPTIONS request includes a message-body (as indicated by the
880   presence of Content-Length or Transfer-Encoding), then the media type
881   &MUST; be indicated by a Content-Type field. Although this
882   specification does not define any use for such a body, future
883   extensions to HTTP might use the OPTIONS body to make more detailed
884   queries on the server.
885</t>
886<t>
887   If the request-target is an asterisk ("*"), the OPTIONS request is
888   intended to apply to the server in general rather than to a specific
889   resource. Since a server's communication options typically depend on
890   the resource, the "*" request is only useful as a "ping" or "no-op"
891   type of method; it does nothing beyond allowing the client to test
892   the capabilities of the server. For example, this can be used to test
893   a proxy for HTTP/1.1 compliance (or lack thereof).
894</t>
895<t>
896   If the request-target is not an asterisk, the OPTIONS request applies
897   only to the options that are available when communicating with that
898   resource.
899</t>
900<t>
901   A 200 response &SHOULD; include any header fields that indicate
902   optional features implemented by the server and applicable to that
903   resource (e.g., Allow), possibly including extensions not defined by
904   this specification. The response body, if any, &SHOULD; also include
905   information about the communication options. The format for such a
906   body is not defined by this specification, but might be defined by
907   future extensions to HTTP. Content negotiation &MAY; be used to select
908   the appropriate response format. If no response body is included, the
909   response &MUST; include a Content-Length field with a field-value of
910   "0".
911</t>
912<t>
913   The Max-Forwards request-header field &MAY; be used to target a
914   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
915   If no Max-Forwards field is present in the request, then the forwarded
916   request &MUST-NOT; include a Max-Forwards field.
917</t>
918</section>
919
920<section title="GET" anchor="GET">
921  <rdf:Description>
922    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
923  </rdf:Description>
924  <iref primary="true" item="GET method" x:for-anchor=""/>
925  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
926<t>
927   The GET method requests transfer of a current representation of
928   the target resource.
929</t>
930<t>   
931   If the target resource is a data-producing process, it is the
932   produced data which shall be returned as the representation in the response and not
933   the source text of the process, unless that text happens to be the output of
934   the process.
935</t>
936<t>
937   The semantics of the GET method change to a "conditional GET" if the
938   request message includes an If-Modified-Since, If-Unmodified-Since,
939   If-Match, If-None-Match, or If-Range header field. A conditional GET
940   requests that the representation be transferred only under the
941   circumstances described by the conditional header field(s). The
942   conditional GET request is intended to reduce unnecessary network
943   usage by allowing cached representations to be refreshed without requiring
944   multiple requests or transferring data already held by the client.
945</t>
946<t>
947   The semantics of the GET method change to a "partial GET" if the
948   request message includes a Range header field. A partial GET requests
949   that only part of the representation be transferred, as described in &header-range;.
950   The partial GET request is intended to reduce unnecessary
951   network usage by allowing partially-retrieved representations to be
952   completed without transferring data already held by the client.
953</t>
954<t>
955   The response to a GET request is cacheable and &MAY; be used to satisfy
956   subsequent GET and HEAD requests (see &caching;).
957</t>
958<t>
959   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
960</t>
961</section>
962
963<section title="HEAD" anchor="HEAD">
964  <rdf:Description>
965    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
966  </rdf:Description>
967  <iref primary="true" item="HEAD method" x:for-anchor=""/>
968  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
969<t>
970   The HEAD method is identical to GET except that the server &MUST-NOT;
971   return a message-body in the response. The metadata contained
972   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
973   to the information sent in response to a GET request. This method can
974   be used for obtaining metadata about the representation implied by the
975   request without transferring the representation body. This method is
976   often used for testing hypertext links for validity, accessibility,
977   and recent modification.
978</t>
979<t>
980   The response to a HEAD request is cacheable and &MAY; be used to satisfy
981   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
982   representation from that resource; if the new field values
983   indicate that the cached representation differs from the current representation (as
984   would be indicated by a change in Content-Length, Content-MD5, ETag
985   or Last-Modified), then the cache &MUST; treat the cache entry as
986   stale.
987</t>
988</section>
989
990<section title="POST" anchor="POST">
991  <iref primary="true" item="POST method" x:for-anchor=""/>
992  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
993<t>
994   The POST method requests that the origin server accept the
995   representation enclosed in the request as data to be processed by the
996   target resource. POST is designed to allow a uniform method to cover the
997   following functions:
998  <list style="symbols">
999    <t>
1000      Annotation of existing resources;
1001    </t>
1002    <t>
1003        Posting a message to a bulletin board, newsgroup, mailing list,
1004        or similar group of articles;
1005    </t>
1006    <t>
1007        Providing a block of data, such as the result of submitting a
1008        form, to a data-handling process;
1009    </t>
1010    <t>
1011        Extending a database through an append operation.
1012    </t>
1013  </list>
1014</t>
1015<t>
1016   The actual function performed by the POST method is determined by the
1017   server and is usually dependent on the effective request URI.
1018</t>
1019<t>
1020   The action performed by the POST method might not result in a
1021   resource that can be identified by a URI. In this case, either 200
1022   (OK) or 204 (No Content) is the appropriate response status code,
1023   depending on whether or not the response includes a representation that
1024   describes the result.
1025</t>
1026<t>
1027   If a resource has been created on the origin server, the response
1028   &SHOULD; be 201 (Created) and contain a representation which describes the
1029   status of the request and refers to the new resource, and a Location
1030   header field (see <xref target="header.location"/>).
1031</t>
1032<t>
1033   Responses to POST requests are only cacheable when they
1034   include explicit freshness information (see &p6-explicit;). A
1035   cached POST response with a Content-Location header field
1036   (see &header-content-location;) whose value is the effective
1037   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1038</t>
1039<t>
1040   Note that POST caching is not widely implemented.
1041   However, the 303 (See Other) response can be used to direct the
1042   user agent to retrieve a cacheable resource.
1043</t>
1044</section>
1045
1046<section title="PUT" anchor="PUT">
1047  <iref primary="true" item="PUT method" x:for-anchor=""/>
1048  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1049<t>
1050   The PUT method requests that the state of the target resource
1051   be created or replaced with the state defined by the representation
1052   enclosed in the request message payload.  A successful PUT of a given
1053   representation would suggest that a subsequent GET on that same target
1054   resource will result in an equivalent representation being returned in
1055   a 200 (OK) response.  However, there is no guarantee that such a state
1056   change will be observable, since the target resource might be acted
1057   upon by other user agents in parallel, or might be subject to dynamic
1058   processing by the origin server, before any subsequent GET is received.
1059   A successful response only implies that the user agent's intent was
1060   achieved at the time of its processing by the origin server.
1061</t>
1062<t>   
1063   If the target resource does not have a current representation and
1064   the PUT successfully creates one, then the origin server &MUST; inform
1065   the user agent by sending a 201 (Created) response.  If the target
1066   resource does have a current representation and that representation is
1067   successfully modified in accordance with the state of the enclosed
1068   representation, then either a 200 (OK) or 204 (No Content) response
1069   &SHOULD; be sent to indicate successful completion of the request.
1070</t>
1071<t>
1072   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1073   as part of the resource state).
1074</t>
1075<t>
1076   An origin server &SHOULD; verify that the PUT representation is
1077   consistent with any constraints which the server has for the target
1078   resource that cannot or will not be changed by the PUT.  This is
1079   particularly important when the origin server uses internal
1080   configuration information related to the URI in order to set the
1081   values for representation metadata on GET responses.  When a PUT
1082   representation is inconsistent with the target resource, the origin
1083   server &SHOULD; either make them consistent, by transforming the
1084   representation or changing the resource configuration, or respond
1085   with a 409 (Conflict) status code and sufficient information
1086   to explain why the representation is unsuitable.
1087</t>
1088<t>
1089   For example, if the target resource is configured to always have a
1090   Content-Type of "text/html" and the representation being PUT has a
1091   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1092   (a) reconfigure the target resource to reflect the new media type;
1093   (b) transform the PUT representation to a format consistent with that
1094   of the resource before saving it as the new resource state; or,
1095   (c) reject the request with a 409 response indicating that the target
1096   resource is limited to "text/html", perhaps including a link to a
1097   different resource that would be a suitable target for the new
1098   representation.
1099</t>
1100<t>
1101   HTTP does not define exactly how a PUT method affects the state
1102   of an origin server beyond what can be expressed by the intent of
1103   the user agent request and the semantics of the origin server response.
1104   It does not define what a resource might be, in any sense of that
1105   word, beyond the interface provided via HTTP.  It does not define
1106   how resource state is "stored", nor how such storage might change
1107   as a result of a change in resource state, nor how the origin server
1108   translates resource state into representations.  Generally speaking,
1109   all implementation details behind the resource interface are
1110   intentionally hidden by the server.
1111</t>
1112<t>
1113   The fundamental difference between the POST and PUT methods is
1114   highlighted by the different intent for the target resource.
1115   The target resource in a POST request is intended to handle the
1116   enclosed representation as a data-accepting process, such as for
1117   a gateway to some other protocol or a document that accepts annotations.
1118   In contrast, the target resource in a PUT request is intended to
1119   take the enclosed representation as a new or replacement value.
1120   Hence, the intent of PUT is idempotent and visible to intermediaries,
1121   even though the exact effect is only known by the origin server.
1122</t>
1123<t>
1124   Proper interpretation of a PUT request presumes that the user agent
1125   knows what target resource is desired.  A service that is intended
1126   to select a proper URI on behalf of the client, after receiving
1127   a state-changing request, &SHOULD; be implemented using the POST
1128   method rather than PUT.  If the origin server will not make the
1129   requested PUT state change to the target resource and instead
1130   wishes to have it applied to a different resource, such as when the
1131   resource has been moved to a different URI, then the origin server
1132   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1133   then make its own decision regarding whether or not to redirect the
1134   request.
1135</t>
1136<t>
1137   A PUT request applied to the target resource &MAY; have side-effects
1138   on other resources.  For example, an article might have a URI for
1139   identifying "the current version" (a resource) which is separate
1140   from the URIs identifying each particular version (different
1141   resources that at one point shared the same state as the current version
1142   resource).  A successful PUT request on "the current version" URI might
1143   therefore create a new version resource in addition to changing the
1144   state of the target resource, and might also cause links to be added
1145   between the related resources.
1146</t>
1147<t>
1148   An origin server &SHOULD; reject any PUT request that contains a
1149   Content-Range header field, since it might be misinterpreted as
1150   partial content (or might be partial content that is being mistakenly
1151   PUT as a full representation).  Partial content updates are
1152   possible by targeting a separately identified resource with state
1153   that overlaps a portion of the larger resource, or by using a
1154   different method that has been specifically defined for partial
1155   updates (for example, the PATCH method defined in
1156   <xref target="RFC5789"/>).
1157</t>
1158<t>
1159   Responses to the PUT method are not cacheable. If a PUT request passes
1160   through a cache that has one or more stored responses for the effective
1161   request URI, those stored responses will be invalidated (see
1162   &p6-invalid;).
1163</t>
1164</section>
1165
1166<section title="DELETE" anchor="DELETE">
1167  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1168  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1169<t>
1170   The DELETE method requests that the origin server delete the target
1171   resource. This method &MAY; be overridden by
1172   human intervention (or other means) on the origin server. The client cannot
1173   be guaranteed that the operation has been carried out, even if the
1174   status code returned from the origin server indicates that the action
1175   has been completed successfully. However, the server &SHOULD-NOT; 
1176   indicate success unless, at the time the response is given, it
1177   intends to delete the resource or move it to an inaccessible
1178   location.
1179</t>
1180<t>
1181   A successful response &SHOULD; be 200 (OK) if the response includes an
1182   representation describing the status, 202 (Accepted) if the action has not
1183   yet been enacted, or 204 (No Content) if the action has been enacted
1184   but the response does not include a representation.
1185</t>
1186<t>
1187   Responses to the DELETE method are not cacheable. If a DELETE request
1188   passes through a cache that has one or more stored responses for the
1189   effective request URI, those stored responses will be invalidated (see
1190   &p6-invalid;).
1191</t>
1192</section>
1193
1194<section title="TRACE" anchor="TRACE">
1195  <rdf:Description>
1196    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1197  </rdf:Description>
1198  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1199  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1200<t>
1201   The TRACE method requests a remote, application-layer loop-back
1202   of the request message. The final recipient of the request
1203   &SHOULD; reflect the message received back to the client as the
1204   message-body of a 200 (OK) response. The final recipient is either the
1205   origin server or the first proxy or gateway to receive a Max-Forwards
1206   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1207   A TRACE request &MUST-NOT; include a message-body.
1208</t>
1209<t>
1210   TRACE allows the client to see what is being received at the other
1211   end of the request chain and use that data for testing or diagnostic
1212   information. The value of the Via header field (&header-via;) is of
1213   particular interest, since it acts as a trace of the request chain.
1214   Use of the Max-Forwards header field allows the client to limit the
1215   length of the request chain, which is useful for testing a chain of
1216   proxies forwarding messages in an infinite loop.
1217</t>
1218<t>
1219   If the request is valid, the response &SHOULD; have a Content-Type of
1220   "message/http" (see &media-type-message-http;) and contain a message-body
1221   that encloses a copy of the entire request message.
1222   Responses to the TRACE method are not cacheable.
1223</t>
1224</section>
1225
1226<section title="CONNECT" anchor="CONNECT">
1227  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1228  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1229<t>
1230   The CONNECT method requests that the proxy establish a tunnel
1231   to the request-target and then restrict its behavior to blind
1232   forwarding of packets until the connection is closed.
1233</t>
1234<t>
1235   When using CONNECT, the request-target &MUST; use the authority form
1236   (&request-target;); i.e., the request-target consists of only the
1237   host name and port number of the tunnel destination, separated by a colon.
1238   For example,
1239</t>
1240<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1241CONNECT server.example.com:80 HTTP/1.1
1242Host: server.example.com:80
1243
1244</artwork></figure>
1245<t>
1246   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1247   except end-to-end protocol Upgrade requests, since the
1248   tunnel must be established first.
1249</t>
1250<t>
1251   For example, proxy authentication might be used to establish the
1252   authority to create a tunnel:
1253</t>
1254<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1255CONNECT server.example.com:80 HTTP/1.1
1256Host: server.example.com:80
1257Proxy-Authorization: basic aGVsbG86d29ybGQ=
1258
1259</artwork></figure>
1260<t>
1261   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1262   sent immediately after the blank line. The usual caveats also apply:
1263   data may be discarded if the eventual response is negative, and the
1264   connection may be reset with no response if more than one TCP segment
1265   is outstanding.
1266</t>
1267
1268<section title="Establishing a Tunnel with CONNECT">
1269<t>
1270   Any successful (2xx) response to a CONNECT request indicates that the
1271   proxy has established a connection to the requested host and port,
1272   and has switched to tunneling the current connection to that server
1273   connection.
1274</t>
1275<t>
1276   It may be the case that the proxy itself can only reach the requested
1277   origin server through another proxy.  In this case, the first proxy
1278   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1279   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1280   unless it has either a direct or tunnel connection established to the
1281   authority.
1282</t>
1283<t>
1284   An origin server which receives a CONNECT request for itself &MAY;
1285   respond with a 2xx status code to indicate that a connection is
1286   established.
1287</t>
1288<t>
1289   If at any point either one of the peers gets disconnected, any
1290   outstanding data that came from that peer will be passed to the other
1291   one, and after that also the other connection will be terminated by
1292   the proxy. If there is outstanding data to that peer undelivered,
1293   that data will be discarded.
1294</t>
1295
1296</section>
1297</section>
1298</section>
1299
1300
1301<section title="Status Code Definitions" anchor="status.codes">
1302<t>
1303   Each Status-Code is described below, including any metadata required
1304   in the response.
1305</t>
1306
1307<section title="Informational 1xx" anchor="status.1xx">
1308<t>
1309   This class of status code indicates a provisional response,
1310   consisting only of the Status-Line and optional header fields, and is
1311   terminated by an empty line. There are no required header fields for this
1312   class of status code. Since HTTP/1.0 did not define any 1xx status
1313   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1314   except under experimental conditions.
1315</t>
1316<t>
1317   A client &MUST; be prepared to accept one or more 1xx status responses
1318   prior to a regular response, even if the client does not expect a 100
1319   (Continue) status message. Unexpected 1xx status responses &MAY; be
1320   ignored by a user agent.
1321</t>
1322<t>
1323   Proxies &MUST; forward 1xx responses, unless the connection between the
1324   proxy and its client has been closed, or unless the proxy itself
1325   requested the generation of the 1xx response. (For example, if a
1326   proxy adds a "Expect: 100-continue" field when it forwards a request,
1327   then it need not forward the corresponding 100 (Continue)
1328   response(s).)
1329</t>
1330
1331<section title="100 Continue" anchor="status.100">
1332  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1333  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1334<t>
1335   The client &SHOULD; continue with its request. This interim response is
1336   used to inform the client that the initial part of the request has
1337   been received and has not yet been rejected by the server. The client
1338   &SHOULD; continue by sending the remainder of the request or, if the
1339   request has already been completed, ignore this response. The server
1340   &MUST; send a final response after the request has been completed. See
1341   &use100; for detailed discussion of the use and handling of this
1342   status code.
1343</t>
1344</section>
1345
1346<section title="101 Switching Protocols" anchor="status.101">
1347  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1348  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1349<t>
1350   The server understands and is willing to comply with the client's
1351   request, via the Upgrade message header field (&header-upgrade;), for a
1352   change in the application protocol being used on this connection. The
1353   server will switch protocols to those defined by the response's
1354   Upgrade header field immediately after the empty line which
1355   terminates the 101 response.
1356</t>
1357<t>
1358   The protocol &SHOULD; be switched only when it is advantageous to do
1359   so. For example, switching to a newer version of HTTP is advantageous
1360   over older versions, and switching to a real-time, synchronous
1361   protocol might be advantageous when delivering resources that use
1362   such features.
1363</t>
1364</section>
1365</section>
1366
1367<section title="Successful 2xx" anchor="status.2xx">
1368<t>
1369   This class of status code indicates that the client's request was
1370   successfully received, understood, and accepted.
1371</t>
1372
1373<section title="200 OK" anchor="status.200">
1374  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1375  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1376<t>
1377   The request has succeeded. The payload returned with the response
1378   is dependent on the method used in the request, for example:
1379  <list style="hanging">
1380    <t hangText="GET">
1381          a representation of the target resource is sent in the response;
1382    </t>
1383    <t hangText="HEAD">
1384          the same representation as GET, except without the message-body;
1385    </t>
1386    <t hangText="POST">
1387      a representation describing or containing the result of the action;
1388    </t>
1389    <t hangText="TRACE">
1390      a representation containing the request message as received by the
1391      end server.
1392    </t>
1393  </list>
1394</t>
1395<t>
1396   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1397   freshness for 200 responses.
1398</t>
1399</section>
1400
1401<section title="201 Created" anchor="status.201">
1402  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1403  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1404<t>
1405   The request has been fulfilled and has resulted in a new resource being
1406   created. The newly created resource can be referenced by the URI(s)
1407   returned in the payload of the response, with the most specific URI
1408   for the resource given by a Location header field. The response
1409   &SHOULD; include a payload containing a list of resource
1410   characteristics and location(s) from which the user or user agent can
1411   choose the one most appropriate. The payload format is specified by
1412   the media type given in the Content-Type header field. The origin
1413   server &MUST; create the resource before returning the 201 status code.
1414   If the action cannot be carried out immediately, the server &SHOULD;
1415   respond with 202 (Accepted) response instead.
1416</t>
1417<t>
1418   A 201 response &MAY; contain an ETag response header field indicating
1419   the current value of the entity-tag for the representation of the resource
1420   just created (see &header-etag;).
1421</t>
1422</section>
1423
1424<section title="202 Accepted" anchor="status.202">
1425  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1426  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1427<t>
1428   The request has been accepted for processing, but the processing has
1429   not been completed.  The request might or might not eventually be
1430   acted upon, as it might be disallowed when processing actually takes
1431   place. There is no facility for re-sending a status code from an
1432   asynchronous operation such as this.
1433</t>
1434<t>
1435   The 202 response is intentionally non-committal. Its purpose is to
1436   allow a server to accept a request for some other process (perhaps a
1437   batch-oriented process that is only run once per day) without
1438   requiring that the user agent's connection to the server persist
1439   until the process is completed. The representation returned with this
1440   response &SHOULD; include an indication of the request's current status
1441   and either a pointer to a status monitor or some estimate of when the
1442   user can expect the request to be fulfilled.
1443</t>
1444</section>
1445
1446<section title="203 Non-Authoritative Information" anchor="status.203">
1447  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1448  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1449<t>
1450   The returned metadata in the header fields is not the
1451   definitive set as available from the origin server, but is gathered
1452   from a local or a third-party copy. The set presented &MAY; be a subset
1453   or superset of the original version. For example, including local
1454   annotation information about the resource might result in a superset
1455   of the metadata known by the origin server. Use of this
1456   response code is not required and is only appropriate when the
1457   response would otherwise be 200 (OK).
1458</t>
1459<t>
1460   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1461   freshness for 203 responses.
1462</t>
1463
1464</section>
1465
1466<section title="204 No Content" anchor="status.204">
1467  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1468  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1469<t>
1470   The server has successfully fulfilled the request, but there is no
1471   additional content to return in the response payload body.  The
1472   resource metadata and representation metadata in the response message's
1473   header fields refer to the target resource
1474   and its current representation, respectively, after the requested action.
1475   For example, if a 204 status code is received in response to a PUT
1476   and the response contains an ETag header field, then the value of
1477   that field is the current entity-tag for the representation that
1478   was successfully PUT.
1479</t>
1480<t>
1481   If the client is a user agent, it &SHOULD-NOT; change its document view
1482   from that which caused the request to be sent. This response is
1483   primarily intended to allow input for actions to take place without
1484   causing a change to the user agent's active document view, although
1485   any new or updated metadata &SHOULD; be applied to the document
1486   currently in the user agent's active view.
1487</t>
1488<t>
1489   The 204 response &MUST-NOT; include a message-body, and thus is always
1490   terminated by the first empty line after the header fields.
1491</t>
1492</section>
1493
1494<section title="205 Reset Content" anchor="status.205">
1495  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1496  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1497<t>
1498   The server has fulfilled the request and the user agent &SHOULD; reset
1499   the document view which caused the request to be sent. This response
1500   is primarily intended to allow input for actions to take place via
1501   user input, followed by a clearing of the form in which the input is
1502   given so that the user can easily initiate another input action.
1503</t>
1504<t>   
1505   The message-body included with the response &MUST; be empty. Note that
1506   receivers still need to parse the response according to the algorithm defined
1507   in &message-body;.
1508</t>
1509</section>
1510
1511<section title="206 Partial Content" anchor="status.206">
1512  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1513  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1514  <rdf:Description>
1515    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1516  </rdf:Description>
1517<t>
1518   The server has fulfilled the partial GET request for the resource
1519   and the enclosed payload is a partial representation as defined in &status-206;.
1520</t>
1521<t>
1522   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1523   freshness for 206 responses.
1524</t>
1525</section>
1526</section>
1527
1528<section title="Redirection 3xx" anchor="status.3xx">
1529<t>
1530   This class of status code indicates that further action needs to be
1531   taken by the user agent in order to fulfill the request.  The action
1532   required &MAY; be carried out by the user agent without interaction
1533   with the user if and only if the method used in the second request is
1534   known to be "safe", as defined in <xref target="safe.methods"/>.
1535   A client &SHOULD; detect infinite redirection loops, since such loops
1536   generate network traffic for each redirection.
1537</t>
1538<x:note>
1539  <t>
1540    <x:h>Note:</x:h> An earlier version of this specification recommended a
1541    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1542    Content developers need to be aware that some clients might
1543    implement such a fixed limitation.
1544  </t>
1545</x:note>
1546
1547<section title="300 Multiple Choices" anchor="status.300">
1548  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1549  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1550<t>
1551   The target resource has more than one
1552   representation, each with its own specific location, and agent-driven
1553   negotiation information (&content-negotiation;) is being provided so that
1554   the user (or user agent) can select a preferred representation by
1555   redirecting its request to that location.
1556</t>
1557<t>
1558   Unless it was a HEAD request, the response &SHOULD; include a representation
1559   containing a list of representation metadata and location(s) from
1560   which the user or user agent can choose the one most appropriate. The
1561   data format is specified by the media type given in the Content-Type
1562   header field. Depending upon the format and the capabilities of
1563   the user agent, selection of the most appropriate choice &MAY; be
1564   performed automatically. However, this specification does not define
1565   any standard for such automatic selection.
1566</t>
1567<t>
1568   If the server has a preferred choice of representation, it &SHOULD;
1569   include the specific URI for that representation in the Location
1570   field; user agents &MAY; use the Location field value for automatic
1571   redirection.
1572</t>
1573<t>
1574   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1575   freshness for 300 responses.
1576</t>
1577
1578</section>
1579
1580<section title="301 Moved Permanently" anchor="status.301">
1581  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1582  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1583<t>
1584   The target resource has been assigned a new permanent URI and any
1585   future references to this resource &SHOULD; use one of the returned
1586   URIs.  Clients with link editing capabilities ought to automatically
1587   re-link references to the effective request URI to one or more of the new
1588   references returned by the server, where possible.
1589</t>
1590<t>
1591   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1592   freshness for 301 responses.
1593</t>
1594<t>
1595   The new permanent URI &SHOULD; be given by the Location field in the
1596   response. Unless the request method was HEAD, the representation of the
1597   response &SHOULD; contain a short hypertext note with a hyperlink to
1598   the new URI(s).
1599</t>
1600<t>
1601   If the 301 status code is received in response to a request method
1602   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1603   then the request &MAY; be automatically redirected by the user agent without
1604   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1605   request unless it can be confirmed by the user, since this might
1606   change the conditions under which the request was issued.
1607</t>
1608<x:note>
1609  <t>
1610    <x:h>Note:</x:h> When automatically redirecting a POST request after
1611    receiving a 301 status code, some existing HTTP/1.0 user agents
1612    will erroneously change it into a GET request.
1613  </t>
1614</x:note>
1615</section>
1616
1617<section title="302 Found" anchor="status.302">
1618  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1619  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1620<t>
1621   The target resource resides temporarily under a different URI.
1622   Since the redirection might be altered on occasion, the client &SHOULD;
1623   continue to use the effective request URI for future requests.
1624</t>
1625<t>
1626   The temporary URI &SHOULD; be given by the Location field in the
1627   response. Unless the request method was HEAD, the representation of the
1628   response &SHOULD; contain a short hypertext note with a hyperlink to
1629   the new URI(s).
1630</t>
1631<t>
1632   If the 302 status code is received in response to a request method
1633   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1634   then the request &MAY; be automatically redirected by the user agent without
1635   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1636   request unless it can be confirmed by the user, since this might
1637   change the conditions under which the request was issued.
1638</t>
1639<x:note>
1640  <t>
1641    <x:h>Note:</x:h> HTTP/1.0 (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>)
1642    and the first version of HTTP/1.1 (<xref target="RFC2068" x:fmt="," x:sec ="10.3.3"/>)
1643    specify that the client is not allowed to change the method on the
1644    redirected request.  However, most existing user agent implementations
1645    treat 302 as if it were a 303 response, performing a GET on the Location
1646    field-value regardless of the original request method. Therefore, a
1647    previous version of this specification
1648    (<xref target="RFC2616" x:fmt="," x:sec="10.3.3"/>) has added the
1649    status codes
1650    <xref target="status.303" format="none">303</xref> and
1651    <xref target="status.307" format="none">307</xref> for servers that wish
1652    to make unambiguously clear which kind of reaction is expected of the
1653    client.
1654  </t>
1655</x:note>
1656</section>
1657
1658<section title="303 See Other" anchor="status.303">
1659  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1660  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1661<t>
1662   The server directs the user agent to a different resource, indicated
1663   by a URI in the Location header field, that provides an indirect
1664   response to the original request.  The user agent &MAY; perform a GET
1665   request on the URI in the Location field in order to obtain a
1666   representation corresponding to the response, be redirected again,
1667   or end with an error status.  The Location URI is not a substitute
1668   reference for the effective request URI.
1669</t>
1670<t>
1671   The 303 status code is generally applicable to any HTTP method.  It is
1672   primarily used to allow the output of a POST action to redirect
1673   the user agent to a selected resource, since doing so provides the
1674   information corresponding to the POST response in a form that
1675   can be separately identified, bookmarked, and cached independent
1676   of the original request.
1677</t>
1678<t>
1679   A 303 response to a GET request indicates that the requested
1680   resource does not have a representation of its own that can be
1681   transferred by the server over HTTP.  The Location URI indicates a
1682   resource that is descriptive of the target resource, such that the
1683   follow-on representation might be useful to recipients without
1684   implying that it adequately represents the target resource.
1685   Note that answers to the questions of what can be represented, what
1686   representations are adequate, and what might be a useful description
1687   are outside the scope of HTTP and thus entirely determined by the
1688   URI owner(s).
1689</t>
1690<t>
1691   Except for responses to a HEAD request, the representation of a 303
1692   response &SHOULD; contain a short hypertext note with a hyperlink
1693   to the Location URI.
1694</t>
1695</section>
1696
1697<section title="304 Not Modified" anchor="status.304">
1698  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1699  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1700  <rdf:Description>
1701    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1702  </rdf:Description>
1703<t>
1704   The response to the request has not been modified since the conditions
1705   indicated by the client's conditional GET request, as defined in &status-304;.
1706</t>
1707</section>
1708
1709<section title="305 Use Proxy" anchor="status.305">
1710  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1711  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1712<t>
1713   The 305 status code was defined in a previous version of this specification
1714   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1715</t>
1716</section>
1717
1718<section title="306 (Unused)" anchor="status.306">
1719  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1720  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1721<t>
1722   The 306 status code was used in a previous version of the
1723   specification, is no longer used, and the code is reserved.
1724</t>
1725</section>
1726
1727<section title="307 Temporary Redirect" anchor="status.307">
1728  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1729  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1730<t>
1731   The target resource resides temporarily under a different URI.
1732   Since the redirection can change over time, the client &SHOULD;
1733   continue to use the effective request URI for future requests.
1734</t>
1735<t>
1736   The temporary URI &SHOULD; be given by the Location field in the
1737   response. Unless the request method was HEAD, the representation of the
1738   response &SHOULD; contain a short hypertext note with a hyperlink to
1739   the new URI(s), since many pre-HTTP/1.1 user agents do not
1740   understand the 307 status code. Therefore, the note &SHOULD; contain the
1741   information necessary for a user to repeat the original request on
1742   the new URI.
1743</t>
1744<t>
1745   If the 307 status code is received in response to a request method
1746   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1747   then the request &MAY; be automatically redirected by the user agent without
1748   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1749   request unless it can be confirmed by the user, since this might
1750   change the conditions under which the request was issued.
1751</t>
1752</section>
1753</section>
1754
1755<section title="Client Error 4xx" anchor="status.4xx">
1756<t>
1757   The 4xx class of status code is intended for cases in which the
1758   client seems to have erred. Except when responding to a HEAD request,
1759   the server &SHOULD; include a representation containing an explanation of the
1760   error situation, and whether it is a temporary or permanent
1761   condition. These status codes are applicable to any request method.
1762   User agents &SHOULD; display any included representation to the user.
1763</t>
1764<t>
1765   If the client is sending data, a server implementation using TCP
1766   &SHOULD; be careful to ensure that the client acknowledges receipt of
1767   the packet(s) containing the response, before the server closes the
1768   input connection. If the client continues sending data to the server
1769   after the close, the server's TCP stack will send a reset packet to
1770   the client, which might erase the client's unacknowledged input buffers
1771   before they can be read and interpreted by the HTTP application.
1772</t>
1773
1774<section title="400 Bad Request" anchor="status.400">
1775  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1776  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1777<t>
1778   The request could not be understood by the server due to malformed
1779   syntax. The client &SHOULD-NOT; repeat the request without
1780   modifications.
1781</t>
1782</section>
1783
1784<section title="401 Unauthorized" anchor="status.401">
1785  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1786  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1787  <rdf:Description>
1788    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1789  </rdf:Description>
1790<t>
1791   The request requires user authentication (see &status-401;).
1792</t>
1793</section>
1794
1795<section title="402 Payment Required" anchor="status.402">
1796  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1797  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1798<t>
1799   This code is reserved for future use.
1800</t>
1801</section>
1802
1803<section title="403 Forbidden" anchor="status.403">
1804  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1805  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1806<t>
1807   The server understood the request, but is refusing to fulfill it.
1808   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1809   If the request method was not HEAD and the server wishes to make
1810   public why the request has not been fulfilled, it &SHOULD; describe the
1811   reason for the refusal in the representation.  If the server does not wish to
1812   make this information available to the client, the status code 404
1813   (Not Found) can be used instead.
1814</t>
1815</section>
1816
1817<section title="404 Not Found" anchor="status.404">
1818  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1819  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1820<t>
1821   The server has not found anything matching the effective request URI. No
1822   indication is given of whether the condition is temporary or
1823   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1824   knows, through some internally configurable mechanism, that an old
1825   resource is permanently unavailable and has no forwarding address.
1826   This status code is commonly used when the server does not wish to
1827   reveal exactly why the request has been refused, or when no other
1828   response is applicable.
1829</t>
1830</section>
1831
1832<section title="405 Method Not Allowed" anchor="status.405">
1833  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1834  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1835<t>
1836   The method specified in the Request-Line is not allowed for the target
1837   resource. The response &MUST; include an
1838   Allow header field containing a list of valid methods for the requested
1839   resource.
1840</t>
1841</section>
1842
1843<section title="406 Not Acceptable" anchor="status.406">
1844  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1845  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1846<t>
1847   The resource identified by the request is only capable of generating
1848   response representations which have content characteristics not acceptable
1849   according to the accept header fields sent in the request.
1850</t>
1851<t>
1852   Unless it was a HEAD request, the response &SHOULD; include a representation
1853   containing a list of available representation characteristics and location(s)
1854   from which the user or user agent can choose the one most
1855   appropriate. The data format is specified by the media type given
1856   in the Content-Type header field. Depending upon the format and the
1857   capabilities of the user agent, selection of the most appropriate
1858   choice &MAY; be performed automatically. However, this specification
1859   does not define any standard for such automatic selection.
1860</t>
1861<x:note>
1862  <t>
1863    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1864    not acceptable according to the accept header fields sent in the
1865    request. In some cases, this might even be preferable to sending a
1866    406 response. User agents are encouraged to inspect the header fields of
1867    an incoming response to determine if it is acceptable.
1868  </t>
1869</x:note>
1870<t>
1871   If the response could be unacceptable, a user agent &SHOULD;
1872   temporarily stop receipt of more data and query the user for a
1873   decision on further actions.
1874</t>
1875</section>
1876
1877<section title="407 Proxy Authentication Required" anchor="status.407">
1878  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1879  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1880<t>
1881   This code is similar to 401 (Unauthorized), but indicates that the
1882   client must first authenticate itself with the proxy (see &status-407;).
1883</t>
1884</section>
1885
1886<section title="408 Request Timeout" anchor="status.408">
1887  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1888  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1889<t>
1890   The client did not produce a request within the time that the server
1891   was prepared to wait. The client &MAY; repeat the request without
1892   modifications at any later time.
1893</t>
1894</section>
1895
1896<section title="409 Conflict" anchor="status.409">
1897  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1898  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1899<t>
1900   The request could not be completed due to a conflict with the current
1901   state of the resource. This code is only allowed in situations where
1902   it is expected that the user might be able to resolve the conflict
1903   and resubmit the request. The response body &SHOULD; include enough
1904   information for the user to recognize the source of the conflict.
1905   Ideally, the response representation would include enough information for the
1906   user or user agent to fix the problem; however, that might not be
1907   possible and is not required.
1908</t>
1909<t>
1910   Conflicts are most likely to occur in response to a PUT request. For
1911   example, if versioning were being used and the representation being PUT
1912   included changes to a resource which conflict with those made by an
1913   earlier (third-party) request, the server might use the 409 response
1914   to indicate that it can't complete the request. In this case, the
1915   response representation would likely contain a list of the differences
1916   between the two versions in a format defined by the response
1917   Content-Type.
1918</t>
1919</section>
1920
1921<section title="410 Gone" anchor="status.410">
1922  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1923  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1924<t>
1925   The target resource is no longer available at the server and no
1926   forwarding address is known. This condition is expected to be
1927   considered permanent. Clients with link editing capabilities &SHOULD;
1928   delete references to the effective request URI after user approval. If the
1929   server does not know, or has no facility to determine, whether or not
1930   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1931   used instead.
1932</t>
1933<t>
1934   The 410 response is primarily intended to assist the task of web
1935   maintenance by notifying the recipient that the resource is
1936   intentionally unavailable and that the server owners desire that
1937   remote links to that resource be removed. Such an event is common for
1938   limited-time, promotional services and for resources belonging to
1939   individuals no longer working at the server's site. It is not
1940   necessary to mark all permanently unavailable resources as "gone" or
1941   to keep the mark for any length of time &mdash; that is left to the
1942   discretion of the server owner.
1943</t>
1944<t>
1945   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1946   for 410 responses.
1947</t>
1948
1949</section>
1950
1951<section title="411 Length Required" anchor="status.411">
1952  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1953  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1954<t>
1955   The server refuses to accept the request without a defined Content-Length.
1956   The client &MAY; repeat the request if it adds a valid
1957   Content-Length header field containing the length of the message-body
1958   in the request message.
1959</t>
1960</section>
1961
1962<section title="412 Precondition Failed" anchor="status.412">
1963  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1964  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1965  <rdf:Description>
1966    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1967  </rdf:Description>
1968<t>
1969   The precondition given in one or more of the request-header fields
1970   evaluated to false when it was tested on the server, as defined in
1971   &status-412;.
1972</t>
1973</section>
1974
1975<section title="413 Request Entity Too Large" anchor="status.413">
1976  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1977  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1978<t>
1979   The server is refusing to process a request because the request
1980   representation is larger than the server is willing or able to process. The
1981   server &MAY; close the connection to prevent the client from continuing
1982   the request.
1983</t>
1984<t>
1985   If the condition is temporary, the server &SHOULD; include a Retry-After
1986   header field to indicate that it is temporary and after what
1987   time the client &MAY; try again.
1988</t>
1989</section>
1990
1991<section title="414 URI Too Long" anchor="status.414">
1992  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1993  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1994<t>
1995   The server is refusing to service the request because the effective request URI
1996   is longer than the server is willing to interpret. This rare
1997   condition is only likely to occur when a client has improperly
1998   converted a POST request to a GET request with long query
1999   information, when the client has descended into a URI "black hole" of
2000   redirection (e.g., a redirected URI prefix that points to a suffix of
2001   itself), or when the server is under attack by a client attempting to
2002   exploit security holes present in some servers using fixed-length
2003   buffers for reading or manipulating the effective request URI.
2004</t>
2005</section>
2006
2007<section title="415 Unsupported Media Type" anchor="status.415">
2008  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2009  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2010<t>
2011   The server is refusing to service the request because the request
2012   payload is in a format not supported by this request method on the
2013   target resource.
2014</t>
2015</section>
2016
2017<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2018  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2019  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2020  <rdf:Description>
2021    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2022  </rdf:Description>
2023<t>
2024   The request included a Range request-header field (&header-range;) and none of
2025   the range-specifier values in this field overlap the current extent
2026   of the selected resource. See &status-416;.
2027</t>
2028</section>
2029
2030<section title="417 Expectation Failed" anchor="status.417">
2031  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2032  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2033<t>
2034   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
2035   could not be met by this server, or, if the server is a proxy,
2036   the server has unambiguous evidence that the request could not be met
2037   by the next-hop server.
2038</t>
2039</section>
2040
2041<section title="426 Upgrade Required" anchor="status.426">
2042  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2043  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2044<t>
2045   The request can not be completed without a prior protocol upgrade. This
2046   response &MUST; include an Upgrade header field (&header-upgrade;)
2047   specifying the required protocols.
2048</t>
2049<figure>
2050<preamble>Example:</preamble>
2051<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2052HTTP/1.1 426 Upgrade Required
2053Upgrade: HTTP/2.0
2054Connection: Upgrade
2055
2056</artwork></figure>
2057<t>
2058   The server &SHOULD; include a message body in the 426 response which
2059   indicates in human readable form the reason for the error and describes any
2060   alternative courses which may be available to the user.
2061</t>
2062</section>
2063</section>
2064
2065<section title="Server Error 5xx" anchor="status.5xx">
2066<t>
2067   Response status codes beginning with the digit "5" indicate cases in
2068   which the server is aware that it has erred or is incapable of
2069   performing the request. Except when responding to a HEAD request, the
2070   server &SHOULD; include a representation containing an explanation of the
2071   error situation, and whether it is a temporary or permanent
2072   condition. User agents &SHOULD; display any included representation to the
2073   user. These response codes are applicable to any request method.
2074</t>
2075
2076<section title="500 Internal Server Error" anchor="status.500">
2077  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2078  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2079<t>
2080   The server encountered an unexpected condition which prevented it
2081   from fulfilling the request.
2082</t>
2083</section>
2084
2085<section title="501 Not Implemented" anchor="status.501">
2086  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2087  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2088<t>
2089   The server does not support the functionality required to fulfill the
2090   request. This is the appropriate response when the server does not
2091   recognize the request method and is not capable of supporting it for
2092   any resource.
2093</t>
2094</section>
2095
2096<section title="502 Bad Gateway" anchor="status.502">
2097  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2098  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2099<t>
2100   The server, while acting as a gateway or proxy, received an invalid
2101   response from the upstream server it accessed in attempting to
2102   fulfill the request.
2103</t>
2104</section>
2105
2106<section title="503 Service Unavailable" anchor="status.503">
2107  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2108  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2109<t>
2110   The server is currently unable to handle the request due to a
2111   temporary overloading or maintenance of the server. The implication
2112   is that this is a temporary condition which will be alleviated after
2113   some delay. If known, the length of the delay &MAY; be indicated in a
2114   Retry-After header field. If no Retry-After is given, the client &SHOULD;
2115   handle the response as it would for a 500 response.
2116</t>
2117<x:note>
2118  <t>
2119    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2120    server must use it when becoming overloaded. Some servers might wish
2121    to simply refuse the connection.
2122  </t>
2123</x:note>
2124</section>
2125
2126<section title="504 Gateway Timeout" anchor="status.504">
2127  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2128  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2129<t>
2130   The server, while acting as a gateway or proxy, did not receive a
2131   timely response from the upstream server specified by the URI (e.g.,
2132   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2133   to access in attempting to complete the request.
2134</t>
2135<x:note>
2136  <t>
2137    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2138    return 400 or 500 when DNS lookups time out.
2139  </t>
2140</x:note>
2141</section>
2142
2143<section title="505 HTTP Version Not Supported" anchor="status.505">
2144  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2145  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2146<t>
2147   The server does not support, or refuses to support, the protocol
2148   version that was used in the request message. The server is
2149   indicating that it is unable or unwilling to complete the request
2150   using the same major version as the client, as described in &http-version;,
2151   other than with this error message. The response &SHOULD; contain
2152   a representation describing why that version is not supported and what other
2153   protocols are supported by that server.
2154</t>
2155
2156</section>
2157</section>
2158</section>
2159
2160
2161<section title="Header Field Definitions" anchor="header.fields">
2162<t>
2163   This section defines the syntax and semantics of HTTP/1.1 header fields
2164   related to request and response semantics.
2165</t>
2166
2167<section title="Allow" anchor="header.allow">
2168  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2169  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2170  <x:anchor-alias value="Allow"/>
2171  <x:anchor-alias value="Allow-v"/>
2172<t>
2173   The "Allow" response-header field lists the set of methods advertised as
2174   supported by the target resource. The purpose of this field is strictly to
2175   inform the recipient of valid request methods associated with the resource.
2176</t>
2177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/>
2178  <x:ref>Allow</x:ref>   = "Allow" ":" <x:ref>OWS</x:ref> <x:ref>Allow-v</x:ref>
2179  <x:ref>Allow-v</x:ref> = #<x:ref>Method</x:ref>
2180</artwork></figure>
2181<t>
2182   Example of use:
2183</t>
2184<figure><artwork type="example">
2185  Allow: GET, HEAD, PUT
2186</artwork></figure>
2187<t>
2188   The actual set of allowed methods is defined by the origin server at the
2189   time of each request.
2190</t>
2191<t>
2192   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2193   understand all the methods specified in order to handle them according to
2194   the generic message handling rules.
2195</t>
2196</section>
2197
2198<section title="Expect" anchor="header.expect">
2199  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2200  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2201  <x:anchor-alias value="Expect"/>
2202  <x:anchor-alias value="Expect-v"/>
2203  <x:anchor-alias value="expectation"/>
2204  <x:anchor-alias value="expectation-extension"/>
2205  <x:anchor-alias value="expect-params"/>
2206<t>
2207   The "Expect" request-header field is used to indicate that particular
2208   server behaviors are required by the client.
2209</t>
2210<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"/>
2211  <x:ref>Expect</x:ref>       = "Expect" ":" <x:ref>OWS</x:ref> <x:ref>Expect-v</x:ref>
2212  <x:ref>Expect-v</x:ref>     = 1#<x:ref>expectation</x:ref>
2213 
2214  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2215  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2216                           *<x:ref>expect-params</x:ref> ]
2217  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2218</artwork></figure>
2219<t>
2220   A server that does not understand or is unable to comply with any of
2221   the expectation values in the Expect field of a request &MUST; respond
2222   with appropriate error status code. The server &MUST; respond with a 417
2223   (Expectation Failed) status code if any of the expectations cannot be met
2224   or, if there are other problems with the request, some other 4xx
2225   status code.
2226</t>
2227<t>
2228   This header field is defined with extensible syntax to allow for
2229   future extensions. If a server receives a request containing an
2230   Expect field that includes an expectation-extension that it does not
2231   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2232</t>
2233<t>
2234   Comparison of expectation values is case-insensitive for unquoted
2235   tokens (including the 100-continue token), and is case-sensitive for
2236   quoted-string expectation-extensions.
2237</t>
2238<t>
2239   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2240   return a 417 (Expectation Failed) status code if it receives a request
2241   with an expectation that it cannot meet. However, the Expect
2242   request-header field itself is end-to-end; it &MUST; be forwarded if the
2243   request is forwarded.
2244</t>
2245<t>
2246   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2247   Expect header field.
2248</t>
2249<t>
2250   See &use100; for the use of the 100 (Continue) status code.
2251</t>
2252</section>
2253
2254<section title="From" anchor="header.from">
2255  <iref primary="true" item="From header field" x:for-anchor=""/>
2256  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2257  <x:anchor-alias value="From"/>
2258  <x:anchor-alias value="From-v"/>
2259  <x:anchor-alias value="mailbox"/>
2260<t>
2261   The "From" request-header field, if given, &SHOULD; contain an Internet
2262   e-mail address for the human user who controls the requesting user
2263   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2264   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2265</t>
2266<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/>
2267  <x:ref>From</x:ref>    = "From" ":" <x:ref>OWS</x:ref> <x:ref>From-v</x:ref>
2268  <x:ref>From-v</x:ref>  = <x:ref>mailbox</x:ref>
2269 
2270  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2271</artwork></figure>
2272<t>
2273   An example is:
2274</t>
2275<figure><artwork type="example">
2276  From: webmaster@example.org
2277</artwork></figure>
2278<t>
2279   This header field &MAY; be used for logging purposes and as a means for
2280   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2281   be used as an insecure form of access protection. The interpretation
2282   of this field is that the request is being performed on behalf of the
2283   person given, who accepts responsibility for the method performed. In
2284   particular, robot agents &SHOULD; include this header field so that the
2285   person responsible for running the robot can be contacted if problems
2286   occur on the receiving end.
2287</t>
2288<t>
2289   The Internet e-mail address in this field &MAY; be separate from the
2290   Internet host which issued the request. For example, when a request
2291   is passed through a proxy the original issuer's address &SHOULD; be
2292   used.
2293</t>
2294<t>
2295   The client &SHOULD-NOT;  send the From header field without the user's
2296   approval, as it might conflict with the user's privacy interests or
2297   their site's security policy. It is strongly recommended that the
2298   user be able to disable, enable, and modify the value of this field
2299   at any time prior to a request.
2300</t>
2301</section>
2302
2303<section title="Location" anchor="header.location">
2304  <iref primary="true" item="Location header field" x:for-anchor=""/>
2305  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2306  <x:anchor-alias value="Location"/>
2307  <x:anchor-alias value="Location-v"/>
2308<t>
2309   The "Location" response-header field is used to identify a newly created
2310   resource, or to redirect the recipient to a different location for
2311   completion of the request.
2312</t>
2313<t>
2314   For 201 (Created) responses, the Location is the URI of the new resource
2315   which was created by the request. For 3xx responses, the location &SHOULD;
2316   indicate the server's preferred URI for automatic redirection to the
2317   resource.
2318</t>
2319<t>
2320   The field value consists of a single URI-reference. When it has the form
2321   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2322   the final value is computed by resolving it against the effective request
2323   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2324</t>
2325<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/>
2326  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>OWS</x:ref> <x:ref>Location-v</x:ref>
2327  <x:ref>Location-v</x:ref>     = <x:ref>URI-reference</x:ref>
2328</artwork></figure>
2329<figure>
2330<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical WSP below, it's necessary this way for xml2rfc-->
2331<artwork type="example">
2332  Location: http://www.example.org/pub/WWW/People.html#tim
2333</artwork></figure><figure><artwork type="example">  Location: /index.html
2334</artwork></figure>
2335<t>
2336   There are circumstances in which a fragment identifier in a Location URI
2337   would not be appropriate:
2338   <list style="symbols">
2339      <t>With a 201 Created response, because in this usage the Location header
2340      field specifies the URI for the entire created resource.</t>
2341      <t>With 305 Use Proxy.</t>
2342   </list>
2343</t>
2344<x:note>
2345  <t>
2346    <x:h>Note:</x:h> This specification does not define precedence rules
2347    for the case where the original URI, as navigated to by the user
2348    agent, and the Location header field value both contain fragment
2349    identifiers. Thus be aware that including fragment identifiers might
2350    inconvenience anyone relying on the semantics of the original URI's
2351    fragment identifier.
2352  </t>
2353</x:note>
2354<x:note>
2355  <t>
2356    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2357    from Location in that the Content-Location identifies the most specific
2358    resource corresponding to the enclosed representation.
2359    It is therefore possible for a response to contain header fields for
2360    both Location and Content-Location.
2361  </t>
2362</x:note>
2363</section>
2364
2365<section title="Max-Forwards" anchor="header.max-forwards">
2366  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2367  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2368  <x:anchor-alias value="Max-Forwards"/>
2369  <x:anchor-alias value="Max-Forwards-v"/>
2370<t>
2371   The "Max-Forwards" request-header field provides a mechanism with the
2372   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2373   methods to limit the number of times that the request is forwarded by
2374   proxies or gateways. This can be useful when the client is attempting to
2375   trace a request which appears to be failing or looping in mid-chain.
2376</t>
2377<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/>
2378  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" <x:ref>OWS</x:ref> <x:ref>Max-Forwards-v</x:ref>
2379  <x:ref>Max-Forwards-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2380</artwork></figure>
2381<t>
2382   The Max-Forwards value is a decimal integer indicating the remaining
2383   number of times this request message can be forwarded.
2384</t>
2385<t>
2386   Each proxy or gateway recipient of a TRACE or OPTIONS request
2387   containing a Max-Forwards header field &MUST; check and update its
2388   value prior to forwarding the request. If the received value is zero
2389   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2390   respond as the final recipient. If the received Max-Forwards value is
2391   greater than zero, then the forwarded message &MUST; contain an updated
2392   Max-Forwards field with a value decremented by one (1).
2393</t>
2394<t>
2395   The Max-Forwards header field &MAY; be ignored for all other request
2396   methods.
2397</t>
2398</section>
2399
2400<section title="Referer" anchor="header.referer">
2401  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2402  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2403  <x:anchor-alias value="Referer"/>
2404  <x:anchor-alias value="Referer-v"/>
2405<t>
2406   The "Referer" [sic] request-header field allows the client to specify the
2407   URI of the resource from which the effective request URI was obtained (the
2408   "referrer", although the header field is misspelled.).
2409</t>
2410<t>
2411   The Referer header field allows servers to generate lists of back-links to
2412   resources for interest, logging, optimized caching, etc. It also allows
2413   obsolete or mistyped links to be traced for maintenance. Some servers use
2414   Referer as a means of controlling where they allow links from (so-called
2415   "deep linking"), but legitimate requests do not always
2416   contain a Referer header field.
2417</t>
2418<t>
2419   If the effective request URI was obtained from a source that does not have its own
2420   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2421   sent with the value "about:blank", or not be sent at all. Note that this
2422   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2423</t>
2424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/>
2425  <x:ref>Referer</x:ref>        = "Referer" ":" <x:ref>OWS</x:ref> <x:ref>Referer-v</x:ref>
2426  <x:ref>Referer-v</x:ref>      = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2427</artwork></figure>
2428<t>
2429   Example:
2430</t>
2431<figure><artwork type="example">
2432  Referer: http://www.example.org/hypertext/Overview.html
2433</artwork></figure>
2434<t>
2435   If the field value is a relative URI, it &SHOULD; be interpreted
2436   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2437   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2438</t>
2439</section>
2440
2441<section title="Retry-After" anchor="header.retry-after">
2442  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2443  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2444  <x:anchor-alias value="Retry-After"/>
2445  <x:anchor-alias value="Retry-After-v"/>
2446<t>
2447   The response-header "Retry-After" field can be used with a 503 (Service
2448   Unavailable) response to indicate how long the service is expected to
2449   be unavailable to the requesting client. This field &MAY; also be used
2450   with any 3xx (Redirection) response to indicate the minimum time the
2451   user-agent is asked wait before issuing the redirected request.
2452</t>
2453<t>
2454   The value of this field can be either an HTTP-date or an integer number
2455   of seconds (in decimal) after the time of the response.
2456</t>
2457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/>
2458  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" <x:ref>OWS</x:ref> <x:ref>Retry-After-v</x:ref>
2459  <x:ref>Retry-After-v</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2460</artwork></figure>
2461<t anchor="rule.delta-seconds">
2462  <x:anchor-alias value="delta-seconds"/>
2463   Time spans are non-negative decimal integers, representing time in
2464   seconds.
2465</t>
2466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2467  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2468</artwork></figure>
2469<t>
2470   Two examples of its use are
2471</t>
2472<figure><artwork type="example">
2473  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2474  Retry-After: 120
2475</artwork></figure>
2476<t>
2477   In the latter example, the delay is 2 minutes.
2478</t>
2479</section>
2480
2481<section title="Server" anchor="header.server">
2482  <iref primary="true" item="Server header field" x:for-anchor=""/>
2483  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2484  <x:anchor-alias value="Server"/>
2485  <x:anchor-alias value="Server-v"/>
2486<t>
2487   The "Server" response-header field contains information about the
2488   software used by the origin server to handle the request.
2489</t>
2490<t>
2491   The field can contain multiple product tokens (&product-tokens;) and
2492   comments (&header-fields;) identifying the server and any significant
2493   subproducts. The product tokens are listed in order of their significance
2494   for identifying the application.
2495</t>
2496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/>
2497  <x:ref>Server</x:ref>         = "Server" ":" <x:ref>OWS</x:ref> <x:ref>Server-v</x:ref>
2498  <x:ref>Server-v</x:ref>       = <x:ref>product</x:ref>
2499                   *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2500</artwork></figure>
2501<t>
2502   Example:
2503</t>
2504<figure><artwork type="example">
2505  Server: CERN/3.0 libwww/2.17
2506</artwork></figure>
2507<t>
2508   If the response is being forwarded through a proxy, the proxy
2509   application &MUST-NOT; modify the Server response-header field. Instead, it
2510   &MUST; include a Via field (as described in &header-via;).
2511</t>
2512<x:note>
2513  <t>
2514    <x:h>Note:</x:h> Revealing the specific software version of the server might
2515    allow the server machine to become more vulnerable to attacks
2516    against software that is known to contain security holes. Server
2517    implementors are encouraged to make this field a configurable
2518    option.
2519  </t>
2520</x:note>
2521</section>
2522
2523<section title="User-Agent" anchor="header.user-agent">
2524  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2525  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2526  <x:anchor-alias value="User-Agent"/>
2527  <x:anchor-alias value="User-Agent-v"/>
2528<t>
2529   The "User-Agent" request-header field contains information about the user
2530   agent originating the request. User agents &SHOULD; include this field with
2531   requests.
2532</t>
2533<t>
2534   Typically, it is used for statistical purposes, the tracing of protocol
2535   violations, and tailoring responses to avoid particular user agent
2536   limitations.
2537</t>
2538<t>
2539   The field can contain multiple product tokens (&product-tokens;)
2540   and comments (&header-fields;) identifying the agent and its
2541   significant subproducts. By convention, the product tokens are listed in
2542   order of their significance for identifying the application.
2543</t>
2544<t>
2545   Because this field is usually sent on every request a user agent makes,
2546   implementations are encouraged not to include needlessly fine-grained
2547   detail, and to limit (or even prohibit) the addition of subproducts by third
2548   parties. Overly long and detailed User-Agent field values make requests
2549   larger and can also be used to identify ("fingerprint") the user against
2550   their wishes.
2551</t>
2552<t>
2553   Likewise, implementations are encouraged not to use the product tokens of
2554   other implementations in order to declare compatibility with them, as this
2555   circumvents the purpose of the field. Finally, they are encouraged not to
2556   use comments to identify products; doing so makes the field value more
2557   difficult to parse.
2558</t>
2559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/>
2560  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" <x:ref>OWS</x:ref> <x:ref>User-Agent-v</x:ref>
2561  <x:ref>User-Agent-v</x:ref>   = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2562</artwork></figure>
2563<t>
2564   Example:
2565</t>
2566<figure><artwork type="example">
2567  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2568</artwork></figure>
2569</section>
2570
2571</section>
2572
2573<section title="IANA Considerations" anchor="IANA.considerations">
2574
2575<section title="Method Registry" anchor="method.registration">
2576<t>
2577  The registration procedure for HTTP request methods is defined by
2578  <xref target="method.registry"/> of this document.
2579</t>
2580<t>
2581   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2582   and be populated with the registrations below:
2583</t>
2584<?BEGININC p2-semantics.iana-methods ?>
2585<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2586<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2587   <ttcol>Method</ttcol>
2588   <ttcol>Safe</ttcol>
2589   <ttcol>Reference</ttcol>
2590   <c>CONNECT</c>
2591   <c>no</c>
2592   <c>
2593      <xref target="CONNECT"/>
2594   </c>
2595   <c>DELETE</c>
2596   <c>no</c>
2597   <c>
2598      <xref target="DELETE"/>
2599   </c>
2600   <c>GET</c>
2601   <c>yes</c>
2602   <c>
2603      <xref target="GET"/>
2604   </c>
2605   <c>HEAD</c>
2606   <c>yes</c>
2607   <c>
2608      <xref target="HEAD"/>
2609   </c>
2610   <c>OPTIONS</c>
2611   <c>yes</c>
2612   <c>
2613      <xref target="OPTIONS"/>
2614   </c>
2615   <c>POST</c>
2616   <c>no</c>
2617   <c>
2618      <xref target="POST"/>
2619   </c>
2620   <c>PUT</c>
2621   <c>no</c>
2622   <c>
2623      <xref target="PUT"/>
2624   </c>
2625   <c>TRACE</c>
2626   <c>yes</c>
2627   <c>
2628      <xref target="TRACE"/>
2629   </c>
2630</texttable>
2631<!--(END)-->
2632<?ENDINC p2-semantics.iana-methods ?>
2633</section>
2634
2635<section title="Status Code Registry" anchor="status.code.registration">
2636<t>
2637   The registration procedure for HTTP Status Codes &mdash; previously defined
2638   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2639   by <xref target="status.code.registry"/> of this document.
2640</t>
2641<t>
2642   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2643   shall be updated with the registrations below:
2644</t>
2645<?BEGININC p2-semantics.iana-status-codes ?>
2646<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2647<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2648   <ttcol>Value</ttcol>
2649   <ttcol>Description</ttcol>
2650   <ttcol>Reference</ttcol>
2651   <c>100</c>
2652   <c>Continue</c>
2653   <c>
2654      <xref target="status.100"/>
2655   </c>
2656   <c>101</c>
2657   <c>Switching Protocols</c>
2658   <c>
2659      <xref target="status.101"/>
2660   </c>
2661   <c>200</c>
2662   <c>OK</c>
2663   <c>
2664      <xref target="status.200"/>
2665   </c>
2666   <c>201</c>
2667   <c>Created</c>
2668   <c>
2669      <xref target="status.201"/>
2670   </c>
2671   <c>202</c>
2672   <c>Accepted</c>
2673   <c>
2674      <xref target="status.202"/>
2675   </c>
2676   <c>203</c>
2677   <c>Non-Authoritative Information</c>
2678   <c>
2679      <xref target="status.203"/>
2680   </c>
2681   <c>204</c>
2682   <c>No Content</c>
2683   <c>
2684      <xref target="status.204"/>
2685   </c>
2686   <c>205</c>
2687   <c>Reset Content</c>
2688   <c>
2689      <xref target="status.205"/>
2690   </c>
2691   <c>300</c>
2692   <c>Multiple Choices</c>
2693   <c>
2694      <xref target="status.300"/>
2695   </c>
2696   <c>301</c>
2697   <c>Moved Permanently</c>
2698   <c>
2699      <xref target="status.301"/>
2700   </c>
2701   <c>302</c>
2702   <c>Found</c>
2703   <c>
2704      <xref target="status.302"/>
2705   </c>
2706   <c>303</c>
2707   <c>See Other</c>
2708   <c>
2709      <xref target="status.303"/>
2710   </c>
2711   <c>305</c>
2712   <c>Use Proxy</c>
2713   <c>
2714      <xref target="status.305"/>
2715   </c>
2716   <c>306</c>
2717   <c>(Unused)</c>
2718   <c>
2719      <xref target="status.306"/>
2720   </c>
2721   <c>307</c>
2722   <c>Temporary Redirect</c>
2723   <c>
2724      <xref target="status.307"/>
2725   </c>
2726   <c>400</c>
2727   <c>Bad Request</c>
2728   <c>
2729      <xref target="status.400"/>
2730   </c>
2731   <c>402</c>
2732   <c>Payment Required</c>
2733   <c>
2734      <xref target="status.402"/>
2735   </c>
2736   <c>403</c>
2737   <c>Forbidden</c>
2738   <c>
2739      <xref target="status.403"/>
2740   </c>
2741   <c>404</c>
2742   <c>Not Found</c>
2743   <c>
2744      <xref target="status.404"/>
2745   </c>
2746   <c>405</c>
2747   <c>Method Not Allowed</c>
2748   <c>
2749      <xref target="status.405"/>
2750   </c>
2751   <c>406</c>
2752   <c>Not Acceptable</c>
2753   <c>
2754      <xref target="status.406"/>
2755   </c>
2756   <c>407</c>
2757   <c>Proxy Authentication Required</c>
2758   <c>
2759      <xref target="status.407"/>
2760   </c>
2761   <c>408</c>
2762   <c>Request Timeout</c>
2763   <c>
2764      <xref target="status.408"/>
2765   </c>
2766   <c>409</c>
2767   <c>Conflict</c>
2768   <c>
2769      <xref target="status.409"/>
2770   </c>
2771   <c>410</c>
2772   <c>Gone</c>
2773   <c>
2774      <xref target="status.410"/>
2775   </c>
2776   <c>411</c>
2777   <c>Length Required</c>
2778   <c>
2779      <xref target="status.411"/>
2780   </c>
2781   <c>413</c>
2782   <c>Request Entity Too Large</c>
2783   <c>
2784      <xref target="status.413"/>
2785   </c>
2786   <c>414</c>
2787   <c>URI Too Long</c>
2788   <c>
2789      <xref target="status.414"/>
2790   </c>
2791   <c>415</c>
2792   <c>Unsupported Media Type</c>
2793   <c>
2794      <xref target="status.415"/>
2795   </c>
2796   <c>417</c>
2797   <c>Expectation Failed</c>
2798   <c>
2799      <xref target="status.417"/>
2800   </c>
2801   <c>426</c>
2802   <c>Upgrade Required</c>
2803   <c>
2804      <xref target="status.426"/>
2805   </c>
2806   <c>500</c>
2807   <c>Internal Server Error</c>
2808   <c>
2809      <xref target="status.500"/>
2810   </c>
2811   <c>501</c>
2812   <c>Not Implemented</c>
2813   <c>
2814      <xref target="status.501"/>
2815   </c>
2816   <c>502</c>
2817   <c>Bad Gateway</c>
2818   <c>
2819      <xref target="status.502"/>
2820   </c>
2821   <c>503</c>
2822   <c>Service Unavailable</c>
2823   <c>
2824      <xref target="status.503"/>
2825   </c>
2826   <c>504</c>
2827   <c>Gateway Timeout</c>
2828   <c>
2829      <xref target="status.504"/>
2830   </c>
2831   <c>505</c>
2832   <c>HTTP Version Not Supported</c>
2833   <c>
2834      <xref target="status.505"/>
2835   </c>
2836</texttable>
2837<!--(END)-->
2838<?ENDINC p2-semantics.iana-status-codes ?>
2839</section>
2840<section title="Header Field Registration" anchor="header.field.registration">
2841<t>
2842   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
2843   with the permanent registrations below (see <xref target="RFC3864"/>):
2844</t>
2845<?BEGININC p2-semantics.iana-headers ?>
2846<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2847<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2848   <ttcol>Header Field Name</ttcol>
2849   <ttcol>Protocol</ttcol>
2850   <ttcol>Status</ttcol>
2851   <ttcol>Reference</ttcol>
2852
2853   <c>Allow</c>
2854   <c>http</c>
2855   <c>standard</c>
2856   <c>
2857      <xref target="header.allow"/>
2858   </c>
2859   <c>Expect</c>
2860   <c>http</c>
2861   <c>standard</c>
2862   <c>
2863      <xref target="header.expect"/>
2864   </c>
2865   <c>From</c>
2866   <c>http</c>
2867   <c>standard</c>
2868   <c>
2869      <xref target="header.from"/>
2870   </c>
2871   <c>Location</c>
2872   <c>http</c>
2873   <c>standard</c>
2874   <c>
2875      <xref target="header.location"/>
2876   </c>
2877   <c>Max-Forwards</c>
2878   <c>http</c>
2879   <c>standard</c>
2880   <c>
2881      <xref target="header.max-forwards"/>
2882   </c>
2883   <c>Referer</c>
2884   <c>http</c>
2885   <c>standard</c>
2886   <c>
2887      <xref target="header.referer"/>
2888   </c>
2889   <c>Retry-After</c>
2890   <c>http</c>
2891   <c>standard</c>
2892   <c>
2893      <xref target="header.retry-after"/>
2894   </c>
2895   <c>Server</c>
2896   <c>http</c>
2897   <c>standard</c>
2898   <c>
2899      <xref target="header.server"/>
2900   </c>
2901   <c>User-Agent</c>
2902   <c>http</c>
2903   <c>standard</c>
2904   <c>
2905      <xref target="header.user-agent"/>
2906   </c>
2907</texttable>
2908<!--(END)-->
2909<?ENDINC p2-semantics.iana-headers ?>
2910<t>
2911   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2912</t>
2913</section>
2914</section>
2915
2916<section title="Security Considerations" anchor="security.considerations">
2917<t>
2918   This section is meant to inform application developers, information
2919   providers, and users of the security limitations in HTTP/1.1 as
2920   described by this document. The discussion does not include
2921   definitive solutions to the problems revealed, though it does make
2922   some suggestions for reducing security risks.
2923</t>
2924
2925<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2926<t>
2927   Like any generic data transfer protocol, HTTP cannot regulate the
2928   content of the data that is transferred, nor is there any a priori
2929   method of determining the sensitivity of any particular piece of
2930   information within the context of any given request. Therefore,
2931   applications &SHOULD; supply as much control over this information as
2932   possible to the provider of that information. Four header fields are
2933   worth special mention in this context: Server, Via, Referer and From.
2934</t>
2935<t>
2936   Revealing the specific software version of the server might allow the
2937   server machine to become more vulnerable to attacks against software
2938   that is known to contain security holes. Implementors &SHOULD; make the
2939   Server header field a configurable option.
2940</t>
2941<t>
2942   Proxies which serve as a portal through a network firewall &SHOULD;
2943   take special precautions regarding the transfer of header information
2944   that identifies the hosts behind the firewall. In particular, they
2945   &SHOULD; remove, or replace with sanitized versions, any Via fields
2946   generated behind the firewall.
2947</t>
2948<t>
2949   The Referer header field allows reading patterns to be studied and reverse
2950   links drawn. Although it can be very useful, its power can be abused
2951   if user details are not separated from the information contained in
2952   the Referer. Even when the personal information has been removed, the
2953   Referer header field might indicate a private document's URI whose
2954   publication would be inappropriate.
2955</t>
2956<t>
2957   The information sent in the From field might conflict with the user's
2958   privacy interests or their site's security policy, and hence it
2959   &SHOULD-NOT;  be transmitted without the user being able to disable,
2960   enable, and modify the contents of the field. The user &MUST; be able
2961   to set the contents of this field within a user preference or
2962   application defaults configuration.
2963</t>
2964<t>
2965   We suggest, though do not require, that a convenient toggle interface
2966   be provided for the user to enable or disable the sending of From and
2967   Referer information.
2968</t>
2969<t>
2970   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
2971   target="header.server"/>) header fields can sometimes be used to determine
2972   that a specific client or server have a particular security hole which might
2973   be exploited. Unfortunately, this same information is often used for other
2974   valuable purposes for which HTTP currently has no better mechanism.
2975</t>
2976<t>
2977   Furthermore, the User-Agent header field may contain enough entropy to be
2978   used, possibly in conjunction with other material, to uniquely identify the
2979   user.
2980</t>
2981<t>
2982   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
2983   that was sent in request header fields within the body of their response.
2984   Clients &SHOULD; be careful with sensitive information, like Cookies,
2985   Authorization credentials, and other header fields that might be used to
2986   collect data from the client.
2987</t> 
2988</section>
2989
2990<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2991<t>
2992   Because the source of a link might be private information or might
2993   reveal an otherwise private information source, it is strongly
2994   recommended that the user be able to select whether or not the
2995   Referer field is sent. For example, a browser client could have a
2996   toggle switch for browsing openly/anonymously, which would
2997   respectively enable/disable the sending of Referer and From
2998   information.
2999</t>
3000<t>
3001   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3002   HTTP request if the referring page was transferred with a secure
3003   protocol.
3004</t>
3005<t>
3006   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3007   sensitive data because that data will be placed in the request-target. Many
3008   existing servers, proxies, and user agents log or display the request-target
3009   in places where it might be visible to third parties. Such services can
3010   use POST-based form submission instead.
3011</t>
3012</section>
3013
3014<section title="Location Headers and Spoofing" anchor="location.spoofing">
3015<t>
3016   If a single server supports multiple organizations that do not trust
3017   one another, then it &MUST; check the values of Location and Content-Location
3018   header fields in responses that are generated under control of
3019   said organizations to make sure that they do not attempt to
3020   invalidate resources over which they have no authority.
3021</t>
3022</section>
3023
3024<section title="Security Considerations for CONNECT">
3025<t>
3026   Since tunneled data is opaque to the proxy, there are additional
3027   risks to tunneling to other well-known or reserved ports.
3028   A HTTP client CONNECTing to port 25 could relay spam
3029   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3030   access to a small number of known ports.
3031</t>
3032</section>
3033
3034</section>
3035
3036<section title="Acknowledgments" anchor="ack">
3037</section>
3038</middle>
3039<back>
3040
3041<references title="Normative References">
3042
3043<reference anchor="Part1">
3044  <front>
3045    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3046    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3047      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3048      <address><email>fielding@gbiv.com</email></address>
3049    </author>
3050    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3051      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3052      <address><email>jg@freedesktop.org</email></address>
3053    </author>
3054    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3055      <organization abbrev="HP">Hewlett-Packard Company</organization>
3056      <address><email>JeffMogul@acm.org</email></address>
3057    </author>
3058    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3059      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3060      <address><email>henrikn@microsoft.com</email></address>
3061    </author>
3062    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3063      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3064      <address><email>LMM@acm.org</email></address>
3065    </author>
3066    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3067      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3068      <address><email>paulle@microsoft.com</email></address>
3069    </author>
3070    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3071      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3072      <address><email>timbl@w3.org</email></address>
3073    </author>
3074    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3075      <organization abbrev="W3C">World Wide Web Consortium</organization>
3076      <address><email>ylafon@w3.org</email></address>
3077    </author>
3078    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3079      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3080      <address><email>julian.reschke@greenbytes.de</email></address>
3081    </author>
3082    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3083  </front>
3084  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3085  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3086</reference>
3087
3088<reference anchor="Part3">
3089  <front>
3090    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3091    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3092      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3093      <address><email>fielding@gbiv.com</email></address>
3094    </author>
3095    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3096      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3097      <address><email>jg@freedesktop.org</email></address>
3098    </author>
3099    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3100      <organization abbrev="HP">Hewlett-Packard Company</organization>
3101      <address><email>JeffMogul@acm.org</email></address>
3102    </author>
3103    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3104      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3105      <address><email>henrikn@microsoft.com</email></address>
3106    </author>
3107    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3108      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3109      <address><email>LMM@acm.org</email></address>
3110    </author>
3111    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3112      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3113      <address><email>paulle@microsoft.com</email></address>
3114    </author>
3115    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3116      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3117      <address><email>timbl@w3.org</email></address>
3118    </author>
3119    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3120      <organization abbrev="W3C">World Wide Web Consortium</organization>
3121      <address><email>ylafon@w3.org</email></address>
3122    </author>
3123    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3124      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3125      <address><email>julian.reschke@greenbytes.de</email></address>
3126    </author>
3127    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3128  </front>
3129  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3130  <x:source href="p3-payload.xml" basename="p3-payload"/>
3131</reference>
3132
3133<reference anchor="Part4">
3134  <front>
3135    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3136    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3137      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3138      <address><email>fielding@gbiv.com</email></address>
3139    </author>
3140    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3141      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3142      <address><email>jg@freedesktop.org</email></address>
3143    </author>
3144    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3145      <organization abbrev="HP">Hewlett-Packard Company</organization>
3146      <address><email>JeffMogul@acm.org</email></address>
3147    </author>
3148    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3149      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3150      <address><email>henrikn@microsoft.com</email></address>
3151    </author>
3152    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3153      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3154      <address><email>LMM@acm.org</email></address>
3155    </author>
3156    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3157      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3158      <address><email>paulle@microsoft.com</email></address>
3159    </author>
3160    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3161      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3162      <address><email>timbl@w3.org</email></address>
3163    </author>
3164    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3165      <organization abbrev="W3C">World Wide Web Consortium</organization>
3166      <address><email>ylafon@w3.org</email></address>
3167    </author>
3168    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3169      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3170      <address><email>julian.reschke@greenbytes.de</email></address>
3171    </author>
3172    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3173  </front>
3174  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3175  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3176</reference>
3177
3178<reference anchor="Part5">
3179  <front>
3180    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3181    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3182      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3183      <address><email>fielding@gbiv.com</email></address>
3184    </author>
3185    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3186      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3187      <address><email>jg@freedesktop.org</email></address>
3188    </author>
3189    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3190      <organization abbrev="HP">Hewlett-Packard Company</organization>
3191      <address><email>JeffMogul@acm.org</email></address>
3192    </author>
3193    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3194      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3195      <address><email>henrikn@microsoft.com</email></address>
3196    </author>
3197    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3198      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3199      <address><email>LMM@acm.org</email></address>
3200    </author>
3201    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3202      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3203      <address><email>paulle@microsoft.com</email></address>
3204    </author>
3205    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3206      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3207      <address><email>timbl@w3.org</email></address>
3208    </author>
3209    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3210      <organization abbrev="W3C">World Wide Web Consortium</organization>
3211      <address><email>ylafon@w3.org</email></address>
3212    </author>
3213    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3214      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3215      <address><email>julian.reschke@greenbytes.de</email></address>
3216    </author>
3217    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3218  </front>
3219  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3220  <x:source href="p5-range.xml" basename="p5-range"/>
3221</reference>
3222
3223<reference anchor="Part6">
3224  <front>
3225    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3226    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3227      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3228      <address><email>fielding@gbiv.com</email></address>
3229    </author>
3230    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3231      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3232      <address><email>jg@freedesktop.org</email></address>
3233    </author>
3234    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3235      <organization abbrev="HP">Hewlett-Packard Company</organization>
3236      <address><email>JeffMogul@acm.org</email></address>
3237    </author>
3238    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3239      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3240      <address><email>henrikn@microsoft.com</email></address>
3241    </author>
3242    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3243      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3244      <address><email>LMM@acm.org</email></address>
3245    </author>
3246    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3247      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3248      <address><email>paulle@microsoft.com</email></address>
3249    </author>
3250    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3251      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3252      <address><email>timbl@w3.org</email></address>
3253    </author>
3254    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3255      <organization abbrev="W3C">World Wide Web Consortium</organization>
3256      <address><email>ylafon@w3.org</email></address>
3257    </author>
3258    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3259      <address><email>mnot@mnot.net</email></address>
3260    </author>
3261    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3262      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3263      <address><email>julian.reschke@greenbytes.de</email></address>
3264    </author>
3265    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3266  </front>
3267  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3268  <x:source href="p6-cache.xml" basename="p6-cache"/>
3269</reference>
3270
3271<reference anchor="Part7">
3272  <front>
3273    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3274    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3275      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3276      <address><email>fielding@gbiv.com</email></address>
3277    </author>
3278    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3279      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3280      <address><email>jg@freedesktop.org</email></address>
3281    </author>
3282    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3283      <organization abbrev="HP">Hewlett-Packard Company</organization>
3284      <address><email>JeffMogul@acm.org</email></address>
3285    </author>
3286    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3287      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3288      <address><email>henrikn@microsoft.com</email></address>
3289    </author>
3290    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3291      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3292      <address><email>LMM@acm.org</email></address>
3293    </author>
3294    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3296      <address><email>paulle@microsoft.com</email></address>
3297    </author>
3298    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3299      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3300      <address><email>timbl@w3.org</email></address>
3301    </author>
3302    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3303      <organization abbrev="W3C">World Wide Web Consortium</organization>
3304      <address><email>ylafon@w3.org</email></address>
3305    </author>
3306    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3307      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3308      <address><email>julian.reschke@greenbytes.de</email></address>
3309    </author>
3310    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3311  </front>
3312  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3313  <x:source href="p7-auth.xml" basename="p7-auth"/>
3314</reference>
3315
3316<reference anchor="RFC2119">
3317  <front>
3318    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3319    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3320      <organization>Harvard University</organization>
3321      <address><email>sob@harvard.edu</email></address>
3322    </author>
3323    <date month="March" year="1997"/>
3324  </front>
3325  <seriesInfo name="BCP" value="14"/>
3326  <seriesInfo name="RFC" value="2119"/>
3327</reference>
3328
3329<reference anchor="RFC3986">
3330 <front>
3331  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3332  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3333    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3334    <address>
3335       <email>timbl@w3.org</email>
3336       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3337    </address>
3338  </author>
3339  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3340    <organization abbrev="Day Software">Day Software</organization>
3341    <address>
3342      <email>fielding@gbiv.com</email>
3343      <uri>http://roy.gbiv.com/</uri>
3344    </address>
3345  </author>
3346  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3347    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3348    <address>
3349      <email>LMM@acm.org</email>
3350      <uri>http://larry.masinter.net/</uri>
3351    </address>
3352  </author>
3353  <date month='January' year='2005'></date>
3354 </front>
3355 <seriesInfo name="STD" value="66"/>
3356 <seriesInfo name="RFC" value="3986"/>
3357</reference>
3358
3359<reference anchor="RFC5234">
3360  <front>
3361    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3362    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3363      <organization>Brandenburg InternetWorking</organization>
3364      <address>
3365        <email>dcrocker@bbiw.net</email>
3366      </address> 
3367    </author>
3368    <author initials="P." surname="Overell" fullname="Paul Overell">
3369      <organization>THUS plc.</organization>
3370      <address>
3371        <email>paul.overell@thus.net</email>
3372      </address>
3373    </author>
3374    <date month="January" year="2008"/>
3375  </front>
3376  <seriesInfo name="STD" value="68"/>
3377  <seriesInfo name="RFC" value="5234"/>
3378</reference>
3379
3380</references>
3381
3382<references title="Informative References">
3383
3384<reference anchor="RFC1945">
3385  <front>
3386    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3387    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3388      <organization>MIT, Laboratory for Computer Science</organization>
3389      <address><email>timbl@w3.org</email></address>
3390    </author>
3391    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3392      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3393      <address><email>fielding@ics.uci.edu</email></address>
3394    </author>
3395    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3396      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3397      <address><email>frystyk@w3.org</email></address>
3398    </author>
3399    <date month="May" year="1996"/>
3400  </front>
3401  <seriesInfo name="RFC" value="1945"/>
3402</reference>
3403
3404<reference anchor="RFC2068">
3405  <front>
3406    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3407    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3408      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3409      <address><email>fielding@ics.uci.edu</email></address>
3410    </author>
3411    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3412      <organization>MIT Laboratory for Computer Science</organization>
3413      <address><email>jg@w3.org</email></address>
3414    </author>
3415    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3416      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3417      <address><email>mogul@wrl.dec.com</email></address>
3418    </author>
3419    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3420      <organization>MIT Laboratory for Computer Science</organization>
3421      <address><email>frystyk@w3.org</email></address>
3422    </author>
3423    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3424      <organization>MIT Laboratory for Computer Science</organization>
3425      <address><email>timbl@w3.org</email></address>
3426    </author>
3427    <date month="January" year="1997"/>
3428  </front>
3429  <seriesInfo name="RFC" value="2068"/>
3430</reference>
3431
3432<reference anchor="RFC2616">
3433  <front>
3434    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3435    <author initials="R." surname="Fielding" fullname="R. Fielding">
3436      <organization>University of California, Irvine</organization>
3437      <address><email>fielding@ics.uci.edu</email></address>
3438    </author>
3439    <author initials="J." surname="Gettys" fullname="J. Gettys">
3440      <organization>W3C</organization>
3441      <address><email>jg@w3.org</email></address>
3442    </author>
3443    <author initials="J." surname="Mogul" fullname="J. Mogul">
3444      <organization>Compaq Computer Corporation</organization>
3445      <address><email>mogul@wrl.dec.com</email></address>
3446    </author>
3447    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3448      <organization>MIT Laboratory for Computer Science</organization>
3449      <address><email>frystyk@w3.org</email></address>
3450    </author>
3451    <author initials="L." surname="Masinter" fullname="L. Masinter">
3452      <organization>Xerox Corporation</organization>
3453      <address><email>masinter@parc.xerox.com</email></address>
3454    </author>
3455    <author initials="P." surname="Leach" fullname="P. Leach">
3456      <organization>Microsoft Corporation</organization>
3457      <address><email>paulle@microsoft.com</email></address>
3458    </author>
3459    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3460      <organization>W3C</organization>
3461      <address><email>timbl@w3.org</email></address>
3462    </author>
3463    <date month="June" year="1999"/>
3464  </front>
3465  <seriesInfo name="RFC" value="2616"/>
3466</reference>
3467
3468<reference anchor='RFC2817'>
3469  <front>
3470    <title>Upgrading to TLS Within HTTP/1.1</title>
3471    <author initials='R.' surname='Khare' fullname='R. Khare'>
3472      <organization>4K Associates / UC Irvine</organization>
3473      <address><email>rohit@4K-associates.com</email></address>
3474    </author>
3475    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3476      <organization>Agranat Systems, Inc.</organization>
3477      <address><email>lawrence@agranat.com</email></address>
3478    </author>
3479    <date year='2000' month='May' />
3480  </front>
3481  <seriesInfo name='RFC' value='2817' />
3482</reference>
3483
3484<reference anchor='RFC3864'>
3485  <front>
3486    <title>Registration Procedures for Message Header Fields</title>
3487    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3488      <organization>Nine by Nine</organization>
3489      <address><email>GK-IETF@ninebynine.org</email></address>
3490    </author>
3491    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3492      <organization>BEA Systems</organization>
3493      <address><email>mnot@pobox.com</email></address>
3494    </author>
3495    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3496      <organization>HP Labs</organization>
3497      <address><email>JeffMogul@acm.org</email></address>
3498    </author>
3499    <date year='2004' month='September' />
3500  </front>
3501  <seriesInfo name='BCP' value='90' />
3502  <seriesInfo name='RFC' value='3864' />
3503</reference>
3504
3505<reference anchor='RFC5226'>
3506  <front>
3507    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3508    <author initials='T.' surname='Narten' fullname='T. Narten'>
3509      <organization>IBM</organization>
3510      <address><email>narten@us.ibm.com</email></address>
3511    </author>
3512    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3513      <organization>Google</organization>
3514      <address><email>Harald@Alvestrand.no</email></address>
3515    </author>
3516    <date year='2008' month='May' />
3517  </front>
3518  <seriesInfo name='BCP' value='26' />
3519  <seriesInfo name='RFC' value='5226' />
3520</reference>
3521
3522<reference anchor="RFC5322">
3523  <front>
3524    <title>Internet Message Format</title>
3525    <author initials="P." surname="Resnick" fullname="P. Resnick">
3526      <organization>Qualcomm Incorporated</organization>
3527    </author>
3528    <date year="2008" month="October"/>
3529  </front> 
3530  <seriesInfo name="RFC" value="5322"/>
3531</reference>
3532
3533<reference anchor='RFC5789'>
3534  <front>
3535    <title>PATCH Method for HTTP</title>
3536    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3537      <organization>Linden Lab</organization>
3538    </author>
3539    <author initials='J.' surname='Snell' fullname='J. Snell' />
3540    <date year='2010' month='March' />
3541  </front>
3542  <seriesInfo name='RFC' value='5789' />
3543</reference>
3544
3545</references>
3546
3547<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3548<t>
3549  This document takes over the Status Code Registry, previously defined
3550  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3551  (<xref target="status.code.registry"/>)
3552</t>
3553<t>
3554  Clarify definition of POST.
3555  (<xref target="POST"/>)
3556</t>
3557<t>
3558  Remove requirement to handle all Content-* header fields; ban use of
3559  Content-Range with PUT.
3560  (<xref target="PUT"/>)
3561</t>
3562<t>
3563  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3564  (<xref target="CONNECT"/>)
3565</t>
3566<t>
3567  Failed to consider that there are
3568  many other request methods that are safe to automatically redirect,
3569  and further that the user agent is able to make that determination
3570  based on the request method semantics.
3571  (Sections <xref format="counter" target="status.301"/>,
3572  <xref format="counter" target="status.302"/> and
3573  <xref format="counter" target="status.307"/>)
3574</t>
3575<t>
3576  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3577  It used to indicate that the target resource must be accessed through the
3578  proxy given by the Location field. The Location field gave the URI of the
3579  proxy. The recipient was expected to repeat this single request via the proxy.
3580  (<xref target="status.305"/>)
3581</t>
3582<t>
3583  Define status 426 (Upgrade Required) (this was incorporated from
3584  <xref target="RFC2817"/>).
3585  (<xref target="status.426"/>)
3586</t>
3587<t>
3588  Reclassify "Allow" as response header field, removing the option to
3589  specify it in a PUT request.
3590  Relax the server requirement on the contents of the Allow header field and
3591  remove requirement on clients to always trust the header field value.
3592  (<xref target="header.allow"/>)
3593</t>
3594<t>
3595  Correct syntax of Location header field to allow URI references (including
3596  relative references and fragments), as referred symbol "absoluteURI" wasn't
3597  what was expected, and add some clarifications as to when use of fragments
3598  would not be appropriate.
3599  (<xref target="header.location"/>)
3600</t>
3601<t>
3602  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3603  extension methods could have used it as well).
3604  (<xref target="header.max-forwards"/>)
3605</t>
3606<t>
3607  Allow Referer field value of "about:blank" as alternative to not specifying it.
3608  (<xref target="header.referer"/>)
3609</t>
3610<t>
3611  In the description of the Server header field, the Via field
3612  was described as a SHOULD. The requirement was and is stated
3613  correctly in the description of the Via header field in &header-via;.
3614  (<xref target="header.server"/>)
3615</t>
3616</section>
3617
3618<?BEGININC p2-semantics.abnf-appendix ?>
3619<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3620<figure>
3621<artwork type="abnf" name="p2-semantics.parsed-abnf">
3622<x:ref>Accept</x:ref> = &lt;Accept, defined in [Part3], Section 6.1&gt;
3623<x:ref>Accept-Charset</x:ref> = &lt;Accept-Charset, defined in [Part3], Section 6.2&gt;
3624<x:ref>Accept-Encoding</x:ref> = &lt;Accept-Encoding, defined in [Part3], Section 6.3&gt;
3625<x:ref>Accept-Language</x:ref> = &lt;Accept-Language, defined in [Part3], Section 6.4&gt;
3626<x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in [Part5], Section 5.1&gt;
3627<x:ref>Age</x:ref> = &lt;Age, defined in [Part6], Section 3.1&gt;
3628<x:ref>Allow</x:ref> = "Allow:" OWS Allow-v
3629<x:ref>Allow-v</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3630<x:ref>Authorization</x:ref> = &lt;Authorization, defined in [Part7], Section 4.1&gt;
3631
3632<x:ref>ETag</x:ref> = &lt;ETag, defined in [Part4], Section 6.1&gt;
3633<x:ref>Expect</x:ref> = "Expect:" OWS Expect-v
3634<x:ref>Expect-v</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3635
3636<x:ref>From</x:ref> = "From:" OWS From-v
3637<x:ref>From-v</x:ref> = mailbox
3638
3639<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
3640<x:ref>Host</x:ref> = &lt;Host, defined in [Part1], Section 2.6&gt;
3641
3642<x:ref>If-Match</x:ref> = &lt;If-Match, defined in [Part4], Section 6.2&gt;
3643If-Modified-Since =
3644 &lt;If-Modified-Since, defined in [Part4], Section 6.3&gt;
3645<x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in [Part4], Section 6.4&gt;
3646<x:ref>If-Range</x:ref> = &lt;If-Range, defined in [Part5], Section 5.3&gt;
3647If-Unmodified-Since =
3648 &lt;If-Unmodified-Since, defined in [Part4], Section 6.5&gt;
3649
3650<x:ref>Location</x:ref> = "Location:" OWS Location-v
3651<x:ref>Location-v</x:ref> = URI-reference
3652
3653<x:ref>Max-Forwards</x:ref> = "Max-Forwards:" OWS Max-Forwards-v
3654<x:ref>Max-Forwards-v</x:ref> = 1*DIGIT
3655<x:ref>Method</x:ref> = token
3656
3657<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
3658
3659Proxy-Authenticate =
3660 &lt;Proxy-Authenticate, defined in [Part7], Section 4.2&gt;
3661Proxy-Authorization =
3662 &lt;Proxy-Authorization, defined in [Part7], Section 4.3&gt;
3663
3664<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
3665<x:ref>Range</x:ref> = &lt;Range, defined in [Part5], Section 5.4&gt;
3666<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
3667<x:ref>Referer</x:ref> = "Referer:" OWS Referer-v
3668<x:ref>Referer-v</x:ref> = absolute-URI / partial-URI
3669<x:ref>Retry-After</x:ref> = "Retry-After:" OWS Retry-After-v
3670<x:ref>Retry-After-v</x:ref> = HTTP-date / delta-seconds
3671
3672<x:ref>Server</x:ref> = "Server:" OWS Server-v
3673<x:ref>Server-v</x:ref> = product *( RWS ( product / comment ) )
3674<x:ref>Status-Code</x:ref> = 3DIGIT
3675
3676<x:ref>TE</x:ref> = &lt;TE, defined in [Part1], Section 9.5&gt;
3677
3678<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.6&gt;
3679<x:ref>User-Agent</x:ref> = "User-Agent:" OWS User-Agent-v
3680<x:ref>User-Agent-v</x:ref> = product *( RWS ( product / comment ) )
3681
3682<x:ref>Vary</x:ref> = &lt;Vary, defined in [Part6], Section 3.5&gt;
3683
3684WWW-Authenticate =
3685 &lt;WWW-Authenticate, defined in [Part7], Section 4.4&gt;
3686
3687<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
3688
3689<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
3690
3691<x:ref>delta-seconds</x:ref> = 1*DIGIT
3692
3693<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
3694<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
3695<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
3696 *expect-params ]
3697
3698<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3699
3700<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
3701
3702<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
3703<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 6.3&gt;
3704
3705<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
3706
3707<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
3708</artwork>
3709</figure>
3710<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3711; Accept defined but not used
3712; Accept-Charset defined but not used
3713; Accept-Encoding defined but not used
3714; Accept-Language defined but not used
3715; Accept-Ranges defined but not used
3716; Age defined but not used
3717; Allow defined but not used
3718; Authorization defined but not used
3719; ETag defined but not used
3720; Expect defined but not used
3721; From defined but not used
3722; Host defined but not used
3723; If-Match defined but not used
3724; If-Modified-Since defined but not used
3725; If-None-Match defined but not used
3726; If-Range defined but not used
3727; If-Unmodified-Since defined but not used
3728; Location defined but not used
3729; Max-Forwards defined but not used
3730; Proxy-Authenticate defined but not used
3731; Proxy-Authorization defined but not used
3732; Range defined but not used
3733; Reason-Phrase defined but not used
3734; Referer defined but not used
3735; Retry-After defined but not used
3736; Server defined but not used
3737; Status-Code defined but not used
3738; TE defined but not used
3739; User-Agent defined but not used
3740; Vary defined but not used
3741; WWW-Authenticate defined but not used
3742</artwork></figure></section>
3743<?ENDINC p2-semantics.abnf-appendix ?>
3744
3745<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3746
3747<section title="Since RFC 2616">
3748<t>
3749  Extracted relevant partitions from <xref target="RFC2616"/>.
3750</t>
3751</section>
3752
3753<section title="Since draft-ietf-httpbis-p2-semantics-00">
3754<t>
3755  Closed issues:
3756  <list style="symbols"> 
3757    <t>
3758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3759      "Via is a MUST"
3760      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3761    </t>
3762    <t>
3763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3764      "Fragments allowed in Location"
3765      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3766    </t>
3767    <t>
3768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3769      "Safe Methods vs Redirection"
3770      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3771    </t>
3772    <t>
3773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3774      "Revise description of the POST method"
3775      (<eref target="http://purl.org/NET/http-errata#post"/>)
3776    </t>
3777    <t>
3778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3779      "Normative and Informative references"
3780    </t>
3781    <t>
3782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3783      "RFC2606 Compliance"
3784    </t>
3785    <t>
3786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3787      "Informative references"
3788    </t>
3789    <t>
3790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3791      "Redundant cross-references"
3792    </t>
3793  </list>
3794</t>
3795<t>
3796  Other changes:
3797  <list style="symbols"> 
3798    <t>
3799      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3800    </t>
3801  </list>
3802</t>
3803</section>
3804
3805<section title="Since draft-ietf-httpbis-p2-semantics-01">
3806<t>
3807  Closed issues:
3808  <list style="symbols"> 
3809    <t>
3810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3811      "PUT side effects"
3812    </t>
3813    <t>
3814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3815      "Duplicate Host header requirements"
3816    </t>
3817  </list>
3818</t>
3819<t>
3820  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3821  <list style="symbols"> 
3822    <t>
3823      Move "Product Tokens" section (back) into Part 1, as "token" is used
3824      in the definition of the Upgrade header field.
3825    </t>
3826    <t>
3827      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3828    </t>
3829    <t>
3830      Copy definition of delta-seconds from Part6 instead of referencing it.
3831    </t>
3832  </list>
3833</t>
3834</section>
3835
3836<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3837<t>
3838  Closed issues:
3839  <list style="symbols"> 
3840    <t>
3841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3842      "Requiring Allow in 405 responses"
3843    </t>
3844    <t>
3845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3846      "Status Code Registry"
3847    </t>
3848    <t>
3849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3850      "Redirection vs. Location"
3851    </t>
3852    <t>
3853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3854      "Cacheability of 303 response"
3855    </t>
3856    <t>
3857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3858      "305 Use Proxy"
3859    </t>
3860    <t>
3861      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3862      "Classification for Allow header"
3863    </t>
3864    <t>
3865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3866      "PUT - 'store under' vs 'store at'"
3867    </t>
3868  </list>
3869</t>
3870<t>
3871  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3872  <list style="symbols"> 
3873    <t>
3874      Reference RFC 3984, and update header field registrations for headers defined
3875      in this document.
3876    </t>
3877  </list>
3878</t>
3879<t>
3880  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3881  <list style="symbols"> 
3882    <t>
3883      Replace string literals when the string really is case-sensitive (method).
3884    </t>
3885  </list>
3886</t>
3887</section>
3888
3889<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3890<t>
3891  Closed issues:
3892  <list style="symbols"> 
3893    <t>
3894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3895      "OPTIONS request bodies"
3896    </t>
3897    <t>
3898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3899      "Description of CONNECT should refer to RFC2817"
3900    </t>
3901    <t>
3902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3903      "Location Content-Location reference request/response mixup"
3904    </t>
3905  </list>
3906</t>
3907<t>
3908  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3909  <list style="symbols"> 
3910    <t>
3911      Added initial proposal for registration process, plus initial
3912      content (non-HTTP/1.1 methods to be added by a separate specification).
3913    </t>
3914  </list>
3915</t>
3916</section>
3917
3918<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3919<t>
3920  Closed issues:
3921  <list style="symbols"> 
3922    <t>
3923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3924      "Content-*"
3925    </t>
3926    <t>
3927      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3928      "RFC 2822 is updated by RFC 5322"
3929    </t>
3930  </list>
3931</t>
3932<t>
3933  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3934  <list style="symbols"> 
3935    <t>
3936      Use "/" instead of "|" for alternatives.
3937    </t>
3938    <t>
3939      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3940      whitespace ("OWS") and required whitespace ("RWS").
3941    </t>
3942    <t>
3943      Rewrite ABNFs to spell out whitespace rules, factor out
3944      header field value format definitions.
3945    </t>
3946  </list>
3947</t>
3948</section>
3949
3950<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3951<t>
3952  Closed issues:
3953  <list style="symbols"> 
3954    <t>
3955      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3956      "Reason-Phrase BNF"
3957    </t>
3958  </list>
3959</t>
3960<t>
3961  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3962  <list style="symbols"> 
3963    <t>
3964      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3965    </t>
3966  </list>
3967</t>
3968</section>
3969
3970<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3971<t>
3972  Closed issues:
3973  <list style="symbols"> 
3974    <t>
3975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3976      "Clarify when Referer is sent"
3977    </t>
3978    <t>
3979      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3980      "status codes vs methods"
3981    </t>
3982    <t>
3983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3984      "Do not require "updates" relation for specs that register status codes or method names"
3985    </t>
3986  </list>
3987</t>
3988</section>
3989
3990<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
3991<t>
3992  Closed issues:
3993  <list style="symbols"> 
3994    <t>
3995      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
3996      "Idempotency"
3997    </t>
3998    <t>
3999      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4000      "TRACE security considerations"
4001    </t>
4002    <t>
4003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4004      "Clarify rules for determining what entities a response carries"
4005    </t>
4006    <t>
4007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4008      "update note citing RFC 1945 and 2068"
4009    </t>
4010    <t>
4011      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4012      "update note about redirect limit"
4013    </t>
4014    <t>
4015      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4016      "Location header ABNF should use 'URI'"
4017    </t>
4018    <t>
4019      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4020      "fragments in Location vs status 303"
4021    </t>
4022    <t>
4023      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4024      "move IANA registrations for optional status codes"
4025    </t>
4026  </list>
4027</t>
4028<t>
4029  Partly resolved issues:
4030  <list style="symbols"> 
4031    <t>
4032      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4033      "Are OPTIONS and TRACE safe?"
4034    </t>
4035  </list>
4036</t>
4037</section>
4038
4039<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4040<t>
4041  Closed issues:
4042  <list style="symbols"> 
4043    <t>
4044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4045      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4046      status codes when fixing this previously)
4047    </t>
4048  </list>
4049</t>
4050</section>
4051
4052<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4053<t>
4054  Closed issues:
4055  <list style="symbols"> 
4056    <t>
4057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4058      "Fragment combination / precedence during redirects"
4059    </t>
4060  </list>
4061</t>
4062<t>
4063  Partly resolved issues:
4064  <list style="symbols"> 
4065    <t>
4066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4067      "Location header payload handling"
4068    </t>
4069    <t>
4070      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4071      "Term for the requested resource's URI"
4072    </t>
4073  </list>
4074</t>
4075</section>
4076
4077<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4078<t>
4079  Closed issues:
4080  <list style="symbols"> 
4081    <t>
4082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4083      "Clarify 'Requested Variant'"
4084    </t>
4085    <t>
4086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4087      "Clarify entity / representation / variant terminology"
4088    </t>
4089    <t>
4090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4091      "Methods and Caching"
4092    </t>
4093    <t>
4094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4095      "OPTIONS vs Max-Forwards"
4096    </t>
4097    <t>
4098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4099      "Status codes and caching"
4100    </t>
4101    <t>
4102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4103      "consider removing the 'changes from 2068' sections"
4104    </t>
4105  </list>
4106</t>
4107</section>
4108
4109<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4110<t>
4111  Closed issues:
4112  <list style="symbols"> 
4113    <t>
4114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4115      "Considerations for new status codes"
4116    </t>
4117    <t>
4118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4119      "Considerations for new methods"
4120    </t>
4121    <t>
4122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4123      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4124    </t>
4125  </list>
4126</t>
4127</section>
4128
4129<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4130<t>
4131  Closed issues:
4132  <list style="symbols"> 
4133    <t>
4134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4135      "Fragment combination / precedence during redirects" (added warning
4136      about having a fragid on the redirect may cause inconvenience in
4137      some cases)
4138    </t>
4139    <t>
4140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4141      "Content-* vs. PUT"
4142    </t>
4143    <t>
4144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4145      "205 Bodies"
4146    </t>
4147    <t>
4148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4149      "Understanding Content-* on non-PUT requests"
4150    </t>
4151    <t>
4152      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4153      "Content-*"
4154    </t>
4155    <t>
4156      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4157      "Header type defaulting"
4158    </t>
4159    <t>
4160      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4161      "PUT - 'store under' vs 'store at'"
4162    </t>
4163    <t>
4164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4165      "duplicate ABNF for Reason-Phrase"
4166    </t>
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4169      "Note special status of Content-* prefix in header registration procedures"
4170    </t>
4171    <t>
4172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4173      "Max-Forwards vs extension methods"
4174    </t>
4175    <t>
4176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4177      "What is the value space of HTTP status codes?" (actually fixed in
4178      draft-ietf-httpbis-p2-semantics-11)
4179    </t>
4180    <t>
4181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4182      "proxies not supporting certain methods"
4183    </t>
4184    <t>
4185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4186      "Migrate CONNECT from RFC2817 to p2"
4187    </t>
4188    <t>
4189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4190      "Migrate Upgrade details from RFC2817"
4191    </t>
4192    <t>
4193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4194      "PUT side effect: invalidation or just stale?"
4195    </t>
4196    <t>
4197      <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4198      "clarify PUT semantics'"
4199    </t>
4200    <t>
4201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4202      "duplicate ABNF for 'Method'"
4203    </t>
4204    <t>
4205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4206      "untangle ABNFs for header fields"
4207    </t>
4208  </list>
4209</t>
4210</section>
4211
4212</section>
4213
4214</back>
4215</rfc>
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