source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1579

Last change on this file since 1579 was 1579, checked in by fielding@…, 8 years ago

Consolidate request-target under message routing. Simplify the
sections on Request Line and Status Line, since what they contain
is defined elsewhere.

Change request-target size limit to request-line size limit, since
that is how it is implemented in practice.

Add SHOULDs for error handling when the method is too long or
embedded whitespace is sent in the request-target.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 194.2 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 "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
108<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
109<front>
110
111  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
112
113  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
114    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email>fielding@gbiv.com</email>
124      <uri>http://roy.gbiv.com/</uri>
125    </address>
126  </author>
127
128  <author initials="J." surname="Gettys" fullname="Jim Gettys">
129    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
130    <address>
131      <postal>
132        <street>21 Oak Knoll Road</street>
133        <city>Carlisle</city>
134        <region>MA</region>
135        <code>01741</code>
136        <country>USA</country>
137      </postal>
138      <email>jg@freedesktop.org</email>
139      <uri>http://gettys.wordpress.com/</uri>
140    </address>
141  </author>
142 
143  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
144    <organization abbrev="HP">Hewlett-Packard Company</organization>
145    <address>
146      <postal>
147        <street>HP Labs, Large Scale Systems Group</street>
148        <street>1501 Page Mill Road, MS 1177</street>
149        <city>Palo Alto</city>
150        <region>CA</region>
151        <code>94304</code>
152        <country>USA</country>
153      </postal>
154      <email>JeffMogul@acm.org</email>
155    </address>
156  </author>
157
158  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
159    <organization abbrev="Microsoft">Microsoft Corporation</organization>
160    <address>
161      <postal>
162        <street>1 Microsoft Way</street>
163        <city>Redmond</city>
164        <region>WA</region>
165        <code>98052</code>
166        <country>USA</country>
167      </postal>
168      <email>henrikn@microsoft.com</email>
169    </address>
170  </author>
171
172  <author initials="L." surname="Masinter" fullname="Larry Masinter">
173    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
174    <address>
175      <postal>
176        <street>345 Park Ave</street>
177        <city>San Jose</city>
178        <region>CA</region>
179        <code>95110</code>
180        <country>USA</country>
181      </postal>
182      <email>LMM@acm.org</email>
183      <uri>http://larry.masinter.net/</uri>
184    </address>
185  </author>
186 
187  <author initials="P." surname="Leach" fullname="Paul J. Leach">
188    <organization abbrev="Microsoft">Microsoft Corporation</organization>
189    <address>
190      <postal>
191        <street>1 Microsoft Way</street>
192        <city>Redmond</city>
193        <region>WA</region>
194        <code>98052</code>
195      </postal>
196      <email>paulle@microsoft.com</email>
197    </address>
198  </author>
199   
200  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
201    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
202    <address>
203      <postal>
204        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
205        <street>The Stata Center, Building 32</street>
206        <street>32 Vassar Street</street>
207        <city>Cambridge</city>
208        <region>MA</region>
209        <code>02139</code>
210        <country>USA</country>
211      </postal>
212      <email>timbl@w3.org</email>
213      <uri>http://www.w3.org/People/Berners-Lee/</uri>
214    </address>
215  </author>
216
217  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
218    <organization abbrev="W3C">World Wide Web Consortium</organization>
219    <address>
220      <postal>
221        <street>W3C / ERCIM</street>
222        <street>2004, rte des Lucioles</street>
223        <city>Sophia-Antipolis</city>
224        <region>AM</region>
225        <code>06902</code>
226        <country>France</country>
227      </postal>
228      <email>ylafon@w3.org</email>
229      <uri>http://www.raubacapeu.net/people/yves/</uri>
230    </address>
231  </author>
232
233  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
234    <organization abbrev="greenbytes">greenbytes GmbH</organization>
235    <address>
236      <postal>
237        <street>Hafenweg 16</street>
238        <city>Muenster</city><region>NW</region><code>48155</code>
239        <country>Germany</country>
240      </postal>
241      <phone>+49 251 2807760</phone>
242      <facsimile>+49 251 2807761</facsimile>
243      <email>julian.reschke@greenbytes.de</email>
244      <uri>http://greenbytes.de/tech/webdav/</uri>
245    </address>
246  </author>
247
248  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
249  <workgroup>HTTPbis Working Group</workgroup>
250
251<abstract>
252<t>
253   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
254   distributed, collaborative, hypertext information systems. HTTP has been in
255   use by the World Wide Web global information initiative since 1990. This
256   document is Part 2 of the seven-part specification that defines the protocol
257   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
258</t>
259<t>
260   Part 2 defines the semantics of HTTP messages as expressed by request
261   methods, request header fields, response status codes, and response header
262   fields.
263</t>
264</abstract>
265
266<note title="Editorial Note (To be removed by RFC Editor)">
267  <t>
268    Discussion of this draft should take place on the HTTPBIS working group
269    mailing list (ietf-http-wg@w3.org), which is archived at
270    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
271  </t>
272  <t>
273    The current issues list is at
274    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
275    documents (including fancy diffs) can be found at
276    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
277  </t>
278  <t>
279    The changes in this draft are summarized in <xref target="changes.since.18"/>.
280  </t>
281</note>
282</front>
283<middle>
284<section title="Introduction" anchor="introduction">
285<t>
286   This document defines HTTP/1.1 request and response semantics.  Each HTTP
287   message, as defined in &messaging;, is in the form of either a request or
288   a response.  An HTTP server listens on a connection for HTTP requests and
289   responds to each request, in the order received on that connection, with
290   one or more HTTP response messages.  This document defines the commonly
291   agreed upon semantics of the HTTP uniform interface, the intentions defined
292   by each request method, and the various response messages that might be
293   expected as a result of applying that method to the target resource.
294</t>
295<t>
296   This document is currently disorganized in order to minimize the changes
297   between drafts and enable reviewers to see the smaller errata changes.
298   A future draft will reorganize the sections to better reflect the content.
299   In particular, the sections will be ordered according to the typical
300   processing of an HTTP request message (after message parsing): resource
301   mapping, methods, request modifying header fields, response status,
302   status modifying header fields, and resource metadata.  The current mess
303   reflects how widely dispersed these topics and associated requirements
304   had become in <xref target="RFC2616"/>.
305</t>
306
307<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
308<t>
309   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
310   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
311   document are to be interpreted as described in <xref target="RFC2119"/>.
312</t>
313<t>
314   This document defines conformance criteria for several roles in HTTP
315   communication, including Senders, Recipients, Clients, Servers, User-Agents,
316   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
317   for definitions of these terms.
318</t>
319<t>
320   An implementation is considered conformant if it complies with all of the
321   requirements associated with its role(s). Note that SHOULD-level requirements
322   are relevant here, unless one of the documented exceptions is applicable.
323</t>
324<t>
325   This document also uses ABNF to define valid protocol elements
326   (<xref target="notation"/>). In addition to the prose requirements placed
327   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
328</t>
329<t>
330   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
331   protocol element from an invalid construct. However, HTTP does not define
332   specific error handling mechanisms, except in cases where it has direct
333   impact on security. This is because different uses of the protocol require
334   different error handling strategies; for example, a Web browser may wish to
335   transparently recover from a response where the Location header field
336   doesn't parse according to the ABNF, whereby in a systems control protocol
337   using HTTP, this type of error recovery could lead to dangerous consequences.
338</t>
339</section>
340
341<section title="Syntax Notation" anchor="notation">
342  <x:anchor-alias value="CR"/>
343  <x:anchor-alias value="DIGIT"/>
344  <x:anchor-alias value="LF"/>
345  <x:anchor-alias value="HTAB"/>
346  <x:anchor-alias value="VCHAR"/>
347  <x:anchor-alias value="SP"/>
348<t>
349   This specification uses the Augmented Backus-Naur Form (ABNF) notation
350   of <xref target="RFC5234"/> with the list rule extension defined in
351   &notation;<xref target="collected.abnf"/> shows the collected ABNF
352   with the list rule expanded.
353</t>
354<t>
355  The following core rules are included by
356  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
357  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
358  DIGIT (decimal 0-9), DQUOTE (double quote),
359  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
360  OCTET (any 8-bit sequence of data), SP (space), and
361  VCHAR (any visible US-ASCII character).
362</t>
363
364<section title="Core Rules" anchor="core.rules">
365  <x:anchor-alias value="obs-text"/>
366  <x:anchor-alias value="quoted-string"/>
367  <x:anchor-alias value="token"/>
368  <x:anchor-alias value="BWS"/>
369  <x:anchor-alias value="OWS"/>
370  <x:anchor-alias value="RWS"/>
371<t>
372  The core rules below are defined in <xref target="Part1"/>:
373</t>
374<figure><artwork type="abnf2616">
375  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
376  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
377  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
378  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
379  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
380  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
381</artwork></figure>
382</section>
383
384<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
385  <x:anchor-alias value="absolute-URI"/>
386  <x:anchor-alias value="comment"/>
387  <x:anchor-alias value="partial-URI"/>
388  <x:anchor-alias value="URI-reference"/>
389<t>
390  The ABNF rules below are defined in other parts:
391</t>
392<figure><!--Part1--><artwork type="abnf2616">
393  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
394  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
395  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
396  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
397</artwork></figure>
398</section>
399</section>
400</section>
401
402<section title="Method" anchor="method">
403  <x:anchor-alias value="method"/>
404  <x:anchor-alias value="extension-method"/>
405<t>
406   The method token indicates the request method to be performed on the target
407   resource (&effective-request-uri;). The method is case-sensitive.
408</t>
409<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
410  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
411</artwork></figure>
412<t>
413   The list of methods allowed by a resource can be specified in an
414   Allow header field (<xref target="header.allow"/>). The status code of the response
415   always notifies the client whether a method is currently allowed on a
416   resource, since the set of allowed methods can change dynamically. An
417   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
418   if the method is known by the origin server but not allowed for the
419   resource, and 501 (Not Implemented) if the method is
420   unrecognized or not implemented by the origin server. The methods GET
421   and HEAD &MUST; be supported by all general-purpose servers. All other
422   methods are &OPTIONAL;; however, if the above methods are implemented,
423   they &MUST; be implemented with the same semantics as those specified
424   in <xref target="method.definitions"/>.
425</t>
426
427<section title="Overview of Methods" anchor="overview.of.methods">
428<t>
429  The methods listed below are defined in <xref target="method.definitions"/>.
430</t>
431<texttable align="left">
432  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
433 
434  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
435  <c>GET</c> <c><xref target="GET"/></c>
436  <c>HEAD</c> <c><xref target="HEAD"/></c>
437  <c>POST</c> <c><xref target="POST"/></c>
438  <c>PUT</c> <c><xref target="PUT"/></c>
439  <c>DELETE</c> <c><xref target="DELETE"/></c>
440  <c>TRACE</c> <c><xref target="TRACE"/></c>
441  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
442</texttable>
443<t>
444  Note that this list is not exhaustive &mdash; it does not include request methods defined
445  in other specifications.
446</t>
447</section>
448
449<section title="Method Registry" anchor="method.registry">
450<t>
451  The HTTP Method Registry defines the name space for the method token in the
452  Request line of an HTTP request.
453</t>
454<t>
455  Registrations &MUST; include the following fields:
456  <list style="symbols">
457    <t>Method Name (see <xref target="method"/>)</t>
458    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
459    <t>Pointer to specification text</t>
460  </list>
461</t>
462<t>
463  Values to be added to this name space require IETF Review
464  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
465</t>
466<t>
467  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
468</t>
469
470<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
471<t>
472   When it is necessary to express new semantics for a HTTP request that
473   aren't specific to a single application or media type, and currently defined
474   methods are inadequate, it may be appropriate to register a new method.
475</t>
476<t>
477   HTTP methods are generic; that is, they are potentially applicable to any
478   resource, not just one particular media type, "type" of resource, or
479   application. As such, it is preferred that new HTTP methods be registered
480   in a document that isn't specific to a single application, so that this is
481   clear.
482</t>
483<t>
484   Due to the parsing rules defined in &message-body;, definitions of HTTP
485   methods cannot prohibit the presence of a message body on either the request
486   or the response message (with responses to HEAD requests being the single
487   exception). Definitions of new methods cannot change this rule, but they can
488   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
489</t>
490<t>
491   New method definitions need to indicate whether they are safe (<xref
492   target="safe.methods"/>), what semantics (if any) the request body has,
493   and whether they are idempotent (<xref target="idempotent.methods"/>).
494   They also need to state whether they can be cached (&caching;); in
495   particular what conditions a cache may store the response, and under what
496   conditions such a stored response may be used to satisfy a subsequent
497   request.
498</t>
499</section>
500
501</section>
502</section>
503
504<section title="Header Fields" anchor="header.fields">
505<t>
506   Header fields are key value pairs that can be used to communicate data about
507   the message, its payload, the target resource, or about the connection
508   itself (i.e., control data).  See &header-fields; for a general definition
509   of their syntax.
510</t>
511
512<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
513<t>
514   New header fields are registered using the procedures described in
515   <xref target="RFC3864"/>.
516</t>
517<t>
518   The requirements for header field names are defined in
519   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
520   defining new fields are advised to keep the name as short as practical, and
521   not to prefix them with "X-" if they are to be registered (either
522   immediately or in the future).
523</t>
524<t>
525   New header field values typically have their syntax defined using ABNF
526   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
527   as necessary, and are usually constrained to the range of ASCII characters.
528   Header fields needing a greater range of characters can use an encoding
529   such as the one defined in <xref target="RFC5987"/>.
530</t>
531<t>
532   Because commas (",") are used as a generic delimiter between field-values,
533   they need to be treated with care if they are allowed in the field-value's
534   payload. Typically, components that might contain a comma are protected with
535   double-quotes using the quoted-string ABNF production (&field-components;).
536</t>
537<t>
538   For example, a textual date and a URI (either of which might contain a comma)
539   could be safely carried in field-values like these:
540</t>
541<figure><artwork type="example">
542  Example-URI-Field: "http://example.com/a.html,foo",
543                     "http://without-a-comma.example.com/"
544  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
545</artwork></figure>
546<t>
547   Note that double quote delimiters almost always are used with the
548   quoted-string production; using a different syntax inside double quotes
549   will likely cause unnecessary confusion.
550</t>
551<t>
552   Many header fields use a format including (case-insensitively) named
553   parameters (for instance, Content-Type, defined in &header-content-type;).
554   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
555   parameter value enables recipients to use existing parser components. When
556   allowing both forms, the meaning of a parameter value ought to be
557   independent of the syntax used for it (for an example, see the notes on
558   parameter handling for media types in &media-types;).
559</t>
560<t>
561   Authors of specifications defining new header fields are advised to consider
562   documenting:
563  <list style="symbols">
564    <x:lt>
565      <t>Whether the field is a single value, or whether it can be a list
566      (delimited by commas; see &header-fields;).</t>
567      <t>If it does not use the list syntax, document how to treat messages
568      where the header field occurs multiple times (a sensible default would
569      be to ignore the header field, but this might not always be the right
570      choice).</t>
571      <t>Note that intermediaries and software libraries might combine
572      multiple header field instances into a single one, despite the header
573      field not allowing this. A robust format enables recipients to discover
574      these situations (good example: "Content-Type", as the comma can only
575      appear inside quoted strings; bad example: "Location", as a comma can
576      occur inside a URI).</t>
577    </x:lt>
578    <x:lt><t>Under what conditions the header field can be used; e.g., only in
579    responses or requests, in all messages, only on responses to a particular
580    request method.</t></x:lt>
581    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
582    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
583    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
584    field's value, insert or delete it.</t></x:lt>
585    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
586    <x:lt><t>Whether the header field is useful or allowable in trailers (see
587    &chunked-encoding;).</t></x:lt>
588    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
589  </list>
590</t>
591</section>
592
593<section title="Request Header Fields" anchor="request.header.fields">
594  <x:anchor-alias value="request-header"/>
595<t>
596   The request header fields allow the client to pass additional
597   information about the request, and about the client itself, to the
598   server. These fields act as request modifiers, with semantics
599   equivalent to the parameters on a programming language method
600   invocation.
601</t>
602<texttable align="left">
603  <ttcol>Header Field Name</ttcol>
604  <ttcol>Defined in...</ttcol>
605
606  <c>Accept</c> <c>&header-accept;</c>
607  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
608  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
609  <c>Accept-Language</c> <c>&header-accept-language;</c>
610  <c>Authorization</c> <c>&header-authorization;</c>
611  <c>Expect</c> <c><xref target="header.expect"/></c>
612  <c>From</c> <c><xref target="header.from"/></c>
613  <c>Host</c> <c>&header-host;</c>
614  <c>If-Match</c> <c>&header-if-match;</c>
615  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
616  <c>If-None-Match</c> <c>&header-if-none-match;</c>
617  <c>If-Range</c> <c>&header-if-range;</c>
618  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
619  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
620  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
621  <c>Range</c> <c>&header-range;</c>
622  <c>Referer</c> <c><xref target="header.referer"/></c>
623  <c>TE</c> <c>&header-te;</c>
624  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
625</texttable>
626</section>
627
628<section title="Response Header Fields" anchor="response.header.fields">
629  <x:anchor-alias value="response-header"/>
630<t>
631   The response header fields allow the server to pass additional
632   information about the response which cannot be placed in the status-line.
633   These header fields give information about the server and about
634   further access to the target resource (&effective-request-uri;).
635</t>
636<texttable align="left">
637  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
638
639  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
640  <c>Age</c> <c>&header-age;</c>
641  <c>Allow</c> <c><xref target="header.allow"/></c>
642  <c>Date</c> <c><xref target="header.date"/></c>
643  <c>ETag</c> <c>&header-etag;</c>
644  <c>Location</c> <c><xref target="header.location"/></c>
645  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
646  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
647  <c>Server</c> <c><xref target="header.server"/></c>
648  <c>Vary</c> <c>&header-vary;</c>
649  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
650</texttable>
651</section>
652
653</section>
654
655<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
656  <x:anchor-alias value="reason-phrase"/>
657  <x:anchor-alias value="status-code"/>
658  <x:anchor-alias value="extension-code"/>
659<t>
660   The status-code element is a 3-digit integer result code of the attempt to
661   understand and satisfy the request.
662</t>
663<t>
664   The reason-phrase is intended to give a short textual description of the
665   status-code and is intended for a human user. The client does not need
666   to examine or display the reason-phrase.
667</t>
668<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"/>
669  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
670  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
671</artwork></figure>
672<t>
673   HTTP status codes are extensible. HTTP applications are not required
674   to understand the meaning of all registered status codes, though such
675   understanding is obviously desirable. However, applications &MUST;
676   understand the class of any status code, as indicated by the first
677   digit, and treat any unrecognized response as being equivalent to the
678   x00 status code of that class, with the exception that an
679   unrecognized response &MUST-NOT; be cached. For example, if an
680   unrecognized status code of 431 is received by the client, it can
681   safely assume that there was something wrong with its request and
682   treat the response as if it had received a 400 status code. In such
683   cases, user agents &SHOULD; present to the user the representation enclosed
684   with the response, since that representation is likely to include human-readable
685   information which will explain the unusual status.
686</t>
687
688<section title="Overview of Status Codes" anchor="overview.of.status.codes">
689<t> 
690   The status codes listed below are defined in <xref target="status.codes"/>
691   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
692   The reason phrases listed here are only recommendations &mdash; they can be
693   replaced by local equivalents without affecting the protocol.
694</t>
695<texttable align="left">
696  <ttcol>status-code</ttcol>
697  <ttcol>reason-phrase</ttcol>
698  <ttcol>Defined in...</ttcol>
699 
700  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
701  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
702
703  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
704  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
705  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
706  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
707  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
708  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
709  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
710
711  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
712  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
713  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
714  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
715  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
716  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
717  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
718
719  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
720  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
721  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
722  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
723  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
724  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
725  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
726  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
727  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
728  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
729  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
730  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
731  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
732  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
733  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
734  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
735  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
736  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
737  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
738
739  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
740  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
741  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
742  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
743  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
744  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
745</texttable>
746<t>
747   Note that this list is not exhaustive &mdash; it does not include
748   extension status codes defined in other specifications.
749</t>
750</section>
751
752<section title="Status Code Registry" anchor="status.code.registry">
753<t>
754  The HTTP Status Code Registry defines the name space for the status-code
755  token in the status-line of an HTTP response.
756</t>
757<t>
758  Values to be added to this name space require IETF Review
759  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
760</t>
761<t>
762  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
763</t>
764
765<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
766<t>
767   When it is necessary to express new semantics for a HTTP response that
768   aren't specific to a single application or media type, and currently defined
769   status codes are inadequate, a new status code can be registered.
770</t>
771<t>
772   HTTP status codes are generic; that is, they are potentially applicable to
773   any resource, not just one particular media type, "type" of resource, or
774   application. As such, it is preferred that new HTTP status codes be
775   registered in a document that isn't specific to a single application, so
776   that this is clear.
777</t>
778<t>
779   Definitions of new HTTP status codes typically explain the request
780   conditions that produce a response containing the status code (e.g.,
781   combinations of request headers and/or method(s)), along with any
782   interactions with response headers (e.g., those that are required, those
783   that modify the semantics of the response).
784</t>
785<t>
786   New HTTP status codes are required to fall under one of the categories
787   defined in <xref target="status.codes"/>. To allow existing parsers to
788   properly handle them, new status codes cannot disallow a response body,
789   although they can mandate a zero-length response body. They can require the
790   presence of one or more particular HTTP response header(s).
791</t>
792<t>
793   Likewise, their definitions can specify that caches are allowed to use
794   heuristics to determine their freshness (see &caching;; by default, it is
795   not allowed), and can define how to determine the resource which they
796   carry a representation for (see <xref
797   target="identifying.response.associated.with.representation"/>; by default,
798   it is anonymous).
799</t>
800</section>
801
802</section>
803
804</section>
805
806<section title="Representation" anchor="representation">
807<t>
808   Request and Response messages &MAY; transfer a representation if not otherwise
809   restricted by the request method or response status code. A representation
810   consists of metadata (representation header fields) and data (representation
811   body).  When a complete or partial representation is enclosed in an HTTP message,
812   it is referred to as the payload of the message. HTTP representations
813   are defined in &payload;.
814</t>
815<t>
816   A representation body is only present in a message when a message body is
817   present, as described in &message-body;. The representation body is obtained
818   from the message body by decoding any Transfer-Encoding that might
819   have been applied to ensure safe and proper transfer of the message.
820</t>
821
822<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
823<t>
824   It is sometimes necessary to determine an identifier for the resource
825   associated with a representation.
826</t>
827<t>
828   An HTTP request representation, when present, is always associated with an
829   anonymous (i.e., unidentified) resource.
830</t>
831<t>
832   In the common case, an HTTP response is a representation of the target
833   resource (see &effective-request-uri;). However, this is not always the
834   case. To determine the URI of the resource a response is associated with,
835   the following rules are used (with the first applicable one being selected):
836</t>
837<t><list style="numbers">
838   <t>If the response status code is 200 or 203 and the request method was GET,
839   the response payload is a representation of the target resource.</t>
840   <t>If the response status code is 204, 206, or 304 and the request method was GET
841   or HEAD, the response payload is a partial representation of the target
842   resource.</t>
843   <t>If the response has a Content-Location header field, and that URI is the same
844   as the effective request URI, the response payload is a representation of the
845   target resource.</t>
846   <t>If the response has a Content-Location header field, and that URI is not the
847   same as the effective request URI, then the response asserts that its
848   payload is a representation of the resource identified by the
849   Content-Location URI. However, such an assertion cannot be trusted unless
850   it can be verified by other means (not defined by HTTP).</t>
851   <t>Otherwise, the response is a representation of an anonymous (i.e.,
852   unidentified) resource.</t>
853</list></t>
854<t>
855  <cref anchor="TODO-req-uri">
856   The comparison function is going to have to be defined somewhere,
857   because we already need to compare URIs for things like cache invalidation.</cref>
858</t>
859</section>
860
861</section>
862
863
864<section title="Method Definitions" anchor="method.definitions">
865<t>
866   The set of common request methods for HTTP/1.1 is defined below. Although
867   this set can be expanded, additional methods cannot be assumed to
868   share the same semantics for separately extended clients and servers.
869</t>
870
871<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
872
873<section title="Safe Methods" anchor="safe.methods">
874<iref item="Safe Methods" primary="true"/>
875<t>
876   Implementors need to be aware that the software represents the user in
877   their interactions over the Internet, and need to allow
878   the user to be aware of any actions they take which might have an
879   unexpected significance to themselves or others.
880</t>
881<t>
882   In particular, the convention has been established that the GET, HEAD,
883   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
884   of taking an action other than retrieval. These request methods ought
885   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
886   This allows user agents to represent other methods, such as POST, PUT
887   and DELETE, in a special way, so that the user is made aware of the
888   fact that a possibly unsafe action is being requested.
889</t>
890<t>
891   Naturally, it is not possible to ensure that the server does not
892   generate side-effects as a result of performing a GET request; in
893   fact, some dynamic resources consider that a feature. The important
894   distinction here is that the user did not request the side-effects,
895   so therefore cannot be held accountable for them.
896</t>
897</section>
898
899<section title="Idempotent Methods" anchor="idempotent.methods">
900<iref item="Idempotent Methods" primary="true"/>
901<t>
902   Request methods can also have the property of "idempotence" in that,
903   aside from error or expiration issues, the intended effect of multiple
904   identical requests is the same as for a single request.
905   PUT, DELETE, and all safe request methods are idempotent.
906   It is important to note that idempotence refers only to changes
907   requested by the client: a server is free to change its state due
908   to multiple requests for the purpose of tracking those requests,
909   versioning of results, etc.
910</t>
911</section>
912</section>
913
914<section title="OPTIONS" anchor="OPTIONS">
915  <rdf:Description>
916    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
917  </rdf:Description>
918  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
919  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
920<t>
921   The OPTIONS method requests information about the
922   communication options available on the request/response chain
923   identified by the effective request URI. This method allows a client to
924   determine the options and/or requirements associated with a resource,
925   or the capabilities of a server, without implying a resource action
926   or initiating a resource retrieval.
927</t>
928<t>
929   Responses to the OPTIONS method are not cacheable.
930</t>
931<t>
932   If the OPTIONS request includes a message body (as indicated by the
933   presence of Content-Length or Transfer-Encoding), then the media type
934   &MUST; be indicated by a Content-Type field. Although this
935   specification does not define any use for such a body, future
936   extensions to HTTP might use the OPTIONS body to make more detailed
937   queries on the server.
938</t>
939<t>
940   If the request-target (&request-target;) is an asterisk ("*"),
941   the OPTIONS request is
942   intended to apply to the server in general rather than to a specific
943   resource. Since a server's communication options typically depend on
944   the resource, the "*" request is only useful as a "ping" or "no-op"
945   type of method; it does nothing beyond allowing the client to test
946   the capabilities of the server. For example, this can be used to test
947   a proxy for HTTP/1.1 conformance (or lack thereof).
948</t>
949<t>
950   If the request-target is not an asterisk, the OPTIONS request applies
951   only to the options that are available when communicating with that
952   resource.
953</t>
954<t>
955   A 200 response &SHOULD; include any header fields that indicate
956   optional features implemented by the server and applicable to that
957   resource (e.g., Allow), possibly including extensions not defined by
958   this specification. The response body, if any, &SHOULD; also include
959   information about the communication options. The format for such a
960   body is not defined by this specification, but might be defined by
961   future extensions to HTTP. Content negotiation &MAY; be used to select
962   the appropriate response format. If no response body is included, the
963   response &MUST; include a Content-Length field with a field-value of
964   "0".
965</t>
966<t>
967   The Max-Forwards header field &MAY; be used to target a
968   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
969   If no Max-Forwards field is present in the request, then the forwarded
970   request &MUST-NOT; include a Max-Forwards field.
971</t>
972</section>
973
974<section title="GET" anchor="GET">
975  <rdf:Description>
976    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
977  </rdf:Description>
978  <iref primary="true" item="GET method" x:for-anchor=""/>
979  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
980<t>
981   The GET method requests transfer of a current representation of
982   the target resource.
983</t>
984<t>   
985   If the target resource is a data-producing process, it is the
986   produced data which shall be returned as the representation in the response and not
987   the source text of the process, unless that text happens to be the output of
988   the process.
989</t>
990<t>
991   The semantics of the GET method change to a "conditional GET" if the
992   request message includes an If-Modified-Since, If-Unmodified-Since,
993   If-Match, If-None-Match, or If-Range header field. A conditional GET
994   requests that the representation be transferred only under the
995   circumstances described by the conditional header field(s). The
996   conditional GET request is intended to reduce unnecessary network
997   usage by allowing cached representations to be refreshed without requiring
998   multiple requests or transferring data already held by the client.
999</t>
1000<t>
1001   The semantics of the GET method change to a "partial GET" if the
1002   request message includes a Range header field. A partial GET requests
1003   that only part of the representation be transferred, as described in &header-range;.
1004   The partial GET request is intended to reduce unnecessary
1005   network usage by allowing partially-retrieved representations to be
1006   completed without transferring data already held by the client.
1007</t>
1008<t>
1009   Bodies on GET requests have no defined semantics. Note that sending a body
1010   on a GET request might cause some existing implementations to reject the
1011   request.
1012</t>
1013<t>
1014   The response to a GET request is cacheable and &MAY; be used to satisfy
1015   subsequent GET and HEAD requests (see &caching;).
1016</t>
1017<t>
1018   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1019</t>
1020</section>
1021
1022<section title="HEAD" anchor="HEAD">
1023  <rdf:Description>
1024    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1025  </rdf:Description>
1026  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1027  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1028<t>
1029   The HEAD method is identical to GET except that the server &MUST-NOT;
1030   return a message body in the response. The metadata contained
1031   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1032   to the information sent in response to a GET request. This method can
1033   be used for obtaining metadata about the representation implied by the
1034   request without transferring the representation body. This method is
1035   often used for testing hypertext links for validity, accessibility,
1036   and recent modification.
1037</t>
1038<t>
1039   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1040   a subsequent HEAD request. It also has potential side effects on
1041   previously stored responses to GET; see &p6-head;.
1042</t>
1043<t>
1044   Bodies on HEAD requests have no defined semantics. Note that sending a body
1045   on a HEAD request might cause some existing implementations to reject the
1046   request.
1047</t>
1048</section>
1049
1050<section title="POST" anchor="POST">
1051  <iref primary="true" item="POST method" x:for-anchor=""/>
1052  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1053<t>
1054   The POST method requests that the origin server accept the
1055   representation enclosed in the request as data to be processed by the
1056   target resource. POST is designed to allow a uniform method to cover the
1057   following functions:
1058  <list style="symbols">
1059    <t>
1060      Annotation of existing resources;
1061    </t>
1062    <t>
1063        Posting a message to a bulletin board, newsgroup, mailing list,
1064        or similar group of articles;
1065    </t>
1066    <t>
1067        Providing a block of data, such as the result of submitting a
1068        form, to a data-handling process;
1069    </t>
1070    <t>
1071        Extending a database through an append operation.
1072    </t>
1073  </list>
1074</t>
1075<t>
1076   The actual function performed by the POST method is determined by the
1077   server and is usually dependent on the effective request URI.
1078</t>
1079<t>
1080   The action performed by the POST method might not result in a
1081   resource that can be identified by a URI. In this case, either 200
1082   (OK) or 204 (No Content) is the appropriate response status code,
1083   depending on whether or not the response includes a representation that
1084   describes the result.
1085</t>
1086<t>
1087   If a resource has been created on the origin server, the response
1088   &SHOULD; be 201 (Created) and contain a representation which describes the
1089   status of the request and refers to the new resource, and a Location
1090   header field (see <xref target="header.location"/>).
1091</t>
1092<t>
1093   Responses to POST requests are only cacheable when they
1094   include explicit freshness information (see &p6-explicit;). A
1095   cached POST response with a Content-Location header field
1096   (see &header-content-location;) whose value is the effective
1097   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1098</t>
1099<t>
1100   Note that POST caching is not widely implemented.
1101   However, the 303 (See Other) response can be used to direct the
1102   user agent to retrieve a cacheable resource.
1103</t>
1104</section>
1105
1106<section title="PUT" anchor="PUT">
1107  <iref primary="true" item="PUT method" x:for-anchor=""/>
1108  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1109<t>
1110   The PUT method requests that the state of the target resource
1111   be created or replaced with the state defined by the representation
1112   enclosed in the request message payload.  A successful PUT of a given
1113   representation would suggest that a subsequent GET on that same target
1114   resource will result in an equivalent representation being returned in
1115   a 200 (OK) response.  However, there is no guarantee that such a state
1116   change will be observable, since the target resource might be acted
1117   upon by other user agents in parallel, or might be subject to dynamic
1118   processing by the origin server, before any subsequent GET is received.
1119   A successful response only implies that the user agent's intent was
1120   achieved at the time of its processing by the origin server.
1121</t>
1122<t>   
1123   If the target resource does not have a current representation and
1124   the PUT successfully creates one, then the origin server &MUST; inform
1125   the user agent by sending a 201 (Created) response.  If the target
1126   resource does have a current representation and that representation is
1127   successfully modified in accordance with the state of the enclosed
1128   representation, then either a 200 (OK) or 204 (No Content) response
1129   &SHOULD; be sent to indicate successful completion of the request.
1130</t>
1131<t>
1132   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1133   as part of the resource state).
1134</t>
1135<t>
1136   An origin server &SHOULD; verify that the PUT representation is
1137   consistent with any constraints which the server has for the target
1138   resource that cannot or will not be changed by the PUT.  This is
1139   particularly important when the origin server uses internal
1140   configuration information related to the URI in order to set the
1141   values for representation metadata on GET responses.  When a PUT
1142   representation is inconsistent with the target resource, the origin
1143   server &SHOULD; either make them consistent, by transforming the
1144   representation or changing the resource configuration, or respond
1145   with an appropriate error message containing sufficient information
1146   to explain why the representation is unsuitable.  The 409 (Conflict)
1147   or 415 (Unsupported Media Type) status codes are suggested, with the
1148   latter being specific to constraints on Content-Type values.
1149</t>
1150<t>
1151   For example, if the target resource is configured to always have a
1152   Content-Type of "text/html" and the representation being PUT has a
1153   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1154   (a) reconfigure the target resource to reflect the new media type;
1155   (b) transform the PUT representation to a format consistent with that
1156   of the resource before saving it as the new resource state; or,
1157   (c) reject the request with a 415 response indicating that the target
1158   resource is limited to "text/html", perhaps including a link to a
1159   different resource that would be a suitable target for the new
1160   representation.
1161</t>
1162<t>
1163   HTTP does not define exactly how a PUT method affects the state
1164   of an origin server beyond what can be expressed by the intent of
1165   the user agent request and the semantics of the origin server response.
1166   It does not define what a resource might be, in any sense of that
1167   word, beyond the interface provided via HTTP.  It does not define
1168   how resource state is "stored", nor how such storage might change
1169   as a result of a change in resource state, nor how the origin server
1170   translates resource state into representations.  Generally speaking,
1171   all implementation details behind the resource interface are
1172   intentionally hidden by the server.
1173</t>
1174<t>
1175   The fundamental difference between the POST and PUT methods is
1176   highlighted by the different intent for the target resource.
1177   The target resource in a POST request is intended to handle the
1178   enclosed representation as a data-accepting process, such as for
1179   a gateway to some other protocol or a document that accepts annotations.
1180   In contrast, the target resource in a PUT request is intended to
1181   take the enclosed representation as a new or replacement value.
1182   Hence, the intent of PUT is idempotent and visible to intermediaries,
1183   even though the exact effect is only known by the origin server.
1184</t>
1185<t>
1186   Proper interpretation of a PUT request presumes that the user agent
1187   knows what target resource is desired.  A service that is intended
1188   to select a proper URI on behalf of the client, after receiving
1189   a state-changing request, &SHOULD; be implemented using the POST
1190   method rather than PUT.  If the origin server will not make the
1191   requested PUT state change to the target resource and instead
1192   wishes to have it applied to a different resource, such as when the
1193   resource has been moved to a different URI, then the origin server
1194   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1195   then make its own decision regarding whether or not to redirect the
1196   request.
1197</t>
1198<t>
1199   A PUT request applied to the target resource &MAY; have side-effects
1200   on other resources.  For example, an article might have a URI for
1201   identifying "the current version" (a resource) which is separate
1202   from the URIs identifying each particular version (different
1203   resources that at one point shared the same state as the current version
1204   resource).  A successful PUT request on "the current version" URI might
1205   therefore create a new version resource in addition to changing the
1206   state of the target resource, and might also cause links to be added
1207   between the related resources.
1208</t>
1209<t>
1210   An origin server &SHOULD; reject any PUT request that contains a
1211   Content-Range header field, since it might be misinterpreted as
1212   partial content (or might be partial content that is being mistakenly
1213   PUT as a full representation).  Partial content updates are
1214   possible by targeting a separately identified resource with state
1215   that overlaps a portion of the larger resource, or by using a
1216   different method that has been specifically defined for partial
1217   updates (for example, the PATCH method defined in
1218   <xref target="RFC5789"/>).
1219</t>
1220<t>
1221   Responses to the PUT method are not cacheable. If a PUT request passes
1222   through a cache that has one or more stored responses for the effective
1223   request URI, those stored responses will be invalidated (see
1224   &p6-invalid;).
1225</t>
1226</section>
1227
1228<section title="DELETE" anchor="DELETE">
1229  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1230  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1231<t>
1232   The DELETE method requests that the origin server delete the target
1233   resource. This method &MAY; be overridden by
1234   human intervention (or other means) on the origin server. The client cannot
1235   be guaranteed that the operation has been carried out, even if the
1236   status code returned from the origin server indicates that the action
1237   has been completed successfully. However, the server &SHOULD-NOT; 
1238   indicate success unless, at the time the response is given, it
1239   intends to delete the resource or move it to an inaccessible
1240   location.
1241</t>
1242<t>
1243   A successful response &SHOULD; be 200 (OK) if the response includes an
1244   representation describing the status, 202 (Accepted) if the action has not
1245   yet been enacted, or 204 (No Content) if the action has been enacted
1246   but the response does not include a representation.
1247</t>
1248<t>
1249   Bodies on DELETE requests have no defined semantics. Note that sending a body
1250   on a DELETE request might cause some existing implementations to reject the
1251   request.
1252</t>
1253<t>
1254   Responses to the DELETE method are not cacheable. If a DELETE request
1255   passes through a cache that has one or more stored responses for the
1256   effective request URI, those stored responses will be invalidated (see
1257   &p6-invalid;).
1258</t>
1259</section>
1260
1261<section title="TRACE" anchor="TRACE">
1262  <rdf:Description>
1263    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1264  </rdf:Description>
1265  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1266  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1267<t>
1268   The TRACE method requests a remote, application-layer loop-back
1269   of the request message. The final recipient of the request
1270   &SHOULD; reflect the message received back to the client as the
1271   message body of a 200 (OK) response. The final recipient is either the
1272   origin server or the first proxy to receive a Max-Forwards
1273   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1274   A TRACE request &MUST-NOT; include a message body.
1275</t>
1276<t>
1277   TRACE allows the client to see what is being received at the other
1278   end of the request chain and use that data for testing or diagnostic
1279   information. The value of the Via header field (&header-via;) is of
1280   particular interest, since it acts as a trace of the request chain.
1281   Use of the Max-Forwards header field allows the client to limit the
1282   length of the request chain, which is useful for testing a chain of
1283   proxies forwarding messages in an infinite loop.
1284</t>
1285<t>
1286   If the request is valid, the response &SHOULD; have a Content-Type of
1287   "message/http" (see &media-type-message-http;) and contain a message body
1288   that encloses a copy of the entire request message.
1289   Responses to the TRACE method are not cacheable.
1290</t>
1291</section>
1292
1293<section title="CONNECT" anchor="CONNECT">
1294  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1295  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1296<t>
1297   The CONNECT method requests that the proxy establish a tunnel
1298   to the request-target and, if successful, thereafter restrict its behavior
1299   to blind forwarding of packets until the connection is closed.
1300</t>
1301<t>
1302   When using CONNECT, the request-target &MUST; use the authority form
1303   (&request-target;); i.e., the request-target consists of only the
1304   host name and port number of the tunnel destination, separated by a colon.
1305   For example,
1306</t>
1307<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1308CONNECT server.example.com:80 HTTP/1.1
1309Host: server.example.com:80
1310
1311</artwork></figure>
1312<t>
1313   Any successful (2xx) response to a CONNECT request indicates that the
1314   proxy has established a connection to the requested host and port,
1315   and has switched to tunneling the current connection to that server
1316   connection.
1317   The tunneled data from the server begins immediately after the blank line
1318   that concludes the successful response's header block.
1319   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
1320   header fields in a successful response.
1321   A client &MUST; ignore any Content-Length or Transfer-Encoding header
1322   fields received in a successful response.
1323</t>
1324<t>
1325   Any response other than a successful response indicates that the tunnel
1326   has not yet been formed and that the connection remains governed by HTTP.
1327</t>
1328<t>
1329   Proxy authentication might be used to establish the
1330   authority to create a tunnel:
1331</t>
1332<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1333CONNECT server.example.com:80 HTTP/1.1
1334Host: server.example.com:80
1335Proxy-Authorization: basic aGVsbG86d29ybGQ=
1336
1337</artwork></figure>
1338<t>
1339   A message body on a CONNECT request has no defined semantics. Sending a
1340   body on a CONNECT request might cause existing implementations to reject
1341   the request.
1342</t>
1343<t>
1344   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
1345   to server &MAY; be sent immediately after the request (before a response
1346   is received). The usual caveats also apply:
1347   data may be discarded if the eventual response is negative, and the
1348   connection may be reset with no response if more than one TCP segment
1349   is outstanding.
1350</t>
1351<t>
1352   It may be the case that the proxy itself can only reach the requested
1353   origin server through another proxy.  In this case, the first proxy
1354   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1355   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1356   unless it has either a direct or tunnel connection established to the
1357   authority.
1358</t>
1359<t>
1360   If at any point either one of the peers gets disconnected, any
1361   outstanding data that came from that peer will be passed to the other
1362   one, and after that also the other connection will be terminated by
1363   the proxy. If there is outstanding data to that peer undelivered,
1364   that data will be discarded.
1365</t>
1366<t>
1367   An origin server which receives a CONNECT request for itself &MAY;
1368   respond with a 2xx status code to indicate that a connection is
1369   established.  However, most origin servers do not implement CONNECT.
1370</t>
1371</section>
1372</section>
1373
1374
1375<section title="Status Code Definitions" anchor="status.codes">
1376<t>
1377   The first digit of the status-code defines the class of response. The
1378   last two digits do not have any categorization role. There are 5
1379   values for the first digit:
1380  <list style="symbols">
1381    <t>
1382      1xx: Informational - Request received, continuing process
1383    </t>
1384    <t>
1385      2xx: Success - The action was successfully received,
1386        understood, and accepted
1387    </t>
1388    <t>
1389      3xx: Redirection - Further action must be taken in order to
1390        complete the request
1391    </t>
1392    <t>
1393      4xx: Client Error - The request contains bad syntax or cannot
1394        be fulfilled
1395    </t>
1396    <t>
1397      5xx: Server Error - The server failed to fulfill an apparently
1398        valid request
1399    </t>
1400  </list>
1401</t>
1402<t>
1403   Each status-code is described below, including any metadata required
1404   in the response.
1405</t>
1406<t>
1407   For most status codes the response can carry a payload, in which case a
1408   Content-Type header field indicates the payload's media type
1409   (&header-content-type;).
1410</t>
1411
1412<section title="Informational 1xx" anchor="status.1xx">
1413<t>
1414   This class of status code indicates a provisional response,
1415   consisting only of the status-line and optional header fields, and is
1416   terminated by an empty line. There are no required header fields for this
1417   class of status code. Since HTTP/1.0 did not define any 1xx status
1418   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1419   except under experimental conditions.
1420</t>
1421<t>
1422   A client &MUST; be prepared to accept one or more 1xx status responses
1423   prior to a regular response, even if the client does not expect a 100
1424   (Continue) status message. Unexpected 1xx status responses &MAY; be
1425   ignored by a user agent.
1426</t>
1427<t>
1428   Proxies &MUST; forward 1xx responses, unless the connection between the
1429   proxy and its client has been closed, or unless the proxy itself
1430   requested the generation of the 1xx response. (For example, if a
1431   proxy adds a "Expect: 100-continue" field when it forwards a request,
1432   then it need not forward the corresponding 100 (Continue)
1433   response(s).)
1434</t>
1435
1436<section title="100 Continue" anchor="status.100">
1437  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1438  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1439<t>
1440   The client &SHOULD; continue with its request. This interim response is
1441   used to inform the client that the initial part of the request has
1442   been received and has not yet been rejected by the server. The client
1443   &SHOULD; continue by sending the remainder of the request or, if the
1444   request has already been completed, ignore this response. The server
1445   &MUST; send a final response after the request has been completed. See
1446   &use100; for detailed discussion of the use and handling of this
1447   status code.
1448</t>
1449</section>
1450
1451<section title="101 Switching Protocols" anchor="status.101">
1452  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1453  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1454<t>
1455   The server understands and is willing to comply with the client's
1456   request, via the Upgrade message header field (&header-upgrade;), for a
1457   change in the application protocol being used on this connection. The
1458   server will switch protocols to those defined by the response's
1459   Upgrade header field immediately after the empty line which
1460   terminates the 101 response.
1461</t>
1462<t>
1463   The protocol &SHOULD; be switched only when it is advantageous to do
1464   so. For example, switching to a newer version of HTTP is advantageous
1465   over older versions, and switching to a real-time, synchronous
1466   protocol might be advantageous when delivering resources that use
1467   such features.
1468</t>
1469</section>
1470</section>
1471
1472<section title="Successful 2xx" anchor="status.2xx">
1473<t>
1474   This class of status code indicates that the client's request was
1475   successfully received, understood, and accepted.
1476</t>
1477
1478<section title="200 OK" anchor="status.200">
1479  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1480  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1481<t>
1482   The request has succeeded. The payload returned with the response
1483   is dependent on the method used in the request, for example:
1484  <list style="hanging">
1485    <t hangText="GET">
1486      a representation of the target resource is sent in the response;
1487    </t>
1488    <t hangText="HEAD">
1489      the same representation as GET, except without the message body;
1490    </t>
1491    <t hangText="POST">
1492      a representation describing or containing the result of the action;
1493    </t>
1494    <t hangText="TRACE">
1495      a representation containing the request message as received by the
1496      end server.
1497    </t>
1498  </list>
1499</t>
1500<t>
1501   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1502   freshness for 200 responses.
1503</t>
1504</section>
1505
1506<section title="201 Created" anchor="status.201">
1507  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1508  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1509<t>
1510   The request has been fulfilled and has resulted in a new resource being
1511   created.
1512</t>
1513<t>
1514   The newly created resource is typically linked to from the response payload,
1515   with the most relevant URI also being carried in the Location header field.
1516   If the newly created resource's URI is the same as the Effective Request URI,
1517   this information can be omitted (e.g., in the case of a response to a PUT
1518   request). 
1519</t>
1520<t>
1521   The origin server &MUST; create the resource before returning the 201 status
1522   code. If the action cannot be carried out immediately, the server &SHOULD;
1523   respond with 202 (Accepted) response instead.
1524</t>
1525<t>
1526   A 201 response &MAY; contain an ETag response header field indicating
1527   the current value of the entity-tag for the representation of the resource
1528   just created (see &header-etag;).
1529</t>
1530</section>
1531
1532<section title="202 Accepted" anchor="status.202">
1533  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1534  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1535<t>
1536   The request has been accepted for processing, but the processing has
1537   not been completed.  The request might or might not eventually be
1538   acted upon, as it might be disallowed when processing actually takes
1539   place. There is no facility for re-sending a status code from an
1540   asynchronous operation such as this.
1541</t>
1542<t>
1543   The 202 response is intentionally non-committal. Its purpose is to
1544   allow a server to accept a request for some other process (perhaps a
1545   batch-oriented process that is only run once per day) without
1546   requiring that the user agent's connection to the server persist
1547   until the process is completed. The representation returned with this
1548   response &SHOULD; include an indication of the request's current status
1549   and either a pointer to a status monitor or some estimate of when the
1550   user can expect the request to be fulfilled.
1551</t>
1552</section>
1553
1554<section title="203 Non-Authoritative Information" anchor="status.203">
1555  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1556  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1557<t>
1558   The representation in the response has been transformed or otherwise
1559   modified by a transforming proxy (&intermediaries;).  Note that the
1560   behavior of transforming intermediaries is controlled by the no-transform
1561   Cache-Control directive (&header-cache-control;).
1562</t>
1563<t>
1564   This status code is only appropriate when the response status code would
1565   have been 200 (OK) otherwise. When the status code before transformation
1566   would have been different, the 214 Transformation Applied warn-code
1567   (&header-warning;) is appropriate.
1568</t>
1569<t>
1570   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1571   freshness for 203 responses.
1572</t>
1573</section>
1574
1575<section title="204 No Content" anchor="status.204">
1576  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1577  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1578<t>
1579   The 204 (No Content) status code indicates that the server has
1580   successfully fulfilled the request and that there is no additional
1581   content to return in the response payload body.  Metadata in the
1582   response header fields refer to the target resource and its current
1583   representation after the requested action.
1584</t>
1585<t>
1586   For example, if a 204 status code is received in response to a PUT
1587   request and the response contains an ETag header field, then the PUT
1588   was successful and the ETag field-value contains the entity-tag for
1589   the new representation of that target resource.
1590</t>
1591<t>
1592   The 204 response allows a server to indicate that the action has been
1593   successfully applied to the target resource while implying that the
1594   user agent &SHOULD-NOT; traverse away from its current "document view"
1595   (if any).  The server assumes that the user agent will provide some
1596   indication of the success to its user, in accord with its own interface,
1597   and apply any new or updated metadata in the response to the active
1598   representation.
1599</t>
1600<t>
1601   For example, a 204 status code is commonly used with document editing
1602   interfaces corresponding to a "save" action, such that the document
1603   being saved remains available to the user for editing. It is also
1604   frequently used with interfaces that expect automated data transfers
1605   to be prevalent, such as within distributed version control systems.
1606</t>
1607<t>
1608   The 204 response &MUST-NOT; include a message body, and thus is always
1609   terminated by the first empty line after the header fields.
1610</t>
1611</section>
1612
1613<section title="205 Reset Content" anchor="status.205">
1614  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1615  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1616<t>
1617   The server has fulfilled the request and the user agent &SHOULD; reset
1618   the document view which caused the request to be sent. This response
1619   is primarily intended to allow input for actions to take place via
1620   user input, followed by a clearing of the form in which the input is
1621   given so that the user can easily initiate another input action.
1622</t>
1623<t>   
1624   The message body included with the response &MUST; be empty. Note that
1625   receivers still need to parse the response according to the algorithm defined
1626   in &message-body;.
1627</t>
1628</section>
1629</section>
1630
1631<section title="Redirection 3xx" anchor="status.3xx">
1632<t>
1633   This class of status code indicates that further action needs to be
1634   taken by the user agent in order to fulfill the request.  If the required
1635   action involves a subsequent HTTP request, it &MAY; be carried out by the
1636   user agent without interaction with the user if and only if the method used
1637   in the second request is known to be "safe", as defined in
1638   <xref target="safe.methods"/>.
1639</t>
1640<t>
1641   There are several types of redirects:
1642   <list style="numbers">
1643      <x:lt>
1644        <t>
1645          Redirects of the request to another URI, either temporarily or
1646          permanently. The new URI is specified in the Location header field.
1647          In this specification, the status codes 301 (Moved Permanently),
1648          302 (Found), and 307 (Temporary Redirect) fall under this category.
1649        </t>
1650      </x:lt>
1651      <x:lt>
1652        <t>
1653          Redirection to a new location that represents an indirect response to
1654          the request, such as the result of a POST operation to be retrieved
1655          with a subsequent GET request. This is status code 303 (See Other).
1656        </t>
1657      </x:lt>
1658      <x:lt>
1659        <t>
1660          Redirection offering a choice of matching resources for use by
1661          agent-driven content negotiation (&agent-driven-negotiation;). This
1662          is status code 300 (Multiple Choices).
1663        </t>
1664      </x:lt>
1665      <x:lt>
1666        <t>
1667          Other kinds of redirection, such as to a cached result (status code 304
1668          (Not Modified), see &status-304;).
1669        </t>
1670      </x:lt>
1671   </list>
1672</t>
1673<x:note>
1674  <t>
1675    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1676    and 302 (Found) were defined for the first type of redirect, and the second
1677    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1678    However it turned out that web forms using POST expected redirects to change
1679    the operation for the subsequent request to retrieval (GET). To address this
1680    use case, HTTP/1.1 introduced the second type of redirect with the status
1681    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1682    As user agents did not change their behavior to maintain backwards
1683    compatibility, the first revision of HTTP/1.1 added yet another status code,
1684    307 (Temporary Redirect), for which the backwards compatibility problems did
1685    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1686    Over 10 years later, most user agents still do method rewriting for
1687    status codes 301 and 302, therefore this specification makes that behavior
1688    conformant in case the original request was POST.
1689  </t>
1690</x:note>
1691<t>
1692   A Location header field on a 3xx response indicates that a client &MAY;
1693   automatically redirect to the URI provided; see <xref target="header.location"/>.
1694</t>
1695<t>
1696   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1697   automatic redirection needs to done with care, since the redirect might
1698   change the conditions under which the request was issued.
1699</t>
1700<t>
1701   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1702   "infinite" redirection loops).
1703</t>
1704<x:note>
1705  <t>
1706    <x:h>Note:</x:h> An earlier version of this specification recommended a
1707    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1708    Content developers need to be aware that some clients might
1709    implement such a fixed limitation.
1710  </t>
1711</x:note>
1712
1713<section title="300 Multiple Choices" anchor="status.300">
1714  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1715  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1716<t>
1717   The target resource has more than one
1718   representation, each with its own specific location, and agent-driven
1719   negotiation information (&content-negotiation;) is being provided so that
1720   the user (or user agent) can select a preferred representation by
1721   redirecting its request to that location.
1722</t>
1723<t>
1724   Unless it was a HEAD request, the response &SHOULD; include a representation
1725   containing a list of representation metadata and location(s) from
1726   which the user or user agent can choose the one most appropriate. Depending
1727   upon the format and the capabilities of
1728   the user agent, selection of the most appropriate choice &MAY; be
1729   performed automatically. However, this specification does not define
1730   any standard for such automatic selection.
1731</t>
1732<t>
1733   If the server has a preferred choice of representation, it &SHOULD;
1734   include the specific URI for that representation in the Location
1735   field; user agents &MAY; use the Location field value for automatic
1736   redirection.
1737</t>
1738<t>
1739   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1740   freshness for 300 responses.
1741</t>
1742
1743</section>
1744
1745<section title="301 Moved Permanently" anchor="status.301">
1746  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1747  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1748<t>
1749   The target resource has been assigned a new permanent URI and any
1750   future references to this resource &SHOULD; use one of the returned
1751   URIs.  Clients with link editing capabilities ought to automatically
1752   re-link references to the effective request URI to one or more of the new
1753   references returned by the server, where possible.
1754</t>
1755<t>
1756   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1757   freshness for 301 responses.
1758</t>
1759<t>
1760   The new permanent URI &SHOULD; be given by the Location field in the
1761   response. A response payload can contain a short hypertext note with a
1762   hyperlink to the new URI(s).
1763</t>
1764<x:note>
1765  <t>
1766    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1767    request method from POST to GET for the subsequent request. If this
1768    behavior is undesired, status code 307 (Temporary Redirect) can be used
1769    instead.
1770  </t>
1771</x:note>
1772</section>
1773
1774<section title="302 Found" anchor="status.302">
1775  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1776  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1777<t>
1778   The target resource resides temporarily under a different URI.
1779   Since the redirection might be altered on occasion, the client &SHOULD;
1780   continue to use the effective request URI for future requests.
1781</t>
1782<t>
1783   The temporary URI &SHOULD; be given by the Location field in the
1784   response. A response payload can contain a short hypertext note with a
1785   hyperlink to the new URI(s).
1786</t>
1787<x:note>
1788  <t>
1789    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1790    request method from POST to GET for the subsequent request. If this
1791    behavior is undesired, status code 307 (Temporary Redirect) can be used
1792    instead.
1793  </t>
1794</x:note>
1795</section>
1796
1797<section title="303 See Other" anchor="status.303">
1798  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1799  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1800<t>
1801   The 303 status code indicates that the server is redirecting the
1802   user agent to a different resource, as indicated by a URI in the
1803   Location header field, that is intended to provide an indirect
1804   response to the original request.  In order to satisfy the original
1805   request, a user agent &SHOULD; perform a retrieval request using the
1806   Location URI (a GET or HEAD request if using HTTP), which
1807   may itself be redirected further, and present the eventual result as an
1808   answer to the original request.
1809   Note that the new URI in the Location header field is not considered
1810   equivalent to the effective request URI.
1811</t>
1812<t>
1813   This status code is generally applicable to any HTTP method.  It is
1814   primarily used to allow the output of a POST action to redirect
1815   the user agent to a selected resource, since doing so provides the
1816   information corresponding to the POST response in a form that
1817   can be separately identified, bookmarked, and cached independent
1818   of the original request.
1819</t>
1820<t>
1821   A 303 response to a GET request indicates that the requested
1822   resource does not have a representation of its own that can be
1823   transferred by the server over HTTP.  The Location URI indicates a
1824   resource that is descriptive of the target resource, such that the
1825   follow-on representation might be useful to recipients without
1826   implying that it adequately represents the target resource.
1827   Note that answers to the questions of what can be represented, what
1828   representations are adequate, and what might be a useful description
1829   are outside the scope of HTTP and thus entirely determined by the
1830   URI owner(s).
1831</t>
1832<t>
1833   Except for responses to a HEAD request, the representation of a 303
1834   response &SHOULD; contain a short hypertext note with a hyperlink
1835   to the Location URI.
1836</t>
1837</section>
1838
1839<section title="305 Use Proxy" anchor="status.305">
1840  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1841  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1842<t>
1843   The 305 status code was defined in a previous version of this specification
1844   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1845</t>
1846</section>
1847
1848<section title="306 (Unused)" anchor="status.306">
1849  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1850  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1851<t>
1852   The 306 status code was used in a previous version of the
1853   specification, is no longer used, and the code is reserved.
1854</t>
1855</section>
1856
1857<section title="307 Temporary Redirect" anchor="status.307">
1858  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1859  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1860<t>
1861   The target resource resides temporarily under a different URI.
1862   Since the redirection can change over time, the client &SHOULD;
1863   continue to use the effective request URI for future requests.
1864</t>
1865<t>
1866   The temporary URI &SHOULD; be given by the Location field in the
1867   response. A response payload can contain a short hypertext note with a
1868   hyperlink to the new URI(s).
1869</t>
1870<x:note>
1871  <t>
1872    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1873    it does not allow rewriting the request method from POST to GET. This
1874    specification defines no equivalent counterpart for 301 Moved Permanently.
1875  </t>
1876</x:note>
1877</section>
1878</section>
1879
1880<section title="Client Error 4xx" anchor="status.4xx">
1881<t>
1882   The 4xx class of status code is intended for cases in which the
1883   client seems to have erred. Except when responding to a HEAD request,
1884   the server &SHOULD; include a representation containing an explanation of the
1885   error situation, and whether it is a temporary or permanent
1886   condition. These status codes are applicable to any request method.
1887   User agents &SHOULD; display any included representation to the user.
1888</t>
1889
1890<section title="400 Bad Request" anchor="status.400">
1891  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1892  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1893<t>
1894   The server cannot or will not process the request, due to a client error (e.g.,
1895   malformed syntax).
1896</t>
1897</section>
1898
1899<section title="402 Payment Required" anchor="status.402">
1900  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1901  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1902<t>
1903   This code is reserved for future use.
1904</t>
1905</section>
1906
1907<section title="403 Forbidden" anchor="status.403">
1908  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1909  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1910<t>
1911   The server understood the request, but refuses to authorize it. Providing
1912   different user authentication credentials might be successful, but any
1913   credentials that were provided in the request are insufficient. The request
1914   &SHOULD-NOT; be repeated with the same credentials.
1915</t>
1916<t>
1917   If the request method was not HEAD and the server wishes to make
1918   public why the request has not been fulfilled, it &SHOULD; describe the
1919   reason for the refusal in the representation.  If the server does not wish to
1920   make this information available to the client, the status code 404
1921   (Not Found) &MAY; be used instead.
1922</t>
1923</section>
1924
1925<section title="404 Not Found" anchor="status.404">
1926  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1927  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1928<t>
1929   The server has not found anything matching the effective request URI. No
1930   indication is given of whether the condition is temporary or
1931   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1932   knows, through some internally configurable mechanism, that an old
1933   resource is permanently unavailable and has no forwarding address.
1934   This status code is commonly used when the server does not wish to
1935   reveal exactly why the request has been refused, or when no other
1936   response is applicable.
1937</t>
1938</section>
1939
1940<section title="405 Method Not Allowed" anchor="status.405">
1941  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1942  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1943<t>
1944   The method specified in the request-line is not allowed for the target
1945   resource. The response &MUST; include an Allow header field containing a
1946   list of valid methods for the requested resource.
1947</t>
1948</section>
1949
1950<section title="406 Not Acceptable" anchor="status.406">
1951  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1952  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1953<t>
1954   The resource identified by the request is only capable of generating
1955   response representations which have content characteristics not acceptable
1956   according to the Accept and Accept-* header fields sent in the request
1957   (see &p3-header-fields;).
1958</t>
1959<t>
1960   Unless it was a HEAD request, the response &SHOULD; include a representation
1961   containing a list of available representation characteristics and location(s)
1962   from which the user or user agent can choose the one most
1963   appropriate. Depending upon the format and the
1964   capabilities of the user agent, selection of the most appropriate
1965   choice &MAY; be performed automatically. However, this specification
1966   does not define any standard for such automatic selection.
1967</t>
1968<x:note>
1969  <t>
1970    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1971    not acceptable according to the accept header fields sent in the
1972    request. In some cases, this might even be preferable to sending a
1973    406 response. User agents are encouraged to inspect the header fields of
1974    an incoming response to determine if it is acceptable.
1975  </t>
1976</x:note>
1977<t>
1978   If the response could be unacceptable, a user agent &SHOULD;
1979   temporarily stop receipt of more data and query the user for a
1980   decision on further actions.
1981</t>
1982</section>
1983
1984<section title="408 Request Timeout" anchor="status.408">
1985  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1986  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1987<t>
1988   The client did not produce a request within the time that the server
1989   was prepared to wait. The client &MAY; repeat the request without
1990   modifications at any later time.
1991</t>
1992</section>
1993
1994<section title="409 Conflict" anchor="status.409">
1995  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1996  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1997<t>
1998   The request could not be completed due to a conflict with the current
1999   state of the resource. This code is only allowed in situations where
2000   it is expected that the user might be able to resolve the conflict
2001   and resubmit the request. The response body &SHOULD; include enough
2002   information for the user to recognize the source of the conflict.
2003   Ideally, the response representation would include enough information for the
2004   user or user agent to fix the problem; however, that might not be
2005   possible and is not required.
2006</t>
2007<t>
2008   Conflicts are most likely to occur in response to a PUT request. For
2009   example, if versioning were being used and the representation being PUT
2010   included changes to a resource which conflict with those made by an
2011   earlier (third-party) request, the server might use the 409 response
2012   to indicate that it can't complete the request. In this case, the
2013   response representation would likely contain a list of the differences
2014   between the two versions.
2015</t>
2016</section>
2017
2018<section title="410 Gone" anchor="status.410">
2019  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2020  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2021<t>
2022   The target resource is no longer available at the server and no
2023   forwarding address is known. This condition is expected to be
2024   considered permanent. Clients with link editing capabilities &SHOULD;
2025   delete references to the effective request URI after user approval. If the
2026   server does not know, or has no facility to determine, whether or not
2027   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2028   used instead.
2029</t>
2030<t>
2031   The 410 response is primarily intended to assist the task of web
2032   maintenance by notifying the recipient that the resource is
2033   intentionally unavailable and that the server owners desire that
2034   remote links to that resource be removed. Such an event is common for
2035   limited-time, promotional services and for resources belonging to
2036   individuals no longer working at the server's site. It is not
2037   necessary to mark all permanently unavailable resources as "gone" or
2038   to keep the mark for any length of time &mdash; that is left to the
2039   discretion of the server owner.
2040</t>
2041<t>
2042   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2043   for 410 responses.
2044</t>
2045</section>
2046
2047<section title="411 Length Required" anchor="status.411">
2048  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2049  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2050<t>
2051   The server refuses to accept the request without a defined Content-Length.
2052   The client &MAY; repeat the request if it adds a valid
2053   Content-Length header field containing the length of the message body
2054   in the request message.
2055</t>
2056</section>
2057
2058<section title="413 Request Representation Too Large" anchor="status.413">
2059  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2060  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2061<t>
2062   The server is refusing to process a request because the request
2063   representation is larger than the server is willing or able to process. The
2064   server &MAY; close the connection to prevent the client from continuing
2065   the request.
2066</t>
2067<t>
2068   If the condition is temporary, the server &SHOULD; include a Retry-After
2069   header field to indicate that it is temporary and after what
2070   time the client &MAY; try again.
2071</t>
2072</section>
2073
2074<section title="414 URI Too Long" anchor="status.414">
2075  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2076  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2077<t>
2078   The server is refusing to service the request because the effective request URI
2079   is longer than the server is willing to interpret. This rare
2080   condition is only likely to occur when a client has improperly
2081   converted a POST request to a GET request with long query
2082   information, when the client has descended into a URI "black hole" of
2083   redirection (e.g., a redirected URI prefix that points to a suffix of
2084   itself), or when the server is under attack by a client attempting to
2085   exploit security holes present in some servers using fixed-length
2086   buffers for reading or manipulating the effective request URI.
2087</t>
2088</section>
2089
2090<section title="415 Unsupported Media Type" anchor="status.415">
2091  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2092  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2093<t>
2094   The server is refusing to service the request because the request
2095   payload is in a format not supported by this request method on the
2096   target resource.
2097</t>
2098</section>
2099
2100<section title="417 Expectation Failed" anchor="status.417">
2101  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2102  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2103<t>
2104   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2105   could not be met by this server, or, if the server is a proxy,
2106   the server has unambiguous evidence that the request could not be met
2107   by the next-hop server.
2108</t>
2109</section>
2110
2111<section title="426 Upgrade Required" anchor="status.426">
2112  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2113  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2114<t>
2115   The request can not be completed without a prior protocol upgrade. This
2116   response &MUST; include an Upgrade header field (&header-upgrade;)
2117   specifying the required protocols.
2118</t>
2119<figure>
2120<preamble>Example:</preamble>
2121<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
2122HTTP/1.1 426 Upgrade Required
2123Upgrade: HTTP/3.0
2124Connection: Upgrade
2125Content-Length: <x:length-of target="s426body"/>
2126Content-Type: text/plain
2127
2128<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2129</x:span></artwork></figure>
2130<t>
2131   The server &SHOULD; include a message body in the 426 response which
2132   indicates in human readable form the reason for the error and describes any
2133   alternative courses which may be available to the user.
2134</t>
2135</section>
2136</section>
2137
2138<section title="Server Error 5xx" anchor="status.5xx">
2139<t>
2140   Response status codes beginning with the digit "5" indicate cases in
2141   which the server is aware that it has erred or is incapable of
2142   performing the request. Except when responding to a HEAD request, the
2143   server &SHOULD; include a representation containing an explanation of the
2144   error situation, and whether it is a temporary or permanent
2145   condition. User agents &SHOULD; display any included representation to the
2146   user. These response codes are applicable to any request method.
2147</t>
2148
2149<section title="500 Internal Server Error" anchor="status.500">
2150  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2151  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2152<t>
2153   The server encountered an unexpected condition which prevented it
2154   from fulfilling the request.
2155</t>
2156</section>
2157
2158<section title="501 Not Implemented" anchor="status.501">
2159  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2160  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2161<t>
2162   The server does not support the functionality required to fulfill the
2163   request. This is the appropriate response when the server does not
2164   recognize the request method and is not capable of supporting it for
2165   any resource.
2166</t>
2167</section>
2168
2169<section title="502 Bad Gateway" anchor="status.502">
2170  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2171  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2172<t>
2173   The server, while acting as a gateway or proxy, received an invalid
2174   response from the upstream server it accessed in attempting to
2175   fulfill the request.
2176</t>
2177</section>
2178
2179<section title="503 Service Unavailable" anchor="status.503">
2180  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2181  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2182<t>
2183   The server is currently unable to handle the request due to a
2184   temporary overloading or maintenance of the server.
2185</t>
2186<t>
2187   The implication is that this is a temporary condition which will be
2188   alleviated after some delay. If known, the length of the delay &MAY; be
2189   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2190   If no Retry-After is given, the client &SHOULD; handle the response as it
2191   would for a 500 response.
2192</t>
2193<x:note>
2194  <t>
2195    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2196    server must use it when becoming overloaded. Some servers might wish
2197    to simply refuse the connection.
2198  </t>
2199</x:note>
2200</section>
2201
2202<section title="504 Gateway Timeout" anchor="status.504">
2203  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2204  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2205<t>
2206   The server, while acting as a gateway or proxy, did not receive a
2207   timely response from the upstream server specified by the URI (e.g.,
2208   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2209   to access in attempting to complete the request.
2210</t>
2211<x:note>
2212  <t>
2213    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2214    return 400 or 500 when DNS lookups time out.
2215  </t>
2216</x:note>
2217</section>
2218
2219<section title="505 HTTP Version Not Supported" anchor="status.505">
2220  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2221  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2222<t>
2223   The server does not support, or refuses to support, the protocol
2224   version that was used in the request message. The server is
2225   indicating that it is unable or unwilling to complete the request
2226   using the same major version as the client, as described in &http-version;,
2227   other than with this error message. The response &SHOULD; contain
2228   a representation describing why that version is not supported and what other
2229   protocols are supported by that server.
2230</t>
2231
2232</section>
2233</section>
2234</section>
2235
2236
2237<section title="Date/Time Formats" anchor="http.date">
2238  <x:anchor-alias value="HTTP-date"/>
2239<t>
2240   HTTP applications have historically allowed three different formats
2241   for date/time stamps. However, the preferred format is a fixed-length subset
2242   of that defined by <xref target="RFC1123"/>:
2243</t>
2244<figure><artwork type="example" x:indent-with="  ">
2245Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2246</artwork></figure>
2247<t>
2248   The other formats are described here only for compatibility with obsolete
2249   implementations.
2250</t>
2251<figure><artwork type="example" x:indent-with="  ">
2252Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2253Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2254</artwork></figure>
2255<t>
2256   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2257   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2258   only generate the RFC 1123 format for representing HTTP-date values
2259   in header fields.
2260</t>
2261<t>
2262   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2263   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2264   equal to UTC (Coordinated Universal Time). This is indicated in the
2265   first two formats by the inclusion of "GMT" as the three-letter
2266   abbreviation for time zone, and &MUST; be assumed when reading the
2267   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2268   additional whitespace beyond that specifically included as SP in the
2269   grammar.
2270</t>
2271<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2272  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2273</artwork></figure>
2274<t anchor="preferred.date.format">
2275  <x:anchor-alias value="rfc1123-date"/>
2276  <x:anchor-alias value="time-of-day"/>
2277  <x:anchor-alias value="hour"/>
2278  <x:anchor-alias value="minute"/>
2279  <x:anchor-alias value="second"/>
2280  <x:anchor-alias value="day-name"/>
2281  <x:anchor-alias value="day"/>
2282  <x:anchor-alias value="month"/>
2283  <x:anchor-alias value="year"/>
2284  <x:anchor-alias value="GMT"/>
2285  Preferred format:
2286</t>
2287<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
2288  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2289  ; fixed length subset of the format defined in
2290  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2291 
2292  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2293               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2294               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2295               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2296               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2297               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2298               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2299               
2300  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2301               ; e.g., 02 Jun 1982
2302
2303  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2304  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2305               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2306               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2307               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2308               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2309               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2310               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2311               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2312               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2313               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2314               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2315               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2316  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2317
2318  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2319
2320  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2321                 ; 00:00:00 - 23:59:59
2322                 
2323  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2324  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2325  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2326</artwork></figure>
2327<t>
2328  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2329  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2330  same as those defined for the RFC 5322 constructs
2331  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2332</t>
2333<t anchor="obsolete.date.formats">
2334  <x:anchor-alias value="obs-date"/>
2335  <x:anchor-alias value="rfc850-date"/>
2336  <x:anchor-alias value="asctime-date"/>
2337  <x:anchor-alias value="date1"/>
2338  <x:anchor-alias value="date2"/>
2339  <x:anchor-alias value="date3"/>
2340  <x:anchor-alias value="rfc1123-date"/>
2341  <x:anchor-alias value="day-name-l"/>
2342  Obsolete formats:
2343</t>
2344<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2345  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2346</artwork></figure>
2347<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2348  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2349  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2350                 ; day-month-year (e.g., 02-Jun-82)
2351
2352  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2353         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2354         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2355         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2356         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2357         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2358         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2359</artwork></figure>
2360<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2361  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2362  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2363                 ; month day (e.g., Jun  2)
2364</artwork></figure>
2365<x:note>
2366  <t>
2367    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2368    accepting date values that might have been sent by non-HTTP
2369    applications, as is sometimes the case when retrieving or posting
2370    messages via proxies/gateways to SMTP or NNTP.
2371  </t>
2372</x:note>
2373<x:note>
2374  <t>
2375    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2376    to their usage within the protocol stream. Clients and servers are
2377    not required to use these formats for user presentation, request
2378    logging, etc.
2379  </t>
2380</x:note>
2381</section>
2382
2383<section title="Product Tokens" anchor="product.tokens">
2384  <x:anchor-alias value="product"/>
2385  <x:anchor-alias value="product-version"/>
2386<t>
2387   Product tokens are used to allow communicating applications to
2388   identify themselves by software name and version. Most fields using
2389   product tokens also allow sub-products which form a significant part
2390   of the application to be listed, separated by whitespace. By
2391   convention, the products are listed in order of their significance
2392   for identifying the application.
2393</t>
2394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2395  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2396  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2397</artwork></figure>
2398<t>
2399   Examples:
2400</t>
2401<figure><artwork type="example">
2402  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2403  Server: Apache/0.8.4
2404</artwork></figure>
2405<t>
2406   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2407   used for advertising or other non-essential information. Although any
2408   token octet &MAY; appear in a product-version, this token &SHOULD;
2409   only be used for a version identifier (i.e., successive versions of
2410   the same product &SHOULD; only differ in the product-version portion of
2411   the product value).
2412</t>
2413</section>
2414
2415
2416<section title="Header Field Definitions" anchor="header.field.definitions">
2417<t>
2418   This section defines the syntax and semantics of HTTP/1.1 header fields
2419   related to request and response semantics.
2420</t>
2421
2422<section title="Allow" anchor="header.allow">
2423  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2424  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2425  <x:anchor-alias value="Allow"/>
2426<t>
2427   The "Allow" header field lists the set of methods advertised as
2428   supported by the target resource. The purpose of this field is strictly to
2429   inform the recipient of valid request methods associated with the resource.
2430</t>
2431<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2432  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2433</artwork></figure>
2434<t>
2435   Example of use:
2436</t>
2437<figure><artwork type="example">
2438  Allow: GET, HEAD, PUT
2439</artwork></figure>
2440<t>
2441   The actual set of allowed methods is defined by the origin server at the
2442   time of each request.
2443</t>
2444<t>
2445   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2446   understand all the methods specified in order to handle them according to
2447   the generic message handling rules.
2448</t>
2449</section>
2450
2451<section title="Date" anchor="header.date">
2452  <iref primary="true" item="Date header field" x:for-anchor=""/>
2453  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2454  <x:anchor-alias value="Date"/>
2455<t>
2456   The "Date" header field represents the date and time at which
2457   the message was originated, having the same semantics as the Origination
2458   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2459   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2460   it &MUST; be sent in rfc1123-date format.
2461</t>
2462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2463  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2464</artwork></figure>
2465<t>
2466   An example is
2467</t>
2468<figure><artwork type="example">
2469  Date: Tue, 15 Nov 1994 08:12:31 GMT
2470</artwork></figure>
2471<t>
2472   Origin servers &MUST; include a Date header field in all responses,
2473   except in these cases:
2474  <list style="numbers">
2475      <t>If the response status code is 100 (Continue) or 101 (Switching
2476         Protocols), the response &MAY; include a Date header field, at
2477         the server's option.</t>
2478
2479      <t>If the response status code conveys a server error, e.g., 500
2480         (Internal Server Error) or 503 (Service Unavailable), and it is
2481         inconvenient or impossible to generate a valid Date.</t>
2482
2483      <t>If the server does not have a clock that can provide a
2484         reasonable approximation of the current time, its responses
2485         &MUST-NOT; include a Date header field.</t>
2486  </list>
2487</t>
2488<t>
2489   A received message that does not have a Date header field &MUST; be
2490   assigned one by the recipient if the message will be cached by that
2491   recipient.
2492</t>
2493<t>
2494   Clients can use the Date header field as well; in order to keep request
2495   messages small, they are advised not to include it when it doesn't convey
2496   any useful information (as is usually the case for requests that do not
2497   contain a payload).
2498</t>
2499<t>
2500   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2501   time subsequent to the generation of the message. It &SHOULD; represent
2502   the best available approximation of the date and time of message
2503   generation, unless the implementation has no means of generating a
2504   reasonably accurate date and time. In theory, the date ought to
2505   represent the moment just before the payload is generated. In
2506   practice, the date can be generated at any time during the message
2507   origination without affecting its semantic value.
2508</t>
2509</section>
2510
2511<section title="Expect" anchor="header.expect">
2512  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2513  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2514  <x:anchor-alias value="Expect"/>
2515  <x:anchor-alias value="expectation"/>
2516  <x:anchor-alias value="expect-param"/>
2517  <x:anchor-alias value="expect-name"/>
2518  <x:anchor-alias value="expect-value"/>
2519<t>
2520   The "Expect" header field is used to indicate that particular
2521   server behaviors are required by the client.
2522</t>
2523<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expect-param"/><iref primary="true" item="Grammar" subitem="expect-value"/><iref primary="true" item="Grammar" subitem="expect-name"/>
2524  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2525 
2526  <x:ref>expectation</x:ref>  = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2527                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2528  <x:ref>expect-param</x:ref> = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2529 
2530  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2531  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2532</artwork></figure>
2533<t>
2534   If all received Expect header field(s) are syntactically valid but contain
2535   an expectation that the recipient does not understand or cannot comply with,
2536   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2537   recipient of a syntactically invalid Expectation header field &MUST; respond
2538   with a 4xx status code other than 417.
2539</t>
2540<t>
2541   The only expectation defined by this specification is:
2542</t>
2543<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2544  100-continue
2545   <list>
2546      <t>
2547        The "100-continue" expectation is defined &use100;. It does not support
2548        any expect-params.
2549      </t>
2550   </list>
2551</t>
2552<t>
2553   Comparison is case-insensitive for names (expect-name), and case-sensitive
2554   for values (expect-value).
2555</t>
2556<t>
2557   The Expect mechanism is hop-by-hop: the above requirements apply to any
2558   server, including proxies. However, the Expect header field itself is
2559   end-to-end; it &MUST; be forwarded if the request is forwarded.
2560</t>
2561<t>
2562   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2563   header field.
2564</t>
2565</section>
2566
2567<section title="From" anchor="header.from">
2568  <iref primary="true" item="From header field" x:for-anchor=""/>
2569  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2570  <x:anchor-alias value="From"/>
2571  <x:anchor-alias value="mailbox"/>
2572<t>
2573   The "From" header field, if given, &SHOULD; contain an Internet
2574   e-mail address for the human user who controls the requesting user
2575   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2576   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2577</t>
2578<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2579  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2580 
2581  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2582</artwork></figure>
2583<t>
2584   An example is:
2585</t>
2586<figure><artwork type="example">
2587  From: webmaster@example.org
2588</artwork></figure>
2589<t>
2590   This header field &MAY; be used for logging purposes and as a means for
2591   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2592   be used as an insecure form of access protection. The interpretation
2593   of this field is that the request is being performed on behalf of the
2594   person given, who accepts responsibility for the method performed. In
2595   particular, robot agents &SHOULD; include this header field so that the
2596   person responsible for running the robot can be contacted if problems
2597   occur on the receiving end.
2598</t>
2599<t>
2600   The Internet e-mail address in this field &MAY; be separate from the
2601   Internet host which issued the request. For example, when a request
2602   is passed through a proxy the original issuer's address &SHOULD; be
2603   used.
2604</t>
2605<t>
2606   The client &SHOULD-NOT;  send the From header field without the user's
2607   approval, as it might conflict with the user's privacy interests or
2608   their site's security policy. It is strongly recommended that the
2609   user be able to disable, enable, and modify the value of this field
2610   at any time prior to a request.
2611</t>
2612</section>
2613
2614<section title="Location" anchor="header.location">
2615  <iref primary="true" item="Location header field" x:for-anchor=""/>
2616  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2617  <x:anchor-alias value="Location"/>
2618<t>
2619   The "Location" header field &MAY; be sent in responses to refer to
2620   a specific resource in accordance with the semantics of the status
2621   code.
2622</t>
2623<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2624  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2625</artwork></figure>
2626<t>
2627   For 201 (Created) responses, the Location is the URI of the new resource
2628   which was created by the request. For 3xx responses, the location &SHOULD;
2629   indicate the server's preferred URI for automatic redirection to the
2630   resource.
2631</t>
2632<t>
2633   The field value consists of a single URI-reference. When it has the form
2634   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2635   the final value is computed by resolving it against the effective request
2636   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2637   navigated to by the user agent, did contain a fragment identifier, and the
2638   final value does not, then the original URI's fragment identifier is added
2639   to the final value.
2640</t>
2641<figure>
2642<preamble>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2643<artwork type="example">
2644  Location: /pub/WWW/People.html#tim
2645</artwork>
2646<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2647</figure>
2648<figure>
2649<preamble>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2650<artwork type="example">
2651  Location: http://www.example.net/index.html
2652</artwork>
2653<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2654</figure>
2655<x:note>
2656  <t>
2657    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2658    that are not valid URI references. This specification does not mandate or
2659    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2660  </t>
2661</x:note>
2662<t>
2663   There are circumstances in which a fragment identifier in a Location URI
2664   would not be appropriate. For instance, when it appears in a 201 Created
2665   response, where the Location header field specifies the URI for the entire
2666   created resource.
2667</t>
2668<x:note>
2669  <t>
2670    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2671    from Location in that the Content-Location identifies the most specific
2672    resource corresponding to the enclosed representation.
2673    It is therefore possible for a response to contain header fields for
2674    both Location and Content-Location.
2675  </t>
2676</x:note>
2677</section>
2678
2679<section title="Max-Forwards" anchor="header.max-forwards">
2680  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2681  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2682  <x:anchor-alias value="Max-Forwards"/>
2683<t>
2684   The "Max-Forwards" header field provides a mechanism with the
2685   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2686   methods to limit the number of times that the request is forwarded by
2687   proxies. This can be useful when the client is attempting to
2688   trace a request which appears to be failing or looping mid-chain.
2689</t>
2690<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2691  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2692</artwork></figure>
2693<t>
2694   The Max-Forwards value is a decimal integer indicating the remaining
2695   number of times this request message can be forwarded.
2696</t>
2697<t>
2698   Each recipient of a TRACE or OPTIONS request
2699   containing a Max-Forwards header field &MUST; check and update its
2700   value prior to forwarding the request. If the received value is zero
2701   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2702   respond as the final recipient. If the received Max-Forwards value is
2703   greater than zero, then the forwarded message &MUST; contain an updated
2704   Max-Forwards field with a value decremented by one (1).
2705</t>
2706<t>
2707   The Max-Forwards header field &MAY; be ignored for all other request
2708   methods.
2709</t>
2710</section>
2711
2712<section title="Referer" anchor="header.referer">
2713  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2714  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2715  <x:anchor-alias value="Referer"/>
2716<t>
2717   The "Referer" [sic] header field allows the client to specify the
2718   URI of the resource from which the effective request URI was obtained (the
2719   "referrer", although the header field is misspelled.).
2720</t>
2721<t>
2722   The Referer header field allows servers to generate lists of back-links to
2723   resources for interest, logging, optimized caching, etc. It also allows
2724   obsolete or mistyped links to be traced for maintenance. Some servers use
2725   Referer as a means of controlling where they allow links from (so-called
2726   "deep linking"), but legitimate requests do not always
2727   contain a Referer header field.
2728</t>
2729<t>
2730   If the effective request URI was obtained from a source that does not have its own
2731   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2732   sent with the value "about:blank", or not be sent at all. Note that this
2733   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2734</t>
2735<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2736  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2737</artwork></figure>
2738<t>
2739   Example:
2740</t>
2741<figure><artwork type="example">
2742  Referer: http://www.example.org/hypertext/Overview.html
2743</artwork></figure>
2744<t>
2745   If the field value is a relative URI, it &SHOULD; be interpreted
2746   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2747   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2748</t>
2749</section>
2750
2751<section title="Retry-After" anchor="header.retry-after">
2752  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2753  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2754  <x:anchor-alias value="Retry-After"/>
2755<t>
2756   The header "Retry-After" field can be used with a 503 (Service
2757   Unavailable) response to indicate how long the service is expected to
2758   be unavailable to the requesting client. This field &MAY; also be used
2759   with any 3xx (Redirection) response to indicate the minimum time the
2760   user-agent is asked to wait before issuing the redirected request.
2761</t>
2762<t>
2763   The value of this field can be either an HTTP-date or an integer number
2764   of seconds (in decimal) after the time of the response.
2765</t>
2766<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2767  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2768</artwork></figure>
2769<t anchor="rule.delta-seconds">
2770  <x:anchor-alias value="delta-seconds"/>
2771   Time spans are non-negative decimal integers, representing time in
2772   seconds.
2773</t>
2774<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2775  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2776</artwork></figure>
2777<t>
2778   Two examples of its use are
2779</t>
2780<figure><artwork type="example">
2781  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2782  Retry-After: 120
2783</artwork></figure>
2784<t>
2785   In the latter example, the delay is 2 minutes.
2786</t>
2787</section>
2788
2789<section title="Server" anchor="header.server">
2790  <iref primary="true" item="Server header field" x:for-anchor=""/>
2791  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2792  <x:anchor-alias value="Server"/>
2793<t>
2794   The "Server" header field contains information about the
2795   software used by the origin server to handle the request.
2796</t>
2797<t>
2798   The field can contain multiple
2799   product tokens (<xref target="product.tokens"/>) and
2800   comments (&header-fields;) identifying the server and any significant
2801   subproducts. The product tokens are listed in order of their significance
2802   for identifying the application.
2803</t>
2804<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2805  <x:ref>Server</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2806</artwork></figure>
2807<t>
2808   Example:
2809</t>
2810<figure><artwork type="example">
2811  Server: CERN/3.0 libwww/2.17
2812</artwork></figure>
2813<t>
2814   If the response is being forwarded through a proxy, the proxy
2815   application &MUST-NOT; modify the Server header field. Instead, it
2816   &MUST; include a Via field (as described in &header-via;).
2817</t>
2818<x:note>
2819  <t>
2820    <x:h>Note:</x:h> Revealing the specific software version of the server might
2821    allow the server machine to become more vulnerable to attacks
2822    against software that is known to contain security holes. Server
2823    implementors are encouraged to make this field a configurable
2824    option.
2825  </t>
2826</x:note>
2827</section>
2828
2829<section title="User-Agent" anchor="header.user-agent">
2830  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2831  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2832  <x:anchor-alias value="User-Agent"/>
2833<t>
2834   The "User-Agent" header field contains information about the user
2835   agent originating the request. User agents &SHOULD; include this field with
2836   requests.
2837</t>
2838<t>
2839   Typically, it is used for statistical purposes, the tracing of protocol
2840   violations, and tailoring responses to avoid particular user agent
2841   limitations.
2842</t>
2843<t>
2844   The field can contain multiple
2845   product tokens (<xref target="product.tokens"/>)
2846   and comments (&header-fields;) identifying the agent and its
2847   significant subproducts. By convention, the product tokens are listed in
2848   order of their significance for identifying the application.
2849</t>
2850<t>
2851   Because this field is usually sent on every request a user agent makes,
2852   implementations are encouraged not to include needlessly fine-grained
2853   detail, and to limit (or even prohibit) the addition of subproducts by third
2854   parties. Overly long and detailed User-Agent field values make requests
2855   larger and can also be used to identify ("fingerprint") the user against
2856   their wishes.
2857</t>
2858<t>
2859   Likewise, implementations are encouraged not to use the product tokens of
2860   other implementations in order to declare compatibility with them, as this
2861   circumvents the purpose of the field. Finally, they are encouraged not to
2862   use comments to identify products; doing so makes the field value more
2863   difficult to parse.
2864</t>
2865<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2866  <x:ref>User-Agent</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2867</artwork></figure>
2868<t>
2869   Example:
2870</t>
2871<figure><artwork type="example">
2872  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2873</artwork></figure>
2874</section>
2875
2876</section>
2877
2878<section title="IANA Considerations" anchor="IANA.considerations">
2879
2880<section title="Method Registry" anchor="method.registration">
2881<t>
2882  The registration procedure for HTTP request methods is defined by
2883  <xref target="method.registry"/> of this document.
2884</t>
2885<t>
2886   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2887   and be populated with the registrations below:
2888</t>
2889<?BEGININC p2-semantics.iana-methods ?>
2890<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2891<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2892   <ttcol>Method</ttcol>
2893   <ttcol>Safe</ttcol>
2894   <ttcol>Reference</ttcol>
2895   <c>CONNECT</c>
2896   <c>no</c>
2897   <c>
2898      <xref target="CONNECT"/>
2899   </c>
2900   <c>DELETE</c>
2901   <c>no</c>
2902   <c>
2903      <xref target="DELETE"/>
2904   </c>
2905   <c>GET</c>
2906   <c>yes</c>
2907   <c>
2908      <xref target="GET"/>
2909   </c>
2910   <c>HEAD</c>
2911   <c>yes</c>
2912   <c>
2913      <xref target="HEAD"/>
2914   </c>
2915   <c>OPTIONS</c>
2916   <c>yes</c>
2917   <c>
2918      <xref target="OPTIONS"/>
2919   </c>
2920   <c>POST</c>
2921   <c>no</c>
2922   <c>
2923      <xref target="POST"/>
2924   </c>
2925   <c>PUT</c>
2926   <c>no</c>
2927   <c>
2928      <xref target="PUT"/>
2929   </c>
2930   <c>TRACE</c>
2931   <c>yes</c>
2932   <c>
2933      <xref target="TRACE"/>
2934   </c>
2935</texttable>
2936<!--(END)-->
2937<?ENDINC p2-semantics.iana-methods ?>
2938</section>
2939
2940<section title="Status Code Registry" anchor="status.code.registration">
2941<t>
2942   The registration procedure for HTTP Status Codes &mdash; previously defined
2943   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2944   by <xref target="status.code.registry"/> of this document.
2945</t>
2946<t>
2947   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2948   shall be updated with the registrations below:
2949</t>
2950<?BEGININC p2-semantics.iana-status-codes ?>
2951<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2952<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2953   <ttcol>Value</ttcol>
2954   <ttcol>Description</ttcol>
2955   <ttcol>Reference</ttcol>
2956   <c>100</c>
2957   <c>Continue</c>
2958   <c>
2959      <xref target="status.100"/>
2960   </c>
2961   <c>101</c>
2962   <c>Switching Protocols</c>
2963   <c>
2964      <xref target="status.101"/>
2965   </c>
2966   <c>200</c>
2967   <c>OK</c>
2968   <c>
2969      <xref target="status.200"/>
2970   </c>
2971   <c>201</c>
2972   <c>Created</c>
2973   <c>
2974      <xref target="status.201"/>
2975   </c>
2976   <c>202</c>
2977   <c>Accepted</c>
2978   <c>
2979      <xref target="status.202"/>
2980   </c>
2981   <c>203</c>
2982   <c>Non-Authoritative Information</c>
2983   <c>
2984      <xref target="status.203"/>
2985   </c>
2986   <c>204</c>
2987   <c>No Content</c>
2988   <c>
2989      <xref target="status.204"/>
2990   </c>
2991   <c>205</c>
2992   <c>Reset Content</c>
2993   <c>
2994      <xref target="status.205"/>
2995   </c>
2996   <c>300</c>
2997   <c>Multiple Choices</c>
2998   <c>
2999      <xref target="status.300"/>
3000   </c>
3001   <c>301</c>
3002   <c>Moved Permanently</c>
3003   <c>
3004      <xref target="status.301"/>
3005   </c>
3006   <c>302</c>
3007   <c>Found</c>
3008   <c>
3009      <xref target="status.302"/>
3010   </c>
3011   <c>303</c>
3012   <c>See Other</c>
3013   <c>
3014      <xref target="status.303"/>
3015   </c>
3016   <c>305</c>
3017   <c>Use Proxy</c>
3018   <c>
3019      <xref target="status.305"/>
3020   </c>
3021   <c>306</c>
3022   <c>(Unused)</c>
3023   <c>
3024      <xref target="status.306"/>
3025   </c>
3026   <c>307</c>
3027   <c>Temporary Redirect</c>
3028   <c>
3029      <xref target="status.307"/>
3030   </c>
3031   <c>400</c>
3032   <c>Bad Request</c>
3033   <c>
3034      <xref target="status.400"/>
3035   </c>
3036   <c>402</c>
3037   <c>Payment Required</c>
3038   <c>
3039      <xref target="status.402"/>
3040   </c>
3041   <c>403</c>
3042   <c>Forbidden</c>
3043   <c>
3044      <xref target="status.403"/>
3045   </c>
3046   <c>404</c>
3047   <c>Not Found</c>
3048   <c>
3049      <xref target="status.404"/>
3050   </c>
3051   <c>405</c>
3052   <c>Method Not Allowed</c>
3053   <c>
3054      <xref target="status.405"/>
3055   </c>
3056   <c>406</c>
3057   <c>Not Acceptable</c>
3058   <c>
3059      <xref target="status.406"/>
3060   </c>
3061   <c>408</c>
3062   <c>Request Timeout</c>
3063   <c>
3064      <xref target="status.408"/>
3065   </c>
3066   <c>409</c>
3067   <c>Conflict</c>
3068   <c>
3069      <xref target="status.409"/>
3070   </c>
3071   <c>410</c>
3072   <c>Gone</c>
3073   <c>
3074      <xref target="status.410"/>
3075   </c>
3076   <c>411</c>
3077   <c>Length Required</c>
3078   <c>
3079      <xref target="status.411"/>
3080   </c>
3081   <c>413</c>
3082   <c>Request Representation Too Large</c>
3083   <c>
3084      <xref target="status.413"/>
3085   </c>
3086   <c>414</c>
3087   <c>URI Too Long</c>
3088   <c>
3089      <xref target="status.414"/>
3090   </c>
3091   <c>415</c>
3092   <c>Unsupported Media Type</c>
3093   <c>
3094      <xref target="status.415"/>
3095   </c>
3096   <c>417</c>
3097   <c>Expectation Failed</c>
3098   <c>
3099      <xref target="status.417"/>
3100   </c>
3101   <c>426</c>
3102   <c>Upgrade Required</c>
3103   <c>
3104      <xref target="status.426"/>
3105   </c>
3106   <c>500</c>
3107   <c>Internal Server Error</c>
3108   <c>
3109      <xref target="status.500"/>
3110   </c>
3111   <c>501</c>
3112   <c>Not Implemented</c>
3113   <c>
3114      <xref target="status.501"/>
3115   </c>
3116   <c>502</c>
3117   <c>Bad Gateway</c>
3118   <c>
3119      <xref target="status.502"/>
3120   </c>
3121   <c>503</c>
3122   <c>Service Unavailable</c>
3123   <c>
3124      <xref target="status.503"/>
3125   </c>
3126   <c>504</c>
3127   <c>Gateway Timeout</c>
3128   <c>
3129      <xref target="status.504"/>
3130   </c>
3131   <c>505</c>
3132   <c>HTTP Version Not Supported</c>
3133   <c>
3134      <xref target="status.505"/>
3135   </c>
3136</texttable>
3137<!--(END)-->
3138<?ENDINC p2-semantics.iana-status-codes ?>
3139</section>
3140<section title="Header Field Registration" anchor="header.field.registration">
3141<t>
3142   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3143   with the permanent registrations below (see <xref target="RFC3864"/>):
3144</t>
3145<?BEGININC p2-semantics.iana-headers ?>
3146<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3147<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3148   <ttcol>Header Field Name</ttcol>
3149   <ttcol>Protocol</ttcol>
3150   <ttcol>Status</ttcol>
3151   <ttcol>Reference</ttcol>
3152
3153   <c>Allow</c>
3154   <c>http</c>
3155   <c>standard</c>
3156   <c>
3157      <xref target="header.allow"/>
3158   </c>
3159   <c>Date</c>
3160   <c>http</c>
3161   <c>standard</c>
3162   <c>
3163      <xref target="header.date"/>
3164   </c>
3165   <c>Expect</c>
3166   <c>http</c>
3167   <c>standard</c>
3168   <c>
3169      <xref target="header.expect"/>
3170   </c>
3171   <c>From</c>
3172   <c>http</c>
3173   <c>standard</c>
3174   <c>
3175      <xref target="header.from"/>
3176   </c>
3177   <c>Location</c>
3178   <c>http</c>
3179   <c>standard</c>
3180   <c>
3181      <xref target="header.location"/>
3182   </c>
3183   <c>Max-Forwards</c>
3184   <c>http</c>
3185   <c>standard</c>
3186   <c>
3187      <xref target="header.max-forwards"/>
3188   </c>
3189   <c>Referer</c>
3190   <c>http</c>
3191   <c>standard</c>
3192   <c>
3193      <xref target="header.referer"/>
3194   </c>
3195   <c>Retry-After</c>
3196   <c>http</c>
3197   <c>standard</c>
3198   <c>
3199      <xref target="header.retry-after"/>
3200   </c>
3201   <c>Server</c>
3202   <c>http</c>
3203   <c>standard</c>
3204   <c>
3205      <xref target="header.server"/>
3206   </c>
3207   <c>User-Agent</c>
3208   <c>http</c>
3209   <c>standard</c>
3210   <c>
3211      <xref target="header.user-agent"/>
3212   </c>
3213</texttable>
3214<!--(END)-->
3215<?ENDINC p2-semantics.iana-headers ?>
3216<t>
3217   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3218</t>
3219</section>
3220</section>
3221
3222<section title="Security Considerations" anchor="security.considerations">
3223<t>
3224   This section is meant to inform application developers, information
3225   providers, and users of the security limitations in HTTP/1.1 as
3226   described by this document. The discussion does not include
3227   definitive solutions to the problems revealed, though it does make
3228   some suggestions for reducing security risks.
3229</t>
3230
3231<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3232<t>
3233   Like any generic data transfer protocol, HTTP cannot regulate the
3234   content of the data that is transferred, nor is there any a priori
3235   method of determining the sensitivity of any particular piece of
3236   information within the context of any given request. Therefore,
3237   applications &SHOULD; supply as much control over this information as
3238   possible to the provider of that information. Four header fields are
3239   worth special mention in this context: Server, Via, Referer and From.
3240</t>
3241<t>
3242   Revealing the specific software version of the server might allow the
3243   server machine to become more vulnerable to attacks against software
3244   that is known to contain security holes. Implementors &SHOULD; make the
3245   Server header field a configurable option.
3246</t>
3247<t>
3248   Proxies which serve as a portal through a network firewall &SHOULD;
3249   take special precautions regarding the transfer of header information
3250   that identifies the hosts behind the firewall. In particular, they
3251   &SHOULD; remove, or replace with sanitized versions, any Via fields
3252   generated behind the firewall.
3253</t>
3254<t>
3255   The Referer header field allows reading patterns to be studied and reverse
3256   links drawn. Although it can be very useful, its power can be abused
3257   if user details are not separated from the information contained in
3258   the Referer. Even when the personal information has been removed, the
3259   Referer header field might indicate a private document's URI whose
3260   publication would be inappropriate.
3261</t>
3262<t>
3263   The information sent in the From field might conflict with the user's
3264   privacy interests or their site's security policy, and hence it
3265   &SHOULD-NOT;  be transmitted without the user being able to disable,
3266   enable, and modify the contents of the field. The user &MUST; be able
3267   to set the contents of this field within a user preference or
3268   application defaults configuration.
3269</t>
3270<t>
3271   We suggest, though do not require, that a convenient toggle interface
3272   be provided for the user to enable or disable the sending of From and
3273   Referer information.
3274</t>
3275<t>
3276   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3277   target="header.server"/>) header fields can sometimes be used to determine
3278   that a specific client or server has a particular security hole which might
3279   be exploited. Unfortunately, this same information is often used for other
3280   valuable purposes for which HTTP currently has no better mechanism.
3281</t>
3282<t>
3283   Furthermore, the User-Agent header field may contain enough entropy to be
3284   used, possibly in conjunction with other material, to uniquely identify the
3285   user.
3286</t>
3287<t>
3288   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3289   that was sent in request header fields within the body of their response.
3290   Clients &SHOULD; be careful with sensitive information, like Cookies,
3291   Authorization credentials, and other header fields that might be used to
3292   collect data from the client.
3293</t> 
3294</section>
3295
3296<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3297<t>
3298   Because the source of a link might be private information or might
3299   reveal an otherwise private information source, it is strongly
3300   recommended that the user be able to select whether or not the
3301   Referer field is sent. For example, a browser client could have a
3302   toggle switch for browsing openly/anonymously, which would
3303   respectively enable/disable the sending of Referer and From
3304   information.
3305</t>
3306<t>
3307   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3308   HTTP request if the referring page was transferred with a secure
3309   protocol.
3310</t>
3311<t>
3312   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3313   sensitive data because that data will be placed in the request-target. Many
3314   existing servers, proxies, and user agents log or display the request-target
3315   in places where it might be visible to third parties. Such services can
3316   use POST-based form submission instead.
3317</t>
3318</section>
3319
3320<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3321<t>
3322   If a single server supports multiple organizations that do not trust
3323   one another, then it &MUST; check the values of Location and Content-Location
3324   header fields in responses that are generated under control of
3325   said organizations to make sure that they do not attempt to
3326   invalidate resources over which they have no authority.
3327</t>
3328<t>
3329   Furthermore, appending the fragment identifier from one URI to another
3330   one obtained from a Location header field might leak confidential
3331   information to the target server &mdash; although the fragment identifier is
3332   not transmitted in the final request, it might be visible to the user agent
3333   through other means, such as scripting.
3334</t>
3335</section>
3336
3337<section title="Security Considerations for CONNECT">
3338<t>
3339   Since tunneled data is opaque to the proxy, there are additional
3340   risks to tunneling to other well-known or reserved ports.
3341   A HTTP client CONNECTing to port 25 could relay spam
3342   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3343   access to a small number of known ports.
3344</t>
3345</section>
3346
3347</section>
3348
3349<section title="Acknowledgments" anchor="acks">
3350<t>
3351  See &acks;.
3352</t>
3353</section>
3354</middle>
3355<back>
3356
3357<references title="Normative References">
3358
3359<reference anchor="Part1">
3360  <front>
3361    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3362    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3363      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3364      <address><email>fielding@gbiv.com</email></address>
3365    </author>
3366    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3367      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3368      <address><email>jg@freedesktop.org</email></address>
3369    </author>
3370    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3371      <organization abbrev="HP">Hewlett-Packard Company</organization>
3372      <address><email>JeffMogul@acm.org</email></address>
3373    </author>
3374    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3375      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3376      <address><email>henrikn@microsoft.com</email></address>
3377    </author>
3378    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3379      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3380      <address><email>LMM@acm.org</email></address>
3381    </author>
3382    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3383      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3384      <address><email>paulle@microsoft.com</email></address>
3385    </author>
3386    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3387      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3388      <address><email>timbl@w3.org</email></address>
3389    </author>
3390    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3391      <organization abbrev="W3C">World Wide Web Consortium</organization>
3392      <address><email>ylafon@w3.org</email></address>
3393    </author>
3394    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3395      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3396      <address><email>julian.reschke@greenbytes.de</email></address>
3397    </author>
3398    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3399  </front>
3400  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3401  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3402</reference>
3403
3404<reference anchor="Part3">
3405  <front>
3406    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3407    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3408      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3409      <address><email>fielding@gbiv.com</email></address>
3410    </author>
3411    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3412      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3413      <address><email>jg@freedesktop.org</email></address>
3414    </author>
3415    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3416      <organization abbrev="HP">Hewlett-Packard Company</organization>
3417      <address><email>JeffMogul@acm.org</email></address>
3418    </author>
3419    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3420      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3421      <address><email>henrikn@microsoft.com</email></address>
3422    </author>
3423    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3424      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3425      <address><email>LMM@acm.org</email></address>
3426    </author>
3427    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3428      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3429      <address><email>paulle@microsoft.com</email></address>
3430    </author>
3431    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3432      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3433      <address><email>timbl@w3.org</email></address>
3434    </author>
3435    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3436      <organization abbrev="W3C">World Wide Web Consortium</organization>
3437      <address><email>ylafon@w3.org</email></address>
3438    </author>
3439    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3440      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3441      <address><email>julian.reschke@greenbytes.de</email></address>
3442    </author>
3443    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3444  </front>
3445  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3446  <x:source href="p3-payload.xml" basename="p3-payload"/>
3447</reference>
3448
3449<reference anchor="Part4">
3450  <front>
3451    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3452    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3453      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3454      <address><email>fielding@gbiv.com</email></address>
3455    </author>
3456    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3457      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3458      <address><email>jg@freedesktop.org</email></address>
3459    </author>
3460    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3461      <organization abbrev="HP">Hewlett-Packard Company</organization>
3462      <address><email>JeffMogul@acm.org</email></address>
3463    </author>
3464    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3465      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3466      <address><email>henrikn@microsoft.com</email></address>
3467    </author>
3468    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3469      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3470      <address><email>LMM@acm.org</email></address>
3471    </author>
3472    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3473      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3474      <address><email>paulle@microsoft.com</email></address>
3475    </author>
3476    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3477      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3478      <address><email>timbl@w3.org</email></address>
3479    </author>
3480    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3481      <organization abbrev="W3C">World Wide Web Consortium</organization>
3482      <address><email>ylafon@w3.org</email></address>
3483    </author>
3484    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3485      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3486      <address><email>julian.reschke@greenbytes.de</email></address>
3487    </author>
3488    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3489  </front>
3490  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3491  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3492</reference>
3493
3494<reference anchor="Part5">
3495  <front>
3496    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3497    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3498      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3499      <address><email>fielding@gbiv.com</email></address>
3500    </author>
3501    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3502      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3503      <address><email>jg@freedesktop.org</email></address>
3504    </author>
3505    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3506      <organization abbrev="HP">Hewlett-Packard Company</organization>
3507      <address><email>JeffMogul@acm.org</email></address>
3508    </author>
3509    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3510      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3511      <address><email>henrikn@microsoft.com</email></address>
3512    </author>
3513    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3514      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3515      <address><email>LMM@acm.org</email></address>
3516    </author>
3517    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3518      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3519      <address><email>paulle@microsoft.com</email></address>
3520    </author>
3521    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3522      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3523      <address><email>timbl@w3.org</email></address>
3524    </author>
3525    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3526      <organization abbrev="W3C">World Wide Web Consortium</organization>
3527      <address><email>ylafon@w3.org</email></address>
3528    </author>
3529    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3530      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3531      <address><email>julian.reschke@greenbytes.de</email></address>
3532    </author>
3533    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3534  </front>
3535  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3536  <x:source href="p5-range.xml" basename="p5-range"/>
3537</reference>
3538
3539<reference anchor="Part6">
3540  <front>
3541    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3542    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3543      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3544      <address><email>fielding@gbiv.com</email></address>
3545    </author>
3546    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3547      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3548      <address><email>jg@freedesktop.org</email></address>
3549    </author>
3550    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3551      <organization abbrev="HP">Hewlett-Packard Company</organization>
3552      <address><email>JeffMogul@acm.org</email></address>
3553    </author>
3554    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3555      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3556      <address><email>henrikn@microsoft.com</email></address>
3557    </author>
3558    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3559      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3560      <address><email>LMM@acm.org</email></address>
3561    </author>
3562    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3563      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3564      <address><email>paulle@microsoft.com</email></address>
3565    </author>
3566    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3567      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3568      <address><email>timbl@w3.org</email></address>
3569    </author>
3570    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3571      <organization abbrev="W3C">World Wide Web Consortium</organization>
3572      <address><email>ylafon@w3.org</email></address>
3573    </author>
3574    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3575      <organization>Rackspace</organization>
3576      <address><email>mnot@mnot.net</email></address>
3577    </author>
3578    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3579      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3580      <address><email>julian.reschke@greenbytes.de</email></address>
3581    </author>
3582    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3583  </front>
3584  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3585  <x:source href="p6-cache.xml" basename="p6-cache"/>
3586</reference>
3587
3588<reference anchor="Part7">
3589  <front>
3590    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3591    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3592      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3593      <address><email>fielding@gbiv.com</email></address>
3594    </author>
3595    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3596      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3597      <address><email>jg@freedesktop.org</email></address>
3598    </author>
3599    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3600      <organization abbrev="HP">Hewlett-Packard Company</organization>
3601      <address><email>JeffMogul@acm.org</email></address>
3602    </author>
3603    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3604      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3605      <address><email>henrikn@microsoft.com</email></address>
3606    </author>
3607    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3608      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3609      <address><email>LMM@acm.org</email></address>
3610    </author>
3611    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3612      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3613      <address><email>paulle@microsoft.com</email></address>
3614    </author>
3615    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3616      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3617      <address><email>timbl@w3.org</email></address>
3618    </author>
3619    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3620      <organization abbrev="W3C">World Wide Web Consortium</organization>
3621      <address><email>ylafon@w3.org</email></address>
3622    </author>
3623    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3624      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3625      <address><email>julian.reschke@greenbytes.de</email></address>
3626    </author>
3627    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3628  </front>
3629  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3630  <x:source href="p7-auth.xml" basename="p7-auth"/>
3631</reference>
3632
3633<reference anchor="RFC2119">
3634  <front>
3635    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3636    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3637      <organization>Harvard University</organization>
3638      <address><email>sob@harvard.edu</email></address>
3639    </author>
3640    <date month="March" year="1997"/>
3641  </front>
3642  <seriesInfo name="BCP" value="14"/>
3643  <seriesInfo name="RFC" value="2119"/>
3644</reference>
3645
3646<reference anchor="RFC3986">
3647 <front>
3648  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3649  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3650    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3651    <address>
3652       <email>timbl@w3.org</email>
3653       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3654    </address>
3655  </author>
3656  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3657    <organization abbrev="Day Software">Day Software</organization>
3658    <address>
3659      <email>fielding@gbiv.com</email>
3660      <uri>http://roy.gbiv.com/</uri>
3661    </address>
3662  </author>
3663  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3664    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3665    <address>
3666      <email>LMM@acm.org</email>
3667      <uri>http://larry.masinter.net/</uri>
3668    </address>
3669  </author>
3670  <date month='January' year='2005'></date>
3671 </front>
3672 <seriesInfo name="STD" value="66"/>
3673 <seriesInfo name="RFC" value="3986"/>
3674</reference>
3675
3676<reference anchor="RFC5234">
3677  <front>
3678    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3679    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3680      <organization>Brandenburg InternetWorking</organization>
3681      <address>
3682        <email>dcrocker@bbiw.net</email>
3683      </address> 
3684    </author>
3685    <author initials="P." surname="Overell" fullname="Paul Overell">
3686      <organization>THUS plc.</organization>
3687      <address>
3688        <email>paul.overell@thus.net</email>
3689      </address>
3690    </author>
3691    <date month="January" year="2008"/>
3692  </front>
3693  <seriesInfo name="STD" value="68"/>
3694  <seriesInfo name="RFC" value="5234"/>
3695</reference>
3696
3697</references>
3698
3699<references title="Informative References">
3700
3701<reference anchor="RFC1123">
3702  <front>
3703    <title>Requirements for Internet Hosts - Application and Support</title>
3704    <author initials="R." surname="Braden" fullname="Robert Braden">
3705      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3706      <address><email>Braden@ISI.EDU</email></address>
3707    </author>
3708    <date month="October" year="1989"/>
3709  </front>
3710  <seriesInfo name="STD" value="3"/>
3711  <seriesInfo name="RFC" value="1123"/>
3712</reference>
3713
3714<reference anchor="RFC1945">
3715  <front>
3716    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3717    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3718      <organization>MIT, Laboratory for Computer Science</organization>
3719      <address><email>timbl@w3.org</email></address>
3720    </author>
3721    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3722      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3723      <address><email>fielding@ics.uci.edu</email></address>
3724    </author>
3725    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3726      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3727      <address><email>frystyk@w3.org</email></address>
3728    </author>
3729    <date month="May" year="1996"/>
3730  </front>
3731  <seriesInfo name="RFC" value="1945"/>
3732</reference>
3733
3734<reference anchor="RFC2068">
3735  <front>
3736    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3737    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3738      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3739      <address><email>fielding@ics.uci.edu</email></address>
3740    </author>
3741    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3742      <organization>MIT Laboratory for Computer Science</organization>
3743      <address><email>jg@w3.org</email></address>
3744    </author>
3745    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3746      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3747      <address><email>mogul@wrl.dec.com</email></address>
3748    </author>
3749    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3750      <organization>MIT Laboratory for Computer Science</organization>
3751      <address><email>frystyk@w3.org</email></address>
3752    </author>
3753    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3754      <organization>MIT Laboratory for Computer Science</organization>
3755      <address><email>timbl@w3.org</email></address>
3756    </author>
3757    <date month="January" year="1997"/>
3758  </front>
3759  <seriesInfo name="RFC" value="2068"/>
3760</reference>
3761
3762<reference anchor="RFC2616">
3763  <front>
3764    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3765    <author initials="R." surname="Fielding" fullname="R. Fielding">
3766      <organization>University of California, Irvine</organization>
3767      <address><email>fielding@ics.uci.edu</email></address>
3768    </author>
3769    <author initials="J." surname="Gettys" fullname="J. Gettys">
3770      <organization>W3C</organization>
3771      <address><email>jg@w3.org</email></address>
3772    </author>
3773    <author initials="J." surname="Mogul" fullname="J. Mogul">
3774      <organization>Compaq Computer Corporation</organization>
3775      <address><email>mogul@wrl.dec.com</email></address>
3776    </author>
3777    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3778      <organization>MIT Laboratory for Computer Science</organization>
3779      <address><email>frystyk@w3.org</email></address>
3780    </author>
3781    <author initials="L." surname="Masinter" fullname="L. Masinter">
3782      <organization>Xerox Corporation</organization>
3783      <address><email>masinter@parc.xerox.com</email></address>
3784    </author>
3785    <author initials="P." surname="Leach" fullname="P. Leach">
3786      <organization>Microsoft Corporation</organization>
3787      <address><email>paulle@microsoft.com</email></address>
3788    </author>
3789    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3790      <organization>W3C</organization>
3791      <address><email>timbl@w3.org</email></address>
3792    </author>
3793    <date month="June" year="1999"/>
3794  </front>
3795  <seriesInfo name="RFC" value="2616"/>
3796</reference>
3797
3798<reference anchor='RFC2817'>
3799  <front>
3800    <title>Upgrading to TLS Within HTTP/1.1</title>
3801    <author initials='R.' surname='Khare' fullname='R. Khare'>
3802      <organization>4K Associates / UC Irvine</organization>
3803      <address><email>rohit@4K-associates.com</email></address>
3804    </author>
3805    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3806      <organization>Agranat Systems, Inc.</organization>
3807      <address><email>lawrence@agranat.com</email></address>
3808    </author>
3809    <date year='2000' month='May' />
3810  </front>
3811  <seriesInfo name='RFC' value='2817' />
3812</reference>
3813
3814<reference anchor='RFC3864'>
3815  <front>
3816    <title>Registration Procedures for Message Header Fields</title>
3817    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3818      <organization>Nine by Nine</organization>
3819      <address><email>GK-IETF@ninebynine.org</email></address>
3820    </author>
3821    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3822      <organization>BEA Systems</organization>
3823      <address><email>mnot@pobox.com</email></address>
3824    </author>
3825    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3826      <organization>HP Labs</organization>
3827      <address><email>JeffMogul@acm.org</email></address>
3828    </author>
3829    <date year='2004' month='September' />
3830  </front>
3831  <seriesInfo name='BCP' value='90' />
3832  <seriesInfo name='RFC' value='3864' />
3833</reference>
3834
3835<reference anchor='RFC5226'>
3836  <front>
3837    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3838    <author initials='T.' surname='Narten' fullname='T. Narten'>
3839      <organization>IBM</organization>
3840      <address><email>narten@us.ibm.com</email></address>
3841    </author>
3842    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3843      <organization>Google</organization>
3844      <address><email>Harald@Alvestrand.no</email></address>
3845    </author>
3846    <date year='2008' month='May' />
3847  </front>
3848  <seriesInfo name='BCP' value='26' />
3849  <seriesInfo name='RFC' value='5226' />
3850</reference>
3851
3852<reference anchor="RFC5322">
3853  <front>
3854    <title>Internet Message Format</title>
3855    <author initials="P." surname="Resnick" fullname="P. Resnick">
3856      <organization>Qualcomm Incorporated</organization>
3857    </author>
3858    <date year="2008" month="October"/>
3859  </front> 
3860  <seriesInfo name="RFC" value="5322"/>
3861</reference>
3862
3863<reference anchor='RFC5789'>
3864  <front>
3865    <title>PATCH Method for HTTP</title>
3866    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3867      <organization>Linden Lab</organization>
3868    </author>
3869    <author initials='J.' surname='Snell' fullname='J. Snell' />
3870    <date year='2010' month='March' />
3871  </front>
3872  <seriesInfo name='RFC' value='5789' />
3873</reference>
3874
3875<reference anchor="RFC5987">
3876        <front>
3877    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3878    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3879      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3880      <address>
3881        <postal>
3882          <street>Hafenweg 16</street>
3883          <city>Muenster</city><region>NW</region><code>48155</code>
3884          <country>Germany</country>
3885        </postal>
3886        <email>julian.reschke@greenbytes.de</email>     
3887        <uri>http://greenbytes.de/tech/webdav/</uri>   
3888      </address>
3889    </author>
3890    <date month="August" year="2010"/>
3891  </front>
3892  <seriesInfo name="RFC" value="5987"/>
3893</reference>
3894
3895</references>
3896
3897<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3898<t>
3899  This document takes over the Status Code Registry, previously defined
3900  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3901  (<xref target="status.code.registry"/>)
3902</t>
3903<t>
3904  Clarify definition of POST.
3905  (<xref target="POST"/>)
3906</t>
3907<t>
3908  Remove requirement to handle all Content-* header fields; ban use of
3909  Content-Range with PUT.
3910  (<xref target="PUT"/>)
3911</t>
3912<t>
3913  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3914  (<xref target="CONNECT"/>)
3915</t>
3916<t>
3917  Broadened the definition of 203 (Non-Authoritative Information) to include
3918  cases of payload transformations as well.
3919  (<xref target="status.203"/>)
3920</t>
3921<t>
3922  Status codes 301, 302, and 307: removed the normative requirements on both
3923  response payloads and user interaction.
3924  (<xref target="status.3xx"/>)
3925</t>
3926<t>
3927  Failed to consider that there are many other request methods that are safe
3928  to automatically redirect, and further that the user agent is able to make
3929  that determination based on the request method semantics.
3930  Furthermore, allow user agents to rewrite the method from POST to GET
3931  for status codes 301 and 302.
3932  (Sections <xref format="counter" target="status.301"/>,
3933  <xref format="counter" target="status.302"/> and
3934  <xref format="counter" target="status.307"/>)
3935</t>
3936<t>
3937  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3938  It used to indicate that the target resource must be accessed through the
3939  proxy given by the Location field. The Location field gave the URI of the
3940  proxy. The recipient was expected to repeat this single request via the proxy.
3941  (<xref target="status.305"/>)
3942</t>
3943<t>
3944  Define status 426 (Upgrade Required) (this was incorporated from
3945  <xref target="RFC2817"/>).
3946  (<xref target="status.426"/>)
3947</t>
3948<t>
3949  Change ABNF productions for header fields to only define the field value.
3950  (<xref target="header.field.definitions"/>)
3951</t>
3952<t>
3953  Reclassify "Allow" as response header field, removing the option to
3954  specify it in a PUT request.
3955  Relax the server requirement on the contents of the Allow header field and
3956  remove requirement on clients to always trust the header field value.
3957  (<xref target="header.allow"/>)
3958</t>
3959<t>
3960  The ABNF for the Expect header field has been both fixed (allowing parameters
3961  for value-less expectations as well) and simplified (allowing trailing
3962  semicolons after "100-continue" when they were invalid before).
3963  (<xref target="header.expect"/>)
3964</t>
3965<t>
3966  Correct syntax of Location header field to allow URI references (including
3967  relative references and fragments), as referred symbol "absoluteURI" wasn't
3968  what was expected, and add some clarifications as to when use of fragments
3969  would not be appropriate.
3970  (<xref target="header.location"/>)
3971</t>
3972<t>
3973  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3974  extension methods could have used it as well).
3975  (<xref target="header.max-forwards"/>)
3976</t>
3977<t>
3978  Allow Referer field value of "about:blank" as alternative to not specifying it.
3979  (<xref target="header.referer"/>)
3980</t>
3981<t>
3982  In the description of the Server header field, the Via field
3983  was described as a SHOULD. The requirement was and is stated
3984  correctly in the description of the Via header field in &header-via;.
3985  (<xref target="header.server"/>)
3986</t>
3987</section>
3988
3989<?BEGININC p2-semantics.abnf-appendix ?>
3990<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3991<figure>
3992<artwork type="abnf" name="p2-semantics.parsed-abnf">
3993<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3994
3995<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3996
3997<x:ref>Date</x:ref> = HTTP-date
3998
3999<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4000
4001<x:ref>From</x:ref> = mailbox
4002
4003<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4004
4005<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4006
4007<x:ref>Location</x:ref> = URI-reference
4008
4009<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4010
4011<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4012
4013<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4014<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4015<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4016
4017<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4018
4019<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4020<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4021
4022<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4023<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4024
4025<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4026
4027<x:ref>date1</x:ref> = day SP month SP year
4028<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4029<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4030<x:ref>day</x:ref> = 2DIGIT
4031<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4032 / %x54.75.65 ; Tue
4033 / %x57.65.64 ; Wed
4034 / %x54.68.75 ; Thu
4035 / %x46.72.69 ; Fri
4036 / %x53.61.74 ; Sat
4037 / %x53.75.6E ; Sun
4038<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4039 / %x54.75.65.73.64.61.79 ; Tuesday
4040 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4041 / %x54.68.75.72.73.64.61.79 ; Thursday
4042 / %x46.72.69.64.61.79 ; Friday
4043 / %x53.61.74.75.72.64.61.79 ; Saturday
4044 / %x53.75.6E.64.61.79 ; Sunday
4045<x:ref>delta-seconds</x:ref> = 1*DIGIT
4046
4047<x:ref>expect-name</x:ref> = token
4048<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4049<x:ref>expect-value</x:ref> = token / quoted-string
4050<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4051 OWS expect-param ] )
4052
4053<x:ref>hour</x:ref> = 2DIGIT
4054
4055<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4056<x:ref>method</x:ref> = token
4057<x:ref>minute</x:ref> = 2DIGIT
4058<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4059 / %x46.65.62 ; Feb
4060 / %x4D.61.72 ; Mar
4061 / %x41.70.72 ; Apr
4062 / %x4D.61.79 ; May
4063 / %x4A.75.6E ; Jun
4064 / %x4A.75.6C ; Jul
4065 / %x41.75.67 ; Aug
4066 / %x53.65.70 ; Sep
4067 / %x4F.63.74 ; Oct
4068 / %x4E.6F.76 ; Nov
4069 / %x44.65.63 ; Dec
4070
4071<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4072<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4073
4074<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4075<x:ref>product</x:ref> = token [ "/" product-version ]
4076<x:ref>product-version</x:ref> = token
4077
4078<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4079
4080<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4081<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4082<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4083
4084<x:ref>second</x:ref> = 2DIGIT
4085<x:ref>status-code</x:ref> = 3DIGIT
4086
4087<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4088<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4089
4090<x:ref>year</x:ref> = 4DIGIT
4091</artwork>
4092</figure>
4093<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4094; Allow defined but not used
4095; Date defined but not used
4096; Expect defined but not used
4097; From defined but not used
4098; Location defined but not used
4099; Max-Forwards defined but not used
4100; Referer defined but not used
4101; Retry-After defined but not used
4102; Server defined but not used
4103; User-Agent defined but not used
4104; reason-phrase defined but not used
4105; status-code defined but not used
4106</artwork></figure></section>
4107<?ENDINC p2-semantics.abnf-appendix ?>
4108
4109<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4110
4111<section title="Since RFC 2616">
4112<t>
4113  Extracted relevant partitions from <xref target="RFC2616"/>.
4114</t>
4115</section>
4116
4117<section title="Since draft-ietf-httpbis-p2-semantics-00">
4118<t>
4119  Closed issues:
4120  <list style="symbols"> 
4121    <t>
4122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4123      "Via is a MUST"
4124      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4125    </t>
4126    <t>
4127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4128      "Fragments allowed in Location"
4129      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4130    </t>
4131    <t>
4132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4133      "Safe Methods vs Redirection"
4134      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4135    </t>
4136    <t>
4137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4138      "Revise description of the POST method"
4139      (<eref target="http://purl.org/NET/http-errata#post"/>)
4140    </t>
4141    <t>
4142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4143      "Normative and Informative references"
4144    </t>
4145    <t>
4146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4147      "RFC2606 Compliance"
4148    </t>
4149    <t>
4150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4151      "Informative references"
4152    </t>
4153    <t>
4154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4155      "Redundant cross-references"
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  Other changes:
4161  <list style="symbols"> 
4162    <t>
4163      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4164    </t>
4165  </list>
4166</t>
4167</section>
4168
4169<section title="Since draft-ietf-httpbis-p2-semantics-01">
4170<t>
4171  Closed issues:
4172  <list style="symbols"> 
4173    <t>
4174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4175      "PUT side effects"
4176    </t>
4177    <t>
4178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4179      "Duplicate Host header requirements"
4180    </t>
4181  </list>
4182</t>
4183<t>
4184  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4185  <list style="symbols"> 
4186    <t>
4187      Move "Product Tokens" section (back) into Part 1, as "token" is used
4188      in the definition of the Upgrade header field.
4189    </t>
4190    <t>
4191      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4192    </t>
4193    <t>
4194      Copy definition of delta-seconds from Part6 instead of referencing it.
4195    </t>
4196  </list>
4197</t>
4198</section>
4199
4200<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4201<t>
4202  Closed issues:
4203  <list style="symbols"> 
4204    <t>
4205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4206      "Requiring Allow in 405 responses"
4207    </t>
4208    <t>
4209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4210      "Status Code Registry"
4211    </t>
4212    <t>
4213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4214      "Redirection vs. Location"
4215    </t>
4216    <t>
4217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4218      "Cacheability of 303 response"
4219    </t>
4220    <t>
4221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4222      "305 Use Proxy"
4223    </t>
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4226      "Classification for Allow header"
4227    </t>
4228    <t>
4229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4230      "PUT - 'store under' vs 'store at'"
4231    </t>
4232  </list>
4233</t>
4234<t>
4235  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4236  <list style="symbols"> 
4237    <t>
4238      Reference RFC 3984, and update header field registrations for headers defined
4239      in this document.
4240    </t>
4241  </list>
4242</t>
4243<t>
4244  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4245  <list style="symbols"> 
4246    <t>
4247      Replace string literals when the string really is case-sensitive (method).
4248    </t>
4249  </list>
4250</t>
4251</section>
4252
4253<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4254<t>
4255  Closed issues:
4256  <list style="symbols"> 
4257    <t>
4258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4259      "OPTIONS request bodies"
4260    </t>
4261    <t>
4262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4263      "Description of CONNECT should refer to RFC2817"
4264    </t>
4265    <t>
4266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4267      "Location Content-Location reference request/response mixup"
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4273  <list style="symbols"> 
4274    <t>
4275      Added initial proposal for registration process, plus initial
4276      content (non-HTTP/1.1 methods to be added by a separate specification).
4277    </t>
4278  </list>
4279</t>
4280</section>
4281
4282<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4283<t>
4284  Closed issues:
4285  <list style="symbols"> 
4286    <t>
4287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4288      "Content-*"
4289    </t>
4290    <t>
4291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4292      "RFC 2822 is updated by RFC 5322"
4293    </t>
4294  </list>
4295</t>
4296<t>
4297  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4298  <list style="symbols"> 
4299    <t>
4300      Use "/" instead of "|" for alternatives.
4301    </t>
4302    <t>
4303      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4304      whitespace ("OWS") and required whitespace ("RWS").
4305    </t>
4306    <t>
4307      Rewrite ABNFs to spell out whitespace rules, factor out
4308      header field value format definitions.
4309    </t>
4310  </list>
4311</t>
4312</section>
4313
4314<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4315<t>
4316  Closed issues:
4317  <list style="symbols"> 
4318    <t>
4319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4320      "reason-phrase BNF"
4321    </t>
4322  </list>
4323</t>
4324<t>
4325  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4326  <list style="symbols"> 
4327    <t>
4328      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4329    </t>
4330  </list>
4331</t>
4332</section>
4333
4334<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4335<t>
4336  Closed issues:
4337  <list style="symbols"> 
4338    <t>
4339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4340      "Clarify when Referer is sent"
4341    </t>
4342    <t>
4343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4344      "status codes vs methods"
4345    </t>
4346    <t>
4347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4348      "Do not require "updates" relation for specs that register status codes or method names"
4349    </t>
4350  </list>
4351</t>
4352</section>
4353
4354<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4355<t>
4356  Closed issues:
4357  <list style="symbols"> 
4358    <t>
4359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4360      "Idempotency"
4361    </t>
4362    <t>
4363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4364      "TRACE security considerations"
4365    </t>
4366    <t>
4367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4368      "Clarify rules for determining what entities a response carries"
4369    </t>
4370    <t>
4371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4372      "update note citing RFC 1945 and 2068"
4373    </t>
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4376      "update note about redirect limit"
4377    </t>
4378    <t>
4379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4380      "Location header ABNF should use 'URI'"
4381    </t>
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4384      "fragments in Location vs status 303"
4385    </t>
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4388      "move IANA registrations for optional status codes"
4389    </t>
4390  </list>
4391</t>
4392<t>
4393  Partly resolved issues:
4394  <list style="symbols"> 
4395    <t>
4396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4397      "Are OPTIONS and TRACE safe?"
4398    </t>
4399  </list>
4400</t>
4401</section>
4402
4403<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4404<t>
4405  Closed issues:
4406  <list style="symbols"> 
4407    <t>
4408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4409      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4410      status codes when fixing this previously)
4411    </t>
4412  </list>
4413</t>
4414</section>
4415
4416<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4417<t>
4418  Closed issues:
4419  <list style="symbols"> 
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4422      "Fragment combination / precedence during redirects"
4423    </t>
4424  </list>
4425</t>
4426<t>
4427  Partly resolved issues:
4428  <list style="symbols"> 
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4431      "Location header payload handling"
4432    </t>
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4435      "Term for the requested resource's URI"
4436    </t>
4437  </list>
4438</t>
4439</section>
4440
4441<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4442<t>
4443  Closed issues:
4444  <list style="symbols"> 
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4447      "Clarify 'Requested Variant'"
4448    </t>
4449    <t>
4450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4451      "Clarify entity / representation / variant terminology"
4452    </t>
4453    <t>
4454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4455      "Methods and Caching"
4456    </t>
4457    <t>
4458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4459      "OPTIONS vs Max-Forwards"
4460    </t>
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4463      "Status codes and caching"
4464    </t>
4465    <t>
4466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4467      "consider removing the 'changes from 2068' sections"
4468    </t>
4469  </list>
4470</t>
4471</section>
4472
4473<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4474<t>
4475  Closed issues:
4476  <list style="symbols"> 
4477    <t>
4478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4479      "Considerations for new status codes"
4480    </t>
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4483      "Considerations for new methods"
4484    </t>
4485    <t>
4486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4487      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4488    </t>
4489  </list>
4490</t>
4491</section>
4492
4493<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4494<t>
4495  Closed issues:
4496  <list style="symbols"> 
4497    <t>
4498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4499      "Fragment combination / precedence during redirects" (added warning
4500      about having a fragid on the redirect may cause inconvenience in
4501      some cases)
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4505      "Content-* vs. PUT"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4509      "205 Bodies"
4510    </t>
4511    <t>
4512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4513      "Understanding Content-* on non-PUT requests"
4514    </t>
4515    <t>
4516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4517      "Content-*"
4518    </t>
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4521      "Header type defaulting"
4522    </t>
4523    <t>
4524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4525      "PUT - 'store under' vs 'store at'"
4526    </t>
4527    <t>
4528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4529      "duplicate ABNF for reason-phrase"
4530    </t>
4531    <t>
4532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4533      "Note special status of Content-* prefix in header registration procedures"
4534    </t>
4535    <t>
4536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4537      "Max-Forwards vs extension methods"
4538    </t>
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4541      "What is the value space of HTTP status codes?" (actually fixed in
4542      draft-ietf-httpbis-p2-semantics-11)
4543    </t>
4544    <t>
4545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4546      "Header Classification"
4547    </t>
4548    <t>
4549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4550      "PUT side effect: invalidation or just stale?"
4551    </t>
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4554      "proxies not supporting certain methods"
4555    </t>
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4558      "Migrate CONNECT from RFC2817 to p2"
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4562      "Migrate Upgrade details from RFC2817"
4563    </t>
4564    <t>
4565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4566      "clarify PUT semantics'"
4567    </t>
4568    <t>
4569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4570      "duplicate ABNF for 'Method'"
4571    </t>
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4574      "untangle ABNFs for header fields"
4575    </t>
4576  </list>
4577</t>
4578</section>
4579
4580<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4581<t>
4582  Closed issues:
4583  <list style="symbols"> 
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4586      "untangle ABNFs for header fields"
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4590      "message body in CONNECT request"
4591    </t>
4592  </list>
4593</t>
4594</section>
4595
4596<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4597<t>
4598  Closed issues:
4599  <list style="symbols"> 
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4602      "Clarify status code for rate limiting"
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4606      "clarify 403 forbidden"
4607    </t>
4608    <t>
4609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4610      "Clarify 203 Non-Authoritative Information"
4611    </t>
4612    <t>
4613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4614      "update default reason phrase for 413"
4615    </t>
4616  </list>
4617</t>
4618</section>
4619
4620<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4621<t>
4622  Closed issues:
4623  <list style="symbols"> 
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4626      "Strength of requirements on Accept re: 406"
4627    </t>
4628    <t>
4629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4630      "400 response isn't generic"
4631    </t>
4632  </list>
4633</t>
4634</section>
4635
4636<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4637<t>
4638  Closed issues:
4639  <list style="symbols"> 
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4642      "Redirects and non-GET methods"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4646      "Document HTTP's error-handling philosophy"
4647    </t>
4648    <t>
4649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4650      "Considerations for new headers"
4651    </t>
4652    <t>
4653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4654      "clarify 303 redirect on HEAD"
4655    </t>
4656  </list>
4657</t>
4658</section>
4659
4660<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4661<t>
4662  Closed issues:
4663  <list style="symbols"> 
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4666      "Location header payload handling"
4667    </t>
4668    <t>
4669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4670      "Clarify status code for rate limiting" (change backed out because
4671      a new status code is being defined for this purpose)
4672    </t>
4673    <t>
4674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4675      "should there be a permanent variant of 307"
4676    </t>
4677    <t>
4678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4679      "When are Location's semantics triggered?"
4680    </t>
4681    <t>
4682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4683      "'expect' grammar missing OWS"
4684    </t>
4685    <t>
4686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4687      "header field considerations: quoted-string vs use of double quotes"
4688    </t>
4689  </list>
4690</t>
4691</section>
4692
4693<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4694<t>
4695  Closed issues:
4696  <list style="symbols"> 
4697    <t>
4698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4699      "Combining HEAD responses"
4700    </t>
4701    <t>
4702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4703      "Requirements for user intervention during redirects"
4704    </t>
4705    <t>
4706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4707      "message-body in CONNECT response"
4708    </t>
4709    <t>
4710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4711      "Applying original fragment to 'plain' redirected URI"
4712    </t>
4713    <t>
4714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4715      "Misplaced text on connection handling in p2"
4716    </t>
4717    <t>
4718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4719      "clarify that 201 doesn't require Location header fields"
4720    </t>
4721    <t>
4722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4723      "relax requirements on hypertext in 3/4/5xx error responses"
4724    </t>
4725    <t>
4726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4727      "example for 426 response should have a payload"
4728    </t>
4729    <t>
4730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4731      "drop indirection entries for status codes"
4732    </t>
4733  </list>
4734</t>
4735</section>
4736
4737</section>
4738
4739</back>
4740</rfc>
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