source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1421

Last change on this file since 1421 was 1421, checked in by julian.reschke@…, 8 years ago

rephrase 303 description (now doesn't imply GET is needed anymore) (see #310)

  • Property svn:eol-style set to native
File size: 174.8 KB
[29]1<?xml version="1.0" encoding="utf-8"?>
[101]2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
[8]3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
[29]14  <!ENTITY ID-VERSION "latest">
[1368]15  <!ENTITY ID-MONTH "August">
[1099]16  <!ENTITY ID-YEAR "2011">
[1101]17  <!ENTITY mdash "&#8212;">
[424]18  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x=''/>">
[1364]19  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x=''/>">
[31]20  <!ENTITY messaging                  "<xref target='Part1' xmlns:x=''/>">
21  <!ENTITY payload                    "<xref target='Part3' xmlns:x=''/>">
22  <!ENTITY conditional                "<xref target='Part4' xmlns:x=''/>">
23  <!ENTITY range                      "<xref target='Part5' xmlns:x=''/>">
24  <!ENTITY caching                    "<xref target='Part6' xmlns:x=''/>">
25  <!ENTITY auth                       "<xref target='Part7' xmlns:x=''/>">
26  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
[205]27  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
28  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
[1396]29  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x=''/>">
[31]30  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]31  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[1309]32  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x=''/>">
[1417]33  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x=''/>">
[580]34  <!ENTITY full-date                  "<xref target='Part1' x:rel='' xmlns:x=''/>">
[31]35  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
36  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
37  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
38  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
[1065]39  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x=''/>">
[31]40  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
41  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
42  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
43  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
44  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
45  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
46  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
47  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
[1417]48  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x=''/>">
[31]49  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
50  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
51  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
52  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
[688]53  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x=''/>">
[31]54  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
55  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
56  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
57  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
58  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
59  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
60  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
61  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
62  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
63  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
[835]64  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
65  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x=''/>">
[31]66  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
67  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
68  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
69  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
70  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
[190]71  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x=''/>">
[263]72  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='' xmlns:x=''/>">
[700]73  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x=''/>">
74  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
75  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x=''/>">
76  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x=''/>">
77  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x=''/>">
78  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x=''/>">
[1415]79  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x=''/>">
[838]80  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x=''/>">
81  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x=''/>">
82  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x=''/>">
[1050]83  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x=''/>">
[1111]84  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x=''/>">
85  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x=''/>">
87<?rfc toc="yes" ?>
[29]88<?rfc symrefs="yes" ?>
89<?rfc sortrefs="yes" ?>
[8]90<?rfc compact="yes"?>
91<?rfc subcompact="no" ?>
92<?rfc linkmailto="no" ?>
93<?rfc editing="no" ?>
[203]94<?rfc comments="yes"?>
95<?rfc inline="yes"?>
[799]96<?rfc rfcedstyle="yes"?>
[8]97<?rfc-ext allow-markup-in-artwork="yes" ?>
98<?rfc-ext include-references-in-index="yes" ?>
[308]99<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
[446]100     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
[286]101     xmlns:x=''
102     xmlns:rdf=''>
[120]105  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
[29]107  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]108    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]109    <address>
110      <postal>
[1106]111        <street>345 Park Ave</street>
112        <city>San Jose</city>
[8]113        <region>CA</region>
[1106]114        <code>95110</code>
[29]115        <country>USA</country>
[8]116      </postal>
[29]117      <email></email>
118      <uri></uri>
[8]119    </address>
120  </author>
[29]122  <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]123    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
[8]124    <address>
125      <postal>
[29]126        <street>21 Oak Knoll Road</street>
127        <city>Carlisle</city>
[8]128        <region>MA</region>
[29]129        <code>01741</code>
130        <country>USA</country>
[8]131      </postal>
[844]132      <email></email>
133      <uri></uri>
[8]134    </address>
135  </author>
137  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]138    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]139    <address>
140      <postal>
[29]141        <street>HP Labs, Large Scale Systems Group</street>
142        <street>1501 Page Mill Road, MS 1177</street>
[8]143        <city>Palo Alto</city>
144        <region>CA</region>
[29]145        <code>94304</code>
146        <country>USA</country>
[8]147      </postal>
[29]148      <email></email>
[8]149    </address>
150  </author>
152  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]153    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]154    <address>
155      <postal>
[29]156        <street>1 Microsoft Way</street>
157        <city>Redmond</city>
158        <region>WA</region>
159        <code>98052</code>
160        <country>USA</country>
[8]161      </postal>
[29]162      <email></email>
[8]163    </address>
164  </author>
166  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]167    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]168    <address>
169      <postal>
[29]170        <street>345 Park Ave</street>
171        <city>San Jose</city>
[8]172        <region>CA</region>
[29]173        <code>95110</code>
174        <country>USA</country>
[8]175      </postal>
[29]176      <email></email>
177      <uri></uri>
[8]178    </address>
179  </author>
181  <author initials="P." surname="Leach" fullname="Paul J. Leach">
182    <organization abbrev="Microsoft">Microsoft Corporation</organization>
183    <address>
184      <postal>
185        <street>1 Microsoft Way</street>
186        <city>Redmond</city>
187        <region>WA</region>
188        <code>98052</code>
189      </postal>
190      <email></email>
191    </address>
192  </author>
194  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
195    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
196    <address>
197      <postal>
[34]198        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
199        <street>The Stata Center, Building 32</street>
200        <street>32 Vassar Street</street>
[8]201        <city>Cambridge</city>
202        <region>MA</region>
203        <code>02139</code>
[29]204        <country>USA</country>
[8]205      </postal>
206      <email></email>
[34]207      <uri></uri>
[8]208    </address>
209  </author>
[95]211  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]212    <organization abbrev="W3C">World Wide Web Consortium</organization>
213    <address>
214      <postal>
215        <street>W3C / ERCIM</street>
216        <street>2004, rte des Lucioles</street>
217        <city>Sophia-Antipolis</city>
218        <region>AM</region>
219        <code>06902</code>
220        <country>France</country>
221      </postal>
222      <email></email>
223      <uri></uri>
224    </address>
225  </author>
[95]227  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
228    <organization abbrev="greenbytes">greenbytes GmbH</organization>
229    <address>
230      <postal>
231        <street>Hafenweg 16</street>
232        <city>Muenster</city><region>NW</region><code>48155</code>
233        <country>Germany</country>
234      </postal>
[609]235      <phone>+49 251 2807760</phone>
236      <facsimile>+49 251 2807761</facsimile>
237      <email></email>
238      <uri></uri>
[95]239    </address>
240  </author>
[31]242  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[440]243  <workgroup>HTTPbis Working Group</workgroup>
[1373]247   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
248   distributed, collaborative, hypertext information systems. HTTP has been in
249   use by the World Wide Web global information initiative since 1990. This
250   document is Part 2 of the seven-part specification that defines the protocol
251   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
254   Part 2 defines the semantics of HTTP messages as expressed by request
255   methods, request header fields, response status codes, and response header
256   fields.
260<note title="Editorial Note (To be removed by RFC Editor)">
261  <t>
262    Discussion of this draft should take place on the HTTPBIS working group
[1268]263    mailing list (, which is archived at
264    <eref target=""/>.
265  </t>
266  <t>
267    The current issues list is at
268    <eref target=""/> and related
269    documents (including fancy diffs) can be found at
[324]270    <eref target=""/>.
[36]271  </t>
[153]272  <t>
[1401]273    The changes in this draft are summarized in <xref target="changes.since.16"/>.
[153]274  </t>
278<section title="Introduction" anchor="introduction">
[162]280   This document defines HTTP/1.1 request and response semantics.  Each HTTP
281   message, as defined in &messaging;, is in the form of either a request or
282   a response.  An HTTP server listens on a connection for HTTP requests and
283   responds to each request, in the order received on that connection, with
284   one or more HTTP response messages.  This document defines the commonly
285   agreed upon semantics of the HTTP uniform interface, the intentions defined
286   by each request method, and the various response messages that might be
[965]287   expected as a result of applying that method to the target resource.
[162]290   This document is currently disorganized in order to minimize the changes
291   between drafts and enable reviewers to see the smaller errata changes.
[980]292   A future draft will reorganize the sections to better reflect the content.
[162]293   In particular, the sections will be ordered according to the typical
294   processing of an HTTP request message (after message parsing): resource
[1163]295   mapping, methods, request modifying header fields, response status,
296   status modifying header fields, and resource metadata.  The current mess
297   reflects how widely dispersed these topics and associated requirements
298   had become in <xref target="RFC2616"/>.
301<section title="Requirements" anchor="intro.requirements">
303   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
304   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
305   document are to be interpreted as described in <xref target="RFC2119"/>.
308   An implementation is not compliant if it fails to satisfy one or more
[847]309   of the "MUST" or "REQUIRED" level requirements for the protocols it
310   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
311   level and all the "SHOULD" level requirements for its protocols is said
312   to be "unconditionally compliant"; one that satisfies all the "MUST"
313   level requirements but not all the "SHOULD" level requirements for its
314   protocols is said to be "conditionally compliant".
[424]318<section title="Syntax Notation" anchor="notation">
[425]319  <x:anchor-alias value="CR"/>
320  <x:anchor-alias value="DIGIT"/>
321  <x:anchor-alias value="LF"/>
322  <x:anchor-alias value="VCHAR"/>
323  <x:anchor-alias value="WSP"/>
[543]325  This specification uses the ABNF syntax defined in &notation; (which
326  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
327  <xref target="collected.abnf"/> shows the collected ABNF, with the list
328  rule expanded.
[425]331  The following core rules are included by
332  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334  DIGIT (decimal 0-9), DQUOTE (double quote),
335  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336  OCTET (any 8-bit sequence of data), SP (space),
337  VCHAR (any visible USASCII character),
338  and WSP (whitespace).
341<section title="Core Rules" anchor="core.rules">
[398]342  <x:anchor-alias value="obs-text"/>
[229]343  <x:anchor-alias value="quoted-string"/>
344  <x:anchor-alias value="token"/>
[356]345  <x:anchor-alias value="OWS"/>
346  <x:anchor-alias value="RWS"/>
[1396]348  The core rules below are defined in <xref target="Part1"/>:
350<figure><artwork type="abnf2616">
[356]351  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
352  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
[398]353  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
[1396]354  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
355  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
359<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]360  <x:anchor-alias value="absolute-URI"/>
[688]361  <x:anchor-alias value="comment"/>
[229]362  <x:anchor-alias value="HTTP-date"/>
[391]363  <x:anchor-alias value="partial-URI"/>
[229]364  <x:anchor-alias value="product"/>
[785]365  <x:anchor-alias value="URI-reference"/>
[206]367  The ABNF rules below are defined in other parts:
[207]369<figure><!--Part1--><artwork type="abnf2616">
[374]370  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
[688]371  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
[229]372  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
[391]373  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
[229]374  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
[785]375  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
[8]381<section title="Method" anchor="method">
[229]382  <x:anchor-alias value="Method"/>
383  <x:anchor-alias value="extension-method"/>
[1161]385   The Method token indicates the request method to be performed on the target
[972]386   resource (&effective-request-uri;). The method is case-sensitive.
[1128]388<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
389  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
392   The list of methods allowed by a resource can be specified in an
[965]393   Allow header field (<xref target="header.allow"/>). The status code of the response
[8]394   always notifies the client whether a method is currently allowed on a
395   resource, since the set of allowed methods can change dynamically. An
[965]396   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
[8]397   if the method is known by the origin server but not allowed for the
[965]398   resource, and 501 (Not Implemented) if the method is
[8]399   unrecognized or not implemented by the origin server. The methods GET
400   and HEAD &MUST; be supported by all general-purpose servers. All other
401   methods are &OPTIONAL;; however, if the above methods are implemented,
402   they &MUST; be implemented with the same semantics as those specified
403   in <xref target="method.definitions"/>.
[1128]406<section title="Overview of Methods" anchor="overview.of.methods">
408  The methods listed below are defined in <xref target="method.definitions"/>.
410<texttable align="left">
411  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
413  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
414  <c>GET</c> <c><xref target="GET"/></c>
415  <c>HEAD</c> <c><xref target="HEAD"/></c>
416  <c>POST</c> <c><xref target="POST"/></c>
417  <c>PUT</c> <c><xref target="PUT"/></c>
418  <c>DELETE</c> <c><xref target="DELETE"/></c>
419  <c>TRACE</c> <c><xref target="TRACE"/></c>
420  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
[1161]423  Note that this list is not exhaustive &mdash; it does not include request methods defined
[1128]424  in other specifications.
[270]428<section title="Method Registry" anchor="method.registry">
430  The HTTP Method Registry defines the name space for the Method token in the
431  Request line of an HTTP request.
[286]434  Registrations &MUST; include the following fields:
435  <list style="symbols">
436    <t>Method Name (see <xref target="method"/>)</t>
437    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
438    <t>Pointer to specification text</t>
439  </list>
[270]442  Values to be added to this name space are subject to IETF review
[591]443  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
[672]446  The registry itself is maintained at <eref target=""/>.
[1037]449<section title="Considerations for New Methods" anchor="">
451   When it is necessary to express new semantics for a HTTP request that
452   aren't specific to a single application or media type, and currently defined
453   methods are inadequate, it may be appropriate to register a new method.
[1042]456   HTTP methods are generic; that is, they are potentially applicable to any
457   resource, not just one particular media type, "type" of resource, or
458   application. As such, it is preferred that new HTTP methods be registered
459   in a document that isn't specific to a single application, so that this is
460   clear.
[1040]463   Due to the parsing rules defined in &message-body;, definitions of HTTP
464   methods cannot prohibit the presence of a message-body on either the request
465   or the response message (with responses to HEAD requests being the single
466   exception). Definitions of new methods cannot change this rule, but they can
467   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
[1042]470   New method definitions need to indicate whether they are safe (<xref
[1261]471   target="safe.methods"/>), what semantics (if any) the request body has,
472   and whether they are idempotent (<xref target="idempotent.methods"/>).
473   They also need to state whether they can be cached (&caching;); in
474   particular what conditions a cache may store the response, and under what
475   conditions such a stored response may be used to satisfy a subsequent
476   request.
[1416]483<section title="Header Fields" anchor="header.fields">
485   Header fields are key value pairs that can be used to communicate data about
486   the message, its payload, the target resource, or about the connection
487   itself (i.e., control data).  See &header-fields; for a general definition
488   of their syntax.
[1417]491<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
493   New header fields are registered using the procedures described in
494   <xref target="RFC3864"/>.
497   The requirements for header field names are defined in
498   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
499   defining new fields are advised to keep the name as short as practical, and
500   not to prefix them with "X-" if they are to be registered (either
501   immediately or in the future).
504   New header field values typically have their syntax defined using ABNF
505   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
506   as necessary, and are usually constrained to the range of ASCII characters.
507   Header fields needing a greater range of characters can use an encoding
508   such as the one defined in <xref target="RFC5987"/>.
511   Because commas (",") are used as a generic delimiter between field-values,
512   they need to be treated with care if they are allowed in the field-value's
513   payload. Typically, components that might contain a comma are protected with
514   double-quotes using the quoted-string ABNF production (&field-rules;).
517   For example, a textual date and a URI (either of which might contain a comma)
518   could be safely carried in field-values like these:
520<figure><artwork type="example">
521  Example-URI-Field: ",foo",
522                     ""
523  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
526   Authors of specifications defining new header fields are advised to consider
527   documenting:
528  <list style="symbols">
529    <t>Whether the field is a single value, or whether it can be a list
530    (delimited by commas; see &header-fields;).</t>
531    <t>Under what conditions the header field can be used; e.g., only i
532    responses or requests, in all messages, only on responses to a particular
533    request method.</t>
534    <t>Whether it is appropriate to list the field-name in the Connection header
535    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t>
536    <t>Under what conditions intermediaries are allowed to modify the header
537    field's value, insert or delete it.</t>
538    <t>How the header might interact with caching (see <xref target="Part6"/>).</t>
539    <t>Whether the header field is useful or allowable in trailers (see
540    &chunked-encoding;).</t>
541    <t>Whether the header field should be preserved across redirects.</t>
542  </list>
[8]546<section title="Request Header Fields" anchor="request.header.fields">
[229]547  <x:anchor-alias value="request-header"/>
[1163]549   The request header fields allow the client to pass additional
[8]550   information about the request, and about the client itself, to the
551   server. These fields act as request modifiers, with semantics
552   equivalent to the parameters on a programming language method
553   invocation.
[1138]555<texttable align="left">
556  <ttcol>Header Field Name</ttcol>
557  <ttcol>Defined in...</ttcol>
559  <c>Accept</c> <c>&header-accept;</c>
560  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
561  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
562  <c>Accept-Language</c> <c>&header-accept-language;</c>
563  <c>Authorization</c> <c>&header-authorization;</c>
564  <c>Expect</c> <c><xref target="header.expect"/></c>
565  <c>From</c> <c><xref target="header.from"/></c>
566  <c>Host</c> <c>&header-host;</c>
567  <c>If-Match</c> <c>&header-if-match;</c>
568  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
569  <c>If-None-Match</c> <c>&header-if-none-match;</c>
570  <c>If-Range</c> <c>&header-if-range;</c>
571  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
572  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
573  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
574  <c>Range</c> <c>&header-range;</c>
575  <c>Referer</c> <c><xref target="header.referer"/></c>
576  <c>TE</c> <c>&header-te;</c>
577  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
[1416]581<section title="Response Header Fields" anchor="response.header.fields">
582  <x:anchor-alias value="response-header"/>
584   The response header fields allow the server to pass additional
585   information about the response which cannot be placed in the Status-Line.
586   These header fields give information about the server and about
587   further access to the target resource (&effective-request-uri;).
589<texttable align="left">
590  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
592  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
593  <c>Age</c> <c>&header-age;</c>
594  <c>Allow</c> <c><xref target="header.allow"/></c>
595  <c>ETag</c> <c>&header-etag;</c>
596  <c>Location</c> <c><xref target="header.location"/></c>
597  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
598  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
599  <c>Server</c> <c><xref target="header.server"/></c>
600  <c>Vary</c> <c>&header-vary;</c>
601  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
[8]607<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
[229]608  <x:anchor-alias value="Reason-Phrase"/>
609  <x:anchor-alias value="Status-Code"/>
[426]610  <x:anchor-alias value="extension-code"/>
[1124]612   The Status-Code element is a 3-digit integer result code of the attempt to
613   understand and satisfy the request.
[1124]616   The Reason-Phrase is intended to give a short textual description of the
[1137]617   Status-Code and is intended for a human user. The client does not need
[1124]618   to examine or display the Reason-Phrase.
620<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"/>
[1124]621  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
[398]622  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
625   HTTP status codes are extensible. HTTP applications are not required
626   to understand the meaning of all registered status codes, though such
627   understanding is obviously desirable. However, applications &MUST;
628   understand the class of any status code, as indicated by the first
629   digit, and treat any unrecognized response as being equivalent to the
630   x00 status code of that class, with the exception that an
631   unrecognized response &MUST-NOT; be cached. For example, if an
632   unrecognized status code of 431 is received by the client, it can
633   safely assume that there was something wrong with its request and
634   treat the response as if it had received a 400 status code. In such
[866]635   cases, user agents &SHOULD; present to the user the representation enclosed
636   with the response, since that representation is likely to include human-readable
[8]637   information which will explain the unusual status.
[1124]640<section title="Overview of Status Codes" anchor="">
[1137]642   The status codes listed below are defined in <xref target=""/>
643   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
644   The reason phrases listed here are only recommendations &mdash; they can be
645   replaced by local equivalents without affecting the protocol.
647<texttable align="left">
648  <ttcol>Status-Code</ttcol>
649  <ttcol>Reason-Phrase</ttcol>
650  <ttcol>Defined in...</ttcol>
652  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
653  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
655  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
656  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
657  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
658  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
659  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
660  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
661  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
663  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
664  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
665  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
666  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
667  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
668  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
669  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
671  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
672  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
673  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
674  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
675  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
676  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
677  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
678  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
679  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
680  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
681  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
682  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
683  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
[1322]684  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
[1124]685  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
686  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
687  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
688  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
689  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
691  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
692  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
693  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
694  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
695  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
696  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
699   Note that this list is not exhaustive &mdash; it does not include
700   extension status codes defined in other specifications.
[262]704<section title="Status Code Registry" anchor="status.code.registry">
706  The HTTP Status Code Registry defines the name space for the Status-Code
[924]707  token in the Status-Line of an HTTP response.
710  Values to be added to this name space are subject to IETF review
[591]711  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
714  The registry itself is maintained at <eref target=""/>.
[1038]717<section title="Considerations for New Status Codes" anchor="">
719   When it is necessary to express new semantics for a HTTP response that
720   aren't specific to a single application or media type, and currently defined
721   status codes are inadequate, a new status code can be registered.
[1043]724   HTTP status codes are generic; that is, they are potentially applicable to
725   any resource, not just one particular media type, "type" of resource, or
726   application. As such, it is preferred that new HTTP status codes be
727   registered in a document that isn't specific to a single application, so
728   that this is clear.
[1043]731   Definitions of new HTTP status codes typically explain the request
732   conditions that produce a response containing the status code (e.g.,
733   combinations of request headers and/or method(s)), along with any
734   interactions with response headers (e.g., those that are required, those
735   that modify the semantics of the response).
738   New HTTP status codes are required to fall under one of the categories
739   defined in <xref target=""/>. To allow existing parsers to
740   properly handle them, new status codes cannot disallow a response body,
741   although they can mandate a zero-length response body. They can require the
742   presence of one or more particular HTTP response header(s).
745   Likewise, their definitions can specify that caches are allowed to use
[1035]746   heuristics to determine their freshness (see &caching;; by default, it is
[1043]747   not allowed), and can define how to determine the resource which they
[1035]748   carry a representation for (see <xref
749   target="identifying.response.associated.with.representation"/>; by default,
[1038]750   it is anonymous).
[874]758<section title="Representation" anchor="representation">
[866]760   Request and Response messages &MAY; transfer a representation if not otherwise
761   restricted by the request method or response status code. A representation
762   consists of metadata (representation header fields) and data (representation
763   body).  When a complete or partial representation is enclosed in an HTTP message,
764   it is referred to as the payload of the message. HTTP representations
765   are defined in &payload;.
[866]768   A representation body is only present in a message when a message-body is
769   present, as described in &message-body;. The representation body is obtained
[8]770   from the message-body by decoding any Transfer-Encoding that might
771   have been applied to ensure safe and proper transfer of the message.
774<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
[965]776   It is sometimes necessary to determine an identifier for the resource
[695]777   associated with a representation.
780   An HTTP request representation, when present, is always associated with an
781   anonymous (i.e., unidentified) resource.
[972]784   In the common case, an HTTP response is a representation of the target
785   resource (see &effective-request-uri;). However, this is not always the
786   case. To determine the URI of the resource a response is associated with,
787   the following rules are used (with the first applicable one being selected):
789<t><list style="numbers">
790   <t>If the response status code is 200 or 203 and the request method was GET,
[972]791   the response payload is a representation of the target resource.</t>
[924]792   <t>If the response status code is 204, 206, or 304 and the request method was GET
[972]793   or HEAD, the response payload is a partial representation of the target
[1374]794   resource.</t>
[994]795   <t>If the response has a Content-Location header field, and that URI is the same
[965]796   as the effective request URI, the response payload is a representation of the
[972]797   target resource.</t>
[994]798   <t>If the response has a Content-Location header field, and that URI is not the
[965]799   same as the effective request URI, then the response asserts that its
800   payload is a representation of the resource identified by the
801   Content-Location URI. However, such an assertion cannot be trusted unless
802   it can be verified by other means (not defined by HTTP).</t>
[695]803   <t>Otherwise, the response is a representation of an anonymous (i.e.,
804   unidentified) resource.</t>
807  <cref anchor="TODO-req-uri">
[823]808   The comparison function is going to have to be defined somewhere,
[695]809   because we already need to compare URIs for things like cache invalidation.</cref>
[8]816<section title="Method Definitions" anchor="method.definitions">
[1161]818   The set of common request methods for HTTP/1.1 is defined below. Although
[8]819   this set can be expanded, additional methods cannot be assumed to
820   share the same semantics for separately extended clients and servers.
823<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
825<section title="Safe Methods" anchor="safe.methods">
[286]826<iref item="Safe Methods" primary="true"/>
[969]828   Implementors need to be aware that the software represents the user in
829   their interactions over the Internet, and need to allow
[901]830   the user to be aware of any actions they take which might have an
[8]831   unexpected significance to themselves or others.
[708]834   In particular, the convention has been established that the GET, HEAD,
[1161]835   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
836   of taking an action other than retrieval. These request methods ought
837   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
[8]838   This allows user agents to represent other methods, such as POST, PUT
839   and DELETE, in a special way, so that the user is made aware of the
840   fact that a possibly unsafe action is being requested.
843   Naturally, it is not possible to ensure that the server does not
844   generate side-effects as a result of performing a GET request; in
845   fact, some dynamic resources consider that a feature. The important
846   distinction here is that the user did not request the side-effects,
847   so therefore cannot be held accountable for them.
851<section title="Idempotent Methods" anchor="idempotent.methods">
[286]852<iref item="Idempotent Methods" primary="true"/>
[1161]854   Request methods can also have the property of "idempotence" in that,
855   aside from error or expiration issues, the intended effect of multiple
[657]856   identical requests is the same as for a single request.
[1161]857   PUT, DELETE, and all safe request methods are idempotent.
[657]858   It is important to note that idempotence refers only to changes
859   requested by the client: a server is free to change its state due
860   to multiple requests for the purpose of tracking those requests,
861   versioning of results, etc.
866<section title="OPTIONS" anchor="OPTIONS">
[286]867  <rdf:Description>
868    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
869  </rdf:Description>
[8]870  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
871  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
[1161]873   The OPTIONS method requests information about the
[8]874   communication options available on the request/response chain
[1161]875   identified by the effective request URI. This method allows a client to
[8]876   determine the options and/or requirements associated with a resource,
877   or the capabilities of a server, without implying a resource action
878   or initiating a resource retrieval.
[1161]881   Responses to the OPTIONS method are not cacheable.
[874]884   If the OPTIONS request includes a message-body (as indicated by the
[8]885   presence of Content-Length or Transfer-Encoding), then the media type
886   &MUST; be indicated by a Content-Type field. Although this
887   specification does not define any use for such a body, future
888   extensions to HTTP might use the OPTIONS body to make more detailed
[280]889   queries on the server.
[391]892   If the request-target is an asterisk ("*"), the OPTIONS request is
[8]893   intended to apply to the server in general rather than to a specific
894   resource. Since a server's communication options typically depend on
895   the resource, the "*" request is only useful as a "ping" or "no-op"
896   type of method; it does nothing beyond allowing the client to test
897   the capabilities of the server. For example, this can be used to test
898   a proxy for HTTP/1.1 compliance (or lack thereof).
[391]901   If the request-target is not an asterisk, the OPTIONS request applies
[8]902   only to the options that are available when communicating with that
903   resource.
906   A 200 response &SHOULD; include any header fields that indicate
907   optional features implemented by the server and applicable to that
908   resource (e.g., Allow), possibly including extensions not defined by
909   this specification. The response body, if any, &SHOULD; also include
910   information about the communication options. The format for such a
911   body is not defined by this specification, but might be defined by
912   future extensions to HTTP. Content negotiation &MAY; be used to select
913   the appropriate response format. If no response body is included, the
914   response &MUST; include a Content-Length field with a field-value of
915   "0".
[1163]918   The Max-Forwards header field &MAY; be used to target a
[893]919   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
920   If no Max-Forwards field is present in the request, then the forwarded
[8]921   request &MUST-NOT; include a Max-Forwards field.
925<section title="GET" anchor="GET">
[286]926  <rdf:Description>
927    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
928  </rdf:Description>
[8]929  <iref primary="true" item="GET method" x:for-anchor=""/>
930  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
[1161]932   The GET method requests transfer of a current representation of
933   the target resource.
[972]936   If the target resource is a data-producing process, it is the
[866]937   produced data which shall be returned as the representation in the response and not
[730]938   the source text of the process, unless that text happens to be the output of
939   the process.
942   The semantics of the GET method change to a "conditional GET" if the
943   request message includes an If-Modified-Since, If-Unmodified-Since,
944   If-Match, If-None-Match, or If-Range header field. A conditional GET
[1161]945   requests that the representation be transferred only under the
[8]946   circumstances described by the conditional header field(s). The
[1161]947   conditional GET request is intended to reduce unnecessary network
[874]948   usage by allowing cached representations to be refreshed without requiring
[8]949   multiple requests or transferring data already held by the client.
952   The semantics of the GET method change to a "partial GET" if the
953   request message includes a Range header field. A partial GET requests
[866]954   that only part of the representation be transferred, as described in &header-range;.
[1161]955   The partial GET request is intended to reduce unnecessary
[866]956   network usage by allowing partially-retrieved representations to be
[8]957   completed without transferring data already held by the client.
960   Bodies on GET requests have no defined semantics. Note that sending a body
961   on a GET request might cause some existing implementations to reject the
962   request.
[888]965   The response to a GET request is cacheable and &MAY; be used to satisfy
966   subsequent GET and HEAD requests (see &caching;).
969   See <xref target=""/> for security considerations when used for forms.
973<section title="HEAD" anchor="HEAD">
[286]974  <rdf:Description>
975    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
976  </rdf:Description>
[8]977  <iref primary="true" item="HEAD method" x:for-anchor=""/>
978  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
980   The HEAD method is identical to GET except that the server &MUST-NOT;
[867]981   return a message-body in the response. The metadata contained
[994]982   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
[8]983   to the information sent in response to a GET request. This method can
[867]984   be used for obtaining metadata about the representation implied by the
[866]985   request without transferring the representation body. This method is
[8]986   often used for testing hypertext links for validity, accessibility,
987   and recent modification.
[888]990   The response to a HEAD request is cacheable and &MAY; be used to satisfy
991   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
992   representation from that resource; if the new field values
[874]993   indicate that the cached representation differs from the current representation (as
[1367]994   would be indicated by a change in Content-Length, ETag
[8]995   or Last-Modified), then the cache &MUST; treat the cache entry as
996   stale.
999   Bodies on HEAD requests have no defined semantics. Note that sending a body
1000   on a HEAD request might cause some existing implementations to reject the
1001   request.
1005<section title="POST" anchor="POST">
1006  <iref primary="true" item="POST method" x:for-anchor=""/>
1007  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
[1161]1009   The POST method requests that the origin server accept the
[972]1010   representation enclosed in the request as data to be processed by the
1011   target resource. POST is designed to allow a uniform method to cover the
1012   following functions:
[8]1013  <list style="symbols">
1014    <t>
1015      Annotation of existing resources;
1016    </t>
1017    <t>
1018        Posting a message to a bulletin board, newsgroup, mailing list,
1019        or similar group of articles;
1020    </t>
1021    <t>
1022        Providing a block of data, such as the result of submitting a
1023        form, to a data-handling process;
1024    </t>
1025    <t>
1026        Extending a database through an append operation.
1027    </t>
1028  </list>
1031   The actual function performed by the POST method is determined by the
[965]1032   server and is usually dependent on the effective request URI.
1035   The action performed by the POST method might not result in a
1036   resource that can be identified by a URI. In this case, either 200
[924]1037   (OK) or 204 (No Content) is the appropriate response status code,
[874]1038   depending on whether or not the response includes a representation that
[8]1039   describes the result.
1042   If a resource has been created on the origin server, the response
[874]1043   &SHOULD; be 201 (Created) and contain a representation which describes the
[8]1044   status of the request and refers to the new resource, and a Location
[994]1045   header field (see <xref target="header.location"/>).
[910]1048   Responses to POST requests are only cacheable when they
1049   include explicit freshness information (see &p6-explicit;). A
[994]1050   cached POST response with a Content-Location header field
[972]1051   (see &header-content-location;) whose value is the effective
[910]1052   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1055   Note that POST caching is not widely implemented.
[888]1056   However, the 303 (See Other) response can be used to direct the
1057   user agent to retrieve a cacheable resource.
1061<section title="PUT" anchor="PUT">
1062  <iref primary="true" item="PUT method" x:for-anchor=""/>
1063  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
[1161]1065   The PUT method requests that the state of the target resource
[1158]1066   be created or replaced with the state defined by the representation
1067   enclosed in the request message payload.  A successful PUT of a given
1068   representation would suggest that a subsequent GET on that same target
1069   resource will result in an equivalent representation being returned in
1070   a 200 (OK) response.  However, there is no guarantee that such a state
1071   change will be observable, since the target resource might be acted
1072   upon by other user agents in parallel, or might be subject to dynamic
1073   processing by the origin server, before any subsequent GET is received.
1074   A successful response only implies that the user agent's intent was
1075   achieved at the time of its processing by the origin server.
[1158]1078   If the target resource does not have a current representation and
1079   the PUT successfully creates one, then the origin server &MUST; inform
1080   the user agent by sending a 201 (Created) response.  If the target
1081   resource does have a current representation and that representation is
1082   successfully modified in accordance with the state of the enclosed
1083   representation, then either a 200 (OK) or 204 (No Content) response
1084   &SHOULD; be sent to indicate successful completion of the request.
1087   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1088   as part of the resource state).
[1158]1091   An origin server &SHOULD; verify that the PUT representation is
1092   consistent with any constraints which the server has for the target
1093   resource that cannot or will not be changed by the PUT.  This is
1094   particularly important when the origin server uses internal
1095   configuration information related to the URI in order to set the
1096   values for representation metadata on GET responses.  When a PUT
1097   representation is inconsistent with the target resource, the origin
1098   server &SHOULD; either make them consistent, by transforming the
1099   representation or changing the resource configuration, or respond
[1168]1100   with an appropriate error message containing sufficient information
1101   to explain why the representation is unsuitable.  The 409 (Conflict)
1102   or 415 (Unsupported Media Type) status codes are suggested, with the
1103   latter being specific to constraints on Content-Type values.
[1158]1106   For example, if the target resource is configured to always have a
1107   Content-Type of "text/html" and the representation being PUT has a
1108   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1109   (a) reconfigure the target resource to reflect the new media type;
1110   (b) transform the PUT representation to a format consistent with that
1111   of the resource before saving it as the new resource state; or,
[1168]1112   (c) reject the request with a 415 response indicating that the target
[1158]1113   resource is limited to "text/html", perhaps including a link to a
1114   different resource that would be a suitable target for the new
1115   representation.
1118   HTTP does not define exactly how a PUT method affects the state
1119   of an origin server beyond what can be expressed by the intent of
1120   the user agent request and the semantics of the origin server response.
1121   It does not define what a resource might be, in any sense of that
1122   word, beyond the interface provided via HTTP.  It does not define
1123   how resource state is "stored", nor how such storage might change
1124   as a result of a change in resource state, nor how the origin server
1125   translates resource state into representations.  Generally speaking,
1126   all implementation details behind the resource interface are
1127   intentionally hidden by the server.
1130   The fundamental difference between the POST and PUT methods is
1131   highlighted by the different intent for the target resource.
1132   The target resource in a POST request is intended to handle the
1133   enclosed representation as a data-accepting process, such as for
1134   a gateway to some other protocol or a document that accepts annotations.
1135   In contrast, the target resource in a PUT request is intended to
1136   take the enclosed representation as a new or replacement value.
1137   Hence, the intent of PUT is idempotent and visible to intermediaries,
1138   even though the exact effect is only known by the origin server.
1141   Proper interpretation of a PUT request presumes that the user agent
1142   knows what target resource is desired.  A service that is intended
1143   to select a proper URI on behalf of the client, after receiving
1144   a state-changing request, &SHOULD; be implemented using the POST
1145   method rather than PUT.  If the origin server will not make the
1146   requested PUT state change to the target resource and instead
1147   wishes to have it applied to a different resource, such as when the
1148   resource has been moved to a different URI, then the origin server
1149   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
[8]1150   then make its own decision regarding whether or not to redirect the
1151   request.
[1158]1154   A PUT request applied to the target resource &MAY; have side-effects
1155   on other resources.  For example, an article might have a URI for
1156   identifying "the current version" (a resource) which is separate
1157   from the URIs identifying each particular version (different
1158   resources that at one point shared the same state as the current version
1159   resource).  A successful PUT request on "the current version" URI might
1160   therefore create a new version resource in addition to changing the
1161   state of the target resource, and might also cause links to be added
1162   between the related resources.
[1158]1165   An origin server &SHOULD; reject any PUT request that contains a
1166   Content-Range header field, since it might be misinterpreted as
1167   partial content (or might be partial content that is being mistakenly
1168   PUT as a full representation).  Partial content updates are
1169   possible by targeting a separately identified resource with state
1170   that overlaps a portion of the larger resource, or by using a
1171   different method that has been specifically defined for partial
1172   updates (for example, the PATCH method defined in
1173   <xref target="RFC5789"/>).
[1158]1176   Responses to the PUT method are not cacheable. If a PUT request passes
1177   through a cache that has one or more stored responses for the effective
1178   request URI, those stored responses will be invalidated (see
1179   &p6-invalid;).
1183<section title="DELETE" anchor="DELETE">
1184  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1185  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
[972]1187   The DELETE method requests that the origin server delete the target
1188   resource. This method &MAY; be overridden by
[823]1189   human intervention (or other means) on the origin server. The client cannot
[8]1190   be guaranteed that the operation has been carried out, even if the
1191   status code returned from the origin server indicates that the action
1192   has been completed successfully. However, the server &SHOULD-NOT; 
1193   indicate success unless, at the time the response is given, it
1194   intends to delete the resource or move it to an inaccessible
1195   location.
1198   A successful response &SHOULD; be 200 (OK) if the response includes an
[874]1199   representation describing the status, 202 (Accepted) if the action has not
[8]1200   yet been enacted, or 204 (No Content) if the action has been enacted
[866]1201   but the response does not include a representation.
1204   Bodies on DELETE requests have no defined semantics. Note that sending a body
1205   on a DELETE request might cause some existing implementations to reject the
1206   request.
[1111]1209   Responses to the DELETE method are not cacheable. If a DELETE request
1210   passes through a cache that has one or more stored responses for the
1211   effective request URI, those stored responses will be invalidated (see
1212   &p6-invalid;).
1216<section title="TRACE" anchor="TRACE">
[286]1217  <rdf:Description>
1218    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1219  </rdf:Description>
[8]1220  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1221  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
[1161]1223   The TRACE method requests a remote, application-layer loop-back
[8]1224   of the request message. The final recipient of the request
1225   &SHOULD; reflect the message received back to the client as the
[874]1226   message-body of a 200 (OK) response. The final recipient is either the
[1173]1227   origin server or the first proxy to receive a Max-Forwards
[866]1228   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1229   A TRACE request &MUST-NOT; include a message-body.
1232   TRACE allows the client to see what is being received at the other
1233   end of the request chain and use that data for testing or diagnostic
[29]1234   information. The value of the Via header field (&header-via;) is of
[8]1235   particular interest, since it acts as a trace of the request chain.
1236   Use of the Max-Forwards header field allows the client to limit the
1237   length of the request chain, which is useful for testing a chain of
1238   proxies forwarding messages in an infinite loop.
[874]1241   If the request is valid, the response &SHOULD; have a Content-Type of
1242   "message/http" (see &media-type-message-http;) and contain a message-body
1243   that encloses a copy of the entire request message.
[888]1244   Responses to the TRACE method are not cacheable.
1248<section title="CONNECT" anchor="CONNECT">
1249  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1250  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
[1161]1252   The CONNECT method requests that the proxy establish a tunnel
1253   to the request-target and then restrict its behavior to blind
1254   forwarding of packets until the connection is closed.
[1161]1257   When using CONNECT, the request-target &MUST; use the authority form
1258   (&request-target;); i.e., the request-target consists of only the
1259   host name and port number of the tunnel destination, separated by a colon.
1260   For example,
[1064]1262<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
[1101]1268   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
[1061]1269   except end-to-end protocol Upgrade requests, since the
1270   tunnel must be established first.
1273   For example, proxy authentication might be used to establish the
1274   authority to create a tunnel:
[1064]1276<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1279Proxy-Authorization: basic aGVsbG86d29ybGQ=
1283   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1284   on a CONNECT request might cause some existing implementations to reject the
1285   request.
1288   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1289   sent immediately after the blank line. The usual caveats also apply:
1290   data may be discarded if the eventual response is negative, and the
1291   connection may be reset with no response if more than one TCP segment
1292   is outstanding.
1295<section title="Establishing a Tunnel with CONNECT">
1297   Any successful (2xx) response to a CONNECT request indicates that the
1298   proxy has established a connection to the requested host and port,
1299   and has switched to tunneling the current connection to that server
1300   connection.
1303   It may be the case that the proxy itself can only reach the requested
1304   origin server through another proxy.  In this case, the first proxy
1305   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1306   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1307   unless it has either a direct or tunnel connection established to the
1308   authority.
1311   An origin server which receives a CONNECT request for itself &MAY;
1312   respond with a 2xx status code to indicate that a connection is
1313   established.
1316   If at any point either one of the peers gets disconnected, any
1317   outstanding data that came from that peer will be passed to the other
1318   one, and after that also the other connection will be terminated by
1319   the proxy. If there is outstanding data to that peer undelivered,
1320   that data will be discarded.
1328<section title="Status Code Definitions" anchor="">
[867]1330   Each Status-Code is described below, including any metadata required
[579]1331   in the response.
1334<section title="Informational 1xx" anchor="status.1xx">
1336   This class of status code indicates a provisional response,
[994]1337   consisting only of the Status-Line and optional header fields, and is
1338   terminated by an empty line. There are no required header fields for this
[8]1339   class of status code. Since HTTP/1.0 did not define any 1xx status
1340   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1341   except under experimental conditions.
1344   A client &MUST; be prepared to accept one or more 1xx status responses
1345   prior to a regular response, even if the client does not expect a 100
1346   (Continue) status message. Unexpected 1xx status responses &MAY; be
1347   ignored by a user agent.
1350   Proxies &MUST; forward 1xx responses, unless the connection between the
1351   proxy and its client has been closed, or unless the proxy itself
1352   requested the generation of the 1xx response. (For example, if a
1353   proxy adds a "Expect: 100-continue" field when it forwards a request,
1354   then it need not forward the corresponding 100 (Continue)
1355   response(s).)
1358<section title="100 Continue" anchor="status.100">
1359  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1360  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1362   The client &SHOULD; continue with its request. This interim response is
1363   used to inform the client that the initial part of the request has
1364   been received and has not yet been rejected by the server. The client
1365   &SHOULD; continue by sending the remainder of the request or, if the
1366   request has already been completed, ignore this response. The server
1367   &MUST; send a final response after the request has been completed. See
[29]1368   &use100; for detailed discussion of the use and handling of this
[8]1369   status code.
1373<section title="101 Switching Protocols" anchor="status.101">
1374  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1375  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1377   The server understands and is willing to comply with the client's
[29]1378   request, via the Upgrade message header field (&header-upgrade;), for a
[8]1379   change in the application protocol being used on this connection. The
1380   server will switch protocols to those defined by the response's
1381   Upgrade header field immediately after the empty line which
1382   terminates the 101 response.
1385   The protocol &SHOULD; be switched only when it is advantageous to do
1386   so. For example, switching to a newer version of HTTP is advantageous
1387   over older versions, and switching to a real-time, synchronous
1388   protocol might be advantageous when delivering resources that use
1389   such features.
1394<section title="Successful 2xx" anchor="status.2xx">
1396   This class of status code indicates that the client's request was
1397   successfully received, understood, and accepted.
1400<section title="200 OK" anchor="status.200">
1401  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1402  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
[965]1404   The request has succeeded. The payload returned with the response
[8]1405   is dependent on the method used in the request, for example:
1406  <list style="hanging">
1407    <t hangText="GET">
[1288]1408      a representation of the target resource is sent in the response;
[8]1409    </t>
1410    <t hangText="HEAD">
[1288]1411      the same representation as GET, except without the message-body;
[8]1412    </t>
1413    <t hangText="POST">
[874]1414      a representation describing or containing the result of the action;
[8]1415    </t>
1416    <t hangText="TRACE">
[874]1417      a representation containing the request message as received by the
[8]1418      end server.
1419    </t>
1420  </list>
[886]1423   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1424   freshness for 200 responses.
1428<section title="201 Created" anchor="status.201">
1429  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1430  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
[758]1432   The request has been fulfilled and has resulted in a new resource being
[8]1433   created. The newly created resource can be referenced by the URI(s)
[856]1434   returned in the payload of the response, with the most specific URI
[8]1435   for the resource given by a Location header field. The response
[856]1436   &SHOULD; include a payload containing a list of resource
[8]1437   characteristics and location(s) from which the user or user agent can
[856]1438   choose the one most appropriate. The payload format is specified by
[8]1439   the media type given in the Content-Type header field. The origin
1440   server &MUST; create the resource before returning the 201 status code.
1441   If the action cannot be carried out immediately, the server &SHOULD;
1442   respond with 202 (Accepted) response instead.
1445   A 201 response &MAY; contain an ETag response header field indicating
[874]1446   the current value of the entity-tag for the representation of the resource
[856]1447   just created (see &header-etag;).
1451<section title="202 Accepted" anchor="status.202">
1452  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1453  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1455   The request has been accepted for processing, but the processing has
1456   not been completed.  The request might or might not eventually be
1457   acted upon, as it might be disallowed when processing actually takes
1458   place. There is no facility for re-sending a status code from an
1459   asynchronous operation such as this.
1462   The 202 response is intentionally non-committal. Its purpose is to
1463   allow a server to accept a request for some other process (perhaps a
1464   batch-oriented process that is only run once per day) without
1465   requiring that the user agent's connection to the server persist
[866]1466   until the process is completed. The representation returned with this
[8]1467   response &SHOULD; include an indication of the request's current status
1468   and either a pointer to a status monitor or some estimate of when the
1469   user can expect the request to be fulfilled.
1473<section title="203 Non-Authoritative Information" anchor="status.203">
1474  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1475  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
[1309]1477   The representation in the response has been transformed or otherwise
1478   modified by a transforming proxy (&intermediaries;).  Note that the
1479   behaviour of transforming intermediaries is controlled by the no-transform
1480   Cache-Control directive (&header-cache-control;).
[1309]1483   This status code is only appropriate when the response status code would
1484   have been 200 (OK) otherwise. When the status code before transformation
1485   would have been different, the 214 Transformation Applied warn-code
1486   (&header-warning;) is appropriate.
[886]1489   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1490   freshness for 203 responses.
1494<section title="204 No Content" anchor="status.204">
1495  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1496  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
[1257]1498   The 204 (No Content) status code indicates that the server has
1499   successfully fulfilled the request and that there is no additional
1500   content to return in the response payload body.  Metadata in the
1501   response header fields refer to the target resource and its current
1502   representation after the requested action.
[924]1505   For example, if a 204 status code is received in response to a PUT
[1257]1506   request and the response contains an ETag header field, then the PUT
1507   was successful and the ETag field-value contains the entity-tag for
1508   the new representation of that target resource.
[1257]1511   The 204 response allows a server to indicate that the action has been
1512   successfully applied to the target resource while implying that the
1513   user agent &SHOULD-NOT; traverse away from its current "document view"
1514   (if any).  The server assumes that the user agent will provide some
1515   indication of the success to its user, in accord with its own interface,
1516   and apply any new or updated metadata in the response to the active
1517   representation.
[1257]1520   For example, a 204 status code is commonly used with document editing
1521   interfaces corresponding to a "save" action, such that the document
1522   being saved remains available to the user for editing. It is also
1523   frequently used with interfaces that expect automated data transfers
1524   to be prevalent, such as within distributed version control systems.
1527   The 204 response &MUST-NOT; include a message-body, and thus is always
1528   terminated by the first empty line after the header fields.
1532<section title="205 Reset Content" anchor="status.205">
1533  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1534  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1536   The server has fulfilled the request and the user agent &SHOULD; reset
1537   the document view which caused the request to be sent. This response
1538   is primarily intended to allow input for actions to take place via
1539   user input, followed by a clearing of the form in which the input is
[1058]1540   given so that the user can easily initiate another input action.
1543   The message-body included with the response &MUST; be empty. Note that
1544   receivers still need to parse the response according to the algorithm defined
1545   in &message-body;.
1549<section title="206 Partial Content" anchor="status.206">
1550  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1551  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
[700]1552  <rdf:Description>
1553    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1554  </rdf:Description>
[29]1556   The server has fulfilled the partial GET request for the resource
[874]1557   and the enclosed payload is a partial representation as defined in &status-206;.
[886]1560   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1561   freshness for 206 responses.
1566<section title="Redirection 3xx" anchor="status.3xx">
1568   This class of status code indicates that further action needs to be
1569   taken by the user agent in order to fulfill the request.  The action
1570   required &MAY; be carried out by the user agent without interaction
1571   with the user if and only if the method used in the second request is
[760]1572   known to be "safe", as defined in <xref target="safe.methods"/>.
[759]1573   A client &SHOULD; detect infinite redirection loops, since such loops
1574   generate network traffic for each redirection.
1577  <t>
[756]1578    <x:h>Note:</x:h> An earlier version of this specification recommended a
[629]1579    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
[969]1580    Content developers need to be aware that some clients might
[629]1581    implement such a fixed limitation.
[563]1582  </t>
1585<section title="300 Multiple Choices" anchor="status.300">
1586  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1587  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
[1029]1589   The target resource has more than one
[965]1590   representation, each with its own specific location, and agent-driven
[29]1591   negotiation information (&content-negotiation;) is being provided so that
[965]1592   the user (or user agent) can select a preferred representation by
1593   redirecting its request to that location.
[866]1596   Unless it was a HEAD request, the response &SHOULD; include a representation
[965]1597   containing a list of representation metadata and location(s) from
[8]1598   which the user or user agent can choose the one most appropriate. The
[866]1599   data format is specified by the media type given in the Content-Type
[8]1600   header field. Depending upon the format and the capabilities of
1601   the user agent, selection of the most appropriate choice &MAY; be
1602   performed automatically. However, this specification does not define
1603   any standard for such automatic selection.
1606   If the server has a preferred choice of representation, it &SHOULD;
1607   include the specific URI for that representation in the Location
1608   field; user agents &MAY; use the Location field value for automatic
[884]1609   redirection.
[886]1612   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1613   freshness for 300 responses.
1618<section title="301 Moved Permanently" anchor="status.301">
1619  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1620  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
[965]1622   The target resource has been assigned a new permanent URI and any
[8]1623   future references to this resource &SHOULD; use one of the returned
1624   URIs.  Clients with link editing capabilities ought to automatically
[965]1625   re-link references to the effective request URI to one or more of the new
[884]1626   references returned by the server, where possible.
[886]1629   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1630   freshness for 301 responses.
[8]1633   The new permanent URI &SHOULD; be given by the Location field in the
[866]1634   response. Unless the request method was HEAD, the representation of the
[8]1635   response &SHOULD; contain a short hypertext note with a hyperlink to
1636   the new URI(s).
[88]1639   If the 301 status code is received in response to a request method
1640   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1641   then the request &MAY; be automatically redirected by the user agent without
[88]1642   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1643   request unless it can be confirmed by the user, since this might
1644   change the conditions under which the request was issued.
1647  <t>
1648    <x:h>Note:</x:h> When automatically redirecting a POST request after
1649    receiving a 301 status code, some existing HTTP/1.0 user agents
1650    will erroneously change it into a GET request.
1651  </t>
1655<section title="302 Found" anchor="status.302">
1656  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1657  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
[965]1659   The target resource resides temporarily under a different URI.
[8]1660   Since the redirection might be altered on occasion, the client &SHOULD;
[965]1661   continue to use the effective request URI for future requests.
1664   The temporary URI &SHOULD; be given by the Location field in the
[866]1665   response. Unless the request method was HEAD, the representation of the
[8]1666   response &SHOULD; contain a short hypertext note with a hyperlink to
1667   the new URI(s).
[88]1670   If the 302 status code is received in response to a request method
1671   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1672   then the request &MAY; be automatically redirected by the user agent without
[88]1673   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1674   request unless it can be confirmed by the user, since this might
1675   change the conditions under which the request was issued.
1678  <t>
[614]1679    <x:h>Note:</x:h> HTTP/1.0 (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>)
1680    and the first version of HTTP/1.1 (<xref target="RFC2068" x:fmt="," x:sec ="10.3.3"/>)
1681    specify that the client is not allowed to change the method on the
1682    redirected request.  However, most existing user agent implementations
1683    treat 302 as if it were a 303 response, performing a GET on the Location
1684    field-value regardless of the original request method. Therefore, a
1685    previous version of this specification
1686    (<xref target="RFC2616" x:fmt="," x:sec="10.3.3"/>) has added the
1687    status codes
1688    <xref target="status.303" format="none">303</xref> and
1689    <xref target="status.307" format="none">307</xref> for servers that wish
1690    to make unambiguously clear which kind of reaction is expected of the
1691    client.
[563]1692  </t>
1696<section title="303 See Other" anchor="status.303">
1697  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1698  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
[1421]1700   The 303 status code indicates that the server is redirecting the
1701   user agent to a different resource, as indicated by a URI in the
1702   Location header field, that is intended to provide an indirect
1703   response to the original request.  In order to satisfy the original
1704   request, a user agent &SHOULD; perform a retrieval request using the
1705   Location URI, which may itself be redirected further, and present
1706   the eventual result as an answer to the original request.
1707   Note that the new URI in the Location header field is not considered
1708   equivalent to the effective request URI.
[1421]1711   This status code is generally applicable to any HTTP method.  It is
[242]1712   primarily used to allow the output of a POST action to redirect
1713   the user agent to a selected resource, since doing so provides the
1714   information corresponding to the POST response in a form that
1715   can be separately identified, bookmarked, and cached independent
1716   of the original request.
1719   A 303 response to a GET request indicates that the requested
1720   resource does not have a representation of its own that can be
1721   transferred by the server over HTTP.  The Location URI indicates a
[965]1722   resource that is descriptive of the target resource, such that the
1723   follow-on representation might be useful to recipients without
1724   implying that it adequately represents the target resource.
[242]1725   Note that answers to the questions of what can be represented, what
1726   representations are adequate, and what might be a useful description
1727   are outside the scope of HTTP and thus entirely determined by the
[602]1728   URI owner(s).
[884]1731   Except for responses to a HEAD request, the representation of a 303
1732   response &SHOULD; contain a short hypertext note with a hyperlink
1733   to the Location URI.
1737<section title="304 Not Modified" anchor="status.304">
1738  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1739  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
[700]1740  <rdf:Description>
1741    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1742  </rdf:Description>
[45]1744   The response to the request has not been modified since the conditions
[700]1745   indicated by the client's conditional GET request, as defined in &status-304;.
1749<section title="305 Use Proxy" anchor="status.305">
1750  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1751  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
[924]1753   The 305 status code was defined in a previous version of this specification
[235]1754   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1758<section title="306 (Unused)" anchor="status.306">
1759  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1760  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1762   The 306 status code was used in a previous version of the
1763   specification, is no longer used, and the code is reserved.
1767<section title="307 Temporary Redirect" anchor="status.307">
1768  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1769  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
[965]1771   The target resource resides temporarily under a different URI.
[954]1772   Since the redirection can change over time, the client &SHOULD;
[965]1773   continue to use the effective request URI for future requests.
1776   The temporary URI &SHOULD; be given by the Location field in the
[866]1777   response. Unless the request method was HEAD, the representation of the
[8]1778   response &SHOULD; contain a short hypertext note with a hyperlink to
[1030]1779   the new URI(s), since many pre-HTTP/1.1 user agents do not
[924]1780   understand the 307 status code. Therefore, the note &SHOULD; contain the
[8]1781   information necessary for a user to repeat the original request on
1782   the new URI.
[88]1785   If the 307 status code is received in response to a request method
1786   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1787   then the request &MAY; be automatically redirected by the user agent without
[88]1788   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1789   request unless it can be confirmed by the user, since this might
1790   change the conditions under which the request was issued.
1795<section title="Client Error 4xx" anchor="status.4xx">
1797   The 4xx class of status code is intended for cases in which the
1798   client seems to have erred. Except when responding to a HEAD request,
[874]1799   the server &SHOULD; include a representation containing an explanation of the
[8]1800   error situation, and whether it is a temporary or permanent
1801   condition. These status codes are applicable to any request method.
[874]1802   User agents &SHOULD; display any included representation to the user.
1805   If the client is sending data, a server implementation using TCP
1806   &SHOULD; be careful to ensure that the client acknowledges receipt of
1807   the packet(s) containing the response, before the server closes the
1808   input connection. If the client continues sending data to the server
1809   after the close, the server's TCP stack will send a reset packet to
[901]1810   the client, which might erase the client's unacknowledged input buffers
[8]1811   before they can be read and interpreted by the HTTP application.
1814<section title="400 Bad Request" anchor="status.400">
1815  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1816  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
[1345]1818   The server cannot or will not process the request, due to a client error (e.g.,
[1342]1819   malformed syntax).</t>
1822<section title="401 Unauthorized" anchor="status.401">
1823  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1824  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
[700]1825  <rdf:Description>
1826    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1827  </rdf:Description>
[700]1829   The request requires user authentication (see &status-401;).
1833<section title="402 Payment Required" anchor="status.402">
1834  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1835  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1837   This code is reserved for future use.
1841<section title="403 Forbidden" anchor="status.403">
1842  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1843  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
[1301]1845   The server understood the request, but refuses to authorize it. Providing
1846   different user authentication credentials might be successful, but any
1847   credentials that were provided in the request are insufficient. The request
1848   &SHOULD-NOT; be repeated with the same credentials.
[8]1851   If the request method was not HEAD and the server wishes to make
1852   public why the request has not been fulfilled, it &SHOULD; describe the
[866]1853   reason for the refusal in the representation.  If the server does not wish to
[8]1854   make this information available to the client, the status code 404
[1301]1855   (Not Found) &MAY; be used instead.
1859<section title="404 Not Found" anchor="status.404">
1860  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1861  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
[965]1863   The server has not found anything matching the effective request URI. No
[8]1864   indication is given of whether the condition is temporary or
1865   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1866   knows, through some internally configurable mechanism, that an old
1867   resource is permanently unavailable and has no forwarding address.
1868   This status code is commonly used when the server does not wish to
1869   reveal exactly why the request has been refused, or when no other
1870   response is applicable.
1874<section title="405 Method Not Allowed" anchor="status.405">
1875  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1876  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
[965]1878   The method specified in the Request-Line is not allowed for the target
[1288]1879   resource. The response &MUST; include an Allow header field containing a
1880   list of valid methods for the requested resource.
1884<section title="406 Not Acceptable" anchor="status.406">
1885  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1886  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1888   The resource identified by the request is only capable of generating
[874]1889   response representations which have content characteristics not acceptable
[1335]1890   according to the Accept and Accept-* header fields sent in the request
1891   (see &p3-header-fields;).
[866]1894   Unless it was a HEAD request, the response &SHOULD; include a representation
1895   containing a list of available representation characteristics and location(s)
[8]1896   from which the user or user agent can choose the one most
[866]1897   appropriate. The data format is specified by the media type given
[8]1898   in the Content-Type header field. Depending upon the format and the
1899   capabilities of the user agent, selection of the most appropriate
1900   choice &MAY; be performed automatically. However, this specification
1901   does not define any standard for such automatic selection.
1904  <t>
1905    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
[994]1906    not acceptable according to the accept header fields sent in the
[901]1907    request. In some cases, this might even be preferable to sending a
[994]1908    406 response. User agents are encouraged to inspect the header fields of
[563]1909    an incoming response to determine if it is acceptable.
1910  </t>
1913   If the response could be unacceptable, a user agent &SHOULD;
1914   temporarily stop receipt of more data and query the user for a
1915   decision on further actions.
1919<section title="407 Proxy Authentication Required" anchor="status.407">
1920  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1921  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1923   This code is similar to 401 (Unauthorized), but indicates that the
[700]1924   client must first authenticate itself with the proxy (see &status-407;).
1928<section title="408 Request Timeout" anchor="status.408">
1929  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1930  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1932   The client did not produce a request within the time that the server
1933   was prepared to wait. The client &MAY; repeat the request without
1934   modifications at any later time.
1938<section title="409 Conflict" anchor="status.409">
1939  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1940  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1942   The request could not be completed due to a conflict with the current
1943   state of the resource. This code is only allowed in situations where
1944   it is expected that the user might be able to resolve the conflict
1945   and resubmit the request. The response body &SHOULD; include enough
1946   information for the user to recognize the source of the conflict.
[874]1947   Ideally, the response representation would include enough information for the
[8]1948   user or user agent to fix the problem; however, that might not be
1949   possible and is not required.
1952   Conflicts are most likely to occur in response to a PUT request. For
[866]1953   example, if versioning were being used and the representation being PUT
[8]1954   included changes to a resource which conflict with those made by an
1955   earlier (third-party) request, the server might use the 409 response
1956   to indicate that it can't complete the request. In this case, the
[866]1957   response representation would likely contain a list of the differences
[8]1958   between the two versions in a format defined by the response
1959   Content-Type.
1963<section title="410 Gone" anchor="status.410">
1964  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1965  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
[965]1967   The target resource is no longer available at the server and no
[8]1968   forwarding address is known. This condition is expected to be
1969   considered permanent. Clients with link editing capabilities &SHOULD;
[965]1970   delete references to the effective request URI after user approval. If the
[8]1971   server does not know, or has no facility to determine, whether or not
1972   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
[884]1973   used instead.
1976   The 410 response is primarily intended to assist the task of web
1977   maintenance by notifying the recipient that the resource is
1978   intentionally unavailable and that the server owners desire that
1979   remote links to that resource be removed. Such an event is common for
1980   limited-time, promotional services and for resources belonging to
1981   individuals no longer working at the server's site. It is not
1982   necessary to mark all permanently unavailable resources as "gone" or
[1101]1983   to keep the mark for any length of time &mdash; that is left to the
[8]1984   discretion of the server owner.
[886]1987   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1988   for 410 responses.
1993<section title="411 Length Required" anchor="status.411">
1994  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1995  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1997   The server refuses to accept the request without a defined Content-Length.
1998   The client &MAY; repeat the request if it adds a valid
1999   Content-Length header field containing the length of the message-body
2000   in the request message.
2004<section title="412 Precondition Failed" anchor="status.412">
2005  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2006  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
[700]2007  <rdf:Description>
2008    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2009  </rdf:Description>
[1163]2011   The precondition given in one or more of the header fields
[45]2012   evaluated to false when it was tested on the server, as defined in
[700]2013   &status-412;.
[1322]2017<section title="413 Request Representation Too Large" anchor="status.413">
2018  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2019  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2021   The server is refusing to process a request because the request
[874]2022   representation is larger than the server is willing or able to process. The
[8]2023   server &MAY; close the connection to prevent the client from continuing
2024   the request.
2027   If the condition is temporary, the server &SHOULD; include a Retry-After
2028   header field to indicate that it is temporary and after what
2029   time the client &MAY; try again.
[465]2033<section title="414 URI Too Long" anchor="status.414">
2034  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2035  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
[965]2037   The server is refusing to service the request because the effective request URI
[8]2038   is longer than the server is willing to interpret. This rare
2039   condition is only likely to occur when a client has improperly
2040   converted a POST request to a GET request with long query
2041   information, when the client has descended into a URI "black hole" of
2042   redirection (e.g., a redirected URI prefix that points to a suffix of
2043   itself), or when the server is under attack by a client attempting to
2044   exploit security holes present in some servers using fixed-length
[965]2045   buffers for reading or manipulating the effective request URI.
2049<section title="415 Unsupported Media Type" anchor="status.415">
2050  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2051  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
[1161]2053   The server is refusing to service the request because the request
2054   payload is in a format not supported by this request method on the
2055   target resource.
2059<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2060  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2061  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
[700]2062  <rdf:Description>
2063    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2064  </rdf:Description>
[1163]2066   The request included a Range header field (&header-range;) and none of
[8]2067   the range-specifier values in this field overlap the current extent
[885]2068   of the selected resource. See &status-416;.
2072<section title="417 Expectation Failed" anchor="status.417">
2073  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2074  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
[1163]2076   The expectation given in an Expect header field (see <xref target="header.expect"/>)
[8]2077   could not be met by this server, or, if the server is a proxy,
2078   the server has unambiguous evidence that the request could not be met
2079   by the next-hop server.
2083<section title="426 Upgrade Required" anchor="status.426">
2084  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2085  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2087   The request can not be completed without a prior protocol upgrade. This
2088   response &MUST; include an Upgrade header field (&header-upgrade;)
2089   specifying the required protocols.
2093<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2094HTTP/1.1 426 Upgrade Required
2095Upgrade: HTTP/2.0
2096Connection: Upgrade
2100   The server &SHOULD; include a message body in the 426 response which
2101   indicates in human readable form the reason for the error and describes any
2102   alternative courses which may be available to the user.
2107<section title="Server Error 5xx" anchor="status.5xx">
2109   Response status codes beginning with the digit "5" indicate cases in
2110   which the server is aware that it has erred or is incapable of
2111   performing the request. Except when responding to a HEAD request, the
[874]2112   server &SHOULD; include a representation containing an explanation of the
[8]2113   error situation, and whether it is a temporary or permanent
[874]2114   condition. User agents &SHOULD; display any included representation to the
[8]2115   user. These response codes are applicable to any request method.
2118<section title="500 Internal Server Error" anchor="status.500">
2119  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2120  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2122   The server encountered an unexpected condition which prevented it
2123   from fulfilling the request.
2127<section title="501 Not Implemented" anchor="status.501">
2128  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2129  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2131   The server does not support the functionality required to fulfill the
2132   request. This is the appropriate response when the server does not
2133   recognize the request method and is not capable of supporting it for
2134   any resource.
2138<section title="502 Bad Gateway" anchor="status.502">
2139  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2140  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2142   The server, while acting as a gateway or proxy, received an invalid
2143   response from the upstream server it accessed in attempting to
2144   fulfill the request.
2148<section title="503 Service Unavailable" anchor="status.503">
2149  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2150  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
[1310]2152   The server is currently unable or unwilling to handle the request due to
2153   reasons such as temporary overloading, maintenance of the server, or rate
2154   limiting of the client.
2157   The implication is that this is a temporary condition which will be
2158   alleviated after some delay. If known, the length of the delay &MAY; be
2159   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2160   If no Retry-After is given, the client &SHOULD; handle the response as it
2161   would for a 500 response.
2164  <t>
2165    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
[901]2166    server must use it when becoming overloaded. Some servers might wish
[563]2167    to simply refuse the connection.
2168  </t>
2172<section title="504 Gateway Timeout" anchor="status.504">
2173  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2174  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2176   The server, while acting as a gateway or proxy, did not receive a
[763]2177   timely response from the upstream server specified by the URI (e.g.,
2178   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
[8]2179   to access in attempting to complete the request.
2182  <t>
[757]2183    <x:h>Note</x:h> to implementors: some deployed proxies are known to
[563]2184    return 400 or 500 when DNS lookups time out.
2185  </t>
2189<section title="505 HTTP Version Not Supported" anchor="status.505">
2190  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2191  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
[172]2193   The server does not support, or refuses to support, the protocol
[8]2194   version that was used in the request message. The server is
2195   indicating that it is unable or unwilling to complete the request
[29]2196   using the same major version as the client, as described in &http-version;,
[8]2197   other than with this error message. The response &SHOULD; contain
[874]2198   a representation describing why that version is not supported and what other
[8]2199   protocols are supported by that server.
[1415]2207<section title="Header Field Definitions" anchor="header.field.definitions">
[117]2209   This section defines the syntax and semantics of HTTP/1.1 header fields
2210   related to request and response semantics.
2213<section title="Allow" anchor="header.allow">
[1120]2214  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2215  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
[229]2216  <x:anchor-alias value="Allow"/>
[1163]2218   The "Allow" header field lists the set of methods advertised as
[1067]2219   supported by the target resource. The purpose of this field is strictly to
[1161]2220   inform the recipient of valid request methods associated with the resource.
[1235]2222<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2223  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
[1067]2226   Example of use:
2228<figure><artwork type="example">
[356]2229  Allow: GET, HEAD, PUT
[1067]2232   The actual set of allowed methods is defined by the origin server at the
2233   time of each request.
[1101]2236   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
[1068]2237   understand all the methods specified in order to handle them according to
2238   the generic message handling rules.
2242<section title="Expect" anchor="header.expect">
[1120]2243  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2244  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
[229]2245  <x:anchor-alias value="Expect"/>
2246  <x:anchor-alias value="expectation"/>
2247  <x:anchor-alias value="expectation-extension"/>
2248  <x:anchor-alias value="expect-params"/>
[1163]2250   The "Expect" header field is used to indicate that particular
[8]2251   server behaviors are required by the client.
[1235]2253<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
2254  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
[356]2256  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2257  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
[229]2258                           *<x:ref>expect-params</x:ref> ]
[356]2259  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2262   A server that does not understand or is unable to comply with any of
2263   the expectation values in the Expect field of a request &MUST; respond
[924]2264   with appropriate error status code. The server &MUST; respond with a 417
2265   (Expectation Failed) status code if any of the expectations cannot be met
[8]2266   or, if there are other problems with the request, some other 4xx
[924]2267   status code.
2270   This header field is defined with extensible syntax to allow for
2271   future extensions. If a server receives a request containing an
2272   Expect field that includes an expectation-extension that it does not
[924]2273   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2276   Comparison of expectation values is case-insensitive for unquoted
2277   tokens (including the 100-continue token), and is case-sensitive for
2278   quoted-string expectation-extensions.
2281   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
[924]2282   return a 417 (Expectation Failed) status code if it receives a request
[8]2283   with an expectation that it cannot meet. However, the Expect
[1163]2284   header field itself is end-to-end; it &MUST; be forwarded if the
[8]2285   request is forwarded.
2288   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
[994]2289   Expect header field.
[924]2292   See &use100; for the use of the 100 (Continue) status code.
2296<section title="From" anchor="header.from">
[1120]2297  <iref primary="true" item="From header field" x:for-anchor=""/>
2298  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
[229]2299  <x:anchor-alias value="From"/>
2300  <x:anchor-alias value="mailbox"/>
[1163]2302   The "From" header field, if given, &SHOULD; contain an Internet
[8]2303   e-mail address for the human user who controls the requesting user
2304   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
[327]2305   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
[1235]2307<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2308  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
[327]2310  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2313   An example is:
2315<figure><artwork type="example">
[356]2316  From:
2319   This header field &MAY; be used for logging purposes and as a means for
2320   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2321   be used as an insecure form of access protection. The interpretation
2322   of this field is that the request is being performed on behalf of the
2323   person given, who accepts responsibility for the method performed. In
[994]2324   particular, robot agents &SHOULD; include this header field so that the
[8]2325   person responsible for running the robot can be contacted if problems
2326   occur on the receiving end.
2329   The Internet e-mail address in this field &MAY; be separate from the
2330   Internet host which issued the request. For example, when a request
2331   is passed through a proxy the original issuer's address &SHOULD; be
2332   used.
2335   The client &SHOULD-NOT;  send the From header field without the user's
2336   approval, as it might conflict with the user's privacy interests or
2337   their site's security policy. It is strongly recommended that the
2338   user be able to disable, enable, and modify the value of this field
2339   at any time prior to a request.
2343<section title="Location" anchor="header.location">
[1120]2344  <iref primary="true" item="Location header field" x:for-anchor=""/>
2345  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
[229]2346  <x:anchor-alias value="Location"/>
[1163]2348   The "Location" header field is used to identify a newly created
[698]2349   resource, or to redirect the recipient to a different location for
2350   completion of the request.
2353   For 201 (Created) responses, the Location is the URI of the new resource
2354   which was created by the request. For 3xx responses, the location &SHOULD;
2355   indicate the server's preferred URI for automatic redirection to the
2356   resource.
[785]2359   The field value consists of a single URI-reference. When it has the form
2360   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2361   the final value is computed by resolving it against the effective request
2362   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
[1235]2364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2365  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2368<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical WSP below, it's necessary this way for xml2rfc-->
2369<artwork type="example">
2370  Location:
2371</artwork></figure><figure><artwork type="example">  Location: /index.html
[785]2374   There are circumstances in which a fragment identifier in a Location URI
[1283]2375   would not be appropriate. For instance, when it appears in a 201 Created
2376   response, where the Location header field specifies the URI for the entire
2377   created resource.
2380  <t>
[785]2381    <x:h>Note:</x:h> This specification does not define precedence rules
[791]2382    for the case where the original URI, as navigated to by the user
[785]2383    agent, and the Location header field value both contain fragment
[1097]2384    identifiers. Thus be aware that including fragment identifiers might
2385    inconvenience anyone relying on the semantics of the original URI's
2386    fragment identifier.
[785]2387  </t>
2390  <t>
[563]2391    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
[866]2392    from Location in that the Content-Location identifies the most specific
2393    resource corresponding to the enclosed representation.
2394    It is therefore possible for a response to contain header fields for
2395    both Location and Content-Location.
[563]2396  </t>
2400<section title="Max-Forwards" anchor="header.max-forwards">
[1120]2401  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2402  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
[229]2403  <x:anchor-alias value="Max-Forwards"/>
[1163]2405   The "Max-Forwards" header field provides a mechanism with the
[698]2406   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2407   methods to limit the number of times that the request is forwarded by
[1173]2408   proxies. This can be useful when the client is attempting to
[698]2409   trace a request which appears to be failing or looping in mid-chain.
[1235]2411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2412  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2415   The Max-Forwards value is a decimal integer indicating the remaining
[901]2416   number of times this request message can be forwarded.
[1173]2419   Each recipient of a TRACE or OPTIONS request
[8]2420   containing a Max-Forwards header field &MUST; check and update its
2421   value prior to forwarding the request. If the received value is zero
2422   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2423   respond as the final recipient. If the received Max-Forwards value is
2424   greater than zero, then the forwarded message &MUST; contain an updated
2425   Max-Forwards field with a value decremented by one (1).
[1161]2428   The Max-Forwards header field &MAY; be ignored for all other request
2429   methods.
2433<section title="Referer" anchor="header.referer">
[1120]2434  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2435  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
[229]2436  <x:anchor-alias value="Referer"/>
[1163]2438   The "Referer" [sic] header field allows the client to specify the
[965]2439   URI of the resource from which the effective request URI was obtained (the
[698]2440   "referrer", although the header field is misspelled.).
[994]2443   The Referer header field allows servers to generate lists of back-links to
[593]2444   resources for interest, logging, optimized caching, etc. It also allows
2445   obsolete or mistyped links to be traced for maintenance. Some servers use
2446   Referer as a means of controlling where they allow links from (so-called
[969]2447   "deep linking"), but legitimate requests do not always
2448   contain a Referer header field.
[965]2451   If the effective request URI was obtained from a source that does not have its own
[812]2452   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
[593]2453   sent with the value "about:blank", or not be sent at all. Note that this
2454   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
[1235]2456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2457  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2460   Example:
2462<figure><artwork type="example">
[356]2463  Referer:
2466   If the field value is a relative URI, it &SHOULD; be interpreted
[965]2467   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
[8]2468   <xref target=""/> for security considerations.
2472<section title="Retry-After" anchor="header.retry-after">
[1120]2473  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2474  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
[229]2475  <x:anchor-alias value="Retry-After"/>
[1163]2477   The header "Retry-After" field can be used with a 503 (Service
[8]2478   Unavailable) response to indicate how long the service is expected to
2479   be unavailable to the requesting client. This field &MAY; also be used
2480   with any 3xx (Redirection) response to indicate the minimum time the
[698]2481   user-agent is asked wait before issuing the redirected request.
2484   The value of this field can be either an HTTP-date or an integer number
[8]2485   of seconds (in decimal) after the time of the response.
[1235]2487<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2488  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
[229]2490<t anchor="">
2491  <x:anchor-alias value="delta-seconds"/>
[212]2492   Time spans are non-negative decimal integers, representing time in
2493   seconds.
2495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
[229]2496  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
[8]2499   Two examples of its use are
2501<figure><artwork type="example">
[356]2502  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2503  Retry-After: 120
2506   In the latter example, the delay is 2 minutes.
2510<section title="Server" anchor="header.server">
[1120]2511  <iref primary="true" item="Server header field" x:for-anchor=""/>
2512  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
[229]2513  <x:anchor-alias value="Server"/>
[1163]2515   The "Server" header field contains information about the
[698]2516   software used by the origin server to handle the request.
2519   The field can contain multiple product tokens (&product-tokens;) and
2520   comments (&header-fields;) identifying the server and any significant
2521   subproducts. The product tokens are listed in order of their significance
2522   for identifying the application.
[1235]2524<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2525  <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> ) )
2528   Example:
2530<figure><artwork type="example">
[356]2531  Server: CERN/3.0 libwww/2.17
2534   If the response is being forwarded through a proxy, the proxy
[1163]2535   application &MUST-NOT; modify the Server header field. Instead, it
[72]2536   &MUST; include a Via field (as described in &header-via;).
2539  <t>
2540    <x:h>Note:</x:h> Revealing the specific software version of the server might
2541    allow the server machine to become more vulnerable to attacks
2542    against software that is known to contain security holes. Server
2543    implementors are encouraged to make this field a configurable
2544    option.
2545  </t>
2549<section title="User-Agent" anchor="header.user-agent">
[1120]2550  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2551  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
[229]2552  <x:anchor-alias value="User-Agent"/>
[1163]2554   The "User-Agent" header field contains information about the user
[1036]2555   agent originating the request. User agents &SHOULD; include this field with
2556   requests.
2559   Typically, it is used for statistical purposes, the tracing of protocol
2560   violations, and tailoring responses to avoid particular user agent
2561   limitations.
2564   The field can contain multiple product tokens (&product-tokens;)
2565   and comments (&header-fields;) identifying the agent and its
2566   significant subproducts. By convention, the product tokens are listed in
2567   order of their significance for identifying the application.
2570   Because this field is usually sent on every request a user agent makes,
2571   implementations are encouraged not to include needlessly fine-grained
2572   detail, and to limit (or even prohibit) the addition of subproducts by third
2573   parties. Overly long and detailed User-Agent field values make requests
2574   larger and can also be used to identify ("fingerprint") the user against
2575   their wishes.
2578   Likewise, implementations are encouraged not to use the product tokens of
2579   other implementations in order to declare compatibility with them, as this
2580   circumvents the purpose of the field. Finally, they are encouraged not to
2581   use comments to identify products; doing so makes the field value more
2582   difficult to parse.
[1235]2584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2585  <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> ) )
2588   Example:
2590<figure><artwork type="example">
[356]2591  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
[29]2597<section title="IANA Considerations" anchor="IANA.considerations">
2599<section title="Method Registry" anchor="method.registration">
[1161]2601  The registration procedure for HTTP request methods is defined by
[270]2602  <xref target="method.registry"/> of this document.
[969]2605   The HTTP Method Registry shall be created at <eref target=""/>
[818]2606   and be populated with the registrations below:
[682]2608<?BEGININC p2-semantics.iana-methods ?>
[270]2609<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
[288]2610<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
[270]2611   <ttcol>Method</ttcol>
[286]2612   <ttcol>Safe</ttcol>
[270]2613   <ttcol>Reference</ttcol>
2614   <c>CONNECT</c>
[286]2615   <c>no</c>
[270]2616   <c>
2617      <xref target="CONNECT"/>
2618   </c>
2619   <c>DELETE</c>
[286]2620   <c>no</c>
[270]2621   <c>
2622      <xref target="DELETE"/>
2623   </c>
2624   <c>GET</c>
[286]2625   <c>yes</c>
[270]2626   <c>
2627      <xref target="GET"/>
2628   </c>
2629   <c>HEAD</c>
[286]2630   <c>yes</c>
[270]2631   <c>
2632      <xref target="HEAD"/>
2633   </c>
2634   <c>OPTIONS</c>
[286]2635   <c>yes</c>
[270]2636   <c>
2637      <xref target="OPTIONS"/>
2638   </c>
2639   <c>POST</c>
[286]2640   <c>no</c>
[270]2641   <c>
2642      <xref target="POST"/>
2643   </c>
2644   <c>PUT</c>
[286]2645   <c>no</c>
[270]2646   <c>
2647      <xref target="PUT"/>
2648   </c>
2649   <c>TRACE</c>
[286]2650   <c>yes</c>
[270]2651   <c>
2652      <xref target="TRACE"/>
2653   </c>
[682]2656<?ENDINC p2-semantics.iana-methods ?>
[255]2659<section title="Status Code Registry" anchor="status.code.registration">
[1101]2661   The registration procedure for HTTP Status Codes &mdash; previously defined
2662   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
[288]2663   by <xref target="status.code.registry"/> of this document.
2666   The HTTP Status Code Registry located at <eref target=""/>
[969]2667   shall be updated with the registrations below:
[682]2669<?BEGININC p2-semantics.iana-status-codes ?>
[255]2670<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
[288]2671<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
[255]2672   <ttcol>Value</ttcol>
2673   <ttcol>Description</ttcol>
2674   <ttcol>Reference</ttcol>
2675   <c>100</c>
2676   <c>Continue</c>
2677   <c>
2678      <xref target="status.100"/>
2679   </c>
2680   <c>101</c>
2681   <c>Switching Protocols</c>
2682   <c>
2683      <xref target="status.101"/>
2684   </c>
2685   <c>200</c>
2686   <c>OK</c>
2687   <c>
2688      <xref target="status.200"/>
2689   </c>
2690   <c>201</c>
2691   <c>Created</c>
2692   <c>
2693      <xref target="status.201"/>
2694   </c>
2695   <c>202</c>
2696   <c>Accepted</c>
2697   <c>
2698      <xref target="status.202"/>
2699   </c>
2700   <c>203</c>
2701   <c>Non-Authoritative Information</c>
2702   <c>
2703      <xref target="status.203"/>
2704   </c>
2705   <c>204</c>
2706   <c>No Content</c>
2707   <c>
2708      <xref target="status.204"/>
2709   </c>
2710   <c>205</c>
2711   <c>Reset Content</c>
2712   <c>
2713      <xref target="status.205"/>
2714   </c>
2715   <c>300</c>
2716   <c>Multiple Choices</c>
2717   <c>
2718      <xref target="status.300"/>
2719   </c>
2720   <c>301</c>
2721   <c>Moved Permanently</c>
2722   <c>
2723      <xref target="status.301"/>
2724   </c>
2725   <c>302</c>
2726   <c>Found</c>
2727   <c>
2728      <xref target="status.302"/>
2729   </c>
2730   <c>303</c>
2731   <c>See Other</c>
2732   <c>
2733      <xref target="status.303"/>
2734   </c>
2735   <c>305</c>
2736   <c>Use Proxy</c>
2737   <c>
2738      <xref target="status.305"/>
2739   </c>
2740   <c>306</c>
2741   <c>(Unused)</c>
2742   <c>
2743      <xref target="status.306"/>
2744   </c>
2745   <c>307</c>
2746   <c>Temporary Redirect</c>
2747   <c>
2748      <xref target="status.307"/>
2749   </c>
2750   <c>400</c>
2751   <c>Bad Request</c>
2752   <c>
2753      <xref target="status.400"/>
2754   </c>
2755   <c>402</c>
2756   <c>Payment Required</c>
2757   <c>
2758      <xref target="status.402"/>
2759   </c>
2760   <c>403</c>
2761   <c>Forbidden</c>
2762   <c>
2763      <xref target="status.403"/>
2764   </c>
2765   <c>404</c>
2766   <c>Not Found</c>
2767   <c>
2768      <xref target="status.404"/>
2769   </c>
2770   <c>405</c>
2771   <c>Method Not Allowed</c>
2772   <c>
2773      <xref target="status.405"/>
2774   </c>
2775   <c>406</c>
2776   <c>Not Acceptable</c>
2777   <c>
2778      <xref target="status.406"/>
2779   </c>
2780   <c>407</c>
2781   <c>Proxy Authentication Required</c>
2782   <c>
2783      <xref target="status.407"/>
2784   </c>
2785   <c>408</c>
2786   <c>Request Timeout</c>
2787   <c>
2788      <xref target="status.408"/>
2789   </c>
2790   <c>409</c>
2791   <c>Conflict</c>
2792   <c>
2793      <xref target="status.409"/>
2794   </c>
2795   <c>410</c>
2796   <c>Gone</c>
2797   <c>
2798      <xref target="status.410"/>
2799   </c>
2800   <c>411</c>
2801   <c>Length Required</c>
2802   <c>
2803      <xref target="status.411"/>
2804   </c>
2805   <c>413</c>
[1322]2806   <c>Request Representation Too Large</c>
[255]2807   <c>
2808      <xref target="status.413"/>
2809   </c>
2810   <c>414</c>
[465]2811   <c>URI Too Long</c>
[255]2812   <c>
2813      <xref target="status.414"/>
2814   </c>
2815   <c>415</c>
2816   <c>Unsupported Media Type</c>
2817   <c>
2818      <xref target="status.415"/>
2819   </c>
2820   <c>417</c>
2821   <c>Expectation Failed</c>
2822   <c>
2823      <xref target="status.417"/>
2824   </c>
[1071]2825   <c>426</c>
2826   <c>Upgrade Required</c>
2827   <c>
2828      <xref target="status.426"/>
2829   </c>
[255]2830   <c>500</c>
2831   <c>Internal Server Error</c>
2832   <c>
2833      <xref target="status.500"/>
2834   </c>
2835   <c>501</c>
2836   <c>Not Implemented</c>
2837   <c>
2838      <xref target="status.501"/>
2839   </c>
2840   <c>502</c>
2841   <c>Bad Gateway</c>
2842   <c>
2843      <xref target="status.502"/>
2844   </c>
2845   <c>503</c>
2846   <c>Service Unavailable</c>
2847   <c>
2848      <xref target="status.503"/>
2849   </c>
2850   <c>504</c>
2851   <c>Gateway Timeout</c>
2852   <c>
2853      <xref target="status.504"/>
2854   </c>
2855   <c>505</c>
2856   <c>HTTP Version Not Supported</c>
2857   <c>
2858      <xref target="status.505"/>
2859   </c>
[682]2862<?ENDINC p2-semantics.iana-status-codes ?>
[921]2864<section title="Header Field Registration" anchor="header.field.registration">
[969]2866   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]2867   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]2869<?BEGININC p2-semantics.iana-headers ?>
[253]2870<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]2871<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]2872   <ttcol>Header Field Name</ttcol>
2873   <ttcol>Protocol</ttcol>
2874   <ttcol>Status</ttcol>
2875   <ttcol>Reference</ttcol>
[253]2877   <c>Allow</c>
2878   <c>http</c>
2879   <c>standard</c>
2880   <c>
2881      <xref target="header.allow"/>
2882   </c>
2883   <c>Expect</c>
2884   <c>http</c>
2885   <c>standard</c>
2886   <c>
2887      <xref target="header.expect"/>
2888   </c>
2889   <c>From</c>
2890   <c>http</c>
2891   <c>standard</c>
2892   <c>
2893      <xref target="header.from"/>
2894   </c>
2895   <c>Location</c>
2896   <c>http</c>
2897   <c>standard</c>
2898   <c>
2899      <xref target="header.location"/>
2900   </c>
2901   <c>Max-Forwards</c>
2902   <c>http</c>
2903   <c>standard</c>
2904   <c>
2905      <xref target="header.max-forwards"/>
2906   </c>
2907   <c>Referer</c>
2908   <c>http</c>
2909   <c>standard</c>
2910   <c>
2911      <xref target="header.referer"/>
2912   </c>
2913   <c>Retry-After</c>
2914   <c>http</c>
2915   <c>standard</c>
2916   <c>
2917      <xref target="header.retry-after"/>
2918   </c>
2919   <c>Server</c>
2920   <c>http</c>
2921   <c>standard</c>
2922   <c>
2923      <xref target="header.server"/>
2924   </c>
2925   <c>User-Agent</c>
2926   <c>http</c>
2927   <c>standard</c>
2928   <c>
2929      <xref target="header.user-agent"/>
2930   </c>
[680]2933<?ENDINC p2-semantics.iana-headers ?>
[290]2935   The change controller is: "IETF ( - Internet Engineering Task Force".
[8]2940<section title="Security Considerations" anchor="security.considerations">
2942   This section is meant to inform application developers, information
2943   providers, and users of the security limitations in HTTP/1.1 as
2944   described by this document. The discussion does not include
2945   definitive solutions to the problems revealed, though it does make
2946   some suggestions for reducing security risks.
2949<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2951   Like any generic data transfer protocol, HTTP cannot regulate the
2952   content of the data that is transferred, nor is there any a priori
2953   method of determining the sensitivity of any particular piece of
2954   information within the context of any given request. Therefore,
2955   applications &SHOULD; supply as much control over this information as
2956   possible to the provider of that information. Four header fields are
2957   worth special mention in this context: Server, Via, Referer and From.
2960   Revealing the specific software version of the server might allow the
2961   server machine to become more vulnerable to attacks against software
2962   that is known to contain security holes. Implementors &SHOULD; make the
2963   Server header field a configurable option.
2966   Proxies which serve as a portal through a network firewall &SHOULD;
2967   take special precautions regarding the transfer of header information
2968   that identifies the hosts behind the firewall. In particular, they
2969   &SHOULD; remove, or replace with sanitized versions, any Via fields
2970   generated behind the firewall.
[994]2973   The Referer header field allows reading patterns to be studied and reverse
[8]2974   links drawn. Although it can be very useful, its power can be abused
2975   if user details are not separated from the information contained in
2976   the Referer. Even when the personal information has been removed, the
[994]2977   Referer header field might indicate a private document's URI whose
[8]2978   publication would be inappropriate.
2981   The information sent in the From field might conflict with the user's
2982   privacy interests or their site's security policy, and hence it
2983   &SHOULD-NOT;  be transmitted without the user being able to disable,
2984   enable, and modify the contents of the field. The user &MUST; be able
2985   to set the contents of this field within a user preference or
2986   application defaults configuration.
2989   We suggest, though do not require, that a convenient toggle interface
2990   be provided for the user to enable or disable the sending of From and
2991   Referer information.
[1036]2994   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
2995   target="header.server"/>) header fields can sometimes be used to determine
2996   that a specific client or server have a particular security hole which might
2997   be exploited. Unfortunately, this same information is often used for other
2998   valuable purposes for which HTTP currently has no better mechanism.
3001   Furthermore, the User-Agent header field may contain enough entropy to be
3002   used, possibly in conjunction with other material, to uniquely identify the
3003   user.
[1161]3006   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
[994]3007   that was sent in request header fields within the body of their response.
[666]3008   Clients &SHOULD; be careful with sensitive information, like Cookies,
[1161]3009   Authorization credentials, and other header fields that might be used to
[666]3010   collect data from the client.
[184]3014<section title="Encoding Sensitive Information in URIs" anchor="">
3016   Because the source of a link might be private information or might
3017   reveal an otherwise private information source, it is strongly
3018   recommended that the user be able to select whether or not the
3019   Referer field is sent. For example, a browser client could have a
3020   toggle switch for browsing openly/anonymously, which would
3021   respectively enable/disable the sending of Referer and From
3022   information.
[172]3025   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
[8]3026   HTTP request if the referring page was transferred with a secure
3027   protocol.
[969]3030   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3031   sensitive data because that data will be placed in the request-target. Many
[823]3032   existing servers, proxies, and user agents log or display the request-target
3033   in places where it might be visible to third parties. Such services can
[172]3034   use POST-based form submission instead.
3038<section title="Location Headers and Spoofing" anchor="location.spoofing">
3040   If a single server supports multiple organizations that do not trust
3041   one another, then it &MUST; check the values of Location and Content-Location
[994]3042   header fields in responses that are generated under control of
[8]3043   said organizations to make sure that they do not attempt to
3044   invalidate resources over which they have no authority.
[1061]3048<section title="Security Considerations for CONNECT">
3050   Since tunneled data is opaque to the proxy, there are additional
3051   risks to tunneling to other well-known or reserved ports.
3052   A HTTP client CONNECTing to port 25 could relay spam
3053   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3054   access to a small number of known ports.
[1364]3060<section title="Acknowledgments" anchor="acks">
3062  See &acks;.
[119]3068<references title="Normative References">
[31]3070<reference anchor="Part1">
[119]3071  <front>
3072    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3073    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3074      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3075      <address><email></email></address>
3076    </author>
3077    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3078      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3079      <address><email></email></address>
[119]3080    </author>
3081    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3082      <organization abbrev="HP">Hewlett-Packard Company</organization>
3083      <address><email></email></address>
3084    </author>
3085    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3086      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3087      <address><email></email></address>
3088    </author>
3089    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3090      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3091      <address><email></email></address>
3092    </author>
3093    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3094      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3095      <address><email></email></address>
3096    </author>
3097    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3098      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3099      <address><email></email></address>
3100    </author>
3101    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3102      <organization abbrev="W3C">World Wide Web Consortium</organization>
3103      <address><email></email></address>
3104    </author>
3105    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3106      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3107      <address><email></email></address>
3108    </author>
3109    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3110  </front>
3111  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3112  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3115<reference anchor="Part3">
[119]3116  <front>
3117    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3118    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3119      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3120      <address><email></email></address>
3121    </author>
3122    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3123      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3124      <address><email></email></address>
[119]3125    </author>
3126    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3127      <organization abbrev="HP">Hewlett-Packard Company</organization>
3128      <address><email></email></address>
3129    </author>
3130    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3131      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3132      <address><email></email></address>
3133    </author>
3134    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3135      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3136      <address><email></email></address>
3137    </author>
3138    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3140      <address><email></email></address>
3141    </author>
3142    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3143      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3144      <address><email></email></address>
3145    </author>
3146    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3147      <organization abbrev="W3C">World Wide Web Consortium</organization>
3148      <address><email></email></address>
3149    </author>
3150    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3151      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3152      <address><email></email></address>
3153    </author>
3154    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3155  </front>
3156  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3157  <x:source href="p3-payload.xml" basename="p3-payload"/>
3160<reference anchor="Part4">
[119]3161  <front>
3162    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3163    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3164      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3165      <address><email></email></address>
3166    </author>
3167    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3168      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3169      <address><email></email></address>
[119]3170    </author>
3171    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3172      <organization abbrev="HP">Hewlett-Packard Company</organization>
3173      <address><email></email></address>
3174    </author>
3175    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3176      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3177      <address><email></email></address>
3178    </author>
3179    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3180      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3181      <address><email></email></address>
3182    </author>
3183    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3185      <address><email></email></address>
3186    </author>
3187    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3188      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3189      <address><email></email></address>
3190    </author>
3191    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3192      <organization abbrev="W3C">World Wide Web Consortium</organization>
3193      <address><email></email></address>
3194    </author>
3195    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3196      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3197      <address><email></email></address>
3198    </author>
3199    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3200  </front>
3201  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3202  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3205<reference anchor="Part5">
[119]3206  <front>
3207    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3208    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3209      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3210      <address><email></email></address>
3211    </author>
3212    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3213      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3214      <address><email></email></address>
[119]3215    </author>
3216    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3217      <organization abbrev="HP">Hewlett-Packard Company</organization>
3218      <address><email></email></address>
3219    </author>
3220    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3221      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3222      <address><email></email></address>
3223    </author>
3224    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3225      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3226      <address><email></email></address>
3227    </author>
3228    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3229      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3230      <address><email></email></address>
3231    </author>
3232    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3233      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3234      <address><email></email></address>
3235    </author>
3236    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3237      <organization abbrev="W3C">World Wide Web Consortium</organization>
3238      <address><email></email></address>
3239    </author>
3240    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3241      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3242      <address><email></email></address>
3243    </author>
3244    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3245  </front>
3246  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3247  <x:source href="p5-range.xml" basename="p5-range"/>
3250<reference anchor="Part6">
[119]3251  <front>
3252    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3253    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3254      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3255      <address><email></email></address>
3256    </author>
3257    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3258      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3259      <address><email></email></address>
[119]3260    </author>
3261    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3262      <organization abbrev="HP">Hewlett-Packard Company</organization>
3263      <address><email></email></address>
3264    </author>
3265    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3266      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3267      <address><email></email></address>
3268    </author>
3269    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3270      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3271      <address><email></email></address>
3272    </author>
3273    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3274      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3275      <address><email></email></address>
3276    </author>
3277    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3278      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3279      <address><email></email></address>
3280    </author>
3281    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3282      <organization abbrev="W3C">World Wide Web Consortium</organization>
3283      <address><email></email></address>
3284    </author>
[601]3285    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3286      <address><email></email></address>
3287    </author>
[119]3288    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3289      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3290      <address><email></email></address>
3291    </author>
3292    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3293  </front>
3294  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3295  <x:source href="p6-cache.xml" basename="p6-cache"/>
3298<reference anchor="Part7">
[119]3299  <front>
3300    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3301    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3302      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3303      <address><email></email></address>
3304    </author>
3305    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3306      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3307      <address><email></email></address>
[119]3308    </author>
3309    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3310      <organization abbrev="HP">Hewlett-Packard Company</organization>
3311      <address><email></email></address>
3312    </author>
3313    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3314      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3315      <address><email></email></address>
3316    </author>
3317    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3318      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3319      <address><email></email></address>
3320    </author>
3321    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3322      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3323      <address><email></email></address>
3324    </author>
3325    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3326      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3327      <address><email></email></address>
3328    </author>
3329    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3330      <organization abbrev="W3C">World Wide Web Consortium</organization>
3331      <address><email></email></address>
3332    </author>
3333    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3334      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3335      <address><email></email></address>
3336    </author>
3337    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3338  </front>
3339  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3340  <x:source href="p7-auth.xml" basename="p7-auth"/>
[119]3343<reference anchor="RFC2119">
3344  <front>
3345    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3346    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3347      <organization>Harvard University</organization>
3348      <address><email></email></address>
3349    </author>
3350    <date month="March" year="1997"/>
3351  </front>
3352  <seriesInfo name="BCP" value="14"/>
3353  <seriesInfo name="RFC" value="2119"/>
[785]3356<reference anchor="RFC3986">
3357 <front>
3358  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3359  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3360    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3361    <address>
3362       <email></email>
3363       <uri></uri>
3364    </address>
3365  </author>
3366  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3367    <organization abbrev="Day Software">Day Software</organization>
3368    <address>
3369      <email></email>
3370      <uri></uri>
3371    </address>
3372  </author>
3373  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3374    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3375    <address>
3376      <email></email>
3377      <uri></uri>
3378    </address>
3379  </author>
3380  <date month='January' year='2005'></date>
3381 </front>
[1003]3382 <seriesInfo name="STD" value="66"/>
[785]3383 <seriesInfo name="RFC" value="3986"/>
[425]3386<reference anchor="RFC5234">
3387  <front>
3388    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3389    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3390      <organization>Brandenburg InternetWorking</organization>
3391      <address>
[728]3392        <email></email>
3393      </address> 
[425]3394    </author>
3395    <author initials="P." surname="Overell" fullname="Paul Overell">
3396      <organization>THUS plc.</organization>
3397      <address>
[728]3398        <email></email>
3399      </address>
[425]3400    </author>
3401    <date month="January" year="2008"/>
3402  </front>
3403  <seriesInfo name="STD" value="68"/>
3404  <seriesInfo name="RFC" value="5234"/>
3409<references title="Informative References">
[129]3411<reference anchor="RFC1945">
3412  <front>
3413    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3414    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3415      <organization>MIT, Laboratory for Computer Science</organization>
3416      <address><email></email></address>
3417    </author>
3418    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3419      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3420      <address><email></email></address>
3421    </author>
3422    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3423      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3424      <address><email></email></address>
3425    </author>
3426    <date month="May" year="1996"/>
3427  </front>
3428  <seriesInfo name="RFC" value="1945"/>
[119]3431<reference anchor="RFC2068">
3432  <front>
3433    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3434    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3435      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3436      <address><email></email></address>
3437    </author>
3438    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3439      <organization>MIT Laboratory for Computer Science</organization>
3440      <address><email></email></address>
3441    </author>
3442    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3443      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3444      <address><email></email></address>
3445    </author>
3446    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3447      <organization>MIT Laboratory for Computer Science</organization>
3448      <address><email></email></address>
3449    </author>
3450    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3451      <organization>MIT Laboratory for Computer Science</organization>
3452      <address><email></email></address>
3453    </author>
3454    <date month="January" year="1997"/>
3455  </front>
3456  <seriesInfo name="RFC" value="2068"/>
[36]3459<reference anchor="RFC2616">
[119]3460  <front>
3461    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3462    <author initials="R." surname="Fielding" fullname="R. Fielding">
3463      <organization>University of California, Irvine</organization>
3464      <address><email></email></address>
3465    </author>
3466    <author initials="J." surname="Gettys" fullname="J. Gettys">
3467      <organization>W3C</organization>
3468      <address><email></email></address>
3469    </author>
3470    <author initials="J." surname="Mogul" fullname="J. Mogul">
3471      <organization>Compaq Computer Corporation</organization>
3472      <address><email></email></address>
3473    </author>
3474    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3475      <organization>MIT Laboratory for Computer Science</organization>
3476      <address><email></email></address>
3477    </author>
3478    <author initials="L." surname="Masinter" fullname="L. Masinter">
3479      <organization>Xerox Corporation</organization>
3480      <address><email></email></address>
3481    </author>
3482    <author initials="P." surname="Leach" fullname="P. Leach">
3483      <organization>Microsoft Corporation</organization>
3484      <address><email></email></address>
3485    </author>
3486    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3487      <organization>W3C</organization>
3488      <address><email></email></address>
3489    </author>
3490    <date month="June" year="1999"/>
3491  </front>
3492  <seriesInfo name="RFC" value="2616"/>
[255]3495<reference anchor='RFC2817'>
3496  <front>
3497    <title>Upgrading to TLS Within HTTP/1.1</title>
3498    <author initials='R.' surname='Khare' fullname='R. Khare'>
3499      <organization>4K Associates / UC Irvine</organization>
3500      <address><email></email></address>
3501    </author>
3502    <author initials