source: draft-ietf-httpbis/latest/p1-messaging.xml @ 185

Last change on this file since 185 was 185, checked in by julian.reschke@…, 12 years ago

Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" -> "trailer-part"), avoid underscore character in rule names ("http_URL" -> "http-URL", "abs_path" -> "path-absolute"), add rules for terms imported from URI spec ("absoluteURI", "authority", "path-absolute", "port", "query", "relativeURI", "host) -- these will have to be updated when switching over to RFC3986; addresses #36.

  • Property svn:eol-style set to native
File size: 178.9 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc-ext allow-markup-in-artwork="yes" ?>
48<?rfc-ext include-references-in-index="yes" ?>
49<rfc obsoletes="2616" category="std"
50     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
51     xmlns:x='http://purl.org/net/xml2rfc/ext'>
52<front>
53
54  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
55
56  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
57    <organization abbrev="Day Software">Day Software</organization>
58    <address>
59      <postal>
60        <street>23 Corporate Plaza DR, Suite 280</street>
61        <city>Newport Beach</city>
62        <region>CA</region>
63        <code>92660</code>
64        <country>USA</country>
65      </postal>
66      <phone>+1-949-706-5300</phone>
67      <facsimile>+1-949-706-5305</facsimile>
68      <email>fielding@gbiv.com</email>
69      <uri>http://roy.gbiv.com/</uri>
70    </address>
71  </author>
72
73  <author initials="J." surname="Gettys" fullname="Jim Gettys">
74    <organization>One Laptop per Child</organization>
75    <address>
76      <postal>
77        <street>21 Oak Knoll Road</street>
78        <city>Carlisle</city>
79        <region>MA</region>
80        <code>01741</code>
81        <country>USA</country>
82      </postal>
83      <email>jg@laptop.org</email>
84      <uri>http://www.laptop.org/</uri>
85    </address>
86  </author>
87 
88  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
89    <organization abbrev="HP">Hewlett-Packard Company</organization>
90    <address>
91      <postal>
92        <street>HP Labs, Large Scale Systems Group</street>
93        <street>1501 Page Mill Road, MS 1177</street>
94        <city>Palo Alto</city>
95        <region>CA</region>
96        <code>94304</code>
97        <country>USA</country>
98      </postal>
99      <email>JeffMogul@acm.org</email>
100    </address>
101  </author>
102
103  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
104    <organization abbrev="Microsoft">Microsoft Corporation</organization>
105    <address>
106      <postal>
107        <street>1 Microsoft Way</street>
108        <city>Redmond</city>
109        <region>WA</region>
110        <code>98052</code>
111        <country>USA</country>
112      </postal>
113      <email>henrikn@microsoft.com</email>
114    </address>
115  </author>
116
117  <author initials="L." surname="Masinter" fullname="Larry Masinter">
118    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
119    <address>
120      <postal>
121        <street>345 Park Ave</street>
122        <city>San Jose</city>
123        <region>CA</region>
124        <code>95110</code>
125        <country>USA</country>
126      </postal>
127      <email>LMM@acm.org</email>
128      <uri>http://larry.masinter.net/</uri>
129    </address>
130  </author>
131 
132  <author initials="P." surname="Leach" fullname="Paul J. Leach">
133    <organization abbrev="Microsoft">Microsoft Corporation</organization>
134    <address>
135      <postal>
136        <street>1 Microsoft Way</street>
137        <city>Redmond</city>
138        <region>WA</region>
139        <code>98052</code>
140      </postal>
141      <email>paulle@microsoft.com</email>
142    </address>
143  </author>
144   
145  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
146    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
147    <address>
148      <postal>
149        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
150        <street>The Stata Center, Building 32</street>
151        <street>32 Vassar Street</street>
152        <city>Cambridge</city>
153        <region>MA</region>
154        <code>02139</code>
155        <country>USA</country>
156      </postal>
157      <email>timbl@w3.org</email>
158      <uri>http://www.w3.org/People/Berners-Lee/</uri>
159    </address>
160  </author>
161
162  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
163    <organization abbrev="W3C">World Wide Web Consortium</organization>
164    <address>
165      <postal>
166        <street>W3C / ERCIM</street>
167        <street>2004, rte des Lucioles</street>
168        <city>Sophia-Antipolis</city>
169        <region>AM</region>
170        <code>06902</code>
171        <country>France</country>
172      </postal>
173      <email>ylafon@w3.org</email>
174      <uri>http://www.raubacapeu.net/people/yves/</uri>
175    </address>
176  </author>
177
178  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
179    <organization abbrev="greenbytes">greenbytes GmbH</organization>
180    <address>
181      <postal>
182        <street>Hafenweg 16</street>
183        <city>Muenster</city><region>NW</region><code>48155</code>
184        <country>Germany</country>
185      </postal>
186      <phone>+49 251 2807760</phone>   
187      <facsimile>+49 251 2807761</facsimile>   
188      <email>julian.reschke@greenbytes.de</email>       
189      <uri>http://greenbytes.de/tech/webdav/</uri>     
190    </address>
191  </author>
192
193  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
194
195<abstract>
196<t>
197   The Hypertext Transfer Protocol (HTTP) is an application-level
198   protocol for distributed, collaborative, hypermedia information
199   systems. HTTP has been in use by the World Wide Web global information
200   initiative since 1990. This document is Part 1 of the seven-part specification
201   that defines the protocol referred to as "HTTP/1.1" and, taken together,
202   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
203   its associated terminology, defines the "http" and "https" Uniform
204   Resource Identifier (URI) schemes, defines the generic message syntax
205   and parsing requirements for HTTP message frames, and describes
206   general security concerns for implementations.
207</t>
208</abstract>
209
210<note title="Editorial Note (To be removed by RFC Editor)">
211  <t>
212    Discussion of this draft should take place on the HTTPBIS working group
213    mailing list (ietf-http-wg@w3.org). The current issues list is
214    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
215    and related documents (including fancy diffs) can be found at
216    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
217  </t>
218  <t>
219    This draft incorporates those issue resolutions that were either
220    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
221    or which were agreed upon on the mailing list between October 2006 and
222    November 2007 (as published in "draft-lafon-rfc2616bis-03").
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   protocol for distributed, collaborative, hypermedia information
231   systems. HTTP has been in use by the World-Wide Web global
232   information initiative since 1990. The first version of HTTP, commonly
233   referred to as HTTP/0.9, was a simple protocol for raw data transfer
234   across the Internet with only a single method and no metadata.
235   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
236   the protocol by allowing messages to be in the format of MIME-like
237   messages, containing metadata about the data transferred and
238   modifiers on the request/response semantics. However, HTTP/1.0 did
239   not sufficiently take into consideration the effects of hierarchical
240   proxies, caching, the need for persistent connections, or name-based
241   virtual hosts. In addition, the proliferation of incompletely-implemented
242   applications calling themselves "HTTP/1.0" necessitated a
243   protocol version change in order for two communicating applications
244   to determine each other's true capabilities.
245</t>
246<t>
247   This document is Part 1 of the seven-part specification that defines
248   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
249   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
250   requirements that enable reliable implementations and adding only
251   those new features that will either be safely ignored by an HTTP/1.0
252   recipient or only sent when communicating with a party advertising
253   compliance with HTTP/1.1.
254   Part 1 defines those aspects of HTTP/1.1 related to overall network
255   operation, message framing, interaction with transport protocols, and
256   URI schemes.
257</t>
258<t>
259   This document is currently disorganized in order to minimize the changes
260   between drafts and enable reviewers to see the smaller errata changes.
261   The next draft will reorganize the sections to better reflect the content.
262   In particular, the sections will be organized according to the typical
263   process of deciding when to use HTTP (URI schemes), overall network operation,
264   connection management, message framing, and generic message parsing.
265   The current mess reflects how widely dispersed these topics and associated
266   requirements had become in <xref target="RFC2616"/>.
267</t>
268
269<section title="Purpose" anchor="intro.purpose">
270<t>
271   Practical information systems require more functionality than simple
272   retrieval, including search, front-end update, and annotation. HTTP
273   allows an open-ended set of methods and headers that indicate the
274   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
275   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
276   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
277   method is to be applied. Messages are passed in a format similar to
278   that used by Internet mail <xref target="RFC2822"/> as defined by the Multipurpose
279   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
280</t>
281<t>
282   HTTP is also used as a generic protocol for communication between
283   user agents and proxies/gateways to other Internet systems, including
284   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
285   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
286   access to resources available from diverse applications.
287</t>
288</section>
289
290<section title="Requirements" anchor="intro.requirements">
291<t>
292   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
293   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
294   document are to be interpreted as described in <xref target="RFC2119"/>.
295</t>
296<t>
297   An implementation is not compliant if it fails to satisfy one or more
298   of the &MUST; or &REQUIRED; level requirements for the protocols it
299   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
300   level and all the &SHOULD; level requirements for its protocols is said
301   to be "unconditionally compliant"; one that satisfies all the &MUST;
302   level requirements but not all the &SHOULD; level requirements for its
303   protocols is said to be "conditionally compliant."
304</t>
305</section>
306
307<section title="Terminology" anchor="intro.terminology">
308<t>
309   This specification uses a number of terms to refer to the roles
310   played by participants in, and objects of, the HTTP communication.
311</t>
312<t>
313  <iref item="connection"/>
314  <x:dfn>connection</x:dfn>
315  <list>
316    <t>
317      A transport layer virtual circuit established between two programs
318      for the purpose of communication.
319    </t>
320  </list>
321</t>
322<t>
323  <iref item="message"/>
324  <x:dfn>message</x:dfn>
325  <list>
326    <t>
327      The basic unit of HTTP communication, consisting of a structured
328      sequence of octets matching the syntax defined in <xref target="http.message"/> and
329      transmitted via the connection.
330    </t>
331  </list>
332</t>
333<t>
334  <iref item="request"/>
335  <x:dfn>request</x:dfn>
336  <list>
337    <t>
338      An HTTP request message, as defined in <xref target="request"/>.
339    </t>
340  </list>
341</t>
342<t>
343  <iref item="response"/>
344  <x:dfn>response</x:dfn>
345  <list>
346    <t>
347      An HTTP response message, as defined in <xref target="response"/>.
348    </t>
349  </list>
350</t>
351<t>
352  <iref item="resource"/>
353  <x:dfn>resource</x:dfn>
354  <list>
355    <t>
356      A network data object or service that can be identified by a URI,
357      as defined in <xref target="uri"/>. Resources may be available in multiple
358      representations (e.g. multiple languages, data formats, size, and
359      resolutions) or vary in other ways.
360    </t>
361  </list>
362</t>
363<t>
364  <iref item="entity"/>
365  <x:dfn>entity</x:dfn>
366  <list>
367    <t>
368      The information transferred as the payload of a request or
369      response. An entity consists of metainformation in the form of
370      entity-header fields and content in the form of an entity-body, as
371      described in &entity;.
372    </t>
373  </list>
374</t>
375<t>
376  <iref item="representation"/>
377  <x:dfn>representation</x:dfn>
378  <list>
379    <t>
380      An entity included with a response that is subject to content
381      negotiation, as described in &content.negotiation;. There may exist multiple
382      representations associated with a particular response status.
383    </t>
384  </list>
385</t>
386<t>
387  <iref item="content negotiation"/>
388  <x:dfn>content negotiation</x:dfn>
389  <list>
390    <t>
391      The mechanism for selecting the appropriate representation when
392      servicing a request, as described in &content.negotiation;. The
393      representation of entities in any response can be negotiated
394      (including error responses).
395    </t>
396  </list>
397</t>
398<t>
399  <iref item="variant"/>
400  <x:dfn>variant</x:dfn>
401  <list>
402    <t>
403      A resource may have one, or more than one, representation(s)
404      associated with it at any given instant. Each of these
405      representations is termed a `variant'.  Use of the term `variant'
406      does not necessarily imply that the resource is subject to content
407      negotiation.
408    </t>
409  </list>
410</t>
411<t>
412  <iref item="client"/>
413  <x:dfn>client</x:dfn>
414  <list>
415    <t>
416      A program that establishes connections for the purpose of sending
417      requests.
418    </t>
419  </list>
420</t>
421<t>
422  <iref item="user agent"/>
423  <x:dfn>user agent</x:dfn>
424  <list>
425    <t>
426      The client which initiates a request. These are often browsers,
427      editors, spiders (web-traversing robots), or other end user tools.
428    </t>
429  </list>
430</t>
431<t>
432  <iref item="server"/>
433  <x:dfn>server</x:dfn>
434  <list>
435    <t>
436      An application program that accepts connections in order to
437      service requests by sending back responses. Any given program may
438      be capable of being both a client and a server; our use of these
439      terms refers only to the role being performed by the program for a
440      particular connection, rather than to the program's capabilities
441      in general. Likewise, any server may act as an origin server,
442      proxy, gateway, or tunnel, switching behavior based on the nature
443      of each request.
444    </t>
445  </list>
446</t>
447<t>
448  <iref item="origin server"/>
449  <x:dfn>origin server</x:dfn>
450  <list>
451    <t>
452      The server on which a given resource resides or is to be created.
453    </t>
454  </list>
455</t>
456<t>
457  <iref item="proxy"/>
458  <x:dfn>proxy</x:dfn>
459  <list>
460    <t>
461      An intermediary program which acts as both a server and a client
462      for the purpose of making requests on behalf of other clients.
463      Requests are serviced internally or by passing them on, with
464      possible translation, to other servers. A proxy &MUST; implement
465      both the client and server requirements of this specification. A
466      "transparent proxy" is a proxy that does not modify the request or
467      response beyond what is required for proxy authentication and
468      identification. A "non-transparent proxy" is a proxy that modifies
469      the request or response in order to provide some added service to
470      the user agent, such as group annotation services, media type
471      transformation, protocol reduction, or anonymity filtering. Except
472      where either transparent or non-transparent behavior is explicitly
473      stated, the HTTP proxy requirements apply to both types of
474      proxies.
475    </t>
476  </list>
477</t>
478<t>
479  <iref item="gateway"/>
480  <x:dfn>gateway</x:dfn>
481  <list>
482    <t>
483      A server which acts as an intermediary for some other server.
484      Unlike a proxy, a gateway receives requests as if it were the
485      origin server for the requested resource; the requesting client
486      may not be aware that it is communicating with a gateway.
487    </t>
488  </list>
489</t>
490<t>
491  <iref item="tunnel"/>
492  <x:dfn>tunnel</x:dfn>
493  <list>
494    <t>
495      An intermediary program which is acting as a blind relay between
496      two connections. Once active, a tunnel is not considered a party
497      to the HTTP communication, though the tunnel may have been
498      initiated by an HTTP request. The tunnel ceases to exist when both
499      ends of the relayed connections are closed.
500    </t>
501  </list>
502</t>
503<t>
504  <iref item="cache"/>
505  <x:dfn>cache</x:dfn>
506  <list>
507    <t>
508      A program's local store of response messages and the subsystem
509      that controls its message storage, retrieval, and deletion. A
510      cache stores cacheable responses in order to reduce the response
511      time and network bandwidth consumption on future, equivalent
512      requests. Any client or server may include a cache, though a cache
513      cannot be used by a server that is acting as a tunnel.
514    </t>
515  </list>
516</t>
517<t>
518  <iref item="cacheable"/>
519  <x:dfn>cacheable</x:dfn>
520  <list>
521    <t>
522      A response is cacheable if a cache is allowed to store a copy of
523      the response message for use in answering subsequent requests. The
524      rules for determining the cacheability of HTTP responses are
525      defined in &caching;. Even if a resource is cacheable, there may
526      be additional constraints on whether a cache can use the cached
527      copy for a particular request.
528    </t>
529  </list>
530</t>
531<t>
532  <iref item="upstream"/>
533  <iref item="downstream"/>
534  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
535  <list>
536    <t>
537      Upstream and downstream describe the flow of a message: all
538      messages flow from upstream to downstream.
539    </t>
540  </list>
541</t>
542<t>
543  <iref item="inbound"/>
544  <iref item="outbound"/>
545  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
546  <list>
547    <t>
548      Inbound and outbound refer to the request and response paths for
549      messages: "inbound" means "traveling toward the origin server",
550      and "outbound" means "traveling toward the user agent"
551    </t>
552  </list>
553</t>
554</section>
555
556<section title="Overall Operation" anchor="intro.overall.operation">
557<t>
558   HTTP is a request/response protocol. A client sends a
559   request to the server in the form of a request method, URI, and
560   protocol version, followed by a MIME-like message containing request
561   modifiers, client information, and possible body content over a
562   connection with a server. The server responds with a status line,
563   including the message's protocol version and a success or error code,
564   followed by a MIME-like message containing server information, entity
565   metainformation, and possible entity-body content. The relationship
566   between HTTP and MIME is described in &diff2045entity;.
567</t>
568<t>
569   Most HTTP communication is initiated by a user agent and consists of
570   a request to be applied to a resource on some origin server. In the
571   simplest case, this may be accomplished via a single connection (v)
572   between the user agent (UA) and the origin server (O).
573</t>
574<figure><artwork type="drawing">
575       request chain ------------------------&gt;
576    UA -------------------v------------------- O
577       &lt;----------------------- response chain
578</artwork></figure>
579<t>
580   A more complicated situation occurs when one or more intermediaries
581   are present in the request/response chain. There are three common
582   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
583   forwarding agent, receiving requests for a URI in its absolute form,
584   rewriting all or part of the message, and forwarding the reformatted
585   request toward the server identified by the URI. A gateway is a
586   receiving agent, acting as a layer above some other server(s) and, if
587   necessary, translating the requests to the underlying server's
588   protocol. A tunnel acts as a relay point between two connections
589   without changing the messages; tunnels are used when the
590   communication needs to pass through an intermediary (such as a
591   firewall) even when the intermediary cannot understand the contents
592   of the messages.
593</t>
594<figure><artwork type="drawing">
595       request chain --------------------------------------&gt;
596    UA -----v----- A -----v----- B -----v----- C -----v----- O
597       &lt;------------------------------------- response chain
598</artwork></figure>
599<t>
600   The figure above shows three intermediaries (A, B, and C) between the
601   user agent and origin server. A request or response message that
602   travels the whole chain will pass through four separate connections.
603   This distinction is important because some HTTP communication options
604   may apply only to the connection with the nearest, non-tunnel
605   neighbor, only to the end-points of the chain, or to all connections
606   along the chain. Although the diagram is linear, each participant may
607   be engaged in multiple, simultaneous communications. For example, B
608   may be receiving requests from many clients other than A, and/or
609   forwarding requests to servers other than C, at the same time that it
610   is handling A's request.
611</t>
612<t>
613   Any party to the communication which is not acting as a tunnel may
614   employ an internal cache for handling requests. The effect of a cache
615   is that the request/response chain is shortened if one of the
616   participants along the chain has a cached response applicable to that
617   request. The following illustrates the resulting chain if B has a
618   cached copy of an earlier response from O (via C) for a request which
619   has not been cached by UA or A.
620</t>
621<figure><artwork type="drawing">
622          request chain ----------&gt;
623       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
624          &lt;--------- response chain
625</artwork></figure>
626<t>
627   Not all responses are usefully cacheable, and some requests may
628   contain modifiers which place special requirements on cache behavior.
629   HTTP requirements for cache behavior and cacheable responses are
630   defined in &caching;.
631</t>
632<t>
633   In fact, there are a wide variety of architectures and configurations
634   of caches and proxies currently being experimented with or deployed
635   across the World Wide Web. These systems include national hierarchies
636   of proxy caches to save transoceanic bandwidth, systems that
637   broadcast or multicast cache entries, organizations that distribute
638   subsets of cached data via CD-ROM, and so on. HTTP systems are used
639   in corporate intranets over high-bandwidth links, and for access via
640   PDAs with low-power radio links and intermittent connectivity. The
641   goal of HTTP/1.1 is to support the wide diversity of configurations
642   already deployed while introducing protocol constructs that meet the
643   needs of those who build web applications that require high
644   reliability and, failing that, at least reliable indications of
645   failure.
646</t>
647<t>
648   HTTP communication usually takes place over TCP/IP connections. The
649   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
650   not preclude HTTP from being implemented on top of any other protocol
651   on the Internet, or on other networks. HTTP only presumes a reliable
652   transport; any protocol that provides such guarantees can be used;
653   the mapping of the HTTP/1.1 request and response structures onto the
654   transport data units of the protocol in question is outside the scope
655   of this specification.
656</t>
657<t>
658   In HTTP/1.0, most implementations used a new connection for each
659   request/response exchange. In HTTP/1.1, a connection may be used for
660   one or more request/response exchanges, although connections may be
661   closed for a variety of reasons (see <xref target="persistent.connections"/>).
662</t>
663</section>
664</section>
665
666<section title="Notational Conventions and Generic Grammar" anchor="notation">
667
668<section title="Augmented BNF" anchor="notation.abnf">
669<t>
670   All of the mechanisms specified in this document are described in
671   both prose and an augmented Backus-Naur Form (BNF) similar to that
672   used by <xref target="RFC822ABNF"/>. Implementors will need to be familiar with the
673   notation in order to understand this specification. The augmented BNF
674   includes the following constructs:
675</t>
676<t>
677   name = definition
678  <list>
679    <t>
680      The name of a rule is simply the name itself (without any
681      enclosing "&lt;" and "&gt;") and is separated from its definition by the
682      equal "=" character. White space is only significant in that
683      indentation of continuation lines is used to indicate a rule
684      definition that spans more than one line. Certain basic rules are
685      in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc. Angle
686      brackets are used within definitions whenever their presence will
687      facilitate discerning the use of rule names.
688    </t>
689  </list>
690</t>
691<t>
692   "literal"
693  <list>
694    <t>
695      Quotation marks surround literal text. Unless stated otherwise,
696      the text is case-insensitive.
697    </t>
698  </list>
699</t>
700<t>
701   rule1 | rule2
702  <list>
703    <t>
704      Elements separated by a bar ("|") are alternatives, e.g., "yes |
705      no" will accept yes or no.
706    </t>
707  </list>
708</t>
709<t>
710   (rule1 rule2)
711  <list>
712    <t>
713      Elements enclosed in parentheses are treated as a single element.
714      Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
715      foo elem" and "elem bar elem".
716    </t>
717  </list>
718</t>
719<t>
720   *rule
721  <list>
722    <t>
723      The character "*" preceding an element indicates repetition. The
724      full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and at most
725      &lt;m&gt; occurrences of element. Default values are 0 and infinity so
726      that "*(element)" allows any number, including zero; "1*element"
727      requires at least one; and "1*2element" allows one or two.
728    </t>
729  </list>
730</t>
731<t>
732   [rule]
733  <list>
734    <t>
735      Square brackets enclose optional elements; "[foo bar]" is
736      equivalent to "*1(foo bar)".
737    </t>
738  </list>
739</t>
740<t>
741   N rule
742  <list>
743    <t>
744      Specific repetition: "&lt;n&gt;(element)" is equivalent to
745      "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element).
746      Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
747      alphabetic characters.
748    </t>
749  </list>
750</t>
751<t>
752   #rule
753  <list>
754    <t>
755      A construct "#" is defined, similar to "*", for defining lists of
756      elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
757      &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
758      (",") and &OPTIONAL; linear white space (LWS). This makes the usual
759      form of lists very easy; a rule such as
760    </t>
761    <t>
762         ( *LWS element *( *LWS "," *LWS element ))
763    </t>
764    <t>
765      can be shown as
766    </t>
767    <t>
768         1#element
769    </t>
770    <t>
771      Wherever this construct is used, null elements are allowed, but do
772      not contribute to the count of elements present. That is,
773      "(element), , (element) " is permitted, but counts as only two
774      elements. Therefore, where at least one element is required, at
775      least one non-null element &MUST; be present. Default values are 0
776      and infinity so that "#element" allows any number, including zero;
777      "1#element" requires at least one; and "1#2element" allows one or
778      two.
779    </t>
780  </list>
781</t>
782<t>
783   ; comment
784  <list>
785    <t>
786      A semi-colon, set off some distance to the right of rule text,
787      starts a comment that continues to the end of line. This is a
788      simple way of including useful notes in parallel with the
789      specifications.
790    </t>
791  </list>
792</t>
793<t>
794   implied *LWS
795  <list>
796    <t>
797      The grammar described by this specification is word-based. Except
798      where noted otherwise, linear white space (LWS) can be included
799      between any two adjacent words (token or quoted-string), and
800      between adjacent words and separators, without changing the
801      interpretation of a field. At least one delimiter (LWS and/or
802      separators) &MUST; exist between any two tokens (for the definition
803      of "token" below), since they would otherwise be interpreted as a
804      single token.
805    </t>
806  </list>
807</t>
808</section>
809
810<section title="Basic Rules" anchor="basic.rules">
811<x:anchor-alias value="OCTET"/>
812<x:anchor-alias value="CHAR"/>
813<x:anchor-alias value="UPALPHA"/>
814<x:anchor-alias value="LOALPHA"/>
815<x:anchor-alias value="ALPHA"/>
816<x:anchor-alias value="DIGIT"/>
817<x:anchor-alias value="CTL"/>
818<x:anchor-alias value="CR"/>
819<x:anchor-alias value="LF"/>
820<x:anchor-alias value="SP"/>
821<x:anchor-alias value="HTAB"/>
822<x:anchor-alias value="CRLF"/>
823<x:anchor-alias value="LWS"/>
824<x:anchor-alias value="TEXT"/>
825<x:anchor-alias value="HEX"/>
826<x:anchor-alias value="token"/>
827<x:anchor-alias value="separators"/>
828<x:anchor-alias value="comment"/>
829<x:anchor-alias value="ctext"/>
830<x:anchor-alias value="quoted-string"/>
831<x:anchor-alias value="qdtext"/>
832<x:anchor-alias value="quoted-pair"/>
833<t>
834   The following rules are used throughout this specification to
835   describe basic parsing constructs. The US-ASCII coded character set
836   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
837</t>
838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="UPALPHA"/><iref primary="true" item="Grammar" subitem="LOALPHA"/><iref primary="true" item="Grammar" subitem="ALPHA"/><iref primary="true" item="Grammar" subitem="DIGIT"/><iref primary="true" item="Grammar" subitem="CTL"/><iref primary="true" item="Grammar" subitem="CR"/><iref primary="true" item="Grammar" subitem="LF"/><iref primary="true" item="Grammar" subitem="SP"/><iref primary="true" item="Grammar" subitem="HTAB"/><iref primary="true" item="Grammar" subitem="DQUOTE"/>
839  OCTET          = &lt;any 8-bit sequence of data&gt;
840  CHAR           = &lt;any US-ASCII character (octets 0 - 127)&gt;
841  UPALPHA        = &lt;any US-ASCII uppercase letter "A".."Z"&gt;
842  LOALPHA        = &lt;any US-ASCII lowercase letter "a".."z"&gt;
843  ALPHA          = UPALPHA | LOALPHA
844  DIGIT          = &lt;any US-ASCII digit "0".."9"&gt;
845  CTL            = &lt;any US-ASCII control character
846                   (octets 0 - 31) and DEL (127)&gt;
847  CR             = &lt;US-ASCII CR, carriage return (13)&gt;
848  LF             = &lt;US-ASCII LF, linefeed (10)&gt;
849  SP             = &lt;US-ASCII SP, space (32)&gt;
850  HTAB           = &lt;US-ASCII HT, horizontal-tab (9)&gt;
851  DQUOTE         = &lt;US-ASCII double-quote mark (34)&gt;
852</artwork></figure>
853<t>
854   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
855   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
856   tolerant applications). The end-of-line marker within an entity-body
857   is defined by its associated media type, as described in &media-types;.
858</t>
859<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
860  CRLF           = CR LF
861</artwork></figure>
862<t>
863   HTTP/1.1 header field values can be folded onto multiple lines if the
864   continuation line begins with a space or horizontal tab. All linear
865   white space, including folding, has the same semantics as SP. A
866   recipient &MAY; replace any linear white space with a single SP before
867   interpreting the field value or forwarding the message downstream.
868</t>
869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
870  LWS            = [CRLF] 1*( SP | HTAB )
871</artwork></figure>
872<t>
873   The TEXT rule is only used for descriptive field contents and values
874   that are not intended to be interpreted by the message parser. Words
875   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
876   <xref target="ISO-8859-1"/> only when encoded according to the rules of
877   <xref target="RFC2047"/>.
878</t>
879<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
880  TEXT           = &lt;any OCTET except CTLs,
881                   but including LWS&gt;
882</artwork></figure>
883<t>
884   A CRLF is allowed in the definition of TEXT only as part of a header
885   field continuation. It is expected that the folding LWS will be
886   replaced with a single SP before interpretation of the TEXT value.
887</t>
888<t>
889   Hexadecimal numeric characters are used in several protocol elements.
890</t>
891<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEX"/>
892  HEX            = "A" | "B" | "C" | "D" | "E" | "F"
893                 | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
894</artwork></figure>
895<t>
896   Many HTTP/1.1 header field values consist of words separated by LWS
897   or special characters. These special characters &MUST; be in a quoted
898   string to be used within a parameter value (as defined in
899   <xref target="transfer.codings"/>).
900</t>
901<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="separators"/>
902  token          = 1*&lt;any CHAR except CTLs or separators&gt;
903  separators     = "(" | ")" | "&lt;" | "&gt;" | "@"
904                 | "," | ";" | ":" | "\" | DQUOTE
905                 | "/" | "[" | "]" | "?" | "="
906                 | "{" | "}" | SP | HTAB
907</artwork></figure>
908<t>
909   Comments can be included in some HTTP header fields by surrounding
910   the comment text with parentheses. Comments are only allowed in
911   fields containing "comment" as part of their field value definition.
912   In all other fields, parentheses are considered part of the field
913   value.
914</t>
915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
916  comment        = "(" *( ctext | quoted-pair | comment ) ")"
917  ctext          = &lt;any TEXT excluding "(" and ")"&gt;
918</artwork></figure>
919<t>
920   A string of text is parsed as a single word if it is quoted using
921   double-quote marks.
922</t>
923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
924  quoted-string  = ( DQUOTE *(qdtext | quoted-pair ) DQUOTE )
925  qdtext         = &lt;any TEXT excluding DQUOTE and "\">
926</artwork></figure>
927<t>
928   The backslash character ("\") &MAY; be used as a single-character
929   quoting mechanism only within quoted-string and comment constructs.
930</t>
931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
932  quoted-pair    = "\" CHAR
933</artwork></figure>
934</section>
935</section>
936
937<section title="Protocol Parameters" anchor="protocol.parameters">
938
939<section title="HTTP Version" anchor="http.version">
940<t>
941   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
942   of the protocol. The protocol versioning policy is intended to allow
943   the sender to indicate the format of a message and its capacity for
944   understanding further HTTP communication, rather than the features
945   obtained via that communication. No change is made to the version
946   number for the addition of message components which do not affect
947   communication behavior or which only add to extensible field values.
948   The &lt;minor&gt; number is incremented when the changes made to the
949   protocol add features which do not change the general message parsing
950   algorithm, but which may add to the message semantics and imply
951   additional capabilities of the sender. The &lt;major&gt; number is
952   incremented when the format of a message within the protocol is
953   changed. See <xref target="RFC2145"/> for a fuller explanation.
954</t>
955<t>
956   The version of an HTTP message is indicated by an HTTP-Version field
957   in the first line of the message. HTTP-Version is case-sensitive.
958</t>
959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/>
960  HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
961</artwork></figure>
962<t>
963   Note that the major and minor numbers &MUST; be treated as separate
964   integers and that each &MAY; be incremented higher than a single digit.
965   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
966   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
967   &MUST-NOT; be sent.
968</t>
969<t>
970   An application that sends a request or response message that includes
971   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
972   with this specification. Applications that are at least conditionally
973   compliant with this specification &SHOULD; use an HTTP-Version of
974   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
975   not compatible with HTTP/1.0. For more details on when to send
976   specific HTTP-Version values, see <xref target="RFC2145"/>.
977</t>
978<t>
979   The HTTP version of an application is the highest HTTP version for
980   which the application is at least conditionally compliant.
981</t>
982<t>
983   Proxy and gateway applications need to be careful when forwarding
984   messages in protocol versions different from that of the application.
985   Since the protocol version indicates the protocol capability of the
986   sender, a proxy/gateway &MUST-NOT; send a message with a version
987   indicator which is greater than its actual version. If a higher
988   version request is received, the proxy/gateway &MUST; either downgrade
989   the request version, or respond with an error, or switch to tunnel
990   behavior.
991</t>
992<t>
993   Due to interoperability problems with HTTP/1.0 proxies discovered
994   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
995   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
996   they support. The proxy/gateway's response to that request &MUST; be in
997   the same major version as the request.
998</t>
999<t>
1000  <list>
1001    <t>
1002      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
1003      of header fields required or forbidden by the versions involved.
1004    </t>
1005  </list>
1006</t>
1007</section>
1008
1009<section title="Uniform Resource Identifiers" anchor="uri">
1010<t>
1011   URIs have been known by many names: WWW addresses, Universal Document
1012   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
1013   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
1014   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
1015   simply formatted strings which identify--via name, location, or any
1016   other characteristic--a resource.
1017</t>
1018
1019<section title="General Syntax" anchor="general.syntax">
1020<t>
1021   URIs in HTTP can be represented in absolute form or relative to some
1022   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
1023   forms are differentiated by the fact that absolute URIs always begin
1024   with a scheme name followed by a colon. For definitive information on
1025   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
1026   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
1027   and <xref target="RFC1808"/>). This specification adopts the
1028   definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
1029   "host", "abs_path", "query", and "authority" from that specification:
1030</t>
1031<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="absoluteURI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="relativeURI"/><iref primary="true" item="Grammar" subitem="uri-host"/>
1032  absoluteURI   = &lt;absoluteURI, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1033  authority     = &lt;authority, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2"/>>
1034  path-absolute = &lt;abs_path, defined in <xref target="RFC2396" x:fmt="," x:sec="3"/>>
1035  port          = &lt;port, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1036  query         = &lt;query, defined in <xref target="RFC2396" x:fmt="," x:sec="3.4"/>>
1037  relativeURI   = &lt;relativeURI, defined in <xref target="RFC2396" x:fmt="," x:sec="5"/>>
1038  uri-host      = &lt;host, defined in <xref target="RFC2396" x:fmt="," x:sec="3.2.2"/>>
1039</artwork></figure>
1040<t>
1041   HTTP does not place any a priori limit on the length of
1042   a URI. Servers &MUST; be able to handle the URI of any resource they
1043   serve, and &SHOULD; be able to handle URIs of unbounded length if they
1044   provide GET-based forms that could generate such URIs. A server
1045   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
1046   than the server can handle (see &status-414;).
1047</t>
1048<t>
1049  <list>
1050    <t>
1051      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
1052      above 255 bytes, because some older client or proxy
1053      implementations might not properly support these lengths.
1054    </t>
1055  </list>
1056</t>
1057</section>
1058
1059<section title="http URL" anchor="http.url">
1060<t>
1061   The "http" scheme is used to locate network resources via the HTTP
1062   protocol. This section defines the scheme-specific syntax and
1063   semantics for http URLs.
1064</t>
1065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URL"/>
1066  http-URL = "http:" "//" uri-host [ ":" port ]
1067             [ path-absolute [ "?" query ]]
1068</artwork></figure>
1069<t>
1070   If the port is empty or not given, port 80 is assumed. The semantics
1071   are that the identified resource is located at the server listening
1072   for TCP connections on that port of that host, and the Request-URI
1073   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
1074   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
1075   the path-absolute is not present in the URL, it &MUST; be given as "/" when
1076   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1077   receives a host name which is not a fully qualified domain name, it
1078   &MAY; add its domain to the host name it received. If a proxy receives
1079   a fully qualified domain name, the proxy &MUST-NOT; change the host
1080   name.
1081</t>
1082</section>
1083
1084<section title="URI Comparison" anchor="uri.comparison">
1085<t>
1086   When comparing two URIs to decide if they match or not, a client
1087   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
1088   URIs, with these exceptions:
1089  <list style="symbols">
1090    <t>A port that is empty or not given is equivalent to the default
1091        port for that URI-reference;</t>
1092    <t>Comparisons of host names &MUST; be case-insensitive;</t>
1093    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
1094    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
1095  </list>
1096</t>
1097<t>
1098   Characters other than those in the "reserved" set (see
1099   <xref target="RFC2396"/>) are equivalent to their ""%" HEX HEX" encoding.
1100</t>
1101<t>
1102   For example, the following three URIs are equivalent:
1103</t>
1104<figure><artwork type="example">
1105   http://example.com:80/~smith/home.html
1106   http://EXAMPLE.com/%7Esmith/home.html
1107   http://EXAMPLE.com:/%7esmith/home.html
1108</artwork></figure>
1109</section>
1110</section>
1111
1112<section title="Date/Time Formats" anchor="date.time.formats">
1113<section title="Full Date" anchor="full.date">
1114<t>
1115   HTTP applications have historically allowed three different formats
1116   for the representation of date/time stamps:
1117</t>
1118<figure><artwork type="example">
1119   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1120   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1121   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1122</artwork></figure>
1123<t>
1124   The first format is preferred as an Internet standard and represents
1125   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1126   <xref target="RFC822"/>). The other formats are described here only for
1127   compatibility with obsolete implementations.
1128   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1129   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1130   only generate the RFC 1123 format for representing HTTP-date values
1131   in header fields. See <xref target="tolerant.applications"/> for further information.
1132</t>
1133<t><list><t>
1134      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1135      accepting date values that may have been sent by non-HTTP
1136      applications, as is sometimes the case when retrieving or posting
1137      messages via proxies/gateways to SMTP or NNTP.
1138</t></list></t>
1139<t>
1140   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1141   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1142   equal to UTC (Coordinated Universal Time). This is indicated in the
1143   first two formats by the inclusion of "GMT" as the three-letter
1144   abbreviation for time zone, and &MUST; be assumed when reading the
1145   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1146   additional LWS beyond that specifically included as SP in the
1147   grammar.
1148</t>
1149<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
1150  HTTP-date    = rfc1123-date | rfc850-date | asctime-date
1151  rfc1123-date = wkday "," SP date1 SP time SP "GMT"
1152  rfc850-date  = weekday "," SP date2 SP time SP "GMT"
1153  asctime-date = wkday SP date3 SP time SP 4DIGIT
1154  date1        = 2DIGIT SP month SP 4DIGIT
1155                 ; day month year (e.g., 02 Jun 1982)
1156  date2        = 2DIGIT "-" month "-" 2DIGIT
1157                 ; day-month-year (e.g., 02-Jun-82)
1158  date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
1159                 ; month day (e.g., Jun  2)
1160  time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
1161                 ; 00:00:00 - 23:59:59
1162  wkday        = "Mon" | "Tue" | "Wed"
1163               | "Thu" | "Fri" | "Sat" | "Sun"
1164  weekday      = "Monday" | "Tuesday" | "Wednesday"
1165               | "Thursday" | "Friday" | "Saturday" | "Sunday"
1166  month        = "Jan" | "Feb" | "Mar" | "Apr"
1167               | "May" | "Jun" | "Jul" | "Aug"
1168               | "Sep" | "Oct" | "Nov" | "Dec"
1169</artwork></figure>
1170<t>
1171      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1172      to their usage within the protocol stream. Clients and servers are
1173      not required to use these formats for user presentation, request
1174      logging, etc.
1175</t>
1176</section>
1177</section>
1178
1179<section title="Transfer Codings" anchor="transfer.codings">
1180<t>
1181   Transfer-coding values are used to indicate an encoding
1182   transformation that has been, can be, or may need to be applied to an
1183   entity-body in order to ensure "safe transport" through the network.
1184   This differs from a content coding in that the transfer-coding is a
1185   property of the message, not of the original entity.
1186</t>
1187<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1188  transfer-coding         = "chunked" | transfer-extension
1189  transfer-extension      = token *( ";" parameter )
1190</artwork></figure>
1191<t>
1192   Parameters are in  the form of attribute/value pairs.
1193</t>
1194<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
1195  parameter               = attribute "=" value
1196  attribute               = token
1197  value                   = token | quoted-string
1198</artwork></figure>
1199<t>
1200   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1201   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1202   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1203</t>
1204<t>
1205   Whenever a transfer-coding is applied to a message-body, the set of
1206   transfer-codings &MUST; include "chunked", unless the message is
1207   terminated by closing the connection. When the "chunked" transfer-coding
1208   is used, it &MUST; be the last transfer-coding applied to the
1209   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1210   than once to a message-body. These rules allow the recipient to
1211   determine the transfer-length of the message (<xref target="message.length"/>).
1212</t>
1213<t>
1214   Transfer-codings are analogous to the Content-Transfer-Encoding
1215   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1216   binary data over a 7-bit transport service. However, safe transport
1217   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1218   the only unsafe characteristic of message-bodies is the difficulty in
1219   determining the exact body length (<xref target="message.length"/>), or the desire to
1220   encrypt data over a shared transport.
1221</t>
1222<t>
1223   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1224   transfer-coding value tokens. Initially, the registry contains the
1225   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1226   "gzip", "compress", and "deflate" (&content-codings;).
1227</t>
1228<t>
1229   New transfer-coding value tokens &SHOULD; be registered in the same way
1230   as new content-coding value tokens (&content-codings;).
1231</t>
1232<t>
1233   A server which receives an entity-body with a transfer-coding it does
1234   not understand &SHOULD; return 501 (Not Implemented), and close the
1235   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1236   client.
1237</t>
1238
1239<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1240<t>
1241   The chunked encoding modifies the body of a message in order to
1242   transfer it as a series of chunks, each with its own size indicator,
1243   followed by an &OPTIONAL; trailer containing entity-header fields. This
1244   allows dynamically produced content to be transferred along with the
1245   information necessary for the recipient to verify that it has
1246   received the full message.
1247</t>
1248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-extension"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1249  Chunked-Body   = *chunk
1250                   last-chunk
1251                   trailer-part
1252                   CRLF
1253 
1254  chunk          = chunk-size [ chunk-extension ] CRLF
1255                   chunk-data CRLF
1256  chunk-size     = 1*HEX
1257  last-chunk     = 1*("0") [ chunk-extension ] CRLF
1258 
1259  chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
1260  chunk-ext-name = token
1261  chunk-ext-val  = token | quoted-string
1262  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1263  trailer-part   = *(entity-header CRLF)
1264</artwork></figure>
1265<t>
1266   The chunk-size field is a string of hex digits indicating the size of
1267   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1268   zero, followed by the trailer, which is terminated by an empty line.
1269</t>
1270<t>
1271   The trailer allows the sender to include additional HTTP header
1272   fields at the end of the message. The Trailer header field can be
1273   used to indicate which header fields are included in a trailer (see
1274   <xref target="header.trailer"/>).
1275</t>
1276<t>
1277   A server using chunked transfer-coding in a response &MUST-NOT; use the
1278   trailer for any header fields unless at least one of the following is
1279   true:
1280  <list style="numbers">
1281    <t>the request included a TE header field that indicates "trailers" is
1282     acceptable in the transfer-coding of the  response, as described in
1283     <xref target="header.te"/>; or,</t>
1284
1285    <t>the server is the origin server for the response, the trailer
1286     fields consist entirely of optional metadata, and the recipient
1287     could use the message (in a manner acceptable to the origin server)
1288     without receiving this metadata.  In other words, the origin server
1289     is willing to accept the possibility that the trailer fields might
1290     be silently discarded along the path to the client.</t>
1291  </list>
1292</t>
1293<t>
1294   This requirement prevents an interoperability failure when the
1295   message is being received by an HTTP/1.1 (or later) proxy and
1296   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1297   compliance with the protocol would have necessitated a possibly
1298   infinite buffer on the proxy.
1299</t>
1300<t>
1301   A process for decoding the "chunked" transfer-coding
1302   can be represented in pseudo-code as:
1303</t>
1304<figure><artwork type="code">
1305    length := 0
1306    read chunk-size, chunk-extension (if any) and CRLF
1307    while (chunk-size &gt; 0) {
1308       read chunk-data and CRLF
1309       append chunk-data to entity-body
1310       length := length + chunk-size
1311       read chunk-size and CRLF
1312    }
1313    read entity-header
1314    while (entity-header not empty) {
1315       append entity-header to existing header fields
1316       read entity-header
1317    }
1318    Content-Length := length
1319    Remove "chunked" from Transfer-Encoding
1320</artwork></figure>
1321<t>
1322   All HTTP/1.1 applications &MUST; be able to receive and decode the
1323   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1324   they do not understand.
1325</t>
1326</section>
1327</section>
1328
1329</section>
1330
1331<section title="HTTP Message" anchor="http.message">
1332
1333<section title="Message Types" anchor="message.types">
1334<t>
1335   HTTP messages consist of requests from client to server and responses
1336   from server to client.
1337</t>
1338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1339  HTTP-message   = Request | Response     ; HTTP/1.1 messages
1340</artwork></figure>
1341<t>
1342   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1343   message format of <xref target="RFC2822"/> for transferring entities (the payload
1344   of the message). Both types of message consist of a start-line, zero
1345   or more header fields (also known as "headers"), an empty line (i.e.,
1346   a line with nothing preceding the CRLF) indicating the end of the
1347   header fields, and possibly a message-body.
1348</t>
1349<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1350  generic-message = start-line
1351                    *(message-header CRLF)
1352                    CRLF
1353                    [ message-body ]
1354  start-line      = Request-Line | Status-Line
1355</artwork></figure>
1356<t>
1357   In the interest of robustness, servers &SHOULD; ignore any empty
1358   line(s) received where a Request-Line is expected. In other words, if
1359   the server is reading the protocol stream at the beginning of a
1360   message and receives a CRLF first, it should ignore the CRLF.
1361</t>
1362<t>
1363   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1364   after a POST request. To restate what is explicitly forbidden by the
1365   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1366   extra CRLF.
1367</t>
1368</section>
1369
1370<section title="Message Headers" anchor="message.headers">
1371<t>
1372   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1373   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1374   entity-header (&entity-header-fields;) fields, follow the same generic format as
1375   that given in <xref target="RFC2822" x:fmt="of" x:sec="2.1"/>. Each header field consists
1376   of a name followed by a colon (":") and the field value. Field names
1377   are case-insensitive. The field value &MAY; be preceded by any amount
1378   of LWS, though a single SP is preferred. Header fields can be
1379   extended over multiple lines by preceding each extra line with at
1380   least one SP or HTAB. Applications ought to follow "common form", where
1381   one is known or indicated, when generating HTTP constructs, since
1382   there might exist some implementations that fail to accept anything
1383   beyond the common forms.
1384</t>
1385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-header"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1386  message-header = field-name ":" [ field-value ]
1387  field-name     = token
1388  field-value    = *( field-content | LWS )
1389  field-content  = &lt;the OCTETs making up the field-value
1390                   and consisting of either *TEXT or combinations
1391                   of token, separators, and quoted-string&gt;
1392</artwork></figure>
1393<t>
1394   The field-content does not include any leading or trailing LWS:
1395   linear white space occurring before the first non-whitespace
1396   character of the field-value or after the last non-whitespace
1397   character of the field-value. Such leading or trailing LWS &MAY; be
1398   removed without changing the semantics of the field value. Any LWS
1399   that occurs between field-content &MAY; be replaced with a single SP
1400   before interpreting the field value or forwarding the message
1401   downstream.
1402</t>
1403<t>
1404   The order in which header fields with differing field names are
1405   received is not significant. However, it is "good practice" to send
1406   general-header fields first, followed by request-header or response-header
1407   fields, and ending with the entity-header fields.
1408</t>
1409<t>
1410   Multiple message-header fields with the same field-name &MAY; be
1411   present in a message if and only if the entire field-value for that
1412   header field is defined as a comma-separated list [i.e., #(values)].
1413   It &MUST; be possible to combine the multiple header fields into one
1414   "field-name: field-value" pair, without changing the semantics of the
1415   message, by appending each subsequent field-value to the first, each
1416   separated by a comma. The order in which header fields with the same
1417   field-name are received is therefore significant to the
1418   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1419   change the order of these field values when a message is forwarded.
1420</t>
1421</section>
1422
1423<section title="Message Body" anchor="message.body">
1424<t>
1425   The message-body (if any) of an HTTP message is used to carry the
1426   entity-body associated with the request or response. The message-body
1427   differs from the entity-body only when a transfer-coding has been
1428   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1429</t>
1430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1431  message-body = entity-body
1432               | &lt;entity-body encoded as per Transfer-Encoding&gt;
1433</artwork></figure>
1434<t>
1435   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1436   applied by an application to ensure safe and proper transfer of the
1437   message. Transfer-Encoding is a property of the message, not of the
1438   entity, and thus &MAY; be added or removed by any application along the
1439   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1440   when certain transfer-codings may be used.)
1441</t>
1442<t>
1443   The rules for when a message-body is allowed in a message differ for
1444   requests and responses.
1445</t>
1446<t>
1447   The presence of a message-body in a request is signaled by the
1448   inclusion of a Content-Length or Transfer-Encoding header field in
1449   the request's message-headers. A message-body &MUST-NOT; be included in
1450   a request if the specification of the request method (&method;)
1451   explicitly disallows an entity-body in requests.
1452   When a request message contains both a message-body of non-zero
1453   length and a method that does not define any semantics for that
1454   request message-body, then an origin server &SHOULD; either ignore
1455   the message-body or respond with an appropriate error message
1456   (e.g., 413).  A proxy or gateway, when presented the same request,
1457   &SHOULD; either forward the request inbound with the message-body or
1458   ignore the message-body when determining a response.
1459</t>
1460<t>
1461   For response messages, whether or not a message-body is included with
1462   a message is dependent on both the request method and the response
1463   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1464   &MUST-NOT; include a message-body, even though the presence of entity-header
1465   fields might lead one to believe they do. All 1xx
1466   (informational), 204 (No Content), and 304 (Not Modified) responses
1467   &MUST-NOT; include a message-body. All other responses do include a
1468   message-body, although it &MAY; be of zero length.
1469</t>
1470</section>
1471
1472<section title="Message Length" anchor="message.length">
1473<t>
1474   The transfer-length of a message is the length of the message-body as
1475   it appears in the message; that is, after any transfer-codings have
1476   been applied. When a message-body is included with a message, the
1477   transfer-length of that body is determined by one of the following
1478   (in order of precedence):
1479</t>
1480<t>
1481  <list style="numbers">
1482    <x:lt><t>
1483     Any response message which "&MUST-NOT;" include a message-body (such
1484     as the 1xx, 204, and 304 responses and any response to a HEAD
1485     request) is always terminated by the first empty line after the
1486     header fields, regardless of the entity-header fields present in
1487     the message.
1488    </t></x:lt>
1489    <x:lt><t>
1490     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1491     is present, then the transfer-length is
1492     defined by use of the "chunked" transfer-coding (<xref target="transfer.codings"/>),
1493     unless the message is terminated by closing the connection.
1494    </t></x:lt>
1495    <x:lt><t>
1496     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1497     decimal value in OCTETs represents both the entity-length and the
1498     transfer-length. The Content-Length header field &MUST-NOT; be sent
1499     if these two lengths are different (i.e., if a Transfer-Encoding
1500     header field is present). If a message is received with both a
1501     Transfer-Encoding header field and a Content-Length header field,
1502     the latter &MUST; be ignored.
1503    </t></x:lt>
1504    <x:lt><t>
1505     If the message uses the media type "multipart/byteranges", and the
1506     transfer-length is not otherwise specified, then this self-delimiting
1507     media type defines the transfer-length. This media type
1508     &MUST-NOT; be used unless the sender knows that the recipient can parse
1509     it; the presence in a request of a Range header with multiple byte-range
1510     specifiers from a 1.1 client implies that the client can parse
1511     multipart/byteranges responses.
1512    <list style="empty"><t>
1513       A range header might be forwarded by a 1.0 proxy that does not
1514       understand multipart/byteranges; in this case the server &MUST;
1515       delimit the message using methods defined in items 1, 3 or 5 of
1516       this section.
1517    </t></list>
1518    </t></x:lt>
1519    <x:lt><t>
1520     By the server closing the connection. (Closing the connection
1521     cannot be used to indicate the end of a request body, since that
1522     would leave no possibility for the server to send back a response.)
1523    </t></x:lt>
1524  </list>
1525</t>
1526<t>
1527   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1528   containing a message-body &MUST; include a valid Content-Length header
1529   field unless the server is known to be HTTP/1.1 compliant. If a
1530   request contains a message-body and a Content-Length is not given,
1531   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1532   determine the length of the message, or with 411 (Length Required) if
1533   it wishes to insist on receiving a valid Content-Length.
1534</t>
1535<t>
1536   All HTTP/1.1 applications that receive entities &MUST; accept the
1537   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1538   to be used for messages when the message length cannot be determined
1539   in advance.
1540</t>
1541<t>
1542   Messages &MUST-NOT; include both a Content-Length header field and a
1543   transfer-coding. If the message does include a
1544   transfer-coding, the Content-Length &MUST; be ignored.
1545</t>
1546<t>
1547   When a Content-Length is given in a message where a message-body is
1548   allowed, its field value &MUST; exactly match the number of OCTETs in
1549   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1550   invalid length is received and detected.
1551</t>
1552</section>
1553
1554<section title="General Header Fields" anchor="general.header.fields">
1555<t>
1556   There are a few header fields which have general applicability for
1557   both request and response messages, but which do not apply to the
1558   entity being transferred. These header fields apply only to the
1559   message being transmitted.
1560</t>
1561<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1562  general-header = Cache-Control            ; &header-cache-control;
1563                 | Connection               ; <xref target="header.connection"/>
1564                 | Date                     ; <xref target="header.date"/>
1565                 | Pragma                   ; &header-pragma;
1566                 | Trailer                  ; <xref target="header.trailer"/>
1567                 | Transfer-Encoding        ; <xref target="header.transfer-encoding"/>
1568                 | Upgrade                  ; <xref target="header.upgrade"/>
1569                 | Via                      ; <xref target="header.via"/>
1570                 | Warning                  ; &header-warning;
1571</artwork></figure>
1572<t>
1573   General-header field names can be extended reliably only in
1574   combination with a change in the protocol version. However, new or
1575   experimental header fields may be given the semantics of general
1576   header fields if all parties in the communication recognize them to
1577   be general-header fields. Unrecognized header fields are treated as
1578   entity-header fields.
1579</t>
1580</section>
1581</section>
1582
1583<section title="Request" anchor="request">
1584<t>
1585   A request message from a client to a server includes, within the
1586   first line of that message, the method to be applied to the resource,
1587   the identifier of the resource, and the protocol version in use.
1588</t>
1589<!--                 Host                      ; should be moved here eventually -->
1590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1591  Request       = Request-Line              ; <xref target="request-line"/>
1592                  *(( general-header        ; <xref target="general.header.fields"/>
1593                   | request-header         ; &request-header-fields;
1594                   | entity-header ) CRLF)  ; &entity-header-fields;
1595                  CRLF
1596                  [ message-body ]          ; <xref target="message.body"/>
1597</artwork></figure>
1598
1599<section title="Request-Line" anchor="request-line">
1600<t>
1601   The Request-Line begins with a method token, followed by the
1602   Request-URI and the protocol version, and ending with CRLF. The
1603   elements are separated by SP characters. No CR or LF is allowed
1604   except in the final CRLF sequence.
1605</t>
1606<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1607  Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1608</artwork></figure>
1609
1610<section title="Method" anchor="method">
1611<t>
1612   The Method  token indicates the method to be performed on the
1613   resource identified by the Request-URI. The method is case-sensitive.
1614</t>
1615<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1616  Method         = token
1617</artwork></figure>
1618</section>
1619
1620<section title="Request-URI" anchor="request-uri">
1621<t>
1622   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1623   identifies the resource upon which to apply the request.
1624</t>
1625<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1626  Request-URI    = "*"
1627                 | absoluteURI
1628                 | ( path-absolute [ "?" query ] )
1629                 | authority
1630</artwork></figure>
1631<t>
1632   The four options for Request-URI are dependent on the nature of the
1633   request. The asterisk "*" means that the request does not apply to a
1634   particular resource, but to the server itself, and is only allowed
1635   when the method used does not necessarily apply to a resource. One
1636   example would be
1637</t>
1638<figure><artwork type="example">
1639    OPTIONS * HTTP/1.1
1640</artwork></figure>
1641<t>
1642   The absoluteURI form is &REQUIRED; when the request is being made to a
1643   proxy. The proxy is requested to forward the request or service it
1644   from a valid cache, and return the response. Note that the proxy &MAY;
1645   forward the request on to another proxy or directly to the server
1646   specified by the absoluteURI. In order to avoid request loops, a
1647   proxy &MUST; be able to recognize all of its server names, including
1648   any aliases, local variations, and the numeric IP address. An example
1649   Request-Line would be:
1650</t>
1651<figure><artwork type="example">
1652    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1653</artwork></figure>
1654<t>
1655   To allow for transition to absoluteURIs in all requests in future
1656   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absoluteURI
1657   form in requests, even though HTTP/1.1 clients will only generate
1658   them in requests to proxies.
1659</t>
1660<t>
1661   The authority form is only used by the CONNECT method (&CONNECT;).
1662</t>
1663<t>
1664   The most common form of Request-URI is that used to identify a
1665   resource on an origin server or gateway. In this case the absolute
1666   path of the URI &MUST; be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1667   the Request-URI, and the network location of the URI (authority) &MUST;
1668   be transmitted in a Host header field. For example, a client wishing
1669   to retrieve the resource above directly from the origin server would
1670   create a TCP connection to port 80 of the host "www.example.org" and send
1671   the lines:
1672</t>
1673<figure><artwork type="example">
1674    GET /pub/WWW/TheProject.html HTTP/1.1
1675    Host: www.example.org
1676</artwork></figure>
1677<t>
1678   followed by the remainder of the Request. Note that the absolute path
1679   cannot be empty; if none is present in the original URI, it &MUST; be
1680   given as "/" (the server root).
1681</t>
1682<t>
1683   The Request-URI is transmitted in the format specified in
1684   <xref target="general.syntax"/>. If the Request-URI is encoded using the "% HEX HEX" encoding
1685   <xref target="RFC2396"/>, the origin server &MUST; decode the Request-URI in order to
1686   properly interpret the request. Servers &SHOULD; respond to invalid
1687   Request-URIs with an appropriate status code.
1688</t>
1689<t>
1690   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1691   received Request-URI when forwarding it to the next inbound server,
1692   except as noted above to replace a null path-absolute with "/".
1693</t>
1694<t>
1695  <list><t>
1696      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1697      meaning of the request when the origin server is improperly using
1698      a non-reserved URI character for a reserved purpose.  Implementors
1699      should be aware that some pre-HTTP/1.1 proxies have been known to
1700      rewrite the Request-URI.
1701  </t></list>
1702</t>
1703</section>
1704</section>
1705
1706<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1707<t>
1708   The exact resource identified by an Internet request is determined by
1709   examining both the Request-URI and the Host header field.
1710</t>
1711<t>
1712   An origin server that does not allow resources to differ by the
1713   requested host &MAY; ignore the Host header field value when
1714   determining the resource identified by an HTTP/1.1 request. (But see
1715   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1716   for other requirements on Host support in HTTP/1.1.)
1717</t>
1718<t>
1719   An origin server that does differentiate resources based on the host
1720   requested (sometimes referred to as virtual hosts or vanity host
1721   names) &MUST; use the following rules for determining the requested
1722   resource on an HTTP/1.1 request:
1723  <list style="numbers">
1724    <t>If Request-URI is an absoluteURI, the host is part of the
1725     Request-URI. Any Host header field value in the request &MUST; be
1726     ignored.</t>
1727    <t>If the Request-URI is not an absoluteURI, and the request includes
1728     a Host header field, the host is determined by the Host header
1729     field value.</t>
1730    <t>If the host as determined by rule 1 or 2 is not a valid host on
1731     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1732  </list>
1733</t>
1734<t>
1735   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1736   attempt to use heuristics (e.g., examination of the URI path for
1737   something unique to a particular host) in order to determine what
1738   exact resource is being requested.
1739</t>
1740</section>
1741
1742</section>
1743
1744
1745<section title="Response" anchor="response">
1746<t>
1747   After receiving and interpreting a request message, a server responds
1748   with an HTTP response message.
1749</t>
1750<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1751  Response      = Status-Line               ; <xref target="status-line"/>
1752                  *(( general-header        ; <xref target="general.header.fields"/>
1753                   | response-header        ; &response-header-fields;
1754                   | entity-header ) CRLF)  ; &entity-header-fields;
1755                  CRLF
1756                  [ message-body ]          ; <xref target="message.body"/>
1757</artwork></figure>
1758
1759<section title="Status-Line" anchor="status-line">
1760<t>
1761   The first line of a Response message is the Status-Line, consisting
1762   of the protocol version followed by a numeric status code and its
1763   associated textual phrase, with each element separated by SP
1764   characters. No CR or LF is allowed except in the final CRLF sequence.
1765</t>
1766<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1767  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1768</artwork></figure>
1769
1770<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1771<t>
1772   The Status-Code element is a 3-digit integer result code of the
1773   attempt to understand and satisfy the request. These codes are fully
1774   defined in &status-codes;. The Reason-Phrase is intended to give a short
1775   textual description of the Status-Code. The Status-Code is intended
1776   for use by automata and the Reason-Phrase is intended for the human
1777   user. The client is not required to examine or display the Reason-Phrase.
1778</t>
1779<t>
1780   The first digit of the Status-Code defines the class of response. The
1781   last two digits do not have any categorization role. There are 5
1782   values for the first digit:
1783  <list style="symbols">
1784    <t>
1785      1xx: Informational - Request received, continuing process
1786    </t>
1787    <t>
1788      2xx: Success - The action was successfully received,
1789        understood, and accepted
1790    </t>
1791    <t>
1792      3xx: Redirection - Further action must be taken in order to
1793        complete the request
1794    </t>
1795    <t>
1796      4xx: Client Error - The request contains bad syntax or cannot
1797        be fulfilled
1798    </t>
1799    <t>
1800      5xx: Server Error - The server failed to fulfill an apparently
1801        valid request
1802    </t>
1803  </list>
1804</t>
1805<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"/>
1806  Status-Code    = 3DIGIT
1807  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
1808</artwork></figure>
1809</section>
1810</section>
1811
1812</section>
1813
1814
1815<section title="Connections" anchor="connections">
1816
1817<section title="Persistent Connections" anchor="persistent.connections">
1818
1819<section title="Purpose" anchor="persistent.purpose">
1820<t>
1821   Prior to persistent connections, a separate TCP connection was
1822   established to fetch each URL, increasing the load on HTTP servers
1823   and causing congestion on the Internet. The use of inline images and
1824   other associated data often require a client to make multiple
1825   requests of the same server in a short amount of time. Analysis of
1826   these performance problems and results from a prototype
1827   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1828   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1829   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1830   T/TCP <xref target="Tou1998"/>.
1831</t>
1832<t>
1833   Persistent HTTP connections have a number of advantages:
1834  <list style="symbols">
1835      <t>
1836        By opening and closing fewer TCP connections, CPU time is saved
1837        in routers and hosts (clients, servers, proxies, gateways,
1838        tunnels, or caches), and memory used for TCP protocol control
1839        blocks can be saved in hosts.
1840      </t>
1841      <t>
1842        HTTP requests and responses can be pipelined on a connection.
1843        Pipelining allows a client to make multiple requests without
1844        waiting for each response, allowing a single TCP connection to
1845        be used much more efficiently, with much lower elapsed time.
1846      </t>
1847      <t>
1848        Network congestion is reduced by reducing the number of packets
1849        caused by TCP opens, and by allowing TCP sufficient time to
1850        determine the congestion state of the network.
1851      </t>
1852      <t>
1853        Latency on subsequent requests is reduced since there is no time
1854        spent in TCP's connection opening handshake.
1855      </t>
1856      <t>
1857        HTTP can evolve more gracefully, since errors can be reported
1858        without the penalty of closing the TCP connection. Clients using
1859        future versions of HTTP might optimistically try a new feature,
1860        but if communicating with an older server, retry with old
1861        semantics after an error is reported.
1862      </t>
1863    </list>
1864</t>
1865<t>
1866   HTTP implementations &SHOULD; implement persistent connections.
1867</t>
1868</section>
1869
1870<section title="Overall Operation" anchor="persistent.overall">
1871<t>
1872   A significant difference between HTTP/1.1 and earlier versions of
1873   HTTP is that persistent connections are the default behavior of any
1874   HTTP connection. That is, unless otherwise indicated, the client
1875   &SHOULD; assume that the server will maintain a persistent connection,
1876   even after error responses from the server.
1877</t>
1878<t>
1879   Persistent connections provide a mechanism by which a client and a
1880   server can signal the close of a TCP connection. This signaling takes
1881   place using the Connection header field (<xref target="header.connection"/>). Once a close
1882   has been signaled, the client &MUST-NOT; send any more requests on that
1883   connection.
1884</t>
1885
1886<section title="Negotiation" anchor="persistent.negotiation">
1887<t>
1888   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1889   maintain a persistent connection unless a Connection header including
1890   the connection-token "close" was sent in the request. If the server
1891   chooses to close the connection immediately after sending the
1892   response, it &SHOULD; send a Connection header including the
1893   connection-token close.
1894</t>
1895<t>
1896   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1897   decide to keep it open based on whether the response from a server
1898   contains a Connection header with the connection-token close. In case
1899   the client does not want to maintain a connection for more than that
1900   request, it &SHOULD; send a Connection header including the
1901   connection-token close.
1902</t>
1903<t>
1904   If either the client or the server sends the close token in the
1905   Connection header, that request becomes the last one for the
1906   connection.
1907</t>
1908<t>
1909   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1910   maintained for HTTP versions less than 1.1 unless it is explicitly
1911   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1912   compatibility with HTTP/1.0 clients.
1913</t>
1914<t>
1915   In order to remain persistent, all messages on the connection &MUST;
1916   have a self-defined message length (i.e., one not defined by closure
1917   of the connection), as described in <xref target="message.length"/>.
1918</t>
1919</section>
1920
1921<section title="Pipelining" anchor="pipelining">
1922<t>
1923   A client that supports persistent connections &MAY; "pipeline" its
1924   requests (i.e., send multiple requests without waiting for each
1925   response). A server &MUST; send its responses to those requests in the
1926   same order that the requests were received.
1927</t>
1928<t>
1929   Clients which assume persistent connections and pipeline immediately
1930   after connection establishment &SHOULD; be prepared to retry their
1931   connection if the first pipelined attempt fails. If a client does
1932   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1933   persistent. Clients &MUST; also be prepared to resend their requests if
1934   the server closes the connection before sending all of the
1935   corresponding responses.
1936</t>
1937<t>
1938   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1939   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1940   premature termination of the transport connection could lead to
1941   indeterminate results. A client wishing to send a non-idempotent
1942   request &SHOULD; wait to send that request until it has received the
1943   response status for the previous request.
1944</t>
1945</section>
1946</section>
1947
1948<section title="Proxy Servers" anchor="persistent.proxy">
1949<t>
1950   It is especially important that proxies correctly implement the
1951   properties of the Connection header field as specified in <xref target="header.connection"/>.
1952</t>
1953<t>
1954   The proxy server &MUST; signal persistent connections separately with
1955   its clients and the origin servers (or other proxy servers) that it
1956   connects to. Each persistent connection applies to only one transport
1957   link.
1958</t>
1959<t>
1960   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1961   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1962   discussion of the problems with the Keep-Alive header implemented by
1963   many HTTP/1.0 clients).
1964</t>
1965</section>
1966
1967<section title="Practical Considerations" anchor="persistent.practical">
1968<t>
1969   Servers will usually have some time-out value beyond which they will
1970   no longer maintain an inactive connection. Proxy servers might make
1971   this a higher value since it is likely that the client will be making
1972   more connections through the same server. The use of persistent
1973   connections places no requirements on the length (or existence) of
1974   this time-out for either the client or the server.
1975</t>
1976<t>
1977   When a client or server wishes to time-out it &SHOULD; issue a graceful
1978   close on the transport connection. Clients and servers &SHOULD; both
1979   constantly watch for the other side of the transport close, and
1980   respond to it as appropriate. If a client or server does not detect
1981   the other side's close promptly it could cause unnecessary resource
1982   drain on the network.
1983</t>
1984<t>
1985   A client, server, or proxy &MAY; close the transport connection at any
1986   time. For example, a client might have started to send a new request
1987   at the same time that the server has decided to close the "idle"
1988   connection. From the server's point of view, the connection is being
1989   closed while it was idle, but from the client's point of view, a
1990   request is in progress.
1991</t>
1992<t>
1993   This means that clients, servers, and proxies &MUST; be able to recover
1994   from asynchronous close events. Client software &SHOULD; reopen the
1995   transport connection and retransmit the aborted sequence of requests
1996   without user interaction so long as the request sequence is
1997   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1998   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1999   human operator the choice of retrying the request(s). Confirmation by
2000   user-agent software with semantic understanding of the application
2001   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2002   be repeated if the second sequence of requests fails.
2003</t>
2004<t>
2005   Servers &SHOULD; always respond to at least one request per connection,
2006   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2007   middle of transmitting a response, unless a network or client failure
2008   is suspected.
2009</t>
2010<t>
2011   Clients that use persistent connections &SHOULD; limit the number of
2012   simultaneous connections that they maintain to a given server. A
2013   single-user client &SHOULD-NOT; maintain more than 2 connections with
2014   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2015   another server or proxy, where N is the number of simultaneously
2016   active users. These guidelines are intended to improve HTTP response
2017   times and avoid congestion.
2018</t>
2019</section>
2020</section>
2021
2022<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2023
2024<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2025<t>
2026   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2027   flow control mechanisms to resolve temporary overloads, rather than
2028   terminating connections with the expectation that clients will retry.
2029   The latter technique can exacerbate network congestion.
2030</t>
2031</section>
2032
2033<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2034<t>
2035   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2036   the network connection for an error status while it is transmitting
2037   the request. If the client sees an error status, it &SHOULD;
2038   immediately cease transmitting the body. If the body is being sent
2039   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2040   empty trailer &MAY; be used to prematurely mark the end of the message.
2041   If the body was preceded by a Content-Length header, the client &MUST;
2042   close the connection.
2043</t>
2044</section>
2045
2046<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2047<t>
2048   The purpose of the 100 (Continue) status (see &status-100;) is to
2049   allow a client that is sending a request message with a request body
2050   to determine if the origin server is willing to accept the request
2051   (based on the request headers) before the client sends the request
2052   body. In some cases, it might either be inappropriate or highly
2053   inefficient for the client to send the body if the server will reject
2054   the message without looking at the body.
2055</t>
2056<t>
2057   Requirements for HTTP/1.1 clients:
2058  <list style="symbols">
2059    <t>
2060        If a client will wait for a 100 (Continue) response before
2061        sending the request body, it &MUST; send an Expect request-header
2062        field (&header-expect;) with the "100-continue" expectation.
2063    </t>
2064    <t>
2065        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2066        with the "100-continue" expectation if it does not intend
2067        to send a request body.
2068    </t>
2069  </list>
2070</t>
2071<t>
2072   Because of the presence of older implementations, the protocol allows
2073   ambiguous situations in which a client may send "Expect: 100-continue"
2074   without receiving either a 417 (Expectation Failed) status
2075   or a 100 (Continue) status. Therefore, when a client sends this
2076   header field to an origin server (possibly via a proxy) from which it
2077   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2078   for an indefinite period before sending the request body.
2079</t>
2080<t>
2081   Requirements for HTTP/1.1 origin servers:
2082  <list style="symbols">
2083    <t> Upon receiving a request which includes an Expect request-header
2084        field with the "100-continue" expectation, an origin server &MUST;
2085        either respond with 100 (Continue) status and continue to read
2086        from the input stream, or respond with a final status code. The
2087        origin server &MUST-NOT; wait for the request body before sending
2088        the 100 (Continue) response. If it responds with a final status
2089        code, it &MAY; close the transport connection or it &MAY; continue
2090        to read and discard the rest of the request.  It &MUST-NOT;
2091        perform the requested method if it returns a final status code.
2092    </t>
2093    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2094        the request message does not include an Expect request-header
2095        field with the "100-continue" expectation, and &MUST-NOT; send a
2096        100 (Continue) response if such a request comes from an HTTP/1.0
2097        (or earlier) client. There is an exception to this rule: for
2098        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2099        status in response to an HTTP/1.1 PUT or POST request that does
2100        not include an Expect request-header field with the "100-continue"
2101        expectation. This exception, the purpose of which is
2102        to minimize any client processing delays associated with an
2103        undeclared wait for 100 (Continue) status, applies only to
2104        HTTP/1.1 requests, and not to requests with any other HTTP-version
2105        value.
2106    </t>
2107    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2108        already received some or all of the request body for the
2109        corresponding request.
2110    </t>
2111    <t> An origin server that sends a 100 (Continue) response &MUST;
2112    ultimately send a final status code, once the request body is
2113        received and processed, unless it terminates the transport
2114        connection prematurely.
2115    </t>
2116    <t> If an origin server receives a request that does not include an
2117        Expect request-header field with the "100-continue" expectation,
2118        the request includes a request body, and the server responds
2119        with a final status code before reading the entire request body
2120        from the transport connection, then the server &SHOULD-NOT;  close
2121        the transport connection until it has read the entire request,
2122        or until the client closes the connection. Otherwise, the client
2123        might not reliably receive the response message. However, this
2124        requirement is not be construed as preventing a server from
2125        defending itself against denial-of-service attacks, or from
2126        badly broken client implementations.
2127      </t>
2128    </list>
2129</t>
2130<t>
2131   Requirements for HTTP/1.1 proxies:
2132  <list style="symbols">
2133    <t> If a proxy receives a request that includes an Expect request-header
2134        field with the "100-continue" expectation, and the proxy
2135        either knows that the next-hop server complies with HTTP/1.1 or
2136        higher, or does not know the HTTP version of the next-hop
2137        server, it &MUST; forward the request, including the Expect header
2138        field.
2139    </t>
2140    <t> If the proxy knows that the version of the next-hop server is
2141        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2142        respond with a 417 (Expectation Failed) status.
2143    </t>
2144    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2145        numbers received from recently-referenced next-hop servers.
2146    </t>
2147    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2148        request message was received from an HTTP/1.0 (or earlier)
2149        client and did not include an Expect request-header field with
2150        the "100-continue" expectation. This requirement overrides the
2151        general rule for forwarding of 1xx responses (see &status-1xx;).
2152    </t>
2153  </list>
2154</t>
2155</section>
2156
2157<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2158<t>
2159   If an HTTP/1.1 client sends a request which includes a request body,
2160   but which does not include an Expect request-header field with the
2161   "100-continue" expectation, and if the client is not directly
2162   connected to an HTTP/1.1 origin server, and if the client sees the
2163   connection close before receiving any status from the server, the
2164   client &SHOULD; retry the request.  If the client does retry this
2165   request, it &MAY; use the following "binary exponential backoff"
2166   algorithm to be assured of obtaining a reliable response:
2167  <list style="numbers">
2168    <t>
2169      Initiate a new connection to the server
2170    </t>
2171    <t>
2172      Transmit the request-headers
2173    </t>
2174    <t>
2175      Initialize a variable R to the estimated round-trip time to the
2176         server (e.g., based on the time it took to establish the
2177         connection), or to a constant value of 5 seconds if the round-trip
2178         time is not available.
2179    </t>
2180    <t>
2181       Compute T = R * (2**N), where N is the number of previous
2182         retries of this request.
2183    </t>
2184    <t>
2185       Wait either for an error response from the server, or for T
2186         seconds (whichever comes first)
2187    </t>
2188    <t>
2189       If no error response is received, after T seconds transmit the
2190         body of the request.
2191    </t>
2192    <t>
2193       If client sees that the connection is closed prematurely,
2194         repeat from step 1 until the request is accepted, an error
2195         response is received, or the user becomes impatient and
2196         terminates the retry process.
2197    </t>
2198  </list>
2199</t>
2200<t>
2201   If at any point an error status is received, the client
2202  <list style="symbols">
2203      <t>&SHOULD-NOT;  continue and</t>
2204
2205      <t>&SHOULD; close the connection if it has not completed sending the
2206        request message.</t>
2207    </list>
2208</t>
2209</section>
2210</section>
2211</section>
2212
2213
2214<section title="Header Field Definitions" anchor="header.fields">
2215<t>
2216   This section defines the syntax and semantics of HTTP/1.1 header fields
2217   related to message framing and transport protocols.
2218</t>
2219<t>
2220   For entity-header fields, both sender and recipient refer to either the
2221   client or the server, depending on who sends and who receives the entity.
2222</t>
2223
2224<section title="Connection" anchor="header.connection">
2225  <iref primary="true" item="Connection header" x:for-anchor=""/>
2226  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2227<t>
2228   The Connection general-header field allows the sender to specify
2229   options that are desired for that particular connection and &MUST-NOT;
2230   be communicated by proxies over further connections.
2231</t>
2232<t>
2233   The Connection header has the following grammar:
2234</t>
2235<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2236  Connection = "Connection" ":" 1#(connection-token)
2237  connection-token  = token
2238</artwork></figure>
2239<t>
2240   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2241   message is forwarded and, for each connection-token in this field,
2242   remove any header field(s) from the message with the same name as the
2243   connection-token. Connection options are signaled by the presence of
2244   a connection-token in the Connection header field, not by any
2245   corresponding additional header field(s), since the additional header
2246   field may not be sent if there are no parameters associated with that
2247   connection option.
2248</t>
2249<t>
2250   Message headers listed in the Connection header &MUST-NOT; include
2251   end-to-end headers, such as Cache-Control.
2252</t>
2253<t>
2254   HTTP/1.1 defines the "close" connection option for the sender to
2255   signal that the connection will be closed after completion of the
2256   response. For example,
2257</t>
2258<figure><artwork type="example">
2259    Connection: close
2260</artwork></figure>
2261<t>
2262   in either the request or the response header fields indicates that
2263   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2264   after the current request/response is complete.
2265</t>
2266<t>
2267   An HTTP/1.1 client that does not support persistent connections &MUST;
2268   include the "close" connection option in every request message.
2269</t>
2270<t>
2271   An HTTP/1.1 server that does not support persistent connections &MUST;
2272   include the "close" connection option in every response message that
2273   does not have a 1xx (informational) status code.
2274</t>
2275<t>
2276   A system receiving an HTTP/1.0 (or lower-version) message that
2277   includes a Connection header &MUST;, for each connection-token in this
2278   field, remove and ignore any header field(s) from the message with
2279   the same name as the connection-token. This protects against mistaken
2280   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2281</t>
2282</section>
2283
2284<section title="Content-Length" anchor="header.content-length">
2285  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2286  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2287<t>
2288   The Content-Length entity-header field indicates the size of the
2289   entity-body, in decimal number of OCTETs, sent to the recipient or,
2290   in the case of the HEAD method, the size of the entity-body that
2291   would have been sent had the request been a GET.
2292</t>
2293<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2294  Content-Length    = "Content-Length" ":" 1*DIGIT
2295</artwork></figure>
2296<t>
2297   An example is
2298</t>
2299<figure><artwork type="example">
2300    Content-Length: 3495
2301</artwork></figure>
2302<t>
2303   Applications &SHOULD; use this field to indicate the transfer-length of
2304   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2305</t>
2306<t>
2307   Any Content-Length greater than or equal to zero is a valid value.
2308   <xref target="message.length"/> describes how to determine the length of a message-body
2309   if a Content-Length is not given.
2310</t>
2311<t>
2312   Note that the meaning of this field is significantly different from
2313   the corresponding definition in MIME, where it is an optional field
2314   used within the "message/external-body" content-type. In HTTP, it
2315   &SHOULD; be sent whenever the message's length can be determined prior
2316   to being transferred, unless this is prohibited by the rules in
2317   <xref target="message.length"/>.
2318</t>
2319</section>
2320
2321<section title="Date" anchor="header.date">
2322  <iref primary="true" item="Date header" x:for-anchor=""/>
2323  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2324<t>
2325   The Date general-header field represents the date and time at which
2326   the message was originated, having the same semantics as orig-date in
2327   <xref target="RFC2822" x:fmt="of" x:sec="3.6.1"/>. The field value is an HTTP-date, as described in <xref target="full.date"/>;
2328   it &MUST; be sent in rfc1123-date format.
2329</t>
2330<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2331  Date  = "Date" ":" HTTP-date
2332</artwork></figure>
2333<t>
2334   An example is
2335</t>
2336<figure><artwork type="example">
2337    Date: Tue, 15 Nov 1994 08:12:31 GMT
2338</artwork></figure>
2339<t>
2340   Origin servers &MUST; include a Date header field in all responses,
2341   except in these cases:
2342  <list style="numbers">
2343      <t>If the response status code is 100 (Continue) or 101 (Switching
2344         Protocols), the response &MAY; include a Date header field, at
2345         the server's option.</t>
2346
2347      <t>If the response status code conveys a server error, e.g. 500
2348         (Internal Server Error) or 503 (Service Unavailable), and it is
2349         inconvenient or impossible to generate a valid Date.</t>
2350
2351      <t>If the server does not have a clock that can provide a
2352         reasonable approximation of the current time, its responses
2353         &MUST-NOT; include a Date header field. In this case, the rules
2354         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2355  </list>
2356</t>
2357<t>
2358   A received message that does not have a Date header field &MUST; be
2359   assigned one by the recipient if the message will be cached by that
2360   recipient or gatewayed via a protocol which requires a Date. An HTTP
2361   implementation without a clock &MUST-NOT; cache responses without
2362   revalidating them on every use. An HTTP cache, especially a shared
2363   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2364   clock with a reliable external standard.
2365</t>
2366<t>
2367   Clients &SHOULD; only send a Date header field in messages that include
2368   an entity-body, as in the case of the PUT and POST requests, and even
2369   then it is optional. A client without a clock &MUST-NOT; send a Date
2370   header field in a request.
2371</t>
2372<t>
2373   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2374   time subsequent to the generation of the message. It &SHOULD; represent
2375   the best available approximation of the date and time of message
2376   generation, unless the implementation has no means of generating a
2377   reasonably accurate date and time. In theory, the date ought to
2378   represent the moment just before the entity is generated. In
2379   practice, the date can be generated at any time during the message
2380   origination without affecting its semantic value.
2381</t>
2382
2383<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2384<t>
2385   Some origin server implementations might not have a clock available.
2386   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2387   values to a response, unless these values were associated
2388   with the resource by a system or user with a reliable clock. It &MAY;
2389   assign an Expires value that is known, at or before server
2390   configuration time, to be in the past (this allows "pre-expiration"
2391   of responses without storing separate Expires values for each
2392   resource).
2393</t>
2394</section>
2395</section>
2396
2397<section title="Host" anchor="header.host">
2398  <iref primary="true" item="Host header" x:for-anchor=""/>
2399  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2400<t>
2401   The Host request-header field specifies the Internet host and port
2402   number of the resource being requested, as obtained from the original
2403   URI given by the user or referring resource (generally an HTTP URL,
2404   as described in <xref target="http.url"/>). The Host field value &MUST; represent
2405   the naming authority of the origin server or gateway given by the
2406   original URL. This allows the origin server or gateway to
2407   differentiate between internally-ambiguous URLs, such as the root "/"
2408   URL of a server for multiple host names on a single IP address.
2409</t>
2410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2411  Host = "Host" ":" uri-host [ ":" port ] ; <xref target="http.url"/>
2412</artwork></figure>
2413<t>
2414   A "host" without any trailing port information implies the default
2415   port for the service requested (e.g., "80" for an HTTP URL). For
2416   example, a request on the origin server for
2417   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2418</t>
2419<figure><artwork type="example">
2420    GET /pub/WWW/ HTTP/1.1
2421    Host: www.example.org
2422</artwork></figure>
2423<t>
2424   A client &MUST; include a Host header field in all HTTP/1.1 request
2425   messages. If the requested URI does not include an Internet host
2426   name for the service being requested, then the Host header field &MUST;
2427   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2428   request message it forwards does contain an appropriate Host header
2429   field that identifies the service being requested by the proxy. All
2430   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2431   status code to any HTTP/1.1 request message which lacks a Host header
2432   field.
2433</t>
2434<t>
2435   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2436   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2437   for other requirements relating to Host.
2438</t>
2439</section>
2440
2441<section title="TE" anchor="header.te">
2442  <iref primary="true" item="TE header" x:for-anchor=""/>
2443  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2444<t>
2445   The TE request-header field indicates what extension transfer-codings
2446   it is willing to accept in the response and whether or not it is
2447   willing to accept trailer fields in a chunked transfer-coding. Its
2448   value may consist of the keyword "trailers" and/or a comma-separated
2449   list of extension transfer-coding names with optional accept
2450   parameters (as described in <xref target="transfer.codings"/>).
2451</t>
2452<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2453  TE        = "TE" ":" #( t-codings )
2454  t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2455</artwork></figure>
2456<t>
2457   The presence of the keyword "trailers" indicates that the client is
2458   willing to accept trailer fields in a chunked transfer-coding, as
2459   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2460   transfer-coding values even though it does not itself represent a
2461   transfer-coding.
2462</t>
2463<t>
2464   Examples of its use are:
2465</t>
2466<figure><artwork type="example">
2467    TE: deflate
2468    TE:
2469    TE: trailers, deflate;q=0.5
2470</artwork></figure>
2471<t>
2472   The TE header field only applies to the immediate connection.
2473   Therefore, the keyword &MUST; be supplied within a Connection header
2474   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2475</t>
2476<t>
2477   A server tests whether a transfer-coding is acceptable, according to
2478   a TE field, using these rules:
2479  <list style="numbers">
2480    <x:lt>
2481      <t>The "chunked" transfer-coding is always acceptable. If the
2482         keyword "trailers" is listed, the client indicates that it is
2483         willing to accept trailer fields in the chunked response on
2484         behalf of itself and any downstream clients. The implication is
2485         that, if given, the client is stating that either all
2486         downstream clients are willing to accept trailer fields in the
2487         forwarded response, or that it will attempt to buffer the
2488         response on behalf of downstream recipients.
2489      </t><t>
2490         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2491         chunked response such that a client can be assured of buffering
2492         the entire response.</t>
2493    </x:lt>
2494    <x:lt>
2495      <t>If the transfer-coding being tested is one of the transfer-codings
2496         listed in the TE field, then it is acceptable unless it
2497         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2498         qvalue of 0 means "not acceptable.")</t>
2499    </x:lt>
2500    <x:lt>
2501      <t>If multiple transfer-codings are acceptable, then the
2502         acceptable transfer-coding with the highest non-zero qvalue is
2503         preferred.  The "chunked" transfer-coding always has a qvalue
2504         of 1.</t>
2505    </x:lt>
2506  </list>
2507</t>
2508<t>
2509   If the TE field-value is empty or if no TE field is present, the only
2510   transfer-coding  is "chunked". A message with no transfer-coding is
2511   always acceptable.
2512</t>
2513</section>
2514
2515<section title="Trailer" anchor="header.trailer">
2516  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2517  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2518<t>
2519   The Trailer general field value indicates that the given set of
2520   header fields is present in the trailer of a message encoded with
2521   chunked transfer-coding.
2522</t>
2523<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2524  Trailer  = "Trailer" ":" 1#field-name
2525</artwork></figure>
2526<t>
2527   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2528   message using chunked transfer-coding with a non-empty trailer. Doing
2529   so allows the recipient to know which header fields to expect in the
2530   trailer.
2531</t>
2532<t>
2533   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2534   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2535   trailer fields in a "chunked" transfer-coding.
2536</t>
2537<t>
2538   Message header fields listed in the Trailer header field &MUST-NOT;
2539   include the following header fields:
2540  <list style="symbols">
2541    <t>Transfer-Encoding</t>
2542    <t>Content-Length</t>
2543    <t>Trailer</t>
2544  </list>
2545</t>
2546</section>
2547
2548<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2549  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2550  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2551<t>
2552   The Transfer-Encoding general-header field indicates what (if any)
2553   type of transformation has been applied to the message body in order
2554   to safely transfer it between the sender and the recipient. This
2555   differs from the content-coding in that the transfer-coding is a
2556   property of the message, not of the entity.
2557</t>
2558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2559  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2560</artwork></figure>
2561<t>
2562   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2563</t>
2564<figure><artwork type="example">
2565  Transfer-Encoding: chunked
2566</artwork></figure>
2567<t>
2568   If multiple encodings have been applied to an entity, the transfer-codings
2569   &MUST; be listed in the order in which they were applied.
2570   Additional information about the encoding parameters &MAY; be provided
2571   by other entity-header fields not defined by this specification.
2572</t>
2573<t>
2574   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2575   header.
2576</t>
2577</section>
2578
2579<section title="Upgrade" anchor="header.upgrade">
2580  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2581  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2582<t>
2583   The Upgrade general-header allows the client to specify what
2584   additional communication protocols it supports and would like to use
2585   if the server finds it appropriate to switch protocols. The server
2586   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2587   response to indicate which protocol(s) are being switched.
2588</t>
2589<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2590  Upgrade        = "Upgrade" ":" 1#product
2591</artwork></figure>
2592<t>
2593   For example,
2594</t>
2595<figure><artwork type="example">
2596    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2597</artwork></figure>
2598<t>
2599   The Upgrade header field is intended to provide a simple mechanism
2600   for transition from HTTP/1.1 to some other, incompatible protocol. It
2601   does so by allowing the client to advertise its desire to use another
2602   protocol, such as a later version of HTTP with a higher major version
2603   number, even though the current request has been made using HTTP/1.1.
2604   This eases the difficult transition between incompatible protocols by
2605   allowing the client to initiate a request in the more commonly
2606   supported protocol while indicating to the server that it would like
2607   to use a "better" protocol if available (where "better" is determined
2608   by the server, possibly according to the nature of the method and/or
2609   resource being requested).
2610</t>
2611<t>
2612   The Upgrade header field only applies to switching application-layer
2613   protocols upon the existing transport-layer connection. Upgrade
2614   cannot be used to insist on a protocol change; its acceptance and use
2615   by the server is optional. The capabilities and nature of the
2616   application-layer communication after the protocol change is entirely
2617   dependent upon the new protocol chosen, although the first action
2618   after changing the protocol &MUST; be a response to the initial HTTP
2619   request containing the Upgrade header field.
2620</t>
2621<t>
2622   The Upgrade header field only applies to the immediate connection.
2623   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2624   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2625   HTTP/1.1 message.
2626</t>
2627<t>
2628   The Upgrade header field cannot be used to indicate a switch to a
2629   protocol on a different connection. For that purpose, it is more
2630   appropriate to use a 301, 302, 303, or 305 redirection response.
2631</t>
2632<t>
2633   This specification only defines the protocol name "HTTP" for use by
2634   the family of Hypertext Transfer Protocols, as defined by the HTTP
2635   version rules of <xref target="http.version"/> and future updates to this
2636   specification. Any token can be used as a protocol name; however, it
2637   will only be useful if both the client and server associate the name
2638   with the same protocol.
2639</t>
2640</section>
2641
2642<section title="Via" anchor="header.via">
2643  <iref primary="true" item="Via header" x:for-anchor=""/>
2644  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2645<t>
2646   The Via general-header field &MUST; be used by gateways and proxies to
2647   indicate the intermediate protocols and recipients between the user
2648   agent and the server on requests, and between the origin server and
2649   the client on responses. It is analogous to the "Received" field of
2650   <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2651   avoiding request loops, and identifying the protocol capabilities of
2652   all senders along the request/response chain.
2653</t>
2654<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2655  Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2656  received-protocol = [ protocol-name "/" ] protocol-version
2657  protocol-name     = token
2658  protocol-version  = token
2659  received-by       = ( uri-host [ ":" port ] ) | pseudonym
2660  pseudonym         = token
2661</artwork></figure>
2662<t>
2663   The received-protocol indicates the protocol version of the message
2664   received by the server or client along each segment of the
2665   request/response chain. The received-protocol version is appended to
2666   the Via field value when the message is forwarded so that information
2667   about the protocol capabilities of upstream applications remains
2668   visible to all recipients.
2669</t>
2670<t>
2671   The protocol-name is optional if and only if it would be "HTTP". The
2672   received-by field is normally the host and optional port number of a
2673   recipient server or client that subsequently forwarded the message.
2674   However, if the real host is considered to be sensitive information,
2675   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2676   be assumed to be the default port of the received-protocol.
2677</t>
2678<t>
2679   Multiple Via field values represents each proxy or gateway that has
2680   forwarded the message. Each recipient &MUST; append its information
2681   such that the end result is ordered according to the sequence of
2682   forwarding applications.
2683</t>
2684<t>
2685   Comments &MAY; be used in the Via header field to identify the software
2686   of the recipient proxy or gateway, analogous to the User-Agent and
2687   Server header fields. However, all comments in the Via field are
2688   optional and &MAY; be removed by any recipient prior to forwarding the
2689   message.
2690</t>
2691<t>
2692   For example, a request message could be sent from an HTTP/1.0 user
2693   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2694   forward the request to a public proxy at p.example.net, which completes
2695   the request by forwarding it to the origin server at www.example.com.
2696   The request received by www.example.com would then have the following
2697   Via header field:
2698</t>
2699<figure><artwork type="example">
2700    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2701</artwork></figure>
2702<t>
2703   Proxies and gateways used as a portal through a network firewall
2704   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2705   the firewall region. This information &SHOULD; only be propagated if
2706   explicitly enabled. If not enabled, the received-by host of any host
2707   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2708   for that host.
2709</t>
2710<t>
2711   For organizations that have strong privacy requirements for hiding
2712   internal structures, a proxy &MAY; combine an ordered subsequence of
2713   Via header field entries with identical received-protocol values into
2714   a single such entry. For example,
2715</t>
2716<figure><artwork type="example">
2717    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2718</artwork></figure>
2719<t>
2720        could be collapsed to
2721</t>
2722<figure><artwork type="example">
2723    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2724</artwork></figure>
2725<t>
2726   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2727   under the same organizational control and the hosts have already been
2728   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2729   have different received-protocol values.
2730</t>
2731</section>
2732
2733</section>
2734
2735<section title="IANA Considerations" anchor="IANA.considerations">
2736<t>
2737   TBD.
2738</t>
2739</section>
2740
2741<section title="Security Considerations" anchor="security.considerations">
2742<t>
2743   This section is meant to inform application developers, information
2744   providers, and users of the security limitations in HTTP/1.1 as
2745   described by this document. The discussion does not include
2746   definitive solutions to the problems revealed, though it does make
2747   some suggestions for reducing security risks.
2748</t>
2749
2750<section title="Personal Information" anchor="personal.information">
2751<t>
2752   HTTP clients are often privy to large amounts of personal information
2753   (e.g. the user's name, location, mail address, passwords, encryption
2754   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2755   leakage of this information.
2756   We very strongly recommend that a convenient interface be provided
2757   for the user to control dissemination of such information, and that
2758   designers and implementors be particularly careful in this area.
2759   History shows that errors in this area often create serious security
2760   and/or privacy problems and generate highly adverse publicity for the
2761   implementor's company.
2762</t>
2763</section>
2764
2765<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2766<t>
2767   A server is in the position to save personal data about a user's
2768   requests which might identify their reading patterns or subjects of
2769   interest. This information is clearly confidential in nature and its
2770   handling can be constrained by law in certain countries. People using
2771   HTTP to provide data are responsible for ensuring that
2772   such material is not distributed without the permission of any
2773   individuals that are identifiable by the published results.
2774</t>
2775</section>
2776
2777<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2778<t>
2779   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2780   the documents returned by HTTP requests to be only those that were
2781   intended by the server administrators. If an HTTP server translates
2782   HTTP URIs directly into file system calls, the server &MUST; take
2783   special care not to serve files that were not intended to be
2784   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2785   other operating systems use ".." as a path component to indicate a
2786   directory level above the current one. On such a system, an HTTP
2787   server &MUST; disallow any such construct in the Request-URI if it
2788   would otherwise allow access to a resource outside those intended to
2789   be accessible via the HTTP server. Similarly, files intended for
2790   reference only internally to the server (such as access control
2791   files, configuration files, and script code) &MUST; be protected from
2792   inappropriate retrieval, since they might contain sensitive
2793   information. Experience has shown that minor bugs in such HTTP server
2794   implementations have turned into security risks.
2795</t>
2796</section>
2797
2798<section title="DNS Spoofing" anchor="dns.spoofing">
2799<t>
2800   Clients using HTTP rely heavily on the Domain Name Service, and are
2801   thus generally prone to security attacks based on the deliberate
2802   mis-association of IP addresses and DNS names. Clients need to be
2803   cautious in assuming the continuing validity of an IP number/DNS name
2804   association.
2805</t>
2806<t>
2807   In particular, HTTP clients &SHOULD; rely on their name resolver for
2808   confirmation of an IP number/DNS name association, rather than
2809   caching the result of previous host name lookups. Many platforms
2810   already can cache host name lookups locally when appropriate, and
2811   they &SHOULD; be configured to do so. It is proper for these lookups to
2812   be cached, however, only when the TTL (Time To Live) information
2813   reported by the name server makes it likely that the cached
2814   information will remain useful.
2815</t>
2816<t>
2817   If HTTP clients cache the results of host name lookups in order to
2818   achieve a performance improvement, they &MUST; observe the TTL
2819   information reported by DNS.
2820</t>
2821<t>
2822   If HTTP clients do not observe this rule, they could be spoofed when
2823   a previously-accessed server's IP address changes. As network
2824   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2825   possibility of this form of attack will grow. Observing this
2826   requirement thus reduces this potential security vulnerability.
2827</t>
2828<t>
2829   This requirement also improves the load-balancing behavior of clients
2830   for replicated servers using the same DNS name and reduces the
2831   likelihood of a user's experiencing failure in accessing sites which
2832   use that strategy.
2833</t>
2834</section>
2835
2836<section title="Proxies and Caching" anchor="attack.proxies">
2837<t>
2838   By their very nature, HTTP proxies are men-in-the-middle, and
2839   represent an opportunity for man-in-the-middle attacks. Compromise of
2840   the systems on which the proxies run can result in serious security
2841   and privacy problems. Proxies have access to security-related
2842   information, personal information about individual users and
2843   organizations, and proprietary information belonging to users and
2844   content providers. A compromised proxy, or a proxy implemented or
2845   configured without regard to security and privacy considerations,
2846   might be used in the commission of a wide range of potential attacks.
2847</t>
2848<t>
2849   Proxy operators should protect the systems on which proxies run as
2850   they would protect any system that contains or transports sensitive
2851   information. In particular, log information gathered at proxies often
2852   contains highly sensitive personal information, and/or information
2853   about organizations. Log information should be carefully guarded, and
2854   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2855</t>
2856<t>
2857   Proxy implementors should consider the privacy and security
2858   implications of their design and coding decisions, and of the
2859   configuration options they provide to proxy operators (especially the
2860   default configuration).
2861</t>
2862<t>
2863   Users of a proxy need to be aware that they are no trustworthier than
2864   the people who run the proxy; HTTP itself cannot solve this problem.
2865</t>
2866<t>
2867   The judicious use of cryptography, when appropriate, may suffice to
2868   protect against a broad range of security and privacy attacks. Such
2869   cryptography is beyond the scope of the HTTP/1.1 specification.
2870</t>
2871</section>
2872
2873<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2874<t>
2875   They exist. They are hard to defend against. Research continues.
2876   Beware.
2877</t>
2878</section>
2879</section>
2880
2881<section title="Acknowledgments" anchor="ack">
2882<t>
2883   This specification makes heavy use of the augmented BNF and generic
2884   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
2885   reuses many of the definitions provided by Nathaniel Borenstein and
2886   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2887   specification will help reduce past confusion over the relationship
2888   between HTTP and Internet mail message formats.
2889</t>
2890<t>
2891   HTTP has evolved considerably over the years. It has
2892   benefited from a large and active developer community--the many
2893   people who have participated on the www-talk mailing list--and it is
2894   that community which has been most responsible for the success of
2895   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2896   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2897   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2898   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2899   VanHeyningen deserve special recognition for their efforts in
2900   defining early aspects of the protocol.
2901</t>
2902<t>
2903   This document has benefited greatly from the comments of all those
2904   participating in the HTTP-WG. In addition to those already mentioned,
2905   the following individuals have contributed to this specification:
2906</t>
2907<t>
2908   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2909   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2910   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2911   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2912   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2913   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2914   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2915   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2916   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2917   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2918   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2919   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2920   Josh Cohen.
2921</t>
2922<t>
2923   Thanks to the "cave men" of Palo Alto. You know who you are.
2924</t>
2925<t>
2926   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2927   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2928   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2929   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2930   Larry Masinter for their help. And thanks go particularly to Jeff
2931   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2932</t>
2933<t>
2934   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2935   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2936   discovery of many of the problems that this document attempts to
2937   rectify.
2938</t>
2939</section>
2940
2941</middle>
2942<back>
2943
2944<references title="Normative References">
2945
2946<reference anchor="ISO-8859-1">
2947  <front>
2948    <title>
2949     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
2950    </title>
2951    <author>
2952      <organization>International Organization for Standardization</organization>
2953    </author>
2954    <date year="1998"/>
2955  </front>
2956  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
2957</reference>
2958
2959<reference anchor="Part2">
2960  <front>
2961    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
2962    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2963      <organization abbrev="Day Software">Day Software</organization>
2964      <address><email>fielding@gbiv.com</email></address>
2965    </author>
2966    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2967      <organization>One Laptop per Child</organization>
2968      <address><email>jg@laptop.org</email></address>
2969    </author>
2970    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2971      <organization abbrev="HP">Hewlett-Packard Company</organization>
2972      <address><email>JeffMogul@acm.org</email></address>
2973    </author>
2974    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2975      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2976      <address><email>henrikn@microsoft.com</email></address>
2977    </author>
2978    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2979      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2980      <address><email>LMM@acm.org</email></address>
2981    </author>
2982    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2983      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2984      <address><email>paulle@microsoft.com</email></address>
2985    </author>
2986    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2987      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2988      <address><email>timbl@w3.org</email></address>
2989    </author>
2990    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2991      <organization abbrev="W3C">World Wide Web Consortium</organization>
2992      <address><email>ylafon@w3.org</email></address>
2993    </author>
2994    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2995      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2996      <address><email>julian.reschke@greenbytes.de</email></address>
2997    </author>
2998    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2999  </front>
3000  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3001  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3002</reference>
3003
3004<reference anchor="Part3">
3005  <front>
3006    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3007    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3008      <organization abbrev="Day Software">Day Software</organization>
3009      <address><email>fielding@gbiv.com</email></address>
3010    </author>
3011    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3012      <organization>One Laptop per Child</organization>
3013      <address><email>jg@laptop.org</email></address>
3014    </author>
3015    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3016      <organization abbrev="HP">Hewlett-Packard Company</organization>
3017      <address><email>JeffMogul@acm.org</email></address>
3018    </author>
3019    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3020      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3021      <address><email>henrikn@microsoft.com</email></address>
3022    </author>
3023    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3024      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3025      <address><email>LMM@acm.org</email></address>
3026    </author>
3027    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3028      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3029      <address><email>paulle@microsoft.com</email></address>
3030    </author>
3031    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3032      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3033      <address><email>timbl@w3.org</email></address>
3034    </author>
3035    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3036      <organization abbrev="W3C">World Wide Web Consortium</organization>
3037      <address><email>ylafon@w3.org</email></address>
3038    </author>
3039    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3040      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3041      <address><email>julian.reschke@greenbytes.de</email></address>
3042    </author>
3043    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3044  </front>
3045  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3046  <x:source href="p3-payload.xml" basename="p3-payload"/>
3047</reference>
3048
3049<reference anchor="Part5">
3050  <front>
3051    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3053      <organization abbrev="Day Software">Day Software</organization>
3054      <address><email>fielding@gbiv.com</email></address>
3055    </author>
3056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3057      <organization>One Laptop per Child</organization>
3058      <address><email>jg@laptop.org</email></address>
3059    </author>
3060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3061      <organization abbrev="HP">Hewlett-Packard Company</organization>
3062      <address><email>JeffMogul@acm.org</email></address>
3063    </author>
3064    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3065      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3066      <address><email>henrikn@microsoft.com</email></address>
3067    </author>
3068    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3069      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3070      <address><email>LMM@acm.org</email></address>
3071    </author>
3072    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3074      <address><email>paulle@microsoft.com</email></address>
3075    </author>
3076    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3077      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3078      <address><email>timbl@w3.org</email></address>
3079    </author>
3080    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3081      <organization abbrev="W3C">World Wide Web Consortium</organization>
3082      <address><email>ylafon@w3.org</email></address>
3083    </author>
3084    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3085      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3086      <address><email>julian.reschke@greenbytes.de</email></address>
3087    </author>
3088    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3089  </front>
3090  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3091  <x:source href="p5-range.xml" basename="p5-range"/>
3092</reference>
3093
3094<reference anchor="Part6">
3095  <front>
3096    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3097    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3098      <organization abbrev="Day Software">Day Software</organization>
3099      <address><email>fielding@gbiv.com</email></address>
3100    </author>
3101    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3102      <organization>One Laptop per Child</organization>
3103      <address><email>jg@laptop.org</email></address>
3104    </author>
3105    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3106      <organization abbrev="HP">Hewlett-Packard Company</organization>
3107      <address><email>JeffMogul@acm.org</email></address>
3108    </author>
3109    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3110      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3111      <address><email>henrikn@microsoft.com</email></address>
3112    </author>
3113    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3114      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3115      <address><email>LMM@acm.org</email></address>
3116    </author>
3117    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3119      <address><email>paulle@microsoft.com</email></address>
3120    </author>
3121    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3122      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3123      <address><email>timbl@w3.org</email></address>
3124    </author>
3125    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3126      <organization abbrev="W3C">World Wide Web Consortium</organization>
3127      <address><email>ylafon@w3.org</email></address>
3128    </author>
3129    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3130      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3131      <address><email>julian.reschke@greenbytes.de</email></address>
3132    </author>
3133    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3134  </front>
3135  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3136  <x:source href="p6-cache.xml" basename="p6-cache"/>
3137</reference>
3138
3139<reference anchor="RFC822ABNF">
3140  <front>
3141    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3142    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3143      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3144      <address><email>DCrocker@UDel-Relay</email></address>
3145    </author>
3146    <date month="August" day="13" year="1982"/>
3147  </front>
3148  <seriesInfo name="STD" value="11"/>
3149  <seriesInfo name="RFC" value="822"/>
3150</reference>
3151
3152<reference anchor="RFC2045">
3153  <front>
3154    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3155    <author initials="N." surname="Freed" fullname="Ned Freed">
3156      <organization>Innosoft International, Inc.</organization>
3157      <address><email>ned@innosoft.com</email></address>
3158    </author>
3159    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3160      <organization>First Virtual Holdings</organization>
3161      <address><email>nsb@nsb.fv.com</email></address>
3162    </author>
3163    <date month="November" year="1996"/>
3164  </front>
3165  <seriesInfo name="RFC" value="2045"/>
3166</reference>
3167
3168<reference anchor="RFC2047">
3169  <front>
3170    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3171    <author initials="K." surname="Moore" fullname="Keith Moore">
3172      <organization>University of Tennessee</organization>
3173      <address><email>moore@cs.utk.edu</email></address>
3174    </author>
3175    <date month="November" year="1996"/>
3176  </front>
3177  <seriesInfo name="RFC" value="2047"/>
3178</reference>
3179
3180<reference anchor="RFC2119">
3181  <front>
3182    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3183    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3184      <organization>Harvard University</organization>
3185      <address><email>sob@harvard.edu</email></address>
3186    </author>
3187    <date month="March" year="1997"/>
3188  </front>
3189  <seriesInfo name="BCP" value="14"/>
3190  <seriesInfo name="RFC" value="2119"/>
3191</reference>
3192
3193<reference anchor="RFC2396">
3194  <front>
3195    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3196    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3197      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3198      <address><email>timbl@w3.org</email></address>
3199    </author>
3200    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3201      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3202      <address><email>fielding@ics.uci.edu</email></address>
3203    </author>
3204    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3205      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3206      <address><email>masinter@parc.xerox.com</email></address>
3207    </author>
3208    <date month="August" year="1998"/>
3209  </front>
3210  <seriesInfo name="RFC" value="2396"/>
3211</reference>
3212
3213<reference anchor="RFC4288">
3214  <front>
3215    <title>Media Type Specifications and Registration Procedures</title>
3216    <author initials="N." surname="Freed" fullname="N. Freed">
3217      <organization>Sun Microsystems</organization>
3218      <address>
3219        <email>ned.freed@mrochek.com</email>
3220      </address>
3221    </author>
3222    <author initials="J." surname="Klensin" fullname="J. Klensin">
3223      <organization/>
3224      <address>
3225        <email>klensin+ietf@jck.com</email>
3226      </address>
3227    </author>
3228    <date year="2005" month="December"/>
3229  </front>
3230  <seriesInfo name="BCP" value="13"/>
3231  <seriesInfo name="RFC" value="4288"/>
3232</reference>
3233
3234<reference anchor="USASCII">
3235  <front>
3236    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3237    <author>
3238      <organization>American National Standards Institute</organization>
3239    </author>
3240    <date year="1986"/>
3241  </front>
3242  <seriesInfo name="ANSI" value="X3.4"/>
3243</reference>
3244
3245</references>
3246
3247<references title="Informative References">
3248
3249<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3250  <front>
3251    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3252    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3253      <organization/>
3254    </author>
3255    <author initials="J." surname="Gettys" fullname="J. Gettys">
3256      <organization/>
3257    </author>
3258    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3259      <organization/>
3260    </author>
3261    <author initials="H." surname="Lie" fullname="H. Lie">
3262      <organization/>
3263    </author>
3264    <author initials="C." surname="Lilley" fullname="C. Lilley">
3265      <organization/>
3266    </author>
3267    <date year="1997" month="September"/>
3268  </front>
3269  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3270</reference>
3271
3272<reference anchor="Pad1995">
3273  <front>
3274    <title>Improving HTTP Latency</title>
3275    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3276      <organization/>
3277    </author>
3278    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3279      <organization/>
3280    </author>
3281    <date year="1995" month="December"/>
3282  </front>
3283  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3284  <annotation>
3285    Slightly revised version of paper in Proc. 2nd International WWW Conference '94: Mosaic and the Web, Oct. 1994,
3286    which is available at <eref target="http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/HTTPLatency.html"/>.
3287  </annotation>
3288</reference>
3289
3290<reference anchor="RFC822">
3291  <front>
3292    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3293    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3294      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3295      <address><email>DCrocker@UDel-Relay</email></address>
3296    </author>
3297    <date month="August" day="13" year="1982"/>
3298  </front>
3299  <seriesInfo name="STD" value="11"/>
3300  <seriesInfo name="RFC" value="822"/>
3301</reference>
3302
3303<reference anchor="RFC959">
3304  <front>
3305    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3306    <author initials="J." surname="Postel" fullname="J. Postel">
3307      <organization>Information Sciences Institute (ISI)</organization>
3308    </author>
3309    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3310      <organization/>
3311    </author>
3312    <date month="October" year="1985"/>
3313  </front>
3314  <seriesInfo name="STD" value="9"/>
3315  <seriesInfo name="RFC" value="959"/>
3316</reference>
3317
3318<reference anchor="RFC1123">
3319  <front>
3320    <title>Requirements for Internet Hosts - Application and Support</title>
3321    <author initials="R." surname="Braden" fullname="Robert Braden">
3322      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3323      <address><email>Braden@ISI.EDU</email></address>
3324    </author>
3325    <date month="October" year="1989"/>
3326  </front>
3327  <seriesInfo name="STD" value="3"/>
3328  <seriesInfo name="RFC" value="1123"/>
3329</reference>
3330
3331<reference anchor="RFC1305">
3332  <front>
3333    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3334    <author initials="D." surname="Mills" fullname="David L. Mills">
3335      <organization>University of Delaware, Electrical Engineering Department</organization>
3336      <address><email>mills@udel.edu</email></address>
3337    </author>
3338    <date month="March" year="1992"/>
3339  </front>
3340  <seriesInfo name="RFC" value="1305"/>
3341</reference>
3342
3343<reference anchor="RFC1436">
3344  <front>
3345    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3346    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3347      <organization>University of Minnesota, Computer and Information Services</organization>
3348      <address><email>fxa@boombox.micro.umn.edu</email></address>
3349    </author>
3350    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3351      <organization>University of Minnesota, Computer and Information Services</organization>
3352      <address><email>mpm@boombox.micro.umn.edu</email></address>
3353    </author>
3354    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3355      <organization>University of Minnesota, Computer and Information Services</organization>
3356      <address><email>lindner@boombox.micro.umn.edu</email></address>
3357    </author>
3358    <author initials="D." surname="Johnson" fullname="David Johnson">
3359      <organization>University of Minnesota, Computer and Information Services</organization>
3360      <address><email>dmj@boombox.micro.umn.edu</email></address>
3361    </author>
3362    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3363      <organization>University of Minnesota, Computer and Information Services</organization>
3364      <address><email>daniel@boombox.micro.umn.edu</email></address>
3365    </author>
3366    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3367      <organization>University of Minnesota, Computer and Information Services</organization>
3368      <address><email>alberti@boombox.micro.umn.edu</email></address>
3369    </author>
3370    <date month="March" year="1993"/>
3371  </front>
3372  <seriesInfo name="RFC" value="1436"/>
3373</reference>
3374
3375<reference anchor="RFC1630">
3376  <front>
3377    <title abbrev="URIs in WWW">Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web</title>
3378    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3379      <organization>CERN, World-Wide Web project</organization>
3380      <address><email>timbl@info.cern.ch</email></address>
3381    </author>
3382    <date month="June" year="1994"/>
3383  </front>
3384  <seriesInfo name="RFC" value="1630"/>
3385</reference>
3386
3387<reference anchor="RFC1737">
3388  <front>
3389    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3390    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3391      <organization>Xerox Palo Alto Research Center</organization>
3392      <address><email>masinter@parc.xerox.com</email></address>
3393    </author>
3394    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3395      <organization>MIT Laboratory for Computer Science</organization>
3396      <address><email>sollins@lcs.mit.edu</email></address>
3397    </author>
3398    <date month="December" year="1994"/>
3399  </front>
3400  <seriesInfo name="RFC" value="1737"/>
3401</reference>
3402
3403<reference anchor="RFC1738">
3404  <front>
3405    <title>Uniform Resource Locators (URL)</title>
3406    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3407      <organization>CERN, World-Wide Web project</organization>
3408      <address><email>timbl@info.cern.ch</email></address>
3409    </author>
3410    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3411      <organization>Xerox PARC</organization>
3412      <address><email>masinter@parc.xerox.com</email></address>
3413    </author>
3414    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3415      <organization>University of Minnesota, Computer and Information Services</organization>
3416      <address><email>mpm@boombox.micro.umn.edu</email></address>
3417    </author>
3418    <date month="December" year="1994"/>
3419  </front>
3420  <seriesInfo name="RFC" value="1738"/>
3421</reference>
3422
3423<reference anchor="RFC1808">
3424  <front>
3425    <title>Relative Uniform Resource Locators</title>
3426    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3427      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3428      <address><email>fielding@ics.uci.edu</email></address>
3429    </author>
3430    <date month="June" year="1995"/>
3431  </front>
3432  <seriesInfo name="RFC" value="1808"/>
3433</reference>
3434
3435<reference anchor="RFC1900">
3436  <front>
3437    <title>Renumbering Needs Work</title>
3438    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3439      <organization>CERN, Computing and Networks Division</organization>
3440      <address><email>brian@dxcoms.cern.ch</email></address>
3441    </author>
3442    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3443      <organization>cisco Systems</organization>
3444      <address><email>yakov@cisco.com</email></address>
3445    </author>
3446    <date month="February" year="1996"/>
3447  </front>
3448  <seriesInfo name="RFC" value="1900"/>
3449</reference>
3450
3451<reference anchor="RFC1945">
3452  <front>
3453    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3454    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3455      <organization>MIT, Laboratory for Computer Science</organization>
3456      <address><email>timbl@w3.org</email></address>
3457    </author>
3458    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3459      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3460      <address><email>fielding@ics.uci.edu</email></address>
3461    </author>
3462    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3463      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3464      <address><email>frystyk@w3.org</email></address>
3465    </author>
3466    <date month="May" year="1996"/>
3467  </front>
3468  <seriesInfo name="RFC" value="1945"/>
3469</reference>
3470
3471<reference anchor="RFC2068">
3472  <front>
3473    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3474    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3475      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3476      <address><email>fielding@ics.uci.edu</email></address>
3477    </author>
3478    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3479      <organization>MIT Laboratory for Computer Science</organization>
3480      <address><email>jg@w3.org</email></address>
3481    </author>
3482    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3483      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3484      <address><email>mogul@wrl.dec.com</email></address>
3485    </author>
3486    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3487      <organization>MIT Laboratory for Computer Science</organization>
3488      <address><email>frystyk@w3.org</email></address>
3489    </author>
3490    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3491      <organization>MIT Laboratory for Computer Science</organization>
3492      <address><email>timbl@w3.org</email></address>
3493    </author>
3494    <date month="January" year="1997"/>
3495  </front>
3496  <seriesInfo name="RFC" value="2068"/>
3497</reference>
3498
3499<reference anchor="RFC2145">
3500  <front>
3501    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3502    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3503      <organization>Western Research Laboratory</organization>
3504      <address><email>mogul@wrl.dec.com</email></address>
3505    </author>
3506    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3507      <organization>Department of Information and Computer Science</organization>
3508      <address><email>fielding@ics.uci.edu</email></address>
3509    </author>
3510    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3511      <organization>MIT Laboratory for Computer Science</organization>
3512      <address><email>jg@w3.org</email></address>
3513    </author>
3514    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3515      <organization>W3 Consortium</organization>
3516      <address><email>frystyk@w3.org</email></address>
3517    </author>
3518    <date month="May" year="1997"/>
3519  </front>
3520  <seriesInfo name="RFC" value="2145"/>
3521</reference>
3522
3523<reference anchor="RFC2324">
3524  <front>
3525    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3526    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3527      <organization>Xerox Palo Alto Research Center</organization>
3528      <address><email>masinter@parc.xerox.com</email></address>
3529    </author>
3530    <date month="April" day="1" year="1998"/>
3531  </front>
3532  <seriesInfo name="RFC" value="2324"/>
3533</reference>
3534
3535<reference anchor="RFC2616">
3536  <front>
3537    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3538    <author initials="R." surname="Fielding" fullname="R. Fielding">
3539      <organization>University of California, Irvine</organization>
3540      <address><email>fielding@ics.uci.edu</email></address>
3541    </author>
3542    <author initials="J." surname="Gettys" fullname="J. Gettys">
3543      <organization>W3C</organization>
3544      <address><email>jg@w3.org</email></address>
3545    </author>
3546    <author initials="J." surname="Mogul" fullname="J. Mogul">
3547      <organization>Compaq Computer Corporation</organization>
3548      <address><email>mogul@wrl.dec.com</email></address>
3549    </author>
3550    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3551      <organization>MIT Laboratory for Computer Science</organization>
3552      <address><email>frystyk@w3.org</email></address>
3553    </author>
3554    <author initials="L." surname="Masinter" fullname="L. Masinter">
3555      <organization>Xerox Corporation</organization>
3556      <address><email>masinter@parc.xerox.com</email></address>
3557    </author>
3558    <author initials="P." surname="Leach" fullname="P. Leach">
3559      <organization>Microsoft Corporation</organization>
3560      <address><email>paulle@microsoft.com</email></address>
3561    </author>
3562    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3563      <organization>W3C</organization>
3564      <address><email>timbl@w3.org</email></address>
3565    </author>
3566    <date month="June" year="1999"/>
3567  </front>
3568  <seriesInfo name="RFC" value="2616"/>
3569</reference>
3570
3571<reference anchor="RFC2821">
3572  <front>
3573    <title>Simple Mail Transfer Protocol</title>
3574    <author initials="J." surname="Klensin" fullname="J. Klensin">
3575      <organization>AT&amp;T Laboratories</organization>
3576      <address><email>klensin@research.att.com</email></address>
3577    </author>
3578    <date year="2001" month="April"/>
3579  </front>
3580  <seriesInfo name="RFC" value="2821"/>
3581</reference>
3582
3583<reference anchor="RFC2822">
3584  <front>
3585    <title>Internet Message Format</title>
3586    <author initials="P." surname="Resnick" fullname="P. Resnick">
3587      <organization>QUALCOMM Incorporated</organization>
3588    </author>
3589    <date year="2001" month="April"/>
3590  </front> 
3591  <seriesInfo name="RFC" value="2822"/>
3592</reference>
3593
3594<reference anchor='RFC3977'>
3595  <front>
3596    <title>Network News Transfer Protocol (NNTP)</title>
3597    <author initials='C.' surname='Feather' fullname='C. Feather'>
3598      <organization>THUS plc</organization>
3599      <address><email>clive@demon.net</email></address>
3600    </author>
3601    <date year='2006' month='October' />
3602  </front>
3603  <seriesInfo name="RFC" value="3977"/>
3604</reference>
3605
3606<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3607  <front>
3608  <title>Analysis of HTTP Performance Problems</title>
3609  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3610    <organization/>
3611  </author>
3612  <date/>
3613  </front>
3614</reference>
3615
3616<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3617  <front>
3618  <title>Analysis of HTTP Performance</title>
3619  <author initials="J." surname="Touch" fullname="Joe Touch">
3620    <organization>USC/Information Sciences Institute</organization>
3621    <address><email>touch@isi.edu</email></address>
3622  </author>
3623  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3624    <organization>USC/Information Sciences Institute</organization>
3625    <address><email>johnh@isi.edu</email></address>
3626  </author>
3627  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3628    <organization>USC/Information Sciences Institute</organization>
3629    <address><email>katia@isi.edu</email></address>
3630  </author>
3631  <date year="1998" month="Aug"/>
3632  </front>
3633  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3634  <annotation>(original report dated Aug. 1996)</annotation>
3635</reference>
3636
3637<reference anchor="WAIS">
3638  <front>
3639    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3640    <author initials="F." surname="Davis" fullname="F. Davis">
3641      <organization>Thinking Machines Corporation</organization>
3642    </author>
3643    <author initials="B." surname="Kahle" fullname="B. Kahle">
3644      <organization>Thinking Machines Corporation</organization>
3645    </author>
3646    <author initials="H." surname="Morris" fullname="H. Morris">
3647      <organization>Thinking Machines Corporation</organization>
3648    </author>
3649    <author initials="J." surname="Salem" fullname="J. Salem">
3650      <organization>Thinking Machines Corporation</organization>
3651    </author>
3652    <author initials="T." surname="Shen" fullname="T. Shen">
3653      <organization>Thinking Machines Corporation</organization>
3654    </author>
3655    <author initials="R." surname="Wang" fullname="R. Wang">
3656      <organization>Thinking Machines Corporation</organization>
3657    </author>
3658    <author initials="J." surname="Sui" fullname="J. Sui">
3659      <organization>Thinking Machines Corporation</organization>
3660    </author>
3661    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3662      <organization>Thinking Machines Corporation</organization>
3663    </author>
3664    <date month="April" year="1990"/>
3665  </front>
3666  <seriesInfo name="Thinking Machines Corporation" value=""/>
3667</reference>
3668
3669</references>
3670
3671
3672<section title="Internet Media Types" anchor="internet.media.type.http">
3673<t>
3674   In addition to defining HTTP/1.1, this document serves
3675   as the specification for the Internet media type "message/http" and
3676   "application/http". The following is to be registered with IANA <xref target="RFC4288"/>.
3677</t>
3678<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3679<iref item="Media Type" subitem="message/http" primary="true"/>
3680<iref item="message/http Media Type" primary="true"/>
3681<t>
3682   The message/http type can be used to enclose a single HTTP request or
3683   response message, provided that it obeys the MIME restrictions for all
3684   "message" types regarding line length and encodings.
3685</t>
3686<t>
3687  <list style="hanging" x:indent="12em">
3688    <t hangText="Type name:">
3689      message
3690    </t>
3691    <t hangText="Subtype name:">
3692      http
3693    </t>
3694    <t hangText="Required parameters:">
3695      none
3696    </t>
3697    <t hangText="Optional parameters:">
3698      version, msgtype
3699      <list style="hanging">
3700        <t hangText="version:">
3701          The HTTP-Version number of the enclosed message
3702          (e.g., "1.1"). If not present, the version can be
3703          determined from the first line of the body.
3704        </t>
3705        <t hangText="msgtype:">
3706          The message type -- "request" or "response". If not
3707          present, the type can be determined from the first
3708          line of the body.
3709        </t>
3710      </list>
3711    </t>
3712    <t hangText="Encoding considerations:">
3713      only "7bit", "8bit", or "binary" are permitted
3714    </t>
3715    <t hangText="Security considerations:">
3716      none
3717    </t>
3718    <t hangText="Interoperability considerations:">
3719      none
3720    </t>
3721    <t hangText="Published specification:">
3722      This specification (see <xref target="internet.media.type.message.http"/>).
3723    </t>
3724    <t hangText="Applications that use this media type:">
3725    </t>
3726    <t hangText="Additional information:">
3727      <list style="hanging">
3728        <t hangText="Magic number(s):">none</t>
3729        <t hangText="File extension(s):">none</t>
3730        <t hangText="Macintosh file type code(s):">none</t>
3731      </list>
3732    </t>
3733    <t hangText="Person and email address to contact for further information:">
3734      See Authors Section.
3735    </t>
3736                <t hangText="Intended usage:">
3737                  COMMON
3738    </t>
3739                <t hangText="Restrictions on usage:">
3740                  none
3741    </t>
3742    <t hangText="Author/Change controller:">
3743      IESG
3744    </t>
3745  </list>
3746</t>
3747</section>
3748<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3749<iref item="Media Type" subitem="application/http" primary="true"/>
3750<iref item="application/http Media Type" primary="true"/>
3751<t>
3752   The application/http type can be used to enclose a pipeline of one or more
3753   HTTP request or response messages (not intermixed).
3754</t>
3755<t>
3756  <list style="hanging" x:indent="12em">
3757    <t hangText="Type name:">
3758      application
3759    </t>
3760    <t hangText="Subtype name:">
3761      http
3762    </t>
3763    <t hangText="Required parameters:">
3764      none
3765    </t>
3766    <t hangText="Optional parameters:">
3767      version, msgtype
3768      <list style="hanging">
3769        <t hangText="version:">
3770          The HTTP-Version number of the enclosed messages
3771          (e.g., "1.1"). If not present, the version can be
3772          determined from the first line of the body.
3773        </t>
3774        <t hangText="msgtype:">
3775          The message type -- "request" or "response". If not
3776          present, the type can be determined from the first
3777          line of the body.
3778        </t>
3779      </list>
3780    </t>
3781    <t hangText="Encoding considerations:">
3782      HTTP messages enclosed by this type
3783      are in "binary" format; use of an appropriate
3784      Content-Transfer-Encoding is required when
3785      transmitted via E-mail.
3786    </t>
3787    <t hangText="Security considerations:">
3788      none
3789    </t>
3790    <t hangText="Interoperability considerations:">
3791      none
3792    </t>
3793    <t hangText="Published specification:">
3794      This specification (see <xref target="internet.media.type.application.http"/>).
3795    </t>
3796    <t hangText="Applications that use this media type:">
3797    </t>
3798    <t hangText="Additional information:">
3799      <list style="hanging">
3800        <t hangText="Magic number(s):">none</t>
3801        <t hangText="File extension(s):">none</t>
3802        <t hangText="Macintosh file type code(s):">none</t>
3803      </list>
3804    </t>
3805    <t hangText="Person and email address to contact for further information:">
3806      See Authors Section.
3807    </t>
3808                <t hangText="Intended usage:">
3809                  COMMON
3810    </t>
3811                <t hangText="Restrictions on usage:">
3812                  none
3813    </t>
3814    <t hangText="Author/Change controller:">
3815      IESG
3816    </t>
3817  </list>
3818</t>
3819</section>
3820</section>
3821
3822<section title="Tolerant Applications" anchor="tolerant.applications">
3823<t>
3824   Although this document specifies the requirements for the generation
3825   of HTTP/1.1 messages, not all applications will be correct in their
3826   implementation. We therefore recommend that operational applications
3827   be tolerant of deviations whenever those deviations can be
3828   interpreted unambiguously.
3829</t>
3830<t>
3831   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3832   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3833   accept any amount of SP or HTAB characters between fields, even though
3834   only a single SP is required.
3835</t>
3836<t>
3837   The line terminator for message-header fields is the sequence CRLF.
3838   However, we recommend that applications, when parsing such headers,
3839   recognize a single LF as a line terminator and ignore the leading CR.
3840</t>
3841<t>
3842   The character set of an entity-body &SHOULD; be labeled as the lowest
3843   common denominator of the character codes used within that body, with
3844   the exception that not labeling the entity is preferred over labeling
3845   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3846</t>
3847<t>
3848   Additional rules for requirements on parsing and encoding of dates
3849   and other potential problems with date encodings include:
3850</t>
3851<t>
3852  <list style="symbols">
3853     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3854        which appears to be more than 50 years in the future is in fact
3855        in the past (this helps solve the "year 2000" problem).</t>
3856
3857     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3858        Expires date as earlier than the proper value, but &MUST-NOT;
3859        internally represent a parsed Expires date as later than the
3860        proper value.</t>
3861
3862     <t>All expiration-related calculations &MUST; be done in GMT. The
3863        local time zone &MUST-NOT; influence the calculation or comparison
3864        of an age or expiration time.</t>
3865
3866     <t>If an HTTP header incorrectly carries a date value with a time
3867        zone other than GMT, it &MUST; be converted into GMT using the
3868        most conservative possible conversion.</t>
3869  </list>
3870</t>
3871</section>
3872
3873<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3874<t>
3875   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3876   simplify the process of date comparison. Proxies and gateways from
3877   other protocols &SHOULD; ensure that any Date header field present in a
3878   message conforms to one of the HTTP/1.1 formats and rewrite the date
3879   if necessary.
3880</t>
3881</section>
3882
3883<section title="Compatibility with Previous Versions" anchor="compatibility">
3884<t>
3885   It is beyond the scope of a protocol specification to mandate
3886   compliance with previous versions. HTTP/1.1 was deliberately
3887   designed, however, to make supporting previous versions easy. It is
3888   worth noting that, at the time of composing this specification
3889   (1996), we would expect commercial HTTP/1.1 servers to:
3890  <list style="symbols">
3891     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3892        1.1 requests;</t>
3893
3894     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3895        1.1;</t>
3896
3897     <t>respond appropriately with a message in the same major version
3898        used by the client.</t>
3899  </list>
3900</t>
3901<t>
3902   And we would expect HTTP/1.1 clients to:
3903  <list style="symbols">
3904     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3905        responses;</t>
3906
3907     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3908        1.1.</t>
3909  </list>
3910</t>
3911<t>
3912   For most implementations of HTTP/1.0, each connection is established
3913   by the client prior to the request and closed by the server after
3914   sending the response. Some implementations implement the Keep-Alive
3915   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3916</t>
3917
3918<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3919<t>
3920   This section summarizes major differences between versions HTTP/1.0
3921   and HTTP/1.1.
3922</t>
3923
3924<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
3925<t>
3926   The requirements that clients and servers support the Host request-header,
3927   report an error if the Host request-header (<xref target="header.host"/>) is
3928   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3929   are among the most important changes defined by this
3930   specification.
3931</t>
3932<t>
3933   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3934   addresses and servers; there was no other established mechanism for
3935   distinguishing the intended server of a request than the IP address
3936   to which that request was directed. The changes outlined above will
3937   allow the Internet, once older HTTP clients are no longer common, to
3938   support multiple Web sites from a single IP address, greatly
3939   simplifying large operational Web servers, where allocation of many
3940   IP addresses to a single host has created serious problems. The
3941   Internet will also be able to recover the IP addresses that have been
3942   allocated for the sole purpose of allowing special-purpose domain
3943   names to be used in root-level HTTP URLs. Given the rate of growth of
3944   the Web, and the number of servers already deployed, it is extremely
3945   important that all implementations of HTTP (including updates to
3946   existing HTTP/1.0 applications) correctly implement these
3947   requirements:
3948  <list style="symbols">
3949     <t>Both clients and servers &MUST; support the Host request-header.</t>
3950
3951     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3952
3953     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3954        request does not include a Host request-header.</t>
3955
3956     <t>Servers &MUST; accept absolute URIs.</t>
3957  </list>
3958</t>
3959</section>
3960</section>
3961
3962<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3963<t>
3964   Some clients and servers might wish to be compatible with some
3965   previous implementations of persistent connections in HTTP/1.0
3966   clients and servers. Persistent connections in HTTP/1.0 are
3967   explicitly negotiated as they are not the default behavior. HTTP/1.0
3968   experimental implementations of persistent connections are faulty,
3969   and the new facilities in HTTP/1.1 are designed to rectify these
3970   problems. The problem was that some existing 1.0 clients may be
3971   sending Keep-Alive to a proxy server that doesn't understand
3972   Connection, which would then erroneously forward it to the next
3973   inbound server, which would establish the Keep-Alive connection and
3974   result in a hung HTTP/1.0 proxy waiting for the close on the
3975   response. The result is that HTTP/1.0 clients must be prevented from
3976   using Keep-Alive when talking to proxies.
3977</t>
3978<t>
3979   However, talking to proxies is the most important use of persistent
3980   connections, so that prohibition is clearly unacceptable. Therefore,
3981   we need some other mechanism for indicating a persistent connection
3982   is desired, which is safe to use even when talking to an old proxy
3983   that ignores Connection. Persistent connections are the default for
3984   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3985   declaring non-persistence. See <xref target="header.connection"/>.
3986</t>
3987<t>
3988   The original HTTP/1.0 form of persistent connections (the Connection:
3989   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3990</t>
3991</section>
3992
3993<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3994<t>
3995   This specification has been carefully audited to correct and
3996   disambiguate key word usage; RFC 2068 had many problems in respect to
3997   the conventions laid out in <xref target="RFC2119"/>.
3998</t>
3999<t>
4000   Transfer-coding and message lengths all interact in ways that
4001   required fixing exactly when chunked encoding is used (to allow for
4002   transfer encoding that may not be self delimiting); it was important
4003   to straighten out exactly how message lengths are computed. (Sections
4004   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4005   <xref target="header.content-length" format="counter"/>,
4006   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4007</t>
4008<t>
4009   The use and interpretation of HTTP version numbers has been clarified
4010   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4011   version they support to deal with problems discovered in HTTP/1.0
4012   implementations (<xref target="http.version"/>)
4013</t>
4014<t>
4015   Transfer-coding had significant problems, particularly with
4016   interactions with chunked encoding. The solution is that transfer-codings
4017   become as full fledged as content-codings. This involves
4018   adding an IANA registry for transfer-codings (separate from content
4019   codings), a new header field (TE) and enabling trailer headers in the
4020   future. Transfer encoding is a major performance benefit, so it was
4021   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4022   interoperability problem that could have occurred due to interactions
4023   between authentication trailers, chunked encoding and HTTP/1.0
4024   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4025   and <xref target="header.te" format="counter"/>)
4026</t>
4027</section>
4028
4029<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4030<t>
4031  Clarify that HTTP-Version is case sensitive.
4032  (<xref target="http.version"/>)
4033</t>
4034<t>
4035  Remove reference to non-existant identity transfer-coding value tokens.
4036  (Sections <xref format="counter" target="transfer.codings"/> and
4037  <xref format="counter" target="message.length"/>)
4038</t>
4039<t>
4040  Clarification that the chunk length does not include
4041  the count of the octets in the chunk header and trailer.
4042  (<xref target="chunked.transfer.encoding"/>)
4043</t>
4044<t>
4045  Fix BNF to add query, as the abs_path production in
4046  <xref x:sec="3" x:fmt="of" target="RFC2396"/> doesn't define it.
4047  (<xref target="request-uri"/>)
4048</t>
4049<t>
4050  Clarify exactly when close connection options must be sent.
4051  (<xref target="header.connection"/>)
4052</t>
4053</section>
4054</section>
4055
4056<section title="Change Log (to be removed by RFC Editor before publication)">
4057
4058<section title="Since RFC2616">
4059<t>
4060  Extracted relevant partitions from <xref target="RFC2616"/>.
4061</t>
4062</section>
4063
4064<section title="Since draft-ietf-httpbis-p1-messaging-00">
4065<t>
4066  Closed issues:
4067  <list style="symbols"> 
4068    <t>
4069      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4070      "HTTP Version should be case sensitive"
4071      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4072    </t>
4073    <t>
4074      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4075      "'unsafe' characters"
4076      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4077    </t>
4078    <t>
4079      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4080      "Chunk Size Definition"
4081      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4082    </t>
4083    <t>
4084      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4085      "Message Length"
4086      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4087    </t>
4088    <t>
4089      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4090      "Media Type Registrations"
4091      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4092    </t>
4093    <t>
4094      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4095      "URI includes query"
4096      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4097    </t>
4098    <t>
4099      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4100      "No close on 1xx responses"
4101      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4102    </t>
4103    <t>
4104      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4105      "Remove 'identity' token references"
4106      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4107    </t>
4108    <t>
4109      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4110      "Import query BNF"
4111    </t>
4112    <t>
4113      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4114      "qdtext BNF"
4115    </t>
4116    <t>
4117      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4118      "Normative and Informative references"
4119    </t>
4120    <t>
4121      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4122      "RFC2606 Compliance"
4123    </t>
4124    <t>
4125      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4126      "RFC977 reference"
4127    </t>
4128    <t>
4129      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4130      "RFC1700 references"
4131    </t>
4132    <t>
4133      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4134      "inconsistency in date format explanation"
4135    </t>
4136    <t>
4137      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4138      "Date reference typo"
4139    </t>
4140    <t>
4141      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4142      "Informative references"
4143    </t>
4144    <t>
4145      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4146      "ISO-8859-1 Reference"
4147    </t>
4148    <t>
4149      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4150      "Normative up-to-date references"
4151    </t>
4152  </list>
4153</t>
4154<t>
4155  Other changes:
4156  <list style="symbols"> 
4157    <t>
4158      Update media type registrations to use RFC4288 template.
4159    </t>
4160    <t>
4161      Use names of RFC4234 core rules DQUOTE and HTAB,
4162      fix broken ABNF for chunk-data
4163      (work in progress on <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4164    </t>
4165  </list>
4166</t>
4167</section>
4168
4169<section title="Since draft-ietf-httpbis-p1-messaging-01">
4170<t>
4171  Closed issues:
4172  <list style="symbols"> 
4173    <t>
4174      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4175      "Bodies on GET (and other) requests"
4176    </t>
4177    <t>
4178      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4179      "rel_path not used"
4180    </t>
4181  </list>
4182</t>
4183<t>
4184  Other changes:
4185  <list style="symbols"> 
4186    <t>
4187       Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4188       "trailer-part"), avoid underscore character in rule names ("http_URL" ->
4189       "http-URL", "abs_path" -> "path-absolute"), add rules for terms
4190       imported from URI spec ("absoluteURI", "authority", "path-absolute",
4191       "port", "query", "relativeURI", "host) -- these will have to be updated
4192       when switching over to RFC3986
4193       (work in progress on <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4194    </t>
4195  </list>
4196</t>
4197</section>
4198
4199</section>
4200
4201</back>
4202</rfc>
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